New Headphone Amplifier Design

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#561
#562
hpasternack said:
Here is my proposal:

1. Ditch the front-end regulators and replace with passive RC filters.
2. Remove the servo. Use an offset trimpot on the input instead.
3. Capacitor-coupled input.
4. On-board regulators similar to Salas' L-Adapter. The Darlington in the Pass regulator is no longer available.
5. Reduce output stage bias. Use board-mounted heatsinks.
6. Switch from BC550/560 to BC549/559 which are still in production.

KSA992F/KSC1845F are still available to order. TTA004B is available. TTC004B is hard to get, but can be had from trusted suppliers on eBay.

As I said, I'm happy to design this board and support the project if people are interested in building it.
Click to expand...
Henry,

I for one would Still love to see further development.
1. I would keep the Servo , .
2. The RC filter simulates better than cap multiplier in my circuit.
3. Add a bias pot trimmer. (see mine attached)
 

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#565
[QUOTE="chakaandgeorgie, post: 7164459, member: 413833"
I have have DC on the output of 150mV and overall current is 400mA.
Is this normal?
Sound is good.
[/QUOTE]
If there's no dc servo ...it's normal.I can't guarantee the sound will be that good after you make the servo work 🙂
 
#567
chakaandgeorgie said:
Thanks for your help. Henry kindly contacted me and it turns out I had the schematic for an older version and I had to replace 6 resistors with the correct value. DC offset now 1mV. Sound is superb. Thanks Henry
Click to expand...
Thank you for the follow-up. I'm glad to hear your amplifier is working well. Good job. My prototype has been running flawlessly all summer and is still my favorite amp of the bunch. The resistor values I sent you reduce the offset to the point that the servo can deal with it. There is a better solution, but it would require changes to the PC layout and I haven't seen the need to bother with that.
 
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#568
I have one of the HPA2 here at the moment on loan from Henry, it's phenomenal. Have never heard such a transparent headphone amplifier. I have decided to build one and am currently converting the design to a mix of SMD and through hole parts to fit my space constraints.

Parts are still readily available for the original through hole design and I recommend it.
20221215_235151.jpg
 
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#569
Kevin1.jpg

Kevin2.jpg


I hope Kevin won't mind me posting photos from his house. I came with three amps to try, plus he brought out the DCG3 I built for him last year.

I'm gratified that Kevin likes the A2. My tastes shifted over the summer and I think I prefer the A2 to the A4 now. It really depends on whether you're in the mood for a very high-end sound, or something more relaxed but slightly less detailed and neutral. Both are good amps IMHO.

I posted over on the Pass forum just now about a modification I made to the A3 to increase its loop gain by 50dB. That's a big change. I was curious to see what would happen. It's easy enough to reverse -- just reinstall four resistors and two capacitors.
 
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#571
That listening comparison in my dining room was quite an eye opener. All of them were good, I thought the A2 stood in a league of its own and still do.

Source: Topping DX-7S connected to a Roon endpoint. (Using RPI4 runnng Ropieee) Headphones are Oppo Planar-3 with slightly modified Pasanen headphone EQ intended for the specific replacement ear cushions I am using on these phones.

https://github.com/jaakkopasanen/AutoEq

Not blind, not scientific, no familiarity or bias towards any device except mine. I had no preconceived notions that I would/should hear any significant difference between any of these devices. Went through the whole lot at least 3 times and at the end I concluded I really like the HPA2 and persuaded Henry to let me hold onto it for a longer test drive. It seems to be a very synergistic match to my planar headphones.
 
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#572
I will put up the power supply files this weekend and post a link. There are five of those boards out in the wild now so I have confidence in the reproducibility of the design.

I don't have any active projects at the moment, but I'm eager to see what Kevin comes up with for his version of the A2.

I plan to keep a much lower profile than before, but I decided to come out of the woodwork again. I would still enjoy seeing some community interest in this project.
 
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#577
Hello!

I read everything about your headphone amplifier with great interest.
I am very impressed!
I would like to rebuild this one. However, not all the data you once shared is available anymore.
Would it be possible to get these from you?
I'm thinking about the A4 version including the Super Regulator.
I hope for a positive feedback from you
Kind regards
Zoltan
 
#578
Hi Henry!
So far a super interesting writeup.
I really like your A2 amplifier, and i would try to do a SMD porting of it using matched transistors.
I read also the paper by Cordell, and so far want to try something similar on it's input stage.
I checked all of the links through the forum and unfortunately they didn't work anymore.
Could you possibly reshare it with us?
Many thanks in advance
 
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