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Old 9th August 2016, 02:45 AM   #1
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Default Please help with cap orientation.

I was hoping to get some help figuring out the proper orientation of the electrolytic caps in the linked circuit. Yes, this is a guitar effect question, but as my question was more theoretical, I was thinking this would be a better forum.

This schematic is a little infamous in the effects world, as it has obvious errors, and Chinese clones are produced based on this schematic, errors included!

The 10 uF electrolytic caps are used in the place of more expensive film caps. I have never 100% understood how to orient electrolytics for this service, but have noted that they are usually oriented so that the + terminal is connected to the active device.

C5 and C10 have been widely identified as the caps to reverse for the circuit to "work" properly. However, I believe C8 and C9 also should be reversed.

Thus, to summarize, C5, C8, C9, and C10 should be reversed. C4, C6, C7, and C16 are correctly oriented. Correct?

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Old 9th August 2016, 07:53 AM   #2
AndrewT is offline AndrewT  Scotland
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The coupling capacitors are included to prevent a DC voltage on one side affecting the DC conditions on the other side. i.e. the coupling capacitors are DC Blocking capacitors.

If there is a difference in DC voltage across the capacitor, then the +ve side of the capacitor goes to the more positive voltage and the -ve side of the capacitor goes to the more negative voltage. A DMM tells you if you have it right, after the event/fact.

Sometimes the AC voltage can be high enough to exceed the DC differential and then the coupling capacitor must be able to survive and operate with voltages of both polarities across it.
In this situation you must use a bi-polar electrolytic, or non polar capacitor (plastic film).

C16 sees roughly half the supply voltage. Here a polar electrolytic is good enough. You have 5 other 10uF coupling caps. Use Bi-Polar for these with a voltage rating exceeding the supply rail voltage.

BUT !!!! the output impedance of that common emitter T4 is very high. This stage really needs a Buffer (emitter follower) to be able to send the signal into the connecting cable.
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Last edited by AndrewT; 9th August 2016 at 07:57 AM.
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Old 9th August 2016, 09:19 AM   #3
DF96 is offline DF96  England
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Quote:
Originally Posted by leadbelly
The 10 uF electrolytic caps are used in the place of more expensive film caps.
Electrolytics are the appropriate technilogy to use here. Daft to use film caps for this circuit.

Quote:
C5 and C10 have been widely identified as the caps to reverse for the circuit to "work" properly. However, I believe C8 and C9 also should be reversed.
C5 and C10 should certainly be reversed. C9 should probably be reversed. C8 probably should be left as it is. It all depends on the exact voltages around T2.

Quote:
Originally Posted by AndrewT
Sometimes the AC voltage can be high enough to exceed the DC differential and then the coupling capacitor must be able to survive and operate with voltages of both polarities across it.
In this situation you must use a bi-polar electrolytic, or non polar capacitor (plastic film).
Just to clarify, AC only overcomes DC if the AC is at sufficiently low frequency that much of the voltage is developed across the cap. I know Andrew knows that, but some readers may not.
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Old 9th August 2016, 01:20 PM   #4
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Many thanks for your thoughtful replies.
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