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el rockyo 22nd February 2009 08:45 PM

Need help with guitar tube pedal schematic.
I have some knowledge of electronics and in the past I've built 2 solid state guitar pedals from existing schematics.

I've been looking around the web for a low voltage tube pedal schematic but I ended up putting some ideas together and drawing a schematic myself (highly influenced by other schematics).
Could someone please have a look at the schematic and tell me if it will work and what needs to be changed?
(I'm a first-timer with tubes)

Note: As the file was too big to upload, I made a website to post the schenatic.

Thank you

Robert McLean 22nd February 2009 09:48 PM

I dont want to sound totally nevative or anything, but there seems to be more and more of these circuits using 12 volt supplies and tubes posted here lately. Is this some kind of trend or cult or something ? I just dont understand it.

Anyway, with the resistance values shown your tubes are going to be drawing in the microamps, if at all. The plate resistances need to be in the 10's of K ohms, the cathode resistor maybe ohms. With hundreds of volts of power supply 100k plate and 1K cathode resistor make sense.

The 1Meg resistor to ground should be on the other side of the coupling capacitor, and should probably be lower in value.

I know the circuit is for distortion and not accurate amplification, but still you cant totally cut off the tube otherwise it is just a glorified capacitor of a few pF.

nigelwright7557 22nd February 2009 10:13 PM

I looked at the distortion cct, if your gonna go for diodes then a simple op-amp fuzz box would do the trick.

You can also get hold of soft limiter ccts that do as good a job as a valve but for much less money.

el rockyo 23rd February 2009 02:21 PM

Thanks for the advise. I posted the changed schematic on the website:

Hope its correct now and ready to build.

Please reply if you have any further advise.

kenpeter 23rd February 2009 09:13 PM

I think your circuit may need two separate plate resistors.

Else the currents are forced equal and opposite, and not
much happens in the way of a voltage swing at the top.

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