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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
Sound Lab Ultimate Sample & Hold (Solved)
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Hilbert



Joined: Jul 05, 2014
Posts: 2
Location: Norway

PostPosted: Sat Jul 05, 2014 10:02 am    Post subject: Sound Lab Ultimate Sample & Hold (Solved)
Subject description: Problems with the sample & hold...
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Hello all,

First post - thank you all for tons of great info and fun reads on this forum!

I recently completed a build of the Sound Lab Ultimate and the Expander, and everything works fine I think except the Sample & Hold. The synth is great fun and I have it hooked up to a mini keyboard via a Doepfer Dark Link and my pc. However the non-functioning S&H is bugging me a bit... If someone could help me a bit with troubleshooting I would be very grateful! Smile

The problem is that the input signal is not sampled at all, but rather passed along to the CV-output. A triangle wave in from the LFO gives practically the same triangle wave out to the CV out of the S&H.

Things I have checked/done:
-wiring
-soldering
-correct components
-changed the two ICs (LF444 and TL071) for similar ones with no luck

Here's the schematic:
http://www.musicfromouterspace.com/forums.html?MAINTAB=SYNTHDIY&PROJARG=SOUNDLAB_ULTIMATE/page2.html&CATPARTNO=SLULTIMATEPCB&PN=1&SONGID=NONE

Referring to Ray's troubleshooting page http://www.musicfromouterspace.com/forums.html?MAINTAB=SYNTHDIY&PROJARG=SOUNDLAB_ULTIMATE/page8.html&CATPARTNO=SLULTIMATEPCB&PN=1&SONGID=NONE, I did some probing and found that the pulses from the sample clock generator look correct up to the junction between R203 and R212, where I only see a ground level (with about 40mV peak-to-peak noise) and no rapidly decaying pulse as I should. The input signal also follows his figures, except for figure 5 from the top where I see no stepping of the triangle wave, i.e. no sampling seems to happen.

Since my ICs seem ok, my suspects are transistor Q11 (PN4391), or maybe the ceramic cap C62 used for the differentiator circuit (turning the top hat pulse to a shorter asymmetric decaying pulse). How realistic is it that this cap is ruined? I'll dig around for a replacement cap, and have ordered some PN4391 (at a terrible price...Sad ) in case that's the culprit. I guess it can't be the styrene cap C60 since something goes wrong with the pulse signal already before the gate to Q11, or am I wrong?

If anyone have any input that would be very motivating - thank you!

-Hilbert

EDIT: links fixed

Last edited by Hilbert on Mon Jul 07, 2014 11:37 am; edited 1 time in total
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Hilbert



Joined: Jul 05, 2014
Posts: 2
Location: Norway

PostPosted: Sun Jul 06, 2014 10:27 am    Post subject: Reply with quote  Mark this post and the followings unread

Got some help from elmegil over at muff-wiggler:
http://www.muffwiggler.com/forum/post-1608085.html#1608085

The solution, in case someone wonders Smile :

It turns out it was a solder bridge shorting the ground side of R211 to R203. I was aware of it but had thought it was on the side of R211 that should be connected to R203, so it looked ok. That's what I get for assuming things Wink. The holes are very close there so one needs to be pretty careful not to short them.

Thanks again to elmegil (I believe he is active here as well).
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elmegil



Joined: Mar 20, 2012
Posts: 1475
Location: Chicago
Audio files: 14

PostPosted: Sun Jul 06, 2014 5:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

You're welcome here too Smile

Sorry I missed it here first, but glad I could help.
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