Cgs synth

>Does anyone know if I can sub a BAT42 for the BAT48 in the CGS 81 dual

processor?

Look at the datasheets:
http://www.vishay.com/docs/85660/bat42,%20b.pdf
http://www.datasheetcatalog.org/datasheet/vishay/85664.pdf

1)Reverse voltage 40 for the BAT48 vs 30. How much signal will it see? As it
is back to back with another diode, it will only see the maximum of the
other diode's forward drop, which is in the order of half a volt. Well, we
ain't getting anywhere near 30 of 40 volts, so that won't make a differece.

2)Forward voltage drop. Both are around 400mV for 10mA through them. No
difference there. The drop for the is greater at 50ma though. Will this matter?

3)Forward current. 350ma for the BAT48. Only 200 for the BAT42. Hmmm....
Looking at the circuit we have 270k at one end connected to a summing node
on an op-amp. Summing node is always zero volts. Other end of diodes goes to
pots that can go between +/- 15. So maximum forward voltage across the 270k
is 15 - diode drop, which we will ignore for the moment. Using ohms law
V/R=I. 15 volts over 270000 ohms = 0.055555 micro amps. Okay, our current is
so tiny we aren't going anywhere near the BAT42's 200mA limit, so that isn't
a problem.

Going back to 2) datasheet doesn't give forward voltage drop values for the
current we are using, but we know it will probably be close enough between
the two diode types. We have worked out that we won't damage the part
because it is being used well within its specification. The only concern
will be its behavior at these undocumented levels.

Conclusion. Stick it in and try it. No harm will come of it. It will
probably do the job.

Reality: All these diodes are doing is providing a tiny dead band in the
middle of the pot's rotation, so that zero is easier to select. Any
variation in the diodes will only vary the width of this tiny gap. In all
likelyhood, you won't be able to tell the difference.

Hopefully next time you have a similar problem, you will have an idea of how
to find out the answer yourself.

Ken

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_______________________________________________________________________
Ken Stone sasami@... otherunicorn@...
Modular Synth PCBs for sale <http://www.cgs.synth.net/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>