# dynahi pictures



## kevin gilmore

The board with the heatsink

http://gilmore.chem.northwestern.edu/dynahi2.jpg

 200khz square wave into 33 ohms
 (i keep burning up the 5 watt load resistors)

http://gilmore.chem.northwestern.edu/dynahi3.jpg

 Yet to install and test the servo...

 Finished pic
http://gilmore.chem.northwestern.edu/dynahi4.jpg


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## Sewer Guy

Most impressive! Very clean. Are you accepting contributions for new load resistors?


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## Iron_Dreamer

Yee-haw, wow! Keep it coming KG! What will the master produce next?


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## JohnFerrier

Hi Kevin,

 That is really nice. Thanks for sharing. I wonder though, why some many amplifiers? I'll confess your pictures do make me interested in building a DynaHi...hmmm....geez it's such an investment in time....kind of like just listening now... dunno... maybe....


 JF


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## kevin gilmore

quote
 I wonder though, why some many amplifiers

 I keep designing better and better things. Which generally means
 more money in parts and increased physical size and power consumption.
 Also better parts become available. Which is definitely the case for
 the output transistors used in this amplifier.

 I'm doing the dynahi and the mig/mig2 this year.

 Then that is going to be it for quite a while for headphone amplifiers.
 For electrostatic amps, i don't know how to do anything better than
 the blue hawaii. For dynamic amps the dynahi and the mig/mig2 are
 about as far as i can go there too.

 Next year, production uberamps. 400 and 800 watt units.

 There is a new preamp in there somewhere.

 There is something else somewhere in there too


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## JohnFerrier

Quote:


  Originally Posted by *kevin gilmore* 
_Next year, production uberamps. 400 and 800 watt units._

 

Yep, seems there is a niche that you can fill...

 I need to check into the mig/mig2...

 And at your convenience...any way to work in that novel Bryston output design?


 JF


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## Edwood

Woah. I'm going to have to try building that one some day. Perhaps I should at least be able to build a Gilmore Lite, first. 
	

	
	
		
		

		
		
	


	




 I suppose my circuit schematic illiteracy won't help either. (ok, not totally illiterate, just not very advanced)

 -Ed


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## was ist los?

Kevin, nice work!!! What do you think is more suitable for Grados, the Dynahi or Dynamic? Will there be a balanced bridge version of this amp?


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## some1x

Will this be a doable project for someone who has never attempted to build an amp before? :


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## gsferrari

1] I see a empty slots in parallel with the resistors. What are those slots for? 

 2] Where can I find schematics of this amp?

 Now - the volume question :-
 ----------------------------

 Mr. Gilmore,

 Would it be more productive if we used a switching circuit which enabled/disabled amplifier blocks depending on the required volume? Wouldnt this offer better sound quality and lower power consumption (also less heat production in Class-A amps) than a Potentiometer/Stepped Attenuator controlled system?

 Basically turning on/off amplifier blocks to control volume instead of using passive components... 
	

	
	
		
		

		
		
	


	




 Is this even possible? What do you think?


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## commando

Quote:


  Originally Posted by *kevin gilmore* 
_Next year, production uberamps. 400 and 800 watt units._

 

Yeah but how will my CD3Ks sound with them?


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## Demolition

Thanks for the photos of the Dynahi board, Kevin. Much more interesting than your mangled finger. 
	

	
	
		
		

		
		
	


	







 D.


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## kevin gilmore

quote
 1] I see a empty slots in parallel with the resistors. What are those slots for? 

 various other options. For example 2 x 20 ohm resistors in parallel for the
 emitter load resistors instead of 1 x 10. Lower inductance. Makes a significant
 difference because the amp has a slew rate of several hundred volts/usec.

 2] Where can I find schematics of this amp?

http://gilmore.chem.northwestern.edu/dynahi.gif

 However there are numerous changes
 The 2 x 15k on the left are 30k
 The 510 in the middle is 100
 the 2 x 510 at the top and bottom are 150
 The 2.5 ohm resistors are 10 ohm or 2 x 20 in parallel each
 The 20k feedback is now 2k
 The 1k to ground is now 100

 quote
 Would it be more productive if we used a switching circuit which enabled/disabled amplifier blocks depending on the required volume? Wouldnt this offer better sound quality and lower power consumption (also less heat production in Class-A amps) than a Potentiometer/Stepped Attenuator controlled system?

 If you are talking of some kind of class H circuit all i can say is YUUUK.
 Better sound quality, not a chance. None of the multistep designs can
 switch fast enough and putting a delay line in series with the audio signal
 so that this could be acomplished would do more harm than good.

 Lower power consumption, who cares. This is not a portable amplifier.
 This amp only pulls a total of about 30 watts.

 The mig2 amp uses 288 watts just to light up the filaments!

 quote
 Will this be a doable project for someone who has never attempted to build an amp before

 Depends on how good you are at the mechanical aspects. Drilling and
 taping the heatsinks, mounting everything... Stuffing the board is easy.

 Many more pictures as soon as the rest of the parts get here.
 Still missing some resistors and one of the heatsinks.


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## aerius

Time to make a trip to the local electronics supply shops to see if they have everything. If they do I've just found my next project.


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## rsaavedra

Quote:


  Originally Posted by *kevin gilmore* 
_This amp only pulls a total of about 30 watts._

 

So I assume this is not a headphone amp, is it easy to make one (a headphone amp that is) with this same circuit design? That ripple-free square wave on the occiloscope is amazingly clean.


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## kevin gilmore

Yes this is a headphone amplifier for all dynamic headphones.
 Including the akg 1000 and grado's.

 It ended up about 15 watts of pure class A. You will need a heat
 sink at least that big.


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## some1x

I think it is a headphone amp- just not terribly efficient one 
	

	
	
		
		

		
			





 ... I wonder if there is a readily available (and affordable) chassis which will naturally work well for this project.


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## kevin gilmore

Define efficient.

 It is certainly far more efficient than a blue hawaii that
 consumes more than 130 watts to put out a few milliwatts of
 power.

 It is certainly way more efficient than a mig2 which consumes
 a total of about 400 watts to put out 5 watts per channel.


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## rsaavedra

Quote:


  Originally Posted by *kevin gilmore* 
_Yes this is a headphone amplifier for all dynamic headphones.
 Including the akg 1000 and grado's._

 

Wow 30 watts seems a lot for headphone amps to me, but what do I know 
	

	
	
		
		

		
		
	


	




 I'm an Electronics-DIY newbie. I'm actually much more experienced at the mechanical aspects of DIY things than the miniature electronic soldering part, so this amp represents a promising DIY project to me.

 Edit: oh now reading the other postings, I guess it might be using 30 watts, but not putting out 30 watts, which is what I thought.


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## gsferrari

Mr. Gilmore,

 This is an amplifier I will be building over the course of these next few weeks. Can you please post a link to the files for the PCB and an updated components list?

 Have you figured out why you are blowing the load resistor?

 Another Gilmore to fiddle with


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## rsaavedra

Quote:


  Originally Posted by *gsferrari* 
_This is an amplifier I will be building over the course of these next few weeks._

 

I'd be interested in trying building it as well, provided Mr. Gilmore doesn't object, and he has the circuit in kind of a finalized stage already.


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## gsferrari

Quote:


  Originally Posted by *rsaavedr* 
_I'd be interested in trying building it as well, provided Mr. Gilmore doesn't object, and he has the circuit in kind of a finalized stage already._

 


 Of course...

 Mr. Gilmore - 

 * do we have your permission to attempt building this circuit?

 * I cant see any power supply components. Do you have any suggestions for the power supply design?

 Thank you sir.

 -gsferrari


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## some1x

What do you think of this case:
http://www.silentpcreview.com/article141-page2.html

 ... wonder who oem'd it


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## gsferrari

That case looks very nice!! 
	

	
	
		
		

		
		
	


	




 I am sure however that we will need a insulating (wood?) layer over it on the top and front to protect against burns...

 The size of the case depends on the power supply requirements because the amplifier board doesnt seem too crowded.

 I dont see the buffers on the board


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## Iron_Dreamer

So this amp outputs 15W of heat, then?


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## Edwood

Quote:


  Originally Posted by *kevin gilmore* 
_quote
 Depends on how good you are at the mechanical aspects. Drilling and
 taping the heatsinks, mounting everything... Stuffing the board is easy.

 Many more pictures as soon as the rest of the parts get here.
 Still missing some resistors and one of the heatsinks._

 

Sweet. Hopefully someone can help me with stuffing the board. I just want to make sure I don't fry anything in the process.

 I am much better with the mechanical aspects than the circuits. Of course, I've had a lot more experience. 

 Since I have no idea how to lay it out on a protoboard, I'll be patiently awaiting someone to have a finished PCB that I could buy.

 BTW, 30watts is nothing. Especially if you want it to drive the K1000's.

 Kevin: Where do you buy your heatsinks from? 

 -Ed


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## gsferrari

http://www.enertron-inc.com/Default.htm

http://www.thermacore.com/

http://www.thermaflo.com/heatsinks.shtml


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## kevin gilmore

thermaflo e3180ux2-50
 a real rip in low quantites ($30 each)
 in large quantities about $5

 I can buy the stuff full length for cheap, but did not want to spend
 the time cuting it up. With one hand partially out of commission for 
 a few weeks, Its worth it to get it the size i want now without having
 to use either a bandsaw or a mill. Without the proper setup milling
 the heatsink the fins will sing like crazy, and therefore score.

 quote
 * do we have your permission to attempt building this circuit?

 I would not publish it if i did not intend for people to build it.

 The current board layout has a couple of mistakes that i know of
 (like the holes for the caps for the opamp are too small) and i want
 to wait for the real servo caps to show up to make sure they are
 the size i think they are. The holes for the output transistors need
 to be shortened by about .15 inch...

 The power supply is next, You will need something that puts out
 +28 at 1 amp and -28 at 1 amp. Regulated really is necessary...
 Think of the dynamic supply massively beefed up with opa541's
 Big pass transistor preregulator puts out + and -45 then the
 opa541's put out +/-28. Same deal with the voltage reference
 and calculate the resistors for the proper voltages.


 quote
 Will there be a balanced bridge version of this amp?

 This would be excessively silly (40 Vrms). Still its obvious
 from the design how to make it balanced.

 Which sounds better. Who knows. Give me a few months to listen...
 But it definitely lights up k1000's like nothing else does.


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## ppl

Any one have a source for the output transistors


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## Subsonic

Quote:


  Originally Posted by *ppl* 
_Any one have a source for the output transistors_

 

I just checked www.bdent.com and they have them.


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## JohnFerrier

Quote:


  Originally Posted by *ppl* 
_Any one have a source for the output transistors_

 


 Hi Phil...

 I guess MCM but I wasn't sure from Kevin's posts if he was still using the 2sc3421/2sa1358. Personally, I'm not up on Toshiba parts to know if these ARE the lastest and greatest (my guess is that they are)...


 JF


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## was ist los?

Hrm... since this amp does work with Grados, i shall look into it. Kevin, what do you think of it's performance with your Grados versus the old dynamic?
 I look forward to anyone else's opinions.
 *EDIT* Kevin, could you give a ballpark cost of the amp?


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## rsaavedra

Quote:


  Originally Posted by *was ist los?* 
_*EDIT* Kevin, could you give a ballpark cost of the amp?_

 

I second that question, also how about a rough estimate of what the power supply chunk might be.


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## Glassman

I think modified Jung super regulator will work here, you just need higher power pass transistor and cooling.. this should be even better than Kevin's power opamp style I think..

 how much of idle current the new output transistors need to sing? I mean what is their 'sweet spot' in your opinion? you were running the older 2SC1815/2SA1015 at ~15mA (or 30mA?) each, what about the new ones?

 also would it be wise to split the power supply for the output stage and the rest? cleaner supply for the lower current and input section that way, would it improve anything?


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## kevin gilmore

quote
 Have you figured out why you are blowing the load resistor

 Lets see, 15 watts into a 5 watt resistor. Got to let the magic
 smoke out once in a while.

 I bought the transistors from www.bdent.com
 A couple of months ago i had everything on a spreadsheet and at
 the time mouser carried them, but no longer.

 The target current for the output transistors is 60 ma each. Makes
 for 240ma which is 13.4 watts. Ended up closer to 300ma. I'll adjust
 it down a bit later.

 Pricing of parts. Who knows. I still have not added up what i spent
 on the blue hawaii's. With power supply probably close to $200 in
 parts. Just the transistors and resistors cost per channel is $40.
 (fairly accurate number not counting servo opamp and connectors)

 quote
 I think modified Jung super regulator will work here, you just need higher power pass transistor and cooling.. this should be even better than Kevin's power opamp style I think..

 Voltage wize the jung regulator would be running the opamps at
 absolutely maximum voltage with a 30 volt output. You would need
 to pick opamps with a higher voltage compliance, otherwise on startup
 the opamps might pop.

 Splitting the power supply rails can't hurt. That way the outputs can
 run off unregulated rails.


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## pooooo

Hi Kevin, 
 1. Don't you think it might be necessary to place some decoupling caps on the board? 
 2. Could you please tell me more about the components around the opamp, such as the dark blue beads and the silver one? Are they shown on the schematic?


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## kevin gilmore

The servo is the same as the other dynamic amplifier. Feedback resistor
 is 1meg, cap is .33uf series resistor to the dc adjust point is 5k.

 Coupling caps can't hurt. When i'm finished the power supply will only
 be a couple of inches away and since its all class A caps are not really
 necessary. The final board will have spaces for caps anyway.

 Final pictures with all the real parts are still a couple of days away. I
 expected parts today, they did not show up. The other heat sink
 and the neutrik connectors are holding up the works.


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## rsaavedra

Looking forward to the final pics, diagram, and part values. Btw, I notice from a birds eye view the circuit schematics resemble the schematics of this other amp of yours. Is the Dynahi sort of an evolution of that one?
 Cheers,
 Raul


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## kevin gilmore

Yes its a version of the other amp with a cascode first stage and
 very fast output transistors. Higher voltages and a lot more class A
 power. The uberamp looks a lot like this too. Except that one is
 going to be balanced only. The group delay on this amplifier is
 less than 5 nanoseconds. Which means that for audio frequencys
 the TIM is unmeasurable. I've yet to see an opamp based amplifier
 that can come anywhere close to this delay time.

 Here is a pdf of the bottom layer with the silkscreen information.
 There are still a few things i want to change to make it perfect

http://gilmore.chem.northwestern.edu/dynahi5.pdf


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## kevin gilmore

And it would have been almost done today except my tech trashed
 one of the transformers...

http://gilmore.chem.northwestern.edu/dynahi5.jpg

 oh well another few days (and another $40)


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## gsferrari

OMG!!

 Thats just ONE channel you showed us before 
	

	
	
		
		

		
			





 LOL This thing is a beast...cant wait to see the finished pics !!


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## JohnFerrier

Kevin,

 Just wondered, with such a sharp 200khz square wave, if you used the JFET input with higher capacitance (or the BJT input pair). Your schematic allowed the choice of either. Notice that paralleling 4 pairs of JFETs that it rolls off at 540khz (an appears to be more of a shark fin wave at 200khz). So a single pair rolls off at 2Mhz (still not going to be a square wave at 200khz).


 JF


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## kevin gilmore

Huh?

 I'm using the dual jfet input transistor. and the dual transistor as
 the cascodes. The second and third stage are bipolar.

 The jfets and transistors are not pin for pin compatable, the board
 i layed out was for the jfets.

 That really is the square wave (no its not clipping) into 33 ohms
 at the voltages and speeds specified.

 The output transistors have a Ft of 120mhz


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## JohnFerrier

Sorry, for the confusion. Just wondered if you used JFETs (2sk389/2sj109) or BJTs (2sc3381/2sa1349) at the input. You answered JFETs. 

 I had posted an observation that a complementary source follower (akin to your input) does not produce such a clean square wave. So, I wonder why. Looking at the Ciss: 2sk389 = 25pF, 2sj109 = 95pF. This means with a series resistance of 1k ohms that the input rolls off at 1.3Mhz. (A phenomena that feedback doesn't correct.) So, the only way to have got such a clean square wave, given the Ciss of the JFETs, is to drive them with a low impedance source. However, in actual use an attenuator usually would add series resistance. Anyways, I think I figured out why my waveform didn't look like yours... (Further, FWIW, I had to add 1k ohm series resistors to prevent my circuit from oscillating with the volume control at the lowest levels. Regardless, a bandwidth of 540khz isn't bad...especially since I also noted that I can't hear up to 20khz...and am glad that most music lays within much lower registers...)

 And, of course, the reason I care is because I've still got the bug to try your work.


 JF


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## kevin gilmore

You would be absolutely correct in your assesment. However everything
 i've been doing for some time now is 50 ohm input impedance. With
 50 ohm cable driven with a 50 ohm source. Absolutely everything 
 terminated in the characteristic impedance of the interconnect cables
 i'm using. The sound difference is astounding.

 Same sort of thing krell is doing with their cast inputs and outputs.
 although they explain it completely differently.

 The bottom line is the amplifer really is that fast, the loop delay is
 way small and the sound is astounding.

 One of the reasons i knocked down the 20k/1k feedback resistors to
 2k/100 ohm.


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## rsaavedra

Quote:


  Originally Posted by *JohnFerrier* 
_I had to add 1k ohm series resistors to prevent my circuit from oscillating with the volume control at the lowest levels._

 

I hope once there's a precise list of parts and the final schematics, there won't be a need to add these sorts of tweaks, right? I worry because if I build this amp, I won't have a way to test it's performance other than listening to it (e.g. I don't have an occiloscope for instance).

 Amp looks Great Kevin. So those regulated power supplies can be purchased all preassembled and ready for this amp it seems? That will be very convenient, a time saver for sure.


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## JohnFerrier

Quote:


  Originally Posted by *rsaavedr* 
_I hope once there's a precise list of parts and the final schematics, there won't be a need to add these sorts of tweaks, right?_

 

I was writing about my amplifier circuit (which is not the same as Kevin's). However, my circuit does meet "Kevin's Rules of Proper Audio Design" : ).


 JF


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## rsaavedra

Quote:


  Originally Posted by *JohnFerrier* 
_I was writing about my amplifier circuit (which is not the same as Kevin's)._

 

Ah ok, my bad sorry, thanks for the clarification.


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## pooooo

Hi Kevin, 
 Could you please let us know what kind of 50ohm source you are using and how you lower the input impedance of the amp to 50ohm? I never knew that such impedance-matching issues could make any difference in audible frequency band. Perhaps I should give it a try.


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## eric343

Quote:


  Originally Posted by *pooooo* 
_Hi Kevin, 
 Could you please let us know what kind of 50ohm source you are using and how you lower the input impedance of the amp to 50ohm? I never knew that such impedance-matching issues could make any difference in audible frequency band. Perhaps I should give it a try. 
	

	
	
		
		

		
		
	


	


_

 

Read the reviews of my Nitrogen cables... the ProSink termination is the brainchild of Kevin and its effects on audio quality have been posted about a lot.


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## aos

I am curious as to why 50 instead of more common 75? I mean isn't it easier to find 75 Ohm cables and sockets rather than 50? Or is 50 commonly used for oscilloscopes and other measurement equipment in your lab so it's what you're dealing on everyday basis? I also belive in impedance matching and usually place 50-100 Ohm at the output though indeed if you don't use same-impedance cable you're not doing much, if anything, so I was planning on experimenting with 75 at some point as they're easier to get.


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## JohnFerrier

I'm thinking if Kevin's source impedance is 50 ohms (not sure how attenuation is done), that the BJTs (2sc3381/2sa1349) would better the JFETs. This is based on information that BJTs are lower noise at <100 ohms, JFETs >100 ohms. BJTs also don't have the same degree of non-linear capacitance. Most people aren't driving their amps with low impedance sources (therefore, JFETs are preferred). May be worth a try some time. FWIW: my amp is all JFET...and not bad sounding into 300 ohm Sennheisers.


 JF


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## kevin gilmore

The big roll of silver cable i have is 50 ohms...

 Now if it was 75 ohms, then that is what i would have used.


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## aos

Quote:


 The big roll of silver cable i have is 50 ohms...

 Now if it was 75 ohms, then that is what i would have used. 
 

That's exactly what I thought the answer would be. I didn't expect "silver" but I should've known better 
	

	
	
		
		

		
		
	


	




. Kevin always seems to have some exotic military grade stuff lying around (tantalum resistors, ultrafast capacitors...).


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## eric343

Quote:


  Originally Posted by *aos* 
_That's exactly what I thought the answer would be. I didn't expect "silver" but I should've known better 
	

	
	
		
		

		
		
	


	




. Kevin always seems to have some exotic military grade stuff lying around (tantalum resistors, ultrafast capacitors...)._

 

That's what you get for running an analytic spectrometry lab for over a decade...


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## kevin gilmore

way over a decade.

 Just got most of the rest of the parts in. Now i'm short one lousy
 resistor...


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## eric343

Quote:


  Originally Posted by *kevin gilmore* 
_way over a decade.

 Just got most of the rest of the parts in. Now i'm short one lousy
 resistor..._

 

LOL! 
	

	
	
		
		

		
		
	


	




 I know *exactly* where you're coming from on that one...


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## Prune

Question: any rough estimate of total cost for amp & power supply? When will we see the final PCB version?

 And by the way, I think it was mentioned somewhere in the forums that someone was working on Blue Hawaii PCBs. How's that coming along?


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## eric343

Quote:


  Originally Posted by *Prune* 
_And by the way, I think it was mentioned somewhere in the forums that someone was working on Blue Hawaii PCBs. How's that coming along?_

 

As far as I know the initial order has already been used / spoken for and there are no plans to order another batch. As it was strictly a private order, I'm going to let the guy who was in charge come forward and post the layouts if he wants to.


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## Prune

Quote:


 I'm going to let the guy who was in charge come forward and post the layouts if he wants to. 
 

That's what I meant, I was looking for layouts or CAD files, not the actual boards.


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## kevin gilmore

My batch of blue hawaii boards is already spoken for.

 There is another person that was given the layout and i have asked
 him whether he is going to have boards made or not. He wanted to
 use 4 ounce copper and go with twice the standard board thickness
 and wanted to add solder grommets to the tube socket holes. I'm not
 sure where he is on this, but those boards won't be cheap.

 My layout on the dynahi still has work necessary. The inital prototype
 board run is just barely acceptable, meaining there are no errors, but
 three different caps have the wrong hole size, plus i did not as of yet
 add the input connectors. I'll release it when its done and not a moment
 sooner.


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## Prune

Well, here's to hoping this other person will tell us when, if at all, we can expect these boards. If not, perhaps Mr. Gilmore will share his Blue Hawaii layouts with the rest of us.

 BTW, can someone disperse my ignorance and explain what solder grommets are?


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## JohnFerrier

Quote:


  Originally Posted by *Prune* 
_BTW, can someone disperse my ignorance and explain what solder grommets are?_

 

Maybe something like Mill-Max's pin receptacles...






http://www.mill-max.com/pin_rec_cata...search=&pr=Rec

 *EDIT* See below. Guess when Kevin writes grommet...he means grommet... hehehe... although from Kevin's description seems kinda like a rivet too... hehe...


 JF


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## kevin gilmore

Think of a standard grommet made from rubber. Now imagine the same
 thing made from brass. You insert it thru the board and then expand
 it into place from the other side. What it does is prevent the lifting
 of the circuit board lands due to heat over a many year period.


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## Edwood

Quote:


  Originally Posted by *eric343* 
_Read the reviews of my Nitrogen cables... the ProSink termination is the brainchild of Kevin and its effects on audio quality have been posted about a lot._

 

What exactly is ProSink termination? (Process, materials, etc.) Or is it not to be public knowledge? Just wondering.

 -Ed


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## eric343

Essentially, it's a terminating resistor matched to the impedance of the cable. From an electrical standpoint, it eliminates reflections of signal within the cable and presents a linear, non-reactive load to the signal. (Most cables have some capacitance and inductance, which make them reactive loads and therefore harder for the source to drive) Interestingly enough, the ProSink termination effectively negates most of the sonic effects that the cable material itself has, leaving only the sonic effects of the connectors. (That's one of the reasons I use a cable geometry that's highly unusual in the world of audio-- normal concerns such as skin effect, strand jumping, etc. are not a factor, and rather the main concern is cable-induced signals that can be lumped under the category of microphonics. And that's where the stiffness comes in, because a stiff cable is less suceptible to microphonics [in addition to the particular materials used].)


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## JohnFerrier

It's also very low in carbohydrates...


 JF


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## aos

Terminating cables is a pretty standard practice everywhere except in audio, though it's becoming more common now as it gets more proponents and articles such as the one in Stereophile from last year (or year before) came out, so that even laymen are becoming familiar with it. Any EE would learn about this within electrical networks theory courses.


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## kevin gilmore

Take two of the most different sounding cables available and properly
 terminate each one. Now listen to them again. It will be almost impossible
 to now tell these cables apart. So all the marketing speak that goes
 with all these cables just got thrown out the window. Bottom line is that
 after properly terminating the cable, all that is now left is the real
 quality of the cable itself, meaning quality of shielding, and consistency
 of impedance over the length of the cable. Many cables with various
 twists and other geometry BS test very poorly for consistent impedance.

 For solid state preamps, driving cables properly is trivial.
 For tube preamps additional work which requires attenuation is
 necessary to properly drive a terminated cable.


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## ServinginEcuador

So...it's starting to sound like Eric's Halogen cables are quite a bit better than expected due to their termination. If what Kevin says is true, the big problem is the fact that the great cables we have are still not terminated properly, and I wonder what would happen if someone could do a good job of properly terminating them?


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## Prune

Are you terminating by a series or parallel resistor? And how do you perform measurement on the cable to determine the correct resistance? And what about the source impedance?


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## kevin gilmore

Series resistor at the source end (in many cases this can be eliminated)
 Parallel resistor at the other end.

 Only 2 ways to correctly measure the impedance of complex cable
 geometrys. One is a TDR. The other is a fast square wave generator
 a decent oscilliscope and a dual 150 ohm pot. One section wired
 in series with the input end of the cable, the other wired in parallel
 to ground. Tune pot for best square wave at the destination. Then
 measure the pot with an ohmmeter. That is the real characteristic
 impedance of the cable.

 The number will be a minimum of 46 ohms, and a maximum of about 120
 ohms. alpha-core cables may be less than 46 ohms, i have not measured
 them.


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## ServinginEcuador

So, by using this means of measurement you're tailoring the load in which you will place in parallel with the cable to each cable you build? How cool. Time consuming, but cool. Ingenious actually.


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## kevin gilmore

Actually i use very high quality 50 ohm cable. So i already know
 what the termination needs to be.

 Its the wacko cables with the various twists and geometrys that
 would have to be measured. That would include, but certainly not
 limited to nordost,audioquest,cardas,analysisplus,kimbercable ,
 mit,monster,alpha-core...

 If you would see a cost book from a high end audio retailer you
 would know exactly why they push these cables so much. Many
 times they make more money on the cables than they do on the
 rest of the system.

 In large quantities really good silver cable is certainly less than $10
 per foot.


----------



## eric343

Quote:


  Originally Posted by *kevin gilmore* 
_In large quantities really good silver cable is certainly less than $10
 per foot._

 

And with the silver cable you're talking about, that means quantities large enough to mean an initial order of $10k, IIRC.


----------



## eric343

Quote:


  Originally Posted by *ServinginEcuador* 
_So...it's starting to sound like Eric's Halogen cables are quite a bit better than expected due to their termination._

 

Nitrogen, actually. The Halogen cables didn't have the termination.

 What Kevin didn't mention is that termination will take care of the cable's effects, but the connectors used *will* affect the sound... the connectors have their own impedance (usually very low for RCA connectors, higher for the eichmanns and both high and well controlled for the new WBTs) and affect the sound.


----------



## aos

that's why I wanted to use coax when I first read the Stereophile article, as these cables are most readily available that have known impedance and I had no means of measuring it. As Kevin mentioned, only really simple geometries can be calculated analytically. I also usually have a series resistor of 50 to 100 Ohms at the output for that purpose.


----------



## Prune

So how do you calculate it then? Say, for example, for the case of Venhaus interconnects. Silver conductors, simple geometry: helix around hollow teflon tube.

 I used awg 28 fine silver, and the tube is PTFE a bit over quarter inch diameter, walls about 1mm. Helix gives about 1" spacing between conductors along the tube. How do I calculate correct termination resistances?


----------



## eric343

Quote:


  Originally Posted by *Prune* 
_So how do you calculate it then? Say, for example, for the case of Venhaus interconnects. Silver conductors, simple geometry: helix around hollow teflon tube.

 I used awg 28 fine silver, and the tube is PTFE a bit over quarter inch diameter, walls about 1mm. Helix gives about 1" spacing between conductors along the tube. How do I calculate correct termination resistances?_

 

http://www.epanorama.net/documents/w...impedance.html

  Quote:


 Characteristic impedance is determined by the size and spacing of the conductors and the type of dielectric used between them. Balanced pair, or twin lines, have a Zo which depends on the ratio of the wire spacing to wire diameter and the foregoing remarks still apply. For practical lines, Zo at high frequencies is very nearly, but not exactly, a pure resistance.

 The following formula can be used for calculating the characteristic impedance of balanced pair near ground: (formula taken from Reference Data for Radio Engineers book published by Howard W. Sams & Co. 1975, page 24-22)

 impedance = (276 / e^(1/2)) * log ((2D/d) * (1 + (D/2h)^2))^(1/2))

 Where:

 * log = logarithm of 10
 * d = wire diameter
 * D = distance between wires in pair
 * e = dielectric constant (= 1 for air)
 * h = distance between balanced pair and ground 

 Not that this formula is only valid for unshielded balanced pair when D and h are order of magnitude larger than d. If the twisted pair is far away from ground (h is nearly infinite), the the effect of the ground is neglegtible and the impedance of the cable can be approximated with simpler formula (my own derivation from formula above):

 impedance = (276 / e^(1/2)) * log ((2D/d)

 For twin line Zo will be typically between 75 and 1000 ohms depending on the intended application. The impedance of typical old telephone pair in the telephone poles in the air has characteristic impedance of around 600 ohms. The telephone and telecommunication cables in use have typically a characteristic impedance of 100 or 120 ohms. 
 

Alternately, find someone with a TDR (like me).


----------



## Prune

Quote:


 h = distance between balanced pair and ground 
 

I'm using a balanced pair and NO ground. What value do I use for h in the full formula?

 Using the simplified formula I get about 500 ohm, which seems a bit high.


----------



## eric343

Quote:


  Originally Posted by *Prune* 
_I'm using a balanced pair and NO ground. What value do I use for h in the full formula?

 Using the simplified formula I get about 500 ohm, which seems a bit high._

 

Infinity 
	

	
	
		
		

		
			





 Actually, just a fairly high number, because there IS a ground nearby.

 If in doubt, send me an email through my profile and I'll TDR your cables for $7 (basically shipping and a small tax to keep the workload within reason-- that offer applies to all DIYers). If I get my digital camera back up and running by then I'll post some pics of the trace, too.


----------



## aos

What's a TDR? Time delay something?

 It's been 10+ years but I believe it was Z = sqrt (C /L) so you would write formulas for capacity per unit of length and inductance per unit of length, which can be expressed by electrical and magnetic fields. Those are simple for a plain straight wire. Then you integrate fields from zero to infinity. Since you can only analytically integrate a small subset of functions, usually only stuff that is super simple gets calculated this way. Or something like that - aren't you studying for EE right now at UBC? Rather hard to believe they wouldn't teach this. For the rest there is numerical calculation or - just measure it, that is going to be the most useful in most cases anyway.


----------



## Prune

Google comes up with Time Domain Reflectometry (far more results with Domain than Delay).

 eric343, I may just take you up on that offer. If I can find a way to ship the cables in a long thin box... If there's one disadvantage to Venhaus' design is that the teflon tube is extremely stiff. Bending the thing sharply enough kinks the tube and a crease forms. I couldn't find foamed PTFE that was anywhere close to the thickness I needed.

 As an aside, can someone tell me how the hell a good director with the biggest movie budget ever, $200 million, can still manage to screw up a movie? Troy is the biggest disappointment this far for 2004. As usual, Ebert's review at the Chicago Suntimes website hits the bullseye IMHO.


----------



## kevin gilmore

Trying to calculate the impedance is pretty much a waste of time unless
 you know the characteristics of the insulator and many other variables.
 The geometry things like spirals around a teflon tube are almost impossible
 to calculate.

 The only way is to measure. The scope/signal generator trick certainly
 works but only gives an average number. A TDR trace gives the full
 picture. And when your trendy and expensive cable shows bumps in
 the TDR trace you know you have a fancy audio filter of some kind.
 Absolutely flat traces indicative of constant impedance are what you
 want, and many of the really good coax cables do this.

 As far as connectors, i like the high line WBT connectors for rca's
 (not quite a perfect impedance match, but nothing is) or Neutrik
 for balanced connections (much closer to a perfect impedance match
 at 50 ohms)


----------



## kevin gilmore

here are the cadcam files

http://gilmore.chem.northwestern.edu/dynahi.zip

 The board is 4.95 x 4.00 (trimmed a little) and is therefore <20sq inch
 (200 holes)


 so these people
http://www.pcbnet.com/a1ad14.asp

 will do them for $15 each (5 piece minimum)

 10k pots are optional, if the servo is out of range, you can add
 the pot in the right place, and then you don't have to match any
 of the components.

 You can and should user 78L15 and 79L15 in which case you have
 to flip the direction of the 78L15 from the silkscreen.


----------



## Prune

Great! So, anyone interested in a group buy?

 BTW, what about the power supply, is there a PCB design for it?


----------



## was ist los?

I'm definitely interested in a group buy.


----------



## rsaavedra

I'm interested in the group buy too. One comment, it seemed to me those power supplies were pre-built, e.g. not assembled by Kevin? Or did you assemble them btw? They had some lettering that made me think they were a preassembled purchased product.


----------



## Prune

I hope Kevin won't have any problem with a few people getting together on a group buy.

 I assume an amp needs two boards, or is one board for two channels? If the former, we only need three people minimum for an order, else five.

 Also, if there's a power supply design, perhaps we could get boards for that too.

 I don't mind organizing the group buy and shipping out the stuff, but as the company is a US one and I'm in Canada, that's probably not be the best way. Unless there's a separate Canadian group buy, depending on how many people are interested.

 BTW, any news on Blue Hawaii boards/layouts?


----------



## kevin gilmore

No power supply design yet.
 There will be, but in the future.

 You can buy the condor supplies from allied. They are about $40 each.
 28 volts @ 1 amp. each

 So its
 $80 for power supplies
 $80 for semiconductors and resistors
 $30 for boards
 $20 for connectors
 $75 for heat sinks (much less in large quantities)
 $?? for the chassis
 plus making the angle heatsinks


----------



## Paragon

Looks like this amp will have to wait till I get some cash flow and more room to store it. I will stick with the first dynamic for now ;P. Looks great tho!

 As for your finger, I know how that is. Altho I went a bit further and ended up cutting the nerve too. That's what happens when you try to rush something in a machine shop. Looks like the same finger, same hand, same place as mine but I had to have a split cast on for a month after surgery.. then hand rehab after than 
	

	
	
		
		

		
			





. Have a nice scare left from it but the docs were able to attach the nerve so I do have feeling now.

 Take your time on thing's people, else ya won't be able to do things for a while.

 <>BTW, is it safe to short the output on the dynamics to act as a mute on power up or will it make the amp go nuts due to a mostly 0 load?


----------



## gsferrari

For what it can do - the price is VERY low 
	

	
	
		
		

		
		
	


	




 Are the parts finalized?


----------



## kevin gilmore

quote
 <>BTW, is it safe to short the output on the dynamics to act as a mute on power up or will it make the amp go nuts due to a mostly 0 load?

 Don't know. May drive the servo nuts, but otherwise will likely not cause
 a problem. May have time to test it later this week.

 quote
 Are the parts finalized?

 Yeah i think so.

 On to the mig2...
 (I can't imagine any but me nutty enough to build one)


----------



## JohnFerrier

Link to prior thread (useful if search is down): http://www4.head-fi.org/forums/showthread.php?t=47601

 I'd estimated $250-$600 depending on enclosure and if one wanted to use dual mono attenuators...


 JF


----------



## kevin gilmore

Final pictures (warning: huge)

http://gilmore.chem.northwestern.edu/dynahif1.jpg
http://gilmore.chem.northwestern.edu/dynahif2.jpg
http://gilmore.chem.northwestern.edu/dynahif3.jpg

 Anyone know of pc board mount 6c33 connectors???


----------



## eric343

Ask the guys in the machine shop to CNC machine you some ceramic? Or modify point-to pint ones...


----------



## was ist los?

Perhaps we can also have a group buy on heatsinks.


----------



## Paragon

I wish somone would start making nice 1/4" jacks that mount from the front with nut in the back. I'm starting to get tired of seeing all the Neutrik lockers.

 Anyhoo.. nice amp! Do the companies pay you to use their IC chip or other products.. cause I think a lot of orders are going to be going in very soon.


----------



## kevin gilmore

I'm no shill. I use the parts i use because they meet my criteria.
 No one pays me anything. Once in a while toshiba sends me free parts.
 (but so does On semi and TI) I would not allow anyone to pay me
 anything to say or do anything.

 I've reduced the gain resistor to 1.2k from 2k because i had too
 much gain in my system.


----------



## Paragon

I figured as much. Just had to prod at you a tad. Getting paid would take all the fun away from DIY.

 Any werd on the grounding idea? Basically like the Zen timer circuit
http://headwize.com/projects/showpro...lerano_prj.htm
 or would I not need somethign like that with the Dynamic amp? Does it create power-on thumps?

 I'm trying to avoid a switch in the signal path.


----------



## JohnFerrier

Quote:


  Originally Posted by *Paragon* 
_





 I'm trying to avoid a switch in the signal path._

 

There are already solder connections and jack connections in the same path...really doubt a good switch (or relay) will further impair the sound...(i.e. an Alcoswitch w/silver contacts...). (Think you can find someone that hear the difference between no switches and ten switches in series?)


 JF


----------



## kevin gilmore

Turn on is a very sharp fast noise, turn off is a slow bump.
 If you are going to add a relay circuit, have the relay short
 to ground thru a pair of back to back diodes. That way it
 does not upset the servo.


----------



## was ist los?

Kevin, i'm curious, when you turn on and off your amps, do you leave the headphone connected? Do you usually leave your amps on all the time?


----------



## rsaavedra

I'm building this amp soon in the following weeks, or if not possible that soon, then early Summer. I have a few questions Kevin:

 1) How about volume pot or attenuator? Don't see it in your pics of the amp.

 2) Wonder if there is a detailed part list available, or maybe whether the schematics have been updated indicating all your final choices of part values.

 3) Should heat sinks have some specific rating or spec? E.g. should they be able to dissipate a specific amount of heat/watts?


 About the PCB group buy, the Canada option I think will most likely be more expensive than from anywhere within the US. Now, not sure if a more centric location in the US might be more convenient than mine though, but I'm willing to purchase the boards and then ship them to the people interested in the group buy. I would have to buy at least 6 of these boards, so 3 prospective builders minimum. I'm one, so at least two interested people please post here your confirmed intent to join the board group buy, and/or please PM me. I'm in Pensacola FL, your final shipping cost would be the fair slice of shipping from manufacture to me, + shipping from me to you. The easiest for me would be to receive the payments through my PayPal personal account. If you are in a more central location and/or would like to be the hub in the group buy, please post about it.

 The heat sinks I'm not so sure about group buying. We would need to be many to make it worth, I think. The sinks are heavy little things. If we are only a few, the group buy plus shipping of the lot + then the individual shipping of a pair of sinks might not be much less (might actually be more) than each of us purchasing the pair separately and paying just one direct shipping. Not sure if some of you might know better or have some suggestions on this. I wonder if there's anything available in home improvement stores that can perform the heat sink function properly (and looks ok too).

 Cheers,
 Raul


----------



## gsferrari

You can have a volume control between the source and the amplifier. I believe this is more effective...

 Get two stepped attenuators (matched) and a pair of IC's. cut the IC's in half and make two IC's with a sa in the middle of each of them. One is for L and one is for R channel...connect between source and amp and use these as volume control...


----------



## rsaavedra

Hmm, I think I'd rather have the volume knob on the amp box than to have a separate little volume control box between source and amp. If I wanted that separation, then I'd rather have a full preamp between source and the amp, quite an overhead on the DIY project (or on the wallet).


----------



## Prune

In such a case it is better to have a volume control at the amplifier end. The output resistance of the potentiometer/attenuator combined with the load capacitance forms a low pass filter. I don't know what the input capacitance of Gilmore's amplifier is, but interconnects between the volume control and amplifier have enough capacitance of their own (unless you use short, low capacitance interconnects). So it's definitely best to put the volume control at the amplifier end, unless you have an active buffer after the volume control. More details at the DACT site: http://www.dact.com/Passive_Preamps.PDF


----------



## rsaavedra

Quote:


  Originally Posted by *kevin gilmore* 
_My batch of blue hawaii boards is already spoken for.
 There is another person that was given the layout and i have asked
 him whether he is going to have boards made or not. He wanted to
 use 4 ounce copper and go with twice the standard board thickness
 and wanted to add solder grommets to the tube socket holes. I'm not
 sure where he is on this, but those boards won't be cheap._

 

Kevin, before any PCB group buy would like to check, did those boards apply to the Blue Hawaii only, or is that person also planning to make "phat" Dynahi boards?


----------



## kevin gilmore

Yes i leave the headphones connected all the time. Usually i leave
 my headphone amps on all the time. The exception is the blue hawaii
 which is more than capable of heating up the entire room over a few
 hour period. The dynahi can also heat up the room.

 This amp does not have a volume knob. No room for it in the box.
 Hooks to the output of the preamp directly. You can certainly
 add one yourself. Most people should consider building the thing in
 a bigger box. If you are going to add a volume knob it should be
 a step attenuator.

 The heat sinks need to get rid of 10 to 15 watts.
 Just depends on how hot you want it to get. This is what i'm using
http://www.thermaflo.com/bin/exdatas...=Change+Length

 The blue hawaii boards and the blue hawaii power supply boards were
 layed out by justin wilson who spent considerable time on them. He owns
 the design for these two boards and he controls what happens to them.

 The one person doing blue hawaii amplifier boards quoted me this
 Quote 1 - $35 each in seems OK for std .062" FR-4, but if temperature stability is an issue, then
 Quote 2 - $80 each for .062" FR-408 would better fit the requirement.
 Quote 3 - $190 each for the FR-408 material in .125" thickness is kind of high at $190 each, but will provide an extremely rigid substrate, helping eliminate board flex when installing or removing the tube

 This is per board (2 amp boards required) not including the power supply
 board. I'm not going to have any more boards made as i have enough. If
 he decides to go thru this he will post himself.

 The dynahi board layout is my own, i did it, i can do whatever i want with
 it and i have given it away. I'm not going to be part of any group buy
 in either direction.


----------



## rsaavedra

Quote:


  Originally Posted by *kevin gilmore* 
_The exception is the blue hawaii
 which is more than capable of heating up the entire room over a few
 hour period. The dynahi can also heat up the room._

 

You know that comment of yours now has me having seconds thoughts about me choosing to build the dynahi. I have the habit of turning off the air conditioning (and in fact the refrigerator too) whenever listening to music at night, so I start from very silent surroundings. If the dynahi is going to heat up my entire livining room in my little apartment, that will ensure rather uncomfortably hot listening sessions during the unforgiving hot Summer nights here in FL. Because of this silly ergonomic issue, I'm now wondering if I should rather try to build an amp that doesn't go too hot.

 Does the dynahi heat up its surroundings more than, let's say, the way the back of a refrigerator heats up the corner of a kitchen?


----------



## Iron_Dreamer

Think about it, each heatsink dissapates 10-15W, which is 20-30W for the whole amp. This is far less than even the average Athlon or P4 powered PC, so it shouldn't heat up the room any more than your computer does. The BH on the other hand...


----------



## JohnFerrier

It would be like a 30 watt light bulb (1/2 of a 60 watt light bulb, etc.)...plus the power supply heat...


 JF


----------



## kevin gilmore

My krell amp is about 50 watts in standby mode. That is enough to
 raise the room temperature 3 or 4 degres. The room is very tight when
 the air/heat is not on and the walls are double insulated because i
 wanted the room ultra quiet...


----------



## rsaavedra

Quote:


  Originally Posted by *Iron_Dreamer* 
_Think about it, each heatsink dissapates 10-15W, which is 20-30W for the whole amp. This is far less than even the average Athlon or P4 powered PC, so it shouldn't heat up the room any more than your computer does. The BH on the other hand..._

 

 Quote:


  Originally Posted by *JohnFerrier* 
_It would be like a 30 watt light bulb (1/2 of a 60 watt light bulb, etc.)...plus the power supply heat..._

 

Well, that would suggest it's not going to be a problem. But is this analogy correct? A 30 watt light bulb I understand consumes 30 watts of power, the rating is not related to heat dissipation but power consumption right? Part of those consumed 30 watts becomes light, part becomes heat. I would think a 30 watt light bulb doesn't dissipate as much as the full 30 watts as heat (or does it?). To produce 30 watts of purely dissipated heat (not total consumed energy) you would need a light bulb of much more power consumption than 30 watts, or please correct me if I'm totally off here.

 Maybe the analogy is perfectly correct, because the amp probably won't be dissipating 30 watts of pure heat, part of those 30 watts is used to create the current in the output signal after all? So it would be indeed equivalent to a 30 watt light bulb case? If so, then heat buildup in the room certainly won't be an issue.


----------



## kevin gilmore

I just measured the power line draw and it is about 60 watts.
 At least 90% is going into pure heat.

 In a 60 watt incandescent lightbulb 99% goes into heat.
 A 60 watt incandescent lightbulb puts out as much light as a 
 15 watt fluorescent bulb.


----------



## JohnFerrier

To give a sense of the overkill consider that a lot of headphones (i.e. HD650/HD600) require about 1 watt max (my average listening level < 1mW)...not saying overkill is bad...


 JF


----------



## kevin gilmore

grado's definitely sound better on more than one watt.
 And k1000's absolutely require a few watts.

 The problem is the range of impedances this amp has to drive.
 From 32 to 300 ohms. For low impedance phones you need the
 bias turned up to keep the unit in class A for the entire audio
 signal. For high impedance phones you could definitely turn down
 the bias and still keep it in class A.

 On the other hand warm transistors sound better than cold ones.


----------



## JohnFerrier

Quote:


  Originally Posted by *kevin gilmore* 
_On the other hand warm transistors sound better than cold ones._

 


 This is a phenomenon I read from others too. I don't understand why this is the case... From my understanding semiconductors tend to be less noisy when cooler... Guess I tailored my amp for lowest noise. Is there a ready explanation that transistors sound better warm? Guess the characteristics of the transistor changes. Well, BJTs and FET probably behave differently. So, ready explanations may not not apply. Maybe it's just a preference through experience... 

 And if I build the DynaHi, it will still be for 300 ohm Sennheisers. It's an amp with a lot of muscle... On the other hand, I think the standard Gilmore V2 is a better match (haven't ruled that one out either).


 JF


----------



## rsaavedra

Quote:


  Originally Posted by *kevin gilmore* 
_I just measured the power line draw and it is about 60 watts.
 At least 90% is going into pure heat.

 In a 60 watt incandescent lightbulb 99% goes into heat.
 A 60 watt incandescent lightbulb puts out as much light as a 
 15 watt fluorescent bulb._

 

Thanks a lot Kevin, those numbers clarify it. So in total, the dynahi is putting out about 54w of heat, I guess the extra 24 watts are due to the power supplies. In any case, still would be similar to the heat a 54w incandescent lightbulb would generate, not bad at all. Sticking to the plan then, I will build it.


----------



## rsaavedra

Quote:


  Originally Posted by *JohnFerrier* 
_And if I build the DynaHi, it will still be for 300 ohm Sennheisers. It's an amp with a lot of muscle... On the other hand, I think the standard Gilmore V2 is a better match (haven't ruled that one out either)._

 

Also planning to drive Senn's (650) with the amp. Why do you think the V2 might be a better match though? I understand that one is best matched for Grado's.


 A side note, about the external attenuator option. You know today I saw the latest Stereophile. They have a review of an external little volume control, made by Placette Audio. The little thing just has inputs outputs, a remote control, and of course, a stepped attenuator. That one with 125 steps!, using super premium film-something resistors. Guess how much is the gadget?... $1000!!!!
http://www.placetteaudio.com/Products.htm

 That would be way too much more than the amp itself, no way. I think I'll go for a steeped att. on the amp box. But I'm leaning towards putting the power supplies on a separate box. That way there will be more room in the audio boards box for the att., and also, later on I can modularly replace the power supplies more eaisly with Kevin's, once he makes public the schematics of his own power supply for the dynahi.


----------



## JohnFerrier

Quote:


  Originally Posted by *rsaavedr* 
_Also planning to drive Senn's (650) with the amp. Why do you think the V2 might be a better match though? I understand that one is best matched for Grado's._

 


 Both amps are great solid state projects. The DynaHi is the latest and greatest with Cascoded stages... The V2 is lower power and uses all low noise transistors (JFETs and BJTs). I prefer low noise topologies (especially knowing how low the typical listening signal level is).

 * ASIDE *
 I just received a CD recorded with tube equipment today (link below). It took six weeks, but very nice soft sweet recording of Shinako Kikuchi singing "Japanese Songs from the 20th Century". I know Kevin has a tube amp (or two), he may want to check out tube recordings from...
http://www.valve-hearts.de/


 JF


----------



## rsaavedra

Kevin btw, wondering more or less when you estimate you might have the PS design, if not too far in the future I would rather wait for them intead of buying those PMC Condor's. Not pressuring at all really, just wondering to see if I should not place the order for the PS's sooner than I should.


----------



## kevin gilmore

I'm starting to think about the power supply now. The condor supplies
 get quite warm, almost too hot to touch. The power supply is going
 to be significant overkill.


 It sounds SOOOOO nice.


 Absolutely great for hd650's with the cardas cable. 
 Live Dame Myra Hess concert yesterday on WFMT to die for
 with sequerra tuner, dynahi and hd650's

 Too many projects in the fire at the moment. A very large box from
 an american semiconductor company showed up yesterday unannounced
 with 200 x 350 volt 15 amp power transistors in it. And 40 driver
 transistors. I think i got the hint. However the driver transistors just
 don't cut it compared to the 2sc3421/2sa1358. And where is the
 rest of the audio lineup?? At least their head is finally coming out of the
 sand.


----------



## kevin gilmore

pretty'd up schematic majority of work done by morsel
 This represents the final parts values. The 33pf cap across
 the feedback resistor is still missing.

http://gilmore.chem.northwestern.edu/dynahi2.gif

 Servo same as the other amp.


----------



## rsaavedra

(Edited out after Kevin's own part list)


----------



## pooooo

Quote:


  Originally Posted by *kevin gilmore* 
_pretty'd up schematic majority of work done by morsel
 This represents the final parts values. The 33pf cap across
 the feedback resistor is still missing.

http://gilmore.chem.northwestern.edu/dynahi2.gif

 Servo same as the other amp._

 

Hi Kevin, 
 I think the second stage is a different from your original drawing. Two transistors are missing.


----------



## pooooo

sorry, redundant post...


----------



## kevin gilmore

I took the cascode transistors out in the second stage. They
 did not increase the performance in any way, if they actually
 lowered the thd i was not able to measure it. Could not tell
 any difference in the sound. So they are gone. They are not
 on the circuit board either.

 silk screen in pdf for those without gerber view
http://gilmore.chem.northwestern.edu/silk.pdf


 board parts for a pair of boards
 (someone check this against pdf)

 Boards (2)

 Caps.
 33 pf (2)
 470 uf/50v (4)
 .1uf (4)
 .47uf (2)

 Leds (4) 1.7 volt red

 Opamps (?) any single low offset opamp (2)

 Resistors
 20 ohm (32) or 10 ohm (16) emitter resistors
 100 (12)
 150 (4)
 500 (4)
 2K (2) feedback resistors currently 1.2k on my unit to reduce gain
 3.3K (4)
 5K (14)
 10K (4) plus 10k (2) input resistors
 30K (4)
 1M (2)
 10k trimpot (2) optional

 Transistors 
 2SA1145 (4)
 2SC3381 (2)
 2SK389 (2)
 2SJ109 (2)
 2SC2705 (4)
 2SA1349 (2)
 2SC3421 (8)
 2SA1358 (8)

 7815 or 78L15 (2)
 7915 or 79L15 (2)


----------



## pooooo

Hi Kevin, 
 I have plenty of LM431 at hand. What do you think about replacing the LEDs with them, and changing the 500ohm resistors to 950ohm ones? 
 And the static power dissipation of the transistors in the second stage is very close to their maximum rating specified in the datasheet (7xx mW/800mW max). Have you ever thought of replacing them with some bigger transistors?


----------



## kevin gilmore

You can try the lm431 but my guess is that when you do you will
 find that the servo no longer functions. The servo depends on the
 very slight changes in voltage across the led when the current
 changes.

 Yes the second stage transistor gets warm, but not out of spec.
 You can certainly try other transistors there if you like. Like one
 of the output transistors.

 I've had my unit on now 24 hours a day since last saturday morning
 and can touch every component and nothing is getting too hot.


----------



## morsel

33pF feedback cap added.


----------



## rsaavedra

Having trouble finding some capacitors in the drawings. There's the gif diagram, and also the pdfs in previous pages of this thread. The gif only has the 33 uf cap, none of the other capacitors are in the gif. The PDF does include some caps, but I can't find in it those 470 uf/50v caps that appear in the part list.

 Also, can sort of try to figure it out from the pictures and the gif, but I can't be sure on the actual PDF. In what exact points on the boards do the inputs, outpus, power cables and ground join? On the gif schematics it's obvious, but for a newbie like me, on the actual PDF board diagram it is not so for me. Blame my newbieness 
	

	
	
		
		

		
		
	


	




 Help much appreciated.


----------



## kevin gilmore

free gerber file viewer here
http://www.pentalogix.com/

 electrolytic caps not marked, the two big round things.


 print these two with the silk pdf all the same size and put on
 top of each other...

http://gilmore.chem.northwestern.edu/topcopper.pdf
http://gilmore.chem.northwestern.edu/bottomcopper.pdf


----------



## rsaavedra

Thanks much Kevin!
 Cheers,
 Raul


----------



## aos

I assume if one were to go for lower power consumption (smaller heatsinks, easier load on power supply), one could go down to one or possibly 2 output transistors, right? Output impedance would be higher and bass woldn't be quite as tight but even one transistor should provide more than enough power for a very satisfying listening.


----------



## morsel

Or go with a pair of nice MOSFETs like the IRFZ24N and IRF9Z34N.


----------



## kevin gilmore

You can certainly take off power transistors and reduce the standing
 power and the amount of power supply. But it won't sound the same.
 Will it sound similar for many headphones, probably yes. Will it be just
 the bass that is effected, i don't think so. The damping factor is just
 about flat across the entire audio band and beyond. Most other
 amps out there have a damping factor curve that shows a significant
 increase in resistance as output frequency rises.

 Lets say i have one output transistor that outputs .5 amp.
 Lets say i have 4 output transistors that output .125 amp each totalling 
 .5 amp. Do these two sound the same, certainly not. Typically the
 silicon area of the 4 transistors because of thermal considerations will
 be less than the silicon area of the one big transistor. This generally
 points to less capacitance and a higher Ft. What about lead inductance?
 4 transistors in parallel are going to have about 1/4 the lead inductance
 of one device. This definitely matters too.

 The absolute best transistors i can find for my uberamp have an Ft of 
 30mhz. While significantly better than all the old stuff out there, there
 is no way these sound the same as transistors with a Ft of 120mhz.

 I'm sure its going to be a few months before people build and then
 listen to this thing. But once they do the oooh's and aaaah's will flow
 like water.

 Those fets might be great as pass elements for the power supply for
 this unit, but certainly not as output devices. Rise and fall times
 are not balanced, significant gate offset and capacitance and in general
 and equivalent Ft of probably less than 10mhz...


----------



## aos

I don't question the validity of using multiple transistors, my question was more related to where would be the sweet spot. I would definitely use at least 2, but the question is whether going from 2 to 4 gives audible improvements, and past that, going to 8 and so on. I guess this is best left to experimentation.


----------



## kevin gilmore

The sweet spot for the output transistors i'm using is somewhere
 in the 80 to 100ma range each.


----------



## morsel

Servo circuit added and minor alterations made to the schematic.


----------



## pooooo

Quote:


  Originally Posted by *kevin gilmore* 
_You can try the lm431 but my guess is that when you do you will
 find that the servo no longer functions. The servo depends on the
 very slight changes in voltage across the led when the current
 changes.

 Yes the second stage transistor gets warm, but not out of spec.
 You can certainly try other transistors there if you like. Like one
 of the output transistors.

 I've had my unit on now 24 hours a day since last saturday morning
 and can touch every component and nothing is getting too hot._

 

Hi Kevin, 
 Thanks for your explanation. The servo is very innovative but I personally don't want that servo in my amp. Just like you, I don't like capactors in signal paths. I think LM431 should be less noisy than LEDs, though such high-frequency noise might not be audible. 
 Are you planning to build a Dynahi with the power supply topology of the previous lower-power version? I have several pieces of OPA541AM at hand and I'm wondering if they are suitable for such usage. 
 BTW, may I ask about your room temperature? It's about 90 degree here at my place during summer, and my original amp (30W quiescent) gets really warm even with two heatsinks four times as big as yours. Almost untouchable unless fans are turned on.


----------



## morsel

Servos like this one are great. I don't like caps in the signal path, either, but this does not count, as its purpose is to integrate the signal to correct for DC offset. This is not the same thing as using a coupling cap on the input or output, in which case the entire signal passes through the cap.


----------



## Prune

This servo reminds me of one here: http://www.tubecad.com/articles_2002...ers/page5.html


----------



## kevin gilmore

opa541 are exactly what i'm planning on using. However the
 pre-regulator needs to be some kind of pass fet because an
 lm317 can't handle the voltage, and you have to keep the
 pre-regulated rails less than +/-40

 Without the ventilation on even in the winter, the media room
 fully powered up can easily hit 85. Usually i leave the fan on 
 and this takes care of the problem. In the summer the ac is
 always on (summer starts about april) and then it is no problem.

 The projector alone puts out 650 watts in heat. The amplifiers
 together put out depending on volume up to 2000 watts.


----------



## rsaavedra

Quote:


  Originally Posted by *kevin gilmore* 
_Caps.
 33 pf (2)
 470 uf/50v (4)
 .1uf (4)
 .47uf (2)_

 

Kevin, other than the 470 uf/50v cap, how about the voltage spec for the others? Think I'll start getting the parts before the boards.


----------



## pooooo

Quote:


  Originally Posted by *kevin gilmore* 
_opa541 are exactly what i'm planning on using. However the
 pre-regulator needs to be some kind of pass fet because an
 lm317 can't handle the voltage, and you have to keep the
 pre-regulated rails less than +/-40_

 

I think LM317/337 are OK for such voltage. I even tried to build a PS unit which outputs 250VDC with LM317 for a tube amp. LM317 works fine as long as the voltage difference between its input and output does not exceed 40V. For high voltage applications, just add some diodes to protect it from transient status such as power-on surge and power-off.


----------



## kevin gilmore

the .1uf need to be 15 volts or better
 the 33pf would need to be 30 volts (minimum you can buy is probably 100v)
 .47 needs to be 15 volts but to fit in the hole the
 exact mouser part is 75-mkt1822447014 which is 100v


----------



## gavinbirss

I have seen from previous posts by master Gilmore that when he posts links to
 hires photos of his circuits that some people hint to the fact that he has to 
 learn how to use photoshop in order to reduce the size of the files.
 This will obviously reduce the quality and the use of a his 15 megapixel camera.

 You can't give a child candy and not expect his to eat it.
 (my point is not that Mr Gilmore is a child ....)

 I am refering to picture file : dynahif2.jpg

 Why does only three led's light up ?

 Is the fourth led located on the right hand side, camera shy or dead ?

 Why does the three led light up anyway and indicate DC being integrated by
 the DC Servo , considering that there is no input ?

 Is the DC Servo going MAD ?

 humour my please since I am only a Kevin Gilmore follower and you, Kevin are the leader.

 Great work ...


 "The problem is the range of impedances this amp has to drive.
 From 32 to 300 ohms. For low impedance phones you need the
 bias turned up to keep the unit in class A for the entire audio
 signal. For high impedance phones you could definitely turn down
 the bias and still keep it in class A."

 How would one go about changing the bias on the fly.

 Does your preamp have a stepped attenuator and how many steps is needed for 
 a 32 ohm load (grado) headphone to produce a dynamic (medium to loud) level.

 How much is the gain in db for your prototype to power 32 ohm headphones.

 Gavin


----------



## rsaavedra

Bumping this, wondering about:
 1) Group buy of the Dynahi boards
 2) Whether the Dynahi fat edition PCB's will be available any time soon.
 3) Any news on the power supplies designed specifically for the Dynahi?


----------



## Sbear

Regarding a pcb group buy- count me in.

 A question regarding these condor power supplies- Are they any good?
 I mean it doesn't seem like you could build something from scratch for much less than 40 bucks a pop, even with less than best transformers and res. caps. So are these power supplies worthy to be used with this amp or they just to get by until Mr. Gilmore comes up with his own design?


----------



## rsaavedra

Double post.


----------



## rsaavedra

Quote:


  Originally Posted by *Sbear* 
_Regarding a pcb group buy- count me in.
 A question regarding these condor power supplies- Are they any good?
 I mean it doesn't seem like you could build something from scratch for much less than 40 bucks a pop, even with less than best transformers and res. caps. So are these power supplies worthy to be used with this amp or they just to get by until Mr. Gilmore comes up with his own design?_

 

Wonder exactly the same. Originally I was planning to possibly build the Dynahi using these condors, and then later on replace them with the Gilmore PS's, but I would rather build the latter ones from the get go.

 I emailed Justin in www.headamp.com asking for Dynahi boards. There are Gilmore V2 circuit boards for sale in his Order page, but the website doesn't have anything Dynahi-related anywhere yet. (Mentioning this because Kevin told me to contact Justin about the fat boards).


----------



## kevin gilmore

quote
 Why does only three led's light up ?

 Is the fourth led located on the right hand side, camera shy or dead ?

 quite clearly you can see that the unit is NOT plugged in or turned on.
 Thats a result from the flash lighting up the silicon... Really, no kidding.
 When the led's are on they are very bright to the camera.

 quote
 You can't give a child candy and not expect his to eat it.
 (my point is not that Mr Gilmore is a child ....)

 Says who? Age has nothing to do with it.
 I really like my camera. And I have 6megabit dsl at home. I really
 don't care... 
	

	
	
		
		

		
			






 The power supplies are sufficient for the first prototype. Thereafter
 the real units will be in a bigger box with one of my typically overspec'd
 power supplies.

 I'm keeping justin busy...


----------



## Sbear

Mr. Gilmore, can you elaborate on the word "sufficient" regarding the use of the condor. Do you mean the Condor makes the amp work but sounds like crap? or does it actually perform well?

 Funds are kinda tight, at least for me, so I'm just trying to get the best bang for the buck.


----------



## aerius

As the saying goes..."when your mom cuts a piece of cake for you for dessert, it's sufficient. when you cut the piece of cake yourself, it's enough". I'm not sure how well that applies to the situation here, but anyways....


----------



## kevin gilmore

The condor supplies put out enough current at a low enough noise
 level and high enough stability to work just fine. They do get
 extremely hot however. I would move up one size in power supplys and
 2 sizes up in box. Or put the supplies in a seperate box.


----------



## gavinbirss

bump
 bump


----------



## gavinbirss

Hello,

 Sorry for seeming impatient but only once my modem got to posting my thread, I noticed that there were already replies.

 Gavin


----------



## rsaavedra

Quote:


  Originally Posted by *kevin gilmore* 
_Or put the supplies in a seperate box._

 

That's what am planning to do, and will leave the case for the supplies for the very end, leaving enough room for the ps upgrades.

 Wonder if there might be another version (higher specs) for some other condor unit, or some other brand, that might still work fine with your amp while getting less hot.


----------



## gavinbirss

Hello,

 "quite clearly you can see that the unit is NOT plugged in or turned on.
 Thats a result from the flash lighting up the silicon... Really, no kidding.
 When the led's are on they are very bright to the camera."

 I feel like a idiot now but this may prove that I need a larger screen to view Mr Gilmore's images at 1:1 view, at also short term memory to remember that there are no input and NO POWER.





 I would appreciate a response to my third remark :

 "The problem is the range of impedances this amp has to drive.
 From 32 to 300 ohms. For low impedance phones you need the
 bias turned up to keep the unit in class A for the entire audio
 signal. For high impedance phones you could definitely turn down
 the bias and still keep it in class A."

 How would one go about changing the bias on the fly.

 Does your preamp have a stepped attenuator and how many steps is needed for a 32 ohm load (grado) headphone to produce a dynamic (medium to loud) level.

 How much is the gain in db for your prototype to power 32 ohm headphones.

 Thanks
 Gavin


----------



## Prune

Quote:


 I feel like a idiot now but this may prove that I need a larger screen to view Mr Gilmore's images at 1:1 view 
 

Browsers probably use a crappy resmapling algorithm for resizing images, and even when making them smaller, they get blurry and have artifacts. The bicubic in Photoshop is not very good either. The best practical resampler is a Lanczos-windowed sinc, which is close to the theoretical optimum. Irfanview is a great free multi-format viewer that offers Lanczos resizing.


----------



## kevin gilmore

quote
 How would one go about changing the bias on the fly.

 Add a pot in parallel with the 100 ohm resistor in the 2nd stage.
 say 200 ohms.


 Does your preamp have a stepped attenuator and how many steps is needed for a 32 ohm load (grado) headphone to produce a dynamic (medium to loud) level.

 Yes my preamp has a stepped attenuator (krell) i think it is 64 steps.
 In any case it is enough. There is plenty of headroom to get to
 100+db. Anyone listening any louder than this is looking for hearing
 damage.

 How much is the gain in db for your prototype to power 32 ohm headphones.


 The schematic shows a voltage gain of 20. I cut it down to 12. The
 reason i cut it down to 12 was i was testing with some ultra high
 efficiency headphones (garbage) and thought there was too much gain. 
 Turns out the gain was not so high afterall. In any case a comfortable
 volume is at 1 o'clock, and i try to set the gain for comfortable at
 12 o'clock.

 Quote:
 I feel like a idiot now but this may prove that I need a larger screen to view Mr Gilmore's images at 1:1 view 

 Actually there is only one display device that i know of that can come
 even close to the 4000 x 3000 resolution. That would be the sony
 qualia2 projector. It is 4000 x 2200. It is not yet available. When it
 is, the price will truely be impressive.


----------



## The_Mac

Quote:


  Originally Posted by *kevin gilmore* 
_quote
 Quote:
 I feel like a idiot now but this may prove that I need a larger screen to view Mr Gilmore's images at 1:1 view 

 Actually there is only one display device that i know of that can come
 even close to the 4000 x 3000 resolution. That would be the sony
 qualia2 projector. It is 4000 x 2200. It is not yet available. When it
 is, the price will truely be impressive._

 

The IBM T221 LCD can do 3840X2400, just in case you're looking for a new monitor for work. Needs two DVI connectors on the Vid Card though.

 And nice looking amp Mr. Gilmore. Thanks for all your generosity to the DIY community.


----------



## kevin gilmore

quote
 The IBM T221 LCD can do 3840X2400

 Absolutely right. We have one at work. I forgot about it. Its just plain
 gorgeous. and cheap to at only $7500. The qualia2 is >$35000


----------



## The_Mac

Quote:


  Originally Posted by *kevin gilmore* 
_quote
 The IBM T221 LCD can do 3840X2400

 Absolutely right. We have one at work. I forgot about it. Its just plain
 gorgeous. and cheap to at only $7500. The qualia2 is >$35000_

 

Actually, prices have dropped to the point where they're only about $4K now, which is really nice. By far one of the best monitors out there for design. An acquaintance uses a pair for Katia work.

 About the amp though, would there be any benefit to using a different LED than red where you have them now? Tangent mentioned that UV (or was it IR) LEDs are lower noise than even a red one, so would that be a suggested way to take it?


----------



## aerius

Finally made it down to the electronics stores and got most of the parts. I still need to look around for heatsinks and get access to a drillpress so I can do a neat job of drilling the holes. Hopefully I can get a working amp by the end of the summer.


----------



## kevin gilmore

The IR diodes should work, not sure of their voltage. Problem is most
 people can't see them. So if you want an indicator that the power
 supplies are working, this won't work. You could always paint them
 with some IR sensitive phosphor. (day glow won't work its UV only)


----------



## pooooo

Quote:


  Originally Posted by *morsel* 
_Servo circuit added and minor alterations made to the schematic.





_

 

Is this the complete schematic? Or do we need any low-pass filter at the input terminal like most other amps?

 I have decided to build this amp and is planning to build it into a rather distinctive chasis. Wish me good luck.


----------



## kevin gilmore

Yep, thats it. But if you want to add a 1k input resistor and
 50pf to ground to slow things down a touch, that works too. 
 A step attenuator will do the same thing.


----------



## chuao

just a quick question: why does the input stage use jfets rather than the same matched transistors as the cascode stages?


----------



## morsel

Those are matched dual JFETs.


----------



## rsaavedra

Anyone started building it already? If so, how did you get the boards? 

 I contacted Justing about the fat boards, but he never replied, guess he is too busy. Will email him again. If not hearing from him I'd be interested in a group buy of the boards. However I'm still slightly wondering whether the layout and minor details of the design for the dynahi has been stabilized.


----------



## pooooo

I have no boards, and this is what I'm going to do. Not finished yet.


----------



## chuao

quote:

 Those are matched dual JFETs.

 yes, so, why use matched dual jfets as opposed to matched dual BJTs? high input impedance doesn't seem to be the reason since kevin terminates his inputs with 50 ohms anyway and the source impedance driving the inverting input is only about 100 ohms.

 those matched jfet pairs are really expensive, people must have a good reason for using them... not that I mind the cost personally, I already bought them anyway.


----------



## chuao

or I guess more to the point, everything in this amp is clearly the result of lots of careful design, so Kevin must have a reason for using them.


----------



## kevin gilmore

Another cube layout. I like it. 12 outputs per channel instead of
 8? 

 I like the sound of the input fets. You can certainly use the dual
 cascode transistors if you like, works fine but different pinout.
 Expensive?? 2sk389 are $3.15 each. 2sj109 $6.74 each. Was
 a lot cheaper when mouser was still selling them. 
 2sc3381 is $2.25 and 2sa1349 at $2.20. Not a lot cheaper.

 Price on the 2sj109 definitely higher than it should be. I was
 paying 3.99 each... 

 All transistors available from www.bdent.com


----------



## chuao

Quote:

 I like the sound of the input fets.


 Ok, suits me...nothing beats experimentation (I'm just too lazy myself). and I fear sockets.

 I guess they're not too expensive for matched devices but the BJT pairs from Toshiba are less than $1. I don't care about the cost at all, I mean, I bought a $70 power transformer so that I could have the voltage headroom for a dual-regulated supply 
	

	
	
		
		

		
		
	


	




 Toshiba does bring them up in their app notes, though, so I figure there's something other than the audiophile fringe that's using them. for the 7x markup or so that commercial electronics gets a few dollars here and there really adds up...


----------



## Prune

Is this right?

 2SA1145 x 4
 2SC2705 x 4
 2SC3381 (dual) x 2
 2SA1349 (dual) x 2
 2SK389 (dual) x 2
 2SJ109 (dual) x 2
 2SC3421 x 8
 2SA1358 x 8

 Comes to about $42 at BDEnt.

 Someone gave $80 estimate before. What am I missing? I got these off the single channel diagram posted a couple of pages back. The opamps are about $2 a piece at Digikey.

 As for heatsinking, I wonder if I can just put them on the 2U rackmount (possibly with a fan) I have, or additional heatsinks will be necessary?

 Finally, which of the Condor models are the power supplies that can be used here?


----------



## kevin gilmore

Still need the resistors and led's. And thermal washers for the
 REQUIRED heat sinks.

www.alliedelec.com

 either of these works
 power one 28 volt 2 amp supply, 2 needed 218-1033
 condor 28 volt 2 amp supply 2 needed 744-5020

 about $55 each.

 The bigger supplies really are necessary the smaller ones get way
 to hot.


----------



## Pars

Quote:


  Originally Posted by *kevin gilmore* 
_Another cube layout. I like it. 12 outputs per channel instead of
 8? 

 I like the sound of the input fets. You can certainly use the dual
 cascode transistors if you like, works fine but different pinout.
 Expensive?? 2sk389 are $3.15 each. 2sj109 $6.74 each. Was
 a lot cheaper when mouser was still selling them. 
 2sc3381 is $2.25 and 2sa1349 at $2.20. Not a lot cheaper.

 Price on the 2sj109 definitely higher than it should be. I was
 paying 3.99 each... 

 All transistors available from www.bdent.com_

 

Ya know, MCM has all the transistors too, and is much cheaper on the 2SJ109s than BDEnt is ($4.35). BD is cheaper on some of them. Ordering all from MCM would run $46.36 while all from BDEnt would be $43.34... using the cheapest pricing would give a total of $32.64, and would have you ordering the 2SJ109, 2SK389, 2SA1349 and 2SC3381 from MCM and the remainder from BDEnt. Didn't check the minimum order policys.

 Did anyone end up doing a group buy on boards for these?


----------



## kevin gilmore

For about the last 6 weeks the 2sj109 and 2sk389 were nowhere
 to be found on mcm's pages. Either they pulled them, or their
 database was messed up. But they did show up on the newark
 webpage and were listed as mcm stock...


----------



## rsaavedra

Quote:


  Originally Posted by *Pars* 
_Did anyone end up doing a group buy on boards for these?_

 

I just talked to Justin of Headamp.com over the phone. He told me there's no plan to stock and offer the Dinahy boards for sale yet, and if he eventually sells them, it will take at least 3-4 months. So the fastest way to get those boards would definitely be to organize a group buy. I once volunteered myself to do the group buy, and some people expressed interest on this thread, but I didn't receive actual cofirmation PM's. Should a separate thread be created to call for a group buy?

 Kevin sorry to ask once again, the last board layout files you posted are final then? Otherwise would be great if you could post the last version of the files you have right now.


----------



## kevin gilmore

absolute latest and final board files.

http://gilmore.chem.northwestern.edu/dynahi.zip

 Added dual paralleled transitors in vas section, because they get
 a bit to hot... You can build it either way, one transistor with 150 ohm
 or two transistors with 300 ohm each.


----------



## rsaavedra

Thanks very much Kevin. Will create a thread calling for the group buy of these boards.


----------



## Prune

Make sure to post a pointer to that thread here.


----------



## rsaavedra

Here's the Dynahi board groupbuy thread: http://www5.head-fi.org/forums/showthread.php?t=78417


----------



## chuao

I'm wondering what's the best way to mount the output transistors onto a heat sink without using thermal grease (which I hate)...since the package is insulated, could I use a thin piece of copper foil to cushion the transistor from the heat sink and fill in the irregularities on the two surfaces?


----------



## MisterX

What is the lead spacing for the resistors on these PCB's going to be?


----------



## pooooo

Picture of my 2-channel p2p wiring except the VAS stage.
 Took me about two nights. All other resistors are on the other side of the board. I fired it up last night. The LED glowed and the voltage drop across the 5k resistors were all about the same (5v). Seems quite OK. 
 The size was much smaller than I expected. If I were to build a second one, I might try to include the power supply circuitry on the same board...


----------



## intlplby

how does the performance of the Dynahi compare to a PPA?


----------



## morsel

Driver transistors are paralleled.


----------



## drubrew

I dont know if it is to late to suggest this but I would like to suggest increasing the hole diameters for all the resistors especially the feedback resistors so that higher quality resistors which have bigger leads can be used more easily. Also a little more room around the 470uf caps to make room for Black Gates and such. This will give users a the option of playing around with higher quality components. I'd like to build one on a budget and one maxed out to see the differences.
 Thanx
 Drew Baird
 Moon Audio


----------



## flecom

Quote:


  Originally Posted by *kevin gilmore* 
_4000 x 3000 resolution._

 

what camera do you have that produces 12Mp images?


----------



## kevin gilmore

what size holes for the resistors do you want??
 They are currently 30 mils

 The camera is a kodak slr/n
 14.3 mp raw, trims to about 12 mp jpeg


----------



## flecom

Quote:


  Originally Posted by *kevin gilmore* 
_what size holes for the resistors do you want??
 They are currently 30 mils

 The camera is a kodak slr/n
 14.3 mp raw, trims to about 12 mp jpeg_

 


 ah yes, not a big fan, noisy, and nikon lenses dont do it for me in the long end of the spectrum... i prefer my Canon 1D 
	

	
	
		
		

		
		
	


	




 i _would_ have a 1D Mark II but alas, working for the public school system limits ones abilities to buy expensive toys 
	

	
	
		
		

		
		
	


	




 i do a lot of sports/action/low light so the 8fps comes in handy 
	

	
	
		
		

		
		
	


	




 plus even at ISO 1600 images come out great


----------



## drubrew

The Vishay VTA 52, VTA 54, VTA 55 all have .80mm lead diameter. I think this is one of the bigger sizes out there. I'm using these on the feedback resistors on the current board. I was able to gentle expand the current holes to get them to work, but on the next set I would rather not do this as I may use these everywhere for the hell of it.
 Thanx
 Drew Baird
 Moon Audio


----------



## Garbz

Indeed i have a large set of Holco H4s here which also have 0.8mm leads. (they should be 0.6 i believe, and no they aren't H2s)

 Either way it's a pain when I drill holes to small.


----------



## strohmie

I bought a set of Holcos for my now-crushed boards, so perhaps it's a good thing that I killed them because I wouldn't have been able to use the Holcos anyways. 
	

	
	
		
		

		
			





 Trying to decide what type of resistor I want to use on the output for the next set I build. Might be interesting to try some exotic brands like the Audio Note tantalums or Rikens (though again these will probably have leads that are too thick). I'm actually going to try to match the transistors better this time around...maybe not to perfection but as close as I can get. And I get to do that for four boards. 
	

	
	
		
		

		
		
	


	




 Might just put rsaavedra's anal edition to shame. 
	

	
	
		
		

		
		
	


	




 Anyone have positive results with exotic resistors? I seem to recall KG was using some unobtainium tants on the output of his.


----------



## chuao

Kevin (or anyone else with a working Dynahi):

 I'm cuious about a couple of specs I don't think I've seen yet for the Dynahi. Don't make measurements just for my sake, but if you've looked at any of these:

 1. What's the small-signal bandwidth for the Dynahi with your 50-ohm driving impedance?

 2. What do the THD-vs-frequency and THD-vs-amplitude plots look like? At what frequency does the distortion start to peak above the noise?

 3. How's the distortion spread among the various harmonics?

 I'm not looking for anything too detailed, just your rough impression if you've seen it on the spectrum analyzer.

 Thanks!


----------



## kevin gilmore

layout with all resistors with 40 mil holes
http://gilmore.chem.northwestern.edu/dynahi7.zip

 quote

 1. What's the small-signal bandwidth for the Dynahi with your 50-ohm driving impedance?

 well into the megahertz region.


 2. What do the THD-vs-frequency and THD-vs-amplitude plots look like? At what frequency does the distortion start to peak above the noise?

 I just don't believe some of the numbers i see coming out of the
 pc based software with the higher end sound cards. Most of these
 numbers come out far lower than my old sound technology 100a which
 tanks at about 100khz. With this unit the thd is in the noise till the
 amp starts clipping.



 3. How's the distortion spread among the various harmonics?

 The only audio spectrum analyzer i have is a very old hp unit
 and its noise floor is only -78db. So i see nothing. My high frequency
 unit has a noise floor of about -90 db, but does not start till 10mhz.


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