Adding a transistor selector switch to a RangeFinder
- Thread starter BJG
- Start date
It can be done, but can I ask why?
Not sure you'll gain a ton vs the biasing issues you may have. I.e., the bias setting that's best for one transistor may not match the next. For Si, this is much less of a problem but for Ge, it could be a big issue.
If you find 2 germs that sound good without rebiasing, then yeah, a 3pdt will work.
You can usually get by with 2 poles, but it's probably not worth the effort in this circuit/easier to just mount them to the switch.
Get a switch with lugs, not pc pins, and wrap the legs through it for an easier time soldering. Match C, B, and E on each side and to the PCB.
Not sure you'll gain a ton vs the biasing issues you may have. I.e., the bias setting that's best for one transistor may not match the next. For Si, this is much less of a problem but for Ge, it could be a big issue.
If you find 2 germs that sound good without rebiasing, then yeah, a 3pdt will work.
You can usually get by with 2 poles, but it's probably not worth the effort in this circuit/easier to just mount them to the switch.
Get a switch with lugs, not pc pins, and wrap the legs through it for an easier time soldering. Match C, B, and E on each side and to the PCB.
I have an OC76 and a CV7007 that bias out within .1V of each other when swapped and I can't decide which one I prefer so I figured why not both. Ive been swapping them back and forth for a while and decided I like both and they feel different enough to have in one circuit. The OC76 has a little less low end and more aggression while the CV7007 feels a little thicker/smoother.
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Feral Feline
Well-known member
You can order a PCB for transistor swapping:
MOONN WHYNOTBOTH? 2 transistors
MOONN WHYNOTMORE? 4 transistors
There used to be a few other places offering such a PCB, but I can't remember who and can't find the answer in my notes.
It's not hard to wire it up yourself, though...
More than likely, you'll want to use the 3PDT method:
When there's a common-leg, you can get away with a DPDT
Here's a 3-transistor Rotary option, in case you find yet one more transistor you like:
or
If you need to adjust the bias...
Lastly here's a Cornish thing that may inspire some extrapolation...
MOONN WHYNOTBOTH? 2 transistors
MOONN WHYNOTMORE? 4 transistors
There used to be a few other places offering such a PCB, but I can't remember who and can't find the answer in my notes.
It's not hard to wire it up yourself, though...
More than likely, you'll want to use the 3PDT method:
When there's a common-leg, you can get away with a DPDT
Here's a 3-transistor Rotary option, in case you find yet one more transistor you like:
or
If you need to adjust the bias...
Lastly here's a Cornish thing that may inspire some extrapolation...
Final Update:
I did a bracket style competition with the Ge transistors I had and originally landed on the CV7007 as my classic Rangemaster sound with a low gain MP39B as option two. I was about to wrap it up when I decided to throw a silicon PNP in there.
All the germaniums sounded like different versions of a Rangemaster while the silicon made it sound like a completely different pedal. There was a little high-gain buzz at first and the bias was high so I had to add some resistors to clean it up and it sounds great now. The silicon has a totally different EQ curve and gain characteristics than the CV7007.
I'm still new to super new to this, but I think I correctly diagramed out what I landed on. Before I box it up, I need to decide if I want the option on a toggle switch or another foot switch. I'm loving how many different sounds I can get with the capacitor array and transistor switch.
I did a bracket style competition with the Ge transistors I had and originally landed on the CV7007 as my classic Rangemaster sound with a low gain MP39B as option two. I was about to wrap it up when I decided to throw a silicon PNP in there.
All the germaniums sounded like different versions of a Rangemaster while the silicon made it sound like a completely different pedal. There was a little high-gain buzz at first and the bias was high so I had to add some resistors to clean it up and it sounds great now. The silicon has a totally different EQ curve and gain characteristics than the CV7007.
I'm still new to super new to this, but I think I correctly diagramed out what I landed on. Before I box it up, I need to decide if I want the option on a toggle switch or another foot switch. I'm loving how many different sounds I can get with the capacitor array and transistor switch.
BuddytheReow
Moderator
(I could be totally wrong in my explanation here, so keep that in mind)
The Ge transistor is biased to 6.75V (trim is maxed out, so I can't get to the recommended 7V). When I first auditioned the Si transistor the voltage jumped to just under 8V. I originally put a 100k pot to ground off the Si transistor to bias it, but found that the pot on full brought me to 6.95V, so I just replaced it with a fixed resistor. When I put together the Si circuit on strip-board, I could add a trim in case I replace the transistor in the future and need to re-bias.
The Ge transistor is biased to 6.75V (trim is maxed out, so I can't get to the recommended 7V). When I first auditioned the Si transistor the voltage jumped to just under 8V. I originally put a 100k pot to ground off the Si transistor to bias it, but found that the pot on full brought me to 6.95V, so I just replaced it with a fixed resistor. When I put together the Si circuit on strip-board, I could add a trim in case I replace the transistor in the future and need to re-bias.
Couple follow-up questions on this approach, as I'm working on a similar implementation...
1. Even with transistors with consistent biasing (I'm using silicon), I'm getting the dreaded pop when switching. I can live with it, but is there a way to avoid it? Also, can it damage my other effects or amp with the spike?
2. If I add a gain pot off the emitter before ground, can I still tie the emitters together and get away with a dpdt?
1. Even with transistors with consistent biasing (I'm using silicon), I'm getting the dreaded pop when switching. I can live with it, but is there a way to avoid it? Also, can it damage my other effects or amp with the spike?
2. If I add a gain pot off the emitter before ground, can I still tie the emitters together and get away with a dpdt?
Kashi
New member
Could someone do a diagram for dummies?
I'm building a Trumpeter fuzz and would like to have a dpdt for Q2 Silicon/ GE.
Edit: finished a stock Trumpeter,
Would like a transistor selector or a Rotobone, any help, tips or Instructions welcomed.
Thanks!
@Feral Feline
I'm building a Trumpeter fuzz and would like to have a dpdt for Q2 Silicon/ GE.
Edit: finished a stock Trumpeter,
Would like a transistor selector or a Rotobone, any help, tips or Instructions welcomed.
Thanks!
@Feral Feline
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Feral Feline
Well-known member
Well, both emitters are connected to ground, so you don't need to put the emitter-legs on the switch.
I've boiled the second diagram in post #4 and what's in the Plush-Cornish diagram/layout right down to what should work for your Trumpeter build:
DPDT Transistor-Swapper
In this case both emitters are going to ground so they don't need to be swapped out, just the Bases and Collectors.
If you've got a circuit that the emitter doesn't go to ground you can still swap out two transistors: add a pole to the switch,
ie make it a 3PDT ON-ON and add the emitters to the switcherooniki.
Plenty of examples online of switching out two transistors, this is mine.
BTW, that's not gibberish in the diagram, that's top-secret code.
(see if you can decipher what it says!)
In this case both emitters are going to ground so they don't need to be swapped out, just the Bases and Collectors.
If you've got a circuit that the emitter doesn't go to ground you can still swap out two transistors: add a pole to the switch,
ie make it a 3PDT ON-ON and add the emitters to the switcherooniki.
Plenty of examples online of switching out two transistors, this is mine.
BTW, that's not gibberish in the diagram, that's top-secret code.
(see if you can decipher what it says!)
As for the B50k vs C50k... you'll have to try both to see what you prefer, but I'd start with the B50k and see if there's any bunching up ie you turn the pot and nothing happens until the last bit of rotation — if there is this sense of bunching up, then the C50k may alleviate that.
If there's no bunching or sudden jumps in the rotation of the B50k, just a smooth transition, then job done!
Kashi
New member
@Feral Feline
Thank you so much.
Beautiful diagram.
I'm in love with this circuit. Really want to learn & explore this one. Should get into breadboarding.
Thanks again!
Thank you so much.
Beautiful diagram.
I'm in love with this circuit. Really want to learn & explore this one. Should get into breadboarding.
Thanks again!