The ua726 (Jup4, Minimoog) sound

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rdemon
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The ua726 (Jup4, Minimoog) sound

Post by rdemon » Mon May 21, 2007 4:18 pm

I'm trying to "reverse engineer" my Jup4 so that I can service it in the future. Anyone know anything about this. I know it is a transistor put out in the 70's.

I think the Jup4 and Minimoog have have this chip. Does this chip have a signature sound like the CEM or SSM?

Do you know anything about the Jup4 filter, does it use an rare chips?

R

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Post by solderguy » Mon May 21, 2007 6:17 pm

Hi - the uA726 ( a matched transistor pair with built-in heater for temperatute stability) is being sold on ebay by a guy from Hong Kong who calls himself "hongkongsuperseller" and has an ebay store called "partspipe". His prices look extremely reasonable (also the shipping). I have not ordered from him myself, but others have mentioned that they are satisfied with their purchases. The uA726 was previously an extremely scarce chip.

Both versions of the JP-4 filter use now hard-to-get custom Roland chips - first version uses several BA662, second version uses an IR3109.

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Post by gilwe » Mon May 21, 2007 6:48 pm

The uA726 has not sound. This unit is consisted of an extremely macthed pair of transistors and an oven which keeps the temperture of the entire unit stable. It can be found in Korg Trident as well. It is usually used for the antilog circuit and controls the scaling of the instrument, i.e, in case it gets defected, C to D will sound like C to F....

I had it going bad on my Trident after I wrongly applied some cooling spary over it while I tried to determine a tuning problem it had, a few years ago. Since than I bought 2 additional units as spares. I recommend anyone who hold a synth which uses this part to have one or two as a spare... these are getting rare and they have no other substitute in those circuits !!

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Post by roginator » Mon May 21, 2007 8:05 pm

ua 726 are in:

Elector Formant
Roland sytem 100. system 100m, system 700, SH 1, SH 2,SH 3a, SH 5, SH 7,SH09, Promars, Jupiter 4
Korg Trident
Moog minimoog
Kawai 100f


as far as I know .....

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Post by nathanscribe » Mon May 21, 2007 8:43 pm

Yep, this was used in quite a few synths circuits. It is just a matched heated transistor pair. If you were techy enough, you could replace it & a couple of related components with something modern and common, but it's probably an ugly little job. There's no reason why the circuit would sound particularly different timbrally though, as its purpose is to provide the oscillator with a supply current, nothing more, as has been previously stated.

More recent designs use the 3046 or 3086 (5 trannies an a DIL 14 IC), or other matched pairs scuh as the MAT02 (IIRC).

Regarding Honkkong ebayer, I've had knobs from them and they were fine and dandy, with delivery being less than 2 weeks, for a good price. Jacks were dirt cheap, and not as good as I wanted - but then, I suppose i got what i paid for. I've heard rumours their suppliers don't always provide them with decent chips, particularly the rarer ones, but I have no idea if there's any truth in that, as with any rumour. I got come chips from them which look the part, but I haven't tested any yet. I suppose if the price is OK, try out a small order and see. If things are to your liking, go back, and if not, don't - same with any seller really. Try chipforbrains too, they have a lot of stuff like this.

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Post by nathanscribe » Mon May 21, 2007 8:50 pm

nathanscribe wrote:Yep, this was used in quite a few synths circuits. It is just a matched heated transistor pair. If you were techy enough, you could replace it & a couple of related components with something modern and common, but it's probably an ugly little job. There's no reason why the circuit would sound particularly different timbrally though, as its purpose is to provide the oscillator with a supply current, nothing more, as has been previously stated.

More recent designs use the 3046 or 3086 (5 trannies an a DIL 14 IC), or other matched pairs scuh as the MAT02 (IIRC).

Regarding Honkkong ebayer, I've had knobs from them and they were fine and dandy, with delivery being less than 2 weeks, for a good price. Jacks were dirt cheap, and not as good as I wanted - but then, I suppose i got what i paid for. I've heard rumours their suppliers don't always provide them with decent chips, particularly the rarer ones, but I have no idea if there's any truth in that, as with any rumour. I got some chips from them which look the part, but I haven't tested any yet. I suppose if the price is OK, try out a small order and see. If things are to your liking, go back, and if not, don't - same with any seller really. Try chipforbrains too, they have a lot of stuff like this.

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Re: The ua726 (Jup4, Minimoog) sound

Post by cLOWNgOD » Sat Oct 31, 2015 2:29 am

Fairchild Hiller (I think they went belly up around 1981?) Here are the specs on the chip:

http://www.classiccmp.org/rtellason/chipdata/ua726.pdf


Looks like a couple of Zeners and some NPNs. Good luck!!

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Re: The ua726 (Jup4, Minimoog) sound

Post by Broadwave » Sat Oct 31, 2015 10:34 am

It's possible, in some cases, to use Doepfer's heater circuit (IC3 3046 bottom left) to replace the u726 - I did this to 3 Frequency Central Roland System M100 VCOs, and it works like a charm.

10 mins to warm up, and off you go - Very stable.

About 5 years ago I bought a bunch of u726s for a Minimoog clone, and they all turned out to be fakes, so buyer beware!

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Re: The ua726 (Jup4, Minimoog) sound

Post by cornutt » Fri Nov 06, 2015 3:49 am

Broadwave wrote: About 5 years ago I bought a bunch of u726s for a Minimoog clone, and they all turned out to be fakes, so buyer beware!
Yeah, there was someone on Ebay that was selling fakes. I got burned on one. I do have one (real) spare 726, and I treat it like gold. I have it in case I ever have to replace one in my EML 101.

Hint: all uA726's were made in metal can packages. If someone is trying to sell you a 726 and it's in a typical DIP package, it's fake.
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