Slambox

[Meowy]

I see a 47K resistor is used in place of the typical "SHO circuit" 100K output resistor (R4). What affect does this have?

Similarly, can the 5.1K resistor (R3) be substituted for a different value?  In simple terms, what would the effect be (electronically and audibly) if you raised or lowered the 5.1K resistor in the Slambox?

[madbean]

There are two different designs for the SHO that have floating around in schematic form over the years. The early ones had the 100k output resistor, and used two 1n914s instead of the Zener to protect the mosfet against electrostatic discharge. At some point, the design was changed into its present form, with the 47k resistor and Zener. As far a the resistor, it does two things: creates a high-pass filter in conjunction with C2 and sets the output impedance of the circuit (since there is no actual volume control).

C2 is sufficiently large enough that a difference of 53k in the output resistor will not attenuate low end frequencies in a significant way. I would not expect a tonal difference necessarily in terms of output impedance, but I suppose it's possible it could have some kind of effect on a subsequent pedal in the chain. I've never experienced any issues in stacking with the circuit in present form, and ideally the lower the output impedance the better.

Changing the 5k1 higher or lower might have some effect on the efficiency with which the mosfet operates, i.e. the total output gain, but having never tried it I can't say exactly whether or not it would have a positive or negative effect, tone-wise. It's such a simple circuit you could breadboard it in five minutes and experiment with small changes in the biasing resistor. That would give you something to go on before committing it to a build.

[madbean]

So, I took a look at the docs he has for the Inventobox which has an SHO schem, and you are right: he lists a 100k. So, I'll go ahead and make a note of that in the Slambox documentation. Either will work just as well (I've always liked mine just fine with a 47k). One other thing I thought of: a 100k might gove a slightly hotter output.

Thanks for bringing this to my attention!