Ib on a rangemaster

[Fast Pistoleros]

hello, I was just thinking if there is a reason to mess with R2 of the voltage divider on a rangemaster? Is there not a stiff bias where the voltage divider sets the Vb and Ib ?  if so, then couldn't you put in a transistor of certain characteristics, like proper leakage and gain for example , and it would basically fall in the load line and operate like a basic common emitter amp?

I am learning a little bit more in school and now question are coming up as to why its so complicated to bias out a RM or a tonebender for example.  I appreciate and thank in advance for any information or help. thank you.

[PRR]

> Is there not a stiff bias where the voltage divider sets the Vb and Ib ?

Stiff? Rule-of-thumb: compare emitter resistor to lower base resistor. 68K/3.9K is 17. To be 10:1 "stiff", the transistor hFE must be 10 times higher: 170.

Does OC44 have hFE>170? Does *every* OC44 in the bucket have hFE>170?

No. Sheet says 40-80. In those days, hFE>100 was uncommon.

So the bias is not "stiff" and the bias will be different with every change of hFE. (And leakage, though it has been too long since I cared about Ge leaking to know what might be reasonable.)

To get "stiff" we would look at 3.9K, multiply by minimum hFE, then divide by 10. 3.9K*40/10 is 16K. What will 16K (or less) input resistance do to guitar tone? It will reduce bass-mid slightly and reduce treble a LOT. Tone-suck. Some of this is useful in a fuzz, but 16K may be too low to be good.

> then couldn't you put in a transistor of certain characteristics, like proper leakage and gain

One pedal, yes.

But when the rock-shop orders *thousands* of pedals, at LOW cost, SOON, hand-selection of transistors kills your business.

Transistors used to cost real money for low performance. Today we could do it "better". But the old ways still have charm.

> a reason to mess with R2 of the voltage divider on a rangemaster?

It sounds different for every mis-bias. The (mis-)bias YOU like may not be the "classroom" bias. (Whatever that would be.)

[Electric Warrior]

Stiff? Rule-of-thumb: compare emitter resistor to lower base resistor. 68K/3.9K is 17. To be 10:1 "stiff", the transistor hFE must be 10 times higher: 170.

Does OC44 have hFE>170? Does *every* OC44 in the bucket have hFE>170?

No. Sheet says 40-80. In those days, hFE>100 was uncommon.

So the bias is not "stiff" and the bias will be different with every change of hFE. (And leakage, though it has been too long since I cared about Ge leaking to know what might be reasonable.)

It depends a lot on which datasheet you refer to.



The yellow jacket Mullards Dallas used to use sure can go up that far. The one I own measures around 200. Leakage is low.

But yeah, there's a wide spread of gains and not every transistor is that gainy. For consistent high gain one would have to look for a different type.

[Fast Pistoleros]

right on, I got ya, this helped me out a lot and explains a lot. yeah, school doesnt  really teach much as far as audio like this goes, I think its more computer/comm/system/tech repair related for the most part. We are in the common amp section and looking at common emitter/base/collector circuits ..my textbook has basically a rm circuit on one of the figured examples for ce amps except they are using a 2n3904 npn in the book.

I probably should of asked on the benders instead of a an RM ..I though an RM would be a more simple way to look at it I was thinking ..I have the RM down but still cant get a any fuzz working properly other than the basic 2 tranny fuzz face. This is where its killing me, I can do a RM and a basic fuzz, but other stuff like the benders wont turn out ..killing me!

I ran an experiment with soft/hard clipping over the weekend and cant get any results either lol..I might have to post a breadboard picture and let you guys see my diode clipping set up ..I thought  the LED's would turn on and off like you see in the bRats ..but maybe I should go back to biasing the circuits and put off diodes until later.  I set up the soft and hard clipping just liek the example but the diodes do not really do anything ..some cut the volume down is all. the basic ce 2n3904 amp sounds amazingly incredible for what it is ..all 7 components of it lol .

and I want to post a public thanks to all the forum members for the tutorials - I am now rolling my own vactrols !! going to attempt a comp with one of my homemade optocouplers soon!

[Gus]

Look at the Brian May treble boost note the 22k