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 Forum index » DIY Hardware and Software » YuSynth
Yusynth S/H-noise module - smoking (literally)
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Coriolis



Joined: Apr 11, 2005
Posts: 616
Location: Stilling, Denmark

PostPosted: Mon Aug 11, 2008 2:37 am    Post subject:  Yusynth S/H-noise module - smoking (literally)
Subject description: - another one for Yves
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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 ( Embarassed ), 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:
Quote:
Operation from split supplies also is possible if the
difference between the two supplies is 3 V to 32 V
(3 V to 26 V for the LM2902), and VCC is at least
1.5 V more positive than the input common-mode
voltage.


Eh? In the schem, it is getting the full +/- 15V, certainly not single supply.
What's up here?

C

Edit: Oh - and is there any reason why I couldn't just use a TL074 instead?

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yusynth



Joined: Nov 24, 2005
Posts: 1219
Location: France

PostPosted: Mon Aug 11, 2008 4:00 am    Post subject: Reply with quote  Mark this post and the followings unread

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.

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Coriolis



Joined: Apr 11, 2005
Posts: 616
Location: Stilling, Denmark

PostPosted: Mon Aug 11, 2008 4:06 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Yves Very Happy
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

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a.b.o.z.



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PostPosted: Mon Aug 11, 2008 4:08 am    Post subject: Reply with quote  Mark this post and the followings unread

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



Joined: Nov 24, 2005
Posts: 1219
Location: France

PostPosted: Mon Aug 11, 2008 4:17 am    Post subject: Reply with quote  Mark this post and the followings unread

Coriolis wrote:
Hi Yves Very Happy
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


OK then I would think that either the LM324 was dead in the first place or you placed it reversed and consequently burned it. The LM324 is perfectly suited for this circuit, now to answer your last question, the choice here is that it's a noise generator and the high noise level of the LM384 compared to that of the TL074 is not an issue since what we want here is getting noise Wink Second point, the LM324 has an advantage compared to the TL074 : it is rather phase-reversal immune which is an important feature to consider for the part of the circuit which generate the RANDOM VOLTAGE and where the output may briefly hit the level of the power rails.

About AOP phase-reversal :
http://www.planetanalog.com/showArticle.jhtml?articleID=59302418

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yusynth



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PostPosted: Mon Aug 11, 2008 4:18 am    Post subject: Reply with quote  Mark this post and the followings unread

a.b.o.z. wrote:
On s&h/noise layout there is 324 but on silkscreen there is 074 as is in BOM for noise submodule.


Either can be used but a LM324 should be prefered (see above)

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yusynth



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PostPosted: Mon Aug 11, 2008 4:21 am    Post subject: Reply with quote  Mark this post and the followings unread

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... Cool
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Coriolis



Joined: Apr 11, 2005
Posts: 616
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PostPosted: Mon Aug 11, 2008 4:25 am    Post subject: Reply with quote  Mark this post and the followings unread

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

Quote:
Second point, the LM324 has an advantage compared to the TL074 : it is rather phase-reversal immune which is an important feature to consider for the part of the circuit which generate the RANDOM VOLTAGE and where the output may briefly hit the level of the power rails.


Ah, well that is a good reason. So if this module suddenly dies, I'll know why...
I'm pretty sure I had the LM324 placed correctly to begin with, but there may also have been solderbridges at that point, which caused trouble.
What I mean is, the symptoms were the same (burning resistors) but the cause may have changed during troubleshooting, from a solderbridge to a reversed chip...easy to become confused then!

Thanks for all the info.

C

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Peake



Joined: Jun 29, 2007
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PostPosted: Mon Aug 11, 2008 10:23 am    Post subject: Reply with quote  Mark this post and the followings unread

yusson wrote:
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... Cool


Well-deserved, sir!
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