This is a modern, less expensive alternative but it comes only in SMD so you have to make an adaptor :
http://www.ti.com/lit/ds/symlink/opa827.pdf
http://www.ti.com/lit/ds/symlink/opa827.pdf
Algar, great work.
shoom, the 2mV offset you get now is more or less the offset of the Opamp used as servo.
When you want even better you need to use something like an OPA627 that is specced down to 0.1mV.
Hi Joachim
2mv is very good by any standards so I feel no great urge to go further but as it happens I have a few 627 in my parts box so may give that a try.😉
But
I’m really pleased with the low level offset I now have.🙂
all good so far

Installed the OPA627 and thermal coupling bracket on input gain transistors. I'll report on the result after stabilization 😉
Are those black resistors Welwyn, or Holco?
Are those black resistors Welwyn, or Holco?
Looks like IRC / TT electronics to my eyes, but maybe Algar can confirm 🙂
These resistors are IRC and yes they seems to be Welwyn so maybe Salas you're right. Here the spectrum of the output, using my CLIO system. Input 1Khz, adjusted for 0dBV at the output.
Offset is not lower than 10mv, usually around a few mv. There is really an improvement using the OPA627 for the servo. I removed the output coupling caps 😉
Offset is not lower than 10mv, usually around a few mv. There is really an improvement using the OPA627 for the servo. I removed the output coupling caps 😉
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Looks like IRC / TT electronics to my eyes, but maybe Algar can confirm 🙂
TT is Welwyn's new name also I think.
These resistors are IRC and yes they seems to be Welwyn so maybe Salas you're right. Here the spectrum of the output, using my CLIO system. Input 1Khz, adjusted for 0dBV at the output.
Offset is not lower than 10mv, usually around a few mv. There is really an improvement using the OPA627 for the servo. I removed the output coupling caps 😉
Good resistors at 25ppm or 15ppm. Nothing is like Vishay VAR, but much less costly too.
The noise floor looks pumped up for a Paradise I think? Experts will tell.
Are those black resistors Welwyn, or Holco?
Or my 'beloved' IRC's (maybe someone took a hint 🙂 as I mentioned these before). I think a very good resistor at a reasonable price. At Mouser they are now listed as IRC/TT.
http://nl.mouser.com/Passive-Compon...P=1yzbpodZ1z0z819Z1z0vpm5&Keyword=irc&FS=True
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The hum is caused by my test setup. I can never remove it when I test phono preamp. If I listen to the Paradise there is no hum, by a low hiss like a tube preamp. The 60Hz and 120Hz noise spikes can probably be discarded from the graph.
Do you use Lpad attenuator for the generator's signal? If not, use 1000R series and 10R shunt 1:100. It will slice generator harmonic noise. 100mV setting will give 1mV from 10 Ohm source resistance.
Very nice build SB!
Your one of the top builders and most dedicated on diyaudio IMO
Great follow through and finish!
Hope the sound lives up to your expectations
Regards
David
Your one of the top builders and most dedicated on diyaudio IMO
Great follow through and finish!
Hope the sound lives up to your expectations
Regards
David
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