JLH Headphone Amp

[museguy]

You're quite welcome! Yes, that's the servo board I offer for these amps.

I've been using a Rat Shack 12.6V-0-12.6V 2A transformer.
If I were getting an Antek, I would get this one:
AS-1212 - 100VA 12V Transformer - AnTek Products Corp

Hope that helps.

Thank you ammel68 !

Do you sell the servo pcb and parts as a kit ? or do you have a BOM ?

Will order the transformer

 

[Ricren]

Hi,
Could anybody point me to the schematic of the servo? Thanks.

 

[Schiller72]

Hi,
Could anybody point me to the schematic of the servo? Thanks.

Hey Ricren, the schematic of the dc servo is here (schematic, left down corner).
Source (rockgrotto proboards com): "JHL" headphone amp | Rock Grotto

 

[Ricren]

Thanks a lot, Schiller.

The LT1169 is 8 dolars in Digikey ( almost half the price of the kit!) and difficult to get here. Could it be replaced with another, easier to get OP AMP?

 

[EUVL]

TL072, LF412, OPA2134, ....
~2.5x noisier.


Patrick

 

[Ricren]

Thanks Patrick, those OPAMS are easy to get, a have a few.
Any suggestion on how to modify the circuit ( increase filtering?) to reduce noise. I guess there's a trade off between capacitance and response time. But the difference is "that" audible?

 

[EUVL]

How can you reduce intrinsic noise of opamps ?
I would also like to know.


Patrick

 

[Ricren]

Of course that was not what i was asking. In case it was not clear, looking to modify the circuit to reduce the incidence of the opamp noise.

 

[EUVL]

Increase R13, but you better simulate first to verify.


Patrick

 

[Ricren]

I'll give it a try, thanks.

 

[Schiller72]

Yesterday I built the servo. I use a OPA2134PA. In Europe, available for 2,89 Euro (Conrad Electronic SE).

An externally hosted image should be here but it was not working when we last tested it.

Start // DC_Offset: +38 mV
after 10 sec. // DC_Offset:. +0,02 mV
after 30 sec. // DC_Offset: +0,45 mV
after 1 min. // DC_Offset: +0,7 mV
after 10 min. // DC_Offset: +1 mV
after 12 min. // DC_Offset: +1,1 mV
after 30 min. // DC_Offset: +1,09 mV
after 50 min. // DC_Offset: +1,5 mV
after 60 min. // DC_Offset: +1,1 mV

That looks good.
A sound test still follows.

Regards
Schiller72

 

[Alex74]

I tested my amp using RMAA. China default KIT. My results:

 

[Nico Ras]

Not sure what you are showing in 3rd pic. Is the test signal 50Hz or is the hum just terrible.

 

[Alex74]

Not sure what you are showing in 3rd pic. Is the test signal 50Hz or is the hum just terrible.

Main signal is 1 kHz. The 50Hz is -80 dB:

Intermodulation distortion test: Two signals: 50 Hz and 1 kHz:

 

[AndrewT]

The intrusion of mains and mains harmonics is terrible.
I'm pretty sure you have a wiring error.

 

[sgrossklass]

Measurement setups involving looping a signal over an external amp with all unbalanced connections have this tendency of picking up mains hum due to the inherent ground loop. The amp on its own may be just fine, best confirmed by listening with sensitive headphones.

 

[Alex74]

The intrusion of mains and mains harmonics is terrible.

Are the -80 dB intrusions terrible?

 

[tonitonitoni]

hi Alex74, if You have laptop with working battery power,use rmaa on pc as playback and on laptop as recording, You will get lot better results ,what interface is used for recording?

 

[Alex74]

if You have laptop with working battery power,use rmaa on pc as playback and on laptop as recording, You will get lot better results ,what interface is used for recording?

.
I haven't laptop. I used Emu0204 with battery power

 

[tonitonitoni]

few people use emu0202 interface on my local forum with very good results but they use separate signal generator or laptop. i used behringer uca202 and creative usb card with ok results, but only when one was on battery powered laptop to cut ground loop.