JLH Headphone Amp DC Servo PCB.

[ammel68]

This is a DC Servo board for the popular and great sounding JLH headphone amplifier.

Anyone who's built one of these amps knows(or should know) that the offset at the outputs is quite high.
I've measured anything from a headphone frying .2V! down to 20mv or so depending on the temperature of the output devices.

To make matters worse, the on board circuitry(10K trimmers, Zeners, etc.) for adjusting the offset does not work to stabilize the offset.

This board will bring the offset down to just a few millivolts.

Price is $4.50/board plus shipping.

 

[e_fortier]

This is interesting, the DC offset drift is the issue that kept me away from the JLH heaphone, looks like a simple solution, can you provide more info ?

Have you tried this PCB ?

Power requirements, +/- ___Vdc, ___mA ? Does it need a separate supply ?

Do you only need a single board for a stereo headphone amp ?

Which IC has been tested and works ?

Thanks,
Eric

 

[ammel68]

I apologize for not being too specific about the board.

Yes, I have tried the board. I'm currently using 2 JLH "Zero Zone" amps and each amp uses one of these boards to control the offset.

No, it does not need a separate supply. You tap off the +-12VDC on the amp board.

Yes, a single board is all that's needed for a stereo headphone amp.

The only IC I've used is a AD712, though I'm sure there are others that will work just as well.

I've left one of my JLH amps on 24/7 for about a month now with no issues from the servo or the amp.

I really like the sound of the JLH amp. I've tried a lot of the popular op-amp/buffer combos and none sound as good to my ears.
Best $20 I've ever spent.

 

[sorinv]

Do you still sell these boards? I would be interested in getting 2 of them (for 2 separate amps).

Thanks

 

[e_fortier]

Hi

You won’t get an answer back, the member has been banned from this forum.

 

[sorinv]

Good catch, I haven't noticed that.

Thanks!

 

[carlmart]

Why do you use a dual IC on each JLH HP amp? Your DC servo uses two opamps per channel?

Try an LF412 in your case, with FET input

 

[e_fortier]

See could easily add the DC servo on a small PCB, see attached schematic

 

[sorinv]

Thanks for the schematic. While I am quite sure I could model that and send some PCBs to print, since my knowledge of electronics is rather basic, I don't have the confidence yet to do that.

I'd rather find someone who knows more about it and already sells some PCBs that are tested and known to be working.

Do you have any recommendation?

Thanks!