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adding more caps to my headphone amp? upgrade transistor?
adding more caps to my headphone amp? upgrade transistor?
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Old 19th December 2017, 04:06 PM   #1
laserscrape is offline laserscrape
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Default adding more caps to my headphone amp? upgrade transistor?

Hi all. the wealth of info on various DIY audio forums drove me down the DIY path instead of the expensive gear path and its been amazing so far. I was lucky enough to realise spending hundreds/thousands on gear doesnt guarantee you'll find that sound you truly love. building and tuning something yourself to sound like your definition of amazing is the right way, and the feeling of doing it yourself excells anything an over-priced piece of gear will offer

I built this headphone amp which you can find it on this site.

Initially I was just really happy that it worked when I flicked the switch but I soon realised it didnt sound amazing, not bad but not great either.

Firstly I tried changing up the op amp to an LM4562, this refined the signature a lot but it was still the same sloppy amp.

Today I upgraded the 4700uf caps to good 8000uf caps taken from an old pioneer amp... all i can say is holy ****! from the minor improvements I got from the op amp what could a couple of power supply caps do? the answer: a lot!

The amp is finally alive, but I feel like I've barely scratched the surface of its potential.

I have a nice collection of polystyrene caps left over from building this amp, and also some electrolytics
Im not very knowledgeable on the electronics side of things so Im looking for advice on how (and if) I should add these to the circuit... in parallel with current caps or in series? etc.

Im also wondering about the power transistors, currently BD139s. for such a simple amp this is really the only part left un-upgraded from the original design.
Should I upgrade these?

Last edited by laserscrape; 19th December 2017 at 04:18 PM.
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Old 19th December 2017, 05:40 PM   #2
Ian Finch is offline Ian Finch  Australia
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After all that hassle to post in the power amplifier forum, we do have a separate headphone systems forum here:
http://www.diyaudio.com/forums/headphone-systems/

Hmm....ancient, massive overkill 8,000uF electrolytics for the power supply of an amp. with a tiny output? This seems like an act that that will be hard to repeat or for others to verify. Best see if you can replicate the sound with new parts too as those old used ones you have chosen probably won't remain in the form you like, for any significant period of time.
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Last edited by Ian Finch; 19th December 2017 at 05:42 PM.
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Old 19th December 2017, 05:46 PM   #3
Keruskerfuerst is offline Keruskerfuerst  Germany
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Can you post the schematics of that headphone amp?
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Old 19th December 2017, 07:18 PM   #4
phase is offline phase  United States
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See post#1 for the schematic.
As long as you are adding capacitors, I would surely try and add a 4.7uf electrolytic between +/- on the op amps.
I don't think the 8,000uf is total overkill, but now that you've experienced the results, it may be a good idea to shop for some newer parts for sure.
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Old 19th December 2017, 07:51 PM   #5
xrk971 is online now xrk971  United States
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adding more caps to my headphone amp? upgrade transistor?
BD139 is a fine output transistor for a HP amp. Try making a push pull with BD140 and use a better IC driver chip. I built this one by Wayne Kirkwood and it rmains the lowest distortion amp I have made or tested. There is also a nice design by ESP that uses BD139/140.

Simple Class A Headphone Amp Using THAT1646

Here is the Kirkwood HPA:
Click the image to open in full size.

You don’t need big caps or better BJTs. It’s all in the design and implementation.

Click the image to open in full size.

FFT:
Click the image to open in full size.
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Old 19th December 2017, 10:31 PM   #6
Pano is offline Pano  United States
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adding more caps to my headphone amp? upgrade transistor?
moved to Headphone Systems
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Old 20th December 2017, 02:48 AM   #7
phase is offline phase  United States
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Also, I would take a .1uf film cap in series with a 15-25 ohm resistor, and place that parallel to both c11, and c12.


I do like that driver chip, very cool.
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Old 20th December 2017, 07:42 AM   #8
laserscrape is offline laserscrape
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Quote:
Originally Posted by phase View Post
See post#1 for the schematic.
As long as you are adding capacitors, I would surely try and add a 4.7uf electrolytic between +/- on the op amps.
I don't think the 8,000uf is total overkill, but now that you've experienced the results, it may be a good idea to shop for some newer parts for sure.
Thanks, I will add that cap. When reading about the op amps I noticed some of the more exotic ones can need a cap to stop oscillation, so that should keep whatever I put it in it happy.
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Old 20th December 2017, 08:08 PM   #9
hpeter is offline hpeter  Slovakia
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Quote:
Originally Posted by laserscrape View Post

The amp is finally alive, but I feel like I've barely scratched the surface of its potential.
opamps have higher PSRR than tube circuits, but still can be affected by crap powersupply.
ideal psu-has zero impedance across whole frequency range.
this is not doable with just few wet capacitors.

wet caps are good maybe up to 1khz, foil caps are much better, stable params.

you "smoothened your power rails with 1000grit sandpaper", but you may try some more.
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Last edited by hpeter; 20th December 2017 at 08:12 PM.
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Old 20th December 2017, 09:24 PM   #10
phase is offline phase  United States
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I wouldn't recommend going without a .01 to .1uf to ground on each rail as well, but the smaller electrolytic part from rail to rail has helped when I had used the lme49720/4556. This was in addition to 47uf parts nearby.
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