Master op amp substitution?

[effegee]

E-lick,

You mention in the "Master" build section:

"The original TR-808 OPA is a μPD4558 but it can be replaced by another with a better signal / noise ratio."


Do you (or anyone) have a recommendation?

[e-licktronic]

Dear effegee,

We did not try other OPA but you can use TL072, NE5532, RC4560, OPA2134, OPA2604...
You can change C17, C23, C19 by high quality audio electrolytic capacitor, replace C22 and C18 by Styroflex capacitor instead of ceramic to get a better SN ration too.

Best regards,
e-licktronic

[gajimicu]

aHi E-lick,
some questions in relation to what you say here:
- the pins are the same for all the OPA you propose ? I mean can I just replace the 4558 by another one without other changes ?
- what is the voltage going through C22 and C18 ? Styroflex are expensive so I'd like to buy the lowest voltage here.
- do you have examples of electrolytic capacitors that would be intersting for C17 C19 and C23 replacement ? I'm lost in all those type of capacitors...

thanks a lot !

[e-licktronic]

Dear effegee,

All this OPA are pin compatible.
50V styroflex capacitor will be enough.
To replace electrolytic capacitor you can use Elna capacitor http://eu.mouser.com/Search/Refine.aspx?Ne=254016&N=1323038+12013592+4294922009 or Nichicon Audio grade capacitors http://eu.mouser.com/Nichicon/Passive-Components/Capacitors/Aluminum-Electrolytic-Capacitors/Aluminum-Electrolytic-Capacitors-Leaded/_/N-75hqw?P=1yztuatZ1z0zlbm

Best regards,
e-licktronic

[ElSchtroumpf]

I've just placed on order for 2 styroflex caps, 3 Elna Silmic II caps and some opamp ics : OPA2134PA, OPA2604 and LM4562. All ics are socketed on my Yocto, so I will try and record some demos with the different ics in place in a few weeks.

For anyone who's interested, I got all of these at Banzai Music, a German web shop.

[Azoora]

Thanks for this info. I'm gonna try this mod as my Yocto is a little noisy from the master out when compressed.

[Shiva Niet]

@Azoora
Don't compress to much. It is really not a good thing to compress to much of your track.
Just use it when you have 1 or 2 sounds that are to low in volume and use it only for these 1 or 2 sounds.
If your Yocto sounds noisy it means its volume is good! And the rest of your track is to loud!
Azoora this is just an advice and I give it in all respect.
If you want to compress everything, well your not my gast, but hey go ahaed.

[hofmann25]

Dear effegee,

We did not try other OPA but you can use TL072, NE5532, RC4560, OPA2134, OPA2604...
You can change C17, C23, C19 by high quality audio electrolytic capacitor, replace C22 and C18 by Styroflex capacitor instead of ceramic to get a better SN ration too.

Best regards,
e-licktronic

Vincent do these changes work for better audio signal flow on individual instruments? Eg, BD C50 1/50 & C48 220p?

[helectromagneticus]

I've done a little bit of homework about the master opamp selection. It's very unlikely that picking another opamp will provide a big reduction in noise. The RC4558 specifies a worst-case input noise of 8nV/rt(Hz), which is not easy to beat with cheap parts. The N5532 is a bit better with 6nV/rt(Hz) at 1kHz, but its worse case input bias current of 800nA is a bit sucky (only 500nA for the RC4558).

You must step outside the usual suspects for these kinds of circuits to get better performance - there are some options if you have money:

• LT1007 (3.8nV/rt(Hz) input noise, 1.7V/us slew rate (minimum, equal to the typical slew rate of the RC4558), much better input offset voltage and input bias current specs) - buy the "A" grade part. Whoops! This doesn't come in a stand dual opamp package!
• LT1677 - a rail-to-rail input and output version of the LT1007. If you're neurotic about headroom, this opamp will give you plenty.
• LT1028A (1.1nV/rt(Hz) input noise (!!!), 11V/us slew rate.

That all being said, shitty electrolytic caps are noisier than the cheap RC4558. I'll take some before/after measurements of the master output noise on my Yocto when the high-quality caps I've ordered arrive. From there, I may do some opamp swapping and see what the results are. I'll be sure to share the results here.

[hofmann25]

Nice work man