Yusynth S/H-noise module - smoking (literally)

[Coriolis]

Rather than spamming Yves's private email, I'm posting this here.

After getting the wavefolder up and running, it's time to finish the Yusynth S/H - Noise module, and of course I'm having problems with it (me being me).

http://yusynth.net/Modular/EN/NOISE/index.html

I'm using the layout with both circuits on one board, and have populated it as shown on Yves' site, including separate 10R resistors and caps for each circuits power supply.

Now, an the noise-side of the board, the two 10R resistors keep burning up!
They light up like little lightbulbs...

So after incinerating my second set of resistors, I left them out, and measured the current. V+ side seems normal (about 30mA), but V- measured a whopping 2A! No wonder stuff was burning...

I checked thoroughly for solderbridges, misplaced components ( ), wrong values, correct polarity of caps, IC's, transistors, etc..

I noticed the LM324 was running quite hot, and pulling it out and measuring amperes with the socket empty, verified my suspicion: I had found the culprit.

I was actually a little unsure of the pinout on this one, since it's markings are a little confusing: it has a clear, u-shape dimple at one end, and a smaller, circular dimple at the other end (it's a TI-chip). reversing it's position didn't exactly help, though by then it may have been burnt out.

Looking at the schem, I see the LM324 is getting bipolar power, but looking in the datasheet, I see it is intended for single-supply operation , although dual-supply seems to an option - but it isn't clear to me in what way:

[yusynth]

Hi Coriolis

The burning of the 10 ohms resistors indicate that there is definitly a short-cut somewhere and a simple test is to remove the ICs of the socket, with no power, take your DVM and use the function Continuity tester and check the two tracks after the 10 ohm resistors if there is a short-cut between these the continuity tester will beep.
If there is no solder bridge take a good magnifying glass and check the tracks : once I had a short-cut due to a very thin copper trace that wasn't complete etched and it was hardly visible with naked eyes.

The LM384 are OK to be used in bipolar mode, you can substitute a TL074 with no problem.

[Coriolis]

Hi Yves
I haven't tested for continuity everywhere, however - I just put in a TL074, and now everything works. I did nothing to the circuit before putting it in, so the conditions ought to be the same as with the LM324, but who knows...

May I ask why you chose the LM324 for this task in the first place?

C

[a.b.o.z.]

On s&h/noise layout there is 324 but on silkscreen there is 074 as is in BOM for noise submodule.

[yusynth]

[yusynth]

[yusynth]

By the way you may be interested to know that the moderators of this forum intend to soon create a dedicated sub-forum for yusynth module support...

[Coriolis]

Sounds good sir - I'll be the main contributor in that subforum..perhaps even it's raison d'etre?

[Peake]