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I am wondering if I went hunting old electronics and I found an NKT275 white dot could I simply swap it for the BC108 in my Analogman Sunface? Are there other values that need changing as well? If it could be changed, could a toggle switch be added and the switch between them? (Is that what's happening with my Barber Trifecta?)









 

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You could swap and switch. Those old germaniums are heat sensitive so soldering with caution (or a heat sink) is recommended. Those Analogman pedals are worth a bunch of money. I’d think twice before modding.
Easiest solution is starting from scratch. It’s just a Fuzzface. I bet the Sunface schematic is around. Then you can put sockets for the transistors.
 

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^ what he said, but also, just swapping in random transistors may or may not work well because the circuit around it is built for different ones, which may have different gain factors or even different impedance. If replacing silicon with germanium things get even more hairy as Ge by defenition have leakage current whereas Si do not. Ge's can be hugely leaky in fact (so much so that the Stupid Simple Overdrive uses the leakage as the bias), and out of the lot you bought, you'd need to measure them up and find a bunch in the forward voltage and leakage range that are acceptable for the circuit.

Doesn't hurt to try (except desoldering is a bitch and sometimes risky). Build something new around it or sub into a pedal that has sockets already. Small Bear electronics has a bunch of good tutorials for simple (and more complex) fuzz circuits, including various versions of the Face, as well as how to measure and select yer transistors. Or try the SSOD I mentioned above (v2 or v4 if you want something with more bells and whistles, but the simplicity of v2 is a beautiful thing). The great thing about the SSOD is that none of the making-sure-it's-in-the-right-range applies as it does with classic fuzz designs, and there's few other parts. If you can't find it I have the schem cuz it's in me build queue.
 

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The advice so far is solid. What surrounds the transistor is predicated on the characteristics of the specific transistor. Many other transistors will work in the same circuit, but require adjustents to the surrounding components that neither you or I are sufficiently knowledgeable about to make.

What I would add to what has been suggested so far is:

1) Install machined sockets for the tranny swap so that nothing has to be heated and the PCB isn't placed at risk from soldering and unsoldering repeatedly.

2) Whatever transistors you are considering subbing, download the datasheet forthose transistors from that manufacturer to be sure of the pinout. Sometimes the very same transistor number can have different pinouts when made by a different company.

3) Corroborate that pinout, if possible, using the hfe setting on your DMM, if you have one. The socket for transistor-testing on the meter will show which is the emitter, collector and base pins. If you can't manage to get an hfe reading of at least 50 or so, then you probably have the transistor pins inserted into the wrong socket, and should reorient the transistor.

4) A bit over 20 years ago, Mike Fuller posted that the optimal hfe values in a classic Fuzz Face (which the Diaz essentially is) are 75-80 for the first transistor, and around 120 for the second one. That's not to say that other values can't sound good and interesting, but those are the values he recommended for constructing Fuzz Faces, and what he used for the "69" pedal.
 
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Discussion Starter #6
Thanks everyone. I think I will leave things as they are...
 

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Warning: If the NKT275 you're thinking of swapping in looks anything like the ones in the pic in your post, don't even waste your time. The prevailing opinion is that those transistors are a far cry (very noisy, for one) from the legendary NOS NKT275's which are about as rare as hen's teeth now. I bought one on E-Bay thinking I had the world by the tail only to later find out they sounded like crap in a treble boost pedal I had here (was tested and closely spec'd to the one used in the TB build, btw).
 

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Part of my DIY pedal build was swapping in/out transistors and diodes. Try it with a cheap kit pedal first to get an idea of the differences. You could also email Analogman for some insight. Might keep the magic smoke in your pedal a little longer.
 
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