[sdiy] AS3394E: Practical power supply?

[Mike Bryant]

Usually yes.  But whereas the 78xx series are unconditionally stable, the 79xx aren’t.  People think they are just PNP versions of the 78xxs, but in fact they use NPN transistors and the load is in the collector.  With the right phase margin on the load and an output electrolytic that’s rolled off enough at high frequencies, you can build a very nice VHF oscillator with them :-)


From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Benjamin Tremblay via Synth-diy
Sent: 19 November 2021 12:26
To: The SynthiMuse
Cc: synth-diy mailing list
Subject: Re: [sdiy] AS3394E: Practical power supply?

Thanks All!

I can’t get advice like this anywhere else. Only other lazy impulse left in me is: I might actually have some 7906 regulators in a bin. Maybe good enough?


On Nov 19, 2021, at 5:59 AM, The SynthiMuse via Synth-diy <synth-diy at synth-diy.org<mailto:synth-diy at synth-diy.org>> wrote:

I think adjusting the voltage on a 7905 with diodes in a non-critical supply is fine except it reminds me....

As a 23 year old junior tech (1981), I got a gentle 'bollocking' for replacing a VCS3 -ve power regulator with a 7905 and a zener to bring it up to the right voltage.
He told me that so much of the synth depended on good PSU regulation that doing this wouldn't give a solid enough rail for stable operation as the voltage could drift up and down with temperature.
I learned my psu lesson.

So, overall,  an LM337-type solution is the one I would go for.

Gerry


On Fri, 19 Nov 2021, 09:34 Gordonjcp, <gordonjcp at gjcp.net<mailto:gordonjcp at gjcp.net>> wrote:
On Thu, Nov 18, 2021 at 03:49:00PM +0000, Tom Bugs via Synth-diy wrote:
> necessary not to compromise the VCO frequency resolution, which ranges from
> -4 to +4 volts, in favor of a -5V
> supply (this is because there needs to be 4 diode drops for the current
> mirrors).Any one of the readily
> available 3-terminal regulators may be used to supply the -6.5V negative

So why not a cheap readily-available 7905 with two diodes in its ground leg?

--
Gordonjcp

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