Bloviater 10M resistor

[BassXtreme]

This is my next project and I'm building it for bass. Would the R2 10M resistor make the sound way too bright for bass? Could I use a lower value like maybe 1M?

[madbean]

Yes, a 1M will be fine there.

[BassXtreme]

finally got all the parts. time to build. I was wondering if there was a way to add a volume or gain control. is there any way to tap in a gain or volume pot? could R18 be substituted with a pot?

[stecykmi]

you can always make a passive volume control with a pot by making a voltage divider. there are a couple ways you could implement this. I would probably put a pot in series with the output of the effect and use the wiper as the output (with the third lug going to ground). you don't get a boost with this configuration, however.

I wouldn't use R18, although fundamentally it would probably work. the difference is the fact that C7 and R18 forms a high pass filter, so changing the resistance changes the corner frequency of the filter (changing frequency response at different gain is usually the sign of poor design).

if you're up for doing some testing, R17 seems to be the feedback resistor for the IC1B. if you make it bigger, the gain of the circuit will increase (thus more volume). if you replace it with a pot, you could have an output gain control. there is a problem, because R17 also forms a filter with C6, so the frequency response of the circuit will change somewhat. I would try something like reducing R17 to something like maybe 30k and putting a 50k log pot in series. this way, the resistance doesn't change _too_ much but probably enough to give you a little gain boost (or drop).

[BassXtreme]

thanks for the info. I was comparing this circuit to a state variable filter I built that uses the same quad chip. the designer put a volume pot right after the output cap instead of a resistor and I was going to emulate that. but then again, it is a different design and i don't know how the caps and resistors interact with each other. I guess the R19
1K resistor on the Bloviator has to be considered also

[madbean]

While C7/R18 does create a filter, it's effect is really not necessary to consider in terms of adding an output pot. The 100k sets the output impedance. R19, actually, is pretty superfluous. It's only justification would be to provide some resistance to the output signal in the absence of a volume pot. So, this is what you will want to eliminate.

I would go with at least a 50kA. 10kA is too low, IMO. 50k will give you a slightly hotter output and maintain the output impedance better.