In article ,
Phil North wrote:
If the PS in the pre-amp is up to it and there's room, I'd add a pair
of cathode followers. This will make it compatible with pretty well
any amp you try to drive it from, and free from any likely cable
problems.
Does PS mean power source?
Power supply. Basically the transformer, rectifier and capacitors that
supply the HT (high tension) and LT (low tension for heaters etc)
There might be room if they aren't too big,
pic 5 in my original post has the bottom taken off. I don't think I'm up
to this yet though.
Well, it would just be an extra valve - something like an ECC82 would be
my choice.
If space is a problem, and you wish it to retain the same external
appearance, a decent op amp will do exactly the same job...
Just googled for op amp and found this:
"The op-amp is basically a differential amplifier having a large voltage
gain, very high input impedance and low output impedance."
It's also tiny in valve terms - but would need its own power supply.
They come in all sorts of types and have many applications. One such would
be as an output buffer to convert a high impedance to a very low one
without altering the gain, and the performance while doing this would have
absolutely no effect on the 'valve' sound whatsoever.
Would that be why it sounded good on Keith's triode amp (input
impediance 100kOhms) but bass weak on the Dynavox (input impediance
20kOhms)?
Absolutely. If you have a lower input impedance than the output one,
you'll loose bass at the very least.
In the days when valves were common for pro use, so were inter stage
matching transformers. A valve mic pre-amp would have both an input and
output matching transformer. With all that implies for cost and
performance.
--
*How do you tell when you run out of invisible ink? *
Dave Plowman
London SW
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