Muffmaster question.

[Artie]

Hi everyone. I just built the Muffmaster as shown on Jack Orman's site. It provides a nice clean 18db boost, but I was under the impression that it would be a treble boost. In fact, it has a subtle treble loss when I go back and forth between on and bypass. I wonder if I misinterpreted its description or if I possibly did something wrong. I used the 2N3904 transistor and all precision resistors. The only variance from the schematic is that I used a 10.4k collector resistor instead of 10k.

Thanks all.

[Artie]

Anyone?   

Edit: Correction: I used a 2N5088 transistor.

[petemoore]

  LEss treble...strange, perhaps there's more bass so it seems like less treble ?
  Shouldn't be...but I haven't looked at the schematic lately, or calculated input impedance etc.
  Try a smaller input cap value ?
  Sounds like it's boosting, I like to measure the bias voltages whenever I complete an active stage.

[Artie]

Hi Pete; Thanks for responding. My bypass switch is actually a 3-position rotary control. I first wired it so that the two "active" positions switched input caps. There was absolutely no difference using the stock .01uf and a 1uf. The only other consideration is, that even though I'm using a 9-volt wall-wart, it actually produces 12 volts. I assume thats because this circuit is virtually no-load. I measured the voltage at the base of of the transistor, and its dead on 1/2 Vcc. Also, I looked at the voltage on a 'scope and its clean and smooth.

When I click the bypass switch back and forth, and adjust the output control for unity gain, the two sounds are almost identical. No bass boost at all. Just a very subtle treble loss. Like putting your tone control on "9". Almost unnoticable.

The funny thing is, I anticipated this thing as having extreme treble-boost, so my first version incorporated Jack's "stupidly wonderful tone control" variation. That control had little affect except to roll off even more treble like a normal tone pot. So I removed it to eliminate that variable.   

Edit: One correction: I used a 2N5088 transistor.

[Artie]

bump

[Artie]

Ok, I think I figured it out. Its so simple. It appears as though the Muffmaster has a 100k input impedance. (R1 in this diagram.) Thats a pretty good load on a passive guitar circuit. If I pre-buffer the input using my Duncan pickup booster, then set the output for unity gain, there's no difference in the sound at all.

Cool. I like circuits that make me think. 
Now . . . on to the next project.