Making an Big Muff emitter mod switchable?

[south_saturn]

Hey guys,

I know I keep coming in with these newbie questions.

I want to make the emitter mod on my big muff switchable with the stock mode. I built the muff on a tonepad board to triangle specs. I have a spare 3PDT switch so I'd like to give this a try. An indicator LED would be nice too.

Thanks for being patient and helpful so far

[aron]

What mod are you talking about? Is there a schematic?

[south_saturn]

Sorry I should really have posted the source of my info:

"Emitter mod: The 2 gain stages of the Muff are tied to the groud by emitter resistors (R12 & R16). These are 390 ohms in Russian models and 100 ohms in NYC models (exact value can differ between models). Jumpering these resistors (replace resistors with a wire) will increase "gainy-ness" of the unit, enlarging em will reduce the "gainy-ness" of the unit. A potmeter can be used to control this value although I noticed I usually used only one setting." from http://www.student.ru.nl/r.kerkhof/Taas/Mods/Big%20Muff.htm

Basically I want to be able to switch between a pair of jumpers and a pair of resistors which occur at different points in the circuit.

[jefe]

This mod should be easy with a 2PDT switch, and since you have a 3PDT you can include the LED. Have you tried the mod yet (without a switch)? Just curious, how does it sound?

It just so happens that I have the BMP Triangle breadboarded right now, and I was looking at the same mods page as you. I was planning on trying some different caps in the tone section tonight, but at some point I may try the emitter mod.

From beavisadio's page on switches:



Look at the lower illustration, using a SPDT - it shows how to switch between two resistors - you'll basically be doing the same thing, but you'll be switching from a resistor to a straight jumper. Using a DPDT, you can now switch between two resisters & jumpers, and then with a 3PDT, you can do the LED.

[Gus]

To do that you MIGHT want switch more than the emitter Rs.  Work out the bias change and gain ver operating point.

Is the sound change the operating point shift or is it the gain change or both?

Look in "The Art of Electronics" look for the BMP type bias circuit.

What is gainy-ness? 

Just build it and find out 

Here is a hint
decide what max value emitter resistor you want then calculate a parallel resistor value to so when added to the max value it gives you your wanted min value resistor.  The max value will always be in circuit and the || will reduce it so if you have a 390 and add a 390 in || you will have 195 ohms.  390 and 330 will be lower.

It will most likely pop when you switch the resistor value. there are ways to reduce the pop but that is extra parts and designing.  For you test reduce the volume to zero before switching to save you speakers

[south_saturn]

I haven't tried the mod yet but it is supposed to mimic the creamy dreamer tone and give a bit more of a wild fuzz tone.

That diagram from dano's site looks good but will it work for switching both resistors out simultaneously?

[jefe]

I haven't tried the mod yet but it is supposed to mimic the creamy dreamer tone and give a bit more of a wild fuzz tone.

That diagram from dano's site looks good but will it work for switching both resistors out simultaneously?

Yes, it will work if you use at least a DPDT. Just use dano's diagram with the SPDT as a reference, then multiply X2 (DPDT) for both resistors. Read that entire page at dano's site - it really helps you understand how switches work.

I'm not making this any clearer to you, am I? I can sketch up a better diagram later tonight if you like. I may even be able to test it out.

[south_saturn]

no no don't worry about that.

I'll have a read and figure it out this weekend, I need something to do while the women go shopping 

I'll get it to work but if I have any trouble I will no doubt come crawling back.

[Gus]

Jeff

Look at the circuits you posted there is NO resistor at all when the switch is switching not a good thing, bad pops........

The bringing in a parallel resistor like I posted will reduce the step response that causes the pop.

The pop can hurt speakers and your ears

[jefe]

I think I follow you Gus. So, I can leave my max value resistor mounted on the board, and wire a switch parallel to it. Then use the switch to "mix in" my parallel resistor to get a lower value. Would that work?

What if you have a make-before-break rotary switch? Would that reduce the chance of pops, or just make things worse?