Op Amps in synth circuits

3phase · Posted: Sat Apr 28, 2007 5:42 am Post subject: Op Amps in synth circuits

Hi, I am modifying a Vermona DRM 1 drummachine wright now..
A very rare unit..the answer of the komunist east to the 808...
Analog drummachine with trigger output for all instruments and midi !!
with the latest OS it even syncs propperly...

However... Because i wasnt satisfied with the general sound i changed a few things around..it turned out that the east german chips vary pretty much.. so just by changing them around it was possible to improve the sound...

next step was to try some alternate op amps... i was testing singl amp chips..

in the DRm 1 we have one to boost the noise generator that is feed to cymbals, hi hats, snare and clap in various portions, and another one that is doing the bass drum...

So a very drastic impact to the general sound of the machine...
and... a test subjekt to hear big differences even in same types from the same manufactor....

I want to share my conclusions with you.

What is good in a mixingdesk not necessarily gives the best result in a synth circuit.

741 are duller than 081.. and 081 is rougher as an 5534 but...
its a matter of taste.. the 741 can win ...

opa are closer to the sound of a 5534 than a 081...even better...as expected..
finer..more detail... more high end...quite the oposite to the 741...

but 741 are actually very nice in synth circuits !!!

The winner in my contest...

and another audio myth approved..old versions from the 70´s in metal cans indeed sound better...clearly better...
So dont throw away your old 741 metal can op amps...
The sounds of the metal cans even when out of the same time,brand aso varys more than on modern op amps...

Another myth regarding 5534 aproved aswell...texas instrumentrs sounds better than signex .....

Even when the opa sounds more on the point ..more attack...more dirrect than an 5543 in this test i ve to admit that the general 5534 sound has a certain charme... some people claim that a good designed 5534 circuit makes expensiv op ams like opa´s´redundant... i see theire point now...
again a matter of taste...but its clearly to get that the opa even while beeing a direct 071 replacement had soundwise the 5534 in mind...you hear the higher slewrate..but... a bit less is nice aswell...
However ..the opa´s´áre more userfriendly and forgiving when placed in the wrong circuit than an 5534...

In the mix stage of the DRM 1 an opa was the winner of the conntest

tl071 and 081 sound different... slightly.... the 071 is a bit finer..but again... in the drum machine the rougher ones win...

Biggest result of the test...

In a synth circuit the sound of an op amp has much higher impact than in an audio processing circuit.
An opa stays a good one but its not automatical the best in a field where taste matters...

Maybe you know all that allready...

Mikmo · Posted: Sat Apr 28, 2007 8:03 am Post subject:

Well i didn't know that.

I knew that there are some differences, but i did not know i was so much.

Craig Anderton writes a little bit about some of the same things in "Electronic projects for musicians", but not as detailed as yuo do heer.

Thanks for sharing.

And also very good that i just found a box full of old metalcan matched pair transistors, maybe the same goes for them as for OPAmps.

3phase · Posted: Sat Apr 28, 2007 8:27 am Post subject:

i ve never heard any rumours that give metal can transistors a better name...

However the myth about old op amps is quite often heard...

with the 741 test i did today it was very dominant...even when the general charakter was the same the metalcans sounded much smoother and clear...

so even when the 741 has a rather mushy sound the metalcan version was a clear winner in the noise generator circuit...

for the BD circuit it wasnt as clear..but the charakter of the op amp shines thru even in this totaly different circuit and it defenetly matched better with the charakter of the noise...

So beside some learning my DRM1 now sounds clearly better than before...

sneakthief · Joined: Jul 24, 2006 Posts: 569 Location: Berlin

i was using my friend's newly-purchased DRM last week - my god, those claps are amazing! and what a great sequencer.

the only let down is the kick drum. it sounds like poo.

he's got the latest os so it syncs perfectly to midi clock.

3phase · Posted: Sun Apr 29, 2007 4:12 am Post subject:

i like the BD... its a short kick..nothing special a spike trigers a resonant filter so no complex sound...
the new op amps helped it..especially the opa in the mix stage gives more kick.

etaoin · Joined: Jun 30, 2005 Posts: 761 Location: Utrecht, NL

Mikmo · Posted: Sun Apr 29, 2007 1:11 pm Post subject:

Well there were only 3 LM394 metal can transistors in the box i found, but a lot of 10 pin UA726 matched transistor with built in heater Smile

Used in Jupiter 4 and other synths as far as i know. Most of them in the original packaging.

Also;

MAT01, MD7002, 2C415, 2V435, AD832

I know the LM394 and UA726 are nice.

Anbody know if the rest of them are any good for synt use ?

sneakthief · Joined: Jul 24, 2006 Posts: 569 Location: Berlin

the mat01 can also be used as a lm394 substitute - it's got worse noise characteristics but i'm not sure if this translates to worse performance in an exponential converter circuit:

MAT01 vs. MAT02:
http://www.analog.com/en/prod/0,,773_865_MAT01,00.html
http://www.analog.com/en/prod/0,,773_865_MAT02,00.html

Mooger5 · Posted: Thu May 10, 2007 2:50 pm Post subject: Re: Op Amps in synth circuits