X-Altra HPA-1 Class A Headphone Amplifier

[chat72]

Thank you for your suggestions, c214/215 are right there at the supply pins of opamp, it might be difficult to see from picture.

All transistors will be bolted down and ground line will be moved as you suggest.

Will report back when I built it.

 

[chat72]

In action, all I can say is this amp is really great. I prefer this over many diy and commercial hp amps. Thank Bonsai for this great work.

I am using toshiba 1837/4793 and bc550. PSU is normal 317/337 at +/-16v. Bias measures from 1e resistor is 90mA and rising slowly. Not sure when it stop. Heatsink underneath is really hot, I need to change that.

 

[Bonsai]

Glad you like it! The bias current stability is not critical as long as it’s within +-10%. However, if it’s running too hot, that isn’t good - you will need to increase the size. The heatsinks I use are 4C/W but you can go to 8C/W - that will give you about 22C above ambient temperature rise.

 

[oxygen22]

Hi Bonsai
In your new project "X-Altra Mini II Line Preamplifier" there are new elements in the scheme "HPA-1 Class A Headphone Amplifier". I am interested in R37/R38 and C25/26. What did you add them for?
Regards
Mark

 

[Bonsai]

Hi, those components are Zobel networks and were added to ensure the output always sees a resistive load which improves the amplifier stability.

 

[wirewiggler]

We’re some headphones reacteding badly, or are you recommending it to all amp for all headphones. I am using Hifiman Ananda with planer drivers at 26 ohms.

 

[Bonsai]

Bill, just seen your post. I have not experienced any problems with my headphones (Audio Technica, Koss, Bose) and the output coil does a good job of isolating any capacitive load so you should not experience any problems. I would recommend all headphone amps use an output coil + Zobel

 

[Bonsai]

Sorry OnAudio, I’m not following your point. Can you elaborate?

 

[OnAudio]

Nice project Bonsai

 

[geoffw1]

I've just built the HPA-1 and added it into my pre-existing preamp. On trying it out, my musician son's words were "Wow!!"

My 74 year-old eyes, aided by my inspection headset, had no problems hand soldering the SMD components. After hand soldering 0805 and smaller components on other projects, the 1206 sized SMD parts seem huge.

 

[Bonsai]

Fantastic - great that it’s up and running and you like the sound. 👍👍👍