CGS92 SSG Acting real slow

snorkeldata · Joined: Nov 18, 2016 Posts: 5 Location: Sweden

The case:
I just built the CGS92 SSG and its only kinda working.

The smooth side oscillates but it is really slow. With both the trimmer and the Rate knob at -15V it oscillates at about 1hz. from what I have read it should be about 2khz with this setting right?

And the stepped side is just not doing anything.

The strange part is that if i feed it +15V in the CV Rate input it becomes fast and nice and behaves as it is supposed to, for both smooth and stepped side.

I have used the following parts:

LM13700 - National
LM3900 - Texas
for PN4250 I used: 2N3906
for J201 i used: 2N5457

Here are my questiones:
Have you experienced this behaviour in the SSG and did you solve it?

Does anyone had a working SSG with any or all of these parts?

Is some of these parts just not right?

Does it make a difference which brand a IC has?
Which is the best LM3900 for example?

Think that´s all.
I would be very happy for a response, I really wanna get this thing running properly!

wackelpeter · Posted: Mon Sep 04, 2017 1:06 pm Post subject:

Build that thing on stripboard some time ago...

But from Ken's notes should be about 100Hz in the smooth section.

Those IC manufacturers shouldn't be critical and almost aren't if at least you didn't got broken IC's from less reliable sellers on eBay or so.

snorkeldata · Joined: Nov 18, 2016 Posts: 5 Location: Sweden

wackelpeter · Posted: Tue Sep 05, 2017 6:46 am Post subject:

As far as i remember i played around with some resistor values... But i really don't remember if i did this because i had some trouble get it working properly or if i wanted to speed it up a bit...

But anyway... Keep us updated and maybe someone else with some more technical insight will chime in.

snorkeldata · Joined: Nov 18, 2016 Posts: 5 Location: Sweden

Ok, I seem to have solved it.

I changed the 2N5457 for J201. (the one from Kens BOM)
And I also changed the LM13700 to CA3080.

Not sure which of them fixed it since I changed them both at the same time.
But it works and runs great!!
Yay!

wackelpeter · Posted: Wed Sep 06, 2017 6:47 am Post subject:

Good to hear you got it fixed.

I had used 2SK30 maybe that was the point why i had or maybe had not, don't remember now, mess around with some resistor values...

Also had some broken LM13700 sometimes, maybe that was the cause... I had 2 were one side wasn't working.... But they've got used in other circuits were i only needed one OTA.

The Bad Producer · Joined: Mar 08, 2009 Posts: 282 Location: The Manhole

I had this problem when using LM13700 vs 3080, I just tried again today (using LM13700) on a new build and same problem, seems odd that using a LM13700 would slow it down, and just using 3080 = works properly... I don't have time right now but it would be worth investigating more as it would certainly be better to use the 13700 vs the 3080's...

By the way, that's the best looking SSG I've ever seen!