Octave on the Omnidrive

[Mark Hammer]

I finally stuck the semi-finished Hollis Omnidrive I had made some time ago into a legended chassis, and fired it up the other night.  I omitted the boost switch on mine and also hard-wired the clipping diodes in one position without a "mode" switch.  That left two switches and 4 pots: gain, tone, blend, volume, octave on/off, filter on/off.  It's a fairly flexible unit though nothing that inspires me very much.  I'll try and sell it off cheap to somebody who doesn't have enough money to buy everything they want.

The most disappointing part is the octave function.  It provides a change in tone, but nothing that I'd call an octave.  I'm wondering if any others had a similar experience and what one might do to make it a little more obvious.  I'm certainly not expecting anything as robust as my Tone Machine, but something that provides a little more zip would be nice.

Any ideas?

[puretube]

maybe a symmetry issue?
- sorry, don`t know the circuit - (link?  )
(pot appliable like iirc, JC proposed for an other octave-doubler...)

[johngreene]

If you are using RG's layout and schematic, change R10 from a 10K to a 15K. That will make the rectified half match the clean level giving more octave. With 10K there the rectified portion is 1/2 the level of the un-rectified portion.

--john

[Mark Hammer]

Thanks for the idea.  I ended up doing a number of changes.  I tried 15k instead of 10k, eventually opting for 30k.  It also occurred to me that maybe the input stage wasn't really hot enough, so I dropped R4 from 100k down to 30k (I have a bunch of 30k resistors sitting around that I look for uses for), and increased C2 a bit to keep the bass.

The assorted changes ended up producing a bigger difference between octave and non-octave settings, though once again I wouldn't describe it as having an obvious octave-up tone.  A Foxx Tone Machine it's not.  Oh well, we tried.  I think I'm almost done futzing around with it, except for the fact that the clean/fuzz balance is thrown off by the extra front-end boost.  I'll stick a fixed resistor between C11 and the blend pot to offset that.