Scott Dorsey wrote:
Phil Allison wrote:
Mike Rivers wrote:
There seem to be two common configurations, one with an input
impedance of around 10 ohms that can be driven by the speaker
output of an amplifier, and the other with an input impedance of
around 2.5 k Ohms, which can be driven by practically anything.
They all have a pretty low output impedance so they can drive
anything.
** Not quite true.
The input and output coils of reverb tanks are inductors, so the
impedance rises with frequency right across the audio band. The
numbers quoted in the published data are for 1kHz only PLUS the
normal input power level is less than 10 milliwatts.
The 8ohm input types cannot be driven direct from an audio amp, it
would massively over power them. Output impedance values vary from
a few hundred ohms to a few thousand at 1kHz.
By directly, he means that they use the same power amp that drives
the speakers in order to drive the reverb tank. There _is_ a
resistive attenuator in there.
Most[1] guitar amps have a drop somewhere about the input of the power
amp/PI with a separate driver. Having the power amp itself drive it
would be a feedback loop.
Having said that... that might be something completely awesome to play
with
[1] many have a digital reverb now, driven as if in an F/X loop.
The Fender AB763 schem has "1/2 7205" where the reverb return is - the
12AX7 to the left of that is the drive. They're all PDFs; a pile of 'em
he
https://schematicheaven.net/fender.html
It's all part of an attempt to keep the total parts count as low as
possible for cost containment. It's a problem since of course the
level into the tank changes as you adjust the total amp gain.
--scott
--
Les Cargill