Rangemaster biasing / sensitivity to Re? (Answer: moderated)

[ChopSauce]

Hi there!

I'll hope that posting here will be as valuable as just reading. Searching here and around was of no help for my question:

- how sensitive is the collector voltage to Re?
(vs. Rg1)

RG writes that Rg1 should be no less than 27k and this value gives me a fair 6.7V with Re=3.9k

I wish trying Re=4k7 was easy but I can only clip Re as is my circuit, so there's no easy way going back if I try a 4k7 and find the voltage rise will be above bounds - for any Rg1 =< 82k... 

EDIT:

It didn't take long for me to decide to try it, so: Re=4k7 (instead of 3k9) gives collector voltage of 7.0V (*) (instead of 6.7V) for the same Rg1=27k
(using RG notations).

Now it's time to button it up and try it... 
___

(*) given the (low) precision of my measuring device.

[ElectricDruid]

Welcome ChopSauce!

When I built one, I bottled it and stuck a trimmer pot in there! (10K, I think) Then it was a question of playing it with the back off and tweaking it until I liked it.

[antonis]

Hi & Welcome, also..

Collector voltage is set by its resistor & current, the later been set by Emitter resistor & voltage..
Emitter voltage is set by 470k/68k Base bias divider resistors plus V_BE..
Hence, Collector voltage is sensitive to ANY of the above mentioned item value..

[ChopSauce]

Thanks!

I should have been aware of the pot technique before building it, of course... 

All my concern was how sensible it is, because there are very few resistor values available "out of the box" between 3k9 and the max RG-recommended value I don't remember right now so I feared falling out of range while going from 3k9 to 4k7.

Lucky it worked for me!

Now I'll have to find an input cap with the right value, but this is slightly out of topic.

[antonis]

If your concern is to find a precisely 5nF cap, your're right about "out of topic"..

P.S.
Grab the closer to 5nF E6 series cap value (i.e. 4n7) and earn peace of mind 'cause positive tolerance (we always think positively, don't we..??) will take care of the value disparity..

Input HPF formed by input cap and 470k//68k//h_FEX3k9 involves -3dB cut-off frequency deviation equal or greater than the one caused from 300pF difference (5n - 4n7)... 

[ChopSauce]

If your concern is to find a precisely 5nF cap, your're right about "out of topic"..

Excellent... 

Nah...

I'm currently testing the pedal with what I have available at hand: a vintage 10n ceramic cap salvaged from some junk device, which has deviated to roughly 8nF.

I was surprised that the pedal was enhancing so much of the mids with that value, so my previous post was something of a subliminary request for comments about the input filter cap value.

I'll stick to the standard value, then - thanks!

[willienillie]

I've been using 5000pF polystyrene caps.

https://www.allelectronics.com/item/cs-502/5000-pf-polystyrene-capacitor/1.html

[ElectricDruid]

The other mod I made to mine was to stick a rotary switch in it that selects different input cap value. I think it has 6 options. I rigged it so the standard value was roughly in the middle, and then tried the next-closest values on either side. Don't remember exactly, but it was a 1n, 2n2, 4n7, 10n, 22n, 47n type thing (those are roughly octaves).

[ChopSauce]

The other mod I made to mine was to stick a rotary switch in it that selects different input cap value. I think it has 6 options. I rigged it so the standard value was roughly in the middle, and then tried the next-closest values on either side. Don't remember exactly, but it was a 1n, 2n2, 4n7, 10n, 22n, 47n type thing (those are roughly octaves).

Good idea. I'll try a switch maybe...

[percyhornickel]

My rangemaster (npn AC127) has on/off/on (3 poles ) switch for input cap : 4.7n/4.7n/10n...   ...so I can have 4.7n /  10n (9.4) / 15n (14.N) and works really great.

Be aware rangemaster works better directly to a dirty channel or with a pedal with very low gain in front. I use a RAT in front...   ...I get a beautiful sound here. 

I put a 100k lineal potentiometer instead 68k, you can move it up and down and believe you will know when you get the right voltage for the sound.

I made a pcb design with the input caps if there´s somebody interested.

Percy

[iainpunk]

i love changing the bias on a range master, it just makes it a super versatile pedal. i like pulling the bias way up just over the gating threshold.
a gated, distorted trebble boost, love it!
i also recommend trying out different transistors if you have multiple. i love the OC171 and the BD140 the most.
i generally don't put in variable input caps, since 4n7 is perfect the way it is.

cheers, Iain

[percyhornickel]

I use 15n when I dare to myself to sing..     ..that way not all the glasses breaks at home .....           ....15n sounds great too.

AC127 is the only one I could get in a store in 2006...