Sound Lab Mark II 2N3904 question

[goat destroyer]

In rays board pic he replaces the 2N3904 with something else, what exactly is going on here and is this the recomended way to build or should I use the 2N3904s that are in the schematic and board layout with the Tempco in the middle just like on the layout? Im a hack and should probably be tackling an easier project but what the hell im going to go for it.

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[magman]

This part of the circuit appears to need matched pair of transistors and a temperature compensating resistor (tempco). It's almost certainly an exponential convertor for an oscillator, which is normally built in this way.

If you can match transistors yourself, this is by far the cheapest route (there are quite a few threads about this already, if you do a quick search).

If you don't want match transistors yourself (or buy matched transistors from Ray), you can used a matched transistor array that has 2 transistors in an 8 pin IC type package, such as an SSM2210 (as shown in these pictures) or an LM394.

It appears that Ray has designed the board so you can pick which option is best for you (either discrete transistors or an IC type package). You pays your money and make your choice.

Hope this helps

Magman

[iopop3]

I can only confirm what magman wrote. They are used by the expo converter in the oscillators and filter. If you buy the "Combo Pack 2" you get three pairs of matched 2n3904s.

I'm 15% into the panel wiring. Then I have mine all ready for the magic smoke test.