changing a resistor in the AMZ Muffer

[mordechai]

What does changing the 330K resistor do on the Muff master?  On the AMZ site, the Muff master is adapted in the Overdrive Pro with a change to a 470K resistor.  I'm not clear on what this actually accomplishes in the context of working the Muff master into a larger circuit, and I'd appreciate some clarification.

[Earthscum]

as far as I can tell, not a whole lot. Raises the input impedance a little bit, and should raise the output (collector) voltage a bit. Maybe add a little bit gain by eliminating a bit of the feedback signal? Other than that, not much.

I would say it's really pretty negligible. If the stage is getting a larger signal, i.e. sitting at the end of the chain, then the voltage difference at the collector may clip the waveform  more symmetrically/asymmetrically and affect the resulting tone.

[mordechai]

Well, I was thinking of placing it at the front end of a circuit, to boost the signal before it hits the second stage (an IC op-amp) to overdrive the second stage.  So perhaps making the resistor s 470K instead of a 330K helps with that goal?

[Earthscum]

Basically, as long as your collector isn't biased too close to either V+ or Gnd to make the signal clip on either, and you have a capacitor between stages, you shouldn't have any issues. As a matter of fact, I just threw one together, and I'm getting 4.65V with the 330k and 5.58V with a 470k, using a 2n5088. If you figure gain based just your collector resistor/emitter resistor, you only have a gain of 10, which is a decent boost to get up to the OP Amp abuse area  

Oh yeah... if you want to really put a hurting on that op amp, strap a 2.2uF or larger cap across the 1k.   

[mordechai]

Oh yeah... if you want to really put a hurting on that op amp, strap a 2.2uF or larger cap across the 1k.   

On the muffer/muff boost schematic, I don't see a 1K...do you mean the resistor coming off the Q1 emitter?  On the schematic I have, it's a 150K, though on the "muffmaster", it reads "1000"  (no K).  I assumed that was a typo and a 150K is called for there, but is it actually a 1K? 

[petemoore]

  Can't see a schematic, 1k sounds like it'd be an emitter resistor which would be made lower impedance to "AC ground'', allowing higher gain amplification...by adding a capacitor across it, the DC bias remains the same but the AC amplification 'sees' the E-resistor as a small value [if the cap across it is big enough] at 'frequency'...caps have increasing impedance as frequency through them gets lower...so the value of the cap allows amplification gain to be frequency selective or the cap is big enough that the 'relevant frequencies' [ie past the lowest frequency of what the guitar goes down to] are all 'full gain'...the AC passes through the cap and looks like ground to the AC amplifier. The cap blocks DC so the 1k still 'sets the DC emitter bias [with the other bias resistors].

[Earthscum]

What does changing the 330K resistor do on the Muff master?  On the AMZ site, the Muff master is adapted in the Overdrive Pro with a change to a 470K resistor.  I'm not clear on what this actually accomplishes in the context of working the Muff master into a larger circuit, and I'd appreciate some clarification.

If you didn't mean the Muff Master circuit, then I guess we're not talking about the same thing. I was talking about the MM circuit specifically. The Emitter resistor in the OD Pro is lowered for more gain, but all the same should apply. Just use a 22uF cap across the smaller than MM emitter resistor. The ODPro first stage has a huge amount of gain compared to the MM, well over 50x gain (just figuring off of the C-E resistors nets you 66.67x gain, minus biasing feedback, but I don't know how much that accounts for, so I just use the baseline and round down for some losses. OPA's are much easier to figure gain).

[mordechai]

What does changing the 330K resistor do on the Muff master?  On the AMZ site, the Muff master is adapted in the Overdrive Pro with a change to a 470K resistor.  I'm not clear on what this actually accomplishes in the context of working the Muff master into a larger circuit, and I'd appreciate some clarification.

If you didn't mean the Muff Master circuit, then I guess we're not talking about the same thing. I was talking about the MM circuit specifically. The Emitter resistor in the OD Pro is lowered for more gain, but all the same should apply. Just use a 22uF cap across the smaller than MM emitter resistor. The ODPro first stage has a huge amount of gain compared to the MM, well over 50x gain (just figuring off of the C-E resistors nets you 66.67x gain, minus biasing feedback, but I don't know how much that accounts for, so I just use the baseline and round down for some losses. OPA's are much easier to figure gain).

No, that is indeed the circuit I had in mind.  I just ddidn't see a 1K anywhere on it.  If you look at R4, the emitter resistor, it reads "1000", not "1K", so I thought it was a typo for the 150K i've seen elsewhere in this same circuit elsewhere on the AMZ site.  I need to look again at how it is changed in the ODPro, as I didn't notice that it was configured for so much more gain than in the Muff Master...

[mordechai]

Oh, wait...I just looked at the ODPro, and saw that the emitter resistor on Q1 reads "150"...not 150K.  So, this is 150 Ohms, yes?  And the "1000" in the Muff Master is 1000 Ohms=1k? 

If I have this right, then instead of strapping the 2.2uf cap across the emitter resistor, why not just lower it to get the same effect of increased gain?  Or -- is it a different effect altogether?