µA726

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obscure wave music
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Joined: Fri Feb 05, 2016 9:06 am

µA726

Post by obscure wave music » Sat Jun 04, 2016 10:20 am

Dear all,

I saw the topic about Minimoog spare parts, but this discussion is locked, and, if I understand it well,
that means us mere mortals cannot reply.....so I start a new thread.

The 726 is important to me firstly because I build Formant modules and the Formant VCO uses 726's.

Now, I'm just an amateur in electronics, but: looking at the 726 datasheet one notices that it is only
a few matched transistors with an oven. There are so many smart people on this forum, so here is my
point: would it be that difficult to make a small PCB ( SMD ) replicating the schematic of the 726 and
populating it with standard components? It could be small enough even to fit as a replacement in the Minimoog,
given that this instrument is not crammed so that there is no space left anywhere to put something
in, maybe with a bit of wiggling.....I tried once ( unsuccesfully ) to replicate the Korg 35 IC.

Or am I seeing this completely wrong ?

Cheers !

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noddyspuncture
Posts: 422
Joined: Wed Sep 16, 2009 7:57 pm

Re: µA726

Post by noddyspuncture » Sat Jun 04, 2016 12:58 pm

obscure wave music wrote:Dear all,

I saw the topic about Minimoog spare parts, but this discussion is locked, and, if I understand it well,
that means us mere mortals cannot reply.....so I start a new thread.

The 726 is important to me firstly because I build Formant modules and the Formant VCO uses 726's.

Now, I'm just an amateur in electronics, but: looking at the 726 datasheet one notices that it is only
a few matched transistors with an oven. There are so many smart people on this forum, so here is my
point: would it be that difficult to make a small PCB ( SMD ) replicating the schematic of the 726 and
populating it with standard components? It could be small enough even to fit as a replacement in the Minimoog,
given that this instrument is not crammed so that there is no space left anywhere to put something
in, maybe with a bit of wiggling.....I tried once ( unsuccesfully ) to replicate the Korg 35 IC.

Or am I seeing this completely wrong ?

Cheers !


Interesting... I am looking forward to seeing the feedback on this... by the way can you elaborate on your Korg35 replication...?
I have just recently bought the SMD transistors needed to have go at that myself... :)

Cheers,
Tom

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latigid on
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Location: Auckland, New Zealand

Re: µA726

Post by latigid on » Sat Jun 04, 2016 7:38 pm

I don't have practical experience with this chip as I've never designed with it, but I've listened in on quite a few discussions at MuffWiggler.

Before rumours (and they're just that at the moment; there's no confirmation that this will happen) of a new run of 726s, there were people looking into plug-in equivalents. I think the gist of it was that you'll get the best tracking out of a monolithic pair, i.e. transistors built off the same substrate. The MAT- series is one I believe. You also have to consider a tempco resistor in most designs, and for these the best type seems to be wire-wound due to tighter tolerances.

So if you could emulate or even improve on these, would it be the same thing? I've noticed two schools of thought in SDIY, one is that instruments have inherent flaws that make them more musical (and possibly cheaper/easier to build), while the other suggests that maximum precision and minimum noise is the only way.

The new Buchla Easels have space for 726s, but in most cases they're not installed. Most users don't complain about poor tracking, but then again if you're into Buchla you're probably not too interested in perfect V/oct pitch. :wink: :twisted: Some say that fabrication in general is much tighter these days, so much so that discrete transistors straight off the same reel can be well matched.

Interestingly, it was just announced that the CEM3340 (VCO on a chip) is now back in production. This was in the MemoryMoog, Prophet 5 and SH-101 if I'm not mistaken. Also probably a bit less exciting for Moog guys, but Doepfer have an oscillator boasting 10 octaves of linear tracking in the design phase.

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latigid on
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Location: Auckland, New Zealand

Re: µA726

Post by latigid on » Sun Jun 05, 2016 11:23 am

Surprise surprise, the Doepfer A-111-2 uses a 3340; Dieter Doepfer was a main influence in getting these CEM chips reissued.

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MC
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Re: µA726

Post by MC » Mon Jun 06, 2016 12:14 pm

Very nice to hear that the CEM3340 is back in production.

Regarding the ua726, the closest equivalent is the "heated IC" approach using the 3046 or 3086. This is what the Prodigy and Source use. The MAT ICs are just a matched pair of NPNs, they don't have any heater component on the substrate. Either approach would still require the tempco which you can still get in SMT format.

BTW, regarding that locked thread *I* did not report anything. I simply abandoned any further discussion.
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jerre77
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Joined: Wed May 02, 2018 2:31 pm

Re: µA726

Post by jerre77 » Wed May 02, 2018 2:37 pm

i have an 726 for sale

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