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Synth clips awfully on speakers/soundcards but NOT on headphones? Halp, Impedance or some other sorcery? Electronics-savvy advice much-needed
db1989
post Jul 12 2013, 22:35
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Google seems to disappoint when it comes to quite vague combinations of terms like these—at least if you don’t already have a degree in electronics! So I would greatly appreciate advice from our electronics-/engineering-savvy members. I think this thread is roughly on-topic. wink.gif

I just bought an old synth. I quickly became disappointed and, just as much, baffled when I realised that any time it’s playing more than one note, it generates horrendous clipping in any speakers or soundcards to which it is connected. The signal appears to be clipping, but it unfortunately doesn’t seem quite that simple, because…

I then discovered this problem does not occur on headphones, which reproduce the synth just fine, as I expected it to sound on the other devices. Also, it sounds pretty quiet there, and indeed, this synth has been claimed to have a low output before. So, the clipping isn’t intrinsic to the outputs, but they’re definitely doing something that speakers, etc. don’t like, causing said devices to read a signal that clips hugely. Because of the low output on headphones, I can’t see how the problem could be due to the outputs being simply too loud/hot, and so I think some other electronic factor must be at work.

What in the world is going on here? Is there any way to assess, and preferably to fix, it? Bear in mind that my knowledge of electronics is, to be charitable, extremely slight. A friend and I think it’s most likely an issue with impedance, perhaps due to the higher-impedance(?) speakers and soundcards drawing a more powerful signal than they should due to some load(?) introduced earlier in the circuitry. However, we can’t make a single guess beyond that and can’t see any component in the pre-amp that is different from what the schematic says it should be. I seem to recall hearing that it may as well be impossible to calculate the impedance introduced by the entire circuit, including the majority that lies beyond the preamps.

Another confusing aspect of this is that the clipping seems to occur only when I try to play more than one voice (read: note) at a time. This makes me wonder if the pre-amp was somehow ‘normalised’ to the maximal no-clip gain for a single voice without any regard for what would happen when something as basic as polyphony was thrown into the mix.

I don’t suppose it’s as simple as shoving a large resistor into the circuit somewhere. :/ Any advice that might help me to salvage this unit will be hugely appreciated. I hope someone might recognise this symptom and be able to suggest the most likely cause—and, with any luck, a feasible solution. Thanks!

Edit: To be clear, this isn’t an intrinsic incompatibility of this type of synth with speakers or soundcards, for I have another one that works just fine. And, again, we couldn’t find any differences between the two that could logically have any affect upon the preamp whatsoever.

Edit again: It has stereo outputs, which naturally have seemingly identical preamps, and both exhibit this problem.

This post has been edited by db1989: Jul 12 2013, 22:48
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pdq
post Jul 23 2013, 16:55
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Film capacitors are not likely to be the cause, both because they very rarely fail, and they would not likely cause your symptoms.

I probably should have asked you first to do some testing. If you have access to a voltmeter, measure the DC voltage at the outputs, both with and without the headphones connected. If the DC voltage is near zero (i.e. hundredths of a volt or less) then this is working correctly and my original guess was wrong.

There is some possibility that the output stage is bipolar (with both positive and negative supplies) and there is no blocking capacitor. A problem with one of the supplies would then cause a DC offset and the kind of symptoms you are seeing.
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Posts in this topic
- db1989   Synth clips awfully on speakers/soundcards but NOT on headphones? Halp   Jul 12 2013, 22:35
- - saratoga   FWIW, a higher impedance load draws less power. P...   Jul 12 2013, 22:47
|- - db1989   Thanks for the reply! QUOTE (saratoga @ ...   Jul 12 2013, 22:56
- - saratoga   Since it happens to both stereo channels, I guess ...   Jul 12 2013, 23:35
- - db1989   QUOTE (saratoga @ Jul 12 2013, 23:35) So ...   Jul 12 2013, 23:52
- - Rotareneg   Like saratoga mentioned, check your power supply f...   Jul 13 2013, 01:26
- - db1989   QUOTE Like saratoga mentioned, check your power su...   Jul 13 2013, 01:35
- - pdq   From the symptoms I would guess that the problem i...   Jul 13 2013, 01:36
- - db1989   This sounds very promising! Thanks a lot. Ev...   Jul 13 2013, 01:43
|- - db1989   Iíve replaced three pairs of electrolytics: two ne...   Jul 23 2013, 16:15
- - Rotareneg   Tantalum caps can fail too, but they tend to short...   Jul 13 2013, 02:29
|- - db1989   QUOTE (Rotareneg @ Jul 13 2013, 02:29) Ta...   Jul 13 2013, 02:39
- - pdq   Film capacitors are not likely to be the cause, bo...   Jul 23 2013, 16:55
|- - db1989   Thanks for replying! QUOTE (pdq @ Jul 23...   Jul 23 2013, 17:15
- - pdq   The big advantage of a bipolar output stage is tha...   Jul 23 2013, 20:26
- - db1989   Well, in lieu of any answers on whether/how transi...   Jul 23 2013, 22:02
- - pdq   I don't think I can shed any further light on ...   Jul 24 2013, 13:39
- - db1989   Heh, well, I tend to get stubborn with things like...   Jul 24 2013, 20:37
- - ktf   You're lucky your headphones still work. I...   Jul 25 2013, 10:21
- - db1989   This happened again! twice! Which did hel...   Apr 20 2014, 02:04
- - DVDdoug   QUOTE I donít suppose itís as simple as shoving a ...   Apr 22 2014, 00:13
- - db1989   …Did you notice my latest post just above yo...   Apr 22 2014, 00:28
- - Rotareneg   You might try the EEVblog, you're bound to fin...   Apr 22 2014, 03:28
- - db1989   Well, again, I know exactly whatís going on proxim...   Apr 22 2014, 18:55
- - KMD   on the face of it its highly unlightly that a soli...   Apr 22 2014, 19:08
|- - db1989   QUOTE (KMD @ Apr 22 2014, 19:08) on the f...   Apr 22 2014, 19:18
- - KMD   One thing that can cause odd clipping sounds or to...   Apr 22 2014, 19:22
- - db1989   And whatís your theory for how that might, specifi...   Apr 22 2014, 19:25
- - KMD   so what are you driving there is it a Brian Eno ha...   Apr 22 2014, 19:28
- - db1989   not relevant and not a tenable attempt at deflecti...   Apr 22 2014, 19:40
- - KMD   OK just saw your comment at 18.:18 . If you di...   Apr 22 2014, 20:04
- - Rotareneg   Is there a schematic for this thing available anyw...   Apr 22 2014, 21:19
- - db1989   Eh, somewhere. That page Iíd already found and see...   Apr 22 2014, 21:33


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