# New DIY Altoids Tin Amp - The Pocket Class A "Wintergreen Handwarmer" by xrk971



## stellarelephant (Jul 30, 2017)

Edit 7/30/17: PCBs are now available at the XRKAudio Etsy Store!

For real!
 Up until now there have been hardly any portable Class A head amp designs, commercial or DIY.
 Here's a brand-new CMOY-sized amp project with the goods! I'll be building a couple of these in the coming weeks and will post my build pics and listening impressions here.
 Until then, here's some info on the little beast:



 An experienced amp builder on the DIYAudio forums, xrk971, with the input of the ever-helpful community over there, is currently finalizing his design for this amp.  In the works are a detailed bill of materials for the build, a circuit schematic, and hopefully a GB (on DIYA, not here!) for printed circuit boards (design courtesy of user BDHM)...all to be found in this thread:

http://www.diyaudio.com/forums/head...2-based-se-class-headamp-without-heat-11.html

 "X" has run extensive simulations of this circuit as well as real-world measurements for THD and FR, and the results look stellar.  Low noise, textbook-perfect harmonic distortion profile, and a razor flat frequency response.  Solid bass.  Plenty of juice, even for 250 Ohm cans (possibly higher).  And most importantly... according to him, it sounds amazing.  It runs slightly warm to the touch, and gets 4-5 hours of battery life.



 What makes it most exciting to me is that it's noob-friendly, with a low parts count, and all through-hole components except for the JFETs.  My solder-slinging experience is limited to much simpler things like speaker crossovers and volume pots, etc., but I think even I'll be able to pull this off.  I'm excited about this little amp project!


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## stellarelephant

The amp in the photos above is X's current prototype, built with his hand-drawn circuit board and all SMT components.  DIYA member BabyDontHertzMe currently has two DIY PCB designs under development and soon to be available for printing.  One will use SMT components like the original, while the other will use all through-hole components to facilitate easier soldering for beginners.


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## Hutnicks

Those look like rechargeables there, is there a charging circuit built in?  A slightly better enclosure would probably eliminate any heat issues
  
 I will be extremely interested to see this in action. thanks for posting this up.


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## nick n

well, I'm down with a couple of boards.


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## stellarelephant

hutnicks said:


> Those look like rechargeables there, is there a charging circuit built in?  A slightly better enclosure would probably eliminate any heat issues
> 
> I will be extremely interested to see this in action. thanks for posting this up.


 
  
 X has reported 4 hours of battery life using that pair of 600 mAh rechargeable Li-Ion batteries you see in the pic (there are now 800 mAh cells on the market, BTW, which I will probably use).  There is also the possibility of reducing bias in the amp circuit and potentially getting upwards of 6 hours.
  
 There was some talk of a charging circuit at one point (it was me who brought this up, in fact) and I think the conclusion was that a charging circuit should indeed be possible to fit in the tin, and that this might appear eventually as an add-on.
  
 Also according to X, the amp never became uncomfortably warm while in use for hours at a time.


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## Hutnicks

stellarelephant said:


> X has reported 4 hours of battery life using that pair of 600 mAh rechargeable Li-Ion batteries you see in the pic (there are now 800 mAh cells on the market, BTW, which I will probably use).  There is also the possibility of reducing bias in the amp circuit and potentially getting upwards of 6 hours.
> 
> There was some talk of a charging circuit at one point (it was me who brought this up, in fact) and I think the conclusion was that a charging circuit should indeed be possible to fit in the tin, and that this might appear eventually as an add-on.
> 
> Also according to X, the amp never became uncomfortably warm while in use for hours at a time.


 

 Thanks. The add in board would be a neat idea. It's winter here so a handwarmer is not a bad idea


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## stellarelephant

nick n said:


> well, I'm down with a couple of boards.




Great! I must reiterate...please express all interest in acquiring these PCBs over at the original DIYA thread. http://www.diyaudio.com/forums/headphone-systems/300862-bf862-based-se-class-headamp-without-heat-11.html
Head-fi no longer allows group buys. 

I'll continue to post updates on the development of the amp here, and I certainly welcome all manner of discussion about this project.


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## nick n

Of course. Will do thanks.


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## stellarelephant

Thanks


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## stellarelephant

This amp is exceptional in yet another way: Single-Ended (SE) circuit topology!  This is absolutely unheard of in portable amps, and until now has been the domain of pricey desktop units such as the higher reaches of the Schiit lineup, all the way up to the $4000 Woo Audio tube amp offerings.  So what's so special about a Single-Ended Class A Design?
  
 To be honest, I had no clue until I did some research today.  Come to find out, Audio God *Nelson Pass* says Class A SE gives the BEST SOUND, bar none.  Here's a quote from him:
  
*"The promise of the transconductance characteristic in power amplifiers in providing the most realistic amplified representation of music is best fulfilled by Mosfets in single-ended Class A circuitry where they can be used very simply and biased to very high currents. [...] In systems where the utmost in natural reproduction is the goal, simple single-ended Class A circuits are the topologies of choice."*
  
 The whole article is pretty awesome, so if you enjoy the challenge of trying to understand a genius' musings, here it is:
 https://passlabs.com/press/single-ended-class
  
 So, SE sounds the best.  The downside?  It's also the least efficient of ANY amp circuit topology...which of course is why we haven't ever seen it in a portable amp before.  4-5 hours of battery life is a bit less than most folks expect from their portable listening setup, although I'd argue that it isn't unreasonably short either...I rarely listen for more than 2 hours a day, myself.  Regardless, if sound quality comes first, this amp is truly something to be excited about.  Can't wait.


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## Hutnicks

stellarelephant said:


> This amp is exceptional in yet another way: it uses a Single-Ended (SE) circuit topology!  This is absolutely unheard of in portable amps, and until now has been the domain of pricey desktop units such as the higher reaches of the Schiit lineup, all the way up to the $4000 Woo Audio tube amp offerings.  So what's so special about a Single-Ended Class A Design?
> 
> To be honest, I had no clue until I did some research today.  Come to find out, Audio God *Nelson Pass* says Class A SE gives the BEST SOUND, bar none.  Here's a quote from him:
> 
> ...


 

 Pass has a great take on audio circuits he is well worth listening to. The heat and inefficiency you mention are the big drawbacks (Why the Krells used to have cooling fans). On something this small you can heat sink the poo out of it to solve the issue there so that just leaves power consumption. 4 or 5 hours is not bad and really if you needed more a spare pair of batteries or perhaps looking for a larger capacity battery might be in order. All depends on how small you want it.
  
 Waiting for pricing to get finalized over there on DIY for the PCB's.


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## stellarelephant

X's Pocket Class A GB has begun on DIYA...only 2 boards left for the first round! 
	

	
	
		
		

		
		
	


	




 
 http://www.diyaudio.com/forums/headphone-systems/300862-bf862-based-se-class-headamp-without-heat-25.html


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## stellarelephant

More are available for a few more days!
  
 "It's a superb sounding single ended (SE) Class A topology that has a predominantly a second harmonic distortion profile with just a tad bit third harmonic and not much else. The noise floor is about -125dB and dynamic range is about 96dB with THD measured to be about 0.029% at 1kHz and driving a 270ohm load at 700mV RMS. Note that most of that HD is H2 so the sound is very much like a nicest SE tube amps. Frequency response with a 47uF output coupling cap was measured at -1.5dB at 20Hz and 45kHz (probably limit of measurement as ADC sampling was 96kHz). The sims show that it can go beyond several MHz on the high end. Best part is that it fits in an Altoids tin and looks like a CMOY headamp - but it's no op amp. It relies on just two FETs. The ever popular BF862 JFET for the input and a ZVN4306 MOSFET for the output stage. The bias runs between 50mA and 60mA which allows it to last about 4 to 5 hours on a pair of 600mAhr Li-ion rechargeable 9v batteries. The amp dissipates about 2w so never gets hot but makes a nice hand warmer for your pocket in the winter. "
  
 X posted the above summary of his amp today as part of this new thread:
 http://www.diyaudio.com/forums/group-buys/302859-xrk971-pocket-class-headamp-gb.html#post4966596
  
 The board being ordered will use both through-hole and SMT components in the circuit, and X says it will be easy to solder.  (I hope he's right for my sake!)

  
 Bonus!  The components are affordable--about $20..  Here is the Mouser BOM::
  
 ---------------------------------------------------------------
  
 Description Part No Qnty
 n-channel power MOSFETs ZVN4306GTA 2
 n junction JFET BF862 771-BF862-T/R 2
 Panasonic OSCON 390uF 20v output caps 20SEPF390M 2
 Output cap bypass WIMA 1uF MKS caps MKS2C041001F00KSSD 2
 Input bypass Wima 2.2uF MKS caps MKS2B042201F00JSSD 2
 Panasonic OSCON 100uF 25v rail caps 20SEP100MX 2
 Switchcraft 3.5mm stereo jacks 35RAPC4BV4 2
 Alps stereo pot with power switch RK0971221Z05 1

 Plus you will need the following 0805 1% metal thin film SMT resistors (qnty):
 33R(2), 47R(2), 270R(12), 1k(2), 15k(1), 47k(2), 100k(2), and qnty 4 x 100nF X7R 0812 MLCC bypass caps, and basic 3mm red or green LED.
  
 ---------------------------------------------------------------
  
 In case you aren't excited yet...here are some listening impressions from the prototype:
  
 "I have been listening to the Pocket Class A for an extended period now and have compared it to some world class head amps designed on this forum. I am happy to report that my listening impressions have not changed regarding how good it sounds. Being battery powered, it is utterly quiet and able to resolve some amazing low level detail when listening from a good DAC. My latest measuremts show an absolute flat noise floor devoid of 60Hz hum at -125dB and a dynamic range of 92dB - well matched to CD quality sound. I am using 47uF output caps at present so at 20Hz there is about a -2dB falloff but I plan on upgrading to a 390uF oscon output cap in the future. This should take the -3dB point to about 5Hz and give this amp the bass extension to meet any audio need. The one area where my "big amps" such as the Salas DCG3 and BF862 preamp with DAO buffer amp have an advantage is bass "slam" due to the fact that they have huge 18v to 20v dual rail multi-ampere power supplies. But for the rest of the music - this little amp surprises me all the time with how great it sounds. Natural, musical, easy on the ears, lively, not sterile, resolving, quiet when needed, expressive, accurate (due to flat response), most of all - enjoyable for hours on end. It beats all my other amps on noise. It is the quietest amp of all with only two transistors in a tight layout that doesn't pick up noise, and ultra quiet batteries to provide juice."
  
 and to sum it up:
  
 "Natural and very musical sound that is engaging, lively, never sterile."


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## Ike1985

I would be interested in doing a review of one of these if someone has a completed one they wouldn't mind sending. I'll pay insured shipping back as well.  I've experience with the ALO CDM, Chord Mojo and soon to be Hugo.


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## stellarelephant

ike1985 said:


> I would be interested in doing a review of one of these if someone has a completed one they wouldn't mind sending. I'll pay insured shipping back as well.  I've experience with the ALO CDM, Chord Mojo and soon to be Hugo.




I've signed up for two boards. Assuming that I'm successful with both builds, I'll have a loaner on hand!


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## Ike1985

stellarelephant said:


> I've signed up for two boards. Assuming that I'm successful with both builds, I'll have a loaner on hand!


 
  
 Excellent, I'd love to get word out about this little gem. I love these sort of projects.  Keep in touch!


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## stellarelephant

Yeah, I think this amp could make quite a splash, if it sounds anywhere near as good as the designer has made it out to be. 22 folks are going in on the initial GB, so that's promising.
  
 Ike1985, It looks like your IEMs are 16 ohms.  I *think* that this amp will give decent bass with a headphone impedance that low, but it may be less sub bass than you are used to.  X originally designed it to match his 250 ohm Beyerdynamic DT880s, and then he modified the deisign to pair well with most over-ear headphones.  Using the 390 uF output capacitors X is now recommending for the build, bass response will be essentially be very flat down to 20 Hz with any headphone of 50 Ohms or more.  With your IEM's there will probably be a little bit of low-end roll-off due to not quite meeting NvAvGuy's famous "1/8 rule" for impedance matching.  There is a way to predict the bass roll-off, which I just learned how to use!  Oh boy, lets do some math!
  
 I learned this from DIYA guru AndrewT, who posted this prediction for the Wintergreen amp with another user's 70 ohm cans, along with his formula here:
  http://www.diyaudio.com/forums/group-buys/302859-xrk971-pocket-class-headamp-gb-3.html
 Quote:
 "It's a passive single pole filter. Calculate the F-3dB
 It will have virtually no roll off @ 60Hz and probably no more than about -0.5dB @ 20Hz 
 F-3dB = 1 / 2PiRC = ~6Hz "
  
 R is the headphone impedance in Ohms and C is the capacitor value in Farads (which is 0.00039390F aka 390uF in this amp).  
  
 So for your 16 ohm IEMs...
 F-3dB = 1 / 2Pi(16 ohms)(0.00039F) = ~26 Hz
  
 If you'd rather cheat, here is an online calculator that does it for you...
 http://learningaboutelectronics.com/Articles/Cut-off-frequency-calculator.php
  
 -3dB at 26 Hz would be subtle but possibly audible, especially in the sub bass, at least.  Do you have any other cans to listen with?  I also may inquire at DIYA about using a larger output cap to pair better with sensitive headphones, although I'm not sure how big a cap will fit or whether if it may have any effect on sound quality in other ways.
  
 The ALO CDM looks insanely nice...did you part ways with yours?  How hot did that thing get?


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## Ike1985

stellarelephant said:


> Yeah, I think this amp could make quite a splash, if it sounds anywhere near as good as the designer has made it out to be. 22 folks are going in on the initial GB, so that's promising.
> 
> Ike1985, It looks like your IEMs are 16 ohms.  I *think* that this amp will give decent bass with a headphone impedance that low, but it may be less sub bass than you are used to.  X originally designed it to match his 250 ohm Beyerdynamic DT880s, and then he modified the deisign to pair well with most over-ear headphones.  Using the 390 uF output capacitors X is now recommending for the build, bass response will be essentially be very flat down to 20 Hz with any headphone of 50 Ohms or more.  With your IEM's there will probably be a little bit of low-end roll-off due to not quite meeting NvAvGuy's famous "1/8 rule" for impedance matching.  There is a way to predict the bass roll-off, which I just learned how to use!  Oh boy, lets do some math!
> 
> ...


 
  
 fascinating post, so much to learn. Thank you!
  
 The CDM was lent to me by a good friend on the forums.  It's incredible.
  
 I will review your post and come back with a more detailed response later, too late now to deciper that and I'm watching ufc!
  
 Bass rolloff is fine and may be just what the bass excessive-treble rolled off A12 needs.  I'll be getting an Empire Ears XR ADEL in a bit to so I'll be able to use that with the AMP if I get to demo it.
  
 Thanks again!


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## stellarelephant

PCBs are in the mail!  I'm awaiting two.  Here's a sneak peak from the one that the designer, Xrk971, recently completed.
  

  
 There has been some discussion on the DIYA thread about substituting different capacitors in this design.  I've decided on upgrading the power rail capacitors in my amps from 100uF Panasonic OSCONs to 1000uF Nichicon UKAs.  I'm told this will significantly lower crosstalk between channels.  For the output caps, I am going to upgrade from 390uF OSCON to a 1000uF OSCON.  *This will lower the output impedance to provide deep bass extension with all headphones, including low impedance cans.*  The treble frequencies are still handled by a 1uF WIMA film bypass caps, which I am not changing from the original design.  I am essentially stuffing my tins with the highest value capacitors that will possibly fit.  In order to accomplish this, I will have to mount the caps on their sides in this fashion and bend the leads a little funny, but it should work just fine and hopefully sound amazing.

 Can't wait to get started!


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## stellarelephant

This amp is now available as a complete and tested board, for those not interested in soldering.  Xrk971 is now building them himself and offering them for sale on eBay, and all you have to do is put the finished PCB in a mint tin and hook up to 9v batteries.  Pocket Class A Headphone Amplifier  
  

  
 Here are some highlights of this design he included in his listing:
  

*Ultra-low -126dB noise floor*
*Tube-like harmonic distortion profile with only 0.028% THD (1kHz 700mV into 270 ohms) that is predominantly second harmonic (90%) *
*Dynamic range of 94.2dB *
*Stereo Cross-Talk of better than -74dB*
*Flat frequency response from 15Hz to 40khz (+/-0.5dB)*


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## stellarelephant

My two boards arrived today!


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## bogde

stellarelephant said:


> My two boards arrived today!


 
 i got mine too. i also have all the parts, hopefully i'll be able to build one of them this weekend.


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## stellarelephant

Congrats, although I'm a bit jealous! I was busy and I only finally placed my Mouser and Digikey orders last night. I also picked up a new soldering iron off Amazon because I doubted my junky RadioShack iron would be up to the task of SMD work. Please keep us updated!


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## bogde

will sure do!


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## xrk971

Hi guys. Glad the boards made it safely to you so quickly. Morde (Finland) has first sound already. He's fast. 

Let me know if you have any questions with the build. 

StellarElephant - your matched FETs were sent out yesterday you should have it soon.


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## stellarelephant

Glad you're here, X!


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## xrk971

Have you guys seen the new data I took from an electrically quieter room?  The noise floor is now -126dB and flat no peaks/bumps at 60Hz. The amp is super quiet, like it is not even turned on when music stops playing (even on my 112dB/mW balanced armature Aurvana 3 IEM's I can't tell it is on).


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## stellarelephant

Awesome.  I figured that the noise at 60 Hz had to be from your home wiring since the amp is DC.  I own an EMF meter that is really fun to take around the house and "see" the fields generated by wall warts, fan motors, wiring, etc.  Definitely made me NOT want to put my bed near the breaker box.
  
 I'll edit the specs I have posted here and in the portable amp forum, to reflect your new results.


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## Lohb

A complete unit installed in the tin would be great...
  
 Great little project anyway!


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## xrk971

lohb said:


> A complete unit installed in the tin would be great...
> 
> Great little project anyway!




If that's stopping you from ordering I could throw in the pre-drilled tin and Kapton heat transfer tape.


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## Hutnicks

xrk971 said:


> If that's stopping you from ordering I could throw in the pre-drilled tin and Kapton heat transfer tape.


 

 Where the devil does one source Kapton tape?


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## xrk971

hutnicks said:


> Where the devil does one source Kapton tape?




Like almost all good things - just search Amazon, for example. The skinny stuff is cheaper and you could just add several strips to make wider. He wide stuff costs more by looks nicer. The adhesive on this tape is amazing. It's silicone based so never gums up or leaves residue. Can take direct soldering iron no fuss. 

https://www.amazon.com/gp/aw/d/B01LXKJXCW/


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## stellarelephant

Digikey has it, but buying an entire roll for $22 seems silly when only a few inches are needed.


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## Lohb

xrk971 said:


> If that's stopping you from ordering I could throw in the pre-drilled tin and Kapton heat transfer tape.


 

 I just meant if it's going commercial like other Altoid amp variant long-time sellers on eBay.


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## xrk971

stellarelephant said:


> Digikey has it, but buying an entire roll for $22 seems silly when only a few inches are needed.




It sounds expensive and it is. But make no mistake this stuff is the dream of plastics. I use it all the time for insulating my transistors from heatsinks instead of mica washers or silicone spacers. It will be handy for a lot of diy projects. OTOH, just use white paper masking tape. Works almost as well. Leaves residue. The blue painters tape looks better and doesn't leave residue. Anything is better than bare shiny metal. I should have tossed in a few inches of it for you gratis when I sent you the matched FETs. Sorry.


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## stellarelephant

Thanks, I should have thought to ask, but it's all good.  I have some frog tape on hand, as well as a little bit of leftover Rustoleum High Heat flat black enamel paint, meant for grills and woodstoves.  By the way, in case folks are wondering, we are talking about adding coatings to the inside of the mint tin to aid in the absorption and dissipation of heat by the metal tin.  Shiny metal with air space next to it is indeed a radiant barrier. 
  
 This cool infrared pic of a hot-water-filled "Leslie's cube" shows emissivity of different surfaces.  I think absorption should be directly proportional to emissivity.  What's surprising is that black and white paint perform relatively the same with this test (I guess color only matters with absorption of visible light).  But yeah, polished metal certainly doesn't like to transfer heat!


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## Hutnicks

xrk971 said:


> Like almost all good things - just search Amazon, for example. The skinny stuff is cheaper and you could just add several strips to make wider. He wide stuff costs more by looks nicer. The adhesive on this tape is amazing. It's silicone based so never gums up or leaves residue. Can take direct soldering iron no fuss.
> 
> https://www.amazon.com/gp/aw/d/B01LXKJXCW/


 

 Awesome, thanks for the info.


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## stellarelephant

X, I received my matched FETs in the mail today.  Thanks!
  
 By the way, I started another thread about the X's complete PCB version of this amp in the portable amp forum:
New Portable Amp - "Pocket Class A" by xrk971 - now available as complete PCB


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## xrk971

stellarelephant said:


> X, I received my matched FETs in the mail today.  Thanks!
> 
> Good luck on the build! It's easy really.
> 
> ...


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## Lohb

Is THE GB still live over at DIYA ?
  
 Luckily I know someone with solder/amp repair/builder skills.


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## xrk971

lohb said:


> Is THE GB still live over at DIYA ?
> 
> Yes we are on GB2.
> 
> Luckily I know someone with solder/amp repair/builder skills.


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## stellarelephant

Just got all my parts today...by some great stroke of luck, FedEx delivered my Mouser and Digikey boxes simultaneously. Hope to have an amp together soon. I got some tiny .015 solder I think will work well. But I am slightly concerned that the 1.5 mm tip on my new iron is a bit bigger than Ideal size. Time will tell!

X, FYI it looks like you are somehow posting your replies within the quote boxes, which makes your reply harder to spot.


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## xrk971

I actually use a pretty big 1/8in wide chisel tip to solder 0805's. Just add solder to one pad first, the take part and touch it solder pad and then solder other end.


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## stellarelephant

xrk971 said:


> I actually use a pretty big 1/8in wide chisel tip to solder 0805's. Just add solder to one pad first, the take part and touch it solder pad and then solder other end.




That's encouraging! I watched a few YouTube videos that show the exact technique you describe. Here we go...


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## xrk971

Happy soldering! If you make a mistake no big deal. Use solder wick to clean it up good as new. Be careful to use ESD protection when soldering FETs or once they are installed. Don't touch board in tin if lid open and you don't have a grounded wrist strap. I blew a few MOSFETs this way.


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## stellarelephant

Wow these bits are tiny. At least I have a nice big blueprint!


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## stellarelephant

I have a wrist strap. I just noticed that the BOM calls for a 15k resistor for the LED and I bought 12k. Will this work ok?

Edit: I looked and I indeed have 15k, as that is included in the DK BOM. But I also have 12k that I believe I added myself because I thought you, X, recommended?


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## xrk971

12k or 15k can work just limits current through LED. 12k is brighter glow but 15k is visible enough.


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## stellarelephant

Thanks. Have to go to bed, but I think my first six resistors look alright. More tomorrow! Is it normal for my joints to have a little sharp point on them from where I lift up the iron when done?


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## Lohb

stellarelephant said:


> Just got all my parts today...by some great stroke of luck, FedEx delivered my Mouser and Digikey boxes simultaneously. Hope to have an amp together soon. I got some tiny .015 solder I think will work well. But I am slightly concerned that the 1.5 mm tip on my new iron is a bit bigger than Ideal size. Time will tell!
> 
> X, FYI it looks like you are somehow posting your replies within the quote boxes, which makes your reply harder to spot.


 

 Will be looking out for your tweaked mousers parts results. I think you substituted out some parts for no low-end roll-off and better sweet-spot for 16 Ohms.
  
 To the designer, mass produce these in a custom CNC'd case (bigger battery capacity space) , a bit lower on the price, and you'll own this price/niche. Well done !


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## xrk971

Not sure about lower price though


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## stellarelephant

X did you see my quick question about the appearance of my solder joints? I have my iron set to around 350c, though who knows how accurate the knob is. It is my first time using 63/37. I get a little point on the top of each joint when I pull the iron away.


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## xrk971

Are you using tin/lead solder? Your point is too small to transfer enough heat to melt solder and have it wet and make a meniscus. Maybe use bigger tip or increase heat. Should not leave a tip like that. Not just cosmetic but indicates solder is not really flowing like a thin less viscous liquid to wet underside of SMT part.


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## stellarelephant

BTW I think that a CNC case and big li-ion battery would raise the reasonable asking price, not lower it! It would be sweet to see though, that's for sure!


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## stellarelephant

xrk971 said:


> Are you using tin/lead solder? Your point is too small to transfer enough heat to melt solder and have it wet and make a meniscus. Maybe use bigger tip or increase heat. Should not leave a tip like that. Not just cosmetic but indicates solder is not really flowing like a thin less viscous liquid to wet underside of SMT part.




I thought this might be the case, as I expected a smoother "bead" for each joint. Yes it's Kester 63/37 tin lead solder with rosin core. I'll crank the heat and see if that helps. Thanks.


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## stellarelephant

A bit more heat (looks like 375c) and a lot more practice, and my joints are looking better. All done with the SMT side!


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## xrk971

That looks good. You are halfway there. The through hole stuff is easy. Cutting holes in tin - if you don't have a paper hole punch is a pain. 

Good luck!


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## stellarelephant

Getting close on the through hole side. Switched to bigger solder for this side so I don't have to feed a mile of the thin stuff for each joint. I'm working in spurts when my son is napping lol. Hopefully I'll get sound tonight after he's down for the count. 

X, did you ever do a listening comparison with and without the WIMA output bypass caps? I think I'll try it. I am also planning to temporarily solder in some long wires so I can A/B different main output caps, by just attaching different caps with alligator clips. I have 3 to test...original 390uF Panasonic OSCON, 470uF Nichicon AK, and 1000uF OSCON. Should be fun to see if I can hear any differences.


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## xrk971

No I never compared without bypass Wima's. Wires with alligator clips is not best connection for sound quality. Maybe at least some header pin connector jacks for quick change.


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## stellarelephant

Its alive!  First impression listening to "Send it On" from Voodoo by D'Angelo: the bass is awesome!  Such ease...tons of power!  I'm feeding the Pocket Class A from the line out of my XDuoo X3, and it's driving my Sennheiser 598 cans quite loudly with the volume knob turned up probably less than a quarter of the way.
 I can't wait to have a long listening session to get acquainted with the sound.  I haven't even soldered in the output caps yet, and this thing already rocks.
  

  
 I've set up a quick and dirty way to compare the sound of different output caps using gator clips attached to wires temporarily soldered to the board...against X's cautions that it would sound crappy... So far I am just listening with 1000uF OSCONs, with no bypass yet, and I'm already pleased!

 I have the original 390uF OSCONs plus some 470uF Nichicon AKs I will be comparing with the caps I have clipped in there now.  Any of these caps will fit in the tin.  I also have the 1uF WIMA film bypass caps, which I'm eager to try.
 The contenders:


 This is my first amp build and my first SMT soldering job...I took my time and it works perfectly.
 Big thanks to xrk971 and BabyDontHertzMe.  I really appreciate all of your advice, X.
 Now I'm going to go revel a bit.


----------



## xrk971

Congratulations on a fine SMT soldering job and to get it to work the first time is so very cool. Enjoy it! Tell us more about the listening impressions when you have spent more time.

What is your bias current across the 4x460R resistor arrays? How well matched are they? Just curious if my matching job did the trick for you.


----------



## stellarelephant

xrk971 said:


> Congratulations on a fine SMT soldering job and to get it to work the first time is so very cool. Enjoy it! Tell us more about the listening impressions when you have spent more time.
> 
> What is your bias current across the 4x460R resistor arrays? How well matched are they? Just curious if my matching job did the trick for you.




I think you mean the 4x470R resistors. If I measured in the right spot, I get about 1.7V on both sides. They are very close...close enough that my ancient multimeter cannot resolve any consistent difference between channels. I think you nailed the transistor matching.

Doing more listening, still with the big caps only. This amp in this configuration adds warmth and BODY to the sound...exactly what was missing from the signal of my analytical xDuoo X3! I like it very much! It is not fatiguing in the least. Back to listening...


----------



## xrk971

Hmmm... you should be measuring about 5.8v across the four 470R resistors if the bias was 50mA. Your player sounded analytical because its opamp output cannot provide the power needed for balanced sound at high and low end.


----------



## stellarelephant

Wow! I do hear differences between the caps. Testing with two tracks. Liquid Spirit by Gregory Porter and So Familiar by Steve Martin and Edie Brickell, both in 24/96 FLAC. 

I've pretty much eliminated the 390uF OSCONs. The 1000uF sounds similar but slightly better, giving a bit more low bass extension and, oddly, more midrange body too. 

 The Nichicon caps surprised me. They are definitely more transparent in the treble. Less creamy. A bit grainier with vocals but far more resolving. OSCONs are smoother...warm and silky but they sound almost rolled off in the treble in this comparison. Nichicon is crisper with improved snap, clarity and sparkle. Bass is still present and nice, but with a tad less fatness and boom down low. Not quite as effortless the OSCONs, probably due at least in part to the fact that the Nichicon is only half the capacitance value. But the Nichicon has more bass texture and possibly more tightness. They reveal the "ropiness" of bass strings and buzz against the fretboard with acoustic bass. These are really treble details that are part of the bass instrument sound. As such, these advantages may be entirely lost with the addition of the 1uF WIMA film bypass, which will take over the treble from the main cap. 

I need to put the WIMAs in now and see what happens. I really wonder which cap will do the best in the bass department alone, when all the treble is handed off to a film cap more suited (or so I've read) for that purpose.

X, at what frequency does the WIMA take over the signal? Or am I wrong to imagine this in terms of a speaker crossover, with a fixed crossover point?


----------



## xrk971

It's the same RC time constant thingy you learned from AndrewT. Just apply the headphone impedance as R. It is like a crossover in that below a certain frequency the contribution of the Wima will be negligible. 

So assuming 250ohm headphones and 1uF film cap then 1/(2 pi R C) = 640Hz. The Wima's cover midrange on up. But since electrolytics go up high too there is paralllel coverage until the electrolytics fall off.


----------



## stellarelephant

xrk971 said:


> Hmmm... you should be measuring about 5.8v across the four 470R resistors if the bias was 50mA. Your player sounded analytical because its opamp output cannot provide the power needed for balanced sound at high and low end.




Well now my multimeter is telling me that my brand new dollar store 9V batteries are only 5.3V. Could that be the reason? I guess you get what you pay for eh?


----------



## xrk971

I use cheap carbon 9v batteries to test things as well. Mine actually measured 9v when new though 

Definitely get some rechargeable 9v (4 pack and charger is $22 on Amazon). They have more capacity than alkaline cells actually (600mAhr) and will allow you listen without burning through cash for batteries. 

Another option is to buy your own RC helicopter LiPo and smart charger circuit and DC to DC step up.


----------



## stellarelephant

I now suspect that the batteries are fine and my multimeter is malfunctioning. It's like 40 years old and has spent a few l subzero winter nights in my shop. It's measuring everything low and very inconsistently. Will borrow a friend's to test again. 

You are right, I need a rechargeable battery solution for economy and convenience. Have you found a suitable combination of parts to work as a li-po setup?

I'm still considering these as a turnkey solution. https://www.amazon.com/gp/aw/review/B01MYLHK7R/RZ9HPFLAKOGY6/ref=cm_cr_dp_mb_rvw_2?ie=UTF8&cursor=2 

I would drill another hole (or two) in the long side of the tin for micro USB and add some smaller holes on the short end to reveal the battery indicator lights on one cell....a handy addition. 

My big question is whether these batteries would still charge correctly without removing them from the amp. Would they be OK to charge if they remain connected in series? And could both cells be charged with a single Micro USB plugged into only one cell?

An Amazon reviewer confirms they can be charged through their regular terminals, so possibly connecting USB to one of them would charge that cell directly and send charge to the other cell through the terminals. But I don't know if this would somehow bypass the overcharge protection of one cell or if perhaps result in incomplete charging. 

"They can even be recharged in a standard 9V LiIon charger, if you prefer. Unlike one of the other brands, which has an inverter between the cells and the connector, and can generate noise in the connected circuitry, these have a charger with the battery connected directly to the terminals. They do not generate any electrical noise or RFI while discharging."


----------



## xrk971

Cool find - I did not even know these existed with built in charging port for microUSB. I am not sure if charging one charges the other, I doubt it because the cells are connected in series and do no make a circuit until power switch is turned on.

A little search shows you can get these for $13/pair if willing to wait for long shipment time from China.

http://www.banggood.com/2PCS-OKcell-9V-800mAh-USB-Rechargeable-Lipo-Battery-for-RC-Helicopter-Model-Microphone-p-1101430.html


----------



## stellarelephant

xrk971 said:


> Cool find - I did not even know these existed with built in charging port for microUSB. I am not sure if charging one charges the other, I doubt it because the cells are connected in series and do no make a circuit until power switch is turned on.




I get continuity as well as (inaccurate) voltage readings across the two batteries with the amp switched off. Am I missing sonething?


----------



## xrk971

Not sure what you are trying to measure with the batteries installed? The cells are connected in series, with the positive of one connected to the negative of the other. When power switch is off, it is an open circuit and if you probe the two ends (not the common +/- series connection), you should get sum of cell voltage circa 18v. When power turned on, the zero load voltage will drop a little but not much as current is circa 120mA total.


----------



## stellarelephant

Lol I get it now...the probes complete the circuit. Duh. Told you I was a noob!

Well for those batteries I guess having two separate micro USB holes in the tin would be fine. They'd charge faster that way anyhow. I'd just get one of these and two cables to charge with.

I'm still interested in your li-po option, if you think that would be more elegant.


----------



## xrk971

You might want a 2A capable USB charger as standard ones will take a long time. I am still working out details of the custom lipo option - nothjing definite yet. It's more complicated for sure. You need protection module, charging module, and DC step up module, oh and don't forget the raw LiPo battery. those things can catch fire at anytime too.


----------



## Hutnicks

xrk971 said:


> You might want a 2A capable USB charger as standard ones will take a long time. I am still working out details of the custom lipo option - nothjing definite yet. It's more complicated for sure. You need protection module, charging module, and DC step up module, oh and don't forget the raw LiPo battery. those things can catch fire at anytime too.


 

 No sweat. Circuit stack and a fusible link and you're good to go


----------



## stellarelephant

xrk971 said:


> It's the same RC time constant thingy you learned from AndrewT. Just apply the headphone impedance as R. It is like a crossover in that below a certain frequency the contribution of the Wima will be negligible.
> 
> So assuming 250ohm headphones and 1uF film cap then 1/(2 pi R C) = 640Hz. The Wima's cover midrange on up. But since electrolytics go up high too there is paralllel coverage until the electrolytics fall off.


 
 *Head explodes*  Dang, you are an electronics ninja.  With this in mind, do you think I ought I to consider a larger WIMA bypass cap to pair with my 50 ohm headphones, to get more midrange clarity?  Wow, so for my 50ohm cans, the 1uF WIMA won't come into play until 3200Hz.  In order to get the same -3db on the bypass as you (640Hz), I'd need around 5uF.  That's probably much bigger size.  But at least the 2.2 uF caps I have purchased for my second amp are the same size.  This is all very fascinating to me.  Also, if I want to experiment with more gator clips (I know, I know 
	

	
	
		
		

		
		
	


	




) could I hook up 2 of the 2.2uF WIMAs I have in series and get the same effect as a 4.4uF bypass?


----------



## xrk971

I only was hoping Wima's kick in above 6k or so for the treble. You want to wire caps in parallel for them to sum up. They decrease in value when in series, like resistors decrease when in parallel. I think 1uF Wima's and 3200 Hz doe 30ohm cans is fine. It wa small a tradeoff of compactness. Some people like using 50uF film caps.  look up motor run caps. You can get oil filled film caps 50uF for cheap. They sound nice too but are the size of car spark coil.


----------



## stellarelephant

Cool. I think I'll try playing around with the different combos, throwing in 1uF, 2.2uF, and 4.4uF (2x paralleled 2.2uF) to see how they affect the sound. Vocals tend to have quite a bit of info around the 2kHz region... it'll be interesting to see if dropping the "crossover point" (bad analogy, I now know) below this region yields significant differences to my ears. Vocals are what I always tend to listen to most when judging realism and transparency for any sound system.


----------



## Hutnicks

xrk971 said:


> I only was hoping Wima's kick in above 6k or so for the treble. You want to wire caps in parallel for them to sum up. They decrease in value when in series, like resistors decrease when in parallel. I think 1uF Wima's and 3200 Hz doe 30ohm cans is fine. It wa small a tradeoff of compactness. Some people like using 50uF film caps.
> 
> 
> 
> ...


 

 Pair em up with wire wound resistors and you have a backpackable solution. Cooling then becomes a moot point.


----------



## stellarelephant

Rofl


----------



## xrk971

hutnicks said:


> Pair em up with wire wound resistors and you have a backpackable solution. Cooling then becomes a moot point.




What are you talking about? The amp already fits in a pocket and has no cooling issues with metal thin film SMT resistors.


----------



## stellarelephant

He was riffing off your motor run caps joke


----------



## stellarelephant

Wow. I love this amp. After a ton of experimentation, I've found a killer output capacitor combo to match my 50 ohm Sennheiser 598 headphones. 

Bass has excellent weight and texture. Mids are rich and electrifying. Vocals are wonderfully engaging--right in my face--in a beautiful, hyper-real way that is totally addictive. Treble is not quite as transparent nor as extended as the Class D amp circuits I am used to, but treble detail is still magically present, with a gorgeous euphonic sparkle. Overall the sound is full-bodied, detailed, attention-grabbing, and just downright sweet. ...And mine isn't even entirely soldered together yet, let alone burned in!

Everything else sounds boring now. X, you've made a true believer out of me. SE Class A magic is real. 

I am using 470uF Nichicon AK series electrolytic output caps with 2.2uF WIMA film bypass. Try it...you'll like it.


----------



## gikigill

Anyone selling a fully built unit?


----------



## xrk971

Fully built with matched FETs and tested and burned in pocket class A headamps are $199:
  
 http://www.ebay.com/itm/-/222413187019?


----------



## bogde

it was a good day today. i managed to fix my first board and finished building the second one, plus managed to install one of the boards in an altoids tin. everything worked out better than i expected. this amp sounds great and can power my dt990 pro just fine, not to mention the hd598cs. i'm yet to test it with my other cans but i don't expect any issues. thanks @stellarelephant for bring this up here on head-fi!


----------



## stellarelephant

Congrats Bodge! I was wondering how you were coming along with your build(s). What did you have to fix on your first board?

Your soldering work looks better than mine! Have you done a lot of DIY before? 

I love the sound this amp lends to my (open) 598 SE cans...I've never heard the Closed CS version but I hope you are getting some of the same awesome synergy I am! I am subbing a different output cap combo as described above, which really brought vocals to life for me.

I'll be interested to hear your impressions of the sound, and I'm especially curious about whether you'll notice any burn-in.

Cheers!


----------



## bogde

stellarelephant said:


> Congrats Bodge! I was wondering how you were coming along with your build(s). What did you have to fix on your first board?
> 
> Your soldering work looks better than mine! Have you done a lot of DIY before?
> 
> ...


 
 thanks! one of the mosfets was defective, apparently, i just replaced it and then it worked like a charm. 
  
 you did a great job with your build actually, having in mind you only used a soldering iron. i used a cheap hot air soldering station (gordak 952) and i it was a lot easier. i've done some soldering before, but i wouldn't say i'm very experienced.
  
 i joined GB2 and i can't wait to get two new boards to play with, i plan to experiment with different caps, just like you did. i just tried my ma900 with this amp and it's a great pairing. i'll let you know if i notice any burn-in. cheers!


----------



## xrk971

Bogde,
 So glad it was all fixed and sounding nice now!  Congratulations.
  
 Great soldering skills by the way - you look like a pro.


----------



## bogde

xrk971 said:


> Bogde,
> So glad it was all fixed and sounding nice now!  Congratulations.
> 
> Great soldering skills by the way - you look like a pro.


 
 thanks! in fairness, that's a picture of the second board, the first one looks messier. i'm happy with both though. eva cassidy sounds simply stunning through this amp into my ma900.


----------



## stellarelephant

Just ordered components for a rechargeable battery setup for my Pocket Class A.
  
 The setup will go like this:
 1) Apple USB Wall Charger, 5V, 1A (I already own this)
 2) iFlash Micro USB Splitter Cable ($8 on Amazon)
 3) 2x OKCell 800mAh LiPo USB-charging Batteries ($12 on AliExpress)

 I really like the idea of being able to charge without taking the batteries out of the tin.  If I punch two extra holes in the side of the tin, I'll be able to plug the micro USB cables in there.  I am not positive if the green charge indicator lights glow only during charging, or also during use, but I may also drill some tiny holes in the tin next to the indicator lights on one cell, so that they will be visible from the outside.
  
 I read an Amazon review of these batteries wherein the buyer stated that the actual capacity of the cells is closer to 400mAh.  I'll still be satisfied with around 3 hours of listening time, if this is the case.  On the other hand, if the advertised capacity of 800mAh is true, then I could get over 5 hours of operation.  They are advertised as reaching full charge in 1.5 hours via the internal charging circuit.  My 1 Amp Apple charger should provide almost enough current for maximum speed charging.  I calculate that if the cells are really 800mAh each, it should take 1.92 hours to charge them both fully.  Not bad.


----------



## stellarelephant

xrk971 said:


> Hmmm... you should be measuring about 5.8v across the four 470R resistors if the bias was 50mA.


 
  
 I re-measured voltage across the four resistors at 4.9V using a new multimeter that my friend gave me.  This is with two half-drained cheapo batteries (measured at 7.2V each just before the test).  What's more--Left and Right channels are perfectly matched, closely enough that any difference is beyond the resolution of my multimeter.  Nice job matching the transistors, X!


----------



## Lohb

stellarelephant said:


> Just ordered components for a rechargeable battery setup for my Pocket Class A.
> 
> The setup will go like this:
> 1) Apple USB Wall Charger, 5V, 1A (I already own this)
> ...


 

 Is there no way to source higher capacity batteries seen in retail amps ?
 I just had to pull my battery in my 2011 tech iBasso PB2 yesterday...

 to prep. for a new one and it did up to 20 hours playback new, though not pure class A.
  
 I think these single cells on 2017 amps are 2500-3000mAh and up maybe, and with Class A this amazing little amp idea going to eat new 400s....3-6 months down the line and half life probably.
  
 I actually use an external battery as well with a 16v SE LPS dongle (32v balanced) that has 8000mAh capacity.
 Energizer could be another way to power it, but it becomes transportable vs truly portable.
  
 ( Photo from member zilch0md )


----------



## xrk971

Looks nice if you can leave it inside case. The LEDs probably only light when charging. There are 2Amp chargers ( square blocks / iPad etc). I don't think 1A charger will be 2hrs for both. You have 5v to 8.4v dc to dc converter, and 800mAhr x 2 cells. Probably closer to 3hrs. My EBL's take 5-6hrs with supplied wall charger.

If you want to roll your own rechargeable batteries. Look for LiPo 3.7v 3000mAHr packs (they have built in protection board). Add dc to dc step up module and adjust it for 16.5v output. Add USB 5v charger module and that would do it. Might not fit in Altoids tin anymore though - those batteries tend to be wide and flat. All available on eBay or Ali.


----------



## xrk971

Some recent work on the amp to make it the NHB (no holds barred) Uber version. Larger input caps 10uF now bypassed with 100nF 100v film caps. Larger 470uF Nichicon AK's on output now bypassed with 2.2uF Wima's. Bass extension now measured to be -0.5dB at 10Hz. 

More here 

http://www.head-fi.org/t/837656/new-portable-amp-pocket-class-a-by-xrk971-now-available-as-complete-pcb/15#post_13337201


----------



## stellarelephant

Pics not showing up for me.  Luckily HF lets you edit posts forever, as far as I can tell.
  
 I love the NHB acronym. 
	

	
	
		
		

		
		
	


	




  That's my mindset now too.  I love the sound of my Pocket Class A.  Now that I have gotten a taste for the effects of cap rolling, I'm obsessed with exploring the options.  I just want to see how far I can push it to the limits!  Doing so while still fitting it in a tiny mint tin is a real challenge!
  
 Your first impressions of the Nichicon output caps on DIYA looked positive, X.  Have you formed a preference for those or the OSCONs?


----------



## xrk971

I keep forgetting that HF has different image requirements than DIYA.  The problem is, it shows up fine on my browser so I don't have any indication it is not working. I think HF has max image size of 1000 pixels x 700 or something like that.  My image links are pointing to DIYA where they are typically 1024x768 which is a standard size medium res image.  I don't know anyone who uses 1000 pix wide a a standard.
  
 Here are revised (downsized images):



  
 Btw, this NHB Convertible (desktop capable) amp now belongs to member gikigill of HF - so I will not be having it with me much longer as it is shipping out tomorrow. So sad - one of the best sounding amps ever. Congratulations to gikigill on his new amp!
	

	
	
		
		

		
		
	


	



  
 I do like the Nichicon AK's a lot - although some aspects of the Oscons are nice as well. It really comes down to user preference.


----------



## funch

Finally got time to build my first one. It's configured bone stock. Worked first try.

 My first listen was using the headphone out jack from my laptop, into an old pair of 
 Senn. HD 497's. Sounded good, but not great. 

 Then I decided to see what it would do with good stuff, so used my Yggy DAC as 
 source, into a pair of mod'ed HD800's. 

 What I can say is without reservation is that this little hand warming wonder 
 definitely scales with better source and 'phones, because the second configuration
 is sounding like a giant killer. Very dynamic and resolving, and it's not even broken
 in yet.

 If this is how good it sounds stock, I can't wait to hear it with upgraded components.
 I'm going to build my second one stock also, but the two I have coming are going to
 get the VIP treatment. I'm planning on building one optimized for low-impedance cans,
 and the other for high-impedance.

 xrk971, this design is proof positive that one doesn't have to spend mega bucks to get
 excellent (trans)portable sound. Outstanding job my friend.


----------



## xrk971

Hi Funch,
 So glad you got it working - it's a snap to build isn't it?  
  


> What I can say is without reservation is that this little hand warming wonder
> definitely scales with better source and 'phones, because the second configuration
> is sounding like a giant killer. Very dynamic and resolving, and it's not even broken
> in yet.
> ...


 
  
 Thank you for the kind words. 
	

	
	
		
		

		
		
	


	



  
 I have dozens of headphone amps, some very nice ones, but I keep finding myself using this simple ol' little amp again and again. I would love to get a different pair of headphones to see what the effect of phones might be.
  
 So far, I know of people using it with the following, and all have loved the sound.
  
 - HD600
 - LCD-2 (70ohm)
 - DT880-250
 - DT770-250
 - MDRV6
 - HD800
 - HD598-50


----------



## stellarelephant

Oh wow, you paired it with reference level gear!
  
 Quote:


> Originally Posted by *funch* /img/forum/go_quote.gif
> 
> Then I decided to see what it would do with good stuff, so used my Yggy DAC as
> source, into a pair of mod'ed HD800's.
> ...


 
  
*"Sounding like a giant killer."*
 Yep.  It lifts my modest budget-fi setup into a _completely_ different league.  I can only imagine what you're hearing!
  
 I've been obsessing over the upgrade possibilities, scouring Mouser for alternate parts that may be suitable for hot-rodding this little amp.
 But I already love the sound exactly the way it is...and mine is held together by alligator clips, lol.  I imagine that I'll hear improvements just by eliminating the inductance of the inch-long copper wires I have my output caps temporarily attached to!
  
 Hey, X, the reason your linked images from DIYA are not working here is because only a logged-in DIYA member can access pics hosted on DIYA.  Found this out the hard way when I tried the same thing.


----------



## xrk971

> I've been obsessing over the upgrade possibilities, scouring Mouser for alternate parts that may be suitable for hot-rodding this little amp. But I already love the sound exactly the way it is.


 
  
 The hot rodding is fun because this amp, like a 1960's muscle car with a large open engine bay and lots of room for hopping it up.  The improvements are sometimes audible, sometimes not.  Silmics are probably a good idea to try.  But you know, it's tough to beat a Wima 2.2uF MKS film cap.


----------



## funch

Team Silmic here.


----------



## xrk971

Alright, I have a Mouser shopping cart open and filling it with various sizes of Silmic II's.


----------



## funch

I found a way around the mint tin limit on cap size. Yah, I know, we're adding more cost, but ....... . Comes in four colors to match your decor too. Sorry, no free mints though.
  
 http://www.hammondmfg.com/pdf/1455J1201.pdf


----------



## gikigill

If it can power an LCD-2, it's pretty much perfect for everything.


----------



## bogde

i've been using mine with my HE400i and Q701s lately, both sound great. i really like how the Q701s sound with this little amp. i also tested the DT990 pro, AKG K240, Sony MA900, HD598Cs - all are powered just fine.
  
 X, do you mind posting mouser links for the caps you used (input 10uF caps, 100nF 100v film caps, 470uF Nichicon AK)? thanks a lot!


----------



## xrk971

Hi Bogde,
Wow you have a lot of nice headphones that you tried out. Glad they all work well. The 10uF and 100nF caps I used were not name brand or anything (CBB 100nF 100v MKT - but they work well) If I were to make it over again I would use 4.7uF Silmic II on the inputs with Wima or Vishay 100nF 100v MKT. let me put together a list of what I would call premium components for the larger caps. The Nichicon AK 470uF 16v cap on the output was suggested by StellarElephant.

On most of my personal projects I tend to use pretty inexpensive but high value components. The stuff for others I usually use name brand components. But for low ESR caps I definitely am a believer in Panasonic OSCONs. Those 390uF output caps are way more expensive than a comparable Silmic.


----------



## xrk971

Bogde,
 Since you requested it, here are some choices to play with - these are for the input and output caps and bypass.  All top-shelf name brand stuff here. Elna Silmic II on electrolytic duty and Wima MKS film on bypass. Also, there is the Nichicon AK on the output if you like. Pair that with a 4.7uF Wima for some astounding bass and clear highs with lush smooth mids.  For $12 it's cheap thrills and lots of fun listening to differences.
  
 Have fun!
  
*http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=3478bcb1a3*


----------



## bogde

thanks a lot for all the details!


----------



## xrk971

Running List of Headphones successfully tested with this amp. Please edit list and update with your own setup. _Include source if possible._
  


> - AKG K240 (Bogde)
> - HD600 with Apollo 8 Blackface (John H. personal communication to xrk971)
> - LCD-2 (70ohm) (Morde)
> - DT990 pro (Bogde)
> ...


----------



## bogde

> - AKG K240 (Bogde)
> - HD600 with Apollo 8 Blackface (John H. personal communication to xrk971)
> - LCD-2 (70ohm) (Morde)
> - DT990 pro (Bogde)
> ...


----------



## bogde

i added the HE400i and AKG Q701s. i removed the HD800, as, unfortunately for me, I don't have those.
  
 i gave my trinity phantom sabres a try with this amp today, just for kicks. with no music playing, i have to go to about 1 o'clock until i hear _any_ background noise. at that volume i can only listen for a few seconds anyway, so i think that's really, really good. as for the sound, i can't do a real A/B test, but it seems to be just as good as my fiio e12a, which is an amp designed specifically for IEMs.


----------



## stellarelephant

Finally got my first board in a tin! Couldn't resist the dragon on the Newmans ginger mints. I am finally mobile and enjoying the heck out of my new stack. The midrange fullness, dynamic impact, and overall engaging sound is excellent. I tried it today as a preamp with my DIY boom box, too. Same great results. It really fleshes out the sound. 



Hole punch on the tin worked out very well. I used a round chainsaw file to enlarge the pot hole. Drilling the LED light went OK but the edges are a tad ragged if you look close. I punched it first with a hammer and nail and then worked up through drill bit sizes. The largest bits tore a bit too much. 

I mounted my board upside down in the tin for stacking convenience with my X3 DAP. This aligns the line out jack with the amp input jack. I mounted the board as low as possible in the tin so that the jacks wouldn't hit the lid lip. In fact the SMT side is flat against the bottom (I covered the bottom with electrical tape). If I had made the holes just a tad higher so the jacks nested up under the lid a tad, Would have been better off. As is, the holes are so low that the board won't sit flat against the bottom...I had to tilt it downward towards the edge.. Because it is wedged in there, the knob protrudes at a slightly download angle. Not perfect, but I can live with it! At least it stacks as planned. 

I am currently running mine with no bypass cap on the output for now. More on this later...


----------



## xrk971

Nice work! I am surprised you were able to mount upside down and volume knob doesn't rub the lid. Looks great. You need sone real batteries my friend. Those are $ store 9v carbon zinc cells.


----------



## Lohb

Could 2 of these boards run dual-mono ?


----------



## xrk971

You mean like a bridged amp?


----------



## stellarelephant

I wanted to post my listening notes for the capacitor options I've listened to over the past few weeks.  I'm including the listening test I did for the last few days with the Nichicon 470uF output caps soldered in place instead of temporarily attached (I believe this cleaned up the signal a bit).  I don't know why I ever bothered using the wires and gator clips.  I found that with them removed and the main caps soldered in, it was much easier to just pressure fit the different bypass caps in place.  I did this from the SMT side of the board, where there was tons of clearance.  I was surprised, but the parts made good contact just placed in the holes.  These impressions were based on listening with Sennheiser HD 598, which have an impedance of 50 Ohms.
  
 1000uF OSCON - no bypass
 -bass effortless
 -vocals fuzzy
 -smooth
  
 360uF OSCON - no bypass
 -more treble
 -less mids and bass
 -smooth
  
 470uF Nichicon AK - no bypass
 -sharper transient attacks, most transparency
 -most treble details and midbass texture
 -most balanced sound
  
 ---after soldering in the Nichicons---
  
 470uF Nichicon AK - no bypass
 -even treble throughout vocal region
 -decent treble clarity, hint of graininess
 -I wish there was a bit more HF extension
 -tightest, most coherent overall sound
  
 470uF Nichicon AK - 1uF WIMA MKS
 -more treble, smoother
 -best high treble of all combos tried
 -less tightness/coherence
  
 470uF Nichicon AK - 2.2uF WIMA MKS
 -more high treble than no bypass, but less than 1uF bypass
 -smooth
 -vocals full-bodied and pleasantly forward in mix
 -still less tightness/coherence
  
 Take it all with a grain of salt.  These are all sighted comparisons.  But after considerable back and forth sighted testing, my current favorite is NO bypass cap.  Even though both bypasses brought forward the treble nicely, I found that they added a very subtle "something funny" or perhaps a null (?) in part of the vocal range.  It almost sounded like a phase issue, where there is cancelling or disagreement rather than coherence.  Maybe I was hearing impedance anomalies at the low corner frequencies of the bypasses...I don't know, or maybe I'm just distinguishing the "hand off" between electrolytic and polyester.  I envy you guys with 250 ohm cans...that puts the corner frequencies of your bypass caps WAY lower, perhaps getting such issues out of the MOST sensitive range of human hearing, the 2-5kHz "vocal presence" range, which is where they occur for me with my 50 ohm cans.
  
 OTHER BYPASS OPTIONS
  
*Larger WIMA MKS*
 One option for me is to use a larger WIMA MKS.  X already thought of this of course 
	

	
	
		
		

		
			




 Even the 6.8uF MKS (14mm tall) will fit in my tin with the way I mounted my board so low!  I'm going to try 3.3uF, 4.7uF, and 6.8uF.  6.8uF would reach down to 470Hz!  I don't think I would hear the subtle "hand off" down that low.  Still, I am a tad skeptical about this strategy, since according to WIMA, the bigger the cap, the worse the dissipation factor at high frequencies. 
 See here: http://www.wima.com/EN/mks2.htm  Hopefully this increased dissipation will be inaudible, but I _think_ I can already hear more high treble from 1uF vs. 2.2uF, so we will see if this is a trade-off with higher capacitance.  Have you tried any of the 4.7uF size yet, X?
  
*Smaller WIMA MKS*
 Another option would be to push my bypass corner frequency _above _the delicate vocal region, closer to 10kHz.  I could accomplish this with a .33uF bypass.  I could still use a MKT but I'm looking at some other options too.  WIMA themselves do not actually recommend MKS caps in the signal path for audio circuits, though I know that they are often used this way with success anyhow...see pg. 7: http://www.tawelectronics.com/wima/WIMA%20Audio.pdf
  
*Smaller Vishay MKT*
This 0.33uF Vishay MKT cap would fit.  Still polyester.  I don't know how these sound compared to WIMA MKS.  If I'm reading the graph on its datasheet correctly, it has a dissipation of 0.01 @ 10 kHz, a smidgen better than the WIMA spec which is .015.  But Vishay also provides more precise measurement data, so it's probably insignificant.  Anyhow, this comparison ranks them a tad higher than MKS: http://www.humblehomemadehifi.com/Cap.html  If fact, he actually mentions good coherence in his impressions.  They are slightly different cap series though.  He compared MKT1822 and MKS4, with wider lead spacings and perhaps other differences.  I'll be comparing MKT370 and MKS2 series.
  
*Smaller WIMA MKP*
 Hey, why stick with Polyester if I can fit a Polypropylene of the same .33 uF value?  I _think_ I can cram this WIMA MKP2 in there, but Mouser calls it a "RF Microwave Film Capacitor" and its datasheet does not mention bypass as an application, nor are they mentioned in the "WIMA for Audio" doc.  Hmm.  What's the difference between MKP2 and MPK4...just size I hope? 
  
*Smaller VISHAY MKP*
 This is a long shot for me, but I've drooled over the Vishay MKP polypropylene caps a bit, which are very highly recommended in the Humblehomemadehifi resource.  Sadly, I think the only one I can fit would be this puny .12uF cap.  Not sure if I'd hear anything at all, since the -3db point (corner frequency) with my 50 ohm cans would be way above human hearing range at 26kHz. 
	

	
	
		
		

		
		
	


	




  Still, for folks with higher impedance headphones, this could be a worthwhile upgrade experiment.  Corner frequency is down to 5kHz for 250 ohms.
  
 Please share your thoughts if you have experience with any of these caps!


----------



## Lohb

xrk971 said:


> You mean like a bridged amp?


 

 I guess so, I just mean true balanced  end-to-end.
  
  
 You should really launch this little beauty on kickstarter, then you can get a really excellent mass order CNC'd case for the amp and bulk order battery.
 My 2100mAh battery for my iBasso PB2 is $20 plus shipping. Quite a good capacity.


----------



## stellarelephant

lohb said:


> You should really launch this little beauty on kickstarter


 
 +1!!!  My brother runs a killer freelance video production firm, btw.  Just sayin'...
Megaffect Production Reel


----------



## bogde

you guys are probably aware of this, but i thought i should post it anyway, maybe it will help somebody. for the led hole something like this works out great: http://www.ebay.com/itm/Fiskars-Crafts123740-1001-Teresa-Collins-Hand-Punch-1-8-Inch-123740-1001-/262816786454
 the 3mm led fits perfectly through the 1/8" whole. and, just like with the 1/4" model, the parts that may stand in the way, like the paper holder (see image), can easily be removed.


----------



## xrk971

lohb said:


> I guess so, I just mean true balanced  end-to-end.
> 
> 
> You should really launch this little beauty on kickstarter, then you can get a really excellent mass order CNC'd case for the amp and bulk order battery.
> My 2100mAh battery for my iBasso PB2 is $20 plus shipping. Quite a good capacity.




I don't quite know what balanced headphone outs mean. Normally in amplifier terminology, balanced inputs are what pros use for long cable runs of signals where there is a positive and negative so that CM noise cancels out. But it seems like balanced headphone outs mean separate mono block amps with separate cables to each channel? The amps currently share a common power bus and ground internally. If you paralleld the amp outputs you could drive twice the current but same voltage. So for current hungry cans this would be good. 

I am testing a prototype with a dedicated LiPo and charging system and dc to dc step up converter to get 16v from the 3.7v 2600mAh LiPo cell. 

The kickstarter route is interesting. So is not having a slick looking CNC'd case stopping you guys from getting an amp like this that has superb sound quality? By all accounts, the reviews that have come in so far have been very positive with regards to sound quality and ability to drive a wide range of headphones and do it well.


----------



## xrk971

stellarelephant said:


> I wanted to post my listening notes for the capacitor options I've listened to over the past few weeks.  I'm including the listening test I did for the last few days with the Nichicon 470uF output caps soldered in place instead of temporarily attached (I believe this cleaned up the signal a bit).  I don't know why I ever bothered using the wires and gator clips.  I found that with them removed and the main caps soldered in, it was much easier to just pressure fit the different bypass caps in place.  I did this from the SMT side of the board, where there was tons of clearance.  I was surprised, but the parts made good contact just placed in the holes.  These impressions were based on listening with Sennheiser HD 598, which have an impedance of 50 Ohms.
> 
> 1000uF OSCON - no bypass
> -bass effortless
> ...





Thanks for the detailed listening impressions of the various setups. Be warned that not soldering in the bypass cap may not give proper results. The HF's being transmitted by the bypass depends on a good solder joint for low impedance. I am surprised you get anomalies with bypass installed and say it doesn't sound as good. This is probably due to improper connection. Think of it as the worst case of a cold solder joint! Bad for sound quality. 

I tried the Silmic 100uF and 1uF Wima in controlled AB testing with an AB switch box and could not hear the difference - except for loss of a small amount of bass extension due to 100uF vs 390uF size. 

I think you should solder one of the 1uF Wima's in place and listen again. Use the Nichicon AK that you like so much. It should sound balanced with nice mids and highs. 

So for now - I am not sold on Silmics vs Oscons.


----------



## stellarelephant

You really believe that simple pressure fit contact isn't good enough to judge SQ by? That's how the headphones connect in the headphone jack... is there a difference?

I can't wait for my USB-rechargeable batteries to come. Very cool that you are prototyping a big rechargeable option, X. 

No perceived treble difference between Silmic and OSCON, eh? We should see what max value Nichicon KZ Muse would fit. These top-of-the-line caps are known for clarity and seem to be preferred by some folks above all other electrolytic caps, except perhaps the legendary Black Gates.


----------



## Lohb

xrk971 said:


> I don't quite know what balanced headphone outs mean. Normally in amplifier terminology, balanced inputs are what pros use for long cable runs of signals where there is a positive and negative so that CM noise cancels out. But it seems like balanced headphone outs mean separate mono block amps with separate cables to each channel? The amps currently share a common power bus and ground internally. If you paralleld the amp outputs you could drive twice the current but same voltage. So for current hungry cans this would be good.
> 
> I am testing a prototype with a dedicated LiPo and charging system and dc to dc step up converter to get 16v from the 3.7v 2600mAh LiPo cell.
> 
> The kickstarter route is interesting. So is not having a slick looking CNC'd case stopping you guys from getting an amp like this that has superb sound quality? By all accounts, the reviews that have come in so far have been very positive with regards to sound quality and ability to drive a wide range of headphones and do it well.


 

 IMO wrapping it in Altoid does it no favours.
 Altoid amps already have the well established image of 'entry-level fun $70 hack amps' even though this is an entirely different topology amp....
 Even the Bluebird amp designer is in to solid billets of machined aluminium now at that $59 price-point.
  
 External design aesthetics are a strong consideration over $100 mark.
  
 https://www.aliexpress.com/item/2016-NEW-Bluebird-amp-portable-headphone-amplifier-U6-PLUS-OPA2604-5V-USB-charging/32665824920.html?spm=2114.01010208.3.2.a1rk3H&ws_ab_test=searchweb0_0,searchweb201602_4_10065_10068_433_434_10136_10137_10138_10060_10062_10141_10056_10140_10055_10054_128_10059_10099_10103_10102_10096_10052_10053_10050_10107_10142_10051_10106_10084_10083_10080_10082_10081_10110_10111_10112_10113_10114_10078_10079_10073_10070_10122_10123_10124,searchweb201603_13,afswitch_1,ppcSwitch_5,single_sort_0_default&btsid=2447d302-4d31-428b-8860-a46d13e30934&algo_expid=dc789155-f704-4de7-8046-fd814c12bf54-0&algo_pvid=dc789155-f704-4de7-8046-fd814c12bf54


----------



## xrk971

Lohb,
Thanks for the feedback. I am indeed already working on a prototype for future release as a commercial product that is wrapped in a very nice case. It's still a ways off though but will look very different and be more cool looking than anything out there. 

I see your point about the case though and the perceived DIY essence of a hack job CMOY amp even though this amp is much much more. 

Never knew about the $59 Bluebird special. Wow, how do they do that for that price? Thanks for the tip.


----------



## xrk971

stellarelephant said:


> You really believe that simple pressure fit contact isn't good enough to judge SQ by? That's how the headphones connect in the headphone jack... is there a difference?
> 
> I can't wait for my USB-rechargeable batteries to come. Very cool that you are prototyping a big rechargeable option, X.
> 
> No perceived treble difference between Silmic and OSCON, eh? We should see what max value Nichicon KZ Muse would fit. These top-of-the-line caps are known for clarity and seem to be preferred by some folks above all other electrolytic caps, except perhaps the legendary Black Gates.




You have a point but headphone jacks are designed for make-break connections with spring pressure contacts etc. here you have pressure or friction fit tinned legs on tinned through hole on PCB. Probably fine but to be sure solder it. You an reverse with a solder sucker.


----------



## stellarelephant

I have desoldering braid but that's it...kinda a pain. I think I'll try some other bypass options first and then solder in my favorite. Did you try the bigger WIMAs out yet?


----------



## xrk971

You really should get a solder sucker. Critical tool like screwdriver etc. braid won't get solder out of a hole. 

I tried 2.2uF Wima's with Nichicon 470uF AK's on the outputs on gikigil's NHB unit. It sounded very nice.

Get these they work well. 

https://www.amazon.com/gp/aw/d/B01C70X7V4/


----------



## tomb

> <snip>
> You really should get a solder sucker. Critical tool like screwdriver etc. braid won't get solder out of a hole.
> </snip>


 
  
 Sorry, saw this passing through.  Braid will easily get solder out of a hole, if used correctly.  Use it on both sides of the pad.  If that doesn't work, fold the tip into a point small enough to fit into the hole.  If that doesn't work, add a bit of solder back to the hole and let the wicking action pull it out completely.  Almost without fail, the solder inside of a pad hole is simply a thin film anyway.
  
 There is a place for a solder sucker, but most of the time with what we do around here, it's a sledgehammer applied to a tiny finish nail.  I use one, but only in cleaning up horribly soldered repairs for other people.  I made do without one until I started doing that last year.


----------



## Lohb

xrk971 said:


> I don't quite know what balanced headphone outs mean. Normally in amplifier terminology, balanced inputs are what pros use for long cable runs of signals where there is a positive and negative so that CM noise cancels out. But it seems like balanced headphone outs mean separate mono block amps with separate cables to each channel? The amps currently share a common power bus and ground internally. If you paralleld the amp outputs you could drive twice the current but same voltage. So for current hungry cans this would be good.


 
 Various levels of design classed as balanced, true end-to-end input to output....Some take single-end input and output balanced to the likes of 4-pin XLR with no shared ground like speaker output
 So in the case of iBasso PB2 the voltage goes from 16v to 32 volts running balanced out over the 3.5" out.
  
 Planar magnetic headphones seem to get better sound-staging/instrument separation/dynamics over single-end though not always.
 SE can be as good or better than balanced, it just depends on topology but I'm rabbiting here to an amp designer, so you'll know best.


----------



## xrk971

I just read up on balanced drive headphones. The closest thing in pure Class A with speakers is what is known as a circlotron. You need two power supplies and the ground is floating with the speaker voicecoil perched between the two amp MOSFETs pushing one way or the other. DC offset is critical here or your cans are toast. I like the built in safety of an output coupler cap. Of course you can only do balanced drive with a DC coupled amp and headphone. 

This would make a good balanced headphone amp for an HE6. 

https://www.passdiy.com/gallery/amplifiers/the-amazing-fet-circlotron-construction-continued


----------



## stellarelephant

bogde said:


> you guys are probably aware of this, but i thought i should post it anyway, maybe it will help somebody. for the led hole something like this works out great: http://www.ebay.com/itm/Fiskars-Crafts123740-1001-Teresa-Collins-Hand-Punch-1-8-Inch-123740-1001-/262816786454
> the 3mm led fits perfectly through the 1/8" whole. and, just like with the 1/4" model, the parts that may stand in the way, like the paper holder (see image), can easily be removed.


 
Great find, Bogde. The perfect tool for the job!


----------



## Lohb

xrk971 said:


> I just read up on balanced drive headphones. The closest thing in pure Class A with speakers is what is known as a circlotron. You need two power supplies and the ground is floating with the speaker voicecoil perched between the two amp MOSFETs pushing one way or the other. DC offset is critical here or your cans are toast. I like the built in safety of an output coupler cap. Of course you can only do balanced drive with a DC coupled amp and headphone.
> 
> This would make a good balanced headphone amp for an HE6.
> 
> https://www.passdiy.com/gallery/amplifiers/the-amazing-fet-circlotron-construction-continued


 

 This also - https://diyaudiostore.com/products/amp-camp-amp-kit
 But there are so many portable balanced amps on the market already that its not as complex as the above, or appears not to be.


----------



## xrk971

lohb said:


> This also - https://diyaudiostore.com/products/amp-camp-amp-kit
> But there are so many portable balanced amps on the market already that its not as complex as the above, or appears not to be.




I have the Pass ACA - it's a single ended Class A design that is very simple - almost as simple as mine. They are not DC coupled so I don't know how you would use cap coupled amps to drive a balanced voice coil. 

They are quite simple one doesn't even need a PCB. Here's my everyday office amp for powering a mini Karlsonator speaker.


----------



## stellarelephant

I found the same 1/8" hole punch (for LED hole) that Bodge found on eBay, on Amazon for only $4, with free Prime shipping.
Fiskars 1/8 Inch Hole Punch
  
 Also found this 5/16" punch that can be used for the volume pot (no more filing!) for $8, also with free Prime shipping.
Darice 5/16 Inch Hole Punch
  
 But this is what I finally bought.  A 3 Pack that includes 1/16, 1/8, and 5/16" punches for only $6!
Darice Hole Punches Value 3-Pack
  
 The 1/16 will be useless, but what a bargain, with free shipping as an add-on item.  I believe you have to spend $35 to even be able to purchase an add-on item.  I had to buy a baby shower gift already so I just threw this in the cart before checkout.  FYI I already own a standard 1/4" hole punch, which works perfectly for the two audio jacks.
  
 I'll report back on my next tin punching experience when this arrives.


----------



## mds2004

Is it bad if c4 and c5s solder is touching each other?


----------



## xrk971

mds2004 said:


> Is it bad if c4 and c5s solder is touching each other?


 
 Not if on same side (like either GND or +ve power rail) - I assume this is the case.  A solder wick can be used to remove excess.  How is rest of build coming along?


----------



## mds2004

This is after 2 hours last night working on 2 boards. I was really surprised how small the resistors are but it went better after figuring out a technique for me. I am still sloppy though. 

I had issues using the wick but I will try more tonight when not in a rush. I just tried c4 and c5s during my lunch break when I ran home from the office.


----------



## mds2004

I am so glad this was posted on this forum because I love doing this so much I may have to buy more than the 4 boards I already purchased from you.


----------



## xrk971

mds2004 said:


> I am so glad this was posted on this forum because I love doing this so much I may have to buy more than the 4 boards I already purchased from you.




Haha - you know they sound better too. Not kidding. Tight layout, precise values, low self inductance, less noise pickup. Once you figure out you want to do a lot of them get solder paste and a hot skillet. You can really bang out perfect welds pronto. 

Seriously, if you need more boards I got more to sell you. 

Looks like you have all the requisite tools: flip up goggles, Hakko tip cleaner, nice solder station, nice rotating vise. I use tape to the table personally. 

Nice work though. Should fire up first time if solder joints are good. 

Good luck! I know you are an addictbsince you snuck home from lunch to solder some more. Try sneaking in a soldering iron and a few tools. Then you have it all. 

Also, if you like the soldering, wait 'till you hear the sound. Then you will be hooked for life.


----------



## stellarelephant

I can confirm that the hole punch set I linked on the last page makes perfect holes for the LED and pot shaft. 


I've been listening to Voodoo by D'Angelo this evening thru my Pocket Class A. My go-to DAP has a dead battery so I stacked the amp with my crusty old Rockboxed iPod Video 5.5 (Wolfson DAC). Surprisingly great sound. Man, I really, really enjoy this amp. The bass is full, deep, and controlled. Voices are clear. And everything just sounds so...nice!


----------



## xrk971

Glad to hear that the $6 punch set works!  I bought a $2.50 hole punch from Staples and guess what? It buckled and warped under the pressure needed to punch through the tin.  So good thing these punches are beefy enough to handle the job at hand!
  
 I am listening to the next gen prototype of a commercial version of this pocket amp - to be released in the future through my new audio products company that I co-founded.  So I can't say too much more other than it will be encased in a beautifully designed housing made with exceeding attention to detail, uber special materials and aesthetics.  What about the insides?  It will be a SE Class A, with Toshiba 2SA1837 CFP topology, a protection relay for turn-on anti-pop protection, dedicated LiPo cell and charging system, and of course, the famous sound signature of this little amp you are listening to now but with better dynamics, and higher resolution.
  
 More fodder for you guys to pine over


----------



## mds2004

Last messup question hopefully.... Is it ok for the solder of the 3rd leg of the mosfet to touch one of the legs of the c2_2 capacitor?


----------



## xrk971

You should try to read schematic as you build and not just use it to populate parts. The mosfet has pins GDS (123). So the S is the pin connected to the output, thus, yes, it's ok. You can also tell this if you look at a bare board you will see pin 3 connected to the output caps.


----------



## stellarelephant

xrk971 said:


> I am listening to the next gen prototype of a commercial version of this pocket amp - to be released in the future through my new audio products company that I co-founded.  So I can't say too much more other than it will be encased in a beautifully designed housing made with exceeding attention to detail, uber special materials and aesthetics.  What about the insides?  It will be a SE Class A, with Toshiba 2SA1837 CFP topology, a protection relay for turn-on anti-pop protection, dedicated LiPo cell and charging system, and of course, the famous sound signature of this little amp you are listening to now but with better dynamics, and higher resolution.
> 
> More fodder for you guys to pine over




That's quite an announcement! Really glad you're taking it to the next level.

It really is all about the sound signature, isn't it? I remember a while back in one of your DIYA amp development threads, somebody used the term "H2 secret sauce" lol. Now I get it. It's so subtle you just sink into the music and enjoy it, and then when you try to go back to an op-amp, everything sounds a bit sour. In contrast, Pocket Class A sounds undeniably natural, musical, alive and pleasant. 

I'm a graphic designer. PM or email me if you want some help cooking up a branding concept for your new venture. I might be persuaded to work for gear! 


Can the "better dynamics" you mention be achieved in the mint tin by increasing bias via resistor swaps? Mine hardly gets warm enough to even notice, so I could push it a little harder maybe. I guess this would impact battery life...


----------



## xrk971

Thanks for the offer. I might take you up on it! Check your bias current across the R7 array of four resistors. Measure voltage at pin 3 of the MOSFETs. It should be at least 5.7v with a fresh set of batteries. 5.7v divided by 117.5ohms is about 50mA (49mA actually) As batteries wear out it will drop a bit. Oh that's another feature of the next gen commercial amp is that it will have a regulated supply so bias will be constant regardless of battery level. So if your bias is much less than 50mA - say 45mA or less then you can increase R3 from 33R to 47R. See if that helps. If not take it to 51R. If you get 55mA it should sound great. No more than 65mA as it gets too hot and batteries won't go far. 

But the dynamics I am talking about come from the change in topology (from Source Follower to Complemetntary Feedback Pair or CFP) and use of the 2SA1837 BJT.


----------



## mds2004

Not pretty but here is the first one. 


I can't test until I get the 9v connectors though.


----------



## xrk971

Not bad for your first one. You might want to take some lighter fluid on a cotton swab and clean up that flux on the board. The flux plus solder particles can sometimes cause a short. When you get a chance - upgrade the 100uF rail caps to 2200uF 16v Nichicons. They improve stereo separation and eliminate turn off thump. If you are really itching to listen - solder wires directly to the nickel plated terminals of disposable 9v batteries to the exposed pins on the other side of the connector. Easy to remove layer. 

Good luck with first sound!


----------



## mds2004

It's alive! 

But no sound. I'm using a male male audio from phone to input, and my headphones in the output. IL dig in deeper tomorrow.


----------



## xrk971

Is LED installed correctly? The flat on the body goes to GND.


----------



## stellarelephant

xrk971 said:


> Not bad for your first one. You might want to take some lighter fluid on a cotton swab and clean up that flux on the board. The flux plus solder particles can sometimes cause a short.




Good tip. I didn't know lighter fluid worked as solvent for flux. I have a jug of naptha (essentially lighter fluid) that I bought to clean guitar fretboards. Might give it a try on my amp boards too.

MDS2004, good luck with your troubleshooting!


----------



## xrk971

mds2004 said:


> It's alive!
> 
> But no sound. I'm using a male male audio from phone to input, and my headphones in the output. IL dig in deeper tomorrow.




Hmm... you are the first to get no sound at all. First thing to check (wearing an ESD wrist strap) is to use a DVM and probe between ground and pin 3 of the MOSFET and ground and PIN 1 of the MOSFET. 
Pin 1 should be around 9 to 11v and pin 3 around 5 to 7v depending on battery level. Those dc voltages tell you that the JFET and MOSFET are operating correctly and not damaged. If pin 3 is circa 0v to 2v it's probably got a blown gate from a ESD zap. If pin 1 is unusually low, the JFET may have a blown gate from an ESD zap. I hope you took precautions for static discharge during all handling and assembly. The FETs are very sensitive. 

If the amp is working, the MOSFET and R7 array will feel warm to the touch. Again, only touch if you are strapped in with ESD grounding strap. 

Good luck!


----------



## xrk971

The Ronson lighter fluid works well as it leaves no residue of its own. I sometimes do a second wipe with denatured ethyl alcohol. I always wipe with ethyl alcohol before beginning SMT reflow soldering with solder paste.


----------



## mds2004

xrk971 said:


> Hmm... you are the first to get no sound at all. First thing to check (wearing an ESD wrist strap) is to use a DVM and probe between ground and pin 3 of the MOSFET and ground and PIN 1 of the MOSFET.
> Pin 1 should be around 9 to 11v and pin 3 around 5 to 7v depending on battery level. Those dc voltages tell you that the JFET and MOSFET are operating correctly and not damaged. If pin 3 is circa 0v to 2v it's probably got a blown gate from a ESD zap. If pin 1 is unusually low, the JFET may have a blown gate from an ESD zap. I hope you took precautions for static discharge during all handling and assembly. The FETs are very sensitive.
> 
> If the amp is working, the MOSFET and R7 array will feel warm to the touch. Again, only touch if you are strapped in with ESD grounding strap.
> ...


 
  
 I should have worn the strap from the beginning and that is most likely the cause. I thought I was careful but obviously was not. Would I be able to just replace the FETs, or do I have to resolder a new board with new parts?
  
 Mosfet M1A
       Pin 1: 2.42V
       Pin 3: .66V
  
 Mosfet M1B
     Pin 1: 2.42V
     Pin 3: .02V


----------



## xrk971

Sorry to hear that. It's not clear if the JFET is the culprit or the MOSFET.  Remove the MOSFETs first then measure pin 1 of the MOSFET again (voltage from JFET drain resistor).  If it is 11v your JFET is ok.


----------



## xrk971

Hi Mds2004,
Any luck fixing the amp?
X


----------



## mds2004

Not yet. Unfortunately I won't have time until this weekend.


----------



## mds2004

Ok so I went ahead and finished the second one and it works great! Unfortunately I forgot my ifi micro black label at work so I cannot compare until after the weekend. But initial impressions on my Sennheiser HD650s are good. I will also compare using my Monoprice Monolith 1060s and FLC 8s.


----------



## bogde

mds2004 said:


> Ok so I went ahead and finished the second one and it works great! Unfortunately I forgot my ifi micro black label at work so I cannot compare until after the weekend. But initial impressions on my Sennheiser HD650s are good. I will also compare using my Monoprice Monolith 1060s and FLC 8s.


 
 nice build, congrats!


----------



## xrk971

Great news! 
Congratulations.


----------



## stellarelephant

mds2004 said:


> Ok so I went ahead and finished the second one and it works great! Unfortunately I forgot my ifi micro black label at work so I cannot compare until after the weekend. But initial impressions on my Sennheiser HD650s are good. I will also compare using my Monoprice Monolith 1060s and FLC 8s.




Glad you've got sound! HD 600/650 have a reputation (not sure if its deserved or not) for being hard to drive. Or at least hard to drive well. How well does the Pocket Class A perform with them? And at what "clock setting" are you cranking the volume pot to? For my HD 598 I turn up to around 11:00 (with the board oriented cap-side-up, as you have yours.) I have dreams of upgrading to HD600 some day...hence my curiosity.


----------



## xrk971

I have had reports from a professional music producer who used this amp with HD600's and they rock. He had an O2 before this and he says the difference is amazing with this little amp. The music just sounds better.


----------



## mds2004

What do you guys use to test between different amps? It is difficult for my untrained ears to discern the differences change changing cables.


----------



## xrk971

I made a small AB test box using two DPDT 12v actuated signal relays, a momentary on switch connected to a 9v battery and DC-DC step up to get 12v to drive relay,and qnty 6 x 3.5mm stereo jacks.  It lets me switch instantaneously between two amps using one source and one headphone.
  
 Once level matched, it is very hard to tell the difference when switching. Many of these effects are more audible over longer term listening - especially effect of 2nd harmonmic profile on sound quality. That gives a subjective feeling of warmth and enhanced tonality, spaciousness. Some test tracks let you hear it right away.  Piano is particularly good as well as drum solos and very dry (like as in an anechoic chamber) acoustic guitar.
  
 Here is an example of my AB test switch box:


----------



## mds2004

Very cool. I will look into some diy plans because I'm not seeing anything using the same source and headphones. 

I thought about making something like this, and using 3.5mm splitter from the source to each amp, which would go into a/b. 

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.amazon.com/Sescom-SES-IPOD-AB-Stereo-MP3-Player/dp/B005TE7GP4&ved=0ahUKEwjStqixxvfSAhWr6oMKHa-RBVgQFgg7MAA&usg=AFQjCNHCPlZyoVp_cI5Zq-GuxPwLbpTJ0A&sig2=9FWeyVhSYyKQNNjHRxhitA


----------



## HiGHFLYiN9

stellarelephant said:


> The amp in the photos above is X's current prototype, built with his hand-drawn circuit board and all SMT components.  DIYA member BabyDontHertzMe currently has two DIY PCB designs under development and soon to be available for printing.  One will use SMT components like the original, while the other will use all through-hole components...


 
 When will the second one be available? I'm not enthusiastic about plucking at SMD resistors


----------



## xrk971

mds2004 said:


> Very cool. I will look into some diy plans because I'm not seeing anything using the same source and headphones.
> 
> I thought about making something like this, and using 3.5mm splitter from the source to each amp, which would go into a/b.
> 
> https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.amazon.com/Sescom-SES-IPOD-AB-Stereo-MP3-Player/dp/B005TE7GP4&ved=0ahUKEwjStqixxvfSAhWr6oMKHa-RBVgQFgg7MAA&usg=AFQjCNHCPlZyoVp_cI5Zq-GuxPwLbpTJ0A&sig2=9FWeyVhSYyKQNNjHRxhitA




I can post the schematic later tonight. It's pretty simple - signal path source input (L/R) goes to common pin on relay 1 and signal on n/c pins goes to amp A input. Amp A output returns to n/c pins on relay 2 and common of relay 2 goes to headphone out. The n/o pins on relay 1 are connected to amp B input and amp B output goes to n/o pins of relay 2. Both relay coils are connected to common signal from momentary on off switch. I use a $0.40 dc step up converter MT306 from China to make 12v from 9v carbon or alkaline cell. System is normallly routed through amp A with no power applied to relay. Pushing switch flips both relays to route signal from source through amp B and back out to headphones. Instantly. Click. When you level match amps you almost can't tell it switches in mid stream. If it weren't for the click of the relays it would be almost imperceptible.


----------



## xrk971

highflyin9 said:


> When will the second one be available? I'm not enthusiastic about plucking at SMD resistors




Sorry but I don't see a through hole version of this coming along. First, it would be much bigger and have a hard time fitting in a mint tin. Secondly, member BabyDontHertzMe, the layout artist, has been MIA for some time now. I hope he is ok. He is in South Africa and if anyone knows of his whereabouts let him know we hope he is OK. 

I can't do layouts in CAD - just hand made one off stuff.

If you have a hard time with SMT's I can sell you a board with all SMTs preinstalled. Just PM me.


----------



## AudioCats

xrk971 said:


> Sorry but I don't see a through hole version of this coming along. First, it would be much bigger and have a hard time fitting in a mint tin.





> .....


 
  
 All-thru-hole will be a lot more diy-able for many people, though.
 Maybe a desktop version that is powered off USB? Losing the batteries can yield quite a bit of extra room, the thru-hole board can probably still fit into a tin. Many might (eventually) want to upgrade the input and output caps, having extra room available provides more upgrading possibilities as well.


----------



## xrk971

Good points. Just need BDHM to get back in the saddle.


----------



## stellarelephant

Audiocats, the SMT work wasn't as hard as I expected, although I did have to buy a $20 soldering iron with a small tip and some tweezers to do it. I may get a magnifier to use for my next board too. If you can get past the SMT part, it would be possible to use much bigger caps with this board if you are not constrained by a mint tin. If you had a truly huge cap, you could even install it from the opposite side of the board from where they were planned to go. They'd sit above the SMT components. Lots of room there.


----------



## xrk971

StellarElephant has a good point. It's not that hard.  In fact, I prefer to do SMT work now over through hole whenever I can because it is faster, neater, tighter layout.  Faster?  Yes, you only work on one side of the board and there is no bending leads, fitting leads, soldering leads, trimming leads.
  
 Even faster than a soldering iron, buy a small syringe of SMT solder paste (consistency of thick toothpaste), use the included hypodermic needle to apply a small dab on each SMT pad.  Place the SMT part in place.  Put board on a small old frypan (junk one you wont't cook food in ever again), put on stove or hotplate medium heat for 2 minutes until paste liquifies silvery shiny and forms nice fillet joints to parts. Remove from heat and let cool.  Done. Perfect solder joints that are clean.
  
 Here is what I used - get these items and you will be an SMT master in no time
  
 Kester solder paste in syringe pre-loaded:
 https://www.amazon.com/gp/product/B006UTCYM2/
  
 Very good magnifier - I use hours on end with no headaches:
 https://www.amazon.com/SE-MH1047L-Illuminated-Multi-Power-Magnifier/dp/B003UCODIA/
  
 Good Swiss tweezers are essential:
 https://www.amazon.com/Rabake-Stainless-Anti-Magnetic-Anti-acid-Precision/dp/B06WRRM8L9/
  
 This iron is very nice - great quality variable temp and heats up fast. The Hakko compatible tips are worth $30 alone.
 https://www.amazon.com/OMorc-60W-Soldering-Iron-Kit/dp/B01HSXVR3A/
  
 Now go for it!  Watch some YouTube videos on SMT soldering and re-flow soldering with a fry pan


----------



## AudioCats

SMD soldering is not a problem for me, but I can see some people might hesitate because of it (especially if they don't already have a fine tip soldering iron).
  
 I guess what I was trying to say was that an oversized thru-hole version, being super easy to build, might gain more popularity.  ( "starving student's desktop class-A headphone amp" ?)


----------



## hte80

xrk971 said:


> I keep forgetting that HF has different image requirements than DIYA.  The problem is, it shows up fine on my browser so I don't have any indication it is not working. I think HF has max image size of 1000 pixels x 700 or something like that.  My image links are pointing to DIYA where they are typically 1024x768 which is a standard size medium res image.  I don't know anyone who uses 1000 pix wide a a standard.
> 
> 
> 
> ...



 



Any particular 10uF cap which you are using? Nichicon something-or-others I'm guessing? Would something like the PW series be fine or am I barking up the wrong tree?


----------



## xrk971

I like Elna Silmic II's. That's what I am using now if needed for a larger value. 10uF is or needed. A 4.7uF is fine.


----------



## stellarelephant

Silimics were the best measuring polar caps of all electrolytics tested by Cyril Bateman. 

Batteries finally came!


----------



## xrk971

How does it sound with the new batteries? And how long can you run before they stop? The LED charging level indicator is very cool. Nice ability to use micro USB charging. Did you make your own dual USB connector to one cable?

Regarding Silmics. What do you think of the grand daddy of output cap combos? 470uF Nichicon AK + 100uF Elna Silmic II + 1uF Wima film.


----------



## stellarelephant

Wow, real batteries make a huge difference.  Even the turn on thump is louder and brighter-sounding, lol.  Still not enough to hurt my ears or headphones, thankfully.  And now its a bona fide hand-warmer too.  Certainly not hot, but now I finally notice that it does warm up.

After charging, the new batteries were each measuring 9.18V.  When I first powered up the amp, I measured 15V DC bias and 6.5V AC signal at the output!  This is more than double what I was averaging with those dollar store carbon-zinc cells.  Maybe a tad too high for my needs, even?

EDIT: I was measuring incorrectly. Bias is actually perfect at 6.5V DC. See post #187. I'm still not sure how to measure AC signal...

I switched back and forth between old and new batteries a bit.  The cheapies (which yielded a modest 6.5 DC bias and 3.5V AC signal at last measurement) are definitely more laid-back sounding, while the new ones sound brighter (not forward or fatiguing in the least, mind you), bringing the amp closer to neutral, to my ears.  New batteries are also a big win in terms of overall excitement, detail retrieval (which is incredibly good now), dynamic power, and perhaps even bass quantity, too.  It sounds like THD (especially H2, let's hope!) has risen along with the voltage.  I quite like the change in the treble, but my initial impression is that the bass seems a tad less transparent than what I was hearing at lower voltages...leaning just a bit towards buzzy...my guess is that the increased harmonics are obscuring the fundamental notes and natural texture a bit?  I've learned recently that capacitor distortion rises along with voltage.  Overall, running this amp hot is more fun, and it sounds mind-blowingly good.  If I had to sum up the improvements in a word, I would say my amp has become "snappier."  It really grabs your attention now.  Does the "sweet spot" for me lie with slightly lower voltage set points?  Maybe, especially if I could get more battery life from the trade-off.

EDIT: After further listening, my impression of bass texture improved. See post #189.






Charging the batteries inside the tin is a partial success.  I made some big (not so pretty but oh so functional) cutouts in the tin using a hole punch to start, followed by wire cutters and pliers, so that my cables could connect there, and hot glued my batteries in place in the tin.  Unfortunately the batteries must sit about 1/4" away from the wall due to the curve of the tin corner, so the holes had to be big enough for not just the actual micro USB connector had to fit inside, but the entire plastic head of the cable too, in order for the connectors to reach the batteries inside.

There are tiny holes in the end of the tin (smallest hole punch from my 3 piece set) to reveal the charge indicator lights of one cell.  From an angle it looks like the light doesn't line up with the hole, but it does.  It's just that the battery is set back a bit from the tin wall due to curving tin corners.

But the big letdown is that I can't use the Y cable I bought (double micro USB) to charge them both simultaneously from a single USB charger.  Well I did it at first actually...it just won't work while the batteries are connected to the amp.  I _can_ charge the batteries in situ if I use two separate chargers with two separate cables.  I think this is because of a shared ground in the cable, which must complete a circuit between the two batteries when they are snapped into the amp's battery connectors.  This situation seems to always send one of the two batteries into some sort of limbo state.  Voltage drops instantaneously to 0.3V (which results in a high pitched noise coming through the headphones when the amp is powered back on.)  The battery comes out of limbo when charged alone with its own cable for a few seconds, and then behaves normally again.

X, I have a somewhat convoluted question for you, oh electronics guru.  Before I ever saw this weird charging behavior, I was listening to the amp and poking around in the amp with my multimeter, and I stuck the probes on both the negative pins of the battery connector on the board (don't ask me why, I'm an artist, not an engineer!).  Oops...Instantly music volume dropped drastically and I heard a high-pitched hum.  I thought I had fried my amp or something at first.  Then I measured the new batteries and found one had dropped to near zero voltage.  I charged it for a few seconds and it was fine again, back above 9V.  Now it works great except for in the charging-in-amp-with-Y-cable situation, when it returns to this same limbo state.  Did I cause ALL this limbo behavior by damaging the battery with my multimeter, or did I just trigger some sort of protection circuitry with my probes, which is now just recurring with my flawed charging setup?  The same finnicky battery makes an audible high-pitch whine when I measure it with my multimeter.  Not through the headphones!  Like something in the battery itself is oscillating while the voltage is read by the multimeter.  I'm not sure if it did this before my initial probe mishap or not, but only one of the batteries does this, so I wonder.  As I said, both batteries perform flawlessly in the amp, no noise. 

Sorry that was long...it was hard to explain.  My hope: If it is a protection circuit, Possibly the finnicky one is just slightly more sensitive so it always trips first, leaving the other one appearing not to have the behavior at all.


----------



## xrk971

You measured 15v at the output of the MOSFETs?! That's not possible unless amp is damaged as it means 127mA bias current. Way out of operational limits. Can you double check? The battery protect smart circuit kicked in when you shorted. Sometimes turn on in rush causes them to kick in and have to turn on off to charge rail caps.


----------



## gikigill

Tested it with higher impedance headphones and much better bass. Needs some retuning for better bass with low impedance cans.


----------



## xrk971

Hi StellarElelphant,
 Can you check the bias current again with the new batteries?  Pin 2 might show what the two batteries are in series or about 16v to 18v.  Pin 3 should be somewhere in 5.5v to 7.5v.
 Thanks,
 X


----------



## stellarelephant

I was taking my measurements from pin 3 of the MOSFET (the pin farthest to the right, right where it meets the bypass cap hole) to the negative terminal of the capacitor. Is this correct? I measured across each output cap too and got exact same readings.

When you say check the bias current again, are you talking about taking an amperage reading somewhere on the circuit or just repeating the voltage measurements I did last night? I know you have a formula for calculating bias current from voltage somehow, and I'd like to learn that trick too! I apologize if you've already described the formula elsewhere. 

I think I'll get time to pull the amp back out of the tin and take measurements tomorrow. I'll have to unglue the batteries to get The board out and access to SMt side (I think I just found a downside to mounting the board upside down!) but I chose hot glue because it is so easy to peel off, at least. 

So you don't think that I damaged the battery by shorting it? It's voltage dropped to zero today while I was just listening. It may just be low on juice and shutting itself off. The other one is still measuring 9V, so it is definitely the weaker of the two cells. I should probably charge fully and see how long it goes for. I have had the amp on and off too many times to really even know what kind of runtime I got. At least 2-3 hours, I think.


----------



## xrk971

Bias current is voltage at pin3 (relative to ground) divided by resistor value for R7 (or 117.5ohms).


----------



## mds2004

Which capacitors would you use to for best sound with no size limit? I was thinking of making one out of wood, or 3D printing a case for it.


----------



## xrk971

i think 1000uF is about the biggest you would need for output at 60ohms. The 1000uF 16v oscon actually can do this and fits in current spot. If using 30ohm cans go with 2200uF 16v caps. Your favorite brand and bypass with usual 1uF 63v Wima film. Panasonic FM or Nichicon AK or Elna Silmic II are all good electrolytics.


----------



## stellarelephant

xrk971 said:


> Bias current is voltage at pin3 (relative to ground) divided by resistor value for R7 (or 117.5ohms).




Thanks,X. Does it sound from my description like I measured in the right place?


----------



## xrk971

That is the correct place to measure but the value makes no sense. What is the value at pin 2 (should be same as two batteries in series). Unless one of your resistors went bad.


----------



## stellarelephant

I guess reading the manual might be warranted every once in a while...
 I had the AC and DC voltage symbols mixed up. 
	

	
	
		
		

		
			




 My meter has a specific setting for measuring 9V batteries, otherwise I probably would have noticed my error sooner...
  

  
 So my DC bias is 6.5V, lol.  Right where you said it should be, X.
  
 Now how do I go about measuring the AC signal?


----------



## xrk971

Good to know you have 55mA bias current. The perfect number for balance between low distortion and low battery consumption.


----------



## stellarelephant

xrk971 said:


> Good to know you have 55mA bias current. The perfect number for balance between low distortion and low battery consumption.




Great. So are you saying that higher bias gives lower THD? Is it the transistors that perform that way? Must greatly outweigh the opposite behavior of caps.

I did a short listening session last night with my freshly recharged OKCell USB batteries and the bass-heavy album "Man About Town" by Mayer Hawthorne. It features everything from live drums and electric bass to uber-deep 808 percussion samples. 

What I first interpreted as a slight buzziness in the bass spectrum seems now in fact to be simply more texture in the low frequencies as revealed by this amazing little amp. It's the same as the treble registers, really. There is less sense of transparency compared to an ultra-low THD amplifier, but filling that open "space" is an insane level of new detail. I think the harmonics are responsible for this, perhaps reinforcing the fundamental frequencies--the same phenomenon that occurs in a fine acoustic instrument... The pleasant warm "sparkle" of this amp really extends all the way up and down the audible range, creating a deeply and finely textured, absolutely full-bodied sound signature. 

Awesome synergy with my xDuoo X3 DAP. Another X3 user SlaterLovesSpam bought a GB board and I look forward to his comments on this pairing when he gets his soldered up!


----------



## xrk971

This amp has a predicted upper bandwidth of 11MHz - that's well into RF range but basically it will let all the treble you can throw at it through without attenuation. So the high frequency detail, if you can hear it, is simply amazing. The texture and tonality you hear is not so much the second order harmonics but the fact that the amp has almost no higher order distortion beyond 3rd or 4th order. This frees up to frequency space and allows the music to get through in an uncluttered way. What you may find in ultra low THD amps with 30 transistors is that although the total THD level may be low, if you look at the spectrum - it is often like a forest of trees of higher order harmonics. The levels are low but they are there in a level that is similar or competing with the H2 and H3, and to our ears, may sound congested, not natural. 

Yes, higher bias drives lower overall THD while keeping yet harmonic profile similar in relative amounts. Higher bias gives more bass authority as well. Running this amp with a clean 19v power supply may really surprise you. Make sure the rail caps are rated for it though. Pushing 16v caps to 19v may spell a firecracker like pop from the caps.


----------



## xrk971

Here is my cap rolling test bed. I have 2.2uF Wima as usual on input plus 4.7uF Silmic II's. On output I have usual 390uF OSCON's and 2.2uF Wima's but with 100uF Silmic II's. Sounds very nice. I also changed power rail caps to 2200uF 24v to allow running at 19v. It's a real heater at 19v vs 16.4. Dynamics are really quite superb.





FFT looks very nice indeed.


----------



## stellarelephant

Oh yeah you mentioned that 3x output cap combo and I think it is a very cool idea. I want to try that also. Did you solder the film on the SMT side of the bypass cap holes? Prolly would still fit in a tin...

For the input caps, even the best electro (Silmic) distorts several times more than a polyester film. I Wouldn't use it for my pocket version, but only for your desktop version, whoch has different resistance, I think you said. I agree that it's probably the best possible choice in that scenario.


----------



## xrk971

Yes if you look at the photo above, you can see that the film cap is on the SMT side. And yes it fits in a tin still. The Silmic 4.7uF input is soldered on the SMT side as well.


----------



## stellarelephant

I have also been toying with the idea of trying another film cap in parallell with the 2.2 uF WIMA on input. A 0.12uF Vishay MKP Polypropylene could fit in the normal spot, with the stock WIMA soldered onto SMT side. The PP would cover most of the sound spectrum for a pocket version with resistance of 47 kilohms, with the polyester handling bass. Corner Frequency for PP would be at 282 Hz. I've been eyeing those Vishays since seeing the HumbleHomemadeHiFi comparisons.


----------



## stellarelephant

Oh wow I didn't see your photos earlier. That thing looks boss! Is that a 12x20mm cap laying on its side for the power rails?


----------



## funch

I've developed a weird problem with my amps (the one I had working and the one I just finished). I installed the 16V/2200uF C3 on both, and switched to the Li-ion batteries. 
  
 When I switch each amp on, the LED will flash very dimly, then go out. I've measured the batteries, and each is outputting 8.38V. 
  
 Any ideas what could be amiss? Have I somehow fried a semiconductor? My first amp worked fine with the Duracells. All I changed were the C3's and batteries.


----------



## xrk971

This is disconcerting but normal. The in rush current to the 2200uF caps causes battery protection circuit to kick in. Turn off to reset battery and then on again quickly. A few times charges caps so it won't go to self protect. This doesn't happen with alkaline or carbon zinc cells.


----------



## funch

Thanks for the quick reply. The process works, but I don't know if I want to chance wearing out the switch prematurely.


----------



## xrk971

The switch is a $2.25 part that can be replaced, albeit by painful desoldering process. How many cycles are they rated for? It only happens with some Li-ion batteries. I have some that don't seem to shutdown as easily. 

I haven't tried this but maybe you could add a 47k trickle charge resistor across the switch contacts and this always keeps the caps in a semi charged state. It would drain your batteries in the off state faster though. 340micro amps trickle charge - will the FETs drain off the charge too fast though?


----------



## funch

xrk971 said:


> The switch is a $2.25 part that can be replaced, albeit by painful desoldering process.


 
  
 True. Maybe I should stop sniveling and just enjoy the music.


----------



## stellarelephant

xrk971 said:


> This is disconcerting but normal. The in rush current to the 2200uF caps causes battery protection circuit to kick in. Turn off to reset battery and then on again quickly. A few times charges caps so it won't go to self protect. This doesn't happen with alkaline or carbon zinc cells.




My OKCell rechargeable batteries do not have any problem like this... but then again I am using just 1000uF rail caps. When I get time, I'll try to do a little test with my batteries to see what happens with more capacitance. I don't currently have any 2200 but I can parallel 2x 1000uF. 

I am considering the bigger rail caps on my second build, but only if normal turn on behavior can be preserved. And I do want to keep a 25V rating, because my batteries run 9.18V each. X, do you have a link for those new rail caps you're using?

Also, a general question: Do power smoothing capacitors have any effect on the sound? I mean beyond the basic improvements that are tied to increased capacitance. Looking around the web, there are some who seem to think that only audio-grade stuff will do. Some use Silmics for their PSU coupling. And then there are others who say no, it isn't in the signal path so you won't hear it. Some say low ESR is the most important spec for power application, with some favoring the Panasonic caps for this reason. I just used Nichocon AK because they were audio grade and compact.


----------



## xrk971

Here are the cheap no name caps I found with 2200uF and 25v rating that fits perfectly. 13mm dia x 20mm long. 

https://m.aliexpress.com/s/item/32741284380.html

Yes, I think I mentioned this before but the 2200uF caps improve stereo separation by a large margin. About 20dB improvement. This gives superior soundstage and imaging. With 100uF caps I measured only -52dB stereo cross talk. With 2200uF the stereo crosstalk is -72dB. 

It also prevents turn-off thump. Turn on thump can be suppressed with a delayed relay for headphone outs. I have this implemented in the next gen commercial product. It's very complex and adds substantial cost to BOM though. The relay is a special gold/palladium contacts unit for high sound quality with a 4mA solenoid coil. So it draws power and will reduce battery life. So I am debating if it really is necessary or is there a clever way to do without a relay. No relay is best for sound quality of course.


----------



## nicoch46

X an off-on-on for soft starT ?


----------



## xrk971

nicoch46 said:


> X an off-on-on for soft starT ?




Hmm... not sure what you mean off then on on for soft start? It is SPST switch so either on or off. Best way is to not plug in phones until after power on.


----------



## nicoch46

X 3way swicth , the fist on is in the middle with a resistor x softstart or only one battery x half B+


----------



## xrk971

Yes that would work but how to get it to work with current volume pot. Easier for me to just click switch a few times.


----------



## stellarelephant

The thump is no biggie for my low-ish impedance cans. One pair is 50 ohm and the other is 32ohm. Both produced just a mild thump. Might be substantially different for other impedance though.


----------



## macky112

Is there a price estimate for a self build?


----------



## xrk971

About $40 to $50 depending on options and cost of shipping.


----------



## funch

I have built three of the four boards that I have received. All use the 2200uF/16V rail cap's, and the stock Wima 2.2uF at C1. The first two use unmatched MOSFETs, the 
 third, and eventually fourth, have a matched set from X, and are from the second group buy.

 The first uses 100uF/25V Silmics/Wima 1uF at C2. (I used the 25V Silmics because I already had them on hand.) Bias is 57.5/59 mA using 33R at R4.

 The second one is completely stock (except for the rail cap's). Bias is 58/59 mA using 47R at R4 (33R produced only 49 mA).

 The third uses OSCON 1000uF/16V at C2, with Wima 6.8uF as bypass. Bias on this one is 58/58mA with 33R at R4 (can you tell that it uses the matched MOSFETs?) 

 I've also tried the Nichi UKA 47uF/Wima 1uF combo as well.

 I don't have any good low impedance 'phones, using only my HD800's. I may pick up a pair of the Massdrop Fostex Th-X00's, which have an impedance of 25 ohms, to try.

 So far, my preference at C2 are the Silmics. To me, the sound is more involved with better spatial imaging, and not quite as aggressive as the OSCONs.

 I still stand by my earlier observation that this amp scales quite well with better 'phones/sources. It's just a matter of futzing with cap's and bias to match your 'phones.


----------



## xrk971

Thanks for the fantastically detailed summary Funch. Glad that the matched FETs actually worked out to give you perfectly matched bias current. 

I have been listening to a Silmic 4.7u and Wima 2.2uF input combo with 390uF oscon and Silmic 100uF plus Wima 1uF output combo. So far I like it a lot. I don't hear the harshness of the oscon but perhaps that is because I have DT880-250's which have a bit of a relaxed treble presentation. I recently got a pair of DT770-250's for a friend and they sounded harsh - too much treble.


----------



## macky112

xrk971 said:


> About $40 to $50 depending on options and cost of shipping.


 
 Thank you for the reply
  
 I am interested in how your amp would compare to this budget class 1 amp
  
 http://www.ebay.com/itm/272321213985?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
  
 any feedback is appreciated


----------



## xrk971

Without seeing the schematic I am guessing - but from looks of it, it uses an opamp front end to drive complementary BJT's in a push-pull mode in class AB.  The written text says it is Class A but I find that not believable given that the TO92 transistors are not heat sinked and a 3.7v 3000mAhr LiPo battery can power it for 7hrs. My calcs show that for a 3.7v cell to go through Dc to Dc step up to make +/-12v rails will give this amp a max of 33mA bias current for 7hrs. 33mA is a very low bias current for true Class A operation. 



 I think it's more likely Class AB. In any case. It's a very different topology. If you like the sound of 24 transistors in an opamp - this will sound good to you.  Single Ended (SE) Class A operation is simple and very direct.  Gives a presentation that is lively, engaging, with a wide soundstage and deep articulate bass. 

Or buy the prebuilt one for $160. I have a 14day guarantee that you like it. I will even pay for shipping back if in Continental US. So really zero risk. 

https://www.etsy.com/listing/522023157/pocket-class-a-headphone-amplifier

There is a really not much risk to build it - I guarantee you will like it. Everyone has so far.


----------



## gikigill

Can certify, like my amp that I got from Xrk971. Now I'm sending it back for further mods since the amp seems to be designed with a lot of flexibility in mind. 

Very clean and full sound from my current configuration for high impedance cans ie above 50ohms or more.


----------



## Hutnicks

xrk971 said:


> Without seeing the schematic I am guessing - but from looks of it, it uses an opamp front end to drive complementary BJT's in a push-pull mode in class AB.  The written text says it is Class A but I find that not believable given that the TO92 transistors are not heat sinked and a 3.7v 3000mAhr LiPo battery can power it for 7hrs. My calcs show that for a 3.7v cell to go through Dc to Dc step up to make +/-12v rails will give this amp a max of 33mA bias current for 7hrs. 33mA is a very low bias current for true Class A operation.
> 
> 
> 
> ...


 

 You dont offer the bare circuit boards on there?


----------



## xrk971

I offer the bare boards and all BOM tips and tricks on the group buy thread here:

http://www.diyaudio.com/forums/group-buys/302859-xrk971-pocket-class-headamp-gb.html

At the bottom of post 1 is the BOM. PM me is you want a bare PCB or matched FETs to go with it. Boards are $12 for 1 and $17 for 2 in US shipping included.


----------



## macky112

Where can you find a parts list?


----------



## xrk971

macky112 said:


> Where can you find a parts list?




I just told you in the above post. The BOM (aka parts list) is at the bottom of post no 1 in the thread. There is even a Digikey shopping cart for you to click on and just pave your order. Doesn't get much easier than that.

Here is cart:

http://www.digikey.com/short/322jv3


----------



## macky112

xrk971 said:


> I just told you in the above post. The BOM (aka parts list) is at the bottom of post no 1 in the thread. There is even a Digikey shopping cart for you to click on and just pave your order. Doesn't get much easier than that.
> 
> Here is cart:
> 
> http://www.digikey.com/short/322jv3




My bad, was walking and didn't refresh my browser before I made my previous pist


----------



## xrk971

gikigill said:


> Can certify, like my amp that I got from Xrk971. Now I'm sending it back for further mods since the amp seems to be designed with a lot of flexibility in mind.
> 
> Very clean and full sound from my current configuration for high impedance cans ie above 50ohms or more.


 
 Glad you liked the sound on high impedance cans gikigill.  Can you tell us which headphones you liked to pair with them (model and impedance)?
  
 I will do my best to tweak the settings (bias current) and caps complement to get extended bass for your low impedance cans.  I am thinking boosting bias from 55mA nominal to 67mA and increasing output caps from 470uF to 1470uF - that should increase the bass extension by 3x or allow impedance 3x lower ( circa 16ohms) than 50ohms to have same bass extension.
  
 The mods will be a 1000uF Panasonic OSCON + 470uF Nichicon AK + 1uF Wima MKS on outputs.  As long as I am at it, I will upgrade your inputs to 4.7uF Elna Silmic II's plus 2.2uF Wima MKS.  I will also upgrade your rail caps to 2200uF 25v rated ones so you can happily drive the system with a 19v desktop PSU for extended dynamics and power output to low impedance cans.  It should be quite the formidable Pocket Amp.


----------



## gikigill

I tried it with the Audeze LCD-2, Sennheiser HD800, which was much better compared to low impedance cans like the TH900 and the SZ2000.

The best part was the power and the clean background of the amp. It's surprising how powerful it is for such a small size especially when it's plugged in.

Turned the volume to max on a JH16 and there was no hiss at all. The JH16 is literally a hiss magnet and the amp passed that test with flying colours.


----------



## xrk971

Those are nice headphones and glad to hear that it sounds great with them. What is the sensitivity on JH16? I tried with my balanced armatures with 112dB sensitivity and did not hear any hiss either.


----------



## gikigill

The JH16 are rated at 18ohms.

Maybe an impedance switch for the next version or maybe 2 versions of the amp for low impedance and high impedance headphones.


----------



## xrk971

If you make it for low impedance it can always drive higher inpedences. The difference is if you have no need for lower impedences then can set bias current a bit lower and reduce battery consumption with no loss in audible performance.


----------



## macky112

xrk971 said:


> Glad you liked the sound on high impedance cans gikigill.  Can you tell us which headphones you liked to pair with them (model and impedance)?
> 
> I will do my best to tweak the settings (bias current) and caps complement to get extended bass for your low impedance cans.  I am thinking boosting bias from 55mA nominal to 67mA and increasing output caps from 470uF to 1470uF - that should increase the bass extension by 3x or allow impedance 3x lower ( circa 16ohms) than 50ohms to have same bass extension.
> 
> The mods will be a 1000uF Panasonic OSCON + 470uF Nichicon AK + 1uF Wima MKS on outputs.  As long as I am at it, I will upgrade your inputs to 4.7uF Elna Silmic II's plus 2.2uF Wima MKS.  I will also upgrade your rail caps to 2200uF 25v rated ones so you can happily drive the system with a 19v desktop PSU for extended dynamics and power output to low impedance cans.  It should be quite the formidable Pocket Amp.




Curious about the 19V desktop PSU option, could you please explain more? Is it a big mod from stick config?


----------



## xrk971

Gill has the Uber NHB with desktop option. It has an external input jack for DC power that switches off the internal batteries and uses 5.5mm coaxial barrel jack with external PSU. It's an unlisted option at the moment - let me know if you want it. It's a lot surgery on the amp to make it happen so cost of amp is quite a bit higher. Look back in this thread and you will see the amp Gill has with external jack. I will repost photo of desktop option here for you to see. Note that the desktop PSU needs to be the ultra-low noise/ripple super regulated variety. The kind they use for high end DACs. Ask for 16.5v, or in Gill's case, can be as high as 19v.


----------



## gikigill

The 19V input is a lifesaver or more appropriately a battery safer cause I'm getting about 5 hours of battery life on a set of 600mah rechargeables.

Make no mistake, this amp has nothing in common with your average Altoids CMoy and I own 2 of those.


----------



## xrk971

gikigill said:


> The 19V input is a lifesaver or more appropriately a battery safer cause I'm getting about 5 hours of battery life on a set of 600mah rechargeables.
> 
> Make no mistake, this amp has nothing in common with your average Altoids CMoy and I own 2 of those.




That's nice that you get 5hrs of life on a charge. Sometimes running for a few hrs at a time and then switching to desktop mode lets the batteries "rest" and sometimes they recover some charge naturally. 

I am going to get some blank tins and offer that as an option. You can then paint or decorate it anyway you like to customize it. 

The only thing in common with CMOY is the tin!


----------



## funch

And the knob.


----------



## xrk971

Actually this amp has little in common with any other portable amp as it is the only SE Class A pocket amp. 

There is indeed something very special about the sound of SE Class A amps given how many people are fans of SET tube amps, and larger SS amps by Pass.

Btw, the NHB amp with and without desktop option is now listed as an option on my shop. 

https://www.etsy.com/shop/XRKAudio


----------



## stellarelephant

I finished a battery life test today with my OKCell USB LiPo batteries. Over four listening sessions I got two hours and ten minutes total.

Shorter than I hoped, but close to what I expected. An Amazon reviewer warned that the 800mAh rating was grossly exaggerated and that the real capacity was around 400mAh. This seems to be the reality. 

On the bright side, these batteries have normal power-on behavior and keep their voltage over 9V til the bitter end. They measure 9.18V when freshly charged and I think the lowest I measured was 9.13V, circa 30 minutes before one cell quit. The weaker cell just switches itself off when it gets low, which is quite obvious, because volume drops a bunch and sound gets distorted. Out of curiosity, I charged the dead cell only and listened to the amp some more to let the stronger cell run its full course. It only lasted an additional 15 minutes.

For me, the convenience of charging my batteries in the tin, via micro USB, plus the steady, surprisingly high voltage these put out, makes them keepers. I can also confirm that these batteries have never gone into any sort of protection mode when charging up my amp's 1000uF rail caps (other users have reported having to switch on/off a few times for proper power up. These just work with the first click.

 I wish they lasted a little longer, but I never really listen for more than 2 hours at a time, so for $11 shipped from AliExpress, I'm happy with these batteries. I plan to buy two more for my second build, and I hope they will give the same turn-on behavior with the larger rail caps I plan to try.


----------



## xrk971

Thanks for the update on those batteries. I might get some myself. The reason they are 400mAhr is that the rating is for the 3.7V native LiPo cell. It goes through a DC to DC step up converter (regulator) which is why it puts out a steady 9.1v. This means there is a high speed switch mode converter. I have done the same thing myself but use a 3000mAhr battery and step up to 16.5v. What I noticed is a broad white noise background at the -90dB level from DC to 1kHz. So even though the switch speed is 1.2MHz there was some background that increased the noise floor. We won't know for sure if these OK brand batteries exhibit same thing but I had to use a CRCRC filter to get rid of it.


----------



## gikigill

Which 3000mah battery are you using Xrk971?


----------



## xrk971

It's under development but I am trying to make an integrated rechargeable battery solution. It's a bare 3.7v 3000mAhr LiPo battery used on tablet PC's and then use a DC step up converter and a USB charger modlule. All separate components. The 50mm x 50mm x 6mm battery is actually 2600 mAhr.


----------



## stellarelephant

Possible switching noise? Ew! Would it be the kind of thing I could hear as hiss if I listened with no music at max volume? Just tried that and thankfully all I can hear is dead silence!


----------



## hte80

xrk971 said:


> Glad you liked the sound on high impedance cans gikigill.  Can you tell us which headphones you liked to pair with them (model and impedance)?
> 
> I will do my best to tweak the settings (bias current) and caps complement to get extended bass for your low impedance cans.  I am thinking boosting bias from 55mA nominal to 67mA and increasing output caps from 470uF to 1470uF - that should increase the bass extension by 3x or allow impedance 3x lower ( circa 16ohms) than 50ohms to have same bass extension.
> 
> The mods will be a 1000uF Panasonic OSCON + 470uF Nichicon AK + 1uF Wima MKS on outputs.  As long as I am at it, I will upgrade your inputs to 4.7uF Elna Silmic II's plus 2.2uF Wima MKS.  I will also upgrade your rail caps to 2200uF 25v rated ones so you can happily drive the system with a 19v desktop PSU for extended dynamics and power output to low impedance cans.  It should be quite the formidable Pocket Amp.


 
  
 Could you elaborate a bit more on how to tune the bias and output capacitorsfor lower impedance headphones?
 [Nevermind, went back a few pages and found the post about capacitance. How should I adjust the bias current though? / Do I need to?]
 I would be looking to use it with ~35-50 ohm headphones. May also use it with some IEMs for the heck of it, and the lowest of my bunch of IEMs would be around 12ohm.
 (Also, how do you plan to fit 3 capacitors in the space allotted for the one output capacitor???)
  


stellarelephant said:


> I finished a battery life test today with my OKCell USB LiPo batteries. Over four listening sessions I got two hours and ten minutes total.
> 
> Shorter than I hoped, but close to what I expected. An Amazon reviewer warned that the 800mAh rating was grossly exaggerated and that the real capacity was around 400mAh. This seems to be the reality.
> 
> ...


 
  
 What caps do you have on the power rails there (dimensions wise)? Wondering if I can get away with some 25mm tall caps and position them how you have yours.


----------



## macky112

Has anybody tried this battery in their build?

https://www.amazon.com/gp/aw/d/B00EJ4NJ7E/ref=mp_s_a_1_14?ie=UTF8&qid=1491737157&sr=8-14&pi=AC_SX236_SY340_QL65&keywords=9v+rechargeable+ebl


----------



## hte80

i think that's what x uses in his.


----------



## xrk971

Yes, but I have to warn folks that fhe qualify control on this brand is marginal. When fhey work, they work well. However be prepared for duds. Failure rate is maybe 30% to 40% out of the box. I have sent 3 boxes back. Amazon is nice for this. I get ones with charger for $21 with 4 batteries.


----------



## xrk971

stellarelephant said:


> Possible switching noise? Ew! Would it be the kind of thing I could hear as hiss if I listened with no music at max volume? Just tried that and thankfully all I can hear is dead silence!




It's very low level -108dB visible on an FFT with switcher I was using. I could not hear it - would not have known if I hadn't measured it. It looks like this. 



I used a CRCRC with 2.2mF and 0.33R to clean it up.

If you can't hear it - don't worry be happy!


----------



## macky112

xrk971 said:


> Yes, but I have to warn folks that fhe qualify control on this brand is marginal. When fhey work, they work well. However be prepared for duds. Failure rate is maybe 30% to 40% out of the box. I have sent 3 boxes back. Amazon is nice for this. I get ones with charger for $21 with 4 batteries.




Thank you for the feedback

I think I'll go with Tenergy 9V 600ma ones because I've had good experience with their Centura AA for my DSLR external flashes, tho not Eneloop grade but close


----------



## stellarelephant

hte80 said:


> Could you elaborate a bit more on how to tune the bias and output capacitorsfor lower impedance headphones?
> [Nevermind, went back a few pages and found the post about capacitance. How should I adjust the bias current though? / Do I need to?]
> I would be looking to use it with ~35-50 ohm headphones. May also use it with some IEMs for the heck of it, and the lowest of my bunch of IEMs would be around 12ohm.
> (Also, how do you plan to fit 3 capacitors in the space allotted for the one output capacitor???)
> ...




I am using 10x20mm 1000uF 25V Nichicon KA audio caps. Biggest reported to fit are 13x20mm. They can be mounted symmetrically too, as X has done. He has a pic a few posts back. For my next build I plan to try some Panasonics, either 1500uF FR or 2000uF HD.

Bias is tuned via R4 resistor value. We just discussed this recently on the DIYA thread. I used the "stock" 33R value, which yielded 55mA bias, and it sounds great with my 50 and 32 ohm cans. I might tweak it a bit and try 47R for my second build, as I'm told it gives a bit more slam for low impedance cans, and lowers THD (in exchange for more heat and shorter battery life). The sound and dynamics are already incredible as is though!


----------



## stellarelephant

xrk971 said:


> It's very low level -108dB visible on an FFT with switcher I was using. I could not hear it - would not have known if I hadn't measured it. It looks like this.
> 
> 
> 
> ...


 
 I have a pretty nice ECHO 24/96 firewire soundcard.  I'd like to learn to make FFT measurements like this...  It would be cool to see what differences, if any, I'd measure from tweaking bias or swapping caps.  I could also see how quiet or noisy my batteries are.  X, are you using the free or paid version of Rightmark RMAA?  I normally use my Mac for audio stuff, but since this is Windows only software, I'll have to dig out my grisly old XP laptop 
	

	
	
		
		

		
		
	


	




, or find an equivalent Mac program.  I recall you talking briefly about a "loopback" measurement at DIYA a while back.  I guess my that would be my first step.  Hopefully the program will perform the calibration itself so I won't have to too much crazy math...


----------



## hte80

stellarelephant said:


> I am using 10x20mm 1000uF 25V Nichicon KA audio caps. Biggest reported to fit are 13x20mm. They can be mounted symmetrically too, as X has done. He has a pic a few posts back. For my next build I plan to try some Panasonics, either 1500uF FR or 2000uF HD.
> 
> Bias is tuned via R4 resistor value. We just discussed this recently on the DIYA thread. I used the "stock" 33R value, which yielded 55mA bias, and it sounds great with my 50 and 32 ohm cans. I might tweak it a bit and try 47R for my second build, as I'm told it gives a bit more slam for low impedance cans, and lowers THD (in exchange for more heat and shorter battery life). The sound and dynamics are already incredible as is though!


 
 funny that, i was thinking of chucking the 1500uf FRs on output 
 no idea if it'll still fit in the tin, but might as well see what sounds good then go about trying to fit it into a case


----------



## funch

Can this amp handle 24VDC? I'm looking to power mine from a 24VDC linear regulated PS.
  
 Of course, I would use 25VDC rail cap's, but would I have to uprate C2's voltage value?


----------



## xrk971

The max voltage on the BF862 JFET is 20v. Although there is a 1k resistor that will drop the rail down by maybe 5 or 6v so should be fine. Let me run a simulation with 24v and see where it is at.

The bigger concern is heat dissipation. You would be burning 1200mW on the four R4 resistors vs 500mW at the lower voltage. The MOSFETs would also be burning off quite a bit of heat more. You could press the SMT side against a soft thick silicone heatsink pad and clamp it tonremoce heat faster and could then drive it hard.


----------



## funch

I think I'll stick with 18V, using this regulator with an AC wall wart: http://www.amb.org/audio/sigma25/


----------



## xrk971

I am testing my desktop version of the pocket amp right now with a 19v SMPS followed by a Linear Tecnolgies LT1963A low-dropout, low noise regulator, I can adjust the output to 18.0v exactly which gives me 113mA bias current in the IRF610 MOSFETs. I tested it with a 33ohm load resistor and then paralleled my 250ohm DT770 with it in order to listen to the effect of a combined circa 30ohm load (combined with 270ohm load resistor on-board). It sounds very good - excellent bass extension as I am running 2x1000uF 16v OSCONs on the output with 1uF Wima bypass and 10uF electrolytic with 0.1uF MKT bypass on the inputs. I installed a rather large 10,000uF 25v Rubycon caps on the power rail to smooth out the linear regulated PSU even further. There is no audible noise or hum from the PSU when using a high quality SMPS from a major brand (HP). This amp is ready to go in a case and will make an excellent fairly compact desktop amp with an easy to use external 19v laptop brick power supply.


----------



## funch

Any plans to do a group buy for the PS board?


----------



## xrk971

You mean the one in above post? That one is from eBay. Look for ultra low noise linear power supplies for DACs and you will see many similar ones.


----------



## funch (May 18, 2017)

Here's my collection. The two on the left use unmatched trannies; the right two use matched. They all use Wima 2.2uF, and Silmic II 4.7uF/25V C1's, and Nichi UHE 1000uF/16V at C3. 

 I will keep the last two, and plan to send the first two on to new owners eventually.






 This one uses Nichi 470uF/16V UKA's and Wima 1uF for C2 to drive low Z 'phones.


 Silmic 100uF/16V and Wima 1uF here at C2 for high Z 'phones.


 This is my NHB unit for low Z 'phones. It uses 470uF/16V Silmic's with 4.7uF Wima's at C2. Since the Silmics are so large .......


  .......... I had to mount the Wima's on the SMD side. Because they are thicker, the tin lid doesn't close all the way at front, but does latch at the back.


 This is my NHB build for hi Z 'phones, and uses 47uF/16V Silmics and .47uF Wima's at C2. 

 FWIW, I much prefer the sound of the Silmic's to the UKA's. The UKA's sound thin to me, with a forward midrange that can sound a bit 'shouty'. The Silmic's are much smoother, but still give plenty of detail.

 Sorry for the poor pic's from my old camera. My photog skills aren't that great either.


----------



## xrk971

Funch,
Thanks for sharing your collection of amps. I am able to solder the 2.2uF Wima's on SMT side and still get lid to close. Is your 4.7uF Wima same size? The trick is to cut the pins of the other cap as close as possible and lay Wima touching the pins. Bend Wima legs 90 deg so they can join protruding solder dab from cap legs coming through. I have to get me some 470uF Silmics. Those are huge! 

Here is closeup of one my NHB's with Wima's on SMT side at C2 and lid still closes. 



Here is dual 1000uF OSCONs for low impedance cans. 



Here is a combo with 1000uF OSCONs and 470uF Nichicon AK's for a balanced system:


----------



## funch

The 4.7uF Wima's are nearly twice the thickness of the 1uF. I didn't really show that clearly in my pic's though. In my pic, the Wima on the right
 is tipped up a bit. I didn't push it back down before I shot the pic.


----------



## xrk971

Ok that won't for then. Don't you think 2.2uF is enough? I know that fits because same size as the 1uF.


----------



## funch

Maybe. I'll try the 2.2's. I was just going by the 10% rule. The lid closes well enough that it doesn't bother me though.


----------



## stellarelephant

funch said:


> Silmic 100uF/16V and Wima 1uF here at C2 for high Z 'phones.
> 
> 
> This is my NHB unit for low Z 'phones. It uses 470uF/16V Silmic's with 4.7uF Wima's at C2. Since the Silmics are so large .......
> ...


 
  
 Oh, wow.  That one (with the huge 470uF Silmic) just looks awesome!!!  Wish I could hear that setup....especially since you say the Silmics sound better than the UKAs, which isn't surprising, considering the Silmic reputation.  I am using the slightly bigger 25V version of the UKA, which theoretically means a lot less distortion from the cap...I can't say I've noticed a "shouty" sound from mine, but I would agree that it isn't the smoothest I've ever heard in my life either, at least without a bypass.  Still looking into bypass options...
  
 What is the purpose of the little Silmics on the input?  I was under the impression that 2.2uF already gets the low corner frequency down to optimal range(2Hz) coming into the amp...essentially perfect, complete bass extension.
  
 Nice work funch.  I'm feeling some amp envy.


----------



## funch

You will have to check with 'X' on the Silmic's at C1. I just copied his lead, and I'm liking what I'm hearing. 
  
 ATM, I'm listening to my DIY 'phones using the ubiquitous Fostex T50RP drivers out of the above amp, and this may the best I've heard these 'phones sound.


----------



## stellarelephant

Funch,
 Whoa, you are listening to music through headphones you built, fed by the amp you built.  That must be one heck of a feeling of accomplishment!  Do you have a link to your headphone build?
  
 So with the big Silmic version, how would you say the amp's treble extension and clarity compares to your other builds?  Any difference?  My goal is to get a bit more "air" out of mine.  More than likely the perfect bypass will do this for me eventually, but I am interested in the Silmics also.
  
 X, can you explain the benefits of a Silmic on the input?


----------



## xrk971

StellarElephant,
More capacitance in the form of the venerable silk paper matrix is always better than less. But in fact, I have a more technical reason on my NHB amps - the entire resistor network is re-tuned for more dynamics and resolution than you can get with just plain old cap rolling. One of the resistors is now a smaller value so it necessitates increasing C1 to keep bass extension low. So why not do it by adding 4.7uF of premier silk paper caps?


----------



## xrk971

I'm working on a big SE Class A desktop amp now. Predicted FFT for 1watt into an 8ohm load looks excellent. Similar profile for 50ohm, 16ohms, etc loads. Capable of delivering 22w of pure Class A power Into 8ohm load and 3.2w into 50ohm loads. Uses three actives in the signal path and four actives total (1 for CCS). Draws 1.13amp bias current and dissipates 40w of heat per channel. So quite the little room heater. 

Schematic is sent out to pro layout artist for developing PCB at present and I should have a PCB in hand in maybe 2 weeks. 

My listening tests with my single channel hand etched prototype have been mesmerizing. The depth and dynamics of the bass is incredible. Works great powering my full range TL speakers that have Fostex FF105WK drivers as well.


----------



## funch

stellarelephant said:


> Funch,
> Whoa, you are listening to music through headphones you built, fed by the amp you built.  That must be one heck of a feeling of accomplishment!  Do you have a link to your headphone build?


 
  
 Scroll down to post #1945. The white gel pads have been long since replaced by Audeze LCD pads. 
  
 http://www.head-fi.org/t/501773/thunderpants/1935


----------



## stellarelephant

xrk971 said:


> StellarElephant,
> More capacitance in the form of the venerable silk paper matrix is always better than less. But in fact, I have a more technical reason on my NHB amps - the entire resistor network is re-tuned for more dynamics and resolution than you can get with just plain old cap rolling. One of the resistors is now a smaller value so it necessitates increasing C1 to keep bass extension low. So why not do it by adding 4.7uF of premier silk paper caps?


 
  
 Ah, I see.  Now I remember that on DIYA you said that you _needed _to use higher capacitance input caps, because with the NHB you changed the local feedback resistor(R2) from 47K to 22K.  Sorry to be dense, but can you explain the benefit of this?  Are you also putting a 68R at R4 in the NHB for higher bias and more slam with low impedance cans?  Any other changes?
  
 If you could give rough estimates of how these resistor substitutions (perhaps individually and combined) affect battery life, that would certainly help me, and possibly others who are planning this build, to weigh the benefits and choose how to customize our builds. 
  
 Fellow Head-Fi member Macky112 just PM'd me yesterday asking about how to tweak the amp for two builds--one for 50 ohm cans and one for 300 ohm.  I gave him the best answer I could based on my capacitor research, but you're in a better position than me to give recommendations, X.


----------



## xrk971

The NHB amp tuning is dependent on amp-to-amp basis so I can't give general values used.


----------



## funch

FYI, I just tried replacing the 4.7 Wima's with 2.2's, but the bass was a tad overpowering, so went back to the 4.7's.


----------



## stellarelephant

funch said:


> FYI, I just tried replacing the 4.7 Wima's with 2.2's, but the bass was a tad overpowering, so went back to the 4.7's.




Good to know. I'm going to try the 4.7 too. What impedance are your DIY cans?

Btw, those things look epic. Why did you replace the earpads? Those gel things look crazy cool. Like sandwiching your head between two sticky cream cheese bagels...I bet the seal was incredible.


----------



## stellarelephant

xrk971 said:


> I'm working on a big SE Class A desktop amp now. Predicted FFT for 1watt into an 8ohm load looks excellent. Similar profile for 50ohm, 16ohms, etc loads. Capable of delivering 22w of pure Class A power Into 8ohm load and 3.2w into 50ohm loads. Uses three actives in the signal path and four actives total (1 for CCS). Draws 1.13amp bias current and dissipates 40w of heat per channel. So quite the little room heater.
> 
> Schematic is sent out to pro layout artist for developing PCB at present and I should have a PCB in hand in maybe 2 weeks.
> 
> My listening tests with my single channel hand etched prototype have been mesmerizing. The depth and dynamics of the bass is incredible. Works great powering my full range TL speakers that have Fostex FF105WK drivers as well.



This sounds like a great project.  I have been using my Pocket Class A as a preamp between my xDuoo X3 DAP and my DIY Aurasound full-range boombox, which has a Tripath amp board inside.  The Pocket Class A really warms things up and brings the vocals to life. (Pic was taken before I had the PCA).






I'm sure the whole thing would sound even better if I tore out the Tripath board and installed one of your 22W desktop amps.  Man, I bet it'd get hot in there though!  I'd probably have to figure out some sort of ventilation for the center cavity where the amp would go.


----------



## funch

stellarelephant said:


> Good to know. I'm going to try the 4.7 too. What impedance are your DIY cans?
> 
> Btw, those things look epic. Why did you replace the earpads? Those gel things look crazy cool. Like sandwiching your head between two sticky cream cheese bagels...I bet the seal was incredible.



The impedance is 50 ohms. I replaced the earpads with the Audeze's as they give much better sound.
The gels are Beyer's and are made for communication use, like in private planes. When you first put them on,
they feel cold and take a while to warm up, which is another reason I sold them.


----------



## stellarelephant

50 ohms--same as my Sennheiser 598.  We are in the same boat in terms of output capacitance needs for bass.  With 470uF we are doing very well and getting about a 6Hz low corner frequency.  I did a bode plot centered on this value, and it turns out the low end rolloff is almost non-existent...better than -1dB at 20Hz and essentially flat from 30 on up.  I'll post a pic when I get access to my other computer.


----------



## stellarelephant

A 470uF cap gives excellent results for 50 ohm cans.  Bass roll-off is a minuscule 0.5dB at 20Hz.


----------



## stellarelephant

Well, I finally ordered a wide variety of capacitors to try in this amp.  Everything from Silmic and Muse electrolytics (even one 47uF bi-polar) to various values of polyester, polypropylene, and polyphenylene sulfide bypasses.  I'm even going to experiment with a few C0G ceramics.  Eagerly awaiting my Mouser box...


----------



## stellarelephant

Elna Silmic II
Nichicon KA, Muse KZ and Muse bipolar ES
Panasonic Oscon and FR
WIMA MKS, MKT, and SMD-PPS. 
Vishay MKT and MKP
Kemet MMK and SMR
Tiny C0Gs from TDK and Kemet

So many combos to try...I've only had a little time to swap and listen but so far all I can say is dang, I can see why everybody loves Silmics!


----------



## macky112

Holy cap rolling batman!

May I suggest you getting some of the header socket pins for your cap rolling?

http://m.ebay.com/itm/3PCS-PCB-Pane...%3A0f729b3f15c0abc320843ac5fffe0b3b%7Ciid%3A1


----------



## stellarelephant (May 17, 2017)

macky112 said:


> Holy cap rolling batman!
> 
> May I suggest you getting some of the header socket pins for your cap rolling?
> 
> http://m.ebay.com/itm/3PCS-PCB-Panel-Female-IC-Breakable-2-54mm-40pin-Single-Row-Round-Header-Socket-/232241763750?hash=item3612b015a6:g:zPkAAOSw3ydVp62l&_trkparms=pageci%3A805a6761-39ed-11e7-869c-74dbd180682a%7Cparentrq%3A0f729b3f15c0abc320843ac5fffe0b3b%7Ciid%3A1



That's probably a good idea except I hate desoldering, and I'd have to remove the sockets later when I put the board back in it's tin.  I've just been pushing the leads through the holes and getting surprisingly reliable contact.

So far I love the 35V 47uF Elna Silmic II on output bypass the best.  It makes a noticeable improvement, whereas the small film bypasses are very hard to hear any difference with.  The 25V 470uF Nichicon AK is already pretty clear-sounding.  Even the 6.8uF WIMA is hard to hear.  But the Silmic rocks the whole sound spectrum.  More transparency, detail, smoothness, and even better bass.  More on my impressions here:

http://www.diyaudio.com/forums/group-buys/302859-xrk971-pocket-class-headamp-gb-64.html#post5081205


----------



## macky112 (May 17, 2017)

Hi @xrk971 ,

I just finished my first board and powered it up.

LED is lit, but no sound is coming through.

where should I start troubleshooting?


----------



## DutchGFX (May 17, 2017)

macky112 said:


> Hi @xrk971 ,
> 
> I just finished my first board and powered it up.
> 
> ...



The obvious thing to check is probe the input connection and output connection for AC voltage. Maybe you simply have a bad joint in your connectors. Other than that, I would probe the pins of the MOSFET and post what your measurements are. gate voltage should be roughly 11.2V (via the spice sim on page 1) and the source should be at roughly 8.5V. 

That's where I would start. 

If those measure correctly, go probe the other labeled nodes in the spice simulation and let me know what doesn't line up. If they are all good we will just have to think a bit more.


----------



## macky112

DutchGFX said:


> The obvious thing to check is probe the input connection and output connection for AC voltage. Maybe you simply have a bad joint in your connectors. Other than that, I would probe the pins of the MOSFET and post what your measurements are. gate voltage should be roughly 11.2V (via the spice sim on page 1) and the source should be at roughly 8.5V.
> 
> That's where I would start.
> 
> If those measure correctly, go probe the other labeled nodes in the spice simulation and let me know what doesn't line up. If they are all good we will just have to think a bit more.


thank you for the reply!

I measured mosfet and only got 2.95V and 3.11V for Pin 3 (the S pin from data sheet https://www.diodes.com/assets/Datasheets/ZVN4306G.pdf) and pins 1 and 2 are all 0v for both mosfets

I had trouble soldering the FETs, maybe poor connection or heat damage?


----------



## DutchGFX (May 17, 2017)

macky112 said:


> thank you for the reply!
> 
> I measured mosfet and only got 2.95V and 3.11V for Pin 3 (the S pin from data sheet https://www.diodes.com/assets/Datasheets/ZVN4306G.pdf) and pins 1 and 2 are all 0v for both mosfets
> 
> I had trouble soldering the FETs, maybe poor connection or heat damage?



Could be. Does the JFET (the first one) have any good voltages? Might be easier if you use this as a reference.





Open the photo in paint or something and put your measured voltages in red at the appropriate locations. You could have broken the FETs but it's unlikely, in my opinion, that you wrecked the FETs on both sides. You don't get sound out of left or right, correct?


----------



## macky112

DutchGFX said:


> Could be. Does the JFET (the first one) have any good voltages? Might be easier if you use this as a reference.
> 
> 
> 
> ...



both channels are silent.

I measured the following:
power = 18V
C1 = 18V (both caps)
C2 = 12V (both channels, both A and B caps)
C3 = 18V
C4 and C5 are all 18V


----------



## DutchGFX

macky112 said:


> both channels are silent.



pm'ed to avoid clogging the thread


Just a separate point, I quite like the minimalist design of this amp


----------



## xrk971 (May 18, 2017)

DutchGFX,
Thanks for stepping in to help!  You are absolutely right.  The first place to start is measure the 3 pins on the MOSFET.  They pretty much tell the whole story. 

Don't worry about clogging thread - this is where questions on how to debug should be posted.

Macky, (You are Babysupra on DIYA I guess)

On MOSFET just these 3 measures (relative to GND) will tell you if amp is working:

1. D (pin 2 or tab) says you have the main power applied to the amp (15 to 18v)
2. G (pin 1) says the gate voltage set by JFET is working (if off then check volts across R3) (7v to 9v)
3. S (pin 3) says bias current is flowing through resistor array and you have Class A action (6v to 8v)

Here is what a nominal DC volts at all points should look like. It may be a little different for battery voltages and particualr JFET and MOSFETs, but not by much - maybe +/- 0.5 to 0.7v typically around the voltages in blue.

Here is schematic with a few more voltage test points:






So the voltages around the JFET should be for DGS, circa 9.6v, 1.8v, 2.0v

For MOSFET DGS, circa 16,4v, 9,6v, 6.9v but in GDS pinout left to right 9.6v, 16.4v. 6.9v.

Across R3 is the voltage that tells you the bias across the JFET is 16.4-9.4v= 6.8v or 6.8mA across 1k

Across R7 is voltage that tells you the main MOSFET bias current 6.9v across 117.5R is 59mA

Voltage on inside (side facing JFET) should be 1.8v and corresponds to the DC bias setpoint on the gate of the JFET.

Install new MOSFETs and repeat measurement and report back - I suspect they are burned out with static zap.


----------



## macky112

HI X and GDFX,

I took some DMM measurements relative to GND, and both right channel and left channel have same measurements:
C1 = C3 = C4 = C5 = JFET DGS = MOSFET DG = 14.8V
C2A = C2B = MOSFET S = 11.8V
R3 = 0V (using DMM 20V reading)

does this mean I have short circuit somewhere?  (maybe even faulty fets?)

attached my pcb for reference.


----------



## DutchGFX

macky112 said:


> R3 = 0V (using DMM 20V reading)



This confuses me. If you get 14.8V on the drain of the JFET, then how can R3 get 0V? It's as if you shorted R3 to ground, while managing to not connect it to the JFET drain, which surely isn't the issue here (I don't think).

Can you measure the voltage ACROSS R3? Put one probe on each end of R3.

At 0V from Drain to Source (they are both 14.8V) I reckon the JFET is in cutoff, so the voltage across R3 would be 0, so therefore both ends of R3 would be at roughly the power supply voltage. Since the MOSFET gate isn't shorted to the source (they are at different voltages) there is no path for current to flow through R3 to ground UNLESS it is flowing straight through the JFET, but the JFET source isn't even at ground, so I just don't see how R3 could be at ground.



I would remove the JFET. Then, since the MOSFET gate and source are both at PSU, it MUST be in saturation. By my calculation, if the JFET isn't present, and the PSU is 16.4V, then the SOURCE voltage on the MOSFET should be like 13.6V.

Remove the JFET, and measure the source voltage with respect to ground. That will tell us if the MOSFET is functioning properly


----------



## macky112

DutchGFX said:


> This confuses me. If you get 14.8V on the drain of the JFET, then how can R3 get 0V? It's as if you shorted R3 to ground, while managing to not connect it to the JFET drain, which surely isn't the issue here (I don't think).
> 
> Can you measure the voltage ACROSS R3? Put one probe on each end of R3.
> 
> ...



sorry for the confusion!

so relative to GND, both ends of R3 reads 14.8V
directly probing both ends of R3 i get 0V

will remove JFETs reply back with measurement


----------



## xrk971 (May 18, 2017)

You measurements are still not clear to me. I would like the black probe of your DMM touching GND on the board (access on the GND pin (closest to edge of PCB) of the 3.5mm jack) and the red DMM probe looking at following on MOSFET:  pin 1 (G), pin 2 (D), and pin 3 (S).  I don't need to know anything about the voltage on the caps.  Only the 3 pins of the MOSFET matter.

What is pin 1 (G) relative to GND?  I assume same as pin 2 (D) = 14.8v?
Pin 3 (S) is 11.8v

Actually, I think you should remove the MOSFET and check to see if the JFET is functioning. The voltage at the drain of the JFET with the MOSFET missing should be the same as with it in place, if everything is working well.

Removing the JFET but leaving the MOSFET leaves no way for you to check if the MOSFET is good and no way to check if the JFET is good.

My guess is that that the MOSFET gate is shorted to the drain, and hence the gate leaks the 14.8v out to the bottom of R3 and thus voltage across R3 is zero.  The MOSFET is basically running as if it is fully turned on with a 3.3v drop corresponding to Vgs for that MOSFET.

If you take out the MOSFET and the voltage across R3 is 6v to 7v, the JFET is good.

If the JFET went bad as in open-circuit, that could cause the MOSFET gate to be at same voltage as the drain with no current flowing through R3.  But it is more likely that MOSFET gate blows before JFET gate blows.

*Edit: * I ran sim with R4 set to a high value to simulate an open circuit on JFET. It gives same values as your measurement.  That the G and D pins of MOSFET same as PSU voltage 14.8v and S is 12v, and no voltage difference acriss R3.  So in light of this, it sounds most likely that:

1. JFET is bad and failed in open circuit
2. cold solder joint on R4 or R5 or S pin of JFET

Try retouching solder points to eliminate cold solder joints around JFET or replace JFET.


----------



## macky112

xrk971 said:


> You measurements are still not clear to me. I would like the black probe of your DMM touching GND on the board (access on the GND pin (closest to edge of PCB) of the 3.5mm jack) and the red DMM probe looking at following on MOSFET:  pin 1 (G), pin 2 (D), and pin 3 (S).  I don't need to know anything about the voltage on the caps.  Only the 3 pins of the MOSFET matter.
> 
> What is pin 1 (G) relative to GND?  I assume same as pin 2 (D) = 14.8v?
> Pin 3 (S) is 11.8v
> ...



black probe on the GND battery pin, and red probe on the DGS of Mosfet, i get following reading:
MOSFET Drain and Gate = 14.8V
MOSFET Source = 11.8V

black probe on the GND battery pin, and red probe on the DGS of JFET, i get following reading:
JFET Source, Drain and Gate = 14.8V

black and red probes on both sides of R3 i get 0V


----------



## xrk971 (May 18, 2017)

Perhaps JFET is fine and R5 is either failed or has cold solder joint.  The attached sim shows a bad R5 (open) gives 14.8v on all pins of JFET and 12v on S of MOSFET.

So check R5's resistance relative to GND, check that it is connected to R4, and check to see if it is connected to GND on one end.


----------



## macky112 (May 18, 2017)

xrk971 said:


> Perhaps JFET is fine and R5 is either failed or has cold solder joint.  The attached sim shows a bad R5 (open) gives 14.8v on all pins of JFET and 12v on S of MOSFET.
> 
> So check R5's resistance relative to GND, check that it is connected to R4, and check to see if it is connected to GND on one end.



bad news, I accidentally reversed polarity of the power supply and blew up MOSFET B's S pin, and I suspect the other MOSFET is also damaged.

but X, i think you are correct, I touched up all of the joints of FETs and R2, R3, R4, R5, and R7s and I am getting normal measurements like you stated previously on the JFET pins and across R3

strangely I am even getting the correct readings on both MOSFET's pins even tho one of them has a visible burnt mark.

I still plugged my DAP just to give it a try and got silence on the right channel and a high pitched hum on the left.

I guess i'll start on my 2nd board because I had trouble removing the MOSFETs on the first board.

pretty bummed about the two damaged mosfets =(((


----------



## macky112

EDIT: double posted...


----------



## xrk971

Sorry to hear you burnt it out - it doesn't always kill an amp to apply reverse polarity. I have done that myself on a big 90w amp and smelled smoke from the wires after 2 seconds.  But amp was fine.  We all do this sooner or later so don't feel too bad.  Glad the DC voltages are checking out - that means your JFETs are probably OK.  No sound probably means MOSFETs are bad - gates are probably burned now because this amp does not have protective zener diodes to clamp the gates.


----------



## macky112

FWIW

RIP Mos'...


----------



## macky112

xrk971 said:


> Sorry to hear you burnt it out - it doesn't always kill an amp to apply reverse polarity. I have done that myself on a big 90w amp and smelled smoke from the wires after 2 seconds.  But amp was fine.  We all do this sooner or later so don't feel too bad.  Glad the DC voltages are checking out - that means your JFETs are probably OK.  No sound probably means MOSFETs are bad - gates are probably burned now because this amp does not have protective zener diodes to clamp the gates.



i found a lot of MOSFETs from the parts bin at work, is there any spec I should be looking for, maybe I can find suitable replacements by any chance?


----------



## DutchGFX (May 18, 2017)

macky112 said:


> i found a lot of MOSFETs from the parts bin at work, is there any spec I should be looking for, maybe I can find suitable replacements by any chance?



Can you also find surface mount resistors? If so, you can always replace the source resistor to match whatever MOSFETS you choose. Again, I defer to X, but most high current MOSFETS should work if they have suitable threshold voltages. The second stage is just a voltage buffer with near 100% negative feedback, so you will be more or less OK if you use any MOSFETS that can drive your cans, but, again, I didn't design it, so it's hard for me to say


----------



## xrk971 (May 18, 2017)

Most N channel MOSFETs can work with some tweaking but it requires a simulation to determine the DC set points which then determine the resistor values.  It's easier to just order more $1.12ea (for 10) ZVN4306GTA's from Mouser.  I have a desktop amp that uses IRF610's but the resistors are all different and took me several days of playing with LTSpice to get the values where I wanted them to obtain the sonic signature characteristic is this amp.  Change the mosfet or the resistors and it's a different sounding amp.  I can't say if it will sound as good but chances are it won't as it takes a lot of effort to tune the circuit. 

You should buy about a dozen at least - discount on 10 or more and you can then match them.

http://www.mouser.com/ProductDetail...=/ha2pyFaduhzzzbly3RCiMvYTDV/uGN047TrGWvUbjs=


----------



## macky112 (May 18, 2017)

DutchGFX said:


> Can you also find surface mount resistors? If so, you can always replace the source resistor to match whatever MOSFETS you choose. Again, I defer to X, but most high current MOSFETS should work if they have suitable threshold voltages. The second stage is just a voltage buffer with near 100% negative feedback, so you will be more or less OK if you use any MOSFETS that can drive your cans, but, again, I didn't design it, so it's hard for me to say



I found a box of mosfet that's labelled 60V 45A and they have K1542 markings on them

upon googling K1542, I found out it is a replacement for NTE2986
http://www.nteinc.com/specs/2900to2999/pdf/nte2986.pdf

is this remotely close in spec to ZVN4306GTA at all?


----------



## DutchGFX

macky112 said:


> I found a box of mosfet that's labelled 60V 45A and they have K1542 markings on them
> 
> upon googling K1542, I found out it is a replacement for NTE2986
> http://www.nteinc.com/specs/2900to2999/pdf/nte2986.pdf
> ...



You might have a rough go trying to solder that onto the surface mount pads...

Those are much beefier transistors than the ZVN4306GTA, they could work, but it's REALLY hard to tell because I can't find a good datasheet for either variant with curves that I can interpret, which makes it rather challenging to determine the feasibility of replacement. Do you have any other NMOS available?


----------



## xrk971 (May 18, 2017)

It has GDS pinouts of same spacing as IRF610 which I know I was able to solder onto the board.  Bend the pins to have a flat of similat length as pad (1.5mm or so) and solder it standing up. Add a local heatsink to it. The input capacitance is much larger so performance probably won't be as detailed. 
But it may be worth just trying it. 

Try it like this - if you have the resistors to make it a 100mA bias Desktop Amp - go for it.

http://www.diyaudio.com/forums/group-buys/302859-xrk971-pocket-class-headamp-gb-38.html#post5014544











It sounds like your PSU has buzz or hum.  You need a very low ripple PSU for this amp. Super regulator or batteries are best.


----------



## macky112

DutchGFX said:


> You might have a rough go trying to solder that onto the surface mount pads...
> 
> Those are much beefier transistors than the ZVN4306GTA, they could work, but it's REALLY hard to tell because I can't find a good datasheet for either variant with curves that I can interpret, which makes it rather challenging to determine the feasibility of replacement. Do you have any other NMOS available?


the other closest one I found would be K942, which is a NTE2985 replacement
http://www.nteinc.com/specs/2900to2999/pdf/nte2985.pdf


----------



## macky112

xrk971 said:


> It has GDS pinouts of same spacing as IRF610 which I know I was able to solder onto the board.  Bend the pins to have a flat of similat length as pad (1.5mm or so) and solder it standing up. Add a local heatsink to it. The input capacitance is much larger so performance probably won't be as detailed.
> But it may be worth just trying it.
> 
> Try it like this - if you have the resistors to make it a 100mA bias Desktop Amp - go for it.
> ...



I soldered on the K942 mofsets following X's style, but the amp doesnt turn on, i checked the battery pins and it bounces between 3V to 5V, I tried both 15V and 18V power supply, same thing.

could the stock R7 array value too far off to turn on the amp?


----------



## DutchGFX

macky112 said:


> I soldered on the K942 mofsets following X's style, but the amp doesnt turn on, i checked the battery pins and it bounces between 3V to 5V, I tried both 15V and 18V power supply, same thing.
> 
> could the stock R7 array value too far off to turn on the amp?



Put your DMM in series with the PSU to measure the current. You could be drawing so much current that your PSU is sagging. Did you change any other components other than the MOSFETS?


----------



## macky112

DutchGFX said:


> Put your DMM in series with the PSU to measure the current. You could be drawing so much current that your PSU is sagging. Did you change any other components other than the MOSFETS?



Just the mosfets 

I'll measure current tomorrow, but they are 40w power supplies tho, if two 9V batteries can power this amp...  unless the new K942 mosfets draws THAT MUCH current...

I have to go pick up my kids from school now, thanks again X and DHFX! to be continued tomorrow lol


----------



## xrk971

The JFET Drain voltage after the 1k might be too high for this mosfet. That's why I said it need to be simulated to set the D.C. Levels properly. If you have an IRF610 and change to the values shown in my last post - it will work.


----------



## macky112

I switched to a 160W 18V power supply and the amp powered up OK.

but I only get sound from RIGHT channel, LEFT channel is silent

new DMM readings:

M1A Pins 1 2 3: 11.9v, 18v, 9v
M1B Pins 1 2 3: 10.64v, 18v, 8.8v
Q1A: Pins G D S: 1.97v, 2.25v, 10.6v
Q1B: Pins G D S: 1.9v, 10.9v, 2.1v      <--- D and S values seems opposite from Q1A!?
across R3A: 7.4v
across R3B: 7.11v 

is the "B" path left channel or right channel?  curious how come the JFET values for S and D are reversed between the A channel and B channel.


----------



## macky112

macky112 said:


> I switched to a 160W 18V power supply and the amp powered up OK.
> 
> but I only get sound from RIGHT channel, LEFT channel is silent
> 
> ...


measuring across R7A 8.8v 
measuring across R7B 9v


----------



## xrk971 (May 19, 2017)

Good news, we are making progress. Did you have a second board with new FETs or did you replace the MOSFETs on first board?

The JFET Q1 and Q2 are laid out in opposite orientation for convenience of routing. This is possible because the JFET is symmetric, that is D & S are interchangeable for the BF862. A very nice feature - it basically works as a gate-controlled variable resistor. So your measurements are right on the mark. From the DC setpoints data, it looks like the amp is fully functional on both channels. Bias current is a bit on high side but ok - at the max allowed thermally (76mA). Your bias currents are actually pretty well matched for both the JFETs and the MOSFETs - it should be an excellent sounding amp.

Why no music out of one channel? Possibly a bad 3.5mm stereo jack connector? I bet, if you take your DMM probe in AC volts mode and touch the S (pin 3) of the MOSFET while playing music loud on the input (assuming input jack pins are good etc), you will see fluctuating AC volts - sign of music.

When the DC setpoints are all good - the amp HAS to WORK! If no music, it is a bad connection somewhere.

These are all excellent values and means the amp should be fully working.

Measurements Show:

M1A Pins 1 2 3: 11.9v, 18v, 9v
M1B Pins 1 2 3: 10.64v, 18v, 8.8v
Q1A: Pins G D S: 1.97v, 2.25v, 10.6v
Q1B: Pins G D S: 1.9v, 10.9v, 2.1v <--- D and S values seems opposite from Q1A!?
across R3A: 7.4v
across R3B: 7.11v
measuring across R7A 8.8v
measuring across R7B 9v​Good luck - you are very close. It is something like a bad cable, bad solder joint, bad jack, bad wire, etc.

A is right channel (look for Ring on 3.5mm jack) and B is left channel (look for tip on 3.5mm jack).


----------



## macky112

Hi X,

this is still the first board, I soldered on K942 mosfets standing up and got these values, I will touch up the solder points of the jacks and see what happens.

also I will monitor the AC currents through the S legs of mosfets

will report back!


----------



## macky112

xrk971 said:


> Why no music out of one channel? Possibly a bad 3.5mm stereo jack connector? I bet, if you take your DMM probe in AC volts mode and touch the S (pin 3) of the MOSFET while playing music loud on the input (assuming input jack pins are good etc), you will see fluctuating AC volts - sign of music.



for this AC volts measurement, I touch red probe on MOSFET S pin and where do I touch the black probe?

I get same 9V readings by only using the red probe on MOSFET S pins, and leaving black probe in the air...


----------



## DutchGFX

macky112 said:


> for this AC volts measurement, I touch red probe on MOSFET S pin and where do I touch the black probe?
> 
> I get same 9V readings by only using the red probe on MOSFET S pins, and leaving black probe in the air...



Unless otherwise specified, you should assume probing a pin means with respect to ground. The voltage at a point/node/pin is generally with respect to ground (black probe on gnd), and the voltage across something is putting one probe on each side of something. You put the red on source and black on gnd and ensure you are getting some AC voltage (with music input, of course)


----------



## macky112

DutchGFX said:


> Unless otherwise specified, you should assume probing a pin means with respect to ground. The voltage at a point/node/pin is generally with respect to ground (black probe on gnd), and the voltage across something is putting one probe on each side of something. You put the red on source and black on gnd and ensure you are getting some AC voltage (with music input, of course)


DMM in AC voltage mode, and in 2V digit reading, with black probe on the GND pin from input jack, I get these readings at following locations:
input jack signal pin closer to edge: 0.068v
input jack signal pin further away from edge: 0.055v
M1A S pin: 0.025v
M1B S pin: 0.014v
output jack signal pin further away from edge: 0.014v
output jack signal pin closer to edge: 0.025v

this is with all volumes (DAP and AMP) at max value.


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## xrk971

If you are using your own random mosfet then I can't guarantee it will work even if DC setpoints are sort of within range.  It strange that it looks like the output is lower than the input. On the side that plays music, is it loud?  14mV AC should make sound and not be silent. So you may have a short to ground on the output somewhere.  This would explain the no sound yet good DC levels. But AC goes to zero. To check for this remove power and set DMM to ohms and measure resistance on output side of C2 and ground. It should be same as RL - about 270ohms pet the schematic.  If it is low like a couple ohms or less, you may have an inadvertent solder bridge to ground on the output.


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## eonfire

Good day to all! I just have a noob question: Can this amp be used for amping IEMs too? Or is this specifically catered for HPs? Thanks!


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## VicOzzy

Great work with this amp, can't wait to try it out.

Does changing the distance between components affect audio quality?
For example, i am planning on building an O2 amp (+ODAC) on a custom enclosure (still using the official PCB), and some of the components, namely the input/output jacks, power, buttons/switches, and potentiometer will not be soldered on the PCB, rather they would be connected through wires to it inside the custom case (which obviously will not be used as a portable amp). Will this affect the overall sound quality of the amp?

I apologise if this might highjack the convo a bit, but i lack permissions still to post a new thread here.
Thank you for your attention.


----------



## rellik

My suggestion would be to build for ergonomics.


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## DutchGFX

VicOzzy said:


> Great work with this amp, can't wait to try it out.
> 
> Does changing the distance between components affect audio quality?
> For example, i am planning on building an O2 amp (+ODAC) on a custom enclosure (still using the official PCB), and some of the components, namely the input/output jacks, power, buttons/switches, and potentiometer will not be soldered on the PCB, rather they would be connected through wires to it inside the custom case (which obviously will not be used as a portable amp). Will this affect the overall sound quality of the amp?
> ...



Nah you're good. Just try to avoid having the wires be near the power line


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## VicOzzy

DutchGFX said:


> Nah you're good. Just try to avoid having the wires be near the power line



Thank you!


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## stellarelephant (May 23, 2017)

eonfire said:


> Good day to all! I just have a noob question: Can this amp be used for amping IEMs too? Or is this specifically catered for HPs? Thanks!



It will amp anything with an impedance between 30 and 600 ohms.  If you are at the extreme low end of that range, you'll probably want to set the bias high for best dynamics and and put in at least 1000uF per channel for the output caps for bass performance.  Otherwise the stock config works great.


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## eonfire

stellarelephant said:


> It will amp anything with an impedance between 30 and 600 ohms.  If you are at the extreme low end of that range, you'll probably want to set the bias high for best dynamics and and put in at least 1000uF per channel for the output caps for bass performance.  Otherwise the stock config works great.



Thanks for the info! Might be considering this amp in the near future but Im leaning towards the built-up unit as my soldering skills is quite next to nil! Thanks again and Good day!


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## rellik (May 23, 2017)

Dont sweat solder skills. It isnt nearly as hard as it seems. Its just about keeping the tip clean. Like rewet a fresh iron with solder and a wet sponge after each joint. It will reduce frustration immensely.

Just dont do what I have seen sometimes by applying solder to the iron tip and paint it onto the joint. Its more like welding. The flux is necessary to get the bond. Just make sure to get the tip touching both/all pieces to be connected. If it doesnt flow on, then clean the tip again. 

Getting the parabola shape is about getting the heat to wick solder into the thru hole. Otherwise the joint may resonate.

Bottlehead stocks a few amazing kits which may be more worth your while than a cmoy or its equivalents. Like I have been mentioning, if something breaks, just fix it or replace it. Dont sweat it otherwise you wont try again.


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## xrk971

IEM's work great and several amps out there are used primarily for IEM's and even earbud types.  

For flying leads to improve ergonomics, be careful to keep leads from input jack to board as short as possible and twist the wires and use as thin of wire as possible.  Shielded thin RG-174 is good. You don't want to pick up noise as this amp is silent.


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## stellarelephant (May 29, 2017)

*Elna Silmic II vs. Nichicon Muse KZ*

I did some fun listening tests with different capacitor combos in this amp.  Bypassing with a 1/10 value top shelf electrolytic does quite a lot for the sound--much more than a 1/100 value film!

After several hours listening back and forth between the 47uF Silmic II and Muse KZ on output bypass duty in the PCA amp, I can say with confidence that the two caps sound quite distinct in this application. Different beasts altogether.

I am not auditioning these caps on their own. They are bypassing my existing 470uF Nichicon KA output caps, so synergy is likely a factor. Also, the Silmic has the slight advantage of a 35V rating vs. the 25V Muse, but the caps are the same capacitance and have identical physical dimensions, so I feel the comparison is reasonable. I used both my xDuoo X3 DAP and Echo Audiofire soundcard as sources, using the Pocket Class A to power my Sennheiser HD598 headphones and also as a preamp, feeding my Tripath-powered Axiom Audio M3 speakers.


 

*Silmic*
As I explained in my earlier post, the Silmic tames the upper mids and low treble in a very smooth and musical way, by “damping” the resonances of the upper frequencies. The easiest way I can describe this sound is to say that notes with a lot of information in the midrange and low treble seem to buzz less and decay faster, lending a certain sense of control and wonderful transparency, as notes pop up and then sink rapidly into a dark background. This is nice and easy on the ears, but I notice that percussion can sound ever-so-slightly hollow and vocals a tad recessed in the mids as a result…smooth but perhaps harmonically incomplete. There is nice air on top, above the threshold of this effect. Synth pads emerge glassy and ghostlike from a cool, serene atmosphere in "Monument" by Robyn. Somehow this squeaky clean sound adds an amazing depth to the soundstage. I can listen "in" to the music more, and I can hear Amos Lee moving closer and further from the microphone as he sings "Bottom of the Barrel", creating a 3-D soundstage. What's more…his foot stomps in the beginning of the song sound convincingly deep. There is tight control, speed, and clarity in the bass registers, with superb weight all the way down to sub-bass. With complex and difficult material, like the rapid dynamic cliffs in the Futuristics remix of "Moonshine" by Bruno Mars, the Silmic keeps its composure, allowing the necessary breathing room in the mix for instrument separation and good dynamics.

*Muse*
The Muse lets everything through. In fact, my amp is subjectively louder with them in place. But volume isn’t the main difference…even if I dial it back, I can hear it. It lifts a veil and adds warmth. Presence, detail, and dynamics are off the chain. The snare drum in “The Bird” by Anderson .Paak simply hits faster and harder, with immediacy and sharp coherence. On top of that, I can now follow the long decay of its reverb tail all the way back down to the noise floor. Micro-details like the triangle “ting” in Daft Punk’s “Give Live Back to Music” come flying out of the mix…whereas I didn’t even notice them with the Silmic. Cymbals and chimes have a hyper-realistic timbre, with all their metallic harmonics beautifully apparent. Unfortunately this tizz carries over into vocal peaks and other sounds as well. While not the cleanest ever, the vocals are awesomely fun…in your face in a most engaging way with the KZ. Voices pop out of the mix with midrange presence, detail, and unabashed sparkle. The fat analog synth lead of Miike Snow's "Black and Blue" rips through the air like electricity…amazing. Bass is powerful, with more overall quantity than the Silmic, but sadly it is a bit less extended, and muddy in comparison. Every sound drips with texture and commands attention…it's like the notes are singing directly into my head. This can come off as compressed and fatiguing with complex material, but with simple arrangements, like Norah Jones' "Burn", the immediacy and realism of her performance is stunning.

Think of it this way:

The Silmic II is Gandalf's sword, Glamdring. Meticulously crafted, it has the heft to deliver solid bass thump and its sound is honed perfectly smooth, delivering balance and extension. Its enchanted blade cooly illuminates musical space, yielding a cool and calm atmosphere, even in the midst of musical chaos.

The Muse KZ is Kylo Ren's lightsaber. Red-hot, it hums with extreme harmonic texture and deals electrifying mids and treble. Every last detail cuts effortlessly through the mix with speed and warmth. But its brute resolving power can sound a touch unrefined (i.e. more distortion), and deep down, it's a little unsure in the bass.

I have actually had a hard time deciding which one I like more. They both bring out different nuances. My musician buddy who had a listen said he preferred vocals on the KZ but overall presentation with the Silmic. He joked that he wants me to build him an amp with a switch to toggle between caps! By the way, the green caps in the second photo are Muse ES bipolars. I left them out because they really didn't do anything audible as bypass caps.


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## xrk971

StellarElephant,
Thank you so much for such a detailed study and your carefully written reports. The Muse cap definitely sounds like it's worth trying.  Wish I knew about your report before ordering my last batch of caps from Mouser. It will have to wait for the next order.  Lately I have been having great luck with this combo:

Output with 1000uF 16v oscon and 100uF 16v Silmic II and 0.47uF 100v Vishay MKT. 

Input with 10uF Silmic II and 2.2uF 50v Wima MKS

Bass, mids, highs are all well represented and smoothness is superb. 1000uF let's me hit some deep bass with 50ohm cans.


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## stellarelephant

Yeah I still keep going back and forth between the two.  I think I'm going to leave the KZ in for a while and see if I get any burn-in improvements ( esp. in the bass) and then to be fair I'll do the same with the Silmic.  If they stay exactly the same, I will probably end up going Silmic. It really is a nice high fidelity sound that never offends. 

Your setup seems like it ought to sound very nice indeed.  When I get around to my second board I'll have to try out a similar output combo.  And I'm curious to experiment with an electro added to the input...to compare it with both the stock WIMA and my DIY PPS cap.


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## xrk971 (Jun 3, 2017)

A nice review of this amp by Michael of Headfonics.com just came out:

http://headfonics.com/2017/06/the-class-a-nhb-pocket-amp-by-xrk-audio/

The NHB unit I provided for the review used 1000uF Oscons + 100uF 16v Silmic II's + 1uF 63v Wima MKS on output and 2.2uF 50v Wima MKS + 4.7uF 35v Silmic II's on input.

I now bought a bunch of 10uF 35v Silmic's that are about the same size as 4.7uF so no point not to use.

But according to the reviewer, here is what he said about the treble:

"Sparkle factor is just incredible, at least to my ear. I can’t see anyone saying this amplifier is lacking treble density, response or substance. If you have a headphone geared for treble, you will adore this amp in terms of both quality and quantity offered. Yes, it does justice and then some to my $600 Audeze iSine20, as well as the Flare Audio..."


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## rellik (Jun 3, 2017)

Panasonic FM and FC are more similar to typical real world applications for use in small and larger sizes. They retain a long life and have quite good extension without making things too quick. Similar to a Koss PortaPro headphone.

If you want to clean the addictive factor from the KZ yet retain some of its sonic qualities, consider Nichicon KX with power supply KA series. KG power supply will sound disparate without a more refined cap preferably a KZ due to frequency bandwidth range. KX and KA are similar to a small slit ported Sony MDR headphone such as Sony MDR-7502. Another great headphone.

Silmic are cloying and stuffy to my ears and alittle slick. Cerafine are much better from the Elna lines. Silmic are kinda like a cross between a Sennheiser and a Beyerdynamic where Beyerdynamic alone seperates from the pack with a lot of the KG note. High powered Sennheiser are like Silmic and high powered Beyerdynamic are line KG. If you want to use Silmic, please have a lot of current on hand. AKA not for CMOY imo.

Grado's are honestly more like Cerafines but can be tamed quite well using KZ, KZ are more like AKG K-701. Something I want from speaker vs portable "rare" headphone use.

My Master and Dynamic are a lot like a cross between KG with alittle Silmic depending on music but overdrive to really strange BHC Aerovox status where everything plays just fine but distorts on the diaphraghm alone vs the coil and magnet.

Here is an example of a well driven Silmic used in power supply you can hear the solen DC bypass and Mills Wirewounds when the Silmic power supply gets drained and relies on the LithIon:


This is the aforementioned design attached to a Sony PCM-F1 Betamax DAC and Sony SL-2001 Betamax (the Real Folk Blues) vs a Krell Foundation Processor and HifiMan HM-801 (be wary that the Krell Foundation is newish and lacks a discernible zipper note):


Here is an example of a well driven Silmic used in Coupling cap position don't know what power supply probably vintage Elna cerafine:


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## stellarelephant

Rellik, wow!  That's a lot of great info to absorb.  And exactly the kind of subjective interpretations I have been looking for. While opinions are easy to come by, this kind of detailed sound analysis is really hard to find. Thank you.  

Since you've obviously done a good deal of cap rolling, what is your opinion about the "sweet spot" for bias voltage vs cap voltage rating?  The output caps in this amp see about 6.5V DC. I have been trying to stick with a 25V or higher rated cap to minimize distortion, but if I opt for 16V, that opens up more options due to smaller sizes for the same capacitance.


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## rellik (Jun 4, 2017)

Lower voltage caps will burn out faster. Bias is really dropping the full B+ to the bias caps. Honestly many of the caps can be a vareity of voltage ratings, check their can size.

Honestly dont know, depends on the amp and cap rolling especially when im trying to guess based on photographs from different capacitor sources. In sincerity, I dont have much experience with BHC Aerovox yet have seen a HiWatt british guitar amp. Straight up black hole.

Otherwise, my handle ("Rellik") looks quite stupid in text rather than on the side.


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## xrk971

Output caps are rated 16v, DC bias there is circa 7v. I doubt that level of DC will burn out an electrolytic designed to work at twice the operating voltage.  On inputs the rating is 16v as well and DC bias there is about 1.5v.


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## macky112 (Jun 12, 2017)

xrk971 said:


> I have had reports from a professional music producer who used this amp with HD600's and they rock. He had an O2 before this and he says the difference is amazing with this little amp. The music just sounds better.


I was reading up on O2 amp while I wait for my new pcb to arrive, because my monoprice m1060 is rec for at least 200mW at 50ohm (can take up to 2W at 50ohm) and the XRK PCA amp we calculated to be about 50mW at 50ohm. Glad I wanted to review both PCA amp threads before my next build attempt and came across this post, so scratch that O2 DIY idea! Now my question is, anyway to boost output power of PCA higher?  Is running an 18v power supply making more output power compare to running two 9v batteries?


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## xrk971 (Jun 12, 2017)

You can make the desktop version of the amp - in DIYaudio thread I show a variant with 125mA bias and uses large IRF610 MOSFETs and large dual 3w 33R resistors in series for 66R source resistors. Voltage is at 19v. It may get a little more power but not in the watts range.

To do 2w at 50ohms will require a true desktop amp like the Silicon Harmony (still under development ). The SH puts out about 40w of heat per channel in pure SE Class A mode of operation.  It runs 28v to 34v power supply.  And to drive 50ohm cans, can make 1w rms and 2w peak.

Here is photo - I am testing and about to out it into a real case.


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## macky112

xrk971 said:


> You can make the desktop version of the amp - in DIYaudio thread I show a variant with 125mA bias and uses large IRF610 MOSFETs and large dual 3w 33R resistors in series for 66R source resistors. Voltage is at 19v. It may get a little more power but not in the watts range.
> 
> To do 2w at 50ohms will require a true desktop amp like the Silicon Harmony (still under development ). The SH puts out about 40w of heat per channel in pure SE Class A mode of operation.  It runs 28v to 34v power supply.  And to drive 50ohm cans, can make 1w rms and 2w peak.
> 
> Here is photo - I am testing and about to out it into a real case.


Ok I'll try the desktop variant first

What is the purpose for 66R source resister?  For protection or dissipate heat?


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## xrk971

Here is link to desktop amp. 

http://www.diyaudio.com/forums/group-buys/302859-xrk971-pocket-class-headamp-gb-38.html#post5014544

Here is schematic:






R7 is the 66ohm source resistor in question. It serves as the "constant" current sink for the class A operation. You need something to draw the heavy bias load through the MOSFET. So for a 125mA bias at about 11v is about 1.4 watts. These run continuously hot so best to reduce the max load so spread over two 3w resistors so they can run forever without stress.


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## funch (Jun 12, 2017)

Seeing those big heatsinks reminded me that I had several tiny 'sinks left over from another project, so I stuck them on my current builds. I got them from Amazon, and they are self-stick.
















[/URL][/IMG]


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## macky112

funch said:


> Seeing those big heatsinks reminded me that I had several tiny 'sinks left over from another project, so I stuck them on my current builds. I got them from Amazon, and they are self-stick.


ooooh may we see some pics please?


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## funch

I would love to post pics, but Photobucket is not working atm. I'm still trying, but ......... .


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## funch (Jun 12, 2017)

Finally got them up. It may have been a problem with Head-Fi. On my end, it's been difficult to
load pages lately. If I try to load a page, it just goes to a blank screen. I have to go back and do it 
again to get it to load.


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## funch

These: https://www.amazon.com/Aluminum-Chi...e=UTF8&qid=1497304608&sr=8-14&keywords=rhs-01


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## macky112

xrk971 said:


> Here is link to desktop amp.
> 
> http://www.diyaudio.com/forums/group-buys/302859-xrk971-pocket-class-headamp-gb-38.html#post5014544
> 
> ...


Hi X, does higher bias current means higher total power output?  If I want to tweak bias current, do I just change the resistance value at R7?


----------



## xrk971

Output power is a combination of voltage swing and current. Power equals current x voltage. But to get an amp to make more power isn't as simple as increasing bias or voltage.  Sure, higher voltages and higher current gives the capability to make more power. But you have to simulate the amp in LTSpice and see what happens when you drive it hard to make more power.  With this SE design, there is a limit as distortion and clipping will take over at some point.  With the simulation I can predict that with a 50ohm load, the output voltage swing is about 5.5v peak to peak before clipping occurs.  So to increase this one can increase bias. But making R7 smaller is not how you do it. You have to adjust R3, R4, R5, and R7 to balance higher bias with achieving symmetric clipping and the correct harmonic distortion profile.  It's a lot of interplay between competing variables.

You are welcome to download LTSpice and run he model and tweak it to see if you can get more power. One thing that can help is using MOSFET for a CCS instead of the resistor R7.


----------



## macky112

xrk971 said:


> Output power is a combination of voltage swing and current. Power equals current x voltage. But to get an amp to make more power isn't as simple as increasing bias or voltage.  Sure, higher voltages and higher current gives the capability to make more power. But you have to simulate the amp in LTSpice and see what happens when you drive it hard to make more power.  With this SE design, there is a limit as distortion and clipping will take over at some point.  With the simulation I can predict that with a 50ohm load, the output voltage swing is about 5.5v peak to peak before clipping occurs.  So to increase this one can increase bias. But making R7 smaller is not how you do it. You have to adjust R3, R4, R5, and R7 to balance higher bias with achieving symmetric clipping and the correct harmonic distortion profile.  It's a lot of interplay between competing variables.
> 
> You are welcome to download LTSpice and run he model and tweak it to see if you can get more power. One thing that can help is using MOSFET for a CCS instead of the resistor R7.



I'll put together this second attempt when pcb arrives. Just making some notes for faster referencing later. So if the new 19V desktop variant build bias current is off from your suggested 125mA, do I start the troubleshooting with changing R7 value?  I.e. If I only get 115mA bias current, do I lower R7 value to bring it closer to 125?


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## xrk971

Macky112:
You should use the resistor values shown in this figure here:





Don't change anything at first.  You want to make sure it works as designed first and then do your tweaking.  Changing R7 will move the bias a small amount.  The bigger one is R3, but that must be balanced by changing R7 and R5 to keep voltage above R7 (MOSFET source pin) approximately 1/2 of Vcc to ensure that clipping is symmetric otherwise you lose head room.

Two 33R 2W or 3W in series work well for R7 as that is 66R and about the same as 67.6R spec'd in schematic above.


----------



## macky112

Hi @xrk971 , could you tell me what is the purpose of C4 and C5 rail bypass caps?  any harm for not populating them?  any harm for replacing them with a single 1uF cap?


----------



## xrk971

They are bypass caps for the large 2200uF main power rail caps. Bypass caps present an ultra low ESR path for high frequency noise to get shunted to ground.  Having two low ESR caps in parallel cuts ESR by half so. Even better.  It will work without them and will work with 1uF cap there.  Just make sure it is a X7R MLCC cap.  It helps to reduce high frequency RF noise from having a chance to reach to MOSFETs.


----------



## macky112

xrk971 said:


> Output power is a combination of voltage swing and current. Power equals current x voltage. But to get an amp to make more power isn't as simple as increasing bias or voltage.  Sure, higher voltages and higher current gives the capability to make more power. But you have to simulate the amp in LTSpice and see what happens when you drive it hard to make more power.  With this SE design, there is a limit as distortion and clipping will take over at some point.  With the simulation I can predict that with a 50ohm load, the output voltage swing is about 5.5v peak to peak before clipping occurs.  So to increase this one can increase bias. But making R7 smaller is not how you do it. You have to adjust R3, R4, R5, and R7 to balance higher bias with achieving symmetric clipping and the correct harmonic distortion profile.  It's a lot of interplay between competing variables.
> 
> You are welcome to download LTSpice and run he model and tweak it to see if you can get more power. One thing that can help is using MOSFET for a CCS instead of the resistor R7.


Could you explain more about using a mosfet instead of R7. How to solder the mosfet pins? What spec mosfet should I use?


----------



## macky112

xrk971 said:


> Macky112:
> You should use the resistor values shown in this figure here:
> 
> 
> ...


Hi X, I have a noob question too embarrassed to ask on the DIYA forum, could you please go over each of the resistors and what their function are?  
For example, what is RL?  From first post on the PCA thread on Diya BOM list, you mentioned RL can be adjusted to high current draw, could you explain more?  And also for R1, R2 etc

Thanks!


----------



## xrk971

macky112 said:


> Could you explain more about using a mosfet instead of R7. How to solder the mosfet pins? What spec mosfet should I use?



Please look carefully at photograph and see how the pins on the MOSFET are bent 90 to form a small "foot" that rests on the SMT solder pad.  The pitch of the pins on the T220 is same as SOT223 (0.100inch).


----------



## macky112

xrk971 said:


> One thing that can help is using MOSFET for a CCS instead of the resistor R7.



My bad for not being clear, I am curious about using another mosfet instead of R7 as you mentioned here for CCS


----------



## xrk971

macky112 said:


> Hi X, I have a noob question too embarrassed to ask on the DIYA forum, could you please go over each of the resistors and what their function are?
> For example, what is RL?



You should read the thread where that circuit was developed: 
http://www.diyaudio.com/forums/solid-state/301164-mosfet-source-follower-headamp.html

http://www.diyaudio.com/forums/solid-state/301164-mosfet-source-follower-headamp-24.html#post4944112

It's too much to discuss what each one does, but this topology is nothing new.  Lookup single ended source follower amplifier. 

Rl is to provide a nominal load to the output so that the capacitors are driving something otherwise when the phones are disconnected it is a pure capacitive load.  RL also helps to bleed off the caps so that after initial turn on transient, there is no "pop" when you insert the headphone jack.


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## xrk971

macky112 said:


> My bad for not being clear, I am curious about using another mosfet instead of R7 as you mentioned here for CCS



The multi JFET output circuit I posted above was a design by another member and the row of JFETs on the bottom are the CCS's.  Same thing can be done with a MOSFET.  Basically, a MOSFET can be biased to flow current and it sets the class A bias current by setting its gate voltage.  You can see this in many single ended class A designs. You need to read up on constant current sources using a MOSFET.

Here is a design for a tube headamp that is single ended class A with a MOSFET CCS that is controlled by a TLM431 programmable zener.  You can replace the tube front end with the BF862 front end that I am using and it would work quite well.  It looks very similar doesn't it.

This is a Sodacose What amp design: 
http://www.diyaudio.com/forums/solid-state/289300-simple-class-hybrid-mosfet-source-follower-13.html


----------



## funch

I fired one of my amps up today, and can confirm that those little heat sinks do work. I can only hold my finger on one for about two seconds.


----------



## xrk971

That means your bias is running real hot.


----------



## funch

I should mention that it was driving my DIY 'phones with T50RP planar drivers, which take a good amount of current. At idle, the 'sinks were much cooler.


----------



## xrk971

That's interesting because SE Class A amps should burn about same amount of heat whether playing music or not. What are T50RP planars?


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## funch (Jun 17, 2017)

T50RP's  are Fostex headphones. A few years ago several Head-Fi'ers started either modifying them or taking them apart and using the planar drivers to make their own headphones.

I find that my version is a bit harder to drive than even the Audeze LCD planars.


----------



## macky112

The bottom paragraph of this post is the reason I am chasing uber output power amps haha

https://www.head-fi.org/f/threads/m...anar-headphones.820107/page-301#post-13550929

I really want the desktop variant to be a winner for me, cmooooooon!


----------



## macky112

Hi X,

Does it make sense for this analogy: a Honda Civic (as an ideal but less powerful amp) and a Ferrari (as an ideal more powerful amp), and both are cruising on the freeway at 60 mph (as my comfortable listening level at X db) then when sub bass are called for (as the car acceleration), the Ferrari amp though playing at same listening level would produce better sub bass?


----------



## xrk971

I think the analogy is partially right.  You are describing dynamic headroom as being important to hearing bass dynamics.  The "Ferrari" can also maintain a higher speed which requires more power.  So lower impedance phones can be played louder with less strain.


----------



## macky112

hi @xrk971 is there any scenario that the AMP may damage a DAP?  I tried changing the rail caps and I think my DAP is damaged?!


----------



## xrk971

If you connect the DAP to the input of the amp it goes to a capacitively coupled input to a JFET gate. There is zero possibility of any excessive DC voltage going back from the JFET to DAP to cause damage. Even if you connect the amp output to the DAP output, the capacitors AC couple to prevent any DC voltage from damaging the output stage of your DAP. 

Describe symptoms of your DAP and why you think amp may have damaged it - it's highly unlikely except in rare event that you have a bad capacitor. So measure the D.C. Volts at the input connnected to your DAP - should be 0v.


----------



## macky112

xrk971 said:


> If you connect the DAP to the input of the amp it goes to a capacitively coupled input to a JFET gate. There is zero possibility of any excessive DC voltage going back from the JFET to DAP to cause damage. Even if you connect the amp output to the DAP output, the capacitors AC couple to prevent any DC voltage from damaging the output stage of your DAP.
> 
> Describe symptoms of your DAP and why you think amp may have damaged it - it's highly unlikely except in rare event that you have a bad capacitor. So measure the D.C. Volts at the input connnected to your DAP - should be 0v.



I thought about it, and it may have happened during my 1st build attempt, it was the scenario with bad soldering on the resistors that caused really weird DMM readings, and without knowing better, during troubleshooting, I tried 2 DAPs (Benjie S5 and Xduoo X02) with my first build, and immediately the S5 went into a reboot cycle (and at the time, I didnt know why it did that).  After the S5 stuck in a reboot cycle, I checked the X02, it booted up fine and was able to navigate the menus, so I tucked it aside without listening to it, and gave up on troubleshooting my first build.

yesterday, I replaced rail caps on my 2nd build to 2200uF and wanted to see if I can hear any difference in bass performance (and now I know better, after reading through the Objective2 thread that a non-functioning Amp can damage both DAP and headphones, so I pulled out my cheapest DAP, Xduoo X02), and that's when I found out one channel of the X02 was dead, and the working right channel has random static sound.

So during troubleshooting my first build and trying to get some sound through it, that was when it may have happened, probably some AC/DC current gotten into the DAPs (due to short or open circuit somewhere on the amp?) and fried something.


----------



## macky112

Hi @xrk971 to reduce size, what would be the lowest voltage rating caps I can use for input caps and output caps for a battery build?


----------



## xrk971

If you look at the D.C. Levels at those caps then add the max voltage swing. 

For input probably not more than +/-2v plus 1.5vdc so a 5v could theoretically work. For output D.C. is about 7v. Max output swing is about +/-5v so 12v would be minimum for output. But for lower distortion you don't want to have a cap too close to limit. I use 35v Elna Silmic and film cap is 50v rated.


----------



## macky112

xrk971 said:


> If you look at the D.C. Levels at those caps then add the max voltage swing.
> 
> For input probably not more than +/-2v plus 1.5vdc so a 5v could theoretically work. For output D.C. is about 7v. Max output swing is about +/-5v so 12v would be minimum for output. But for lower distortion you don't want to have a cap too close to limit. I use 35v Elna Silmic and film cap is 50v rated.


Thank you for the explanation!

If I want to roll caps in my other devices, would measuring the positive leg of a cap relative to ground give me a good idea of what voltage rating I need?


----------



## xrk971

Yes - plus add possible AC component.


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## xrk971 (Jun 28, 2017)

Here is a new single ended to balanced output phase splitter under development with Hugh Dean of Aspen Amplifiers.  This circuit follows the Pocket Class A ethos of simplicity for a purity of sound - it uses just two transistors and runs pure Class A single ended mode of operation (just like the amp) with very low distortion.  Can drive two 27k ohms loads to 10v peak to peak.  It has perfect analog phase splitting. Oscope screen shows actual music and you can see the positive and negative phase outputs. So combining this with a single Pocket Class A amp yields a single balanced channel out.  I will build up another one and then modify my OB-1's for balanced drive then have a test listen.

Combining two of these and two of the Pocket Class A amps but modified for higher bias desktop use might be a nice addition to the current lineup.

The phase splitter is unity gain and requires 45v Vcc in order to produce the full 10v p-p output swing.  It can run at lower voltage if we only need a few volts to feed into the power amp stage. But for lowest distortion, a 45v rail will give 0.0027%THD to drive 1.4v (0dBu) into the amp stages.


----------



## gwompki

Hello all.  I'm way late to the party.  This looks like a killer build!

 I read most of this thread and a good chunk of the thread over on DIY Audio.  Is there still a place to buy just the PCBs?  I see the populated PCBs on @xrk971  Etsy shop but was wondering if you could buy just the board still?  The group buy posting on DIYA doesn't seem to have been updated in a while.  Thanks and apologies if this has been covered elsewhere.


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## xrk971 (Jun 29, 2017)

Let me put the PCBs up on Etsy.

.... ok done.


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## gwompki

xrk971 said:


> Let me put the PCBs up on Etsy.
> 
> .... ok done.



Thanks!  Just curious, if you buy the kit are the FETs matched or is it just luck of the draw?  I'm trying to decide how lazy I feel


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## xrk971 (Jun 29, 2017)

Kit includes matched FETs. You just need to provide the tin and cut the holes. 

I can provide a blank tin with precut holes for $10 if you are real lazy.


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## gwompki

Excellent.  Now I just need to decide if my laziness or budget will win out!


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## gwompki

Just ordered a kit to build one bone stock and a pcb for experimentation later.  Can't wait!  

Will try them with my HD-6XX and TH-X00 as well as various budget earbuds.


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## xrk971

Thanks for the order.  What impedance are your earbuds?


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## gwompki (Jul 1, 2017)

xrk971 said:


> Thanks for the order.  What impedance are your earbuds?



Earbuds are anything from 16 ohm to 300 ohm.

HD6XX (Sennheiser HD650) is 300 ohm.  This is the most picky set I have.  Looking forward to this pairing.

Fostex TH-X00 are 25 ohm bio dyna drivers.


----------



## gwompki

Just got my kit today.  Incredibly fast responses and shipment from @xrk971.  Awesome guy to deal with!

This is my first time with SMD components.  Let's just say this not going to be my best looking build LOL.  If it were all through hole I could probably have all of the on board components soldered in under 45 minutes.  I'm about an hour in and have 6 resistors on the board .  The solder paste and hot plate method are looking really good for my 2nd build.

One question for @xrk971...if I use standard Duracell 9V batteries will that be Ok with the 25V 2200uF caps?  I know you specify the rechargeable which have 8.4V max if I recall correctly.


----------



## xrk971 (Jul 4, 2017)

SMD is slow at first due to learning curve. You will soon find that it is way faster than through hole as no leads to bend or clip and only one side of board to work on.  Apply solder to one bare pad.  Place part and hold in place with pressure from tweezer.  Touch iron to pad with solder puddle to remelt. Then add solder to other pad. That's it. Removing is trickier but alternately heat ends while lifting with tweezer. 

9v alkalines are fine. Even with 16v 2200uF caps. It's only 9v for a few minutes. Your 25v rated caps are well above 18v so no issues there.  

Good luck.


----------



## gwompki

It's alive!  Very impressed so far with the HD6XX.  I only got about 20 minutes to listen after I finished building, but so far so good.  More detailed impressions to follow... hopefully this weekend.

Don't laugh too hard at my soldering work on this one.  Next one will be better


----------



## xrk971

Nice!


----------



## macky112

Hi @xrk971 could you help me understand the I/V, LPF, AMP and BUF stages of an amp and how rolling different opamps at each stage may affect sound?


----------



## xrk971

I am trying to avoid opamps. They add many many transistors to the signal path. They are not Class A in general.  

I/V is current to voltage converter. Buffer is a unity gain amp and generally provides lots of current but no voltage gain.  So you drive it with a good preamp and as a "master" and the current buffer does what the master tells it. 

The Pocket Class A is a good preamp as it can drive loads as low as 300ohms to 10v peak to peak. Add a current buffer capable of several amps and you can drive most speakers to a decent volume. 

When you say rolling opamps it generally means a power amp with an opamp front end that's interchangeable.  Most opamps nowadays are all very low distortion and neutral. They use lots of negative feedback and have a harmonic profile that may be low by not pleasing like SE Class A. 

So I guess short answer is, use this Pocket Amp as a front end to any of your other amps and it's like "rolling a SE Class A" opamp into your system.


----------



## macky112

Another question is there any benefit between 16v power supply vs +\- 8V?


----------



## xrk971

On a single ended Class A amp the ps is single voltage.  On a push pull amp the supply is dual rail. Is there advantage with dual rail ? Well it doesn't use caps in output path.  Some people don't like caps but I don't have a problem with it.


----------



## macky112

xrk971 said:


> On a single ended Class A amp the ps is single voltage.  On a push pull amp the supply is dual rail. Is there advantage with dual rail ? Well it doesn't use caps in output path.  Some people don't like caps but I don't have a problem with it.


I see. Thanks!

Then if is it a single voltage ps for push-pull amp then its not good right?


----------



## xrk971

You can't have single rail on push pull - at least not without an output cap.


----------



## macky112

xrk971 said:


> You can't have single rail on push pull - at least not without an output cap.


Ah I see ok, maybe that's why ppl weren't very fond of single rail ps on those budget dap threads that I frequent because of the output caps!


----------



## gwompki

I'm going to go ahead and post a mini review thats focused primarily on the Sennheiser HD-6XX (aka HD-650).  I only have about 4 hours on it at this point so these are early impressions.

I have tried this headphone from a variety of budget amps(Little Bear B4, Fiio E12A, Little Dot 1+, and an old 70s integrated amp...also straight from the output of my LG V20 which is supposedly adept at driving these phones according to Jude).  I had been  happy listening to vinyl with these phones through my old integrated amp as it has gobs of power.  However, when using a digital source everything felt way too laid back and warm.  All of the other amps either felt too warm or the low end wasn't present enough, etc.  I had grown accustomed to listening straight from my V20 but I always thought I was missing out on something....low end, sound stage, etc.

Now here comes the Pocket Class A (PCA).  Using the V20 as a source my HD-6XX came alive.  I'm still trying to find the words to describe what I'm hearing when A/Bing between the LG's output and the PCA.  It is very noticeable...all of the instruments seem to spread way out and I can clearly identify each one.  The low end is much more coherent and tangible to a certain extent.  Everything is much more authoritative in general.  I have noticed that more power will make the HD-6XX sound less congested, but none of my other amps offer the same level of dynamics that the PCA does.  Suffice it to say I am enjoying this little beast immensely!

I have only spent a small amount of time with the Fostex TH-X00 and this amp so far as they are easy to drive.  However, early testing is also very positive.  This amp seems to really make them shine.  Can't wait to spend more time with them.


----------



## stellarelephant

Nice work on your amp, Gwompki.  
I'll agree...it's so nice to to hear headphones adequately powered!
I notice an immediate difference with every can I've tried with the PCA, but I'll bet the effect is huge with the HD6XX.

I too thought that surface mount soldering was hard until I watched this tutorial. 
You already made it through, but this demonstrates the technique X described:


----------



## stellarelephant (Jul 9, 2017)

Update on my first build:
I ended up soldering in the 35V 47uF Silmics as bypasses for the 25V 470uF Nichicon KA output caps.  This added some bass heft and treble clarity, and yielded a smoother and more neutral sound signature over the KA alone, which I felt was a bit midrange-centric by itself.  It's a great sounding amp that I have been listening to constantly with headphones, as well as using as a preamp for my car stereo and full-range mini system.

I've recently discovered something special about this amp: it really likes to be driven hard with a hot signal.  Surprisingly enough, I find it sounds even more revealing when I feed it the amped headphone signal from my DAP, instead of using the auxilary output.  It also rocks with the powerful signal I get out of my Firewire audio interface, which is noticeably louder than a standard line out, and is intended for balanced studio monitors (though I'm using it single-ended).  I did not expect this effect, and I am curious if anyone else agrees.


----------



## stellarelephant (Jul 9, 2017)

And now for my second build!  This time around, I pulled out all the stops.

-All resistors are 1/5 Watt Vishay MELF
-Higher bias via R4 value of 51R
-Bit higher dummy load via RL value of 1K
-Power rail caps are 25V 1500uF Panasonic FR
-Power bypasses are original value, but TDK C0G
-Input caps are my DIY stacked and leaded 2x 63V .68uF WIMA SMD-PPS
-Still auditioning output cap options (about to order more)

  

Powered by my OKCell USB batteries, this amp measures 7.5VDC (divided by the R7 parallel array value of 117.5R, times 1000 = a toasty 63.8 mA bias current!)  I have only had time to listen through one battery cycle, but I can say for sure that dynamics and detail are just superb.

I auditioned my DIY PPS input caps vs. the stock polyesters, and quickly heard a difference (hopefully not my subjective bias 

). The polyesters have a creamy sound with a lot of bloom and soft treble. The PPS opens up the sound significantly with better precision, speed, and especially more air--exactly what I was hoping for!  I soldered them in without hesitation.  They require some sanding of the inner side of the input jack to slide in, at least with the caps shrink-wrapped like I did.

I need to place an order for more output caps to experiment with, but right now I am loving the sound of this amp with the trusty 25V 470uF Nichicon KA standing alone on output duty.  I want to use this amp on the go in a tin, so I am exploring other options that will fit.  So far my Mouser cart has three other Nichicon audio grades-- FW, KW, and FG (Fine Gold...high hopes for this one!).  I am also going to order the big 16V 470uF Silmics that Funch used, and also X's current favorite cap combo.

I also borrowed a pair of ATH M-50s from a friend, so I can really judge bass quality better going forward with my listening tests.


----------



## xrk971

gwompki said:


> I'm going to go ahead and post a mini review thats focused primarily on the Sennheiser HD-6XX (aka HD-650).  I only have about 4 hours on it at this point so these are early impressions.
> 
> I have tried this headphone from a variety of budget amps(Little Bear B4, Fiio E12A, Little Dot 1+, and an old 70s integrated amp...also straight from the output of my LG V20 which is supposedly adept at driving these phones according to Jude).  I had been  happy listening to vinyl with these phones through my old integrated amp as it has gobs of power.  However, when using a digital source everything felt way too laid back and warm.  All of the other amps either felt too warm or the low end wasn't present enough, etc.  I had grown accustomed to listening straight from my V20 but I always thought I was missing out on something....low end, sound stage, etc.
> 
> ...



Gwompki,
Thanks for youy listening impressions.  Nice to hear that it gave you a sound that was lacking in all your other amps.  The HD-6XX sound like they were made for this amp.  The lowish bias current will favor high impedance cans that's for sure.  But to hear that instruments opening up and more coherent and authoritative bass makes my day.  There really is something special when an amp uses very few components and is SE Class A.


----------



## xrk971 (Jul 9, 2017)

StellarE:


stellarelephant said:


> I've recently discovered something special about this amp: it really likes to be driven hard with a hot signal.  Surprisingly enough, I find it sounds even more revealing when I feed it the amped headphone signal from my DAP, instead of using the auxilary output.  It also rocks with the powerful signal I get out of my Firewire audio interface, which is noticeably louder than a standard line out, and is intended for balanced studio monitors (though I'm using it single-ended).  I did not expect this effect, and I am curious if anyone else agrees.



I think I notice the same thing, I usually set my sources quite loud, maybe 70% of max.

Great work on your second amp. Looks very cool and powerful.


----------



## stellarelephant

I've been playing around with the limited capacitor stock I have at the moment.
Early impressions rolling output caps with my new amp:

25V 1000uF Nichicon KA - Good bass, forward and slightly hot mids, soft upper treble lacks some air.  Nice balance between detail and euphonic warmth and presence.
25V 1000uF Panasonic FR - Neutral/analytical, with powerful deep bass and great airy treble extension.  Cooler mids.  Brighter presentation, lively dynamics.
16V 1000uF Panasonic OSCON - Perfectly neutral response, with tight bass control.  Pleasantly smooth, integrated, somewhat distant sound.  Soft treble details and restrained dynamics.
25V 47uF Nichicon KZ - Not nearly enough capacitance for bass with my low-R cans, but wow.  Wonderfully clear and engaging mids and treble.  If I only had the 300 ohm HD600...


----------



## gwompki

I've found a weird issue on my build...I bought some EBL rechargeable 9V batteries from Amazon that arrived yesterday.  I charged them overnight then unplugged and set aside this morning.  I had been using Duracell 9V with no problem for the past week.  Tonight I suspected the Duracell were getting weak so I swapped in two of the EBL's and....no sound.  Thought maybe I had pulled out one of the battery snap leads so I swapped back in the Duracell to test and the sound was back.  Thought maybe the EBL didn't charge properly so I measured all 4 at 8.4V.  Couple of other symptoms...LED lights up but seems to be a bit less bright, Also when I turn it on I hear a tiny click out of the right driver as opposed to the louder whoomp I hear from both channels when I power it on with the Duracells.  

Is it possible that all 4 EBL batteries are bad or is there something else at play here?  Haven't had a chance to take voltage readings on the circuit yet.  Might need some guidance on that if it comes down to it.


----------



## xrk971

I guess you did not read the thread - normal issue with EBL's smart self protect circuit cutting off power due to turn on transient.  The rail caps suck a lot of current upon initial turn on and the battery has a smart circuit that thinks it is a short.  Solution is to turn on/off quickly and about 2-3 clicks it should stay on as each cycle charges caps more until they don't draw too much. 

Some EBLs are DOA. I have had to return several.


----------



## gwompki

Oops!  Between reading this and the thread on DIYA I'm sure I have forgotten a lot.  Thanks for the quick reply.  That solved the issue.  Thought I was going crazy.


----------



## funch

Are you doing the on-off-on-off-on procedure?

Dang 'X', you were too fast on the keyboard.


----------



## stellarelephant (Jul 11, 2017)

What X and Funch said.

Also: If you tire of the multiple on/off workaround, the OKCells I use don't have this issue, and give a little extra voltage to boot, though runtime is a little less, at just over 2 hours. Quality control isn't perfect.  I have had one cell out of four go bad after less than ten charges.  The others are plugging right along though.  Also note that these put out just over 18V and probably deserve 20V or 25V power rail caps.


----------



## gwompki

stellarelephant said:


> What X and Funch said.
> 
> Also: If you tire of the multiple on/off workaround, the OKCells I use don't have this issue, and give a little extra voltage to boot, though runtime is a little less, at just over 2 hours. Quality control isn't perfect.  I have had one cell out of four go bad after less than ten charges.  The others are plugging right along though.  Also note that these put out just over 18V and probably deserve 20V or 25V power rail caps.



Thanks guys!  It's pretty amazing the audible difference going back and forth between the fully charged EBL and Duracell that are down to 7.1V.


----------



## xrk971

So in a way, the OK cells may not last as long, but during their 2 hr life, the output is consistently high.  I have not measured them for noise, I suspect there is some as there is a DC step up converter but its probably noise high above audio band.


----------



## stellarelephant

So I did a test fit and discovered that it is impossible to populate the PCA board with 12.5mm wide caps on both input and output, and still have room for two 9v batteries in the tin.  I was crossing my fingers and everything, but no dice.

This means that if I want to use a big fat output cap like Funch did, I have two options. One is to use a  smaller 10mm wide power rail cap like he did. But I already soldered in a 12.5mm wide Panny on the power rails, and I like it. The second option is to make the batteries smaller!




Popped one open, and was surprised at the size reduction. The actual cell is small enough that I could probably fit four of them in the tin...but using two, I'll have plenty of room for big caps to hang out over the edge of the PCB.

Another advantage is that I ought to be able to glue the micro USB ports flush with the tin surface now, which was impossible before.  I had to cut large messy holes in the side of my first tin to accommodate the full diameter of the male USB plug housing. Now I can probably just keep it neat with a hole punch.

But of course this begs the question, isn't there a better way entirely?  It would be awfully nice to be able to charge my amp with a single USB cable instead of two. And even nicer if the battery capacity was larger. It is now quite obvious to me that a much larger cell could fit in the tin, probably doubling runtime, at least.   X, do you have any insights or recommendations for adding a purpose-made battery and charging circuit to this amp?  I really like the full 18V power, by the way


----------



## gwompki (Jul 14, 2017)

stellarelephant said:


> So I did a test fit and discovered that it is impossible to populate the PCA board with 12.5mm wide caps on both input and output, and still have room for two 9v batteries in the tin.  I was crossing my fingers and everything, but no dice.
> 
> This means that if I want to use a big fat output cap like Funch did, I have two options. One is to use a  smaller 10mm wide power rail cap like he did. But I already soldered in a 12.5mm wide Panny on the power rails, and I like it. The second option is to make the batteries smaller!
> 
> ...



Very cool stuff!  I like where this is headed.

I wonder if a larger enclosure would help accommodate different batteries and associated charging circuitry.  Actually I would love to see the PCA in a more permanent enclosure.  I have to fly tomorrow and as much as I want to bring the PCA with me, I'm terrified of it being confiscated (or worse) by TSA.  Anyone flown with one before?

The little bear B4 is a very manageable size imho ...I'm willing to sacrifice my chassis  for experimentation to fit the PCA if someone wants to take on that project.


----------



## stellarelephant

gwompki said:


> Very cool stuff!  I like where this is headed.
> 
> I wonder if a larger enclosure would help accommodate different batteries and associated charging circuitry.  Actually I would love to see the PCA in a more permanent enclosure.  I have to fly tomorrow and as much as I want to bring the PCA with me, I'm terrified of it being confiscated (or worse) by TSA.  Anyone flown with one before?
> 
> The little bear B4 is a very manageable size imho ...I'm willing to sacrifice my chassis  for experimentation to fit the PCA if someone wants to take on that project.



Lol yeah I guess they might look a little suspicious. Never seen that little tube amp before.  Handsome.  But I guess the PCA must slay it in terms of SQ if you are considering stealing its case!?!

Honestly I sorta love the humble DIY aesthetic of the Altoids tin.  And after seeing the piddly size of the bare 9V cells I'm currently using, I think there is room for a much bigger battery in the tin.  I just have zero knowledge of how to make it happen.


----------



## gwompki

stellarelephant said:


> Lol yeah I guess they might look a little suspicious. Never seen that little tube amp before.  Handsome.  But I guess the PCA must slay it in terms of SQ if you are considering stealing its case!?!
> 
> Honestly I sorta love the humble DIY aesthetic of the Altoids tin.  And after seeing the piddly size of the bare 9V cells I'm currently using, I think there is room for a much bigger battery in the tin.  I just have zero knowledge of how to make it happen.



You're correct...the B4, while solid with the right OpAmp, just doesn't compare to the PCA.  Those little sub-mini tubes definitely impart a good bit of tube flavor, which is nice, but side by side with the PCA the sound signature seems flat and lifeless.  

The PCA is so nice and compact you could probably fit a micro DAC in a larger enclosure as well lol.

I agree in terms of the diy aesthetic...it is a lot of fun.  I might try my hand at fitting the PCA in the other enclosure one of these days just for travel purposes.


----------



## xrk971

If you cracked open the Ok cell, you will see it uses a 800mAhr 3.6v LiPo.  Look on eBay for a 3000mAhr LiPo and swap them out. The old charger and step up should handle everything for you.  The cells you buy typically have a built in smart auto protect to prevent over charge, over discharge, and shorts.  

You can also make your own from scratch with a DC step up and a USB charger.  Nice thing with your own DC step up is you can set it for 18v from 3000mAhr. 18v/3.6v And that gives you equivalent 600mAhr battery.


----------



## stellarelephant

xrk971 said:


> If you cracked open the Ok cell, you will see it uses a 800mAhr 3.6v LiPo.  Look on eBay for a 3000mAhr LiPo and swap them out. The old charger and step up should handle everything for you.  The cells you buy typically have a built in smart auto protect to prevent over charge, over discharge, and shorts.
> 
> You can also make your own from scratch with a DC step up and a USB charger.  Nice thing with your own DC step up is you can set it for 18v from 3000mAhr. 18v/3.6v And that gives you equivalent 600mAhr battery.



X, you make it sound so easy!  So do you think one of these cheap adjustable step ups would work?  Would I need to worry about noise?


----------



## xrk971

That's exactly what I use. You may. Need an 0.47R series resistor after step up so it doesn't doesn't shut down with turn-on transient. You can find them for $0.40 ea on eBay. Get extra as they blow up when you turn pot too far. I have smoked a few already. Literally flames from the the little IC. But once setup right is very reliable. 1.2Mhz switch frequency so not audible.  I use a RCRCRC with 3.3R and 2200uF.


----------



## stellarelephant

Nice.  I'm sorry if you have explained all this before (I think you did discuss this in the complete PCB thread maybe?).  The RCRCRC filter with 6600uF total seems like it'll eat up some serious space! The EBL and OKCell 9V LiPo batteries we are using don't have a filter like that built in, do they?  I guess I'm wondering why I would need it with a single large cell if it isn't necessary with the two smaller ones.  Or are you just conditioning the power to a degree that is far superior to what two purchased 9V LiPo cells can produce?


----------



## stellarelephant

Wow, even with the cheapest Digikey shipping, my order came in two days!  Got some more members of the Nichicon lineup here to evaluate.
Why didn't I remember to charge my batteries last night?  Lol.  Waiting anxiously...

 

16V 470uF FG    /    25V 330uF FG    /    25V 1000uF FW    /    25V 1000uF KW

All identical 10x20 can sizes, but different values.  I'm basically trying the biggest caps from each series that'll fit my board.  I may end up using a lower capacitance value if overall SQ justifies it...even if that means a tiny bit of bass roll off with my 50 ohm cans.  I'm even going to audition a 220uF Silmic when my PartsConnexion order arrives.  I'm going to let my ears be the final judge, and I believe different caps do have different bass quality outside of simple capacitance value, but here are predicted bass responses for the different values I'm trying.  I have a 1K resistor at RL in parallel with the 50R headphone load, so the total load is 47.6.


----------



## xrk971

The EBL's don't have a step up - I think they use maybe 3 internal cells.  It has dropping voltage with time so no DC step up.

The OK's don't have it and if you can't hear it it is fine to not use CRC filter with the other DC step up.  I only added it because I could measured a broad -90dB noise hump from 1k down with the DC switcher step up. 2200uF RCRCRC actually fits in tin with 3000mAHr LiPo and charger an step up.


----------



## stellarelephant (Jul 18, 2017)

Great info.  I really need to get set up to make measurements with my sound card.  For now, I just bought some Duracells to compare audible hiss from the amp with them vs. OKCells.  In the long run I hope to copy your 3K mAh setup.  How many hours of runtime do you get out of it?


----------



## stellarelephant (Jul 18, 2017)

Can any Nichicon capacitor dethrone the Panasonic FR as my current favorite in the PCA?





Here are my listening impressions:

*25V 1000uF KW*
Reasonably pleasant, but the treble is quite dulled.  Nicely engaging, slightly grainy mids.  Bass extends low but is a little uncontrolled and surprisingly quiet for a 1000uF cap.  Subpar detail and dynamics.

*25V 1000uF FW*
Brighter than KW.  More balanced mids sit on par with the rest of the spectrum.  Clearer treble, with some sparkle, but still lacking air up top--stuffy.  Good presence in mids, with just the right amount of bite.  Bass quantity is better than KW but a bit distorted.

*16V  470uF FG*
A small step closer to KZ sound in resolution and overall engagement.  Smoother than KW or FW, with a balanced frequency response.  Deep, punchy and controlled bass.  Still a bit "closed in" vs. Panasonic.  A bit short on high treble.  Can sound strained in louder passages.

*25V 330uF FG*
A hair smoother than the 16V, with a little more treble.  Just enough bite in the mids to make vocals "in your face" without being gritty.  Surprisingly good bass, though theoretically less quantity than the other FG.  Again, the soundstage is small and stuffy.  Where is the high treble, Nichicon?  In the KZ only, I guess.  Sheesh.

*25V 1000uF KA*
I've already auditioned the KA a lot, but mostly the 470uF.  The KA actually stands out from the typical Nichicon "house sound" IMO.  It has a slightly mid-centric signature with enough treble to sparkle some, though the treble is a tad hot.  Midrange and vocals come forward in the mix nicely, but without grain--they are the smoother than even the FG.  Bass has decent weight and control.  Somehow I find the KA more natural in timbre than all the others--the sound is clearer, though not particularly airy or exciting.

---------------

*25V 1000uF Panasonic FR*
FAR more neutral and revealing than all of these Nichicons.  Maybe its the ultra low ESR…it just gets out of the way and lets the music come through.   It gives the cleanest and most spacious presentation, with excellent detail and real air on top for a beautifully open soundstage.  The bass is awesomely powerful with deeper extension than any of the Nichicons, and tight control.  Blackest background.  Fastest transients.  Need I say more?  If I had to nitpick, I'd wish for a touch more warmth and presence in the mids, but I suppose that might just be a coloration that suits my taste.  These caps simply sound REALISTIC.

With the Pannys in place, I played the amp today for my buddy who has a degree in audio engineering.  He kept repeating the words "unbelievable!" and "crisp!"  He also commented on the superb instrument separation and his jaw dropped when he heard the bass drop =).

I am awaiting a package of Elna Silmic, Elna Cerafine, and Nichicon KZ in the mail…KZ is too big for this build, but I want to hear it anyway.  I'll be impressed indeed if any of them sound better than my current setup!

All the caps tested are 10x20mm, but have different voltages and capacities.  For reference, here's the predicted bass response of each cap value I tried in this test paired with my 50 Ohm cans in parallel with the 1K resistor load.


----------



## xrk971

Did you compare to 1000uF 16v SEPF OSCON?


----------



## xrk971

stellarelephant said:


> Great info.  I really need to get set up to make measurements with my sound card.  For now, I just bought some Duracells to compare audible hiss from the amp with them vs. OKCells.  In the long run I hope to copy your 3K mAh setup.  How many hours of runtime do you get out of it?



3000mAhr at 3.6v step up to 16.5v gives about 650mAhr, so same as EBL's - about 4.5hrs.


----------



## stellarelephant

xrk971 said:


> Did you compare to 1000uF 16v SEPF OSCON?



I have indeed auditioned that OSCON, in both my builds now. I found it to be extremely well balanced thorough the frequency range, with excellent bass weight and particularly great bass control, with a full, creamy, sound signature. But it has a soft/dull one-dimensionality to my ears, and fails to engage me. It seems short on detail compared to the other caps I have tried.

More cap tests to come, with some of the best-regarded audio caps this round...but I think the Panny FR may still reign supreme.


----------



## xrk971

What's the part number for the FR cap on Mouser or Digikey? Is there a 3300uF 35v version? I could use for the HyQu MP.


----------



## stellarelephant

The one I'm using is manufacturer part number EEU-FR1E102. I found out that there is also a longer 10x25mm 25V that would fit just as easily in the PCA, which gets you a smidgen more capacity...1200uF.  That's part number EEU-FR1E122L. I haven't heard it but I would assume it sounds the same, and ought to crank out bass even with 30 ohm cans.  1000uF is perfect for me though. On my third build I will probably audition the bigger one just for grins, and possibly omit the battery connector socket to accommodate 12.5x25mm 25V 1800uF FR rail caps, theoretically improving stereo separation a tiny bit over my current 1500uF, right?  I think at that point I will have the board completely stuffed edge to edge with FR 

There are definitely 35V FR caps also!


----------



## xrk971

Thanks for the info. I will order some for the PCA and for the new HyQu amp.


----------



## gwompki

@stellarelephant

Good write up on the caps!  

Stupid question...are you using those as the rail caps?  Or one of the other positions?


----------



## Sodacose (Jul 28, 2017)

Pic of my build with stock values!

And here's a guest post review I wrote up after building this amp:

https://audioprimate.blog/2017/07/18/pocket-class-a-diy-headphone-amp-by-xrk971/

All-in-all, it's a great amplifier! Sound is excellent and it pairs really well with what I assume to be the typical companion gear (smartphone, streaming services, mid to high impedance headphones).

Well done, XRK!


----------



## xrk971

Thanks so much for the review Sodacose! I am looking forward to building your hybrid tube amp as well.  Never had a tube amp before so that will be cool.


----------



## Sodacose

My pleasure, seriously.  It is really interesting to compare the two amps: lots in common between them. I'd say 'great minds think alike' but I'm not so sure about my own


----------



## stellarelephant (Jul 28, 2017)

Yeah, great review Sodacose. It reads as very balanced, and full of useful descriptions and comparisons.  Glad you agree that this amp rocks.  Why isn't the link working anymore?



gwompki said:


> @stellarelephant
> 
> Good write up on the caps!
> 
> Stupid question...are you using those as the rail caps?  Or one of the other positions?



I do have 1500uF FR soldered in on the rails too, but all the comparisons I have been doing are for output caps, including the 1000uF FR.


----------



## stellarelephant (Jul 28, 2017)

*Output Caps, Final Round:*
BEST OF THE BEST electrolytic capacitors duke it out for a place in my no-holds-barred PCA. 

The majority of my listening tests for this round were performed through ATH-M50 headphones, which I have found to be invaluable for giving an honest rendering of sonic differences.  These findings were confirmed through further comparisons using my HD598 and also feeding my Tripath->Aurasound system.  Sources were a wide variety of FLAC files played both from my XDuoo X3 or my Mac's ECHO soundcard.  This test was intended to compare caps of similar size that will fit into the available space on my PCB for this particular build.  Voltage and capacitance ratings thus vary across caps tested, but all caps are 10x20mm unless marked with an asterisk, which means they are 12.5x25mm.



*Elna Cerafine *
values tested: 16V 330uF, 25V 220uF, 25V 470uF*
I can see why a few people like these more than Silmics.  They have more midrange forwardness and bite to them, and at first blush seem to offer a more engaging sound.  However, their treble can be a little harsh after a while, and the response is rather poorly extended on both extremes of the frequency spectrum, resulting in a less detailed, somewhat boomy and congested sound, with noticeably less bass control than the Silmic.  Not my cup of tea.

*Elna Silmic II*
value tested: 16V 220uF
Bass has rather flawless texture, speed, and extension, even with a marginally undersized 220uF cap.  A polite, soft midrange and treble makes you want to crank the volume, and the overall sound is nice and full.  It hides the flaws of harsh recordings, but also seems to push vocals farther away and hide some harmonic texture, resulting in an odd hollowness in midrange timbre.  I'd say these sound spacious due to decent extension and a somewhat exaggerated treble sparkle, but the high treble is missing.   I particularly dislike the way these do metal percussion.  Cymbals and hi-hats do not sound realistically metallic.  Other than that, these sound great, if slightly veiled in parts of the spectrum.

*Nichicon Muse KZ*
value tested: 25V 330uF*
Nice.  These are quite detailed, with a beautiful, jangly midrange and sparkly treble that gives an incisive "electric" sound to the upper ranges.  Vocals really jump out and grab my attention so that song lyrics have excellent intelligibility.  The overall presentation is ever so slightly on the hot/forward side of neutral, with a hint of upper mid harshness, but the overall timbre is natural, with enough treble to give an open soundstage.  Metal strings and percussion sound right.  This size gives impactful, fast, and detailed bass with my 50R cans.  With these, I never feel like I'm missing any detail whatsoever, and I wouldn't say the soundstage is huge, but certainly bigger than either Elna.  They're lightning fast, and darn revealing.

*Panasonic FR*
value tested: 25V 1000uF
I've described these before, but I'll compare them here to the others in this lineup.

- They're really just better than the Cerafine in every respect.

- Compared to Silmic, they have a strikingly similar smoothness in the mids,  but this time the effect isn't exaggerated by a contrived treble sparkle, maintaining a more natural timbre overall.  FR has much more clarity and extension than the Silmic in the high treble, for a wider soundstage with real air.  I chalk this up to less distortion.  Switching from Silmic to FR is like lifting a thin veil.  Chimes and cymbals are simultaneously less fatiguing and more realistic.  Bass is powerful and full, with effortless extension from the 1000uF size, but a little less textured than the sweet Silmic bass.  In fact, I'd say the entire presentation is a little "slower" than the Silmic, which has a bit snappier attack.  Most importantly, these FR are even less fatiguing than the already smooth Silmic. There, I said it.

- Compared to the Muse, this FR sounds a lot smoother, with much less of that addictive Muse midrange texture, and a slower transient attack speed.  FR has a cooler presentation, with more extension up high, and slightly less distortion throughout the spectrum.  Bass isn't quite as punchy nor textured in the midbass region as what the Muse puts out, but upon listening back and forth, I feel the FR bass is more neutral, with deeper extension due to more capacitance.  FR has a better soundstage due to its superior treble transparency, and sounds less fatiguing.  I'd say the two are evenly matched for detail, with the KZ giving more speed and midrange zing and overall a fuller body, but the FR letting more micro details come through the mix by virtue of clearer imaging and a more neutral signature.

 

*Conclusion:*

FR is the only electrolytic I have heard that actually gives this amp an expansive soundstage, with real air, even with a closed headphone.  Silmic and Muse, while both great in their own ways, always sound "on my ears" while with the FR, music seems to come from slightly "beyond my ears".  The FR sound has a certain magic to me because it sounds less dense than the other electros, highlighting the silence between notes and giving instruments a good amount of breathing room.  The subtle but delicious consequence of this effect is that "space" is better represented through a delicate rendering of reverb tails and other subtleties of the recording. I can listen to the PCA more comfortably at higher volumes with the FR than with any other cap--it never grates me in the least.  Most importantly, its neutral signature encourages me to just kick back and enjoy the music instead of analyzing the sound and wishing for improvements--something that can be quite hard for me with other caps.  Silmic and Muse sound great, and each have subtle tonal colorations which may certainly appeal more to personal tastes or give great synergy with certain equipment.  But I feel that if measured, the Panny would show significantly less distortion than either of the others.  That's how it sounds to me, anyway. YMMV.  Try them and see!


----------



## Sodacose

stellarelephant said:


> Yeah, great review Sodacose. It reads as very balanced, and full of useful descriptions and comparisons.  Glad you agree that this amp rocks.  Why isn't the link working anymore?



Weird, I don't know what happened with the link but I just fixed it.  Might have been an edit that screwed with the address or something.


----------



## xrk971

Ok, ok, ok... I just built up a new amp with FR 1000uF 25v outputs - no film bypass.  On inputs I am using 10uF 35v Silmic II no film bypass. I wonder if this will color the sound signature to that of Silmic? Listening right now - no problems driving my 16ohm KZ ZS5 IEM's (106dB).  Bass is full and deep for 1000uF. I am trying to see if I can hear a difference in treble detail. Hard to tell. May have to get out my A/B switch box.  The sound is very nice overall though. I am pretty convinced that film bypasses are not really audible now when using good electrolytics to start with.  Running 62mA bias current, source is just my phone at present.  So real test will be FLAC running 192kHz 24bit files with A/B switch box.  More to come....


----------



## stellarelephant

Man, that one looks snazzy.^  Wish I'd bought a white LED for mine!  X, if I had to pick one word to describe you, it'd be "prolific."

I imagine you will hear a significant difference, especially with those supertweeter-equipped IEMs you just picked up!
Still, the overall result ought to differ some from what I'm hearing, since my latest impressions are based on the amp with PPS input caps.  I feel these add significant treble transparency themselves.


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## xrk971 (Jul 28, 2017)

LEDs to last a lifetime.

http://s.aliexpress.com/iM3A3Q3e

This is s/n 22 so I have gotten lots of practice.

What's the Mouser/Digikey part number for the PPS stack you made?


----------



## stellarelephant (Jul 29, 2017)

xrk971 said:


> What's the Mouser/Digikey part number for the PPS stack you made?



Haha, I was hoping you'd ask!
SMDIC03680TB00KQ00

Heads up:  When soldered in, my pair of PPS stacks extend about 2mm past the pot housing, towards the center of the board.  Fitting 10mm rail caps and 10mm output caps is no sweat, but 10mm + 12.5mm pushes my rail cap slightly over the board's long edge.  I think fitting batteries in the tin will be a little harder.

I thought of a way to save about 1mm of space by soldering two leads on with an offset:
Top is what I did.  Bottom is what I'll do next time. 


Oh yeah, and if you use these, be sure to take some sandpaper to the inside plastic edge of the input jack housing so that the caps can slide in there.


----------



## xrk971

How many PPS caps are stacked in parallel? 4 x 0.68 = 2.72uF? $12 per cap is steep!


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## stellarelephant (Jul 29, 2017)

Just two of them per channel. The corner frequency is 2.5 Hz so essentially perfect bass.

I guess I only posted this info at DIYA. All I can say is that the difference in clarity with PPS is worth the bit of effort it takes to make your own.
http://www.diyaudio.com/forums/group-buys/302859-xrk971-pocket-class-headamp-gb-70.html#post5087318


----------



## xrk971

Ok $6 per cap is better but cost of those caps is more than half the BOM


----------



## stellarelephant

xrk971 said:


> Ok $6 per cap is better but cost of those caps is more than half the BOM



Yeah if you like the sound, you may have to introduce the (totally) TNHB model lol.

I wonder if there is any wiggle room in the 47K value of the R2 local feedback resistor?  If a larger resistor could be substituted without issue, then a smaller value cap could be used. Maybe an off-the-shelf through-hole PPS solution.  I really like the sound of the Kemet SMR series too, but they aren't as compact as the stack I made.


----------



## xrk971 (Jul 29, 2017)

Making R2 100k is possible but you tradeoff resolution.  Sometimes I like making it 22k even in which case a 4.7uF is needed.

Those PPS's you linked are presently out of stock at Mouser.


----------



## stellarelephant (Jul 30, 2017)

That's fascinating.  Can you elaborate on how local feedback resistor value affects the resolution???

If you don't want to wait for those SMD-PPS parts, you could try the 1uF KEMET SMR and get essentially the same bass (better than -0.1dB at 20Hz).  Or raise R2 to 56K if you want it "perfect." But probably not worth raising it if resolution is at stake.  I doubt even Quincy Jones could hear a 0.1dB difference at 20Hz lol. 

Grrr...Why didn't I think to try them out when testing input caps???  They might actually sound better than my stacks since they are internally wound, not stacked construction.  I did try them at the PCA output the other day, to couple to my boombox, and was blown away at the SMR's crystal transparency and immediacy...the bass was lacking of course in that scenario.  But I think they have potential here.

Looking at my pair of SMRs next to the board, I'd say you'll have to do even more sanding on the input jack than I did, but they should fit just fine, and actually be less work than my stack.  They'll also not have the problem of protruding into the board past the pot...
If you don't try it, I will!!!


----------



## gwompki

Just now got my secondary/experimental board up and running.

 

So far I prefer the stock but I have so many mod options.  Lots of fun to come.


----------



## xrk971

Another amp on a plank...
HyQu is now transportable between rooms in the house.


----------



## stellarelephant

HyQu...drool...



gwompki said:


> So far I prefer the stock but I have so many mod options.  Lots of fun to come.



Hey gwompki, will you share what mods you're trying on your second build?


----------



## gwompki

stellarelephant said:


> HyQu...drool...
> 
> 
> 
> Hey gwompki, will you share what mods you're trying on your second build?



Sure thing...so far have only tried those Elna Silmic on the input caps.  Quite a few other caps I need to try on the output.


----------



## xrk971

I am going to be at the Schiit Storm this Saturday in Gaithersburg.  Will be bringing Pocket Amps, Silicon Harmony, and HyQu for demo.

See you there!

https://www.head-fi.org/threads/dc-...-august-12-2017-gaithersburg-maryland.855135/


----------



## gwompki

@xrk971 I know you mentioned having a set of KZ ZS5.  I got them recently as well and was wondering what cap configuration you were using in the PCA with these.  The ZS5 seems to be lacking a bit of dynamics with the amp in stock form.  Guessing that is due to their very low impedence.


----------



## stellarelephant

For driving very low impedance I think you'll want the largest 16V output caps possible, and you might want to tune bias a little higher. 

Here is my 63mA build, newly outfitted for passive cooling.  I painted the inside of the lid for heat transfer. Thanks for the link to the tiny heat sinks, Funch!


----------



## xrk971

Gwompki,
I am currently using 1000uF Panasonic FR's and they sound fine relative to dynamics. I need to build a new one with dual 1000uF OSCONs and see if better.  In testing, they almost as powerful as full a size headphone on a desktop amp.  I can't have my iPhone volume above 70% with PCA on full volume playing some jazz with drums. The drums are very dynamic. The highs are superb with a super tweeter actually sticking into the ear tube. Did you get the upgraded gold cable? That's what I am using - have not even bothered to use stock black vinyl cables.


----------



## gwompki

Thanks XRK and stellarelephant.  I do have a set of 1000uF panasonic FR that I will try to swap in and see.  I will also try tuning the bias a bit to see what that does.  Looking forward to trying them out!

I did not get the upgraded cable for the ZS5 as I heard the only benefit was less microphonics.  If you think its a worthy upgrade though I will give it a shot eventually.


----------



## stellarelephant

Gwompki, 
Another thought on maximizing performance with those 16 ohm IEMs...  I know you were using the EBL batteries. If you want to quickly test the effects of increasing bias before changing resistors, swap in some fresh alkaline batteries and see if you can hear a difference.  18v vs 16.5v.


----------



## xrk971

Good idea StellarE! I like simple things that you can try right away with minimum cost/effort. Actually, I always ship my amps preloaded with a set of alkalines to let the customer enjoy right away and to verify that it works. Most people don't have rechargeables on hand.


----------



## gwompki

Alright think I discovered the reason for the big discrepancy in the sound between my new build and my first one.  I have swapped out quite a few caps on the output now and I think what it came down to is the whole time was I had the polarity backwards when using electrolytics.  Doh!  The low end has returned to my new build and with the 1000uF caps it is quite a fire breather.  

Time for even more tweaking!


----------



## xrk971

Glad you found the cause. The caps become a dead short when backwards and you are lucky it did not blow up.


----------



## gwompki

:O!  That's terrible...I had been listening quite a bit that way.  I'm not 100% sure I had them backwards, but I kept feeling the low end was lacking and when I put the latest round in the bass definitely returned in a big way.


----------



## stellarelephant

Quick update: my mosfets now stay nice and cool with the tiny heat sinks and painted tin interior (which defeats the radiant barrier nicely, dissipating most of the heat right through the lid). I can run the amp indefinitely and the sinks become just mildly warm to the touch.


----------



## sdouble

Hi guys , as you may know, i'm a noob in the audio business. so please forgive me if my question is idiotic. Looking at the amp scheme I wonder why you put the pot in the input stage. A pot is a noisy device. In principle, I guessed that it may be worthwhile to put the pot after the BF862 amplification stage.


----------



## xrk971

A pot is same as two resistors acting as a voltage divider.  Once the pot is stationary, the noise is Johnson noise from two resistors - not much.  Should we avoid resistors in our circuits because it adds noise?  Well, this amp sort of does that with a minimal number of resistors but that wasn't the point.  Too many people worry about pots in the signal path - use a decent moderately priced (under $5) one like this Alps RK09 series and it works fine. This amp has no scratchy noise when adjusting volume because there is no current through the high impedance gate of the JFET.  If you put the pot between the JFET and the MOSFET, there is more current there because the capacitance of the  MOSFET gate is higher, and there will be more noise especially when adjusting volume while music is playing.


----------



## sdouble (Aug 25, 2017)

my pint was that the pot is not just a resistor. The trimmer may grab some noise.
I agree that the input cap of the mosfet is much higher than that of the JFET but the imput impedance of the MOSFET is also high. I intend to use a SMD pot, the Bourns PTR902-2020K-A103-ND


----------



## stellarelephant (Sep 2, 2017)

Woot woot!  DIYAudio member Raptorlightning has successfully implemented a USB-charging single cell lithium battery pack in the Pocket Class A!  The amp can also run directly off USB power with this setup--a major benefit IMO. 

He used a LiPo cell and three small circuits: an off-the-shelf boost converter board, a custom load-sharing board with a micro USB power input, and a tiny custom cap multiplier board that keeps the battery from going into auto-protect when the big capacitors charge up at turn on.

I'm hoping to do the same for my builds as soon as I fully understand his approach.


----------



## Hutnicks

stellarelephant said:


> Woot woot!  DIYAudio member Raptorlightning has successfully implemented a USB-charging single cell lithium battery pack in the Pocket Class A!  The amp can also run directly off USB power with this setup--a major benefit IMO.
> 
> He used a LiPo cell and three small circuits: an off-the-shelf boost converter board, a custom load-sharing board with a micro USB power input, and a tiny custom cap multiplier board that keeps the battery from going into auto-protect when the big capacitors charge up at turn on.
> 
> I'm hoping to do the same for my builds as soon as I fully understand his approach.



Hoo Yah. That is what I have been awaiting. Need to explore this big time.

On insane clown mode. I have an almost irresistible urge to go old school with this design and do a point to point wired version. I will consult a therapist obviously before going there, but still....

On heat dissipation. There are several great choices out there readily available at most large hardware retailers. Begining with aluminum paint available at Home depot, to hammertone copper, Krylon Silve and gold plate. A lot of the above mentioned were pioneered in the laptop trade as coatings to inhibit rf interference and somewhat alleviate the heat generated by high clocked cpu's in an enclosed space.


----------



## xrk971

Well this was almost hand made P2P for the serial number Zero:


----------



## Hutnicks

Hmm not seeing an image there.


----------



## xrk971

Ok I had to re upload as it was on DIYA server and you probably don't have an account there.  

Here it is...


----------



## Hutnicks

Actually I do, which is all the more puzzling.


----------



## stellarelephant (Sep 4, 2017)

Raptorlightning kindly shared Gerbers for the two custom PCBs that enable his battery mod, as well as a BOM, schematics, and some instructions.

For folks without a DIYA account, you can also grab them here:
https://www.dropbox.com/s/y5hk5w1mlvtjya2/Raptorlightning Mod.zip?dl=0

I ordered several of each board from OSH Park a few days ago.  The two zipped folders within the main folder I've linked worked perfectly for me when I uploaded them for printing.  If you order from OSH Park, as Raptor and I did, expect to get a warning that they can't do slot drills.  According to Raptor, this is fine and just means you'll have to use wire cutters to trim the micro USB jack somehow.   I assume this will make sense once I see the part and the board.

To do the mod, you'll also need a MT3608 boost module and a 2600mAh 3.7V tablet battery that measures 7.8x52x51mm.
Both items are all over eBay and AliExpress. They look like this:

Anybody have tips for cutting PCB traces?  X-acto knife?


----------



## funch

X-acto would be my weapon of choice.


----------



## macky112

stellarelephant said:


> Raptorlightning kindly shared Gerbers for the two custom PCBs that enable his battery mod, as well as a BOM, schematics, and some instructions.
> 
> For folks without a DIYA account, you can also grab them here:
> https://www.dropbox.com/s/y5hk5w1mlvtjya2/Raptorlightning Mod.zip?dl=0
> ...



May I know an estimate of the total cost to do this mod?


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## stellarelephant

Pretty cheap.  The three boards can each be had for less than a dollar.  Battery is like $10.  I haven't made a Mouser/Digikey cart with the BOM yet, but I am hoping the assorted parts needed to populate the load sharing board and cap mx board will total $5 or so plus shipping.  Ballpark $20, all shipped?  About the same as buying some rechargeable 9V batteries and a charger.


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## xrk971

Hi StellarE, would you mind running a GB for us?  I am in for 4 sets of boards.


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## funch

Me too.


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## stellarelephant

xrk971 said:


> Hi StellarE, would you mind running a GB for us?  I am in for 4 sets of boards.



I'd love to, but man, I am covered up with work and house projects for the foreseeable future.  I'll be lucky if I find time to get the mod done!  With free shipping available for all the parts, I'm not sure it would really help much anyhow.  Except maybe for folks outside the US.


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## xrk971 (Sep 9, 2017)

That's cool StellarE - we have all have been there, and totally know that family and "yes, Honey" duties always come first if one wants longevity with diy.


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## stellarelephant (Sep 14, 2017)

Just filled up a Digi-Key cart with parts for the RaptorLightning mod.  All the components for one mod add up to about $9.50 plus shipping (cheapest shipping option is $3.50). Adding in the battery and the 3 boards, I'm at about $26 total cost for the mod, not including the few cents worth of extra wire I'll need to connect all the boards together.  X, can you recommend a certain wire gauge?

I had to substitute a different 1uF cap and 47R resistor, as the ones on the BOM were not available.
Also, here is the 47uF cap that Raptor used (this replaces the 100uF on the BOM): https://www.digikey.com/scripts/DkSearch/dksus.dll?Detail&itemSeq=238395325&uq=636409334171526774
Other than those three parts, I'm ordering using the exact part numbers on the BOM Raptor provided.


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## stellarelephant

I soldered up my first cap MX but failed my first attempt at the USB load sharing board.  Tiny pins under that micro USB jack... Must buy a fine solder tip and liquid flux!
  

In the meantime...I bought some new planar Mayflower V1 cans.  These are a T50RP v3 modded for accurate frequency response. 

 

I was worried that the Pocket Class A wouldn't have enough juice for them, but alas, it seems this amp fears no headphone. According to X, it helps that I'm running the amp at full 18V. It probably also helps that I boosted bias further with my resistor values.  And thank goodness my x3 player puts out a generous 1.5v line out signal.  First impressions tell me that I have headroom to spare (pot set at about 2:00 is loud) with good dynamics and more detail than I have ever gotten from a headphone before.


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## Brooko

For anyone interested - there is now a Showcase item - so please add your reviews.

My review is here : https://www.head-fi.org/showcase/xrk-audio-nhb-portable-class-a.22873/reviews#review-19723

This really is an incredible sounding piece of kit.


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## stellarelephant

Brooko said:


> For anyone interested - there is now a Showcase item - so please add your reviews.
> 
> My review is here : https://www.head-fi.org/showcase/xrk-audio-nhb-portable-class-a.22873/reviews#review-19723
> 
> This really is an incredible sounding piece of kit.



Hi Brooko.  Great in-depth review with nice pairings and relevant comparisons.  This amp has serious mojo and I'm glad you hear it too!


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## Brooko

Thanks. Can't wait until the new batteries arrive as the current 2 hour play time is getting pretty frustrating  And I agreed to buy it today. I'm paying full price.  Its just very worth it.


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