transistors in a DIP

[marc]

Could this 4 transistors in one DIP be used to build a more compact stompbox (big muff, jumbo tone bender, etc...)?

http://americanmicrosemi.com/newproducts/transistorarrays/pdf/mpq3904.pdf

marc.

[Paul Perry (Frostwave)]

You can certainly use transistors in a dip, but usually they aren't more compact than discrete transistors. If you want compact, go surface mount!

[Jay Doyle]

The advantage of using transistors in a DIP is that the transistors are matched pretty much as good as you can get them because they are grown in the same conditions on the same substrate.

For a BMP, this doesn't matter as they are used as AC devices and any tolerance variations in the caps and resistors used in each stage will throw off the matching. Also in the example that you show in your link the transistors are low gain.

One place where they ARE extremely useful is in making discrete opamps and specifically a discrete OTA that I am working on in a tremolo. Because an opamp's biasing arrangements usually rely on constant current supplies made by current mirrors (the 3080OTA app. note has a great writeup on this), DC matching is critical. Other cases include the input transistors where matching reduces CMRR and Input Voltage offset (and therefore input bias current) as well as overall "balancing" of the stages, especially when more than one differential amplifier is used in the circuit, as it is in the case of my OTA. FWIW, I am using a CA3086.

More than you needed to know but...

Jay Doyle

[Ge_Whiz]

If you're going to follow the 'transistors on a chip' line, you'd do better to play with the CMOS 4007. See

http://www.ee.nmt.edu/~thomas/ee321_f00/labs/lab12.html

I've built a nice homebrew distortion/compressor with this chip. Dirt cheap, too.