Hello all. Noob question.

[Greenballs]

Hello.

I've been building pedals for almost a year now (mainly boost, OD and fuzz pedals) and have got to a point where I can buy a few 'mojo' parts without fear of frying them with the soldering iron.

I recently built myself a Sunface clone, using OC139 GE transistors, and it sounded great on the breadboard and great once I had boxed it up with no issues, until I tried to integrate it into my pedalboard.

During my experimentations with pedal positioning (I'm aware that the Sunface should be first in the chain) out of curiosity I tried placing the Sunface after a Jfet overdrive I'd built that has a buffer incorporated into the circuit and while it didn't sound horrendous, it was too bright sounding. It was after doing this that I noticed a loss of gain in the Sunface.

I thought this might be down to the power supply on my board (a Palmer PWT 12) which powers more pedals than it has outputs by means of splitter cables (although the Sunface is on its own isolated output) so I tried powering it alone with a Diago Powerstation and while some gain was recovered it still wasn't where it had been previously.

So, after all that, my question is, can a high impedance signal cause damage to GE transistors?

Thanks in advance!

[ElectricDruid]

Welcome Greenballs!

I don't see how the output from one pedal could really damage the next one, at least not if the circuits are well-designed. Protecting yourself from the outside world is basic stuff that any circuit has to do. The thing you said about "I'm aware that the Sunface should be first in the chain" makes me slightly suspicious because it's usually half-baked super-simple pedals that are fussy like that, and that might mean the Sunface is not well protected.

However, I'd say this is more likely a coincidence. You were doing stuff, and the Sunface started losing gain. So it's obvious to assume that the "doing stuff" caused the loss of gain. But it might have happened anyway, and you were bound to be doing *something* when it did.

I'd do some experiments with the Sunface on it's own. I think your idea about the power is good. Try running just the Sunface without the other loads on the power supply and see what happens. Try a different supply if you have one.

[Greenballs]

Thanks for the reply @ElectricDruid, much appreciated. I did wonder if it was more likely to be a power supply or a biasing issue.

Just out of interest, what could cause a GE transistor to become suddenly less efficient, an issue with the transistor itself or would it be more likely the components around the transistor that were at fault? Or a bad solder joint for example?

[KarenColumbo]

I'm probably not of much help - I've never had the problem of a transistor of any kind showing deviations in volume IF it was properly biased and be-circuited. I often had JFETs varying in volume for some time after fiddling around with source and drain resistances. But they all got a grip on it after some seconds. And GE transistors make the end of their (un)natural life span known by showing symptoms like "snowing".
Could you post a schematic of the respective pedal?

[Bunkey]

And GE transistors make the end of their (un)natural life span known by showing symptoms like "snowing".

Curiosity peaked.
Can you elaborate on this?

Ta 

[Greenballs]

I'm probably not of much help - I've never had the problem of a transistor of any kind showing deviations in volume IF it was properly biased and be-circuited. I often had JFETs varying in volume for some time after fiddling around with source and drain resistances. But they all got a grip on it after some seconds. And GE transistors make the end of their (un)natural life span known by showing symptoms like "snowing".
Could you post a schematic of the respective pedal?

Hi

The volume of the pedal is fine, no issues at all there, its the level of gain that has decreased. Here's the schematic:




As you can see, it's a fuzz face with a couple of trimpots added. I tweaked a couple of resistor values on the breadboard until it sounded as I wanted it to, so its not 100% faithful to the verified Sunface schematics that I found online.

I too am curious as to what you mean by 'snowing'.

[iainpunk]

i have a few of those OC139's and they seem to be very temperature dependent, more than the OC71 or AC127 for instance. are you in the same temperature room? have you tried a Föhn to warm the inside or the fridge to cool the pedal?

cheers

[Bunkey]

Have you double checked the trimpots? Some of the multi-turns seem to wander about a bit and take a while to settle down.

I'd set all my own biases right when I built the thing but it sounded well off-base and I haven't used it since. Really dark, woolly and just pants..
I double-checked it there and the 1.4v Q1 was sitting at a hair over 1v! Q2 trimpot is very sensitive too, half a turn (25t) takes it from broken to awesome - It's like a different pedal.

Based on this experience, trimmer/bias drift would be my best guess..

[aron]

Yeah, my thinking too. Trimmers.

[Greenballs]

i have a few of those OC139's and they seem to be very temperature dependent, more than the OC71 or AC127 for instance. are you in the same temperature room? have you tried a Föhn to warm the inside or the fridge to cool the pedal?

cheers

I've only played through the pedal in my kitchen, which I'm pretty sure is at a fairly consistent temperature. Good to know though, thanks.

[antonis]

Kitchen consistent temperature means NO COOKING..

[Greenballs]

Have you double checked the trimpots? Some of the multi-turns seem to wander about a bit and take a while to settle down.

I'd set all my own biases right when I built the thing but it sounded well off-base and I haven't used it since. Really dark, woolly and just pants..
I double-checked it there and the 1.4v Q1 was sitting at a hair over 1v! Q2 trimpot is very sensitive too, half a turn (25t) takes it from broken to awesome - It's like a different pedal.

Based on this experience, trimmer/bias drift would be my best guess..

I hadn't considered this as I wasn't aware that trimmer/bias drift was a thing, but I am now. Cheers! I'll have a look at it again later.

[duck_arse]

have you tried a Föhn to warm the inside or the fridge to cool the pedal?

Föhn = hair dryer?

[BJM]

Föhn = hair dryer?

Yes.... It's also a warm dry wind at the north side of the Alps mountains in Europe but I don't think Iainpunk was referring to that

[antonis]

No human being living under sea level can be conversant with mountain originated winds... 

[iainpunk]

No human being living under sea level can be conversant with mountain originated winds... 

i live in saintPetersBurgi'm not a time traveling Tsar Nicholas the 2nd
i live in the netherlands, yes yes, but Arnhem is about half above the NAP
i spend 80% of the time i'm home in my bedroom, upstairs, which is above sea level.
my Gf's home is at +73 meters NAP,
but yes, i meant hair dryer, not the winds.

cheers

[Bunkey]

No human being living under sea level can be conversant with mountain originated winds... 

i live in saintPetersBurgi'm not a time traveling Tsar Nicholas the 2nd
i live in the netherlands, yes yes, but Arnhem is about half above the NAP
i spend 80% of the time i'm home in my bedroom, upstairs, which is above sea level.
my Gf's home is at +73 meters NAP,
but yes, i meant hair dryer, not the winds.

cheers

That there's the makings of a song.

He lives in a houseboat, The Arnhem, a real fine vessel
Spends a lot of his time upstairs, above sea level.
Föhn, Föhn, Föhn propulsion!
Iain Schmaloer, comer and goer, at +73 meters.

[duck_arse]

Föhn = hair dryer?

Yes.... It's also a warm dry wind at the north side of the Alps mountains in Europe but I don't think Iainpunk was referring to that

indeed, the warm wind was the first translation I found, but I thought it a little impractical for the hobbyist/pedal builder. now, if you were some sort of king or tsar, it'd be a different story.

[BJM]

indeed, the warm wind was the first translation I found, but I thought it a little impractical for the hobbyist/pedal builder. now, if you were some sort of king or tsar, it'd be a different story.

Maybe if you're Swiss and want to dry wood for your DIY alphorn.......