# "Millett Hybrid" redux: NuHybrid headphone amp, using the Korg Nutube



## pmillett

I just published the design of a DIY hybrid headphone amp using the new Korg Nutube 6P1.
  
 It's a lot like the original "Millett Hybrid" that I published 15 years ago.  Instead of an old car radio tube, though, this one uses the new Korg Nutube.  The Nutube has been popular with DIYers in Japan since it started shipping at the end of last year, but so far I haven't seen it a lot outside Japan.
  
 Like the original Millett hybrid, the whole thing runs off of a 24V power supply, so it's safe.  I used OPA551 opamps to drive the headphones, but you can use others as well.
  
 You can find all the details on my web page, at http://www.pmillett.com/nuhybrid.html
  
 Pete


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## tomb

Ordered!
  
 Looks great, Pete!  I'm interested in trying it out.
  
 BTW, it looks like there is a mixup in your diodes between the BOM and the schematic/board.  As best I can tell, the schematic/board is correct, but the BOM is not.  The diodes should be as follows in labeling the parts bag from Mouser/DigiKey:
  
 D1 - P6KE33A
 D2 - 1N5245B Zener
 D3, D4 - IN4148
 D5 - Lumex LED
  
 Got a workable replacement for the relay - maybe an Omron?  Mouser and DigiKey are both out of stock - late-April for Mouser.  DigiKey says their delivery date is overdue.  Maybe they'll update soon.


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## pmillett

Thanks, I'll check the BOM.

The BOM has an alternate listed for the relay from Tyco/Axicom, which was in stock at Mouser last time I looked.

Pete


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## tomb

pmillett said:


> Thanks, I'll check the BOM.
> 
> The BOM has an alternate listed for the relay from Tyco/Axicom, which was in stock at Mouser last time I looked.
> 
> Pete


 

  
 Ah - great!  I missed that.  Mouser has over 2,000 of them.


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## strangecargo

Was this announced just a few hours ago? I was just randomly searching for the original Millett hybrid because I was fondly reminiscing about building one years ago and came across this thread. I've ordered a board from your eBay store, Pete. Is the BOM listed on the Mouser project corrected now?


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## pmillett

tomb said:


> BTW, it looks like there is a mixup in your diodes between the BOM and the schematic/board.  As best I can tell, the schematic/board is correct, but the BOM is not.  The diodes should be as follows in labeling the parts bag from Mouser/DigiKey:


 
 OK, I have updated the BOM and assembly manual with the right diode reference designators.  Don't know how I missed that - thanks!
  
 Pete


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## pmillett

strangecargo said:


> Was this announced just a few hours ago? I was just randomly searching for the original Millett hybrid because I was fondly reminiscing about building one years ago and came across this thread. I've ordered a board from your eBay store, Pete. Is the BOM listed on the Mouser project corrected now?


 
  
 Yes, I just posted this Sunday night.  Been working on it for a while, but just got the final PCB together to take pictures for the assembly manual...
  
 The BOM is corrected - you might have to reload it to avoid getting a cached version.
  
 Pete


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## strangecargo

pmillett said:


> Yes, I just posted this Sunday night.  Been working on it for a while, but just got the final PCB together to take pictures for the assembly manual...
> 
> The BOM is corrected - you might have to reload it to avoid getting a cached version.
> 
> Pete


 
 Pete, was it just the diode reference designators that were incorrect? I may have ordered the parts already from the existing BOM 
	

	
	
		
		

		
		
	


	




. I'll be okay if it was all the right parts but just labelled incorrectly. Looking forward to building another Millett Hybrid!


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## pmillett

strangecargo said:


> Pete, was it just the diode reference designators that were incorrect? I may have ordered the parts already from the existing BOM
> 
> 
> 
> ...


 
 That's correct - the parts and quantities were correct, just the reference designators on the diodes were scrambled.  So you should be fine.
  
 Pete


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## strangecargo

Received the PCB/NuTube in the mail today. My Mouser order should arrive tomorrow. Looks like I need to go fish my soldering iron and scope out of storage. Hopefully I'll get it assembled sometime this weekend.
  
 I still have an external power supply I made for my original Millett Hybrid. I just measured it with my DMM is it's putting out ~27V. Should that be okay to power the NuHybrid, Pete?


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## vixr

Woo Hoo!!! ordered my board, sorting thru the BOM now! Thank you sir for another awesome project!!!


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## Sodacose

Haha, aw man.  I just finished a hybrid inspired by your original:
  
 http://www.head-fi.org/t/838886/my-take-on-the-starving-student-el-estudiante
  
 Now I've got to build another?  
  
 Thanks for sharing, Pete!


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## pmillett

strangecargo said:


> I still have an external power supply I made for my original Millett Hybrid. I just measured it with my DMM is it's putting out ~27V. Should that be okay to power the NuHybrid, Pete?


 
  
 Yes, that should work fine!
  
 Pete


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## vixr

would it be possible to use an Alps "blue velvet" 50k ohms pot with this amp? I have a few spares, I could wire one off board...


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## Sodacose

If you wire it off board, I don't see any reason that a Blue Velvet wouldn't work.


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## vixr

sodacose said:


> If you wire it off board, I don't see any reason that a Blue Velvet wouldn't work.


 
 so, the higher Ohms value isn't an issue?


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## Sodacose

Maybe Pete will comment, but I don't think there would be major input capacitance with the buffer that follows it to create a hf roll off.


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## vixr

sodacose said:


> Maybe Pete will comment, but I don't think there would be major input capacitance with the buffer that follows it to create a hf roll off.


 
 Thanks for the speedy answers, I have gone the other way and used a 50k Ohms pot in place of a 100k pot with great success. It was done on the 6DJ8 "Headwatt" amp by Bruce Heran...


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## Sodacose

I bet the lower pot value was a parts availability choice. Hard to find dual gang audio taper in 50k-100k values from digikey/mouser. At guitar parts values (250k+) then you do usually have to start taking into account what it is feeding.


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## vixr

sodacose said:


> I bet the lower pot value was a parts availability choice. Hard to find dual gang audio taper in 50k-100k values from digikey/mouser. At guitar parts values (250k+) then you do usually have to start taking into account what it is feeding.


 
 I actually did try to find a 100k DG AT pot for a few hours on the interwebs, the closest I could get was two singles that allowed the shaft from either pot to be inserted into the back of the other pot. Seemed dubious at best...didn't buy them.


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## tomb

sodacose said:


> Haha, aw man.  I just finished a hybrid inspired by your original:
> 
> http://www.head-fi.org/t/838886/my-take-on-the-starving-student-el-estudiante
> 
> ...


 

 I hate to keep playing Polly Prompter in this thread, but "original" and "starving student" do not belong together.  They are separated by about 6 years, at least.
	

	
	
		
		

		
			





  Pete is probably being too polite to correct this, but he seems to be stating that the NuHybrid is a redux of _origina_l Millett Hybrid, first designed and published by Pete in Audio Xpress magazine - *all the way back in 2002*.  Here's a copy of that article:
_*Build A Low-Voltage Tube Hybrid Headphone/Line Amp*_

  
 The Millett Hybrid was then followed by the revMH Millett Hybrid, designed by Drew Dunn and Nate Maher and released in 2005-2006.  AMB actually was the first to use the OPA551 on Pete's Millett Hybrid design instead of the BUF634 (with the revH Millett Hybrid PCB).  A little later on, Steinchen designed a discrete buffer for the revMH Millett Hybrid that became known as the MH Diamond Buffer Boards:

  
 The MH design was later followed by the Millett Hybrid MAX, designed by Colin Toole using Pete's original design with a maxed out power supply and discrete, heat-sinked diamond buffer.  Then there was the Millett Hybrid MiniMAX, and finally, the Millett Hybrid MOSFET-MAX, which is still available on PCB today.  All of these were based on low-voltage, space charge tubes - the 12AE6, 12FM6, and 12FK6.  They also used 24V walwarts, although most were tweaked to 27VDC (see earlier post in this thread) through the use of 24VAC walwarts.  All of this is documented in great detail on *diyforums.org* and can be gleaned from looking on *Pete's site* at the different headphone amp designs.

  
 Pete will correct me if I'm wrong, but the Starving Student was somewhat of a departure from the Millett Hybrid family.  It came along in 2008, with Pete's and Nate Maher's posted as the first two builds.  It originally used point-to-point construction, high-voltage tubes (they started out at $1-$2!), a 48V surplus Cisco VoIP telephone power supply, and uniquely - used the tube heaters to bias the output buffer MOSFETs (none of which existed in any of the Millett Hybrid variants).
  
 A little later after Pete came out with the Starving Student, Dsavitsk designed the first PCB for the Starving Student.  We sold batches of kits a number of times, referring to the design as the Starving Student Millett Hybrid, or SSMH.  Those kit batches are now rare, because the tube itself became rare - the 19J6.
  
 Anyway, I've finished my NuHybrid except for soldering in the NuTube itself.  I want to rinse and clean up the board in the morning, and I'm not quite sure whether the Korg NuTube is moisture-proof.  I'll report back when I get it hooked up and running. 
	

	
	
		
		

		
		
	


	




 
  
  
 P.S. At some period along the timeline described above, Tyll Hertsens actually sold a version of Pete's Millett Hybrid as a HeadRoom headphone amplifier.  I've never had the pleasure, but I know Nate had one and it was probably closest to the Millett Hybrid MAX in design and used the same tubes, power specs, etc.:


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## Sodacose

Thanks for the clarification and reading, tomb. I was referring to the original Starving Student design as found on Pete's website:

http://www.pmillett.com/starving.htm


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## tomb

sodacose said:


> Thanks for the clarification and reading, tomb. I was referring to the original Starving Student design as found on Pete's website:
> 
> http://www.pmillett.com/starving.htm


 

 Yes, but you referred to the Starving Student as "a hybrid" that was Pete's "original," which is why I clarified. 
	

	
	
		
		

		
		
	


	



  
 Maybe I'm just anal about it because I've been following, building, selling, and documenting Pete's hybrids for quite a few years, now.


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## tomb

Here's mine so far:
  

  
 As I said, I'm waiting to clean up the bottom of the board before installing the NuTube, in case it's not moisture-proof.  The smallness of the PCB surprised me.  I was actually expecting something on the order of the revMH Millett Hybrid PCB, but this thing is about half the size.  I used some left-over MiniMAX caps that are really too large for the space, but I got them in somehow. 
	

	
	
		
		

		
		
	


	




  I also will install a couple of Vitamin Q's for the output bypasses - C4 and C7, but they'll have to go on the bottom of the board.  There's no room at all with those caps.  I also jumpered R8 and R9.  We'll see how that works instead of 1R resistors, but I always preferred the sound when jumpering the output resistors on the Millet Hybrid, et al.  We'll see how it goes. 
	

	
	
		
		

		
		
	


	




 
  
 P.S. This took me about an hour to get this far, but I was working fairly fast.  It should be pretty easy for most to put together.


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## Sodacose

Hi Pete (if you're still here). Can you talk at all about why you decided to use the Nutube as a voltage gain device? It's an interesting "tube" with some challenges to overcome, so I'm just curious about the overall design goal and how the NuTube fit into it. 

Seems it has some size/efficiency advantages. And maybe it just sounds good (I know this isn't your first amp using it).


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## pmillett

vixr said:


> would it be possible to use an Alps "blue velvet" 50k ohms pot with this amp? I have a few spares, I could wire one off board...


 
  
 Sure, it will work fine.
  
 The resistance here isn't very important.  Since it is driving a source follower, it has very little loading capacitance to contend with (though the gate capacitance of a MOSFET is high, the gate and source move together, so the resulting capacitance is very low).
  
 I picked 10k mostly because a lower input resistance seems to help with noise pickup.  But 50k or 100k are fine.
  
 Pete


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## pmillett

tomb said:


> As I said, I'm waiting to clean up the bottom of the board before installing the NuTube, in case it's not moisture-proof.  The smallness of the PCB surprised me.  I was actually expecting something on the order of the revMH Millett Hybrid PCB, but this thing is about half the size.  I used some left-over MiniMAX caps that are really too large for the space, but I got them in somehow.
> 
> 
> 
> ...


 
  
 Wow, you're fast!
  
 I think the Nutube should be fine with cleaning solvents or water... it's all glass and metal, and is sealed.
  
 You are spot on about R8 and R9 - some people will like zero ohms better than 1 ohm, and some might also prefer 10-33 ohms there.  It depends on your headphones and listening preferences.
  
 I'm anxious to hear your listening impressions, especially as compared to the other Millett hybrid variants!
  
 Pete


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## pmillett

sodacose said:


> Hi Pete (if you're still here). Can you talk at all about why you decided to use the Nutube as a voltage gain device? It's an interesting "tube" with some challenges to overcome, so I'm just curious about the overall design goal and how the NuTube fit into it.
> 
> Seems it has some size/efficiency advantages. And maybe it just sounds good (I know this isn't your first amp using it).


 
  
 Good question.
  
 Part of the reason is just "because it's there".  It's new, and in interesting part.
  
 Compared to normal tubes, it can be operated at very low power - 700mV @ 17mA for the filament, and you can use B+ of 12V with no problem.  The same is true of a few of the "hearing aid" tubes, but they have gotten difficult to find - at least the good ones.  So I see the Nutube as being used in places like portable amp and guitar pedals, places where normal tubes don't work very well.
  
 The biggest issue with the Nutube is that it has very low transconductance.  Coupled with the fact that it works best in A2, you really need to put a buffer in front to drive the grid.
  
 Within those constraints, the Nutube is quite linear.  And it acts just like any other directly heated triode.  You can tune it by changing bias, plate load, and feedback (if used) to change the resulting characteristics. So, you can build a hybrid amplifier (headphone, power, class D, etc.) that winds up sounding like a single ended triode amp.  I guess that's the "sounds good" part.  Though SE triodes certainly are not everybody's favorite sound.
  
 By the way, I've got an article coming up in next month's audioXpress that talks more about it.
  
 Pete


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## Sodacose

Killer, thanks for the insight.  I'll be watching for the audioXpress article!


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## pmillett

TOMB (I guess the first person finishing an amp) has noticed a couple of issues with the amp that I want to make everybody aware of...
  
 First, there still can be a bit of a thump when turning the amp on.  This is caused by the time it takes to charge the output caps.  You can eliminate this by changing R3 and R4 from 10k to 1k.
  
 You still get some noise when you power the amp off.  I don't think it is enough to damage anything.  If you are worried about it, I guess you can always unplug the headphones like with the old original hybrid and starving student...
  
 There is also noise when setting the volume control to zero.  The faster you turn the knob, the worse the noise.  I thought that this was just a cheap volume control pot, but it turns out there is actually some instability that causes some HF oscillation when the volume control is near zero.  Until I figure out the best fix, either move the knob very slowly, or avoid turning it all the way down.  I know, it's not ideal, but I will figure out how to fix it within a few days.
  
 Thanks, TOMB!
  
 Pete


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## tomb

OK.  With the help of a very good friend - Dsavitsk of ECP Audio - we've solved the oscillation issue with the volume pot.  There is now no noise whatsoever in my volume pot travel.  Gate stoppers on the MOSFETs fixed it.  A Gate stopper consists of a 1K resistor inserted between the Gate leg of the MOSFET (center pin) and the center pin connection on the PCB.  It takes some solder acrobatics, but most of you will probably have an easier time of it than I did, since I had already trimmed the MOSFET pins pretty short when I first built the NuHybrid.  Here's some pics -
  
 This is Q2 and Q3, with the 1K resistor inserted between the Gate leg of each MOSFET and the other lead of the resistor inserted into the Gate leg's pad on the PCB:

  
 Basically, what you are looking at is one resistor lead is bent down vertically and inserted into the center hole on the PCB for the MOSFET.  The other resistor lead is bent 180 degrees back over toward the MOSFET, whose Gate leg (center pin) is bent back up horizontally and soldered to the resistor lead on top of the resistor.  As I said - yours probably won't look like this if you still have long leads on the MOSFETs.  Note that I had to relocate the R19, R20, R22, and R23 resistors to the bottom of the PCB to make room for the Gate stopper resistors:
  


 You can also see the 0.33uf Sonicap Gen IIs that I used for bypasses on the output caps.
  
 Same Gate stopper applied to the MOSFET in the relay-delay:
  


 This MOSFET is for the relay.  It's not really in the signal path, but Dsavitsk suggested there might be some bleed-over if it oscillated, too.  So, I put one here, too - just in case.  The Gate stopper resistor had to twist over to the side because of C1.  Be very careful if you do it this way that you don't short one of the outside legs of the MOSFET with the Gate leg and resistor lead.
  
 Also note the C2 cap was upsized.  This is a very inexpensive Murata 47uf 25V electrolytic.  25V is probably too low a rating, but I'm using a linear-regulated walwart at 24VDC anyway, so I doubt seriously it's going to be exposed to anything more than 24V.  Still, the point is that you can find a bigger cap pretty easily (no high quality needed here) that should fit without any trouble.  In my case, this extended the delay on power-up from about 6 seconds with the original cap to something over 30 seconds.  Yeah, that's a hassle to wait that long, but when it kicks in now, there's only a very low "tap" that you can hear.  Although, the "tap" sounds like a spoon tapping on a crystal glass.
	

	
	
		
		

		
			





  Before, the relay was engaging before my output caps had fully charged and was causing a nasty voltage spike and thump.  There is still a turn-off thump, but I'm used to dealing with that a bit more than a turn-on one.
  
 Here are a couple of overall pics -

  
 and catching the glow from the NuTube -

  
 Despite the camera setting, the NuTube glow is easily seen in daylight, unless you have some glare on the transparent NuTube cover.  You can compare the green with the LED near the power switch.  The NuTube glows with a very nice "ocean green" color just like some LEDs that I've sold as options on the Starving Student. 
	

	
	
		
		

		
		
	


	



  
 One other thing to note - the NuTube definitely has some microphonics, but it takes a real wallop to hear it.  Unlike glass tubes with microphonics, the NuTube will "sing" at a very high-frequency pitch - like the crystal tap mentioned above.  I will say that the only thing that causes this is being very rough and forceful when plugging in your headphones.  There are a couple of reasons I was doing this - 1) I was plugging in after powering up, until I was certain that the turn-on thump was gone, and 2) with that little PCB setup on some metal standoffs, it takes some forceful action to hold it and plug the headphones in.  If you are gentle and insert the jack slowly, you will _not_ start the NuTube ringing.  A good thing to mention is that nothing else I've done will cause it to ring - tapping it directly, shaking the PCB, or tapping anything else on the PCB.  It only occured when violently shaking everything up plugging in the phones.
  
 So how does it sound?  I've been doing a lot of FM tuner work lately, so that's all I've heard it on thus far.  However, I directly compared it to a pair of Mini3s and PIMETAs that I've been using in that work.  The NuHybrid compares favorably to the Mini3, at least in this setup with a highly-modded Sony ES tuner.  Detail is good, bass slam is great (note that I used 1000uf on the output caps) and it sounds very dynamic.  The PIMETAs are smoother, but I think that may be a combination of the OPA627s in the PIMETAs, along with a very low gain.  That's the last issue, I think - the NuHybrid has very high gain.  I don't see any feedback loops except on the opamps and those are set to unity.  Pete - if you have any suggestions on how to tame the gain, it will be greatly appreciated.
  
 I'll report back when I get in some listening time on a quality DAC.  Thank you Pete for this new toy and thanks to Dsavitsk for the oscillation solution!


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## pmillett

Thanks Tomb.

I think an even simpler solution will be to simply replace the 2N7000 FETs in the buffers with 2N3904 NPN transistors. I haven't tried it yet, but it should work just fine, and may have lower distortion than the MOSFETs.

I'll try it when I get home Sunday.

Pete


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## tomb

pmillett said:


> Thanks Tomb.
> 
> I think an even simpler solution will be to simply replace the 2N7000 FETs in the buffers with 2N3904 NPN transistors. I haven't tried it yet, but it should work just fine, and may have lower distortion than the MOSFETs.
> 
> ...


 
 Cool.  Yes, that would be a good deal simpler than what I did with the MOSFETs. 
	

	
	
		
		

		
		
	


	



  
 Any suggestions on lowering the gain?


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## JamieMcC




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## proid

Hi Pete, since this amp use both the nutube for gain and opa551 for output buffer like the sankanagu, do they share any similarity in sound signature?


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## Heffa

The Kemet relay is out of stock in the Swedish Mouser (not sure if they use the same stock as other countries or not), does anyone know of a good replacement that could work intead? 
Also, the 2N7000 FETs are oos, but I'll wait and order until Pete have tested the suggested 2N3904 NPN transistors instead.


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## dsavitsk

pmillett said:


> Thanks Tomb.
> 
> I think an even simpler solution will be to simply replace the 2N7000 FETs in the buffers with 2N3904 NPN transistors.




Hfe on those is max 300. At the 10mA running through these, the base current will likely drag the voltage too much. A darlington (2N6426 perhaps?) might work.


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## pmillett

dsavitsk said:


> Hfe on those is max 300. At the 10mA running through these, the base current will likely drag the voltage too much. A darlington (2N6426 perhaps?) might work.




Yes, we'll need to lower the current through the transistor. I'll try 10k instead of 1k on the emitter and see if it measures OK.

Pete


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## Heffa

heffa said:


> The Kemet relay is out of stock in the Swedish Mouser (not sure if they use the same stock as other countries or not), does anyone know of a good replacement that could work intead?
> Also, the 2N7000 FETs are oos, but I'll wait and order until Pete have tested the suggested 2N3904 NPN transistors instead.


 
 ...and apparently I didn't even read the first page of this thread - I see now that this question have already been answered there 
	

	
	
		
		

		
		
	


	




 
  
 Btw, I think I spotted another small mixup between the BOM and the actual schematics - C6 & C7.
  
 In the BOM C7 is a 470uF Nichicon electrolytic, but it should really be C6.
 Likewise, C6 in the BOM is one of the WIMA film caps, but it should be C7.
  
 I guess it should be obvious to everyone trying to assemble the amp, but I thought it could be worth mentioning anyway.


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## pmillett

proid said:


> Hi Pete, since this amp use both the nutube for gain and opa551 for output buffer like the sankanagu, do they share any similarity in sound signature?


 
  
 There is some similarity.  If anything this one is a bot more "tubey".  On the Sangaku I use a much higher B+ voltage, and also a tiny bit of NFB around the tube.  That way it can drive a much higher output signal without too much distortion.
  
 Pete


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## pmillett

heffa said:


> In the BOM C7 is a 470uF Nichicon electrolytic, but it should really be C6.
> Likewise, C6 in the BOM is one of the WIMA film caps, but it should be C7.
> 
> I guess it should be obvious to everyone trying to assemble the amp, but I thought it could be worth mentioning anyway.


 
  
 Thanks!  I will fix the documentation.
  
 Pete


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## pmillett

OK...
  
 I've made an update to the design to eliminate instability in the 2N7000 buffers when the volume control is near zero, and to reduce the power-on noise in the headphones.
  
 Q2 & Q3 are changed to 2N3904 transistors.  R3 & R4 are now 1k, and R21 & R24 are 10k.  The resistor quantities in the BOM remain unchanged, basically two pairs were just swapped around.  Q1 remains 2N7000 FET.  So, the only new components are Q2 and Q3.
  
 I measure no differences between using the 2N3904 and 2N7000.
  
 I have updated the documentation and the Mouser BOM.
  
 For you early adopters in the USA (postage outside the USA is 10 times the cost of the transistors) that already bought parts, send me a PM and I'll drop a couple of 2N3904's in the mail for you.  Sorry for the trouble!
  
 Pete


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## strangecargo

pmillett said:


> OK...
> 
> I've made an update to the design to eliminate instability in the 2N7000 buffers when the volume control is near zero, and to reduce the power-on noise in the headphones.
> 
> ...


 
 Pete, I was about to sit down and populate the PCB when I saw this. I don't have any 2N3904 (I'll be emailing you shortly). If I wanted to build the NuHybrid now and swap out Q2 and Q3 when I get the right transistors, should I still swap those resistor pairs?


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## pmillett

strangecargo said:


> Pete, I was about to sit down and populate the PCB when I saw this. I don't have any 2N3904 (I'll be emailing you shortly). If I wanted to build the NuHybrid now and swap out Q2 and Q3 when I get the right transistors, should I still swap those resistor pairs?


 
  
 Yes, use the updated resistor values, even with the 2N7000.  I just tried it, and actually the oscillation goes away with 10k resistors on the followers.  So maybe no need to change to 2N3904 at all.
  
 I'll do some more measurements tomorrow to confirm that everything is OK.
  
 Pete


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## strangecargo

Complete, but I experience a HF ringing/oscillation noise on power on or whenever the NuTube sees any vibration (it seems crazy microphonic) that slowly fades away over time. Sounds kind of like tapping on a wine glass, but the ringing takes an impossibly long time to fade away. Comes back if I tap the NuTube or even touch the amp in any way. Tube noise also seems to be abnormally high (very audible on Fostex TH-X00). I swapped the resistor values but I used the 2N7000 transistors in a the Q positions. It does amplify music though. Where should I start debugging this?


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## gikigill

So where can I buy one fully built or even semi built?


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## pmillett

strangecargo said:


> Complete, but I experience a HF ringing/oscillation noise on power on or whenever the NuTube sees any vibration (it seems crazy microphonic) that slowly fades away over time. Sounds kind of like tapping on a wine glass, but the ringing takes an impossibly long time to fade away. Comes back if I tap the NuTube or even touch the amp in any way. Tube noise also seems to be abnormally high (very audible on Fostex TH-X00). I swapped the resistor values but I used the 2N7000 transistors in a the Q positions. It does amplify music though. Where should I start debugging this?


 
  
 That is the normal microphonic behavior of the Nutube.  Unfortunately there is nothing to debug...
  
 The filament of the tube oscillates like a piano string when subject to shock or vibration.  When the muting relay activates, it puts enough of a mechanical vibration into the PCB that it excites the filament ringing.
  
 Due to it's low gm, it is also not the quietest device around.  The Fostex are quite efficient, making the noise and microphonics more noticeable.
  
 Pete


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## strangecargo

pmillett said:


> That is the normal microphonic behavior of the Nutube.  Unfortunately there is nothing to debug...
> 
> The filament of the tube oscillates like a piano string when subject to shock or vibration.  When the muting relay activates, it puts enough of a mechanical vibration into the PCB that it excites the filament ringing.
> 
> ...


 

 I wasn't expecting ringing this severe, after reading @tomb describe how hard it was to excite the filament. It's very loud (I thought that the plug-in noise was some kind of OS alert noise I hadn't heard before) and even the slightest rub or touch on the casing of the amp (or turning the volume pot) will set off the ringing, which I can hear on HD650s, TH-X00, and K7XX, though the tube noise is not quite as audible on the HD650 and K7XX.


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## pmillett

gikigill said:


> So where can I buy one fully built or even semi built?


 
  
 Keep watching this thread.  Maybe strangecargo will want to sell his 
  
 Seriously, I'm sure some builders will decide it's not to their liking.  That is always the case, especially with tube amps.
  
 Pete


----------



## strangecargo

pmillett said:


> Keep watching this thread.  Maybe strangecargo will want to sell his
> 
> Seriously, I'm sure some builders will decide it's not to their liking.  That is always the case, especially with tube amps.
> 
> Pete


 
 Pete, the ringing is still audible ~25 seconds after the power-on relay clicks. Is that really typical? How does Korg handle this in the effects pedals they've been making with the Nutube?


----------



## pmillett

strangecargo said:


> Pete, the ringing is still audible ~25 seconds after the power-on relay clicks. Is that really typical? How does Korg handle this in the effects pedals they've been making with the Nutube?


 
  
 That seems extreme.  Even with sensitive IEMs I only hear ringing for ~10 seconds after the relay pulls in.  At that point the ringing is below the noise level.
  
 Did you use the adhesive foam to stick the tube onto the PCB?  Just curious, as I'm not sure if it helps or hurts...
  
 Pete


----------



## tomb

strangecargo said:


> pmillett said:
> 
> 
> > Keep watching this thread.  Maybe strangecargo will want to sell his
> ...




Maybe there's a variance in microphonics from NuTube to NuTube as with glass tubes?

I can confirm that mine is a bit easier to start ringing than I first reported, but I haven't experienced it going for 25 seconds. However, the ringing is sort of as you say - more of a high-pitched tone that is hard to distinguish as not being electronic in nature.


----------



## pmillett

tomb said:


> Maybe there's a variance in microphonics from NuTube to NuTube as with glass tubes?
> 
> I can confirm that mine is a bit easier to start ringing than I first reported, but I haven't experienced it going for 25 seconds. However, the ringing is sort of as you say - more of a high-pitched tone that is hard to distinguish as not being electronic in nature.


 
  
 I've seen a little tube-to-tube variation, but not a lot.  Certainly not 2x from one to another...
  
 Pete


----------



## tomb

I definitely installed the foam under mine. Maybe that's strangecargo's issue?


----------



## strangecargo

pmillett said:


> That seems extreme.  Even with sensitive IEMs I only hear ringing for ~10 seconds after the relay pulls in.  At that point the ringing is below the noise level.
> 
> Did you use the adhesive foam to stick the tube onto the PCB?  Just curious, as I'm not sure if it helps or hurts...
> 
> Pete


 
 I used the adhesive foam. Maybe I got a particularly microphonic Nutube? Even lightly brushing the side of the plastic case or carefully setting my finger on one of the OPA551s will set off audible ringing.


----------



## pmillett

strangecargo said:


> I used the adhesive foam. Maybe I got a particularly microphonic Nutube? Even lightly brushing the side of the plastic case or carefully setting my finger on one of the OPA551s will set off audible ringing.


 
  
 It may also be that you got a particularly noisy relay...
  
 With IEMs, I can also hear noise if I run my finger along the knob or case.  I wouldn't use this amp with IEMs, more because of the tube noise than the microphonics.  The same may apply to very sensitive headphones.
  
 With less sensitive headphones like the HD600, I don't hear noise at all, and just a small "tink" sound when the muting relay activates.
  
 Pete


----------



## strangecargo

pmillett said:


> It may also be that you got a particularly noisy relay...
> 
> With IEMs, I can also hear noise if I run my finger along the knob or case.  I wouldn't use this amp with IEMs, more because of the tube noise than the microphonics.  The same may apply to very sensitive headphones.
> 
> ...


 
 Hmm. With the HD650, it takes ~20 seconds for the ringing to fade away. I *am* using the Axicom alternative part from the BOM, as the Kemet relay was backordered at Mouser. Perhaps it has a considerably more violent switching mechanism. I can still hear my fingers on the case (and subsequent ringing) with the HD650 though.


----------



## tomb

strangecargo said:


> pmillett said:
> 
> 
> > It may also be that you got a particularly noisy relay...
> ...



JMHO, but the violence of the relay is reduced to almost zero if you increase the time for it to engage.

I installed the 1K resistors on the output caps, but it had almost no effect. There is probably enough voltage remaining to leave the relay causing noise upon engaging. Again, JMHO, but upsizing the relay cap to 470uf will stop that.


----------



## Heffa

strangecargo said:


> I *am* using the Axicom alternative part from the BOM, as the Kemet relay was backordered at Mouser. Perhaps it has a considerably more violent switching mechanism.




I just ordered the same relay, together with the rest of the BOM from Mouser as well... We'll see if I experience the same ringing in my amp once the parts arrive and I have found the time to actually build it.


----------



## tomb

This may seem like cheating, but a longer relay time (~30 sec) also gives plenty of time for the NuTube to settle down before you can listen.

A longer relay start cures a lot of ills ...


----------



## pmillett

OK, I made a discovery - the microphonic "ping" at power-up has nothing to do with the relay engagement.  It is noise induced from flipping the power switch.
  
 I tried leaving the power switch turned on, and instead turned the amp on and off by switching the AC to the adapter.  The relay pulls in after 10 seconds. No "ping" noise (well, none in HD600s - I'm sure there is still some noise in efficient headphones or IEMs).
  
 I also tried moving the power switch very slowly... also no ping sound.
  
 It is true that if the delay is lengthened, you won't hear it as much when you flip the power switch.  But I guess I don't quite understand why it matters.  Let's say it takes 20 seconds (from the time you hit the power switch) for the ringing to calm down.  You can make the power on delay more than 20 seconds and you won't hear it.  Or you leave the power on delay at 10 seconds (which is where it is now) and you hear a decaying ringing for 10 seconds.  It's not that loud...
  
 Pete


----------



## smellor

Hey Pete,
  
 I bought your board+nutube and am waiting to receive the parts from Mouser. Looking forward to build it. I am a new builder, so i decided i would use this build to try my hand at customizing the case. Having positive experiences with the cases from Hifi2000 (an italian vendor) who supplied the case for a recent diyaudio amp build, i bought a relatively large economy case from them, which i can play around with. One of the things i was thinking was to mount the nutube on the outside top of the case, since it looks so nice, and connect it through holes in the top via wires insulated with heatshrink tubing. I wonder if this would affect the performance to any great extent? My feeling says probably not, but i am a novice in this area so i would rather take the word of someone who actually knows what hes talking about  Apart from the leads connecting it to the PCB, are there any exposed parts that carry voltages in the nutube?
  
 Best,
 Silas


----------



## HiGHFLYiN9

Any changes to the NuTube buffer based on discoveries with the headphone amp? I know most implementations will not have a volume knob, but there would still be the on-off switch.


----------



## pmillett

smellor said:


> Hey Pete,
> 
> I bought your board+nutube and am waiting to receive the parts from Mouser. Looking forward to build it. I am a new builder, so i decided i would use this build to try my hand at customizing the case. Having positive experiences with the cases from Hifi2000 (an italian vendor) who supplied the case for a recent diyaudio amp build, i bought a relatively large economy case from them, which i can play around with. One of the things i was thinking was to mount the nutube on the outside top of the case, since it looks so nice, and connect it through holes in the top via wires insulated with heatshrink tubing. I wonder if this would affect the performance to any great extent? My feeling says probably not, but i am a novice in this area so i would rather take the word of someone who actually knows what hes talking about  Apart from the leads connecting it to the PCB, are there any exposed parts that carry voltages in the nutube?
> 
> ...


 
  
 I think the biggest risk would be noise pickup.  Try and keep the wires as short as you can.
  
 There is no exposed metal on the Nutube package other than the pins, so they are all that needs to be insulated.
  
 Pete


----------



## pmillett

highflyin9 said:


> Any changes to the NuTube buffer based on discoveries with the headphone amp? I know most implementations will not have a volume knob, but there would still be the on-off switch.


 
  
 I haven't tried to get the buffer to oscillate, but it might be unstable with very low DC resistance across the inputs.  This would apply only to the input buffers - the output buffers have a high resistance on the gate (the Rp of the Nutube is pretty large) so they should be fine.
  
 To be safe, you can either change to 10k resistors on the source terminals of the 2N7000s - that seems to lower the gm enough that there's no oscillation - or change to 2N3904 + 10k like on the headphone amp.
  
 Pete


----------



## tedk84

I just finished my build and ran into a problem:

The amp started, but one side of the headphone was quiet, while the other side sounded normal. one side of the tube isnt nearly as bright as the other one. I was/am able to set 11V for both test points. Can you guys help me? I used two jumper cables to work around the fact that i ordered the wrong relay (5.1mm instead of 2.54mm spacing) -.- ... When i cross the cables, the quiet side changes left<>right.

http://imgur.com/a/4VPl2


----------



## pmillett

I can't see anything wrong from the photo.  I assume you've double-checked solder joints for shorts and opens...
  
 It is odd that you can still adjust the bias to get 11V and there is a difference in  the glow.  That indicates a big difference in the current through each triode.
  
 Can you check the voltages on the tube pins (to ground)?  Starting at the top (towards the input jack), you should get:
  
 1 - 0.7V
 2 - 0.7V
  
 3 - 2V
  
 4 - 12V
 5 - 0V
 6 - 0V
 7 - 12V
  
 8 - 2V
  
 9 - 0.7V
 10 - 0.7V
  
 Voltages are approximate, some variation is expected.  Let me know what you measure, that may give a clue.
  
 Pete


----------



## tedk84

Oh god, is was really late last night.... 
I mistook L_out for GND and GND for L_out. After i checked this morning, GND>L_Out was 11V, and GND>R_out was ~22V (...). So i fixed that and checked everything - works. 

Thanks anyway Pete


----------



## pmillett

Ah, OK, good.  That makes sense.  Was there a short on the plate, or just bias adjustment?
  
 Pete


----------



## tedk84

no, just bias adjustment, no shorts


----------



## mitsu763

Received my board today. Not sure when I'll get to it but this will be my first build.

Is the Bill of Material up to date on Mouser?


----------



## pmillett

mitsu763 said:


> Is the Bill of Material up to date on Mouser?




Yes, it should be good.

Pete


----------



## ericj

I swear i saw a thread either here or diyaudio where someone asked Pete if he'd make boards for the NuTube buffer + Class-D amp referred to on the website, Pete said it has an SMT chip so that would be problematic, etc. 
  
 Can't find it. 
  
 Anyway. I humbly raise the existence of the TPA3122D2N. DIP-16 package, 2x15w or 1x30w into 4 ohms per chip (with typical class-D power vs. thd curve) at 28v single supply, $2.88 each at Mouser. Though of course there's the output network to consider, which adds a few bucks. 
  
A couple of these in a PBTL configuration are louder than the classic ta2020 T-Amp with no surface mount parts or heatsink required. Plenty of oomph for near-field, dormitories, office-go-boom, etc. 
  
Not that i have actually heard one. But it's substantially similar to the other current TPA3xxx chips, which are generally well regarded in the low-volt low-dollar arena.


----------



## pmillett

ericj said:


> I swear i saw a thread either here or diyaudio where someone asked Pete if he'd make boards for the NuTube buffer + Class-D amp referred to on the website, Pete said it has an SMT chip so that would be problematic, etc.
> 
> Can't find it.
> 
> ...


 
  
 I think it was on DIY Audio...
  
 Yup, I did think of that class D as a possibility.  Pretty wimpy though 
  
 Another option would be to re-design the board I have to make everything through hole except the class D (MP7770).  50 watts is nice.
  
 My thought would be to pre-solder the IC onto the board (I have a small reflow oven, and placing only one part is pretty easy).
  
 Thoughts?
  
 Pete


----------



## Heffa

pmillett said:


> Another option would be to re-design the board I have to make everything through hole except the class D (MP7770).  50 watts is nice.
> 
> My thought would be to pre-solder the IC onto the board (I have a small reflow oven, and placing only one part is pretty easy).
> 
> Thoughts?


 
  
 I myself wouldn't mind a SMD-variant either...
 SMD soldering isn't that hard once you get the hang of it unless you go for REALLY tiny 0201 or such, and the boards usually looks really nice (to me at least).
 0603 package and up isn't that hard to do manually imho.
  
 (and I do mean imperial sizes, 0603 metric I have never tried 
	

	
	
		
		

		
			





 )


----------



## pmillett

heffa said:


> I myself wouldn't mind a SMD-variant either...
> SMD soldering isn't that hard once you get the hang of it unless you go for REALLY tiny 0201 or such, and the boards usually looks really nice (to me at least).
> 0603 package and up isn't that hard to do manually imho.
> 
> (and I do mean imperial sizes, 0603 metric I have never tried :rolleyes:  )




The problem is that parts like the MP7770 have an exposed pad on the back side that is used as the heat sink. It has to be soldered down to a ground plane, and soldered well, or the part will overheat. So normally that requires reflow, either with an oven or rework tool (a fancy heat gun).

It is possible to put a big through hole pad there and fill it with solder from the back of the PCB... it's a little kludgey, but I have done it that way. 

The pin pitch is also pretty fine for somebody without a lot of SMD soldering experience.

Pete


----------



## Heffa

Aaah, then it's a little bit different - I didn't think of that


----------



## ericj

pmillett said:


> The problem is that parts like the MP7770 have an exposed pad on the back side that is used as the heat sink. It has to be soldered down to a ground plane, and soldered well, or the part will overheat. So normally that requires reflow, either with an oven or rework tool (a fancy heat gun).
> 
> It is possible to put a big through hole pad there and fill it with solder from the back of the PCB... it's a little kludgey, but I have done it that way.
> 
> ...


 
  
 Well, I'm not personally very invested in this. I'm not dying to build something with the nutube just yet. 
  
 50W would be much nicer than 30W, particularly considering the typical power vs. distortion curves on class-D devices. If they say 30w, they mean 12w clean.
  
 I agree that the thermal pad is a consideration. And even though i have a cheap chinese hot air system and a bit of smd experience, I'm a bit wary of such devices at home.


----------



## HiGHFLYiN9

I have to get an order into PCX and figured I'd add the parts I need for the NuHybrid . For those of us who prefer carbon film resistors, can the 475K be replaced with 470K 2%, and can the 33.2K be replaced with 33K 2%? T.I.A.


----------



## HiGHFLYiN9

...guess I'll have to wait for Pete to come back


----------



## Heffa

My NuHybrid is shaping up. 
I had to use a few oversized capacitors since those in the BOM was out of stock at Mouser, but there where enough space on the PCB so no issues at all there.
I will not be using the original case, but a Hammond 15something case I had in my bin. That will also gives me enough space for an ALPS Blue Velvet and some nice Neutrik inputs & 6.35mm headphone jack.


----------



## HiGHFLYiN9

Looks great! I have the same helping hands / Panavise combo


----------



## Heffa

highflyin9 said:


> Looks great! I have the same helping hands / Panavise combo


 
 Yea, the Panavise/HobbyCreek Helping Hand combo is awesome


----------



## ericj

heffa said:


> Yea, the Panavise/HobbyCreek Helping Hand combo is awesome


 
  
 Wow, that's over $100 in jigs to hold your stuff. 
  
 I just use this: https://goo.gl/C2dYoY


----------



## HiGHFLYiN9

The Quadhands from Amazon are really nice too, they are $40 or so.


----------



## Heffa

What I like most about the Panavise jig is that it's so sturdy I can rest my hand on it when soldering, without moving the board in any way.
 The Hobby Creek helping hands I got separately later, because it integrates so well with the Panavise stuff.
  
 Anyway, we are derailing the thread a bit here 
	

	
	
		
		

		
		
	


	



  
 When I added temorary power/input/output to be able to test the amp yesterday evening I was really tired, so just when I was about to test it I realized I had hooked the ALPS pot to the headphone outlet by mistake.
  
 Lesson learned - don't try to solder expensive stuff while beeing dead tired!


----------



## gikigill

Already own the SSMH and looking forward to the Nutube shortly if I can get the sale through


----------



## tomb

ericj said:


> heffa said:
> 
> 
> > Yea, the Panavise/HobbyCreek Helping Hand combo is awesome
> ...


 
  
 I've been using this piece of white pine for the last 10 years.  Seems to work well enough.
	

	
	
		
		

		
		
	


	




  It's been through dozens of Millett MAXes/MiniMAXes, Starving Students, T1s, T3s, and any number of prototypes - also the NuHybrid.  Put the part in the PCB, turn it over and press down onto the wood while soldering to keep things flush.
  

  
 Yes, I use some helping hands when doing SMD, but even then - these were $3 (on sale) Harbor Freight specials:

  
 A little electrical tape on the corners keeps the cheap alligator clips from scratching the PCB.  The magnifying glass provides a good steady back-support, too.
  
 I'm not sure what the piece of white pine cost me, but I will unfortunately have to bite the bullet and replace it soon.  It's getting some burn marks and too many indentations from pressing resistors flush against a PCB while soldering.
  





 
  
 P.S. Oh - that's an old PC mouse pad underneath to keep the board from sliding.


----------



## pmillett

highflyin9 said:


> I have to get an order into PCX and figured I'd add the parts I need for the NuHybrid . For those of us who prefer carbon film resistors, can the 475K be replaced with 470K 2%, and can the 33.2K be replaced with 33K 2%? T.I.A.


 
 Sorry for the delay, for some reason I didn't get an email notification...
  
 Yes, 470k and 33k 2% are fine here.
  
 Pete


----------



## Heffa

It's alive! ☺️
Time to cut out the front & back panels for the Hammond box I'm going to put the amp in...oh, and also test it with my good headphones. I have only tested it with some crappy no-name so far.


----------



## HiGHFLYiN9

Looks great!! Good 'ol Neutrik locking TRS and Alps Blue, can't go wrong with either. Do you have a Greenlee punch for the DIN size stuff?


----------



## Heffa

highflyin9 said:


> Do you have a Greenlee punch for the DIN size stuff?


 
 I do not, but now after I have googled what it is I wish I had 
 I usually build my panels using a good old drill, Dremel and small files...
 Last time I built a panel I promised myself to use the 3D printer and print a panel the next time, but naturally my old one is broken at the moment and my new one is still in prototype stage so it's not usable yet.
  
 Have you used a Greenlee punch? Are they good for aluminium panels and such? No bending of the panel when using it?


----------



## HiGHFLYiN9

I have four of them, one for DIN connectors and the rest for tube sockets. They're exquisitely expensive but worth it if you build a lot. Great for aluminum, steel and copper as long as it's not super thick. It won't bend it. I've heard of people running into problems with diecast metal, but I've personally had no issues. Gives a super clean cut... no need for deburring, etc. 
  
 Looking forward to see that 3D printed panel when you're back up and running  
  
 As far as my NuHybrid, the parts are coming... I just have to be patient. 
	

	
	
		
		

		
			





 Trying to decide between a Hammond case and a cigar box for enclosure.


----------



## ericj

highflyin9 said:


> I have four of them, one for DIN connectors and the rest for tube sockets. They're exquisitely expensive but worth it if you build a lot. Great for aluminum, steel and copper as long as it's not super thick. It won't bend it. I've heard of people running into problems with diecast metal, but I've personally had no issues. Gives a super clean cut... no need for deburring, etc.
> 
> Looking forward to see that 3D printed panel when you're back up and running
> 
> ...


 
  
 I just cut my panels with an abrasive waterjet system.


----------



## HiGHFLYiN9

ericj said:


> I just cut my panels with an abrasive waterjet system.


 
 Eric, since it sounds like you have it the easiest, want to cut ours out too?


----------



## ericj

haha that might be doable .  . . . 
  
 I frequent a makerspace that has a small 2-axis waterjet system. About a 3'x7' cutting area iirc. Costs $55/hr in increments of .01 hour for me to use it. That's only slightly low pricing (an hour of cutting uses $20 worth of abrasive and a lot of electricity) but i also have a key to the shop and can wander in and use it whenever i want. The university charges $1/minute but since i am not a student or even technically a faculty dependent anymore i would have to talk my way in, and they probably wouldn't let me use it at 8pm on a sunday. 
  
 I am considering cutting faceplates for some amps out of stone tile. I got some really detailed vent work going for my Max.Custom tube protectors are standard hardware + a few minutes in cad + a few minutes cutting + whatever finishing. Waterjet does leave the edges of soft metals kinda rough, and sometimes there is some haze from overspray during piercing. 
  
 I might be willing to cut out some panels for cost of cutting + donation to the makerspace. we're too disorganized and chaotic to figure out how to charge people dues let alone how much that should be but every now and then we get in commercial waterjet work that pays the bills for a month or two.


----------



## HiGHFLYiN9

Nice! There are similar places in Baltimore / Catonsville, MD, but nothing with a waterjet system... and they are quite disorganized as well, seems to be par for the course. I'm certain some of the people here would be interested, and a donation to a facility that empowers builders to build is an easy spend in my book.


----------



## JustinDT

Just finished putting together a NuHybrid and it sounds amazing but I do have an issue.

It sounds as if the gain is incredibly high, had to switch from my ethers to my DT 770 250 Ohms just to get a listenable level. The only part different from the BOM is the TKD pot. I looked over the solder joints and all look good. Is there anything besides de-soldering and checking each component separately that I can do to troubleshoot?


----------



## HiGHFLYiN9

You're using a 10K pot, correct?


----------



## JustinDT

Yes, it is a 10kOhm pot.


----------



## HiGHFLYiN9

You may have to ask Pete which resistors dictate the gain so you can swap them out. 

Has anyone tried rolling the op-amps yet?


----------



## HiGHFLYiN9 (May 25, 2017)

This thread is awfully quiet. Here's an image of my semi-populated PCB:






Going to put it in a wood box to give that retro table radio feel. FYI you can upgrade the film caps to Polypropylene WIMAs, they'll fit.


----------



## NuClear235

I have my too. I am just start buildind. Still wait for some devices from Mouser...


----------



## Heffa

I just finished my NuHybrid Headphone amp yesterday night.
It worked fine before I put it in the Hammond enclosure, so hopefully it will still work fine when I get the chance to actually try it out for real tonight 
Oh, and the volume knob is only temporary until the right one arrives.


----------



## NuClear235

Bravo. I should do it the same way 
Plastic unshielded box is the shame...


----------



## HiGHFLYiN9 (Jun 1, 2017)

Very nice! Can you share with members what model Hammond you used? I like it much better than the Serpac, but the Serpac is cheap and good for people on a limited budget.

I finished mine over the weekend and have been letting it break in. Initial listening sessions have been very positive. I shielded the wooden box I made with copper tape electrically connected to the front and back aluminum panels.





































Not completely done, but close  if you're wondering, the brown boxes are closely matched Russian Silver Mica coupling caps. They're huge for 0.1uF, but sound mighty good.

A shout out to TomB for the initial build and parts updates


----------



## Heffa

Wow, that looks awesome - I love the retro radio feeling of your build! Well done indeed! 

My enclosure is a Hammond 1455N1601

In the picture you can see my power supply (AMB Sigma11) in two separate 1455N1201BK boxes, one for the transformer and one for the actual Sigma11. 
It has four 24V outputs so it can drive several amps at once, even though it have only driven my PPA amp (in the black 1455N1601BK enclosure) for the last 6 years  or so 
 

I need to change the resistor for the LED, it's way too bright at the moment


----------



## HiGHFLYiN9

Nice! Lookin gewd!  Based on your mention I'm going to put together an AMB Sigma11 myself to hang with the NuHybrid  Are you running 100VA or so to handle 4 outputs? I just ordered a 50VA (up from the 25VA in the BOM) from Antek for $23 shipped, such a good deal. It should fit in the 2200 series case, but just barely. Build Build Build.


----------



## Evgeni

I have built mine a month ago. It's a wonderful amp for my HD-650 and I love it. 

I have a slight problem though. If I touch the pot (it's the upgraded TKD pot as recommended by Pete) I can hear a buzzing noise. This somehow disappears if I crank it up to max. What could be the problem? Maybe I should ground the pot body or something?

Also I can hear the pot generating noises when close to zero which I thought would not be a problem with a pot this price...


----------



## HiGHFLYiN9

It does sound like a grounding issue. Grounding the metal part of the pot could help. I assume the knob you are using is metal and not plastic?


----------



## hav2uo4

Evgeni said:


> I have built mine a month ago. It's a wonderful amp for my HD-650 and I love it.
> 
> I have a slight problem though. If I touch the pot (it's the upgraded TKD pot as recommended by Pete) I can hear a buzzing noise. This somehow disappears if I crank it up to max. What could be the problem? Maybe I should ground the pot body or something?
> 
> Also I can hear the pot generating noises when close to zero which I thought would not be a problem with a pot this price...


HiGHFLYiN9 is correct, I can confirm it's a grounding issue.  I also have the TKD pot (with a large plastic, pseudo metallic knob).  It used to buzz very loudly when I touched it.  Also picked up A LOT of noise from nearby devices.  The noise was so bad the amp was unusable.  Soldered a wire onto a ground connection and wrapped it around the knob's threads and clamped it down with the supplied nut.  Fixed a lot of noise problems.  The circuit still seems prone to picking up noise from other devices (even with volume knob removed), but careful amp placement and wire routing helps a great deal.

Another noise observation from my amp.  I had random noise coming from the right channel.  It'd usually get triggered by input signals.  Figured I had a cold joint somewhere, so I reflowed every right channel connection.  Didn't fix the problem.  So I only used my least sensitive headphones.  After quite a bit of use, problem has mostly gone away.  It's still audible on my highest efficiency headphones, but it's mostly tolerable.  Wondering if it's coming from the nuhybrid tube itself and it's burned itself in.

But with my higher efficiency phones, it was nearly impossible to get a good volume setting.  So I bought an attenuation cable and it gave me better volume control and made the noise floor completely inaudible for even my highest efficiency headphones.  Wish I would have had one sooner.  Below is a link to the one I have (hope it's not against the forum rules - no affiliation, just like it).
http://www.garage1217.com/garage1217_diy_tube_headphone_amplifiers_012.htm

Some of you guys have made some really nice looking cases (I went with the plastic half-case in the BOM).  I imagine the shielding helps with many of the noise problems I described, can anyone confirm?


----------



## HiGHFLYiN9

Other than the pings here and there with startup I haven't noticed anything (I haven't tested it much yet). The whole thing from front to back is shielded, so that may be helping. I'd imagine a device like the NuTube would pick up noise from cellular signals, so if your phone is close by, you'd likely hear it. I had a Manley that would pick up cell phone noise and it took a while to figure out where it was coming from.


----------



## silverfishla

Hey guys, I'm going to build this amp soon as I am receiving some of the parts that I need.  I had a question about the Op amps (and their function in the unit).   Are the Opamps used singles or duals, and what is the function of each?  Is one for right and left channel or is one a buffer?  I'm a newbie, so I apologize for asking such basic questions.  I've read over and looked over P. Milletts schematics and information on his DIY page.  Most of the explanations he gives are about constructing the unit but not what all of the separate pieces do ( I guess that's just assumed that we should know, but I don't).  Can anyone draw out a schematic and explain what each part actually does (that is so much to ask, so I don't expect that it is a very reasonable request, but I'm giving it a shot anyways  ).  Your amps all look great and are an inspiration.


----------



## vixr

OPA551PA is a buffer, if you look at the first post in this thread, you will see the link that Pete supplied, all your questions will be answered there...


----------



## trevmex

This looks really fun to make. I have a noobie question about it, though. Will this amp work with low impedance headphones


----------



## hav2uo4

trevmex said:


> This looks really fun to make. I have a noobie question about it, though. Will this amp work with low impedance headphones


This amp is able to drive all my low and high impedance headphones with ease.  But if they're highly efficient you may experience some background hiss/noise and have trouble getting volume settings that aren't too loud.  But an attenuation cable can be built easily enough or purchased relatively cheaply and solves both problems.  It's a neat little amp.  Can be a microphonic little devil, but I'd recommend without hesitation.  Hats off to Pete!


----------



## trevmex

I just ordered the PCB and tube! There are some things in the BOM that are out of stock at Mouser, so I created another parts list that will work. I checked with Pete before buying it. His only concern is that the Elna caps might be a little tight, but it is all in stock.

The parts list is at https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=12aebf4006, or go to http://www.mouser.com/Tools/Tools.aspx and enter in Access ID 12aebf4006. Looking forward to building this!


----------



## ken_chuang

I just gotten the PCB and Nutube too. I realized there were reports of microphonic noise, so I ordered a regular pot rather than a stepper. Then I stumbled on this Nutube Guide ( http://korgnutube.com/en/guide/ ), where there is a section on "To prevent microphonic noise".

For my build, I am planning to try the following to address microphonic noise.
- Wrap Nutube over with thread seal tape (aka. PTFE tape or plumber's tape), similar to tube damping rings. 
- Acrostic damping material inside chassis.


----------



## HiGHFLYiN9

This one might be easiest "Placing a heavy metal plate (e.g. lead) on the surface of a Nutube can also reduce noise." Trimming a piece of steel and putting it on top with double sided tape wouldn't require much effort. Also, if you put some footers on your chassis (I used EAR, they're less than $1 each, http://www.partsconnexion.com/isolation_ear.html ) should help. 

I don't think it's really possible to decouple the tube from the PCB it's connected to due to all the solder connections. The best bet would be to give it its own PCB off board or *move the potentiometer off the board*. 

It's fun to think about. This is a new audio device that not many people have used yet, so best practices haven't been established.


----------



## trevmex

OK, just got the big bag o' stuff from Mouser, and the tube and board. Just waiting on the upgraded pot and footers from PartsConnexion and I'll get started!


----------



## HiGHFLYiN9

Keep us updated


----------



## trevmex

Got the upgraded pot and the EARs. Now I'm ready to go!


----------



## hav2uo4

trevmex said:


> Got the upgraded pot and the EARs. Now I'm ready to go!


Awesome! When you're slinging it together I'd recommend soldering a wire into one of your ground connections you can use to ground the body of your pot.


----------



## trevmex

hav2uo4 said:


> Awesome! When you're slinging it together I'd recommend soldering a wire into one of your ground connections you can use to ground the body of your pot.



Can you share a picture of how you did this? I read your description, but can't quite picture it in my head.


----------



## hav2uo4 (Jul 16, 2017)

Hope this works...Pete's multi-pot footprint is excellent for hacking a ground connection.  I had to file a small notch into the inside of the case to clear the wire.


----------



## HiGHFLYiN9 (Jul 18, 2017)

I added a cool little engraved plate to mine, feels complete now. I also built AMB's o11 power supply for it as a nice little improvement over the wall wart.


----------



## SlingBlade

I'm about to order the Buffer. Have any of you have played with bias of the NuTube to get more even order distortion, and if so, what are your impressions?


----------



## HiGHFLYiN9

I haven't myself. It's a little tricky to get access to the bias in my setup.


----------



## trevmex

Can someone recommend a knob for the TKD 2CP601-10K?


----------



## trevmex

As promised, here are the progress pics!
         
And there you go. I don't have the right headphone connector to test it at home, so I'll let everyone know how it sounds tomorrow.

I highlighted *hav2uo4*'s pot ground wire and the EARs. Hope they make it sing!


----------



## trevmex

Here is the full gallery from last night!


----------



## trevmex

I just tried the NuHybrid out with my Grado SR60i phones. Sounds great!!!

Now, I want to put a clear plastic lid on the setup with some slits for air to get in. Can anyone recommend a place to get a plastic lid for the box Pete suggested?


----------



## Evgeni

Guys, you were right about solving noise issues by grounding the pot: that solved my problem. However I haven't applied this fix permanently (like on the hav2uo4's picture above) yet, I just tested it with a wire. But in the meanwhile I replaced the switching supply with a linear supply I ordered from eBay and that kind of halved the noise.

However I am currently totally noise-free. Here's the "fix". I was mainly using my NuHybrid with my HD-650. However I recently bought Beyerdynamic DT-880 600-ohm and man, that's a combination made in heaven! The Beyers just sound incredible, it's a butter creamy sound. I can't hear them sound this way with any of my other amps. This amp really shines with these headphones. Really, guys, you MUST try this combination, it's probably my best setup ever! And they are absolutely noise free this way which I contribute to high-impedance (and low-sensitivity).

BTW, I tried to change the bias through the trims while listening to music and I can't hear any change whatsoever. It's either the harmonic content change can be noticed only with an oscilloscope and not audible or it's my ears (or I don't know what to listen for). But right now I just followed Pete's advice to set them at 11V.


----------



## hav2uo4

trevmex said:


> I just tried the NuHybrid out with my Grado SR60i phones. Sounds great!!!
> 
> Now, I want to put a clear plastic lid on the setup with some slits for air to get in. Can anyone recommend a place to get a plastic lid for the box Pete suggested?


Build looks awesome, nice job.  Glad it's working out for you.  Not sure about a plastic lid.  Data sheet seems to suggest that isolation from the air (no slits) can be better for microphonics (I smacked a fruit fly ~10ft away and it started ringing...haha).  But the regulator does get toasty, it probably needs some airflow (I squeezed a heatsink on mine which is somewhat visible on the previous picture I posted).


----------



## hav2uo4

Evgeni said:


> Guys, you were right about solving noise issues by grounding the pot: that solved my problem. However I haven't applied this fix permanently (like on the hav2uo4's picture above) yet, I just tested it with a wire. But in the meanwhile I replaced the switching supply with a linear supply I ordered from eBay and that kind of halved the noise.
> 
> However I am currently totally noise-free. Here's the "fix". I was mainly using my NuHybrid with my HD-650. However I recently bought Beyerdynamic DT-880 600-ohm and man, that's a combination made in heaven! The Beyers just sound incredible, it's a butter creamy sound. I can't hear them sound this way with any of my other amps. This amp really shines with these headphones. Really, guys, you MUST try this combination, it's probably my best setup ever! And they are absolutely noise free this way which I contribute to high-impedance (and low-sensitivity).
> 
> BTW, I tried to change the bias through the trims while listening to music and I can't hear any change whatsoever. It's either the harmonic content change can be noticed only with an oscilloscope and not audible or it's my ears (or I don't know what to listen for). But right now I just followed Pete's advice to set them at 11V.


Interesting PS observations, Evgeni.  I got some promising results with another method.  I was trouble-shooting some noisy Russian tubes on my project amber amp and found that my noise problems went away when I ran a ground wire from my mains line to the negative out from the switching regulator (be super careful if trying this).  Dead silent.  Tried it on my nuhybrid with the same results.  Crazy quiet! Now my work computer sound card seems to have an unreasonable noise floor!  YMMV, but I seem to have some really dirty AC.


----------



## silverfishla

Stupid question.  Are the opamps in this unit singles or duals?


----------



## trevmex

hav2uo4 said:


> (I squeezed a heatsink on mine which is somewhat visible on the previous picture I posted).



Got a part number for your heatsink?


----------



## trevmex

Evgeni said:


> linear supply I ordered from eBay



Can you send a link to the linear supply you bought?


----------



## trevmex

silverfishla said:


> Are the opamps in this unit singles or duals?



It uses two TI OPA551PAs (http://www.mouser.com/ProductDetail/Texas-Instruments/OPA551PA/?qs=wgAEGBTxy7kLauCnM%2btIHQ==). They are singles.


----------



## hav2uo4

trevmex said:


> Got a part number for your heatsink?


577002B00000G.  Any std package with 0.25" fin height or less should work.  Might be able to pull off up to ~0.40" if mounted backward (pointed away from the 1/4 jack).  I have a few in that range in my cart for whenever I pull the trigger on another digikey order.  Even with the small heatsink I measure up to ~140F.  Probably OK, but I'd prefer to have it run cooler.


----------



## trevmex

Well, I accidentally left my NuHybrid on all day while I was at work and came home to listen to some music tonight. It sounds amazing having been on all day. I imagine that isn't the best idea, but the difference is noticeable!


----------



## silverfishla

trevmex said:


> It uses two TI OPA551PAs (http://www.mouser.com/ProductDetail/Texas-Instruments/OPA551PA/?qs=wgAEGBTxy7kLauCnM%2btIHQ==). They are singles.


Hey thanks a lot for answering my question. When I finally get the parts for my build, I think I'm going to stick a couple of Sparko's Labs singles in there if the specs match up.


----------



## hav2uo4

silverfishla said:


> Hey thanks a lot for answering my question. When I finally get the parts for my build, I think I'm going to stick a couple of Sparko's Labs singles in there if the specs match up.


Interesting module.  Datasheet mentions unity gain stability issues and output current isn't as high as the OPA551, so wonder if you'd run into issues with harder to drive HPs and higher volumes.  I haven't tried rolling myself as the OPA551s seem to be great performers, but keep us up to date if you try it.


----------



## hav2uo4

trevmex said:


> Well, I accidentally left my NuHybrid on all day while I was at work and came home to listen to some music tonight. It sounds amazing having been on all day. I imagine that isn't the best idea, but the difference is noticeable!


Ha, I've done the same.  Did sound good, but it may be because I'm coming back to a warm amp after a rough day at work.  haha.


----------



## Evgeni

trevmex said:


> Can you send a link to the linear supply you bought?


Here it is, very happy so far. 
https://www.ebay.com/itm/302219535754


----------



## Sythrix

I just built this and am really enjoying it but had a few questions about the upgraded pot. I installed it and also put the grounding wire on, but it whenever I turn the volume up or down there is distortion during the actual turning.

Also, at the very bottom and top end the amp just starts crackling and hissing. If this is the behavior of a $40 pot I'd hate to see the original, but I think it is something else, maybe something I didn't do correctly? When not changing volume it sounds sublime. Anyone else have this behavior?


----------



## pmillett

For the input buffer transistors Q2 and Q3, did you use 2N3904 transistors?  I saw some oscillation that produced noise like you described when I used FETs in those positions.

Pete


----------



## Evgeni

Sythrix said:


> Also, at the very bottom and top end the amp just starts crackling and hissing. If this is the behavior of a $40 pot I'd hate to see the original, but I think it is something else, maybe something I didn't do correctly? When not changing volume it sounds sublime. Anyone else have this behavior?



Yes, I have this behavior too with the upgraded pot. Slight hissing and cracking at the bottom and top positions. Other than that it’s a great little amp and it’s currently my main amp.



pmillett said:


> For the input buffer transistors Q2 and Q3, did you use 2N3904 transistors?  I saw some oscillation that produced noise like you described when I used FETs in those positions.
> 
> Pete


Pete, I am using the 2N3904 transistors, so probably the reason for the top/bottom noise is something else?


----------



## Sythrix

pmillett said:


> For the input buffer transistors Q2 and Q3, did you use 2N3904 transistors?  I saw some oscillation that produced noise like you described when I used FETs in those positions.
> 
> Pete



Yes those are the ones I ordered per the BOM. I remember I put them on first for Q so I wouldn't confuse them.

It sounds good to me and honestly I don't care about the extreme bottom and top because I'll never actually go there. Just want to make sure I didn't mess anything up.

It could be they just sent me a slightly dirty/imperfect pot which causes the noise during turning? Or maybe I need to redo the ground connection? 



Evgeni said:


> Yes, I have this behavior too with the upgraded pot. Slight hissing and cracking at the bottom and top positions. Other than that it’s a great little amp and it’s currently my main amp.
> 
> 
> Pete, I am using the 2N3904 transistors, so probably the reason for the top/bottom noise is something else?



Well good to know I'm not alone.


----------



## Sythrix

Just got home and confirmed the 2N3904s are in Q2 and Q3. I think it must have something to do with the pot itself or some failing I haven't seen yet on my install or grounding of it.


----------



## pmillett

Well, I'm not real sure what would be causing this.  I didn't notice noise like that on the one I built with the upgraded pot.

The noise that was caused by oscillation using the FET was very loud.  I would expect a little noise as the pot hits its limits, but nothing terrible.

Pete


----------



## Sythrix

pmillett said:


> Well, I'm not real sure what would be causing this.  I didn't notice noise like that on the one I built with the upgraded pot.
> 
> The noise that was caused by oscillation using the FET was very loud.  I would expect a little noise as the pot hits its limits, but nothing terrible.
> 
> Pete



Not a big deal. I might tear it apart one day to see if I can figure it out, but for now it's just not enough of an issue for me to bother. The sound is so good that I am making it my main bedroom amp for music and TV/movies.

Anyways, thanks for getting back to me! I am a fan of your work and am just about ready to start the Butte to accompany my PC.


----------



## trevmex

Sythrix said:


> I just built this and am really enjoying it but had a few questions about the upgraded pot. I installed it and also put the grounding wire on, but it whenever I turn the volume up or down there is distortion during the actual turning.
> 
> Also, at the very bottom and top end the amp just starts crackling and hissing. If this is the behavior of a $40 pot I'd hate to see the original, but I think it is something else, maybe something I didn't do correctly? When not changing volume it sounds sublime. Anyone else have this behavior?



I have the upgraded pot as well and grounded it as well, it hisses at the very bottom and crackles at the very top. I don't get distortion when tuning, though (I used all the recommended upgraded parts on the BOM/site).

The amp _is_ hyper-sensitive to any jostling, though. I put EARs on it, which seems to help, and I bought the enclosed version of the box Pete recommends (but haven't gotten around to putting the top on yet).

Still, I love it, though. I am thinking of making a DAC to complement it, but haven't decided what to build...


----------



## Sythrix

trevmex said:


> I have the upgraded pot as well and grounded it as well, it hisses at the very bottom and crackles at the very top. I don't get distortion when tuning, though (I used all the recommended upgraded parts on the BOM/site).
> 
> The amp _is_ hyper-sensitive to any jostling, though. I put EARs on it, which seems to help, and I bought the enclosed version of the box Pete recommends (but haven't gotten around to putting the top on yet).
> 
> Still, I love it, though. I am thinking of making a DAC to complement it, but haven't decided what to build...



The distortion while turning and at the bottom and top seems to be fading away with time. I think I was shipped a substandard pot, but since I already soldered it, it's not eligible for return.

I used "Isolate It!" Sorbothane feet to steady it, which seems to limit ringing to when I plug in a pair of headphones or very slight when I am adjusting the volume.

I also am going to build a DAC!

I decided on the https://www.amb.org/audio/gamma2/ (which requires that you also build the γ1, as it's an extension to it). It's basically two DACs and outputs in one case. That way I'll be able to wire two different amps (if I want) to the one brick housing the γ2 and γ1 (with one slightly higher quality output, given the more advanced γ2). Came out a little over $300 after all parts and a σ25 power supply with the σ78 regulator (optional, but lower noise than wall-warts). Could probably easily do it in the low to mid $200 range if you just used the USB power or something. There really aren't a lot of options for DIY DACs out there.

I was going to go for the γ3 but the cost of all the parts and the front panels, on top of my non-existent knowledge of building power supplies, led me towards these builds instead. I'm going to have someone guide me through putting together the σ25 power supply so I at least get some familiarity with building them before attempting something as complicated as the γ3's.

I'm just a little concerned about the reports I've been reading of the old SSMH and how it sometimes damaged the γ2 and γ1 because of some kind of power problem. I'm guessing it's not going to be an issue, but Pete did say the NuHybrid was based on the old Millett Hybrid design...  All the parts are already on their way, so I hope it doesn't have the same problem or I'll be building another DAC soon enough after this one, lol.


----------



## silverfishla

I'm currently building this amp right now.  In the wings, I've got some Sparkos Labs singles waiting to be installed in this when it is finished.  I have installed some Nichicon Muses KZ capacitors for the big ones and fine gold (like in the BOM) for the small ones.  I have a question though...which Capacitor placements on the board are the most resposible for the sound of the amp?  Which ones are resposible for the input section and the output section?  Sorry for such a dumb question, but I am basically building this like a "paint by numbers" and don't really know what capacitors on the board do what.  Reason I ask is, I have been changing caps on a portable tube amp recently and found that I really like the sound of those Nichicon blue Audio caps that are available.  I want to know which caps on the nutube amp (should I swap them out) are the most responsible for the "sound", so I can see if they make a difference (when I finish my build)


----------



## Sythrix (Sep 24, 2017)

silverfishla said:


> I'm currently building this amp right now.  In the wings, I've got some Sparkos Labs singles waiting to be installed in this when it is finished.  I have installed some Nichicon Muses KZ capacitors for the big ones and fine gold (like in the BOM) for the small ones.  I have a question though...which Capacitor placements on the board are the most resposible for the sound of the amp?  Which ones are resposible for the input section and the output section?  Sorry for such a dumb question, but I am basically building this like a "paint by numbers" and don't really know what capacitors on the board do what.  Reason I ask is, I have been changing caps on a portable tube amp recently and found that I really like the sound of those Nichicon blue Audio caps that are available.  I want to know which caps on the nutube amp (should I swap them out) are the most responsible for the "sound", so I can see if they make a difference (when I finish my build)



I'm sure someone more knowledgeable will jump in if I'm wrong, but looking at the circuit, C3 and C6 are directly before you reach your relay, then the phones themselves. However, don't discount the small electrolytic ones, because the Nutube is using them, per the NuHybrid website:

_The output of the buffer is coupled using a 10uF capacitor into the Nutube grids. _http://www.pmillett.com/nuhybrid.html​Which to me says that they are responsible for the sound being delivered to the op-amps, or the "buffer" stage. In other words, all of the electrolytic capacitors are probably important. That said, a good capacitor is doing its job when it *doesn't *affect your sound quality...read this here (go to post #8) by stv014 (I don't know how to properly link/quote from a separate thread, if there's a way to do that) who explains it quite well I think.

I say use whatever capacitors make you happy or look the best as long as they are within spec, because if they're doing their job right, all that's going to matter is how well they lend an aesthetic flavor to your build. Good luck! Also, I would love to hear how those discrete op-amps work out for you.


----------



## pmillett

Sythrix is correct, those are the most important.

The input coupling caps C20 and C21 are also directly in the signal path, but they are smaller film capacitors and if you use what's on the BOM (Wima) they are already pretty good.

The problem can be finding better electrolytic caps that will fit on the PCB.  Audiophile electrolytics tend to be bigger than normal ones.  The BOM has Nichicon "Fine Gold" caps, which are pretty good.  You may be able to find Elma caps that can be made to fit as well.

Pete


----------



## silverfishla

Thanks guys!


----------



## silverfishla

Hey guys.  So I'm sort of in the last 1/3 stretch to finish my amp build.  Waiting for some parts to show up or come to be in stock.  I have a few very basic questions... 1) I've decided to lift some of the components off the board in order to fit in my casing better and have ordered some more panel mount friendly parts.  My question is, what is the right size wire to wire the components (jacks and rca) to the board?  Does it matter what wire I use?  2) Does anyone know of a good panel mount DC jack and headphone jack?  They all seem to be of the same quality.  Is there some that are nicer looking?
Here are some pics of my project so far...


----------



## HiGHFLYiN9

Looks very nice. The wire length doesn't matter, you can mount the RCAs wherever they look aesthetically pleasing. If this were a larger build and you had to run the wire a foot or longer, then shielded wire can be of benefit. 24 gauge wire is generally best for signal, although if you have something between 20-26 laying around it will work fine. For the headphone jack, a lot of people like the Neutrik locking jack or the Neutrik NMJ series, at least in the headphone world. Switchcraft seems to be the go-to in the guitar market. Make sure to order a stereo version (if you shop in a hurry, the monos look very similar). The DC jacks are all quite similar. Switchcraft would be a good brand if you were looking for one.


----------



## CJG888

+1 on the Neutrik locking jack.


----------



## silverfishla

HiGHFLYiN9 said:


> Looks very nice. The wire length doesn't matter, you can mount the RCAs wherever they look aesthetically pleasing. If this were a larger build and you had to run the wire a foot or longer, then shielded wire can be of benefit. 24 gauge wire is generally best for signal, although if you have something between 20-26 laying around it will work fine. For the headphone jack, a lot of people like the Neutrik locking jack or the Neutrik NMJ series, at least in the headphone world. Switchcraft seems to be the go-to in the guitar market. Make sure to order a stereo version (if you shop in a hurry, the monos look very similar). The DC jacks are all quite similar. Switchcraft would be a good brand if you were looking for one.


Thanks, I'm going to look into it.  I do have some 20gauge wire that I can use.  I probably will use it, since I have it.  It's pretty nice SPC wire milspec.  





CJG888 said:


> +1 on the Neutrik locking jack.


  Guys, I saw the locking jack...and I like it...but it might mess up my aesthetic!  Hahaha.  Maybe if I can find a silver one....


----------



## silverfishla (Oct 7, 2017)

Hey guys.  Does anyone here have some extra parts?  I can't seem to source what goes in K1 and D1.  K1 is: NEC Tokin Kemet-PCB Low signal relay PCB 24v DC non latch.  D1 is: ST Microelectronics- Transient Voltage Suppressor SM6T.  
These two items are on backorder from Mouser and one won't be in until Mid November and the other in January!
Are there other parts that I can use from Mouser that will work?  Sorry, I just can't reliably figure out what I'm looking at there.  Brands, voltages, etc.  I just don't want to get it wrong.
If anyone has an extra one of these I'd be willing to trade for something that you might need.  PM me.
I have switches, caps, copper shielding tape, guitar pots, knobs, etc.  Stuff you might be able to use for this or other electronics builds.


----------



## pmillett

On the PDF and XLS BOM on the web page, there is an alternate part shown for the relay which looks to be in stock at Mousey.  For D1, just search for 'P6KE33A'.  Any manufacturer is fine, there are many.

Pete


----------



## pmillett

Gotta love autocorrect.  Mousey = Mouser.


----------



## silverfishla

Thank you @pmillet, I will check that out.  I'm so curious to hear this amp!


----------



## silverfishla

I am at the very end stage of my build!  I just need to finish wiring it up.  I've got a few last questions though that I want to make sure I get right...

 
I've decided to install a stereo jack off board and want to make sure I wire this up right.  What numbers correspond to the Ring, Tip, and Sleeve of the jack?  The PCB has six soldering points, but I assume that I only have to use 3 of them.  Can anyone tell me which ones correspond to the Ring Tip and Sleeve?
 
I've also decided to install the 24v DC jack off the PCB.  Can someone also confirm which numbers correspond to the Ring Tip and Sleeve of the back of the installing DC jack?
 
Lastly, do I need this third wire connected to the On/Off toggle switch?  Or can I just leave it off?

My thanks in advance.


----------



## pmillett

On the headphone jack: 2 = tip, 4 = ring, 6 = sleeve.

On the power jack:  3 = tip = positive, 1 = sleeve = negative.

On the power switch:  You only need the two pins farthest from the PCB edge
 (green and white wires in the pic).

Pete


----------



## SasaKudo (Oct 20, 2017)

@pmillett : It seems that the dimension of the upper left hole in the PCB drawing is wrong (it's 2,8125 right now, bigger than the PCB itself).

The assembly guide also mentiones that I could find the DXF file of the PCB on your website, but I wasn't able to find it (Wanted to use it to design a 3D printed case).

Thank you for the hard work!


----------



## Daniel Bauza

Hello all, first off I'd like to thank you for all the valuable info you post and discuss which helps further noobs such as myself learn more about DIY projects. I built the Nutube a couple of months ago and I noticed an imbalance in the right channel. I'd have the volume at zero but could still hear right channel. Today all hell broke loose. The right channel is blasting even with the volume all the way down. Could use some guidance?


----------



## pmillett

That's pretty much always the symptom of the grounded end of the volume pot being disconnected from ground.  Check the solder on the volume pot.  Or, it could be defective or broken.

Pete


----------



## pmillett

SasaKudo said:


> @pmillett : It seems that the dimension of the upper left hole in the PCB drawing is wrong (it's 2,8125 right now, bigger than the PCB itself).
> 
> The assembly guide also mentiones that I could find the DXF file of the PCB on your website, but I wasn't able to find it (Wanted to use it to design a 3D printed case).
> 
> Thank you for the hard work!



Sorry for the delay, I've been traveling again.  When I get home tomorrow I can generate a DXF file for you.

Pete


----------



## HiGHFLYiN9

I'm surprised the NuTube hasn't found its way into a tube overdrive pedal yet. The only guitar pedal it seems to be in right now is a strange Miku anime sing along pedal.


----------



## Daniel Bauza

Thanks Pete, resoldered the contacts and It cleared up considerably.
Very low signal coming from right channel but only noticeable with my Grado’s


----------



## silverfishla

Daniel Bauza said:


> Thanks Pete, resoldered the contacts and It cleared up considerably.
> Very low signal coming from right channel but only noticeable with my Grado’s


Have you checked your gain settings and are they of equal value?


----------



## Daniel Bauza

Yes I have and they appear to be exact
11.0


----------



## pmillett

Daniel Bauza said:


> Yes I have and they appear to be exact
> 11.0


Unfortunately that's pretty common for small volume control pots.  They all... suck.  Lots of channel imbalance at low volume settings. 


Pete


----------



## Daniel Bauza

bummer... other than that I love the sound. Going to put it up against audio-gd R2R later this week.


----------



## silverfishla (Oct 23, 2017)

So, I finally finished my Millett Nutube amp a few days ago.  I think it sounds great and getting better.  I'm running a couple of SparkosLabs singles in there at the moment and from initial comparisons with the ones on the BOM, I think that they are fantastic.  I don't have a final assessment yet, as I'm still letting everything settle in and trying different headphones.  Here are a few pictures though.
I also have a couple of Burson V5i singles coming in to try out.  I'll post my op amp impressions when I get a little time with them...
   
Thanks @pmillett , that was a really fun build and the amp sounds great!

*There's supposed to be a little green rabbitt that shows up on the front of the amp when ON.  I'll have to change to a stronger LED to make it show up though...but I'm going to make that happen!  I call this amp my Millett Nutube "White Rabbit" amp.


----------



## pmillett

SasaKudo said:


> @pmillett : It seems that the dimension of the upper left hole in the PCB drawing is wrong (it's 2,8125 right now, bigger than the PCB itself).
> 
> The assembly guide also mentiones that I could find the DXF file of the PCB on your website, but I wasn't able to find it (Wanted to use it to design a 3D printed case).
> 
> Thank you for the hard work!



Yeah, that dimension should be 3.125.  I grabbed the 'x' location instead of 'y'.

I'm attaching the DXF file (inch units, zipped).

Pete


----------



## SasaKudo

pmillett said:


> Yeah, that dimension should be 3.125.  I grabbed the 'x' location instead of 'y'.
> 
> I'm attaching the DXF file (inch units, zipped).
> 
> Pete



Thx. I'm currently designing my case. It will take some days until I got the 3D print right (PETG). Hopefully the big MOSFET won't radiate too much heat for the case to handle material wise.


----------



## Zemo

I've missed all the diy tinkering, so I thought this might be a good project to get back into practice with a soldering iron. Thanks for putting this together, Pete!

One question - I have a bunch of wima film caps at 250v 1uf...any benefit to using these over the 1nf caps anywhere? Just trying to think of easy upgrades with parts I've got lying around...


----------



## pmillett

Zemo said:


> I've missed all the diy tinkering, so I thought this might be a good project to get back into practice with a soldering iron. Thanks for putting this together, Pete!
> 
> One question - I have a bunch of wima film caps at 250v 1uf...any benefit to using these over the 1nf caps anywhere? Just trying to think of easy upgrades with parts I've got lying around...


They might be difficult to fit on the PCB, but the 1uF caps would work fine.  You will get a bit better low frequency response...

Pete


----------



## arteom

silverfishla said:


> So, I finally finished my Millett Nutube amp a few days ago.  I think it sounds great and getting better.  I'm running a couple of SparkosLabs singles in there at the moment and from initial comparisons with the ones on the BOM, I think that they are fantastic.  I don't have a final assessment yet, as I'm still letting everything settle in and trying different headphones.  Here are a few pictures though.
> I also have a couple of Burson V5i singles coming in to try out.  I'll post my op amp impressions when I get a little time with them...
> 
> Thanks @pmillett , that was a really fun build and the amp sounds great!
> ...



Great looking build!


----------



## flyinggeek

Just finished my NuTube and love the way it sounds. Also laser cut a case for it...


----------



## GunnerXL

Just received the board today, but the opamp is currently sold out in mouser. Can anyone would kind enough to suggest another op-amp to replace OPA551PA in this? i'm relatively new in audio, doesn't have too much experience with op-amps.


----------



## SasaKudo

GunnerXL said:


> Just received the board today, but the opamp is currently sold out in mouser. Can anyone would kind enough to suggest another op-amp to replace OPA551PA in this? i'm relatively new in audio, doesn't have too much experience with op-amps.



Your forum profile says that you are located in germany. If that's really the case, you could order the OPA551PA from reichelt.de oder conrad.de since they both have the chip available for order. I also thought about replacing the OPA551 for something different, but in the end didn't do so. The OPA551 has a nice hight current output and is kinda nice to use as a buffer opamp.


----------



## SasaKudo

I finished my 3D printed case. You can find the files on thingiverse.


----------



## randytsuch

Nice case.  How's the temperature inside?  Not too hot?


----------



## jekjek

SasaKudo said:


> I finished my 3D printed case. You can find the files on thingiverse.


Nice case
How much it cost?


----------



## SasaKudo

randytsuch said:


> Nice case.  How's the temperature inside?  Not too hot?



Only the linear regulator gets hot and there is still enough headroom for air to flow through convection. Since I used PETG (which is stable up to ~80°C) there shouldn't be any problem and my test leaving it on for 12 hours didn't show any real heat problems.



jekjek said:


> Nice case
> How much it cost?



Print takes around 14 hours on a Prusa i3 MK2S. I think I used around 150g PETG, which results in material cost of around 4~5 €. If you don't have a 3D printer, you could go to a Makespace or Fablab and print it there. That would cost you around 20~30 € here at my town.


----------



## silverfishla (Dec 8, 2017)

I received a pair of Burson V5i single op-amps a few weeks ago and I must say that these little silvery guys are incredibly great sounding in this amp.
I've let the op-amps run in the Millett Nu-Tube amp for about a 100 hours total, just to let things settle in, as things tend to do...

The op-amps that PM provide on the BOM list, are actually good sounding already.  They sound clear and concise.  I wanted to see if I could find a more tailored sound to my liking though.
The Burson V5i Singles sound different from those on the BOM list.  I think they sound much better.  They have a certain enveloping characteristic that is very engaging and lush.
I think that they add depth to the soundstage and have a very pleasing and clear vocal presence.  I especially enjoy how these make a female voice sound bold and present, not tinny or thin.  Just great here.
The V5i also adds a nice pillow of bottom end that makes the Bass sound closer to what I like to hear...energetic, bouncy, and well rounded.  It's just does a great job of enveloping you with sounds instead of presenting them in front of you.  With the V5i, I think I have found my personal favorite so far in an op amp for this amp.

Now, I also have the Sparkos Labs singles.  I like those too, but I actually think, in this case, the Bursons beat those ones out.  The Sparkos Labs singles are extremely up-front and bold.  It's like everything is turned up to 11 on those (I even turned down the gain to about 10).  Bass is up, Mids are up, Treble is up.  Those are very clear sounding too, but are a bit fatiguing to listen to for long periods of time.  The Bursons just have more space and lushness with it's clarity.

I also used a Pono Player, Shanling M3s, Aune M1, and a Zishan Z2 as my sources.  You know, source matters.  I found that the Pono Player had a nice mix of analog quality and clarity through this amp.  The M1 has a really bold LO, but very clear sounding.  The Shanling was decent but not very warm.  The Zishan Z2 just delivered a full analogy sound which is pretty impressive and headphone filling.

Also, I used Sony Z7, Sennheiser 650, Beyerdynamic T90, Massdrop AKG KXXXXX as my headphones.  The Sony's are the best match here for me with it's big soundstage and bolder bass.  I also really liked the AKG set with this amp and the Bursons, a really spacious musical pairing.


----------



## drpro

Thank you Pete for such a nice project and easy build.  Finally got all of the parts from Mouser and Digikey, took about 1.5 hours to construct.  Applied power and works well and sounds great.


----------



## drpro

Finally got a pair of Burson V6 vivid opamps in place.  Still letting them age.  Sounding great though.


----------



## coinmaster (Dec 30, 2017)

I wouldn't touch the circuit design of this amp with a 10 foot pole (no offense to the designer) but I am curious to know how the nutube module compares to traditional tubes. Any thoughts?


----------



## HiGHFLYiN9 (Dec 30, 2017)

Let me try to break it down. I assume there will be new iterations of the NuTube, and hopefully other companies will throw in as well, but this is for the current Korg NuTube.

*NuTube Pros:*
Perceived warmth and harmonics of traditional tubes
Low voltage (safer for DIYers, easier to implement in battery powered circuits as power will last longer and filament does not have to be starved)
Smaller form factor than traditional tubes
Longer life - 30,000 hours
Does not generate notable heat like traditional vacuum tubes 

*NuTube cons*
Notably more microphonic (sensitive to vibrations) than tubes typically used for audio. There are suggestions from Korg on how to reduce this
No current ability to "roll" like socketed op-amps or tubes. You can mount it on a socketed carrier, but there are no other Nutube types to try
Pricier than current production driver tubes ($49.99)

Is the Korg NuTube going to take over tube audio? Nope, but it's a unique product design and should implement well in products that require its advantages.


----------



## HiGHFLYiN9

.. double post, please delete.


----------



## coinmaster

Hmmmm, I wonder. With the right circuit and careful biasing this tube can be very linear.
I've cooked up a masterpiece of a design for this tube I guess I'll find out when I wire it up.


----------



## silverfishla

I'm really starting to enjoy my Senn HD650's with this amp.


----------



## pmillett

HiGHFLYiN9 said:


> Let me try to break it down. I assume there will be new iterations of the NuTube, and hopefully other companies will throw in as well, but this is for the current Korg NuTube.
> 
> *NuTube Pros:*
> Perceived warmth and harmonics of traditional tubes
> ...



That is a very good summary, I agree...

Pete


----------



## eixe

Hi everyone, happy owners of a Nutube device, or experienced with electronic.

I have completed the NuHybrid Headphone Amplifier, checked Everything, read this thread for questions and answers, and guess what ?
I writes you because the voltage can't reach 11V between Ground (test point 3) and both L/R Outs (tests points 1/2). Going from the minimum, it stuck at 6.09V, with R17 and R18 (1Kohm) at the most.
An important fact is from 5.5V to 6.09, the glow gradually turn off.

I did not run complete listening test for now, but double checked everything (components value and position, welds) multiple time and here I am.
I got music in my kamikaze headphones, it sounds okay except a buzz wich the pot's grounding have not totally eradicate. I guess this is another trouble wich will wait for the enclosure time.

I have purchased the Mouser's shared project from P. Millet website, and the PCB+Nutube from himself, so their is no unrecommended part, except ins and outs (RCA, 1/4, DC jack, and switch), and a temporary 100K pot laying around. I did this part accordingly to the recommandation for Silverfishla's interrogations (posts #167-#168)

Here are the active components I got :
2N3904BU *2 : BJT NPN Transistor General Purpose
2N7000 : MOSFET N-CHANNEL 60V 200mA
UA78M33CKCS : Linear Voltage Regulators 3.3 V 500mA Fix Pos Voltage Regulator
Opamp 551, 6P1 Nutube.

My power supply is a switching type 24dc capable of 1.5A, with the + centered.

I hope this bunch of infos will help you to help me !

Thanks for your attention.


----------



## silverfishla (Jan 6, 2018)

eixe said:


> Hi everyone, happy owners of a Nutube device, or experienced with electronic.
> 
> I have completed the NuHybrid Headphone Amplifier, checked Everything, read this thread for questions and answers, and guess what ?
> I writes you because the voltage can't reach 11V between Ground (test point 3) and both L/R Outs (tests points 1/2). Going from the minimum, it stuck at 6.09V, with R17 and R18 (1Kohm) at the most.
> ...


Hi, something about the posts 167 and 168...there is a section in there where Pete says to use the green wire and white wire to connect the on/off switch.  That didn't work for me.  The amp didn't turn on.  I wired it with the  other wires like in this pic.
   I'm not sure if Pete was mistaken, or my amp is on the verge of blowing up (just kidding) but the way I wired it, worked.
Otherwise, everything else, I wired as instructed on those posts.
Maybe someone else could chime in, since I should have clarified that or asked back at those posts.


----------



## eixe (Jan 6, 2018)

Thank you for clarifying this point. Visibly the farthest pad of the PCB leads nowhere or on the ground plane. So I wired it anyway, as the BOM's switch. However the two other pads seem to be on a single path for the power, on the other side of the PCB.

Yet I have no clue for the Bias problem, this goes far beyond my present electronical knowledge.

This is actually a very pleasant project to do, and the VFD is inspiring for some original enclosure design, as I can see on this thread.


----------



## pmillett

eixe said:


> Hi everyone, happy owners of a Nutube device, or experienced with electronic.
> 
> I have completed the NuHybrid Headphone Amplifier, checked Everything, read this thread for questions and answers, and guess what ?
> I writes you because the voltage can't reach 11V between Ground (test point 3) and both L/R Outs (tests points 1/2). Going from the minimum, it stuck at 6.09V, with R17 and R18 (1Kohm) at the most.
> ...


If the Nutube is no longer lit when you get 6.09V on the plate, then there can only be a couple of things wrong...

Did you verify that the 24V supply is really putting out 24V?  Measure the voltage to ground at both sides of R10.  It should read close to 24V at both ends.

Also double check that R5 is 40.2 ohms, not k, and that R13 and R14 are 475k.

Pete


----------



## eixe

pmillett said:


> 40.2 ohms, not k



R10 is 40K2 on mine. Thank you Pete Millet for your quick expertise.

I'll get back to you with a completed amp, in a nice enclosure I hope.

Have a nice day.


----------



## pmillett

eixe said:


> R10 is 40K2 on mine. Thank you Pete Millet for your quick expertise.
> 
> I'll get back to you with a completed amp, in a nice enclosure I hope.
> 
> Have a nice day.


Hang on, 40k2 might be right.  Let me check.  Can you measure the voltages on it?


----------



## eixe

I get 17,2V, between "in and out" of R10. Is it the voltage drop caused by R10 or the voltage out of R10 (with a voltage drop of 6,8V in that case) ?
The schematic says it should be a 40.2R resistor instead of 40K2.


----------



## pmillett

eixe said:


> I get 17,2V, between "in and out" of R10. Is it the voltage drop caused by R10 or the voltage out of R10 (with a voltage drop of 6,8V in that case) ?
> The schematic says it should be a 40.2R resistor instead of 40K2.


OK, 40.2 ohms is correct.  I forgot that this node also feeds the input buffers.  So if you have 40.2 k there, you'll get too big of a drop.  That's your problem.


----------



## szpunk (Jan 14, 2018)

I buy the "Buffer" version...and later i want to use it to drive my headphone. I tried connect the buffer to my A47 headphone amp first, OMG, Huge distortion which i only get the sound...Yes, gain too high i know.

So i bulid the OPAMP current buffer follow the Nuhybrid Headphone AMP schematic. It's no distortion this time, but i got continuous noise floor. I did bypass the output mosfet follower, no effect, then i replace the input MOSFET 2N7000 with 2N3904, OK, i can enjoy the music now!


----------



## 2oobz

I just built the headphone amp.  Surprising headroom and power.  My favorite build is still the Jonokuchi, but I digress.  The nutube is definitely microphonic with a high frequency tone for the first few second after startup or if you touch the tube.  Has anyone worked out a mod to subdue the microphonics?


----------



## HiGHFLYiN9

2oobz said:


> I just built the headphone amp.  Surprising headroom and power.  My favorite build is still the Jonokuchi, but I digress.  The nutube is definitely microphonic with a high frequency tone for the first few second after startup or if you touch the tube.  Has anyone worked out a mod to subdue the microphonics?


It is inherent in the design. Per Korg: "as the Nutube is a directly-heated type tube, it can be affected by vibrations. Suppressing the microphonic effect can be done more easily than with a conventional vacuum tube, as ‘Nutube’ does not generate heat. We are also planning on offering accessories that can be used to suppress any microphonic effect." There are some various mounting suggestions in Korg's data sheets that can assist with vibrations, as well as mounting the chassis on EAR feet as described earlier in the thread. That's about as good as it's going to get for right now...


----------



## silverfishla

I tried using the Line Out on my amp, and it doesn’t seem to be working at all.  Is there something I’m missing?  Source to Line In then Line Out to amp.  What is supposed to be happening here and does the pot control Line Out intensity or not?  I wanted to check out what it does, but I don’t get a signal coming through.


----------



## Detectit (Feb 5, 2018)

OK after some research on building my next DIY amp. This is going to be next...
Researched some Gilmore amps. But documentation is very cluttered. Maybe one step to far.

This is very well documented just like my finished SSHM. Which i enjoy.

One question. ...as esthetic is very important to me.
Could I raise the Korg tube module from the PCB and just wire it.? So i can mount it somewhere else?
Its not far away from the pcb. I want raise the Korg Module on the enclosure.


----------



## ThermalAlchemy (Feb 5, 2018)

Wow, this amp kicks ass on my IPhone , my Surface Pro 4, and even my $400+ IFI Black Label DAC AMP. I feel like I dropped the soap in the mans prison shower room after buying the IFI Black Label compared to Pete’s nu-tube AMP. On my un-tube amp I only turn up the volume between 9 and 11 at  1 o’clock it too loud. On the IFI Black Label I need to MAX out the  knob to  distortion. On my DarkVoice 336 se I only can turn it up 9  o’clock and 11 o’clock max. Can’t wait to build the next one, Pmillett keep them coming.
     Can we have a XLR headphone amp next?.


----------



## Detectit (Feb 5, 2018)

I am sourcing the parts. And I will go for a onboard linear power supply.

This time i want to try those R core transformators.
These come with different voltage outputs.
15v 15v 9v 9v secundairies.
Can I wire 15V and 9V in serie to get 24v?
Or better take 30v and step down on regulator?

And the Volume Pot TKD 2CP 601 is recommended. But wont be a stepped Atennuator be even beter? The price is bit cheaper.


----------



## pmillett

Detectit said:


> I am sourcing the parts. And I will go for a onboard linear power supply.
> 
> This time i want to try those R core transformators.
> These come with different voltage outputs.
> ...



You should be able to wire a 15V and 9V winding together to get 24VAC.  Rectified that will get you close to 33V DC.  That is uncomfortably lose to the 35V rating on the electrolytic caps.  So you should either change the caps to 50V - if you can find some that will fit - or use a voltage regulator on your power supply to drop it to 24V.  That would be the best option.  Then you could use the two 15V windings in series...

You can use a stepped attenuator, it just won't fit on the PCB.

Pete


----------



## pmillett

Detectit said:


> OK after some research on building my next DIY amp. This is going to be next...
> Researched some Gilmore amps. But documentation is very cluttered. Maybe one step to far.
> 
> This is very well documented just like my finished SSHM. Which i enjoy.
> ...



Sure, you can mount the Nutube a bit off the board.  Don't go more than an inch or two or it may pick up noise...

Pete


----------



## pmillett

silverfishla said:


> I tried using the Line Out on my amp, and it doesn’t seem to be working at all.  Is there something I’m missing?  Source to Line In then Line Out to amp.  What is supposed to be happening here and does the pot control Line Out intensity or not?  I wanted to check out what it does, but I don’t get a signal coming through.



Does the headphone out work?

The line out is connected to the headphone jack and is only active when the headphones are unplugged.  It is the same as the headphone out, with some 150 ohm resistors in series.

Pete


----------



## HiGHFLYiN9

ThermalAlchemy said:


> I feel like I dropped the soap in the mans prison shower room after buying the IFI Black Label compared to Pete’s nu-tube AMP.


Lol, that's quite illustrative. Given that Pete's offering his intellectual property completely for free (he doesn't make any money on the PCB sales) and the Korg is offered at a discounted rate with the PCB, it's not surprising it mops the floor with a commercial offering in the same price range. Most of what you pay for with commercial audio is distribution, overhead, marketing, packaging and overly fancy aesthetics. 



ThermalAlchemy said:


> Can’t wait to build the next one, Pmillett keep them coming. Can we have a XLR headphone amp next?.


Hear hear!


----------



## silverfishla

pmillett said:


> Does the headphone out work?
> 
> The line out is connected to the headphone jack and is only active when the headphones are unplugged.  It is the same as the headphone out, with some 150 ohm resistors in series.
> 
> Pete


The headphone out does work.  I'm going to follow the leads and see if I've got everything wired up and soldered correctly.


----------



## Detectit

pmillett said:


> You should be able to wire a 15V and 9V winding together to get 24VAC.  Rectified that will get you close to 33V DC.  That is uncomfortably lose to the 35V rating on the electrolytic caps.  So you should either change the caps to 50V - if you can find some that will fit - or use a voltage regulator on your power supply to drop it to 24V.  That would be the best option.  Then you could use the two 15V windings in series...
> 
> You can use a stepped attenuator, it just won't fit on the PCB.
> 
> Pete



How much current do i need?  2x15vac is 0,5a output


----------



## pmillett

Detectit said:


> How much current do i need?  2x15vac is 0,5a output



0.5A is fine.

Pete


----------



## Detectit (Feb 5, 2018)

silverfishla said:


> The headphone out does work.  I'm going to follow the leads and see if I've got everything wired up and soldered correctly.



Does the headphone connector Pins closes when you plug out the plug?


----------



## pmillett

Detectit said:


> Does the headphone connector Pins closes when you plug out the plug?



Correct.  The headphone jack has switch contacts.  When there is nothing plugged in, the output is routed to the preamp out.  When  headphones are plugged in, the preamp out is disconnected.

Pete


----------



## silverfishla

Detectit said:


> Does the headphone connector Pins closes when you plug out the plug?


I think you are right, I did not install the jack that was in the BOM.  It's an open connector.



pmillett said:


> Correct.  The headphone jack has switch contacts.  When there is nothing plugged in, the output is routed to the preamp out.  When  headphones are plugged in, the preamp out is disconnected.
> Ahh, I see.  Electronics. :/  Haha.  Can I make a jumper or switch that can toggle the input to the output?  Simpler to just get a closed type jack, I suppose.
> Pete



Ahh, I see.  Electronics. :/  Haha.  Can I make a jumper or switch that can toggle the input to the output?  Simpler to just get a closed type jack, I suppose.


----------



## silverfishla (Feb 7, 2018)

So if I connect a closed switched jack to the headphone output to make my Line Out work, do I have to wire all six connectors to the board?  I only ask because I have the headphone jack floating above and off the board.  And just to make sure that I have to replace the one that's already in there.


----------



## pmillett

silverfishla said:


> So if I connect a closed switched jack to the headphone output to make my Line Out work, do I have to wire all six connectors to the board?  I only ask because I have the headphone jack floating above and off the board.  And just to make sure that I have to replace the one that's already in there.



You would need to get a jack that has switch contacts on tip and ring, and add two more wires to connect those contacts back down to the board.

If you don't care if the line out is active all the time (with or without headphones plugged in), you can also just connect jumper wires across the jack pins on the PCB.


----------



## silverfishla

pmillett said:


> You would need to get a jack that has switch contacts on tip and ring, and add two more wires to connect those contacts back down to the board.
> 
> If you don't care if the line out is active all the time (with or without headphones plugged in), you can also just connect jumper wires across the jack pins on the PCB.


Thanks Pete.  Is there any downside to soldering in the jumpers and having the Line Out active all the time?  Will it (or might it) create any unwanted side effects (like noise or something)?


----------



## pmillett

silverfishla said:


> Thanks Pete.  Is there any downside to soldering in the jumpers and having the Line Out active all the time?  Will it (or might it) create any unwanted side effects (like noise or something)?


No, no side effects.  Mostly I did this so that your speakers would mute when you plug in the headphones...

Pete


----------



## HiGHFLYiN9

Rocking a Switchcraft open frame TRS jack I see, good stuff  Those are my favorite for guitar gear. They make switching mono jacks, but I'm not sure about stereo...


----------



## silverfishla

pmillett said:


> No, no side effects.  Mostly I did this so that your speakers would mute when you plug in the headphones...
> 
> Pete


Thanks Pete, I just soldered the jumpers in about a half hour ago.  Like you said, no noticeable side effects at all.  Sounds great!



HiGHFLYiN9 said:


> Rocking a Switchcraft open frame TRS jack I see, good stuff  Those are my favorite for guitar gear. They make switching mono jacks, but I'm not sure about stereo...


My favorite jacks for guitar stuff too!  That's why I went with it, tried and true.


----------



## jacc1234

I just built this amp and have a few questions. Overall it came together easily, I was able to set the output bias to 11v for both L and R and I does produce sound. 

My main problem is a constant interference in the background with or without a source plugged in. I would say its on the mid range and the character of the noise changes if I mess with the volume but its always present. 

Also, when I power the amp on there is a really high pitch harmonic sound which I believe is from the tube. If I don't disturb it, this seems to go away. I have seen a few other posts reporting this.

I stuck to the mouser project link but this ESD suppressor was backorderd:
https://www.mouser.com/ProductDetail/511-P6KE33A

So I subbed this "alternative packaging" version:
https://www.mouser.com/ProductDetai...P6KE33ARL?qs=sGAEpiMZZMv1cg40gLeF3moQwjhEPwXa

They seemed identical but I am very much an amateur at this so any feedback would be appreciated. 

I am looking forward to posting a full build log once I hopefully get this all sorted out. 

Thanks for putting this great project together!


----------



## pmillett

jacc1234 said:


> I just built this amp and have a few questions. Overall it came together easily, I was able to set the output bias to 11v for both L and R and I does produce sound.
> 
> My main problem is a constant interference in the background with or without a source plugged in. I would say its on the mid range and the character of the noise changes if I mess with the volume but its always present.
> 
> ...



No issues with the TVS substitution, it is basically the same part.

The ringing you hear when you turn the amp on is indeed the tube, the filament singing like a tuning fork when excited.

Not sure about the noise, though. It could be some EMI coupling in...  Have you tried moving the amp to a different location?  

What kind of headphones are you using?

If they are very efficient (IEMs usually) you may hear the noise floor of the tubes.  That is pretty mush a hissing or rushing sound...

Pete


----------



## jacc1234

pmillett said:


> No issues with the TVS substitution, it is basically the same part.
> 
> The ringing you hear when you turn the amp on is indeed the tube, the filament singing like a tuning fork when excited.
> 
> ...



Thanks for your reply Pete! I really appreciate all the work you put into providing this DIY project to the community.

I did try moving the amp to a different location and was listening with my Grado SR225.  I did not try any other headphones as a test but I will give that a try tonight and report back!


----------



## jacc1234 (Mar 19, 2018)

Ok I have run a few more tests and I am fairly sure the noise is EM interference. If I touch the bare metal on the pot I can faintly hear the radio. I have tested this with two pairs of headphones.

I have had EM issues with other equipment like my guitar so I am going to take the amp to work tomorrow and see if it behaves any better.

Below an image of my soldering job on the pot. Some of the rear pins are bridged with the empty holes that I think are used if you install the upgraded POT. Is that an issue?

I am going to run through each component and ensure every solder joint looks good and that it is in the right place. I took my time during the build so I am fairly confident that the right components are in the right locations but its possible I made a mistake somewhere.


----------



## jacc1234

Ok another update. I took the amp to my office to try and eliminate any possible environmental EMI and the issue is still present. If I touch the bare metal of the pot it gets worse. I am not sure if the following is helpful but, if I touch the tops of C13 and C14 the noise gets significantly louder but if I touch any of the tops of C3, C5 or C6 the noise is mostly gone.


----------



## pmillett

jacc1234 said:


> Ok another update. I took the amp to my office to try and eliminate any possible environmental EMI and the issue is still present. If I touch the bare metal of the pot it gets worse. I am not sure if the following is helpful but, if I touch the tops of C13 and C14 the noise gets significantly louder but if I touch any of the tops of C3, C5 or C6 the noise is mostly gone.



Yes, sounds like "normal" noise from the environment.  Touching C13 or C14 basically connects a giant antenna - you - to the grid of the tube, and the noise you pick up gets sent into the amplifier input.

Likely the biggest noise source is coming from the power adapter.  The power adapter is ungrounded, meaning it has no reference to a "real" ground.  To make matters worse, they typically have an EMI filter that has "Y" capacitors from each side of the AC line to the negative output of the adapter.  So if all is floating, the filter actually injects 60Hz onto the negative side of the output, which is ground in the amp.

When the amp is connected to a source that has a "real" ground (like a CD player or DAC that has a three-wire AC cord), often this noise goes away.  In some cases, it can get worse, though, if there is excessive noise current flowing back through the ground.  A computer source (soundcard or USB DAC) can be good, or bad.  Unfortunately it is unpredictable.

If you can find a real ground, connecting a wire from there to the ground of the amp may help.  It is possible to pick this up from the ground pin of an AC outlet or even the screw that holds the cover plate on.  But you need to be very careful not to accidentally contact the line voltage!

Pete


----------



## jacc1234

pmillett said:


> Yes, sounds like "normal" noise from the environment.  Touching C13 or C14 basically connects a giant antenna - you - to the grid of the tube, and the noise you pick up gets sent into the amplifier input.
> 
> Likely the biggest noise source is coming from the power adapter.  The power adapter is ungrounded, meaning it has no reference to a "real" ground.  To make matters worse, they typically have an EMI filter that has "Y" capacitors from each side of the AC line to the negative output of the adapter.  So if all is floating, the filter actually injects 60Hz onto the negative side of the output, which is ground in the amp.
> 
> ...



Thanks for all the details. I will say the the interference I am hearing is much louder than I have experienced with any other amps or dacs. I will see if I can connect it to a real ground and post results. 

I was hoping to use this connected to a usb dac or phone so would a grounded power supply make a difference?


----------



## hav2uo4

2oobz said:


> I just built the headphone amp.  Surprising headroom and power.  My favorite build is still the Jonokuchi, but I digress.  The nutube is definitely microphonic with a high frequency tone for the first few second after startup or if you touch the tube.  Has anyone worked out a mod to subdue the microphonics?


I came up with an air-isolated shock-mount using an 18650 battery case.  There are a couple of young kids above my place and when they stomp overhead it's enough get the nutube resonating.  The only time I notice any ringing now is when I change the stepped attenuator setting with my most sensitive headphones.


----------



## hav2uo4

jacc1234 said:


> Thanks for all the details. I will say the the interference I am hearing is much louder than I have experienced with any other amps or dacs. I will see if I can connect it to a real ground and post results.
> 
> I was hoping to use this connected to a usb dac or phone so would a grounded power supply make a difference?


I've had luck attaching the circuit ground to my outlet's ground (don't try this unless you're confident you know what you're doing).  Also changing the physical placement of the amp can make a big difference.   An old girlfriend left one of those yoga foam block things at my place and it's useful for propping the amp to a sweet spot where there's very little noise.  It looks like crap...but closing your eyes fixes that eyesore...and it makes the music sound better...haha.


----------



## jacc1234 (Mar 25, 2018)

hav2uo4 said:


> I've had luck attaching the circuit ground to my outlet's ground (don't try this unless you're confident you know what you're doing).  Also changing the physical placement of the amp can make a big difference.   An old girlfriend left one of those yoga foam block things at my place and it's useful for propping the amp to a sweet spot where there's very little noise.  It looks like crap...but closing your eyes fixes that eyesore...and it makes the music sound better...haha.



I have had some luck with re-positioning and depending on how things end up at my office might consider looking into attaching it to a ground.

Are you just attaching the amp ground to the rounded ground slot in the outlet, or are you actually opening the outlet and connecting it to the internal ground wire?

Thanks!


----------



## hav2uo4

jacc1234 said:


> I have had some luck with re-positioning and depending on how things end up at my office might consider looking into attaching it to a ground.
> 
> Are you just attaching the amp ground to the rounded ground slot in the outlet, or are you actually opening the outlet and connecting it to the internal ground wire?
> 
> Thanks!


I just run an alligator clip from the ground of another amp that uses all three prongs and clip it to the barrel connector of my nutube amp.  But that wouldn't fly in an office environment...haha.  The round slot would be good enough if you re-purposed a power cord and made sure to insulate hot and neutral well so they'll never contact anything.  But depending on source, sometimes it's less noisy to let the amp "float."


----------



## JImmye00

I was hoping to build a nice case for this unit.  Does anyone have a schematic drawing of a case they built so i know the dimensions of where all my holes need to be drilled? Thanks!


----------



## silverfishla

JImmye00 said:


> I was hoping to build a nice case for this unit.  Does anyone have a schematic drawing of a case they built so i know the dimensions of where all my holes need to be drilled? Thanks!


I just bought a case that had dimensions for the fit of the pcb and room heightwise, then eyeballed it.  Of course, I also lifted the input, outputs, volume knob, power switch to off the board.  I can link you to that case if you like.  You can see it in a previous post.  If you mean that you want a case for your completed project (as per build), I can't really help there...


----------



## technicus

Hello everyone! I just bought the PCBs and got the order in to Mouser the other day. As I was reading the forums about headphones and resistor selections as well as odd noise I have two questions:

1) I have the Sony MDR-V6 headphones (63 ohms), would a different resistor selection be more suitable?

2) Some people were mentioning noise... I was able to find a desktop style power supplies (like your laptop power supply) which were grounded that meet the 24v @ 1A requirement (1.25A if you want to be precise):
Cui 490-SDI30-24-U-P5
Phihong 552-PSAC30U-240L6

Cost of either is about $17.50 so $5 more. I also tend to favor the desktop style as I have power strips and a wallwart wouldn't work usually. I also have this thing that everything must have a ground...


----------



## JImmye00

silverfishla said:


> I just bought a case that had dimensions for the fit of the pcb and room heightwise, then eyeballed it.  Of course, I also lifted the input, outputs, volume knob, power switch to off the board.  I can link you to that case if you like.  You can see it in a previous post.  If you mean that you want a case for your completed project (as per build), I can't really help there...



If you could link me the post that would really help. Thanks


----------



## JImmye00

hav2uo4 said:


> Hope this works...Pete's multi-pot footprint is excellent for hacking a ground connection.  I had to file a small notch into the inside of the case to clear the wire.




I just put together everything for my build but the volume pot.  dont wanna mess it up since its so expensive.  so im guessing that the pot goes in to the rear two rows of holes in the pcb so that the pot is flush with the front of the PCB?  next question is from this pictuyre it looks like you soldered in the second from the front and "bridged to the third row?  or am i seeing things?  last question is ground the pot where is the best place to do this on the pot?


----------



## JImmye00

pmillett said:


> Well, I'm not real sure what would be causing this.  I didn't notice noise like that on the one I built with the upgraded pot.
> 
> The noise that was caused by oscillation using the FET was very loud.  I would expect a little noise as the pot hits its limits, but nothing terrible.
> 
> Pete



Pete, i purchased the upgraded pot that you recommended which rows on the pcb does this pot get inserted into? dont wanna guess and mess it up being it was 40$
Thanks!


----------



## johnnyb

technicus said:


> Hello everyone! I just bought the PCBs and got the order in to Mouser the other day. As I was reading the forums about headphones and resistor selections as well as odd noise I have two questions:
> 
> 1) I have the Sony MDR-V6 headphones (63 ohms), would a different resistor selection be more suitable?
> 
> ...


I would think that these types of switching power supplies would be noisy compared to the wallwart. Perhaps someone can recommend a good linear power supply that puts out 24v that would be a suitable wallwart replacement?


----------



## jekjek

johnnyb said:


> I would think that these types of switching power supplies would be noisy compared to the wallwart. Perhaps someone can recommend a good linear power supply that puts out 24v that would be a suitable wallwart replacement?



I am using International Power 24v Power Supply as below 

https://www.ebay.com/itm/INTERNATIO...m=302432244590&_trksid=p2045573.c100705.m4780

I bought a new old stock at 5 dollar excluding shipping


----------



## technicus

jekjek said:


> I am using International Power 24v Power Supply as below
> 
> https://www.ebay.com/itm/INTERNATIONAL-POWER-IHB24-1-2-POWER-SUPPLY-120-240V-AC-24V-DC-D575275/302432244590?_trkparms=ao=1&asc=20170105155410&meid=0861ab70ac6e4d13b94c5393cffbd6bc&pid=100705&rk=1&rkt=1&&itm=302432244590&_trksid=p2045573.c100705.m4780
> 
> I bought a new old stock at 5 dollar excluding shipping



Somewhere I have a bunch of these that I got from dumpster diving a long time ago... don't know why I didn't bother to check if they were switching versus linear.


----------



## jekjek

technicus said:


> Somewhere I have a bunch of these that I got from dumpster diving a long time ago... don't know why I didn't bother to check if they were switching versus linear.



I boxed this power supply using standard ATX PSU case from a computer. 
I hope it help this community


----------



## technicus

Got my PCB with the Nutube in today, now I just need the bits. That being said, does anyone know if the PCB was tinned for lead-free?


----------



## pmillett

technicus said:


> Got my PCB with the Nutube in today, now I just need the bits. That being said, does anyone know if the PCB was tinned for lead-free?


It has tin/lead HASL (hot air solder leveled) coating.

Pete


----------



## pmillett

JImmye00 said:


> Pete, i purchased the upgraded pot that you recommended which rows on the pcb does this pot get inserted into? dont wanna guess and mess it up being it was 40$
> Thanks!


The photo above shows it... it should really only fit one way unless you force it.  The edge of the pot should be aligned with the edge of the PCB.

Pete


----------



## JImmye00

pmillett said:


> The photo above shows it... it should really only fit one way unless you force it.  The edge of the pot should be aligned with the edge of the PCB.
> 
> Pete



Pete
Thanks for the quick reply and thanks for all you have done for DIY audio. Next up is the starving student


----------



## silverfishla

JImmye00 said:


> If you could link me the post that would really help. Thanks


Hi, here's the box I used.  You will just have to make some side rails to hold the PCB in place.  Everything fits nicely and compactly.
https://www.aliexpress.com/item/1-1.../1982085848.html?spm=a2g0s.9042311.0.0.1cr9En


----------



## JImmye00

silverfishla said:


> Hi, here's the box I used.  You will just have to make some side rails to hold the PCB in place.  Everything fits nicely and compactly.
> https://www.aliexpress.com/item/1-1.../1982085848.html?spm=a2g0s.9042311.0.0.1cr9En



Thanks for the suggestion


----------



## technicus

johnnyb said:


> I would think that these types of switching power supplies would be noisy compared to the wallwart. Perhaps someone can recommend a good linear power supply that puts out 24v that would be a suitable wallwart replacement?



I have both the wallwart and the desktop one. Mouser was cool enough to send the desktop one free as they couldn't update the order in time.

Any ways, both are switching power supplies. I'll return them as I did find a linear 24v @ 1.2A one off of eBay.


----------



## technicus

I've been reading the thread and seen some awesome builds.

Aside from the Burson opamps and Sonicap bypass caps, any other tweaks/upgrades people have made? I dunno about the opamps but the Sonicap seems an inexpensive one to do up front.

George


----------



## HiGHFLYiN9

You can use Takman carbon film resistors, they're pretty affordable from soniccraft.com


----------



## jacc1234

What is everyone doing for microphonics? I think I got my background noise issues under control but I find the microphonics of the to be a problem. I saw one post where there was an involved suspension system being used but that seems like overkill. I really like the sound but am a bit disappointed with the ringing I get whenever the cable more or when someone sneezes.


----------



## silverfishla

jacc1234 said:


> What is everyone doing for microphonics? I think I got my background noise issues under control but I find the microphonics of the to be a problem. I saw one post where there was an involved suspension system being used but that seems like overkill. I really like the sound but am a bit disappointed with the ringing I get whenever the cable more or when someone sneezes.


Did you build a case for it?  I've got speaker spikes on mine.  I don't hear any microphonics after the initial "Ping!" when flipping the On switch.  Have you read the suggestions from Korg about keeping the Nu-tube as mute as possible?  They suggest putting a metal plate on top of it.


----------



## technicus

I had thought about putting a thicker piece of glass on it so that I could see the glow. Saw a piece of flint glass, optical plate, on eBay that was of the proper dimensions but I'll be putting this into an enclosure and won't be able to see the tube anyways and I'll put something else on it. And, as that was a piece of optical glass, it was pricey for what it was.

Another option might be one of those prisms from an education place as they'll be cheaper and you'll still see some tube glow if that's your thing.

Could possibly go to a window place and see if they have any scrap that's about the size. Window glass is leaded and is quite possibly weighs more than what I found on eBay. Then use a thin film of clear silicone to adhere it to the NuTube.


----------



## jacc1234

silverfishla said:


> Did you build a case for it?  I've got speaker spikes on mine.  I don't hear any microphonics after the initial "Ping!" when flipping the On switch.  Have you read the suggestions from Korg about keeping the Nu-tube as mute as possible?  They suggest putting a metal plate on top of it.



I am using the stock half enclosure on the BOM but will look into a case.

Another question I have is about setting the bias. I am using fairly sensitive (23 Ω) headphones at work currently, and am wondering if there is a suggested bias voltage below 11V. I have it set to 8V currently and still can't turn my volume past 1/4. Would going even lower possibly be beneficial?


----------



## pmillett

jacc1234 said:


> I am using the stock half enclosure on the BOM but will look into a case.
> 
> Another question I have is about setting the bias. I am using fairly sensitive (23 Ω) headphones at work currently, and am wondering if there is a suggested bias voltage below 11V. I have it set to 8V currently and still can't turn my volume past 1/4. Would going even lower possibly be beneficial?


Changing the bias only has a small effect on the gain - it primarily changes the makeup of the distortion.  If you go lower you will increase the distortion.  There is no easy way to lower the gain of the amp... the best thing may just be to attenuate the inputs.

Pete


----------



## jobous (Apr 30, 2018)

Hi !!!. I'm trying to deside how to build this amp !!!  (cause i'm going to build it !!!) . In every photo i saw , the original enclosure is without the top. My question is : Is there (somewhere!!!) the upper part of the original enclosure or there isnt any ???
I ask this cause if it is an open construction (!!!) , i 'll have to choose an another enclosure (any proposition ???, i've noticed a hammond in previous posts) to fit it.
Second , the original pot is 10k. If i choose the alps RK27 - 100k there will be any problem?? I'm asking cause of the fisrt question, maybe i decide to go to a panel mount solution (pot, power connection , rca inputs etc).

Guys thanks in advance !!!


----------



## pmillett

jobous said:


> Hi !!!. I'm trying to deside how to build this amp !!!  (cause i'm going to build it !!!) . In every photo i saw , the original enclosure is without the top. My question is : Is there (somewhere!!!) the upper part of the original enclosure or there isnt any ???
> I ask this cause if it is an open construction (!!!) , i 'll have to choose an another enclosure (any proposition ???, i've noticed a hammond in previous posts) to fit it.
> Second , the original pot is 10k. If i choose the alps RK27 - 100k there will be any problem?? I'm asking cause of the fisrt question, maybe i decide to go to a panel mount solution (pot, power connection , rca inputs etc).
> 
> Guys thanks in advance !!!


The upper part of that case cannot be used - I just used the lower part as sort of a pedestal.  Lots of people put this into another enclosure, and connect the rear panel connectors - and sometimes also the front ones and pot - with wires.

A 100k pot is fie.

Pete


----------



## jobous

Thanks Pete !!! I'll do it with another enclosure !!!


----------



## silverfishla

@pmillett Pete, do you think that there is any chance that you might do a balanced version of this amp?  That would be amazing.


----------



## CatalinM

Hey guys!

I'm looking to start a build using some "premium" components (because why not?), but I'm having some issues sourcing an R8/9. So I need to ask: what would be the impact of replacing this with a "slightly" larger resistor, say 2R2? Cause if it's something like a volume drop, that might actually be a good thing.


----------



## pmillett

CatalinM said:


> Hey guys!
> 
> I'm looking to start a build using some "premium" components (because why not?), but I'm having some issues sourcing an R8/9. So I need to ask: what would be the impact of replacing this with a "slightly" larger resistor, say 2R2? Cause if it's something like a volume drop, that might actually be a good thing.


It won't make a big difference.  More than a volume difference, it sets the output impedance - or damping factor - of the output.

Some people prefer an even larger resistor, depending on the headphone impedance.  It changes the sound.  For high impedance headphones some people go as high as 150 ohms, though this is too much for most modern headphones.  On the other hand, if you are driving inefficient low impedance headphones, you want this to be as low as possible, even 0 ohms.

Pete


----------



## CatalinM (May 26, 2018)

Thanks, Pete!

My target cans right now (and probably for the foreseeable future) have a 64ohm impedance, so I'll probably be fine with 2R2 then.

PS: One more question. Can I use a bigger bypass cap (C4 and C7) on the output caps? Say 0.68uF.


----------



## AddiDub

Hey Guys, 

few weeks ago i ordered everything i need for my nuhybrid headphone amp. I want to run it together with my old AKG240 Studio - which has 600 Ohm impedance. Any suggestions for parts value changes like R8/R9? I got the following resistor values at home: 10R, 12R7, 33R, 49R. Which one would fit best to drive a 600 Ohm Headphone? Any further suggestions?



pmillett said:


> You are spot on about R8 and R9 - some people will like zero ohms better than 1 ohm, and some might also prefer 10-33 ohms there.  It depends on your headphones and listening preferences.



Many thanks to Pete for creating this kit and making the nutube available!


----------



## pmillett

I don't think it will make a big difference.  As I recall the K240 was designed to the old IEC standard that specified a source impedance of 120 ohms.  But you might like the sound better with a low source impedance.

If it were me, I'd stick in 33 ohms...

Pete


----------



## Wyd4

Very interested in this, but would have more chance soldering with a cannon .


----------



## CatalinM

Finished mine some 20 mins ago. Really happy with the overall sound, even though it's really microphonic. I kinda regret soldering the volume pot on the board as it sends vibrations when you hit it's minimum stop - I'll probably desolder it and add some wires to decouple it from the board.

I had to change some parts though, namely C10, C12 and C15... the Elna's I got were too large and didn't fit, so I changed them with some Nichicon's that were rated at 25V and thus smaller. I checked the schematic and these 3 didn't have any high voltage on them so the switch seemed safe... and it hasn't blown in my face, so we're good.

PS: I noticed a significant channel imbalance at very low (barely audible) levels. I'd blame it on the TKD pot, even if it's really disappointing for such an expensive pot (the Alps Blue Velvet I have in my Aikido preamp doesn't have such issues).


----------



## Dule

Hello,
I am having trouble with my nuhybrid amp. Can't get 11 V on the right channel, I get around 4.4 max. Left channel is fine. I tried plugging headphones and right channel is noisy, a humming sound.

I have measured voltage on both R13 and R14 and on one side they both have 23.77V but on the other sides of resistors one (R14) is 10.72V and the other (R13) is 6.28V . Both resistors are 475k checked and rechecked few times.

Does anybody know what might be the problem?


----------



## HiGHFLYiN9

You might want to flip-flop the op-amps, that's an easy thing to check.


----------



## Dule

Dule said:


> Hello,
> I am having trouble with my nuhybrid amp. Can't get 11 V on the right channel, I get around 4.4 max. Left channel is fine. I tried plugging headphones and right channel is noisy, a humming sound.
> 
> I have measured voltage on both R13 and R14 and on one side they both have 23.77V but on the other sides of resistors one (R14) is 10.72V and the other (R13) is 6.28V . Both resistors are 475k checked and rechecked few times.
> ...





Solved  One of the pins on op amp was not soldered properly. I have checked all the joints something like 10 times and missed this every time, only when I changed angle of light I saw it . Anyway, it is working now all good.


----------



## CatalinM

I finally had a chance to test this out with my main headphones, a pair of Audio Technica A500, but I can't say I'm very happy with the sound. These headphones always had a light bass - it goes really low, but it's not powerful, unless you apply some EQ. They're also very open and detailed. Unfortunately, through the NuHybrid, the bass remains light, but the brightness is just a little too much. I'll let the amp run for a day or so to burn it in and see if that changes anything.

On another note, I'll build a separate linear power supply and I was thinking about putting it in a different case. Now, I've never done this before and I'm not sure how I should handle grounding / earth connection between the two cases. The power supply would not be floating, so it'll probably have GND connected to mains earth through a filter most probably. Should I connect the amp's aluminium case to the power supply GND?


----------



## CatalinM

After some 50hrs of almost continuous music playback through the amp I feel it has gotten slightly better, but it's still too bright. With the Samson SR850, it's just a little too glassy, but with the Audio Technica it gets some really searing highs, depending on recording. It's really annoying, as the overall sound is significantly better than my 2017 Macbook's audio out (one of the best for any computer out there), but those blistering highs make it hard to enjoy on 50% of the recordings.

Does anyone have an idea for a tweak here?


----------



## HiGHFLYiN9

You can try adding some speaker grill cloth between the headphone driver and your ear. https://www.parts-express.com/parts-express-speaker-grill-cloth-black-yard-70-wide--260-335


----------



## CatalinM

That doesn't sound very... exact. Plus the fact that I would have to change that grill when listening to other amps.


----------



## pmillett

CatalinM said:


> After some 50hrs of almost continuous music playback through the amp I feel it has gotten slightly better, but it's still too bright. With the Samson SR850, it's just a little too glassy, but with the Audio Technica it gets some really searing highs, depending on recording. It's really annoying, as the overall sound is significantly better than my 2017 Macbook's audio out (one of the best for any computer out there), but those blistering highs make it hard to enjoy on 50% of the recordings.
> 
> Does anyone have an idea for a tweak here?


Try moving the bias point off center a bit - set it for maybe 9V or 8V instead of 11V,  This will introduce more 2nd harmonic which tends to smooth out the highs...

Pete


----------



## CatalinM

Hi Pete,

I did that actually. The last 10-15 hrs of the burn-in (and listening afterwards) were done with bias set around 8.25V. 

I think the lack of bass on the AT headphones makes me push the volume up, which accentuates the highs, but either way it's still a bit glassy. Is there anything I could change? Maybe R8/9 or the output coupling caps? I do want to get some Burson v6 opamps in there anyway, although I'm not sure that would improve the situation.


----------



## pmillett

You can try increasing R8/R9.  Not sure if it will help or hurt with these headphones.  I know with Grados I like to put 50-100 ohms in series or they sound too harsh to me...

Opamps probably won't make much difference.


----------



## CatalinM (Aug 11, 2018)

I switch R8/R9 from 2.2 to 100 ohms and it had some effect (less on the highs, more on the volume I'd say... now I have to turn the volume pot higher to get the same loudness, which is an improvement in its own). This didn't fix the issue entirely, so I tried HiGHFLYiN9's advice and took a dampener sheet from the Samson headphones and inserted it in the Audio Technicas - surprising improvement.

All in all, it's usable now, event though I'm not entirely satisfied with the solution. I'll go ahead and continue the work on the external power supply and upgrade the opamps.

Doing some critical listening, I'd say that - in my particular combination - it has a pronounced bump in the 2-3khz range, which I'd be happy to get rid of, without sacrificing what's above that. I feel that particular range brings out the cymbals too much and causes fatigue.


----------



## Evgeni

pmillett said:


> Try moving the bias point off center a bit - set it for maybe 9V or 8V instead of 11V,  This will introduce more 2nd harmonic which tends to smooth out the highs...
> 
> Pete


That’s an interesting suggestion. Since I’m mostly after “fun” sound rather than neutral/uncolored, what’s the bias with most 2nd harmonics so that I can listen to “tube” sound? Is it as low as possible or the 8-9V is the sweet spot? I understand what’s fun depends on the listener but anyway, what would you recommend as the most “fun” bias?


----------



## caenlenfromOCN (Aug 27, 2018)

@pmillett here is a diy sort of liek starving student with some modifications that a friend made me, it sounds equal or better than Lyr 3 imo. I know you probably don't care, just thought I'd share since your technically like the person that started this whole thing years ago. wiring is done a lot different, I don't know much about this stuff, but you can see for yourself, pics below. let me know what you think, cheers!  It had some noise issues at low volume at first, but then he repaired it for me and now 0 noise floor and no channel imbalance that I can tell, and sounds great with all my cans, even planars. my only complaint is that the vlume knob gains power too fast, so i end at 9am for most of my cans on the knob. i need to get some 600 ohm cans of some kind and see if they sound good with this, im sure they would.


----------



## CatalinM

I've replaced the OPA551's with a pair of Burson Audio V6 Classic and I think they improved the sound quite a bit. On first impression the bass was tighter and soundstage was slightly larger, with more clarity and separation between instruments... everything seems more layered, in a very balanced way. I let them burn in for about 5 days straight, but the evolution was linear and I can't really say how it changed now without doing an A/B.

I'm now curious to replace the C3/C6 from Silmic II to Audio Note Kaisei... but they're not available in 35V and the 63V version is too big. Would it be safe to put in 25Vs ?

Here's a pic of the current state of affairs:


----------



## pmillett

25V caps is close to the limit.  If your power supply really measures 24V or less, it will work.

Pete


----------



## CatalinM

I’m working on a highly regulated supply, built around an Amb Labs σ78. It’s probably overkill, but it’ll be a fun build and I’ll be sure it outputs 24V. 

However, speaking about C3 ans C6, shouldn’t they have only the bias voltage (when idling), plus minus the signal amplitude? So I’d imagine it should be way lower than 24V unless you max out volume. Please correct if I’m not getting this right.


----------



## pmillett

Right - during normal operation, C3 and C6 are charged to wherever the bias is, normally around 11V.  But you also have to consider what can happen at power-up, power-down, and if the output gets shorted.  In some cases you may get more than that voltage applied.  So the safest thing is to keep their rating greater than the maximum possible voltage that could get applied, even in a fault condition.

All that said, you're right, if your supply is 24.0V then a 25V cap should be OK here.

Pete


----------



## CatalinM

Makes sense. Thanks, Pete!


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## gdogpwns (Sep 22, 2018)

I am building this right now and I am having a peculiar issue. I am not getting any sound out, and when I probe the test points, the Nutube begins to flicker. I am new to this type of thing, where should I begin diagnosing?

If it helps, I was confused and soldered the volume knob to where it bridges to those pads immediately (almost touching) above them. Could this be the problem?

The two glowing sections (is my noob showing yet?) of the NuTube seem to be glowing at different brightnesses and the side closest to the headphone jack flickers very slightly if watched.

Thanks for all of your work by the way. Can't wait to hear this.

EDIT: All of a sudden, the tube begins to glow when I turn it on then fades out. The LED remains lit. I accidentally began probing with my multimeter set to 200V AC instead of DC. Could I have broken something in the process?


----------



## CatalinM

Having your multimeter set to 200V AC shouldn't break anything there. From what you're describing, it seems the filaments are not properly powered - have a look around C12 and C15. Maybe the caps are bad or there's a short somewhere. Or a cold solder joint.


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## gdogpwns (Sep 23, 2018)

CatalinM said:


> Having your multimeter set to 200V AC shouldn't break anything there. From what you're describing, it seems the filaments are not properly powered - have a look around C12 and C15. Maybe the caps are bad or there's a short somewhere. Or a cold solder joint.


I gave a good look around C12 and C15 and resoldered those points but nada.

I've noticed a new symptom. Previously, I would get no audio at all. Now my headphones crackle on power on as well as a high pitched ringing (not microphonics I believe). My right-bias side of the NuTube is not glowing at all now, and the readings from the test point do not change on it no matter how much I turn it. It also pops on power up, and I believe that there is a circuit in place to prevent that.

Thanks again for your help CatalinM.

EDIT: I am now getting audio. I think that I just did a bad soldering job (went out and got a new iron, my last one was falling apart.) But the same part of the Nutube is flickering. While reading the test points of the right bias, I noticed that it climbs from about 1.1V to 2.1V (or thereabouts) then drops back down. I guess this means the capacitor (C15?) is charging then discharging. Any ideas?


----------



## CatalinM

Hmmm, it seems there's still something wrong with your power supply. Use your DMM to measure between the positive supply of the opamps (pin 7 on either of one) and the GND test point. It should read a solid 24V. If that's ok, start measuring the filament supplies, as the general power supply is OK. Use the GND test point and the plus pin on C12 and C15. This should read 700mV, as per Pete's documentation.


----------



## gdogpwns

gdogpwns said:


> I gave a good look around C12 and C15 and resoldered those points but nada.
> 
> I've noticed a new symptom. Previously, I would get no audio at all. Now my headphones crackle on power on as well as a high pitched ringing (not microphonics I believe). My right-bias side of the NuTube is not glowing at all now, and the readings from the test point do not change on it no matter how much I turn it. It also pops on power up, and I believe that there is a circuit in place to prevent that.
> 
> Thanks again for your help CatalinM.





CatalinM said:


> Hmmm, it seems there's still something wrong with your power supply. Use your DMM to measure between the positive supply of the opamps (pin 7 on either of one) and the GND test point. It should read a solid 24V. If that's ok, start measuring the filament supplies, as the general power supply is OK. Use the GND test point and the plus pin on C12 and C15. This should read 700mV, as per Pete's documentation.


Okay, I found something strange. Reading from the GND test point (I measured this from the back of the PCB if that matters) and C12 and C15, it shows ~250mV for each but it also seems to sometimes fluctuate all the way down to ~120mV. Both filaments are not glowing either now. Any ideas?


----------



## CatalinM

Have a look at the schematic. You have a power supply that should give you 24V. Start measuring from the power supply input and follow the path to your filaments. C5 should measure 24V. The output of the U3 regulator should measure 3.3V (C10 as well). 

Let us know what you find.


----------



## gdogpwns

CatalinM said:


> Have a look at the schematic. You have a power supply that should give you 24V. Start measuring from the power supply input and follow the path to your filaments. C5 should measure 24V. The output of the U3 regulator should measure 3.3V (C10 as well).
> 
> Let us know what you find.


I am still trying to make mine work, sadly. I think it's just bad solder from Lowe's that oxidized and my Lowe's soldering iron that was falling apart also didn't help. Probably goofed up a lot of my motherboard. I actually melted a pad and I am not sure if it is a problem since I do not see any trace on the PCB. I highlighted the pin I am talking about below.

I probably messed up some trace with how bad that soldering iron was. I have access to a good one now, so I may just start placing wires at the bottom of the board. The filaments like to glow after I resolder those points, then they usually sound very crackly then one (or both) filaments power off with a loud pop in my headphones. I also noticed in the documentation that there should be a 10 second mute when I turn it on that I am not experiencing. Could this be related?


----------



## silverfishla

gdogpwns said:


> I am still trying to make mine work, sadly. I think it's just bad solder from Lowe's that oxidized and my Lowe's soldering iron that was falling apart also didn't help. Probably goofed up a lot of my motherboard. I actually melted a pad and I am not sure if it is a problem since I do not see any trace on the PCB. I highlighted the pin I am talking about below.
> 
> I probably messed up some trace with how bad that soldering iron was. I have access to a good one now, so I may just start placing wires at the bottom of the board. The filaments like to glow after I resolder those points, then they usually sound very crackly then one (or both) filaments power off with a loud pop in my headphones. I also noticed in the documentation that there should be a 10 second mute when I turn it on that I am not experiencing. Could this be related?


Why don't you post a picture of both sides of your board and see if anyone here can do some visual diagnosis of what you have going on....


----------



## gdogpwns

silverfishla said:


> Why don't you post a picture of both sides of your board and see if anyone here can do some visual diagnosis of what you have going on....


Here ya go!


----------



## silverfishla

gdogpwns said:


> Here ya go!


Hmm.  My first inclination would be to recheck my solder joints.  I would get a magnifying glass and wiggle each component from the opposite side and see if I could see any movement from the solder side, or crack.  I might just retouch any that I might have doubts about with new solder.  That's what I would do first.  You've got a lot of flux on your board,  I might clean that off first with some alcohol.


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## gdogpwns (Sep 29, 2018)

I got the amp working for about ten minutes until it broke again. Here's what I'm noticing:

1. The pins on both filaments are taking in the exact same amount of volts.
2. The output of the left filament (the non-working one) is significantly lower than the right filament .

It seems to only work sometimes after I solder. I'm assuming that I either got a broken Nutube (unlikely) or I broke it myself (extremely likely) and heating it gets it going for a short amount of time. Should I just suck it up and buy another Nutube if these are my symptoms?


----------



## CatalinM

If the input is fine, you might have a bad tube (or a solder connection is still bad).

On a separate issue, I enjoyed Pete's suggestion to increase R8/R9 and now I'm thinking about taking it a step further. I'd install a rotary switch that would allow me to route the signal through various resistors (1, 22, 47, 80, 100) so I can adjust it anytime for the cans I'm using. What do you guys think?


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## gdogpwns (Oct 14, 2018)

Decided to suck it up and buy mostly all new parts (saved the case, opamps, and power supply) and rebuild it from scratch. The amp working fine now. Sounds absolutely incredible. I'm so glad to finally hear my HD-6XXs at their full potential. Thanks, Pete!

Edit: I have gotten some listening in now and the device isn't as microphonic as some people are describing. I guess it's dependent on the particular Nutube. In the few moments where my broken Nutube was working, it was definitely microphonic as hell. This one sounds incredible. I can't compare this to any other tube amps since this is my first, but it sounds very rich.


----------



## SchwarzeWolke

Just ordered one a week ago and thought I bought a cheap TKD 2CP601 via Ebay. It turned out that I bought a 1kOhm one and not 10kOhm... Tried to find it on the schematics but didn't find it. Am I right that 1kOhm is just to low and would not work?


----------



## pmillett

SchwarzeWolke said:


> Just ordered one a week ago and thought I bought a cheap TKD 2CP601 via Ebay. It turned out that I bought a 1kOhm one and not 10kOhm... Tried to find it on the schematics but didn't find it. Am I right that 1kOhm is just to low and would not work?


The amp is fine with 1k, but the source that you're using it might not like it.  It will present a 1k load to the source.  Some sources are fine with 1k, others might distort a little more with a 1k load than a 10k load.  And tube sources may not work well at all.

I am guessing that phones should be fine with it.  If you're using a DAC, check to see if they specify a minimum load impedance...

Pete


----------



## SchwarzeWolke

Thx Pete! 
I got some problems with the availabilty of two components and maybe some more might have this problem:
Two components from KEMET are at least here in Germany not available.

EC2-24NJ


SU9V-05020
For the low signal relay I've found some alternative from Omrom and Panasonic. They're much more expensive but I don't want to wait until next year...
For the common mode filter chokes, I just found alternatives with a little higher inductance. Sorry for asking but I don't have experience with such stuff and don't know if I can replace them.


----------



## pmillett

SchwarzeWolke said:


> Thx Pete!
> I got some problems with the availabilty of two components and maybe some more might have this problem:
> Two components from KEMET are at least here in Germany not available.
> 
> ...


Yeah, that relay seems to be perpetually out of stock.  I know that the TE V23079A1005B301 works fine, and as it is a common footprintt I'm sure there are others.

Nothing critical about the common mode choke, anything that fits in the holes will work.  Higher impedance is actually better.

Pete


----------



## MrKazador (Dec 16, 2018)

Its been a few years since I built my o2 and wanted something new/different. I don't know if I have bad hearing but its not that microphonic. When you first turn it on there is a high pitch ring but it goes away after about 10 seconds. I have to tap on the case real hard to get it to ring, with normal usage I don't hear anything.


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## ilikepooters

Ordered the PCB and NuTube and also the parts from Mouser.

The power adaptor says unavailable in my country (guess it's because it's US version) will the following be ok that i found on ebay?
https://www.ebay.co.uk/itm/Mean-Wel...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

This is my first DIY project, wish me luck!


----------



## pmillett

Yup, that should work.

Pete


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## docentore

Hey folks and happy New Year.

I'm thinking of building this amp as my small desktop amp. Just wondering if it would be enough to drive the T50rp MK2 (Argons)?
Anyone tried the combination?
My apologies if the question was asked and answered before.


----------



## ilikepooters

OPA551's drive the output to the headphones and rated at 380 mA, 2 of them so 380 mA per channel theoretically, no idea what that is in watts.


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## pukkita (Jan 7, 2019)

Been a while since last time...

First of all, THANKS Pete for sharing this project and making it easy and basically giving away the PCB!

Been following you since early 20's  (pukka, but can't seem to recover the pass, went on to Senns 6xx and ditched the K701).

I built it yesterday, took about 3 hours (been out of DIY some years) and worked perfect right out of the bat.

Assembled it stock, only modification from stock BOM:  changed the WIMAs for MKP (fit perfectly, 505-MKP2D031001F00KF) and got the TKD pot.

I did the pot grounding mod, set bias to 11V.

Used one of the zillion switched 24V adapters for PoE I have around (network admin).

Zero noise. I can hear the high microphonic pitch for about a couple seconds at turn on, that's all.

Really impressed with the sound of this amp. Euphonic, great freq balance,  great dynamics,sweet highs and incredible detail... so far have tested it only from an iPhone Xs out (superb!!!).

I see myself building this amp as gifts for my relatives!

Definitely, the best project for someone looking to delve into tubes/DIY safely, with killer price/performance.






Sorry but the forum screws my attempts at posting pictures.


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## SchwarzeWolke

Finished the build last evening. It just looks phenomenal!!!
Thanks Pete for the opportunity and also sharing everything from assembly manual to BOM.
There is one thing I've stumbled upon: In the BOM on your website, there are 35V/470uF Nichicon large caps mentioned. In the BOM on the Mouser website, which I also used, they have been switched to 50V/470uF caps. After searching this thread, I've just found some pictures from recent builds where also the 50V versions were installed. Am I right that this is no problem? I thought that given how caps work, this should be any problem at all.
Sound is really good, I ordered an A/B-switcher to be able to listen to my Massdrop THX AAA 789 in comparison to the Nutube Hybride. Will post my impressions maybe next week.
Microphonics are there with really sensitive In-Ears. With my HD-6xx I didn't have any problems. Might also be that the Nutube needs some time switched on, right now I've left it on for about ten minutes and will try it maybe in an hour or so again.
Assembly was fairly easy and you were right with the statement, that this might be a good beginners project! Maybe the O2Objective will be my next project, had a lot fun soldering this amp to a working unit.


----------



## pukkita

Loving this amp! really diggin the nutube sound signature and of course, your implementation! Awesome sinergy with HD6XX. Huge sound, incredible microdetail... but the thing I like most is how it brings the texture or timbre from instruments... not only acoustic, i.e. electric guitar/bass sounds how it would on stage next to an amp!

Lovin it so much that wondered how using nutube(s) for I/V DAC output stage would sound...


----------



## ilikepooters (Jan 8, 2019)

Finished building mine. No pics because looks basically the same as everyone elses except for my amateurish soldering  Took 90 minutes to build roughly. Used cardas quad, this is my first ever proper soldering roject.

Powers HE-500's really well, cranked the volume way up to more than i'm comfortable with and no sign of any bass clipping, wonderfully tight and controlled.

It makes me feel like buying Lyr 3 was wasted money, this little DIY project punches way over it's price bracket and is definitely on a par.


----------



## ilikepooters

OK so op-amp rolling...

Ordered up a couple of AD8397's and a couple of DIP-8 adaptors. Unity Gain stable and 24v.

But is there any danger of it oscillating in this circuit? Heard they can be quite fussy op-amps.


----------



## pmillett

ilikepooters said:


> OK so op-amp rolling...
> 
> Ordered up a couple of AD8397's and a couple of DIP-8 adaptors. Unity Gain stable and 24v.
> 
> But is there any danger of it oscillating in this circuit? Heard they can be quite fussy op-amps.



There is always a little chance that an opamp will oscillate driving some headphones.  Headphones are complex impedances, and if  they present too much capacitance, the circuit can become unstable.  I've not heard of it happening on this amp, but have seen a couple of cases with other opamp-based amps.

That's largely why the series resistors R8 and R9 are there, they make the circuit more forgiving.  If you do have oscillation you can make them larger to mitigate it.  But the resistor will probably change the sound more than the opamp swap...

Pete


----------



## SchwarzeWolke

In its natural habitat.

   
Have tried my new A/B switcher and it is really hard to hear some differences between the Massdrop and the Nutube. The Massdrop is one hell of a machine, so kudos to the Nutube that it can step up to it!
Only question for me now is if I should keep both amps. I'm more the "just keep what you are using" guy and I just have one pair of ears...


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## pukkita (Jan 10, 2019)

Couldn't agree more... I found the nuhybrid to be extremelly transparent, to put an analogy with graphics, I find it kind of "unsharp mask" the sound, enhancing it, keeping details but enhancing "contrast", while remaining *incredibly* transparent.

It *really* reflects the the source quality, and makes it more lush and enjoyable.

It doesn't make the sound "slow", or compress/shift the dynamics like other tube amps, truly all-terrain and enjoyable with all kinds of music, be it Rock, EDM, metal or Vocal/Jazz.

Sounded beautifully straight out of the macbook line out, but what incredible change after switching to a DDDAC mkII! need more listening hours though.

Have A/B'd it vs a Loxjie P20, both from same DAC source (Audirvana-> HiFimeDIY Sabre USB DAC 2 (ES9023) SPDIF -> Stock Ultramatch Pro in Upsampling mode, feeding SE to NuHybrid and Balanced to the Loxjie P20, HD6XX used in both cases.

Main difference is in soundstage presentation, the NuHybrid being more "in your head" and "perpendicular to your ears", while the Loxjie P20 (what an amp too!)  creates a wider, more centered and slightly laid back soundstage.

I know I'm comparing apples to oranges, the point is I'm curious how a Balanced Amp Nutube implementation will sound, @pmillett: have you by chance tested it? Really curious about a I/V Nutube DAC too...

As main critical component affecting the sound on the NuHybrid is the volume pot, thought about using a similar implementation as the Loxjie (NJW1195) will be of great benefit for the NuHybrid....

Using Switched PSUs in both. I've  tested linear PSUs and found I actually prefer (quality) switched ones, kind of more "energetic" or livelier sound presentation.


----------



## docentore

ilikepooters said:


> OK so op-amp rolling...
> 
> Ordered up a couple of AD8397's and a couple of DIP-8 adaptors. Unity Gain stable and 24v.
> 
> But is there any danger of it oscillating in this circuit? Heard they can be quite fussy op-amps.


Interested to hear your opinion on the AD8397


----------



## silverfishla

Any of us here that have built the Nutube headphone amp thinking about building Pete’s new stereo Nutube amp?  I just saw it on his pages.  Looks really interesting, I want to go for it.


----------



## ThermalAlchemy

silverfishla said:


> Any of us here that have built the Nutube headphone amp thinking about building Pete’s new stereo Nutube amp?  I just saw it on his pages.  Looks really interesting, I want to go for it.


 Does it have XLR capabilities is it running Dual mono inside with two separate power supplies ?  I would be up for that especially if I could run optional exterior power supply .  Especially if it had  out to be used as a preamp .  I could use it with my Nelson pass mono blocks that have been converted to XRL as a preamp itself .  Or use some of Nelson Passes preamp like the BA-1 or the BA-3 with XLR .  Sounds like an excellent marriage made by the Audio Gods


----------



## AddiDub

I finished my build of the NuHybrid amp few days ago and i am very happy with it until now. The PCB and tube arrived fast and save and i ordered the components at mouser using the ready made BOM - very convient! It was my first "tube" project and thats why i choose the NuHybrid. After i finished the build the amp worked straight away - lucky me.. 

I use the NuHybrid amp together with my DIY jFet phono preamp to listen to my records. It really sounds better then using the headphone output of my integrated amplifier. Maybe it is because it has more capabilities to drive my DT770 Pro 250 Ohm headphones compared to the other amp. I have some favourite records that i use for subjective listening tests like Fat Freddys Drop - BOATS or Absolute Beginner - Blast Action Heroes. This might sound awful to some audiophiles ears but i really like them for testing stuff, because both records have loads of deep but well defined basslines. With headphones you only get a CLEAN bass if amp and headphone match very well. On my integrated amplifier the bass of both records sounds muddy and boomy. But with the NuHybrid amp and my DT770s the bass is much cleaner and well defined. 

I would like to know what NwAvGuy would say about the NuHybrid amp. Clearly not the "objective" approach but very good sounding and it looks well engineered. Fun Fact: I missed that there is a portable version of the NuHybrid amp now and got me a DIY kit for the "objective2" amp at Head'nHiFi. It is also good in driving my bigger cans and thats why i like it as much as PMillets NuHybrid amp. And the O2 costs only 95 Euro including shipping for a really complete kit including the optional lower power version.

Thanks PMillet for all your works and for making nice NuTube circuits available to the public


----------



## cgnman59

I finished the NuHybrid Headphone amplast week. I made no modifications at all, just made it the way Pete specified. I should note my soldering skills are average at best and I struggle to understand and read a schematic. So I approach any project like this with a certain amount of trepidation. Pete though, made this project as easy as possible. You can just link to the project on Mouser and add the parts listed to the cart. He was quick to send the PCB and Nutube. It went together with no trouble at all. So following his directions I powered it up. The Nutube lit up with a cool light blue glow and the green led lit up. So that's good news. I adjust the bias to the 11 volts recommended by Pete. Plugged in my headphones, turned up the volume, started the CD player and...silence?? So check everything again and discovered I had not soldered two pins of the K1 relay. Okay, solder those and try again. This time music. How does it sound? Well I think it sounds very good. I use a pair of Sony MDR-V6 headphones I have owned since they first came out in the early 90's. I played Boston, the Berlin Philharmonic, "The Planets" Alison Krauss and The Dave Brubeck Quartet. The NuHybrid handled them all easily and made listening enjoyable. It is also quiet, no hiss evident. I have to admit I don't listen often at home with headphones. A couple of years ago I built Pete's DCPP Engineer Amplifier. This is my main rig. So I put the NuHybrid between my DAC and the DCPP to find out how it sounded through my Klipsch KG3.5 speakers. I was amazed at how good the two sound together. A great song to test with is The Dave Brubeck Quartet song, "Three To Get Ready" This is a very dynamic piece from his landmark LP, "Take Five." It features each member of the group. With the NuHybrid and DCPP I am hearing more detail than I thought possible right down to the slight rasp of the reed as Paul Desmond plays the sax. Best of all this little amp is inexpensive and easy to put together.


----------



## docentore

I'm building my NuHybrid now but I have few questions about possible upgrades, mostly caps. Can bipolar caps be used (10uF) instead of standard ones?


----------



## docentore

pmillett said:


> There is always a little chance that an opamp will oscillate driving some headphones.  Headphones are complex impedances, and if  they present too much capacitance, the circuit can become unstable.  I've not heard of it happening on this amp, but have seen a couple of cases with other opamp-based amps.
> 
> That's largely why the series resistors R8 and R9 are there, they make the circuit more forgiving.  If you do have oscillation you can make them larger to mitigate it.  But the resistor will probably change the sound more than the opamp swap...
> 
> Pete



Hi Pete

If I were to test the AD8397 in NuHybrid will I need to alter the pinout as AD is 2 channel opamp and OPA551 single with different pinout.
Thanks


----------



## Wiljen

docentore said:


> Hi Pete
> 
> If I were to test the AD8397 in NuHybrid will I need to alter the pinout as AD is 2 channel opamp and OPA551 single with different pinout.
> Thanks



Yes, you'd have to alter the design.  They make boards for using two single opamps in place a single double but I've never seen a drop in for using 1/2 a double in a single socket.


----------



## tomb (Jan 24, 2019)

Wiljen said:


> Yes, you'd have to alter the design.  They make boards for using two single opamps in place a single double but I've never seen a drop in for using 1/2 a double in a single socket.


^ This.

Even further, Pete states that the OPA551 is in the circuit as a buffer, not really what you'd think of as an opamp.  He suggests the BUF634 would work.*  If that's compatible, it may be that the old Intersil buffers sometimes used in the original Millett Hybrid may be compatible (HA3-5002).

Also, one of the most aggressive buffer chips could be compatible, but Pete would need to confirm this.  The LMH6321 is a very aggressive buffer chip, reportedly capable of 700ma for short bursts (maybe the buffer version of the AD8397?).  Tangent used it in his latest PIMETA design instead of the BUF634.  At first glance, it appears to be pin-compatible so it may work.

If you use the BUF634, you can stack them on top of each other and solder the pins together.  This will give you more current burst capability.  It was an old trick we used to do with both the PIMETA and Millett Hybrid.  However, having tried all of them (including the OPA551) in the Millett Hybrid and PIMETA, I can tell you that the LMH6321 just by itself is better than two stacked BUF634s.

At least one individual who used to frequent Head-Fi claimed that the TO-220 version of the BUF634 was even more superior if you heat-sinked it, which is what Pete did on his original Millett Hybrid that was published in AudioXpress magazine.  I don't know if that is true, but it gives you more possibilities.

However, I would pursue the LMH6321 if Pete can confirm that it may work.  You'll need Brown Dog adapters because that chip is SOIC-8.

* To be clear, Pete states, "You can substitute your favorite opamp or buffer for the OPA551.  It needs to support a 24V power supply, and be unity gain stable.  Other than that it's up to you."  However, if the purpose is for current, some of the more familiar opamps may be fairly limited in that capability.  Use of a true current buffer chip, such as those mentioned above, might be more optimum.


----------



## docentore (Jan 31, 2019)

Ok, so I have managed to get the amp assembled. Used Vishay-Dale resistors for most of the parts (apart from 1Ohm R8 and R9). As electrolityc caps I used Elna Simic - I had to C4 and C7 to the bottom of the PCB.


Got the bias set at 11V but I've noticed that left lamp is dimmed. Anyone had this before? Is there anything I should be worried? I haven't tried connecting headphones, will try tomorrow. I've checked all solder points and they look fine.
EDIT: all fine, stupid me. I was setting bias for one channel probing L&R testpoints, doh!

EDIT2 (don't want to double post): Amp works brilliantly. Drives my T50RP MK2 ArgonMod quite well. Anyone tried different values of R8/R9 for T50RP or other planars? They are 50Ohms.

EDIT3: palyed around with single opamps I have. 
OPA604 -meh, nothing special
OPA134 - WOW, winner, to me sounds better than OPA551
AD8065 and OPA1641 - couldn't test them as DIP adapter I got does not fit the socket.


----------



## Prabeer Patankar (Feb 1, 2019)

Hello Pete

I recently built this amp and experimented with a couple of single opamps I had in my possession.

I tried OPA2209 ( good details and faster than stock but quite edgy and noisy). AD797 ( very quiet background, good details especially in the lower end however it’s not unity gain stable. It’s most probably oscillating as it heats up quite a bit). I got the Sparkos Ss3601 singles after reading a post on this thread and they are quite good. The extension on either side is very good. The amp sounds faster and there more details and separation.
Last week at a Audio meet up I carried this amp along with my Cayin iHA-6. We connected a Audio Note DAC 0.1x to the Nutube and fed the pre out to the iHA-6. Listening on my LCD-X and the demo Meze Empyrean and HD800 available there at the meet up, the synergy was so beautiful. The sweetness of the DAC was just flowing through to the drivers. Amazing micro details and a lush 3D soundscape. When we took the Nutube out of the chain and fed the DAC directly to the Cayin the whole magic disappeared. There was no 3D enveloping sound stage, the vertical stage and layering between the instruments disappeared. The details were still there but the sweetness disappeared. Maybe there was a impedance mismatch between the DAC and the Cayin.

I am not a electronics guy. Just someone who can solder by numbers. Can any of you more experienced guys tell me what is the input impedance of this amp. The guy who had got the Audio Note DAC to the meet is Aernoud Dekker, the India CEO of Audio Note and he has been asking me about this ever since. Such has been the effect of this little guy.

Thanks in advance
( I am trying to figure out how to post pics of the amp here)

Prabeer


----------



## ilikepooters

Prabeer Patankar said:


> Hello Pete
> 
> I recently built this amp and experimented with a couple of single opamps I had in my possession.
> 
> ...



Nice enclosure!! Where can i get one?


----------



## Prabeer Patankar

ilikepooters said:


> Nice enclosure!! Where can i get one?


Hi
A friend helped me source it from a fabricator in Delhi, India. It was custom made for his Nutube build and the fabricator had a spare lying with him.


----------



## Prabeer Patankar

ilikepooters said:


> Nice enclosure!! Where can i get one?


Hi
A friend helped me source it from a fabricator in Delhi, India. It was custom made for his Nutube build and the fabricator had a spare lying with him.


----------



## Prabeer Patankar

Sorry for the repeat post


----------



## cgnman59

I've used the NuHybrid as a pre between a Topping D10 DAC and my Millett Engineer's Amp going through Klipsch KG3.5 speakers. I find it is great as a pre and has helped tamed some of my music that has been a bit harsh through the Klipsch. I agree with you on the soundstage as well. Incredible what Pete has accomplished with the Nutube and about $65 in parts. And really like the enclosure. Very sharp.


----------



## tomb

Prabeer Patankar said:


> <snip>
> I am not a electronics guy. Just someone who can solder by numbers. Can any of you more experienced guys tell me what is the input impedance of this amp. The guy who had got the Audio Note DAC to the meet is Aernoud Dekker, the India CEO of Audio Note and he has been asking me about this ever since. Such has been the effect of this little guy.
> 
> Thanks in advance
> ...


Except for one notable exception (the O2), almost every single headphone amplifier design places the volume pot in the signal path right after the RCA jacks.  Therefore, the input impedance is equal to the impedance of the volume pot.  If you used the Alps RK097 volume pot that Pete specified in the BOM, then 10K is the answer.


----------



## Prabeer Patankar

tomb said:


> Except for one notable exception (the O2), almost every single headphone amplifier design places the volume pot in the signal path right after the RCA jacks. Therefore, the input impedance is equal to the impedance of the volume pot. If you used the Alps RK097 volume pot that Pete specified in the BOM, then 10K is the answer.



Thanks for the reply Tomb, I am using the TKD pot which is also 10K.


----------



## Prabeer Patankar

cgnman59 said:


> I've used the NuHybrid as a pre between a Topping D10 DAC and my Millett Engineer's Amp going through Klipsch KG3.5 speakers. I find it is great as a pre and has helped tamed some of my music that has been a bit harsh through the Klipsch. I agree with you on the soundstage as well. Incredible what Pete has accomplished with the Nutube and about $65 in parts. And really like the enclosure. Very sharp.



Thanks cgnman59. 

It’s pairing very well with my Atoll IN200SE in power amp mode too. I am very happy with this build.


----------



## Luckbad

HiGHFLYiN9 said:


> Very nice! Can you share with members what model Hammond you used? I like it much better than the Serpac, but the Serpac is cheap and good for people on a limited budget.
> 
> I finished mine over the weekend and have been letting it break in. Initial listening sessions have been very positive. I shielded the wooden box I made with copper tape electrically connected to the front and back aluminum panels.
> 
> ...



Is that an enclosure that can be purchased somewhere? I super dig it.


----------



## HiGHFLYiN9

Thanks! I actually just used scraps of 4" pine and routed the ends. Pretty easy to do even if you don't work with wood very often


----------



## Kitchener

This might be a stupid question, would it be possible to lift the Nutube off the PCB and run wires from the pins to the PCB?
-And then mount the Nutube to the chassis with, I don't know, a simple DIY bracket.
I suppose the pins are quite soft and prone to snapping if you apply any force to them, so the wires would ideally have to be held in place by something.
The gallery over at korgnutube.com has a stereo amp with the Nutubes mounted on small, seperate PCBs but I was thinking of a more ...errr "ghetto" sollution to putting the glow front/top and center on a Millett Nuhybrid.


----------



## pmillett

Kitchener said:


> This might be a stupid question, would it be possible to lift the Nutube off the PCB and run wires from the pins to the PCB?
> -And then mount the Nutube to the chassis with, I don't know, a simple DIY bracket.
> I suppose the pins are quite soft and prone to snapping if you apply any force to them, so the wires would ideally have to be held in place by something.
> The gallery over at korgnutube.com has a stereo amp with the Nutubes mounted on small, seperate PCBs but I was thinking of a more ...errr "ghetto" sollution to putting the glow front/top and center on a Millett Nuhybrid.



Sure, you can do that.  The pins are fragile so be careful.  Or, you can buy a little PCB for $6:  https://www.ebay.com/itm/Blank-Carr...735398?hash=item33d3eb2626:g:wN4AAOSw~epZf0B8

Pete


----------



## docentore

pmillett said:


> Sure, you can do that.  The pins are fragile so be careful.  Or, you can buy a little PCB for $6:  https://www.ebay.com/itm/Blank-Carr...735398?hash=item33d3eb2626:g:wN4AAOSw~epZf0B8
> 
> Pete



Should we be careful about cable length etc so it wont pick up the noise? Of course not talking about foot long cable (or meter ).


----------



## pmillett

They are high impedance nodes, so I would keep the wires as short as possible.  Not more than a couple of inches...

Pete


----------



## Kitchener

Great info there, thanks a lot Pete.
That carrier PCB should definitely be helpful, I'm looking at the Nutube (NT) data sheet and (I have to admit that I am, pardon my french, a dumbass) I am having trouble with the pins on the NT.
Would I just run wires from the same connectors as the NT pins or use the other connections?
Looking at the NT I count ten pins, looking at the data sheet I see this.

 
And I think I've identified the pins on the NT correctly below:
1 - F1
2 - F1
4 - G1
7 - A1
8 - GND
9 - F2
10 - A2
14 - G2
16 - F3
17 - F3

But I can't identify the same names on the carrier board below:
 

So, repeating myself here but, do I use the connectors on the sides or just run the wires from the same holes as the NT pins?


----------



## pmillett

The carrier PCB has the pins duplicated on both edges of the board.  So you only need to connect one side (e.g., JP3 and JP1).

Carrier=Amp [Nutube pin #]

P1=A1 [7], P2=A2 [10] (anode or plate)
G1=G1 [4], G2=G2 [14] (grid)
F1=F1 [1], F2=F3 [17] (these are the ends of the filament)
FC (either pin) = GND [8] and/or F2 [9] (these are connected together on the carrier and also on the amp, so you only need one wire)

So they all line up, except FC and GND/F2 (the tube has it in the middle, the carrier on the ends).

Hopefully that makes sense?

Pete


----------



## Kitchener

pmillett said:


> The carrier PCB has the pins duplicated on both edges of the board.  So you only need to connect one side (e.g., JP3 and JP1).
> 
> Carrier=Amp [Nutube pin #]
> 
> ...


Yeah, that adds up!
Thanks a lot. Now I can start planning a neat little case for it.

This will be my next project once I finish the Jonokuchi I've got lined up.
-in fact, I'm the pain in the rear that's been pestering you on eBay


----------



## cgnman59

I am really enjoying this little amp as a pre to my DCPP amp. But I am now thinking it would be great to add a rotary switcher so I can switch between several inputs. Any recommendations on a good switcher?


----------



## HiGHFLYiN9

If you want super nice quality, the Elma 04-1264 is great. Goldpoint also makes one that is very similar. If you're looking for something nearly as good for less $$, Grayhill switches are also excellent.


----------



## Alkolor

Hello. New guy here. Going for this as my first amp build!

First off, thanks to Pete for this and all the other builds he offers. It's great that he shares these designs, and I doubt this will be the only one I take on.
Second, thanks to all the people here. Having read through this thread, I have some ideas for my build, and I can tell this will be a good community to be a part of.

I just ordered the board and tube, and I have a few questions regarding deviating some of the BoM components before I order them. Most of it has to do with the electrolytic capacitors as many seem to customize their selections and one of the default ones is out of stock right now.

1. Can anyone verify how much room there is for the larger electrolytics? The default ones are out of stock, and I wanted to upgrade those as is. I see pictures where I believe people are fitting Ø16mm caps, but wonder if Ø18mm can be fit. This mainly applies to C3 and C6. I couldn't find the DXF files on Pete's site to measure everything.
2. Can anyone confirm that the Ø8mm Elna's listed as an upgrade on Pete's BoM fit without a lot of trouble? I'd like to upgrade to those, but those clusters look very tight.
3. I saw some people up-sized C3 and C6 to 1000uF, with tomb citing it for improving bass response I think. Is that the case, and does it have any undesirable effects on the rest of the range?
4. Should all the electrolytics be audio grade, or is it only important for the signal ones (C3, C6, C13, C14)? I was thinking of upgrading those 4 and changing the rest to endurance caps like Nichicon UPW or Panasonic FR since they're all decoupling the supply lines.
5. Having read some points about changing the values for R8 and R9, does anyone have any recommendations for their values? I will be using HD6XX's.
6. Any other tips, mods, or upgrades anyone is willing to recommend will be appreciated. I'm willing to spend a bit more to have some fun with this ($200 max for the package). I will be getting the TKD pot.
7. I'm planning to build a custom wood case when it warms up here (will be in the stock base until then). I'm thinking of something like a wood base with semi-open sides and a glass top. Anyone have wisdom or lessons learned to share with their enclosure building?

Thanks everyone. Looking forward to the build.


----------



## ThermalAlchemy

Alkolor said:


> Hello. New guy here. Going for this as my first amp build!
> 
> First off, thanks to Pete for this and all the other builds he offers. It's great that he shares these designs, and I doubt this will be the only one I take on.
> Second, thanks to all the people here. Having read through this thread, I have some ideas for my build, and I can tell this will be a good community to be a part of.
> ...



 Being kind of a newbie myself one thing I have learned if you’re going to do a custom case you don’t have to worry so much about the size of the caps .  You can always install the capacitors from the bottom side of the board where you have plenty of room .  Don’t worry the electrons won’t know they’re upside down Lol.


----------



## Alkolor (Feb 11, 2019)

ThermalAlchemy said:


> You can always install the capacitors from the bottom side of the board where you have plenty of room .



This is true, and I have considered mounting the adjacent film caps under the board to get the extra clearance, but I'd also prefer to keep the aesthetic of a fully populated board since I plan to keep it visible. I also don't want it to end up too tall, which under-mounting any of the electrolytics would do. My other concern is that the caps may be large enough to contact the solder points of the film caps, but I don't think Ø2mm would push it that far. Either way, I don't have a good way to measure it myself.


----------



## ThermalAlchemy

Alkolor said:


> This is true, and I have considered mounting the adjacent film caps under the board to get the extra clearance, but I'd also prefer to keep the aesthetic of a fully populated board since I plan to keep it visible. I also don't want it to end up too tall, which under-mounting any of the electrolytics would do. My other concern is that the caps may be large enough to contact the solder points of the film caps, but I don't think Ø2mm would push it that far. Either way, I don't have a good way to measure it myself.



 Another option you can slightly leave  A little more lead laying on your resistors and adjacent components .  Then you need to leave push them over at an angle and then cook them back up in a straight position so they look  correct .  This way you can push out one or 2 mm in each direction . It’s OK to use lead spacing on your capacitor that’s just  One or two or maybe even 3 mm wider or you just carefully bend stand in shape them underneath it to your hole spacing. If you would really like to use much wider caps can you find resistor through holes in the way you can stand up your resistors tombstone style send a lead down the side bend it in the 90 over the top of the board.  Then you can have the capacitor overlap and drop-down on top of the resistor hole.  Just be careful of your resistor lead placement underneath so they do not contact the lead of the capacitor


----------



## NuClear235 (Feb 11, 2019)

Alkolor said:


> Hello. New guy here. Going for this as my first amp build!
> 
> First off, thanks to Pete for this and all the other builds he offers. It's great that he shares these designs, and I doubt this will be the only one I take on.
> Second, thanks to all the people here. Having read through this thread, I have some ideas for my build, and I can tell this will be a good community to be a part of.
> ...



What about to use on PCB universal pinout for both sizes of pots, like is in PIMETA v2 ?
For small and big one (Blue Velvet) ...
https://tangentsoft.net/audio/pimeta2/bitmaps/brd-2.01.png

And for capacitors use "two holes" for possibillity to use more sizes?
It has Millet MiniMax and is it perfect...
http://www.diyforums.org/MAX/layout/MAXlay.jpg


----------



## Alkolor

I think I'm decided on the spacing for the large caps now. I'll be avoiding Ø18 as those have been deemed a negligible change, and I believe this thread has picture confirmation of Ø16 caps fitting in the normal spacing.

I'd still appreciate hearing anyone's thoughts on audio grade vs. high endurance type electrolytics in the coupling (C3, C6, C13, C14) vs decoupling (the rest) positions, if I've understood the circuit correctly, as well as output resistor choices (R8, R9) that people have tried. This is all very interesting, but still quite mysterious.



ThermalAlchemy said:


> Another option you can slightly leave  A little more lead laying on your resistors and adjacent components .  Then you need to leave push them over at an angle and then cook them back up in a straight position so they look  correct .



It's still a pretty tight space on the board since I'd be working in the lineup of the RCA outs and a couple of the film caps and large electrolytics. I'm sure I could figure something out if I really wanted to use those Ø18 caps, but after messaging Pete and getting his feedback, I think I'll be working with Ø16 or less since the 1000uF up-size would have negligible effect on my headphones. I think I'll avoid any lead acrobatics for now, but thank-you for your input.



NuClear235 said:


> What about to use on PCB universal pinout for both sizes of pots, like is in PIMETA v2 ?
> For small and big one (Blue Velvet) ...
> https://tangentsoft.net/audio/pimeta2/bitmaps/brd-2.01.png


https://tangentsoft.net/audio/pimeta2/bitmaps/brd-2.01.png

I think the default board has multiple pot spacing options, at least enough for the one I will be using.



NuClear235 said:


> And for capacitors use "two holes" for possibillity to use more sizes?
> It has Millet MiniMax and is it perfect...
> http://www.diyforums.org/MAX/layout/MAXlay.jpg



These are interesting, but I'm sticking with the default board for this build. I'll look at custom boards or designing my own if I get deeper into this stuff.


----------



## docentore

Alkolor said:


> I think the default board has multiple pot spacing options, at least enough for the one I will be using.


Not compatible with the Blue Alps RK27. I will be mounting mine on daughter board off the board. This will also help with mocrophonics when changing volume.


----------



## NuClear235

Here is pisture of better universal PCB design easy to use axial or radial capacitors. (under the orange ones)
https://cdn.head-fi.org/a/10239859_thumb.jpeg




Alkolor said:


> I think I'm decided on the spacing for the large caps now. I'll be avoiding Ø18 as those have been deemed a negligible change, and I believe this thread has picture confirmation of Ø16 caps fitting in the normal spacing.
> 
> I'd still appreciate hearing anyone's thoughts on audio grade vs. high endurance type electrolytics in the coupling (C3, C6, C13, C14) vs decoupling (the rest) positions, if I've understood the circuit correctly, as well as output resistor choices (R8, R9) that people have tried. This is all very interesting, but still quite mysterious.
> 
> ...


----------



## tomb (Feb 12, 2019)

Alkolor said:


> I think I'm decided on the spacing for the large caps now. I'll be avoiding Ø18 as those have been deemed a negligible change, and I believe this thread has picture confirmation of Ø16 caps fitting in the normal spacing.
> 
> I'd still appreciate hearing anyone's thoughts on audio grade vs. high endurance type electrolytics in the coupling (C3, C6, C13, C14) vs decoupling (the rest) positions, if I've understood the circuit correctly, as well as output resistor choices (R8, R9) that people have tried. This is all very interesting, but still quite mysterious.
> </snip>.



I can offer some opinions based on experience, but they're still only opinions.  C13 and C14 might benefit with a film cap, but you'd have to use something like a Wima film or similar, because very little else will fit.  As for using FG electrolytic caps all over, why not?  They're audio grade, but with the switcher power supply, they may do as much benefit in the power decoupling role as in the signal path.  It was probably simpler to just spec and buy all FG caps and be done with it.  The ones in the signal path are bypassed with Wima film caps, anyway.  Probably in this situation, upsizing the caps may have as much benefit as improving the quality.

I would not recommend the use of power caps in the signal path, if you can keep from it.  There are instances where that's done, but reasonably good audio-grade electrolytics (Nichicon ES, FG, KZ, or Elna RFS Silmic) are more available now than in the past, so there's not really any reason not to use them.  Power quality caps do not sound very good.  The bypass Wimas will temper this to a large degree, but they will still sound worse.  The audio-grade electrolytics are inexpensive enough anyway.

EDIT: If you are looking for more specifics, you will get more bass with Nichicon ES caps, but you need to bypass them with films.  They have tremendous bass, but are not very good with highs.  Nichicon KZ are excellent all-around, but are often detailed to the point of sounding etch-like.  Nichicon FG are good all-around, but sort of a compromise between the other two.

Elna Silmic RFS II are as good as the old Black Gate NZ caps, IMHO.  However, they are HUGE for their ratings.  You may have to compromise on rating or figure out some ingenious mounting methods.


----------



## Alkolor

tomb said:


> C13 and C14 might benefit with a film cap, but you'd have to use something like a Wima film or similar, because very little else will fit.



That's an interesting idea to consider, but quickly looking over the ones available in 10uf, I would have to get into more spacing acrobatics than I'd like to for this build. Do you know what using a smaller capacitance one would do? The 4.7uF ones look small enough to fit.




tomb said:


> As for using FG electrolytic caps all over, why not?  They're audio grade, but with the switcher power supply, they may do as much benefit in the power decoupling role as in the signal path.  It was probably simpler to just spec and buy all FG caps and be done with it. ... I would not recommend the use of power caps in the signal path, if you can keep from it.



I'm in the "why not?" category here as to making things complicated by diversifying the BOM and looking at different brands, as well as the mixed opinions on how much audio grade really matters. Cost isn't much of a factor for only a few caps. It's been a fun learning experience to question these things. I guess it would be better to phrase my question "is there any downside to using power caps in the positions that are not coupling the signal path?" I plan to keep C3, C6, C13, and C14 as audio grade (being the coupling caps in the signal path), but could save some space and get higher endurance with some power caps for the rest. Seeing your use of the UPW for C5 and C11 earlier in the thread sort of sparked this question. 



tomb said:


> Nichicon KZ are excellent all-around, but are often detailed to the point of sounding etch-like.  Nichicon FG are good all-around, but sort of a compromise between the other two.
> 
> Elna Silmic RFS II are as good as the old Black Gate NZ caps, IMHO.  However, they are HUGE for their ratings.  You may have to compromise on rating or figure out some ingenious mounting methods.



I have these 3 types lined up as my possible choices for the 4 signal path caps, or all of them if I decide not to go with the power caps elsewhere. Elna's are currently the front runner in the "why not?" upgrade due to their recommendations in many posts. The 470uF ones should fit as they are Ø16, which I see fitting in earlier pictures in this thread, but the 1000uF ones are out (only FG comes in Ø16 and they're out of stock right now - I'd prefer to keep the 35V rating). For the 10uF caps, I'm unsure if I could squeeze in Ø8 for the 50V ones to match stock ratings, but the 35V ones match the stock FG size and are noted as "upgrade" on Pete's BOM.

For the power caps, if I go that route, I am looking at UPW's. I like the higher stats on the Panasonic FR's, but for some reason the 10uF ones are listed as $56 on Mouser right now and are out of stock. I could get the B version and deal with wide lead spacing though.

Thanks for your response.


----------



## tomb (Feb 12, 2019)

Alkolor said:


> That's an interesting idea to consider, but quickly looking over the ones available in 10uf, I would have to get into more spacing acrobatics than I'd like to for this build. Do you know what using a smaller capacitance one would do? The 4.7uF ones look small enough to fit.


Go down in smaller capacitance, and you'll lose bass response.  That said, Pete probably has a safety factor built in, so 4.7uf ones might work.  However, Wima makes MKS film caps with lead spacing of only 5mm.  It will take a bit of acrobatic lead bending (if you don't want to just squish them in there), but they'll probably fit easily enough.  Almost ANY film cap is going to be better than an electrolytic in the signal path.  C13 and C14 AC-couple the FETs to the NuTube, so there might be quite an improvement.




> I'm in the "why not?" category here as to making things complicated by diversifying the BOM and looking at different brands, as well as the mixed opinions on how much audio grade really matters. Cost isn't much of a factor for only a few caps. It's been a fun learning experience to question these things. I guess it would be better to phrase my question "is there any downside to using power caps in the positions that are not coupling the signal path?" I plan to keep C3, C6, C13, and C14 as audio grade (being the coupling caps in the signal path), but could save some space and get higher endurance with some power caps for the rest. Seeing your use of the UPW for C5 and C11 earlier in the thread sort of sparked this question.


No, there's no downside with using good quality power caps in power positions.  I would argue, though, that Panasonic FM and Nichicon UHE are better than both of the ones you mentioned.

Here's the thing: without trying to be critical, the NuTube Millett Hybrid uses a switching AC adapter.  It's a good quality adapter, to be sure, with only about 150mV of ripple.  However, you can hear improvements in ripple down into the single digits of mV in some headphone amps.  A high quality linear-regulated adapter (Jameco has some nice, inexpensive ones) might be down around 50mV of ripple, or at least three times quieter than the supply Pete spec'd for the NuTube.  Maybe the lower one makes a noticeable difference in sound quality, I don't know.  We'd have to ask Pete to find out.  Switching adapters very easily adjust themselves to a wide range of line power (120 or 240 without a conversion plug).  Linear-regulated adapters can't do that.  So, the switching power supply ensures that the NuTube MH can be built all over the world without hassle and great results.  It's just an educated guess on my part why the switching power supply was selected.  Again, we'd have to ask Pete to know for sure.

However, if you can hear the effects of the ripple (not the ripple itself, necessarily), then that means the power supply is partially heard through the amplifier circuit.  In that case, it might be more beneficial to use audio-quality electrolytics for the power supply, too.  IOW, the fact that they may sound "good" may be more important than the fact that they have more ESR and less ripple current rating than a good power cap.



> I have these 3 types lined up as my possible choices for the 4 signal path caps, or all of them if I decide not to go with the power caps elsewhere. Elna's are currently the front runner in the "why not?" upgrade due to their recommendations in many posts. The 470uF ones should fit as they are Ø16, which I see fitting in earlier pictures in this thread, but the 1000uF ones are out (only FG comes in Ø16 and they're out of stock right now - I'd prefer to keep the 35V rating). For the 10uF caps, I'm unsure if I could squeeze in Ø8 for the 50V ones to match stock ratings, but the 35V ones match the stock FG size and are noted as "upgrade" on Pete's BOM.


A further note from the above answer on film caps - many film caps' leads are quite easily adjusted to different spaced pads on the PCB; electrolytics, not so much.



> For the power caps, if I go that route, I am looking at UPW's. I like the higher stats on the Panasonic FR's, but for some reason the 10uF ones are listed as $56 on Mouser right now and are out of stock. I could get the B version and deal with wide lead spacing though.


That $56 is probably a Mouser error.  I've seen that happen before on other parts.  You might just call them if you really want that cap.  While not quite as good, the Panasonic FC is perfectly fine.

You might just have to read up on the spec sheet, though - or compare with DigiKey to make certain, because this one: EEU-FR1H100B is only 33 cents.  The only problem is that Mouser says the lead spacing is 5mm, but the diameter is 5mm, too - that's impossible.  So there may be a good chance that the lead spacing is actually 2mm on that cap.  It's worth investigating by studying the datasheet on the Mouser page for that cap.

If you want a great power cap, look at both the ESR and ripple current rating.  I think actually that ESR (less is better) is more important in digital circuits (DACs), whereas the ripple current (more is better) is better for power applications.



> Thanks for your response.



One thing is probably certain above all else - this is way too much analysis/thinking for the NuTube.  It's inexpensive enough to buy some of all of these parts and then try them out on your own to see what differences you may notice, if any.


----------



## pmillett

What Tomb says 

You might be able to fit in the 10uF Wima MKS part.   I used it on the class D hybrid.  For a 10uF film cap it's pretty small.

One goal with this design was to make it as affordable as possible.  That's why I used the electrolytic coupling caps there and also the switching adapter.  Not to mention the international issues.  That's also why I used the same caps in various positions - to simplify the BOM.  That said, I don't think there is a huge difference in this circuit between audio grade caps and good low ESR caps...

It can't hurt to use a linear adapter, assuming it has reasonable filtering and/or is regulated so that it doesn't have a lot of 120Hz output ripple.  120Hz ripple will probably cause more audible artifacts than the switching regulator ripple.  C1 and C5 are the most important to help reduce the ripple, so using a switching adapter, low ESR is important for these two.  For some reason I tend to use Nichicon electrolytics... UPW are OK, but Tomb is right, UHE is better.  UPW's have been around for many years - UHE are newer and in general have lower ESR.

Pete


----------



## Alkolor (Feb 13, 2019)

tomb said:


> One thing is probably certain above all else - this is way too much analysis/thinking for the NuTube.  It's inexpensive enough to buy some of all of these parts and then try them out on your own to see what differences you may notice, if any.



I won't deny that, but half of my fun is the research and discussion around component selection. As a designer (in another field), I get the value of simplicity in design and the BOM, but also like to see what I can customize in a 1-off build. When you know simplicity is a design factor, you wonder what you can do if you throw it out. I also don't often get the chance to trial with different components for only a few bucks, so I'll heed your advice and give that a go. I have some time before Pete can ship the NuTube and board, so right now, I'm cruising the forums and datasheets.

I'll definitely look at getting film caps for C13 and C14. My spacing concerns for any of the caps aren't due to the leads but the body footprint. Bending the leads in won't be a problem, but fitting an 11x7.5 film cap next to the tube, resistors, and other caps will take some doing. Plus, for under $1, I can have a pair of electrolytics in case I can't manage the film cap. It seems like a good candidate for under board mounting since the film cap won't be like sticking a 25mm+ electrolytic on the bottom, and they'd be much easier to lie on their side (or just under-mount those 4 resistors for space up top). I could do the same with C4 or C7 to make room for the larger 1000uF caps too. So many options. I'll also be looking into the linear power adapter.

As for all the types, I made a spreadsheet of the specs (part of my enjoyment). Across mentions from various forums, I've compared UFG. UKZ, and RFS for audio caps, and UPW, UHE, FR, FM, and FC for power caps. That probably stirred the fire of "why audio caps?" since they don't list all the specs and rate lower in most areas compared to power caps. So they will fall into my "why not" category wherever I decide to use them. The UHE vs UPW was unclear in this one since UPW has higher ripple and lower ESR for the 10uF's, but the reverse is the case in the 470uF's, but UHE's have a higher life rating both ways. The frequent mentions of UPW caps and the datasheet noting them for switching power supplies made them seem like a good reference point, but UHE being a newer series makes sense. The Panasonic caps have a similar flip-flop in ratings between FR and FM, and FR may similarly be the newer series, but they also beat the Nichicons across the board for specs.

I looked at the EEU-FR1H100B and it is tapped style. I bet the leads are just bent out to make that spacing, which isn't an issue. Thanks for pointing that one out. Oddly, the FM series doesn't have any 10uF options.

Thanks for entertaining my rambles


----------



## tomb (Feb 13, 2019)

Alkolor said:


> I won't deny that, but half of my fun is the research and discussion around component selection. As a designer (in another field), I get the value of simplicity in design and the BOM, but also like to see what I can customize in a 1-off build. When you know simplicity is a design factor, you wonder what you can do if you throw it out. I also don't often get the chance to trial with different components for only a few bucks, so I'll heed your advice and give that a go. I have some time before Pete can ship the NuTube and board, so right now, I'm cruising the forums and datasheets.
> 
> I'll definitely look at getting film caps for C13 and C14. My spacing concerns for any of the caps aren't due to the leads but the body footprint. Bending the leads in won't be a problem, but fitting an 11x7.5 film cap next to the tube, resistors, and other caps will take some doing. Plus, for under $1, I can have a pair of electrolytics in case I can't manage the film cap. It seems like a good candidate for under board mounting since the film cap won't be like sticking a 25mm+ electrolytic on the bottom, and they'd be much easier to lie on their side (or just under-mount those 4 resistors for space up top). I could do the same with C4 or C7 to make room for the larger 1000uF caps too. So many options. I'll also be looking into the linear power adapter.


Lying on their side underneath the PCB is perfectly fine.  You would be surprised at how many film caps are shoe-horned in to odd places in an electronic project.



> As for all the types, I made a spreadsheet of the specs (part of my enjoyment). Across mentions from various forums, I've compared UFG. UKZ, and RFS for audio caps, and UPW, UHE, FR, FM, and FC for power caps. That probably stirred the fire of "why audio caps?" since they don't list all the specs and rate lower in most areas compared to power caps. So they will fall into my "why not" category wherever I decide to use them. The UHE vs UPW was unclear in this one since UPW has higher ripple and lower ESR for the 10uF's, but the reverse is the case in the 470uF's, but UHE's have a higher life rating both ways. The frequent mentions of UPW caps and the datasheet noting them for switching power supplies made them seem like a good reference point, but UHE being a newer series makes sense. The Panasonic caps have a similar flip-flop in ratings between FR and FM, and FR may similarly be the newer series, but they also beat the Nichicons across the board for specs.
> 
> I looked at the EEU-FR1H100B and it is tapped style. I bet the leads are just bent out to make that spacing, which isn't an issue. Thanks for pointing that one out. Oddly, the FM series doesn't have any 10uF options.



Having been at this now for a number of years, I can give you some insight on cap history - at least from a headphone DIY perspective.  Traditionally, Nichicon had UPW and Panasonic had FC.  Those were the quality power caps that everyone used and recommended.  They are still just fine for almost any electrolytic application but in the audio signal path.  Both FC and UPW were considered high-performance and still probably have the widest ranges of sizes and ratings of "quality" electrolytic caps.  The difference was that Nichicon UPW were available at Mouser, but not Panasonic.  DigiKey carried the Panasonic, but not Nichicon (at least I think they didn't have them in the early days).  Along the way (early 2000's, I think), Panasonic hit the market with the FM caps and everyone swooned.  That lasted for quite a while.  I think Nichicon came out with UHEs sometime later, but they never gained the reputation of the Panasonic FMs (for some unknown reason).  The Panasonic FRs are a recent addition.  There are many, many other series of caps made by both Nichicon and Panasonic with better ratings than the UPW/FC, UHE/FM, but not with as large an offering.  Anyway, that's the background: from the perspective of dealing with both Mouser and DigiKey through the years.  It may be that Nichicon and Panasonic always had these caps, or had them years before, but the key to us DIY-ers was when Mouser and DigiKey started offering them.

As a for instance, neither one had the audio-grade Nichicons or Elnas in the early days (1990s to mid 2000s).  One had to order them from Handmade Electronics, PartsConnexion, etc.



> Thanks for entertaining my rambles


----------



## docentore

I'm still testing other op-amp options. How to confirm that amp is oscilatting or not? By looking for the sound artifacts? By checking the heat coming from IC?


----------



## ShizzyGuo

Does this amp power low impedance planar headphones well? Or should that be avoided because of damping factor issues


----------



## pukkita

Have a pair of HE-560v3 on the way, will post back...


----------



## CatalinM

I'm using it with a pair of Hifiman Ananda and I haven't noticed any issues.


----------



## orderingrabbits

I'm having an odd sort of issue. I bought a stepped attenuator and wired them to the volume pot pads, and it works great. However, the first couple steps of volume and the last step are really noisy, and when the attenuator is set to these positions I can pick up radio (like, it's clear enough I can actually recognize the songs and what people are saying) by touching the RCA ground with one hand and moving around my other hand. Any idea what might be going on? Other people say that noise increases at the extremes of the normal volume pot, is this just the same issue? I get enough volume throughout the clean section so it's not a huge problem but I'm just checking to make sure this isn't a symptom of a larger problem.


----------



## Alkolor

Just ordered the rest of my components. Now to play the waiting game..

After much deliberation, I decided on all the cap changes I wanted to try. Since they were so cheap, I also picked up a full set worth of Elna's and Pan FR's for the 10uF caps in case I feel like changing things up. List of my changes and initial build plan below.

10uF WIMA caps at C13 and C14 for an improvement on the input signal, and a backup one I may try at C1 for ripple smoothing
22uF Pan FR's at C2 and C10 for added muting time and regulator output overhead

10uF Elna's for the remaining spots
470uF Pan FR's at C5 and C11 for low ESR in these power spots
1000uF Elna's at C3 and C6 for possible bass improvement with lower impedance headphones
80mV ripple AC adapter (nearly half)

TKD pot and a fancy knob
There will be some lead wiring acrobatics and under board mounting to fit the larger components, but the challenge will be fun. Hopefully these don't turn out to be a bad idea.

Thanks tomb and Pete for the feedback, and this thread for all the info.

Can't wait to build!


----------



## docentore

Another day another mod. I have replaced the C13 and C14 with film 10uF (WIMA MKS2) caps and C20+C21 with MKS2 2.2uF.
Testing this with 2 AD825's I have received today - liking so far. Still waiting for OPA627 to come for tests (bought some on ebay but I theink they are too cheap to be genuine, not going to bother).


----------



## ShizzyGuo

Can I leave it on 24/7? Any downsides besides life expectancy of tubes which I heard were rated pretty high


----------



## pmillett

ShizzyGuo said:


> Can I leave it on 24/7? Any downsides besides life expectancy of tubes which I heard were rated pretty high



Sure.  Korg quotes the lifetime at 30,000 hours.  That's 3.42 years if you leave it on all the time.

As far as I can tell, this is based on the lifetime of a vacuum fluorescent display as quoted by Noritake.  The Nutube may actually last significantly longer, since the plate current used is lower (because the brightness of the phosphor doesn't matter much).  The failure will be a very gradual degradation of characteristics, not a sudden failure...

I am not aware of any failures yet...

Pete


----------



## gaz2613

If anyone knows anyone who is looking to move their NuHybrid Headphone amp on please let me know as I would like another one. I am based in the UK. Love this little amp! Got some Burson V5i's on the way for my current one to try out.


----------



## gaz2613

I have been listening to mine and notice a distortion in high notes such as instruments and even on high vocals that sound almost like a crackle when I turn the volume up. When listening at quite a low volume it's crystal clear. Would it be worth adjusting the bias voltage higher than 11v?

It was doing this with the original OPA551 opamps as well as the Burson V5i ones.

Please help


----------



## pmillett

gaz2613 said:


> I have been listening to mine and notice a distortion in high notes such as instruments and even on high vocals that sound almost like a crackle when I turn the volume up. When listening at quite a low volume it's crystal clear. Would it be worth adjusting the bias voltage higher than 11v?
> 
> It was doing this with the original OPA551 opamps as well as the Burson V5i ones.
> 
> Please help



One way to find out - try it!  Try moving the bias up, and also down, maybe 2V at a time, and see what happens.  You can't hurt anything...

Pete


----------



## Varoudis (Mar 16, 2019)

Hi all,
I need help with troubleshooting! I think I have burned my head and I can see..probably a silly mistake!
I have attached photos and measurements. Back photo is misty as I sprayed the flux to see the joints better.
- With Pete's advice I have re-flow all pins (nothing changed).
- Voltage on TPs is very unstable, goes up/down 1V...
- RCA-Out have AC+DC voltage .. if you plug phones you get super cool noise...amplified... (see measurements)
- I have double check the resistor values with an online calculator.. they seem ok. Can you spot something?? Pete's photo online has 10k R3/4 .. BOM has 1k (I have 1k).
- I get DC.. all over the place.. even with the DC coupled Outs.
- GND on PS side has 50mV difference from TP-GND (the board side)???

Something is leaking like hell?? IC dead? Diode?
How should I approach it? I have test equipment (scope, power supply, good DMM etc) and its not my first project, I have build a number of HAM projects, transmitters etc...

Any ideas?

EDIT: most voltages are referenced to TP3. I have some PS-GND referenced measurements.


----------



## gaz2613

I have noticed the bias on mine seems to fluctuate. When I first set mine it was around 5 mins for the bias to settle before I set it to 11v. A few weeks later when I checked them it was at 10.35v and settle at around 10.65v after 5 mins so I reset back to 11v. I have distortion on mine too on high notes and vocals when volume is turned up so not sure if mine has an issue or whether the bias needs adjusting as I have not gotten round to testing further yet.


----------



## Varoudis

Settling like this sound okish. Mine is just amplifying noise and cracks like full volume... lol
There is something wrong with leak on the ground side or something..


----------



## docentore

gaz2613 said:


> I have noticed the bias on mine seems to fluctuate. When I first set mine it was around 5 mins for the bias to settle before I set it to 11v. A few weeks later when I checked them it was at 10.35v and settle at around 10.65v after 5 mins so I reset back to 11v. I have distortion on mine too on high notes and vocals when volume is turned up so not sure if mine has an issue or whether the bias needs adjusting as I have not gotten round to testing further yet.


I'd agree with Varoudis on this. There has to be leak somewhere. Wash the board with some good PCB cleaner.
Mine does not fluctuate at all, I've set is @11V and it stays like that.


----------



## gaz2613

Mine starts off a little under 11v and then gradually comes up to the 11v I set it to. My distortion problem turned out to be my Beyerdynamic DT990 Pro headphones. I tried some Denon D2000's and the distortion was gone so the Beyerdynamic ones will be going back to Amazon.


----------



## Varoudis

False alarm guys!
My build was soooooo "broken" that I tested everything with any sort of test equipment that usually you don't need for a simple build like this... that I couldn't see in front of me...
I had forgot a super static pudding all the time when I was testing the amp.


The amp is very nice! Voltage is super stable to 1mV... (I ended up tuning to 10.000V!!) Very clean sound and minimal hiss with even unity gain (I haven't test it with my sensitive Klipsch speakers though).
Ill use it as a tube unity gain preamp (tube distortion in essence  )

One observation that I didn't expect is that the amp reverses the waveform. I though that the tube stage with flip it once and then the OpAmp with flip it again :S


----------



## docentore

Varoudis said:


> False alarm guys!
> My build was soooooo "broken" that I tested everything with any sort of test equipment that usually you don't need for a simple build like this... that I couldn't see in front of me...
> I had forgot a super static pudding all the time when I was testing the amp.
> 
> ...


What was wrong?


----------



## Varoudis

Sorry I didnt say it clearly.
I usually have a desk mat for my electronics work (in my home office/ mancave).
As I didn’t, I kept one of Mouser’s black pudding.... uber school boy error.... this pud is there you let any discharge go through easily... so uder currents flew all over my board every time I was testing...

Heheheh memes about my stupidity welcome!!

Now on a positive note. What opamps have you used with this amp?
Any measurements for the highend or lowend extention?

Cheers


----------



## docentore

Varoudis said:


> Now on a positive note. What opamps have you used with this amp?
> Any measurements for the highend or lowend extention?
> 
> Cheers



I have tested good few: OPA627, OPA604, AD825, AD8065, NE5534, OPA134, AD797, ADA4610. Can't hear much difference tbh and I have no hw (and knowledge) do perform any measurments. Went back to OPA551 as it gives more current than other ones and I'm running the amp with T50RP-Argons.


----------



## Varoudis

Are all this plug and play compatible?
I might try one or two for the highend a bit.

My work has to do with psychoacoustic and illusions so... I dont know if Im really listening to some highend harsh but will see.

I dont think I care about current and gain as I only need unit gain 1x.

Thanks for the info!


----------



## docentore (Mar 19, 2019)

Varoudis said:


> Are all this plug and play compatible?
> I might try one or two for the highend a bit.
> 
> My work has to do with psychoacoustic and illusions so... I dont know if Im really listening to some highend harsh but will see.
> ...


Some of them come in DIP package, they are drop in compatible, some in SOIC package and need adapter.
Check these out, to me they did sound a bit different, on a plus ofcourse:
NE5534 (DIP), OPA134 (DIP), AD797(DIP or SOIC), ADA4610 (SOIC).

On another note: I've asked my nephew to design and print case for me. I've linked him to SasaKudo case for inspiration and Pete's website for dimensions. (don't mind the knob, new one is being printed)






But, there is a but. The pcb dimensions on Pete's site are wrong. @pmillett FYI


----------



## Pricklyears101

Hi all,

This is my first attempt at diy headphone amp. My previous experience at diy is assembling a tube amp from elekit(tu-8100) which worked flawlessly despite me having no soldering uexperience. Im thinking of making it semi-portable with a li-ion 3000mah rechargable battery for power supply instead of the wall wart and micro-usb input. I'm thinking of using this..
	

	
	
		
		

		
		
	


	




https://www.ebay.com/itm/USB-3-7V-L...Step-Up-5V-9V-12V-24V-Converter-/192209125071


The problem is, the output is adjustable to 24v but less than 1.04a. Any other way i can work around this?


----------



## Alkolor

Hello Prickly,

I think you’ll have to look for another converter unit that is capable of handling more power. The references on that one indicate about 7W (volts x amps), and the Nuhybrid uses a 25W power supply. I doubt it uses all 25W, but the difference leaves a lot of range. I measured 16-17W from the wall to my Nuhybrid, but I wouldn’t depend on the tool I used for the best accuracy. Maybe you can rig up a spot between the supply and the Nuhybrid to check the current with a multimeter and get a better answer. Then select a unit that can provide 24V at that current plus some more for overhead. You’ll also need to select a battery, or use a multiple configuration, that is capable of delivering your power needs with capacity that can last as long as you want.

I would also question how steady the output is on a small unit like that. I tried to use a similar unit to power a PC fan once, and it seemed to make it stutter and not spin up, which was odd since it had worked in the video I referenced. Maybe all it needed was a smoothing circuit.

I’m sure there’s something out there that will work. I’ve seen people use similar concepts to power much bigger things.

Regards,


----------



## docentore

Pricklyears101 said:


> Hi all,
> 
> This is my first attempt at diy headphone amp. My previous experience at diy is assembling a tube amp from elekit(tu-8100) which worked flawlessly despite me having no soldering uexperience. Im thinking of making it semi-portable with a li-ion 3000mah rechargable battery for power supply instead of the wall wart and micro-usb input. I'm thinking of using this..
> 
> ...


I know you have mentioned semi-portable but you need to know that this amp is very prone to microphonics, smallest move or shake produces high pitch hoise.


----------



## Pricklyears101

Hey guys thank you so much for taking the time to reply.

@Alkolor yeah i saw some youtube videos of that as well, maybe it was made with the same guy idk. He was playing around with different input/output voltages and currents, seeing which one failed or passed his test. Yeah i guess it was unrealistic of me to try and come up with ways to somehow power the amp from a typical 5v1a usb outlet but coming from someone with no electrical background it was a good learning experience. Especially when i could just buy the Nutekt HA-KIT for 3 times the price and assemble everything without hassle. 

@docentore 
Semi-portable in my case means not having to constantly rely on a wall wart and being self powered. I'm definitely not going to throw this into a bag for portable use. Yes i understand from previous posts how microphonic it can be and im looking at the ways recommended by korg for isolation, which i think has been discussed in a previous post as well.

Anyway if someone managed to design a battery power supply using conmonly found 3.7v li-ion around the specifications of this amp, I'd be happy to learn from you. Cheers all! Happy DIYing!


----------



## pmillett

Pricklyears101 said:


> Hi all,
> 
> This is my first attempt at diy headphone amp. My previous experience at diy is assembling a tube amp from elekit(tu-8100) which worked flawlessly despite me having no soldering uexperience. Im thinking of making it semi-portable with a li-ion 3000mah rechargable battery for power supply instead of the wall wart and micro-usb input. I'm thinking of using this..
> 
> ...



The actual current draw of the amp is about 80mA.  So that would provide plenty of current for this amp.

Pete


----------



## pmillett

docentore said:


> But, there is a but. The pcb dimensions on Pete's site are wrong. @pmillett FYI



Sorry about that, just updated it.

(I assume the only dimension that was wrong was the height (should be 3.125)?

Pete


----------



## docentore

pmillett said:


> Sorry about that, just updated it.
> 
> (I assume the only dimension that was wrong was the height (should be 3.125)?
> 
> Pete



That's right . not to worry, this build gave me most fun in years, DIY and sq wise


----------



## ThermalAlchemy

Pricklyears101 said:


> Hi all,
> 
> This is my first attempt at diy headphone amp. My previous experience at diy is assembling a tube amp from elekit(tu-8100) which worked flawlessly despite me having no soldering uexperience. Im thinking of making it semi-portable with a li-ion 3000mah rechargable battery for power supply instead of the wall wart and micro-usb input. I'm thinking of using this..
> 
> ...



       The only thing to worry about some battery chargers do not give any regards to a clean signal because their only chore was to charge a battery not having to worry about sensitive electronics in audio


----------



## Alkolor

@Pricklyears101 



pmillett said:


> The actual current draw of the amp is about 80mA.  So that would provide plenty of current for this amp.
> 
> Pete



I definitely had the wrong tool for that measurement. Sorry about that, but It's what I had at the moment. Seems like that charger unit is worth a shot for a few bucks, and a smoothing circuit could help ensure a clean signal. I'm interested to hear what you come up with.


----------



## Pricklyears101 (Mar 25, 2019)

Wow thanks for your reply @pmillett So if it's 80mA current draw then theoretically it'll work! For the dc step up/li-ion charger at 24V output is around 0.3A which is more than enough. I will definitely run some tests on a dummy load to ensure it really works before assembling everything. If my calculations are correct, run time with a 3Ah li-ion battery is under 6h, which is meh but I think still reasonable considering other portable tube amps out there. Battery(3.7v x 3Ah = 11.1Wh) / Amp(24V x 0.08A = 1.92W) = 5.78h?
I'm guessing even if I lay the big caps on the underside horizontally to make it easier to fit into an enclosure, theoretically I would still have space for the power supply board and battery. Of course I need everything to arrive so I can test it out irl but yeah I'm excited just thinking about it.


I've read previous post somewhere that there's isn't alot of volume play if you're using iems since there is no gain switch in the circuit. So instead of altering the circuit, I'm thinking of just using an attenuation cable like the IFI audio iematch. If anyone else has any experience with using iems with the amp, do let me know how it goes. The specs of my iem are as follows:

Sony MDR-EX600
32 ohms @ 1kHz
107 db/mW

Neither sensitive nor hard to drive. Reason this amp got me interested is because I'm fairly sensitive to sibilance. The iems have a 6kHz spike and 10 band EQs can only alter 8kHz & 4kHz, tried playing around with those and it helps abit but there's still abit of sibilance left and making major alterations makes around that freq range reduces top end, making everything dull and taking away the magic. And even order harmonics 'subjectively' helps with sibilance. And to my surprise it sounds somewhat similar to a HD600(yes VERY debatable, but it's only my humble opinion). So if the rumors are true that tubing a HD600 sounds heavenly, then I guess the same can be made here. I hope I don't get flak for using iems on such an amp. It was my first move into hifi stuff beyond free earbuds when i just graduated from a starving student to a working adult and it holds sentimental value, and a seductive midrange besides the sibilance.

If there is still space under the pcb, maybe I'll add a dac board as well, but that is for the future. I saw some good ones at diyinhk site. They even have NOS R2R dacs! What a combo that would be, potential end game. I'll post updates here once the shipments arrive, hope everything goes smoothly.



Once again, thanks guys for your useful inputs, and many thanks to @pmillett. Happy DIYing!


----------



## docentore (Mar 26, 2019)

Just last question @pmillett - have you ever had chance to measure power output @ Standard 32Ohm (or any other load)?


----------



## pmillett

docentore said:


> Just last question @pmillett - have you ever had chance to measure power output @ Standard 32Ohm (or any other load)?


About 6.5V RMS into 30 or 150 ohms, or 1.3 watts into 30 ohms.

Pete


----------



## docentore

pmillett said:


> About 6.5V RMS into 30 or 150 ohms, or 1.3 watts into 30 ohms.
> 
> Pete


So it should be little bit over 1W with my 50ohm T50RPs.
Cool


----------



## Varoudis

pmillett said:


> ....



Hi pete,

I have added the little jem between the picoreplayer and my denon amp and sounds excellent.
I remember that at some point I read a small description from you regarding the bias voltage (maybe on diyaudio, cant remember).

Can you describe the differences if you go lower or higher?
I remember reading that lower makes the highs more “sweet” or something (very scientific terminology... hehe sorry)
What would be the usable range?

Thanks 

Ps: snake-oil observations/untrained ears: with the studio monitors (yamaha) the highs felt hard but with my floor standing Klipsch they sound like a charm. Might be the space too or the yamahas are known for the dry sound (thats why we like them for the job)


----------



## Alkolor (Mar 28, 2019)

I finally finished my Nuhybrid build!

The amp has been in service for just over a month, and it's been great step up in my listening experience. Having proper power behind my headphones makes the music sound full, and it's been nice to have something to boost my phone so I can properly listen in places other than at my computer. I now understand what the comments meant by the Nutube being microphonic. It makes a high pitch ringing sound in response to some contact and sharp movement. I mostly notice it when the relay activates or when I brush the volume dial. However, I don't pick it up when I move the amp around or if I bang on my desk. It's significantly damped when using my high impedance headphones, and I can't really notice it while music is playing.

It was a good beginners build. Very straight forward, especially with Pete's instructions. It took a bit of extra planning the assembly order to account for some of my selected over-sized components, but it all came together with a bit of patience. I can confirm that the 10uF WIMA capacitors fit in the stock Serpac base with a couple small washers as spacers. The difficult part with those was their very short leads that barely had the length to go through the board after bending to fit the spacing. Other than the visible differences in capacitor selection, I increased C2 to 22uF to lengthen the muting circuit timing as some had mentioned a decaying noise. It makes the timing ~12sec, which I find to be a reasonable waiting period. I can't say if I would have noticed the difference had I not mixed up the BOM, but it feels good to have made it my own in a small way.

I made the base from 1/2in oak for the perimeter, craft ply for the bottom, and square dowel for the standoffs, all held together with glue and finished with a dye stain and poly. I recessed some EAR feet so that it only sits a couple mm off the table. The top uses machine screws, washers, and spacers to hold up a piece of acrylic. It doesn't offer much for isolation, but it shows off the Nutube and other components while providing good protection. I felt like this was one I wanted to be able to look at all the time.

While building, I had the thought that you could mount the Nutube to the bottom of the board to make it the tallest thing on that side and mount the whole thing upside down in order to display it through an opening in a custom enclosure. I'm not sure if that would harm anything, but it doesn't seem like it would to me unless the regulator heat collecting upward is too much. The power switch going the other way would bug me until I got used to it, but it seemed like a way to be able to present just the Nutube through an enclosure without mounting it off-board and messing with jumper wires you need to keep short.

I've stated working on building Pete's Butte amplifier, with a couple add-ons planned. This one has impressed me, and I will be be building more of his designs to keep the fun going. Thanks Pete for these designs and thanks to all in the thread for your contributions to my experience.

Happy listening!


----------



## jobous (Mar 30, 2019)

Hi !!! Finally i got into the game !!! I was waiting from last summer due some problems i had. Two days ago i managed to order from Pete the pcb and the tube !!!!!
Now i'm close to order the remains from mouse. I will  go to a panel mount solution (pot, power connection , rca inputs etc) using  Hammond 1455N1601BK enclosure.
The only thing that i'm still behind is the choise for the 4 Electrolytic Capacitors for C3,C5,C6 and C11. There isnt nay UFG1V471MHM in stock right know till the end of the next month.
So i have to decide between NICHICON UFG1H471MHM 50V (16x25) and ELNA RFS-50V471MJ8#5 (SILMIC II) (16x35.5). Both are in stock.
So 2 questions :
First , there will be any problem using one of the last two Capacitors cause diameter is 16mm and the one Pete has in BOM is 12 mm. Does it fit ??? Till now in forum , i have seen 3 or more guys who have made that choise. What about NICHICON KZ series (same dimensions as ELNA)??
Second , there is a big  price difference between NICHICON (1,28 €/pc) and ELNA (2,95 €/pc).
Worth the choise of ELNA ?? (two for one !!!)

Thanks in advance


----------



## Alkolor

I think Ø16 capacitors will fit. I also noted caps of that size fitting in other build pictures in this thread, and Ø16 just fit when I was drawing scaled circles over the board layout to answer the same question. The ones I used were Ø18 (previous post pics) and I had to mount the C4 and C7 film caps on the bottom.

From all that I read for this project, it's debatable if there's much difference between the electrolytic capacitors when it comes to performance. I went with ELNA's because it was only a few bucks more and many people in various threads swore by them. A very "why not" decision. However, I only used them in C3 and C6 since they're directly in the audio path. I used Panasonic FR's for the other two for high life and low ESR. I think the ELNA RFS35V471MJ7#5 would be a closer match to stock at the same 35V and cut the price down a bit. The KZ are above FG on Nichicon's own chart and would make a good substitute as well. I think you'd be looking at the UKZ1H471MHM. I noted one post in my searches that said the ELNAs sounded more tube like where the KZs sound flatter. I can't say if that's true and took it with a grain of salt, but it was the only sound description I came across.


----------



## docentore

New version of case with correct dimensions - thanks @pmillett


----------



## MrKazador

Occasionally my amp will pick up a weird ticking noise with no input. It doesn't change with volume and if I hover my hand over the tube, it goes away... I haven't been able to figure out what is causing it.


----------



## pmillett

MrKazador said:


> Occasionally my amp will pick up a weird ticking noise with no input. It doesn't change with volume and if I hover my hand over the tube, it goes away... I haven't been able to figure out what is causing it.


Sounds like WiFi.  It can cause a ticking noise, especially if it's near a router.

Pete


----------



## MrKazador

My router is 3ft away but it wasn't an issue before unless I didn't notice it, the ticking is hard to hear. I did move to a new house but all my equipment is the same.


----------



## TravAndAlex

I've got one of these cheapo Chinese 24v power supplies kicking around.  Any concerns with it working with this?  Noise or something else I haven't considered?


----------



## pmillett

TravAndAlex said:


> I've got one of these cheapo Chinese 24v power supplies kicking around.  Any concerns with it working with this?  Noise or something else I haven't considered?


It should be OK.

Pete


----------



## TravAndAlex (Apr 19, 2019)

pmillett said:


> It should be OK.
> 
> Pete


Thanks Pete!

Board arrived a few days ago.  Assembled that afternoon!  Power supply works well.

Designed a hardwood case that will hold both boards. Aluminum stock will be used for front and back panels.

Now my question is, does a classy nutube badge exist for purchase?  Or perhaps a Pete Millett designs emblem or anything like that?

Since the power supply will be sitting to the right (viewed from front) of the amp board, there will be 3 inches of blank aluminum on the front.

Progress to date shot might give a better idea of what I mean (just imagine the aluminum front panel).

What do I do with that space?


----------



## TravAndAlex

Ok.  Screwed up the pics.  On my phone damnit.  

Note this is just a test fit.


----------



## jobous (Apr 21, 2019)

Hi !!! Slowly but steady (once in a week !!!) till now , i've managed to complete the board except the Nutube and the others that they will not solder in pcb. My Hammond case will arrive in the first week of May , cause it is out of stock at Mouser.
I would like to ask if anyone has use Metal Pushbutton - Latching (illuminated) instead of toggle switch and what type of  Metal Pushbutton??
I think that will be a visual upgrade , specially in the front... In that case i will solder the PCB tips for LED directly to Pushbutton tips for illumination. LED voltage must be 24 V ??


----------



## TravAndAlex

Just about finished it up this Easter morning. I like the internal power supply and the overall shape of the box.


----------



## TravAndAlex

Just because I finally got a decent picture of the tube glow.


----------



## jobous

Beautiful !!! Nice work.


----------



## TravAndAlex

jobous said:


> Beautiful !!! Nice work.


Thanks!  I fricking love DIY. 

Just because I took a badass picture.


----------



## jobous

I'm trying to understand which pushbutton to choose. I mean which voltage, take into acount that there is already the R5 (10K).
The pushbutton is from Onpow (16mm_LAS2GQ series). Anyhelp here ??!!


----------



## jobous (Apr 28, 2019)

I just finished my board, everything seems to be OK. Power on and the i see the light !!!!
Still some problems to solve , expecting enclosure this week to finish the amp.
Set bias to 11V, tried to listen but i was unlucky ,  the one of the two rca cables was faulty and i dont have another one.
I hear a constantly noise (increasing-decreasing  using volume), but i dont know if is a ground issue....


----------



## Pricklyears101

Anyone knows the output impedance of these?


----------



## TravAndAlex

A few updates to my build.  Copper lined the case to combat RFI. Installed a Khadas Tone Board DAC internally (which of course required fabricating a new rear panel).  Added a yellow power LED for the DAC on the right side of the front panel to balance the amp power LED.  

Overall I’m really impressed.  Yup. Rings like a bell when the relay clicks on.  Stock volume pot is noisy at either extreme but good at any reasonable listening levels.  Sound really great with anything from PortaPros, to HD 650s and even plenty of power for 600 Ohm Beyer T1s.  Color me very impressed.


----------



## jobous

Hi again. Now a have a major problem. I decide to change the cables from the pcb to the pot (smaller cables) and now the sound is very bad.
It sounds like it is very far , like a well and there isnt any bass at all !!!
I dont now why this happened. Has to do with the pot or the pcb (cause when i try to unsolder the old ones and solder the new cables , i have to say i didnt do a fine job there) ??? 
Or something else ??
I changed again with the original cables but there wasnt any difference.
Any help would appreciated. i'm very dissapointed cause except the ground issue the sound was amazing....


----------



## jobous (May 5, 2019)

Problem resolved !!!!! The omp voltage was 10.85 V and when i correct it back to 11.00 V ,  the sound came back to normal. I wasnt aware that is so sensitive to such a small voltage difference (0.15 V).

Now all is in place !!! Amazing sound ,no ground issues ,  i will enjoy it for sure. 

   

I have tested it only with my Sennheiser HD25. I'm looking forward to try with the HD58X ...

Thanks Pete for giving me the change to build my first amp.


----------



## Desert Rat

My NuHybrid Headphone amp makes a noticeable pop in the headphones when switching off the power. Power up delay works fine. Loud enough to be alarming. Build is in a DIYaudio store Galaxy chassis with jacks and input pot (Alps RK27, 10K audio taper) off board.
Is this unusual? Any suggestions? Pardon if this has been covered previously, I'm new to the forum.


----------



## TravAndAlex (May 26, 2019)

Wrote up my build log with tips, tricks and info as an article for Headphonesty if anyone is interested.  Designed to be a one stop shop for info. 

If anyone thinks I missed anything important, just let me know!


----------



## Kitchener

TravAndAlex said:


> Wrote up my build log with tips, tricks and info as an article for Headphonesty if anyone is interested.  Designed to be a one stop shop for info.
> 
> If anyone thinks I missed anything important, just let me know!


Brilliant write-up.
Great work, beautiful amp.


----------



## pmillett

Desert Rat said:


> My NuHybrid Headphone amp makes a noticeable pop in the headphones when switching off the power. Power up delay works fine. Loud enough to be alarming. Build is in a DIYaudio store Galaxy chassis with jacks and input pot (Alps RK27, 10K audio taper) off board.
> Is this unusual? Any suggestions? Pardon if this has been covered previously, I'm new to the forum.



It is normal to hear a pop when the power is turned off.  It's easy to delay the operation of the output relay to kill the turn-on pop, but when you power off, the voltage collapses fast and it takes some time for the relay to drop.
I measure about a 1.5V pulse at the output that lasts about 10mS.  I don't think that can damage any headphones, though it would be quite loud in low-Z headphones or IEMs.

It is possible to speed up the delay circuit and improve the pulse a little bit, maybe dropping it by half.  But it will still be pretty loud.  You can do this by changing R2 to 150k and D2 to a 20V zener, 1N5250.

Otherwise, about all you can do is unplug the headphones...


----------



## Desert Rat

I'd like to share my mods to this headphone amp. I don't seem to have permission to add photos to this post, so here is a text only description:

NuHybrid Headphone Amp Mods

After building and listening to the Nelson Pass B1 Korg preamp and comparing it to the Pete Millett's Nutube Buffer preamp, I found I liked the sound of Nelson's Korg tube setup a bit better. I figured out how to make Pete's Buffer sound more like Nelson's B1 Korg and then it was onward to the NuHybrid headphone amp.

Not obvious is that all 3 circuit designs invert the signal. This happens at the NuTube itself. This is easy to correct with loudspeakers by reversing the loudspeaker/amplifier connection wiring but not easy with headphones unless you want to take them apart and rewire them. Listening tests confirmed that I preferred the correct polarity with loudspeakers, so I decided to add input transformers with reversed primaries to the NuHybrid to also correct that circuit.

I first experimented with some inexpensive Triad TY-250P transformers I had around just for evaluation purposes. Imaging was very much improved but their lack of shielding, excessive phase shift in the low bass and higher THD proved unacceptable. I ended up purchasing and installing a pair of Jensen JT-11P-1 1:1 high quality line input transformers and installing them with the primary winding connections reversed.

Here is what I did to modify the NuHybrid Headphone amp to compensate for the polarity inversion and to have it sound more like the Pass B1 Korg. The build was done in a DIYaudio Galaxy chassis with all jacks, power switch, LED and volume pot mounted off the PCB and on the chassis panels.


The Jensen input leads are configured as unshielded twisted pairs connected directly to the isolated RCA input jacks. Input polarity is reversed with respect to the transformer output. The RCA jack shells (grounds) are tied together and connected to circuit ground to eliminate hum when a source is connected. The output leads of the transformers are configured as unshielded twisted pairs and connected directly to the volume pot inputs. The transformer can shields and internal electrostatic shields are connected to circuit ground at the input side of the board. I provided a direct chassis ground connection at that point a with the series resistor/cap to chassis ground connection shown in the Jensen data sheet. A dedicated ground wire was run from the volume pot ground terminals to circuit ground at the input side of the board. Since I was using a 10K pot, the Jensen data sheet damping network was not required. Even though my pot is an Alps RK27, it has excessive noise at the extreme CCW rotation, which seems to be a problem with 10K pots in general. If I end up changing it to something like a 50K, I'll add the recommended damping network.


I bypassed the on-board PCB volume pot connections altogether and went straight from the pot to some slightly larger Kemet 220 nF input caps that were then connected to the PCB at the C20 and C21 locations. Shielded coax connections from the pot to the caps input sides are grounded only at the PCB end.


I changed the NuTube plate resistors R13 and R14 to 332K.


I set the plate voltage at TP1 and TP2 to about +9.75 volts. I found this is best adjusted while listening to music and set to your preference. I also found that anything over +10.5 volts made the magic go away.

So how does it sound? With the resistor and plate voltage mods, I think it sounds better than the stock 475K plate resistors with voltage set closer to half-supply. Smoother, with no loss of dynamics or detail. Correcting the signal polarity with the transformers made a very significant improvement in detail and imaging. Yes, they cost as much as the PCB, tube and board components combined but once you hear the difference, there is no going back.


----------



## gaz2613

Desert Rat said:


> I'd like to share my mods to this headphone amp. I don't seem to have permission to add photos to this post, so here is a text only description:
> 
> NuHybrid Headphone Amp Mods
> 
> ...




Are you saying that for the line in and line out connections on the board the positive is actually the negative and the ground is the positive? That's my understanding of reversed signal polarity. If that's the case then that would mean the signal would be connected to ground if the negative is actually the positive surely or am I missing something?


----------



## tomb

Personally, I think someone's getting mixed up, here (could be me, though!).

AFAIK, inverting the signal is actually what allows negative feedback.  If the signal was not inverted, a feedback connection back to the input would blow up, become unstable, runaway, etc.  It is the inversion of the signal that allows the feedback loop to close, and thereby work.  In other words, the music signal is inverted by the OPA551 opamp in the NuTube Millett Hybrid circuit.  That signal becomes negative.  It's then fed back into the input side of the opamp as a negative music signal.  Now the opamp has two signals that are input, one positive and one negative.  The opamp is then able to compare/correct to minimize the voltage offset between the two.  That minimizes distortion and noise.  As I understand it, that's how negative feedback works.

I am not familiar with Nelson Pass's Korg preamp, but if it is simply an amplifier circuit without feedback, I'm guessing that trying to eliminate the signal inversion at the input to the NuTube hybrid is not the way to go about creating a zero-feedback circuit.


----------



## pmillett

An interesting discussion about the audibility of inverted polarity:

https://hydrogenaud.io/index.php/topic,55323.0.html

Pete


----------



## Desert Rat

gaz2613 said:


> Are you saying that for the line in and line out connections on the board the positive is actually the negative and the ground is the positive? That's my understanding of reversed signal polarity. If that's the case then that would mean the signal would be connected to ground if the negative is actually the positive surely or am I missing something?



This is AC, not DC. You can tie either 'positive' or 'negative' of an AC signal to circuit ground to unbalance the signal. Reversed polarity in this case means that the audio signal comes out of the circuit 180 degrees out of phase from the way it went into the circuit.

This can be corrected in loudspeaker systems which use 4 separate conductors, 2 per channel, by reversing the balanced wiring connection between the amplifier and the loudspeaker, either at the amplifier end or at the loudspeaker end of each channel's 2-conductor wire. Since headphones typically tie the "negative" from each channel together and use a 3-wire system, it is impossible to do this unless you take the headphones apart and then reverse the connections at the transducers themselves.


----------



## Desert Rat

tomb said:


> Personally, I think someone's getting mixed up, here (could be me, though!).
> 
> AFAIK, inverting the signal is actually what allows negative feedback.  If the signal was not inverted, a feedback connection back to the input would blow up, become unstable, runaway, etc.  It is the inversion of the signal that allows the feedback loop to close, and thereby work.  In other words, the music signal is inverted by the OPA551 opamp in the NuTube Millett Hybrid circuit.  That signal becomes negative.  It's then fed back into the input side of the opamp as a negative music signal.  Now the opamp has two signals that are input, one positive and one negative.  The opamp is then able to compare/correct to minimize the voltage offset between the two.  That minimizes distortion and noise.  As I understand it, that's how negative feedback works.
> 
> I am not familiar with Nelson Pass's Korg preamp, but if it is simply an amplifier circuit without feedback, I'm guessing that trying to eliminate the signal inversion at the input to the NuTube hybrid is not the way to go about creating a zero-feedback circuit.



The BJT input buffer does not invert the signal. The signal comes out of the Korg triode 180 degrees out of phase from going in, thus inverted. The opamp buffer does not invert the signal. The opamp in the Millett NuHybrid circuit is configured as a non-inverting unity gain buffer. The signal is connected to the non-inverting (+) input of the opamp. The opamp output is tied both to the center pin of the output jack (via a capacitor for DC blocking) as well as directly back to the inverting (-) input of the opamp with zero resistance in the connection. This is how the gain of the opamp is set to unity.


----------



## Desert Rat

pmillett said:


> An interesting discussion about the audibility of inverted polarity:
> 
> https://hydrogenaud.io/index.php/topic,55323.0.html
> 
> Pete



He does make a point about clean vs distorted signals. The way I have the triode set up in my build, with 332K plate resistors and +9.75V at TP1 and TP2, the circuit is theoretically producing about 1.5% negative phase second order harmonic distortion at 1V out. I posit that with that level of distortion, you can hear the difference between an inverted and a non-inverted signal. I have yet to try listening to the uncorrected (inverted) polarity output with the same amount of positive phase second order harmonic distortion, established by going to the high side of the half-supply plate voltage point. I'm not sure that would be valid since the tube characteristics might be different in other ways with +13 or +14V on the plates, especially since the amount of distortion generated seems to be dynamically dependent on the signal level going through the tube.

I feel that there is validity to maintaining the polarity of the original recording due to the way the transient wave fronts are reproduced. Not just at a high level, like kick drum beats, but also at a low level within the stereo mix. I realize I haven't done any blind A-B testing, and may just be "hearing what I expect to hear" but I'm a musician, a piano tuner, and was in the pro audio industry as a systems and loudspeaker designer for 40 years. And yes, my ears are not what they used to be as regards high frequency response but I can still hear differences in imaging, detail and clarity and I personally find that correct polarity at the transducers just sounds better.


----------



## tomb

Desert Rat said:


> The BJT input buffer does not invert the signal. The signal comes out of the Korg triode 180 degrees out of phase from going in, thus inverted. The opamp buffer does not invert the signal. The opamp in the Millett NuHybrid circuit is configured as a non-inverting unity gain buffer. The signal is connected to the non-inverting (+) input of the opamp. The opamp output is tied both to the center pin of the output jack (via a capacitor for DC blocking) as well as directly back to the inverting (-) input of the opamp with zero resistance in the connection. This is how the gain of the opamp is set to unity.



OK - I was the one getting mixed up, apparently.  Thanks for the explanation.


----------



## RestlessZombi (Jun 10, 2019)

Can someone answer a quick question, half way through the build and will be finishing it tonight (yay !) but I just checked and the adaptor I have is 24v but 2.91A DC, is this going to cause issues and i should hold off testing till i have something lower?

I'm guessing something more like 24V 1A is more suitable?

Sorry if this has been asked before, read the last 10 pages and the first 15 so far and not seen an answer.


----------



## pmillett

RestlessZombi said:


> Can someone answer a quick question, half way through the build and will be finishing it tonight (yay !) but I just checked and the adaptor I have is 24v but 2.91A DC, is this going to cause issues and i should hold off testing till i have something lower?
> 
> I'm guessing something more like 24V 1A is more suitable?
> 
> Sorry if this has been asked before, read the last 10 pages and the first 15 so far and not seen an answer.


That should work fine.

Pete


----------



## Alkolor

That should work, provided the polarity is also correct, meaning that the + and - connections on your alternate supply physically match (which one is on the outside or inside of the connector). From the spec sheet, it looks like the one on the BOM has + on the inside. Adaptors usually have the symbol for polarity on them.

Amps are more like a maximum supported spec. The device will draw as much as it needs, and your adapter needs to be rated high enough to supply what’s asked for. So, having a higher amperage rated adaptor is fine. There’s some posts earlier on where I learned the stock adapter is even way over as someone else was considering a lower power supply.


----------



## RestlessZombi

Thanks for the reply, it was perfectly timed... 

It's Alive 

Thanks for the design, Instructions and BOM, Much easier to make.. Time for some listening..


----------



## Geezer Rock 001

Hello to all who visit this thread and especially to Pete.

   I discovered this branch of the rabbit hole after I got interested in a NuHybrid build that Torq had for sale on the board. He is great to deal with and the amp delivered today. Torq's build was flawless and it sounded excellent!

  I was interested in the NuHybrid  because I was looking for a hybrid amp that I could roll Sparkos op amps into. I have a set in a Burson Fun and imo they are far superior to any of big B's offerings.

I rolled the Sparkos in this afternoon and they take a great sounding amp to another level. Again imo.

Pete, thank you for sharing so much of your expertise with the general public. I am so impressed with the performance of the NuHybrid that I plan to try my hand at building a Butte amp very soon.


----------



## slowpogo

I'm about to pull the trigger on this project and have just a few questions.

C3, C5, C6, C11 are designated 470uf 35v. Would 680uf 35v be okay in any of these positions?

Like many around here I like the Dale RN55 resistors. Some of the values for this project are only available in the 1/5 watt resistors from that series. Would 1/5w be enough for this project?


----------



## Alkolor

Hello slowpogo,

I think the upsized capacitors would be fine. I used 1000uf for C3 and C6 in mine since some had done the same for a stated increase in bass response. I used the billed 470uf for C5 and C11, but have upsized capacitance in similar circuit placement for other builds. From what I could gather when researching for my build, increased capacitance on a decoupling capacitor can improve ripple smoothing on the line, but capacitance is also selected based on the frequency it is meant to filter.


----------



## pmillett

slowpogo said:


> I'm about to pull the trigger on this project and have just a few questions.
> 
> C3, C5, C6, C11 are designated 470uf 35v. Would 680uf 35v be okay in any of these positions?
> 
> Like many around here I like the Dale RN55 resistors. Some of the values for this project are only available in the 1/5 watt resistors from that series. Would 1/5w be enough for this project?



Yup, that is fine, if the caps will fit in the space available.  Dale RN55 are fine too.

Pete


----------



## slowpogo

I built the NuHybrid, fully populated the board.  Plugged my adapter in, turned it on.  The choke started smoking.  I turned it off quickly.

Wondering what the hell went wrong, I double checked polarities of everything, solder joints, etc. and it all looked fine.  Turns out...I was using the same Triad wall wart that I used with my Millett Hybrid Max, thinking it was 24VDC.  It's actually 24VAC.  **many expletives***

So I briefly put 24VAC into the amp.  Obviously the choke is toast, but what else is likely damaged?


----------



## docentore

Check electrolityc caps


----------



## slowpogo

My 470uf electrolytics are socketed and they test fine. I think I’ll replace the choke, and the following 10uf and diode. Everything beyond the diode was likely protected from negative voltage, right?

It’s always humbling to remember that despite a fair amount of experience, you can still make idiotic mistakes.


----------



## RestlessZombi

slowpogo said:


> My 470uf electrolytics are socketed and they test fine. I think I’ll replace the choke, and the following 10uf and diode. Everything beyond the diode was likely protected from negative voltage, right?
> 
> It’s always humbling to remember that despite a fair amount of experience, you can still make idiotic mistakes.




I've just ordered my third PCB after making a few mistakes along the way. Nothing at fault of the creator, but my own lack of concentration. First time i made it fine but wanting to put it in an enclosure i tried to removed the "In" RCA and the solder point came off with it. Still trying to fix the second PCB at the moment, ordered the third PCB to make a proper job of it (plus new parts  ). Cap C11 is the issue on the second, solder point on ground came off so i had to "mend" it.. Now all checks out but no glow from the tube and only getting 1.2v on the test points no matter how I adjust it.

Again,i messed up, not the board.


----------



## slowpogo (Aug 24, 2019)

I replaced a few parts as described above and voila, my Nuhybrid was in business. 

I built mostly with the recommended parts, except the capacitors and the pot (TKD). The input 0.1ufs are ClarityCap SA, which are not that expensive ($4 each) but a very clear upgrade over Wimas.  For the power section electrolytics  I used Panasonic EEW-PS, which seem to be the new champion in terms of very low ESR while still being compact (the ones I'm using are 470uf 80V and still not huge).  A mix of Elna Silmic II and Cerafine for the 10uf, except for C13-14 which are Wima film caps.  They're big, but they fit fine on the bottom of the board (and would fit on the top too with some creativity).  For C3 and C6, I'm using some old Black Gate NX 680uf caps I had from a previous build.  They still sound wonderful.  I tried a few other types in C3/C6 out of curiosity: Black Gate Std, Elna Silmic and Cerafine, and Nichicon FG. 

They all sounded good and I'd be happy to use any of them, with the caveat that the Cerafine had recessed vocals, but was otherwise fantastic for, say, jazz.  This might bring out the Black Gate skeptics -- I wouldn't pay the crazy prices they go for on ebay these days, but they were absolutely worth the extra bucks at the original prices when they were still being made, if you were in a "spare no expense" mindset.  The NX in particular are very vivid sounding, and it's not just a vague feeling of mojo; I can point to specific things that simply aren't there with the others. They manage to be very dimensional with no lack of detail but also have a certain richness, and the backdrop behind the sound feels "blacker" somehow.

Anyway, I'm really happy with the amp. I just built a WHAMMY and I feel I've got two poles covered: a highly detailed, neutral reference amp (WHAMMY) and a more fun, euphonic type amp (NuHybrid).


----------



## JRRJ

Hi - I'm new here and need help with this amp.  I've built a few things, including the MiniMax (love the sound), but am pretty clueless.  Here is the problem:  no sound of any sort from my NuHybrid, not from the headphone jack, not from the RCAs.  The tubes light up, I've biased them at about 11v, checked and re-checked parts locations, volume and jack wiring and other wiring.  Because of the absolute silence I am wondering if the relay is functioning.  If it's not, could it be the relay itself or some obvious mistake involving it?  Sorry, but I haven't figured out how to post pics here.  Any ideas are welcome.   Thanks.


----------



## Alkolor

Hello JRRJ,

When I start mine up and the relay activates, I can hear a faint hiss and click from it. It takes about 10-12sec on mine since I used a larger C2, and  I think the normal capacity C2 has been reported to take about 6sec. Does yours make any noticeable sound? Otherwise, bridging between pins 4 and 5 or 8 and 9 on the relay would bypass it so you could test one channel and see if it is just the relay. These would be the first and second pin from the side by the larger capacitors. Looking at it from the side with the components as pictured on Pete's site, the top two would be 8 and 9 for the right channel, and the bottom two would be 4 and 5 for the left channel.

Good luck with your troubleshooting.


----------



## JRRJ

Alkolor said:


> Hello JRRJ,
> 
> When I start mine up and the relay activates, I can hear a faint hiss and click from it. It takes about 10-12sec on mine since I used a larger C2, and  I think the normal capacity C2 has been reported to take about 6sec. Does yours make any noticeable sound? Otherwise, bridging between pins 4 and 5 or 8 and 9 on the relay would bypass it so you could test one channel and see if it is just the relay. These would be the first and second pin from the side by the larger capacitors. Looking at it from the side with the components as pictured on Pete's site, the top two would be 8 and 9 for the right channel, and the bottom two would be 4 and 5 for the left channel.
> 
> Good luck with your troubleshooting.



Thank you for the suggestion.  I first replaced the diodes and the relay (foolish fit of impatience, in the process making a mess of the underside of the board) and the situation did not change.  Jumping those pins to bypass the relay as you suggested has yielded audio -- and revealed a new problem -- oscillation on both channels.  This is where I have stopped for the night, as frustration and fatigue take over.


----------



## Alkolor

I’d keep looking at the rest of the muting circuit components and their connections/orientations (capacitor, MOSFET, etc.), and check if the circuit is receiving power. Until it’s activating property, it seems likely the issue is in there somewhere. I didn’t think of it before, but with the relay in, it would be creating a ground connection through the nominal relay position when you bridge to bypass. I haven’t dealt with oscillation yet to know if that could be a cause, but I would guess it doesn’t help. You’d need to bridge to connection with the relay removed to prevent that. Unless you happen to remove the relay again, I’d go at the activation problem first though. It seems to be the bigger problem for now.


----------



## JRRJ

Thank you again.  I ended up starting from scratch because of the damage I did to the board.  And it works, and sounds fantastic.


----------



## SanderFI

I've build the NuHybrid in the last couple of weeks in between job and family  Used the stock parts exept the pot, offboard Alps 50k.

It works, nice glow on the tube, voltages within spec and sounds great but... I wonder why it is noisy when not playing music. So i shorted the input to find out if its coming from my source or if its inherent to my build. The noise is still here so i guess it is part of the NuTube? The noise can be described as grey noise. When music starts playing i cannot hear it anymore, it's drowned out bij the music. But still.. is it supposed to have an noticeable noise level?

I'm using a Denon Ah-D7200 headphone with 25ohm impedance. Could the low impedance have anything to do with it? Can i change the gain of the amp?


----------



## AddiDub

I have built this beauty months ago and still have a second set of PCB including NuTube and parts (according to the official BOM) lying around. So if there is someone located in Europe who wants to build this, please contact me. Set of parts will be going for €90,- plus shipping.

Regards, Andreas


----------



## gaz2613

SanderFI said:


> I've build the NuHybrid in the last couple of weeks in between job and family  Used the stock parts exept the pot, offboard Alps 50k.
> 
> It works, nice glow on the tube, voltages within spec and sounds great but... I wonder why it is noisy when not playing music. So i shorted the input to find out if its coming from my source or if its inherent to my build. The noise is still here so i guess it is part of the NuTube? The noise can be described as grey noise. When music starts playing i cannot hear it anymore, it's drowned out bij the music. But still.. is it supposed to have an noticeable noise level?
> 
> I'm using a Denon Ah-D7200 headphone with 25ohm impedance. Could the low impedance have anything to do with it? Can i change the gain of the amp?



Hi you need to check the ground of the Alps pot. If you don't have one, attach a ground wire to the body of the pot to eliminate noise. Also to eliminate noise at either end of the pot on absolute minimum and absolute maximum, you need to attach 100 ohm resistors to the middle pins of the pot. Hope this helps.


----------



## stephengee77 (Jan 15, 2020)

The one I built has a clicking sound and a high pitch hiss. It does play audio, but the noise is still very audible. Does anyone know what the cause could be?

Edit: I have isolated the problem to likely be an induction problem or something similar. When I take the amp out of the chasis and hold up the pcb up in the air, the ringing goes away. When I put anything near the bottom of the pcb, it makes noise again.


----------



## ClaudiuS

Hi Andreas, I am interested in your set. Because I am a newbie I can post only once per day. So my response might take some time.

Regards,
Claudiu.


----------



## HumanFly1977

Hi, I'm very much a novice with electronics, but I successfully built a NuHybrid a few months ago. It had been working great until recently—it seems like the headphone jack (the Neutrik NRJ6HF as per the BOM) has become wonky. I only get audio out of one side now, and the only way I can get audio on both sides is if I pull the headphone plug out so it locks to the middle clip in the jack, but then the audio is mono. I don't even know how to begin troubleshooting this problem. Did the jack fail and need to be replaced? Is it just a bad solder job? Any help would be appreciated—thanks.


----------



## HiFan (Mar 16, 2020)

HI all,

I'd like to share some experience on this amp. This is my first DIY project, and the first successful one. I then went through a great length to get the most out of this circuit.In the process I gained a lot of experiences, skills, and interests in DIY.

Let's start with my first built. This amp really sounds good and I had a lot of fun. However I think the hiss is quite unbearable once opamps are changed. So I started thinking about how to improve it.



Then I went through a series of builds and settle with this. You can see I got some jump wires linking to something beneath the board. It is a Super Regulator board. This board is a fantasic regulator and can turn the switching PSU to a high performance PSU. You might also noticed that I got a small black block sitting next to HP jack in place of ua78m33cks LDO. That is a tarco TRS DC buck converter.





In the original design, when OPAMPs are changed, background noise would very likely to be strange. I have tried a variety of opamps. Opamps like LT1354, AD8065, etc would produce a constant "wooooo" sound. That's probably a character of the LDO.

With Traco, that "wooooo" goes away but hiss is a tiny bit stronger (depending on the opamps you use). However the benefit is huge here since the range of usable opamps becomes wider. And Traco really runs cool. It is not warm at all after running for a whole day.

To address the hiss Traco introduces, I think 2 things might work: 1) use an opamp whose PSRR is higher (closer to 0), like AD8055 and HA5002; 2) swapping out the 10uf grounding cap with a larger cap, such as ZLH, then bypass with a MLCC.

I think the SuperReg is overkill, if I am to build a new one I won't use it.  In Pete's original design, filtering caps for the power section is too small. If you don't want to build a new PSU reguator as I did, at least consider putting in a 1000uF cap in the place of C1 or D1 (in Parallel).  

I actually plan to add a few more jump wires to the bottom and put more filtering caps into the output of traco.

This is a really fun project.

[Update] I use jump wire to hook up 4 extra caps to increase the 10uf grounding capacitance to a totally around 370uf (Traco's maximum load capcitance is 470uf). I used a ZLH 120uf, a EPCOS 41858 220uf, a epcos c0g, and a vishay 0.1uf MKP film cap. Now noise floor is really low (AD8055) and barely noticeable with audio-technica LS70 iem. In fact my Ha21 has the same level of hiss when used open frame. If you use less sensitive headphones or put it in a case, I think hiss will be completely gone. I am quite happy.

[Update 2] OPA209 works better to my taste than other opamps I have tried, including SS3601.


----------



## ken_chuang (May 10, 2020)

Here's my NuHybrid headphone amp build.

Main upgrades
1) Sigma11 Power Supply Unit
2) OPA1611AID opamp with extended 200MA current (green circuit board).

Works well with my Sennheiser HD800 S headphone.


----------



## HiFan

ken_chuang said:


> Here's my NuHybrid headphone amp build.
> 
> Main upgrades
> 1) Sigma11 Power Supply Unit
> ...



Nice build! Have you tried opa209? I found it cleaner than 1611 in this circuit.


----------



## ken_chuang

HiFan said:


> Nice build! Have you tried opa209? I found it cleaner than 1611 in this circuit.


Thanks for your reply. I had not tried OPA209 yet, great to know it works better too. I had been mainly looking out for high voltage (24V), high current (200MA) opamp options so far.


----------



## HiFan

ken_chuang said:


> Thanks for your reply. I had not tried OPA209 yet, great to know it works better too. I had been mainly looking out for high voltage (24V), high current (200MA) opamp options so far.



That circuit is picky on the opamps. I have tried a few but only opa209 and LT1357 families works. Some will have higher white noise in the background than others. 

However, your opa1611s are interesting. I don’t know such mod exists.


----------



## ken_chuang

HiFan said:


> However, your opa1611s are interesting. I don’t know such mod exists.



Search for "OPA1611AID with Extended 200MA Current Class A Output Single OP AMP Module", many e-commerce sites sell them.

This is my 1st time trying this kind of modded opamp too.


----------



## HiFan

ken_chuang said:


> Search for "OPA1611AID with Extended 200MA Current Class A Output Single OP AMP Module", many e-commerce sites sell them.
> 
> This is my 1st time trying this kind of modded opamp too.



I looked at your photos a bit more. Did you ground your board and case? I normally would sand around power, screw, and pot holes so they they can be connected electronically. Pot shaft definitely need it.


----------



## ken_chuang (May 11, 2020)

HiFan said:


> I looked at your photos a bit more. Did you ground your board and case? I normally would sand around power, screw, and pot holes so they they can be connected electronically. Pot shaft definitely need it.



I didn't do ground for this. Looks like I should. I am getting noise from just slight re-positioning my interconnect between my phono preamp and this. Thanks for your feeback on this.


----------



## AlexKB (Dec 30, 2020)

Hey everyone, I'm curious if anybody has identified a middle-ground pot?  I'm definitely new to DIY, but have been hunting around (dangerous I know) and found a couple possibilities but also their possible pitfalls...

Also, a couple general questions...

From reading through the thread, it seems like 10 k-ohm resistance was selected to minimize noise.  What would the impact be of selecting a 1 / 5 / 20 k-ohm resistance pot?

How important is power rating?  Is  there a meaningful difference in this build between a 25 mW rating and a 50 mW rating?  Does a much higher power rating, say 500 mW matter?

Is my understanding correct that PCB Mount / through hole has stronger pins to provide a sturdy mount whereas panel mount / PC pin relies on a panel for strength so pins are much weaker?  Or maybe it is incorrect to pair those as always accompanying each other?  I'm planning on using the case in the BOM.

I'm intrigued by the Vishay P9A2X000DFRX1103ML at approx. $20, which I assume is due to its improved rated life of 25,000 cycles and Conductive Plastic element.  The Alps is only rated to 15,000 and I could find no mention of the element type in the datasheet.  Perhaps there's no way it is worth 10x as much though?  Also, the shaft is a smaller diameter and shorter, which perhaps complicates mounting in the BOM case?

Similarly intrigued by the  Bourns 81A2A-B28-D15/D15L although it has a 250 mW power rating, is a panel mount, and much larger shaft dimensions.

Is there a reason why the Alps Blue Velvet is a bad pick?   RK27112A0-S20-C0-A103 

Appreciate any guidance offered...

Thanks!


----------



## Desert Rat

AlexKB said:


> Hey everyone, I'm curious if anybody has identified a middle-ground pot?  I'm definitely new to DIY, but have been hunting around (dangerous I know) and found a couple possibilities but also their possible pitfalls...
> 
> Also, a couple general questions...
> 
> ...


You would not want to typically go lower than 10K as it would start to load the source too much and potentially change the sound. You want to stay with audio taper if possible. I've used 20K and even 50K with success in headphone amplifiers.  A TT Electronics PCB mount 10K is conductive plastic, 100,000 cycles, audio taper and only $2.53
P092N-FC25AR10K BI Technologies / TT Electronics | Mouser 
An Alps RK27 is probably the best pick for chassis panel mount. The larger diameter provides a better audio taper and better channel-to-channel tracking. It's carbon but highly regarded by many as having excellent sound quality. I have probably a dozen installed in various projects and only ever had one bad one that was a bit scratchy at the low end of the rotation.


----------



## AlexKB

Thanks for pointing me in that direction, Desert Rat.

Another question... I've noticed that for the voltage regulator, the primary part on the BOM, TI Instruments UA78M33CKCS, has an output current of 500 mA whereas the alternative part, Microchip MIC2940A-3.3WT, has an output current of 1.25 A.  Is this actually just a maximum output current based on the what the circuit tries to 'pull' from it?  Or if the output current is constant, why does the circuit still operate correctly?  Is there any meaningful difference in this circuit between the two items?

Also, if increasing the 0.1 uF film caps to 1.0 uF film caps, would this just be done for the caps after the Nutube (C4, C7, C8, C9), or would it apply to all of the 0.1 uF caps?  I'm sure I'm betraying the full extent of my ignorance, but hopeful for any input before I start wildly experimenting....


----------



## Desert Rat

"actually just a maximum output current based on the what the circuit tries to 'pull' from it" is the correct answer.

"Is there any meaningful difference in this circuit between the two items?" No.

You could up the value of C20 and C21. Not sure C18, C19, C8 and C9 are worth the bother.


----------



## PastorOfMuppets (Jan 9, 2021)

New to the forum and DIY. I got the kit and the parts and am having some difficulty. I have soldered all the pieces onto the board but it's not working. The power light isn't coming on either. In fiddling with it when I use my multimeter to bypass the common mode inductor at least the light comes on. I'm a little at my limit after that for knowing what to do other than resolder all the things which hasn't worked. Thoughts on how to debug or troubleshoot? Thanks!

Edit: the default Alps potentiometer is sold out and I think I ordered something that won't work so...maybe that's it? now i have to get the thing out, the thing that's not supposed to come out _great_


----------



## PastorOfMuppets

PastorOfMuppets said:


> New to the forum and DIY. I got the kit and the parts and am having some difficulty. I have soldered all the pieces onto the board but it's not working. The power light isn't coming on either. In fiddling with it when I use my multimeter to bypass the common mode inductor at least the light comes on. I'm a little at my limit after that for knowing what to do other than resolder all the things which hasn't worked. Thoughts on how to debug or troubleshoot? Thanks!
> 
> Edit: the default Alps potentiometer is sold out and I think I ordered something that won't work so...maybe that's it? now i have to get the thing out, the thing that's not supposed to come out _great_



nope my inductor was bad on the non-ground side. if i bypassed it, it worked. so...i'm doing that for now...how big of an issue is it if i bypass the inductor?


----------



## Goodmonson

Hello everyone, I recently put together a NuHybrid kit and am looking for some troubleshooting help. I am at the point in the assembly guide that instructs you to use the bias trim pots to adjust test point voltage to 11 volts. On the L bias pot, I was able to do that successfully, while on the R bias side the test point voltage climbs slowly to about 17 volts and stays steady. The R bias pot does not appear to affect the voltage at all. I have checked part positions, polarities, and reflowed each joint a couple of times. I tested the voltage division of both bias trim pots (I know in-circuit measurement is inaccurate but both appear to operate completely identically, so I think they are likely fine). I also swapped the op-amps around a couple of times to no effect. I have been following the schematic to try to narrow down what parts are between the bias pots and the test points, but I am not sure what might be likely subjects or how to test them. Anyone have any ideas? Hoping it's not a problem with the Nutube itself. Thanks very much!


----------



## ChetJettison

HiFan said:


> HI all,
> 
> I'd like to share some experience on this amp. This is my first DIY project, and the first successful one. I then went through a great length to get the most out of this circuit.In the process I gained a lot of experiences, skills, and interests in DIY.
> 
> ...


Hey there. 
I just built a NuHybrid amp, and I've noticed hiss when using sensitive IEMs or Closed Back headphones. I found your post here, and I see you've done something that perhaps reduces the hiss. I've read your description, but I don't quite understand it because my electronics knowledge is not strong. Could you describe what you did to resolve the hiss issue with a bit more specifics, so that I, a complete novice, could understand and implement it? Seems like maybe you changed out some caps. Which caps, by number, did you change? And to what? I'd be grateful for any help you can provide.


----------



## manito (Jun 11, 2021)

hi, im new in DIY and  looking for Sparkos op-amps to made  this project. In their site they preconice to use their power suplies with their Panasonic EEU-FR1H101B 100uF 50V  with their regulators:

https://sparkoslabs.com/discrete-voltage-regulators-audio-power-supply/
https://sparkoslabs.com/product/dual-power-supply/

what do you think about that guys...?


----------



## SnookHaus

manito said:


> hi, im new in DIY and  looking for Sparkos op-amps to made  this project. In their site they preconice to use their power suplies with their Panasonic EEU-FR1H101B 100uF 50V  with their regulators:
> 
> https://sparkoslabs.com/discrete-voltage-regulators-audio-power-supply/
> https://sparkoslabs.com/product/dual-power-supply/
> ...


Hello and welcome,

  I am new to DIY as well and just finished this amp as my first project. It sounds nice to me and I don't have a lot of the microphonics  that others talk about. Just the initial "ting". 

 Regarding the Sparkos Labs op-amps:  They are a quality item!  However, I seem to remember reading in this thread that the op-amps don't play a large role in the sound quality of this particular amplifier. Others with more knowledge than I can suggest what specific part played a larger role in better sound quality. 

  Also, when I was ordering my parts from Mouser there was one particular resistor that was backordered everywhere.  I was able to procure them but shipping was expensive. I purchased  a few extras; enough for 3 extra amps. I am willing to mail them for free in the US to those that need them. The part # is: MF1/4DC1001F  KOA Speer Metal Film Resistor, 1000 Ohms 0.25W 500V.


----------



## manito

SnookHaus said:


> Hello and welcome,
> 
> I am new to DIY as well and just finished this amp as my first project. It sounds nice to me and I don't have a lot of the microphonics  that others talk about. Just the initial "ting".
> 
> ...


im tying to deal with capacitors actually but there are so many choices, maybe someone could put here an actualized list with the best choices...


----------



## SnookHaus

manito said:


> im tying to deal with capacitors actually but there are so many choices, maybe someone could put here an actualized list with the best choices...


Do you have the BOM(build of materials) from the spreadsheet or the project code from Mouser?


----------



## SnookHaus

manito said:


> im tying to deal with capacitors actually but there are so many choices, maybe someone could put here an actualized list with the best choices...



http://www.mouser.com/Tools/Tools.aspx and enter this access code: b68a30231c


----------



## manito

SnookHaus said:


> Do you have the BOM(build of materials) from the spreadsheet or the project code from Mouser?


Yes but reading the thread i noticed that some guys sugested diferent capacitors to improve quality...


----------



## manito (Jun 13, 2021)

sorry for my very basic questions but I am not an expert in electronics. Why did you put only + 24v and not +24 and -24v in this assembly? that would have been better to remove ground noise no ...?


----------



## SnookHaus

manito said:


> Yes but reading the thread i noticed that some guys sugested diferent capacitors to improve quality...


Here is a blog that lists some alternatives:  http://www.diyaudioblog.com/2017/05/millett-nuhybrid-headphone-amp-using.html?m=1


----------



## gaz2613

Evening all, I have been busy over the last few months designing power supplies for headphone amp projects and this one may be of interest to some of you. It's called the Artemis PSU and it's a single rail power supply which can be configured for different output voltages by swapping out the voltage regulators. I have an early version of this board powering my NuHybrid and it's dead silent!

More info below:

https://www.audiosy.net/2021/03/17/first-look-artemis-single-rail-power-supply-rev-b/


----------



## Minternal (Aug 3, 2021)

Might be some dumb questions as I'm very new to electronics, but just wanted to make sure:

Would the line out (acting as a preamp) contain the tube colored sound? Yes, as seen in the schematic, both the headphones and line out jacks are connected to the output of the nutube.
Would the device be able to output sound to the headphone jack and the line out jack at the same time? Probably, since both hp and line out are always connected to each other. What probably happens is a lower volume output for each since the same signal is being shared.
My use case is that I want to use this device to color the sound and provide an easy static way to bridge my dac to both my headphones and my speakers - as I often switch between them.


----------



## Zachik

Hi Pete and all,

First, I would like to thank Pete for this awesome DIY design!
After reading the entire thread, and getting the PCB and tube from Pete, I am getting ready to order the components. In normal times, it is a challenge due to mod / upgrade desires but nowadays supply is an added challenge...
So, *I have a couple BOM questions before placing my orders* (Mouser AND DigiKey, since neither have all components):
1. 10uF caps: should I go for Nichicon FG (Fine Gold) 50V or Elma Silmic RFS 35V? Price difference is approx. 10 cents/cap, so price difference is NOT a factor.
2. C3 & C6 caps: I read couple posts recommending 1000uF instead of the "stock" 470uF for better bass response. So, in order to fit the PCB (due to case I am going to use, I cannot use parts under the PCB) - I can either use the Nichicon* FG* 470uF or Nichicon* FW* 1000uF. Opinions?
3. 0.1uF caps: BOM calls for WIMA but they're not available. Alternate part is by TDK. Any other recommendations, or the TDK sound good and I should not bother with changing those and stick with TDK?
4. K1 (PCB Low Signal Relays - PCB 24VDC NON-LATCH): both Mouser and DigiKey are out of stock for the recommended parts in the BOM. Any alternatives??
5. Q2 & Q3 (BJT NPN Transistor General Purpose): again, both are out of stock   Any drop-in alternatives?
6. R17 & R18 (Through Hole Trimmer Resistors - 1.0Kohms 6mm SQ): same   Any drop-in replacement alternatives?
7. OPA551PA vs. OPA134PA: someone posted a while ago that the latter is WAY better than the recommended opamp. Anyone else tried the OPA134PA in this amp?

Thanks in advance for any pointers, opinions and thoughts 

Zachi.


----------



## HiGHFLYiN9

CoryGillmore said:


> I suppose the next evolution of such a concept was the omni-directional drivers, like Ohm Walsh and those other ones that are like 500k lol. The latter ones actually have omni-directional drivers for highs, mids and even the sub. The drivers are spherical, very cool.





Zachik said:


> Hi Pete and all,
> 
> First, I would like to thank Pete for this awesome DIY design!
> After reading the entire thread, and getting the PCB and tube from Pete, I am getting ready to order the components. In normal times, it is a challenge due to mod / upgrade desires but nowadays supply is an added challenge...
> ...



1. For reliability I'd choose the Nichicon over the currently manufactured Elnas. 
2. Can't comment regarding the bass change. FG is marketed as a higher quality audio capacitor by Nichicon, for whatever it's worth. 
3. I wouldn't worry about this, they're both low-cost metalized polypropylene and any audible difference is probably dubious. 
4.,5.,6. Mouser has a "search similar" feature with a checklist, so you pull up the part in Mouser and then check off the important stuff (like voltage, size, current, ratings, etc.) and see what is closest. Generally the little changes to the letters of a part are sometimes unimportant things (to us) like how they pack the parts for shipment. You can read the datasheet (it's a PDF in Mouser) and it will tell you what the letters mean so you can confirm. We can walk you through this if you post the parts numbers here that you need.


----------



## Zachik

Could someone please assist with off-PCB wiring for the volume pot?




Which pad goes to each of the pot pins:

Input Left
Input Right
Input Gnd
Output Left
Output Right
Output Gnd
I am in the final stages of wiring the audio signals to the off-PCB RCA inputs, volume pot and headphone jack. I believe I figured out the headphone jack and RCAs, and only got the volume pot left to be wired... 

Thanks!


----------



## Alkolor

Minternal said:


> Might be some dumb questions as I'm very new to electronics, but just wanted to make sure:
> 
> Would the line out (acting as a preamp) contain the tube colored sound? Yes, as seen in the schematic, both the headphones and line out jacks are connected to the output of the nutube.
> Would the device be able to output sound to the headphone jack and the line out jack at the same time? Probably, since both hp and line out are always connected to each other. What probably happens is a lower volume output for each since the same signal is being shared.
> My use case is that I want to use this device to color the sound and provide an easy static way to bridge my dac to both my headphones and my speakers - as I often switch between them.


I believe the headphone jack in the BOM is a switched type, so it disconnects the line out when headphones are in. You'd need to change to an unswitched type to have both outputting at the same time.



Zachik said:


> Could someone please assist with off-PCB wiring for the volume pot?
> 
> 
> Which pad goes to each of the pot pins:
> ...



Did you get one of the recommended pots that fits the board? If so, just see where it fits up on board and connect the same points with wires off board.

If not, I'm going to take a crack at this.

I only have my NuHybrid and build pictures to look at and follow the traces, and the spec sheets I'm finding don't tell me the pinouts. Given how pots work though, I think it would be pretty hard to screw something up badly. Use this advice at your own risk.


The 6 holes in the middle are bridged by being next to each other, so each pair of those is the same connection.
Similarly, the upper 3 and lower 3 are bridged as pairs as well, so each upper and lower hole is the same connection.
The pots designed to go with this board are stacked per channel (L/R), so pick 1 set on your pot for the inner 6 holes and 1 set for the outer 6. Having them backward would switch your speakers at worst. The board is designed for using 2 different size pots, which is why there's 2 sets of holes.

I don't think pots care about direction, so as long as you get the grounding right, flipping in and out shouldn't change anything. You can check the grounding holes with a multimeter by checking a pot hole to another known ground hole.

The ones toward the inside of the board (left) are all grounds. They're all connected, so it doesn't matter which 2 holes you connect to the pot grounds. I connected my pot case to one of those holes too, so I'm pretty sure on them being grounds.
The ones in the middle are the outputs. You can see the traces on the bottom of the board go from the middle holes to C20 and C21. The inner pair goes to C20, so they're right, and the outer pair goes to C21,making them left.
The ones toward the outside of the board (right) are the inputs. You can see the traces on the top of the board coming from the line in. The inner pair is right, and the outer pair is left.

So for mapping, the holes in your picture go:

123

145
145

123

Input Left = 3
Input Right = 5
Input Gnd = 1
Output Left = 2
Output Right = 4
Output Gnd =1


Zachik said:


> 1. 10uF caps: should I go for Nichicon FG (Fine Gold) 50V or Elma Silmic RFS 35V? Price difference is approx. 10 cents/cap, so price difference is NOT a factor.
> 2. C3 & C6 caps: I read couple posts recommending 1000uF instead of the "stock" 470uF for better bass response. So, in order to fit the PCB (due to case I am going to use, I cannot use parts under the PCB) - I can either use the Nichicon* FG* 470uF or Nichicon* FW* 1000uF. Opinions?


I'm one of those guys who asked the same questions and spent way too much time choosing caps. I probably wouldn't have noticed the difference from the BOM caps, but it was fun to learn and make mine unique.

1. I went with Elna's simply for the marketing. I'm sure it's not practically different. I squeezed the fatter 50V ones in there, but it was rough. I bought a set of 35V just in case they didn't fit. Also, just to be different, I undermounted WIMA film caps for C13 and C14 since they were in the signal path, and 10uf films were available in a manageable size. It was really hard to mount them since the leads were so short, but I made it. That whole cluster was really a chore with the size changes I made.

2.  I liked the look of the giant Elna caps on the board, so why not. I did have to buy a deeper case to undermount the film caps between them. In theory, a signal cap will pass lower frequencies if it has higher capacity. Capacitors block flow when they fill up, so having more capacitance will let a longer low frequency pass better. I don't think I actually ran the calc, and just went with 1000uF like a couple others. I'd stick with the audio marketed FG caps (or other audio caps) simply for the heck of it. I asked Pete about it when buying the PCB, and he doesn't believe there's a discernable difference between audio and power grade caps, and even that the power grade caps are better since they often have better specs on paper. I know their life ratings were often higher at least. He also told me something about how the signal technically back flows through all the caps and not just the signal path caps, but that was beyond me. On the capacitance, Pete said there would be no difference with my HD650s, but lower impedance like 32ohm headphones would get a slightly increase in bass response


----------



## pmillett

So... yes, the post above looks correct.  Saying that a different way:

The front row of 3 pins is connected to the rear row and is for the left channel, and the two middle rows are connected and are for the right channel.  So you can use either the front/rear for left and either of the middle rows for right.

The leftmost holes are connected to ground, which is the CCW pin of the volume control.

The middle pins are the wiper of the pot, which is the input to the amplifier.

The right holes are connected to the input jacks, which goes to the CW terminal of the pot.

Hopefully that makes sense?

Pete


----------



## Zachik

Thanks for confirming, Pete!


----------



## Zachik

Finally... about time I share a few photos of my finished build   
My build consists of:
* Pete Millett's PCB
* RCA inputs, volume pot, headphone jack and power switch - all mounted off-PCB 
* Artemis Linear PSU (designed by @gaz2613 - see post #489 on this thread)
* Custom case 

Here is everything inside the case:





Here is a photo of the case closed with the cool front panel visible:




Thanks everyone who answered my questions, and a special thanks to @gaz2613 who supported the PSU side of the design with so much patience!


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## larcenasb (Feb 24, 2022)

Finally planning my build, very excited about this amp!


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## larcenasb (Feb 24, 2022)

Prabeer Patankar said:


> Hello Pete
> 
> I recently built this amp and experimented with a couple of single opamps I had in my possession.
> 
> ...


Wow, that enclosure is gorgeous!! I'm going to try and do something similar. If it's not too much trouble, what are the dimensions of the enclosure? Thanks.

Congrats on your build!


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## colinharding

The builds here look great and I think I’ll join the club in a couple months time.

May be an unusual comparison but has anyone compared this to the portable kit nutube that Pete offers (Nu:tekt)? I may just end up building both


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