Small Bear Tweak-o for bass

[scruff311]

I am looking to build my first stomp box for a bass and I've decided the Tweak-O would be a nice start from small bear electronics (http://www.smallbearelec.com/Projects/TweakO/TweakO.htm). The schematic is provided on that link. My question is this: Since I will be using this for bass, what components should I swap out for others?

Thanks

[PRR]

To let bass's bottom-octave pass:

C5 = 47uFd
C7 = 0.1uFd

Bass is not just a deep guitar; it may take much more tweaking to find a really happy sound. However the larger C5 C7 will at least sound like a bass plus boost-distort, and there's no cookbook for fuzz-tone.

It's a good plan and an excellent article. Go ahead and BUILD IT. What's the worst can happen? If you can't find a groovy bass-fuzz-tone in it, put the small caps in and swap it to a guitarist.

[scruff311]

Thanks for the response. I just placed my order along with the parts you recommended and am anxiously awaiting my package. Question for you though... how do you know that those 2 caps in particular are the ones that need to be changed? I understand that higher capacitance will move the cutoff frequency for a high pass filter lower, but what I don't understand by looking at the schematic that those 2 caps are the ones responsible. If you could shed some insight into this, I would greatly appreciate it.

Thanks!

[petemoore]

  To me the numbers mean ratios of ups and downs, I'm studying to understand and calculate more accurately.
  That's all you really need to know to tweek the tweek-o.
  Since capacitors increase their impedance as the frequency of signal going through them decreases...
  C7, the output cap is a HP [cuts bass] filter, larger values move the impedance curve to lower frequency registers.
  C5 feeds the AC gain of the transistor, in this case the impedance curve starts at 'guitar registers' a curve of increasing impeding to AC as frequency decreases. This keeps the low end 'tight' for guitar, but may sound as weak bass balance as frequencies drop below the low notes on a guitar where AC gain has dropped markedly. A larger cap here feeds AC with less impedance to lower freq's.
  Formed the 'other way' C4 and C6 are LP filters=cuts highs...still using capacitors increasing impedance to lower frequencies [always the case with capacitors] through this path, all signal would otherwise be shunted to a DC rail [v+ in this case]. Larger values will lower the register by letting more of the high frequencies get shunted.

[scruff311]

Thanks for the reply. Can you maybe elaborate as to how you can identify each setup as either LP or HP? To me, they all look like an R and C in parallel.

[blooze_man]

Lots of info here http://www.geofex.com/

[scruff311]

Neat site. Cool explanation on the science of distortion. I didn't see a nice page on identifying LP from HP RC filters however. The only one that is really obvious to me in the schematic is the C7 R7 HP filter.

[petemoore]

  Try AMZ online Calculator and Labs Notebook.

[Gus]

You could build it stock, it might work fine as is.  PRR posted some good points I do think C7 might need to be increased.

You need to think about the difference between bass and guitar.

The bass strings have a bigger magnetic core and that with the pickup can generate  a larger signal.

So sometimes you might even want lower value input caps for a bass if you don't want to overload circuit at the lows as much.

Try different input cap values and test this for yourself and adjust to taste.

I do not see an input pull down(anti pop) resistor in the schematic

[scruff311]

would said pull down resistor be added before C1 in series? what magnitude resistor would be sufficient?