Easy Drive - How could you make this use 2 transistors?

[robbiemcm]

I was thinking about whether you could make the easy drive have two transistors.. will this even be worth it.. will it result in more gain? And I'm not sure how one would go about doing it, so I copied the schematic and would just like someone to tell me whether it's right or what changes I would have to make so that it would work.



(I removed the gain pot at the bottom because mine didn't work for some reason, it did nothing)

Thanks for any help you can provide,
Robbie

[lovekraft0]

My guess is if it works at all, it'll be an oscillator - two inverting stages plus feedback generally makes one (because the feedback is now in phase with the input), but since there's no bias on Q2's base, I'm not sure it'll do anything at all.

[WGTP]

Check out the threads about Darlinton circuits.  You can get really high gain and use a GE if you like.   

[robbiemcm]

So you're saying Q2 would have to have a resistor to ground between the capacitor and Q2. I was wondering whether it would, but I decided not to put anything there because there isn't one for Q1. This wasn't even theoretical it was just a guess, but maybe someone can tell me why Q1 doesn't need one.

[robbiemcm]

Bump..

Anyone? I still don't know what I'm meant to do..

[robbiemcm]

Please can someone help me with this, I can't find any useful information explaining how. Even if you don't feel like telling me, I'm sure someone can help me dig up some links that will explain how to add a second transistor in.

[petemoore]

  Not exactly sure, but I do see a 510k path from the base of Q1 to V+, that's enough to bias the base I think [not sure what the cap does], and teh diodes may have some biasing function, Q1Base biase is 'above' the transistor at any rate.
  Try throwing a 1meg from Q2base to ground...that should work for pulling the base to bias.
  Where is it...Geo...or AMZ...shows many ways to bias a transistor base.
  Resistor from base to ground...you see this around enough
  Resistor string...ground to base...base to V+ [a divider of sorts] look at LPB, notice it's V+ base bias resistor is 'X %age' larger than the one to ground.
  Resistor from base to collector...470k ? 1 meg ?
  Circuit Snippets, any of these schematics can be used to see bias setups.
  There are plenty of ways to do it, lots of choices, not sure of every detail or how that relates to your design...just look at schems, and resistors connecting to the base to get an idea of one bias type that will probably work.

[toneman]

On the tranny on the right,
a NPN tranny needs a positive bias voltage/positive current into the base.
No base biasing.
MayB a 270K to 470K to B+ 

Or ask RG or Joe.... 

T

[Steben]

Just omit the 0.1 cap between base Q2 and collector Q1! Instant biasing like in many circuits like the FF eg! Just make sure the collector1 voltage (resulting in the base2 voltage) is acceptable according to your taste. I suggest staring at 4.5Volts. Tweaking it (trimpot at collector to power) can result in assymetric gain in Q1 and Q2 (like in a Rangemaster).

But I concur in trying to use a Darlington instead of a single transistor in the stock Easy Drive. You will have more treble fuzz because of the higher input impedance.

[jmusser]

This circuit is so good in my book, that I wouldn't want to risk doing anything to the tone. It's been one of the few circuits for me that have been magic right off the drawing board. I'd figure that if you added another transistor to it, you'just have to call it something else, because it would cease being the Easy Drive.

[PenPen]

Just omit the 0.1 cap between base Q2 and collector Q1! Instant biasing like in many circuits like the FF eg! Just make sure the collector1 voltage (resulting in the base2 voltage) is acceptable according to your taste. I suggest staring at 4.5Volts. Tweaking it (trimpot at collector to power) can result in assymetric gain in Q1 and Q2 (like in a Rangemaster).

But I concur in trying to use a Darlington instead of a single transistor in the stock Easy Drive. You will have more treble fuzz because of the higher input impedance.

Err, don't you effectively GET a Darlington by simply adding another bi-polar? I remember seeing it on FolkUrban, you add a second trans, emitter Q1 to base Q2, then tie the two collectors together, and use the emitter on Q2 as the E for your new Darlington.

Here's the page:
http://www.geocities.com/tpe123/folkurban/fuzz/fuzz.html