AMZ Overdrive Pro question

[DaveTV]

What's the best way to get more gain at the output of the Overdrive Pro? It seems as though the volume control needs to be all the way up in order to match the bypassed signal level. It would sure be nice to be able to give a little boost to the distorted signal.

[Rob Strand]

You lose a bit of signal on that on because of the tone controls.  You don't lose drive however because the tone controls are after the gain stage.

If you have a spare opamp put a non-inverting stage with a gain of 2 or 3 after the tone control.

[WGTP]

Wouldn't using 2 diodes on each side instead of 1 increase the output?  It may reduce the distortion some, but that should be insurmountable.  A lot of the distortion is coming from the op amp.  Or using LED's would increase it even more?  Or my favorite, 1 silicon and 1 LED.  

[acromarty]

Yes, using two diodes or changing them to something with larger forward voltages like LEDs will increase the output signal level, and reduce the amount of clipping at the same setting of the drive pot.
With this type of circuit most of the distortion comes from the diodes, modified by the tone circuit which follows. The drive pot controls the gain of the opamp stage driving the signal into clipping across the diodes. Remember that the diodes will start to clip at a signal level of about 0.7V for silicon diodes, while the opamp can produce output signals up to at least 5-6V even with something basic like a 741. A modern rail-to-rail opamp will output signals almost up to the 9V supply, i.e. nearly 4.5V peak-to-peak.
The diodes then clip the output from the opamp to a maximum signal level equal to their forward voltage, 0.7V peak-to-peak. More drive gives a heavily clipped output signal more like a square wave with lots of harmonics, less drive gives clipping only at the peaks of the signal and a smoother overdrive.
Two diodes gives clipping at twice the signal, 1.4V peak-to-peak, but less of the input waveform will be squared off. LEDs typically have a forward voltage of around 2V so give a larger signal and less clipping. The type of diode also has an effect on how sharply the clipping occurs, depending on their voltage/current characteristics.

Sorry for the long discussion :-)

[Rob Strand]

Wouldn't using 2 diodes on each side instead

It works but yes it does affect the tone a bit.  IIRC if you used a dual opamp there is a spare opamp on the unit.  A post EQ boost *only* increases the level.