Blending Two Transistors

[NoCoffeeForKitty]

My posting this means that I am on the verge of giving up and accepting that it is simply impossible, but I'm wondering if anybody here has any ideas on how to blend between two different transistors or even if it would accomplish what I'm hoping it would.

I'm new to pedal building (most likely obviously), and there's a two different transistors that I really like how they sound in this build, but they are radically different sounds. I'm hoping that it's possible to blend between them to reach all of the sounds in between. I know I can build a switch to go between them, but a blend knob would be far more useful.

I've considered the possibility of simply using three separate pots to control each part individually, but that seems like it would be bulky and ugly on top, and it would be a pain to keep all three knobs in the exact same position.

Is this even a possibility, or should I just give up now and go with the switch?

[induction]

Would you consider telling us what circuit and which transistors you're talking about? A link to a schematic wouldn't go amiss, either. It's hard to address your question otherwise. We'd just be guessing.

[NoCoffeeForKitty]

It's a modified Devi ever soda meiser circuit. I'm looking to change the third MPSA18 in the stock circuit between that and a 2N5088. I'm not sure if I'm allowed to post a link to the actual schematic. If so, I can post a link to that too.

Thanks.

[duck_arse]

please post circuit, yes.

you can build the front end, up to the offending transistor, then build that stage twice (a different transistor in each, obvs.). blend the two outputs with a pot.

also, as induction says, welcome to the forum.

[NoCoffeeForKitty]

http://tagboardeffects.blogspot.com/2010/12/effector-13-devi-soda-meiser.html?m=1

This is what I've been going off of.

So everything from the Q3 on would be built twice, right? So then would the wires connecting to 1 & 3 on the volume pot be connected to each side of the blend knob?

[duck_arse]

^ that, I'm afraid, is a layout. we need the circuit diagram, as I think that last stage gets a bit tricky.

[NoCoffeeForKitty]

http://www.diystompboxes.com/smfforum/index.php?topic=108126.0

sorry about that. I found the actual schematic posted at this link.

[PRR]

> change the third MPSA18 ...that and a 2N5088

"MPSA18 ...See 2N5088 for characteristics."

So they are "the same part" for engineering purposes.

This particular circuit is very funky, "shouldn't work". It does, but in a funky way, and with unpredictable interactions.

My inclination would be to build *two* complete circuits and add a cross-fade after that. Sorry if that seems like too much.

[duck_arse]

are you having this thing on the breadboard, or ewetube videos? if on the breadbord, here is an excercise - put your type 1 into the circuit and measure the voltages around Q3 and Q4. then swap to type 2, and remeasure. then post type numbers and voltages. if your meter has a transistor tester, give us the hFE readings as well.

[PRR]

That soda-thing's last "stage" has always baffled me.

I asked the Idiot what he thought. SPICE tole me (obvious once you see it) that the upside-down PNP's C-B junction is a diode and puts current into the NPN Base. Which conducts until the bottom of the 10K gets too low to support two diode drops.

And seen alone, the PNP's reverse Beta makes a big difference. This is never given on most data-sheets and is not normally controlled in production. It works out as the small-difference of two main diffusions which are critical for normal use. As long as both of those are OK, nobody looks at the small difference.

So it's not that two type-numbers sound different. It is that a part made Aug 1989 won't be the same (in this odd way) as a part made May 2001. They try to be consistent, but mostly for the numbers they are selling, not the numbers that nobody (but Devi) ever cares about.

[duck_arse]

ahh - so! a bazz fuss soda?