question about theory behind biasing a rangemaster

[joelap]

Hey, question (based off of the austin treble blaster layout on geofex.com).

If I wanted to replace Rb1 with a trimpot in order to more effectively bias to -7V (or in my case using NPN 7V) on the collector, how should I set the boost pot when measuring collector voltage?  Arent you essentially by varying the boost pot changing the voltage going to the collector?  Or is it the output voltage being increased while the collector voltage remains constant?  I'm thinking about replacing Rb1 with a 50k trimpot and a 20k-30k resistor in series to be able to fine tune the biasing on the collector, and I'm not understanding the effect that the placement of the boost pot would have on collector voltage.  Is the boost pot irrelevent to collector voltage?

Thanks for the help.

Joe

[zachomega]

The Collector load is a contant 10k ohms on the rangemaster.  The output is taken from various points along that 10k ohm load which results in changing the output volume but not the load itself. 

Therefore it really doesn't matter where you have the volume control set. 

-Zach Omega

[joelap]

The Collector load is a contant 10k ohms on the rangemaster.  The output is taken from various points along that 10k ohm load which results in changing the output volume but not the load itself. 

Therefore it really doesn't matter where you have the volume control set. 

-Zach Omega

Ahhhh ok I see now.  There is nothing changing in regards to the collector, but the wiper is the point where it changes and has no effect on the collector.  There's something they didnt teach in electronics 1    thanks!

One final thing: since metal film and low noise caps are preferred for the rangemaster to keep hiss and noise down, would a trimpot increase that hiss?

[zachomega]

I built my rangemaster clone with all carbon film resistors and generic poly caps.  The thing I was picky about was the transistor itself.  I used a low leakage (under 50 micro amp) 2SB175 transistor.  All things considered, I think the effect is very quiet...especially given how many people criticize it for hiss.  With the thing all of the way up you can hear a bit of noise, but nothing terribly offensive. 

So to answer your question...maybe it will...but there are other factors you can look into to minimize noise.  I suppose your lead dress could have just as much influence over the noise of the pedal as the resistors or transistor.

-Zach Omega

[JonFrum]

For a great discussion of component types - in tube amps, but applicable here - read this:

http://aikenamps.com/TI_Aiken_Q&A.html