X-Altra HPA-1 Class A Headphone Amplifier

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#45
Another SMD project smashed. Very enjoyable build, good size pads and easy layout.

Using OPA1656 op-amps, 2SC3324-BL for Q1/Q6 and 2SC1571/2SA1930 for output.

Will get a 15V supply together and test later 🙂
 

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#48
This is a nice little amp Andrew, I like the smooth BJT sound, very clear and accurate, they suit the Elear's well. I have HE-500's here and the amp drives them quite good but ran out of volume range as most amps do, they need some driving, however everything sounds lovely.

OPA1656 with toshiba BJT's works really well. 🙂

Using a Muses volume with Sjostrom Diamond buffer boards between pot and amp. PSU is Gilmore golden reference +/- 15V with fancy LT4320 mosfet bridges
 

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#49
Fantastic. Glad you like it. Maybe you need to raise the front end gain a bit (reduce R12 and R25). If you change these to 680 Ohms, that will give you a gain of about 7.8x

I can’t find the spec for your headphones. Are they 18 or 22 Ohms? Do you know the sensitivity?

(I assume you are not running into clipping issues BTW)
 
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#51
Ok - so absolutely no problem to drive. I recommend you just increase the 1st stage gain - there’s a table in the presentation that shows you how to do it - ie R12 and R25 values.

I increased my second build gain to 7.8x (my pre is nominally 1V RMS out on all inputs).
 
#53
Bonsai said:
BTW, which if your two headphones do you prefer?
Click to expand...

If you put a gun to my head right now and told me to choose, the HE-500's would stay. Rare sound for the money, rich deep and dark sound. Bass and mids really are outstanding but they need ZMF Eikon pads to get the best. The Focals are the best all rounder I have heard, again for the money cannot be beaten to my ears.

After leaving the Altra on over night it seems to have improved. This is a powerful little amp and drives the 500's just fine really, the sound suits the planars well. After thrashing it for hours the heatsinks are just nicely warm, I think you could just get away with the next size down if needed. Impressive sound from this little amp, hefty bass and very clean mids, very clean accurate sound all round..

I forgot to mention that I had to solder the output wires to the resistors under the boards as there was no sound with the relay in the path, I may have misunderstood - do the two pins need to be open or shorted for music? I think I tried both...

On future iterations of the PCB would you provide footprint for standard DIP8 adapters to try rolling? I'll consider building another with Muses op amps. Have you tried BJT op-amps yet?
 
#54
Thanks for the feedback. I haven’t heard the HE’s but will have to give them a try.

For the relay, I just connected it across the +15V supply to energize it for now. I have a PSU board with a mute control output coming shortly (and a discrete line stage so you can make a complete,etc preamp).

I will have to look into adding the SO8 footprint.
 
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#57
If anyone wants to try Bonsai's HPA, mine is in the classifieds. Premium build with Susumu 0.1% and Vishay MELF. OPA1656, Toshiba BJT's. Really excellent clear sound with some punch, very powerful for it's size. I'll include PCB for Elvee's dual denoiser regulator.

I shall build another with Sanken BJT's and maybe OPA1642. Increased gain with 680R should be better for the HE-500's. The planars sound good on this amp.

Andrew, I'll send Sankens when they arrive. Toshiba incoming 😉
 
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#58
I'm holding off on building this until I get a new soldering station. My old Weller station was great for the TH parts back in the day, and I don't want to lose parts due to too much heat. So next week I get to kick off the build.
 
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