[sdiy] uA726 transistor array

[harrybissell]

The uA726 is also extraordinarily stingly with heater
current... and therefore does not heat the whole synth
at the same time (making everything ELSE drift).

I tried some experiments using an LM399 with the
heatshield removed... and epoxied to a matched pair.
It did work... but I'd say not as well as a diff pair and
tempco...

An experiment with better quad transistors like the
MAT-04... or those.. I mean THAT transistor arrays
might be better than the 3046....

H^) harry

Magnus Danielson wrote:

> From: Takuya KATAYAMA <cxh02175 at nifty.com>
> Subject: Re: [sdiy] uA726 transistor array
> Date: Sat, 12 Oct 2002 21:53:44 +0900
>
> Hi Takuya, Mike and others!
>
> > Hello Mike and the List!
> >
> > I cant recommend two individual Tr's instead of uA726.
> > uA726 is a matched MONOLITHIC pair Tr's with controlled heater.
> >
> > If you need pin-for-pin compatible replacement, uA726 had already
> > obsoleted, you know.
> > Instead of uA726, we make some feedback control circuit with TR array
> > such as CA(LM)3046.
> > It is very steadly and work well.
>
> Well, yes. Out dear listmaintainer has an example on his webpage on how to do
> this.
>
> I've looked at the detailed schematic for the uA726 and it is possible to
> acheive the same functionality. Weither the CA3046 has good enought properties
> on the actual transistor parameters to match the transitors in the uA726 is
> however one objection I recall for that setup. There is an issue about which
> transitors really have to be tightly connected together thermally. The uA726
> layout is quite ingenious and use more than the 5 transistors in the CA3046 to
> operate. While a direct clone might not be the best road to pass, then the
> question comes up if one can make another setup wich comes near or outperforms
> the uA726. One of the benefits is the trimable temperature, linear and fast
> control and overcurrent protection.
>
> However, the aspect of thermal connectivity such as in the uA726 probably calls
> for at least a few transitors to reside on the same chip.
>
> Cheers,
> Magnus