Slambox - SHO

[masterlk]

Is the Slambox an exact clone of the SHO? Does it have the 5 Meg input impedance and output level of 8 volts as described on the makers website? Just curious.

[jkokura]

It does have an input impedance of 5M ohms.

You know how you can tell? Take a look at the schem. Notice that 10M ohm to ground, and the other 10M ohm to the power? That's the input impedance setup. Usually, R1 in Madbean projects is the input impedance indicator - take that value and divide it in two and you usually get your input impedance. In this case, it's 10M, so that makes it 5M input impedance. Usually pedals have a 1M ohm for their input impedance resistor, making the pedal have a 500k impedance.

As for the 8 volt output, I don't know. I know that the schem that's available is based on the verified by Zachary Vex schematic. Vex has made his stuff public because of his little experiment box thing. You can easily get pretty much any schematic of his now, straight from them.

Jacob

[masterlk]

Wow! That's really cool Jacob, thanks for letting me know that. So now I will be looking at all the
R1's to see what they are! I noticed that the two builds that I have done so far, the Fatpants and the Sunking that the R1's for those are not 1M but the R2's are both 1M. Are the R2's in those pedals the input impedance resistors?


So then is there any advantage to having a higher input impedance? Could you change the input resistor in any pedal without goofing with the sound or harming the rest of the circuit?

[madbean]

In general, input impedance is set by any pulldown resistor, any resistor connected to virtual ground (4.5v), a combination thereof, or in their absence the input impedance of the component at the input of the effect, for example an op-amp or transistor. In the case of a pulldown resistor, you get the added benefit of a "de-popper". This works because with most DC circuits, you generally have a capacitor that acts as a decoupler for the AC input (we want to eliminate alternating current and only work with direct current in our effects, usually). This cap can store a charge after the effect is bypassed. By including the pulldown, a path to ground is created to allow that current to bleed out, so that when the effect is engaged again there is no instantaneous current gap with the charged decoupling cap (that's what causes the pop).

The 1M pulldown you see in a lot of true bypass circuits is doing double duty of setting the high input impedance and acting as that 'de-popper'. It's not always true that the higher input impedance the better. If you take the SHO as an example, the reason it is so bright is because of that fat 5M input, which essentially rejects high frequency loss. But, this high input impedance might not work as well in a situation where you are applying 500+ gain to the input signal like you have in the typical Tubescreamer. All that high end has to be attenuated somehow or it's just going to sound damn awful.

There's no harm to having high input impedance with your effects, but like I said it may not always result in a "better" sound by just arbitrarily increasing it. IMO, some circuits sound better with a LOWER impedance, like a Fuzz Face. Fuzzes sound best with some of that high end trimmed out.