Small Clone Flanging Question - Mark Hammer

[Rayman]

I was wondering if it is possible to add the "delay time" control from the Ibanez SC10 (schem link below) to the Small Clone.

http://www.freeinfosociety.com/electronics/schempage.php?cat=1

The SC10 Delay Time control gives a real "flanging" type effect to the signal.  The circuit comes off the "Depth Control" pot which is normally to ground on the Small Clone.  I may be simplifying this, but could the SC10 "Delay Time" circuitry (starting with Q10) be added to the Small Clone?

[Mark Hammer]

The HF clock generator simply puts out a clock pulse corresonding to the voltage it sees at the appropriate input.  That voltage could be a varying one from an LFO, a steady one from a DC source, or some combination of the two.  Any modulation pedal that incorporates a "manual" (AKA "initial", "delay") control in addition to rate and depth, essentially combines varying proportions of fluctuating and DC sources to feed the clock generator.  So, in principle, yes you can, though obviously not in any manner that is easily adapted to the existing board, whether EHX, Tonepad, or some other 3rd party.

The simpler thing to do is just change the value of the 150pf clock-range cap.  You won't get the continuous control of the SC10 format, but you will be easily able to get repeatable sounds with a toggle, without having to mess with add-on boards and what not.  Finding a spot to install a toggle is easier too.

A useful set of ranges could be easily nailed by placing a second cap of 100pf in series with the existing 150pf unit.  Wire up a SPDT 3-position (on-off-on) toggle such that the common goes to the junction of the two caps, and each outside switch lug goes to the other side of one of the caps.  That will nail you effective capacitances of 150pf, 100pf, and 60pf, which will score you thicker chorus (stock), thinner chorus, and flangier chorus (suitable for nice Leslie sims).  I suppose you could also consider 82pf instead of 100pf, giving you 150pf, 82pf, and 53pf values and their associated ranges, but I think the 150+100 combo will work out well enough.  I have something like that on my Zombie Chorus, and I quite like it.  There will be a slight click/pop when switching ranges, but it's not the sort of thing you'll do mid-song anyways.

Do note that you will NOT be able to achieve the more robust flanger sounds in the absence of any regeneration.  Adding regen to this chorus starts to make things more complicated than they need to be.

[Rayman]

Thanks Mark.  I saw the 150pf cap change in your previous posts.  I'll try subbing smaller cap values.  I was wondering if the SC10 delay time control is doing anything different than achievable with just changing out the 150 pf cap.  I read a few posts that said the "flange" type effect is subtle, and that the 2.2uf cap at the LM358 would have to be changed as well as add the feedback signal.  With the SC10 delay time control, I get a rather significant flange "type" effect.  It doesn't do jet airplane sounds, but it gets me close to "Barracuda" without an actual flange pedal.

Thanks again, I'll swap out the 150pf and see if that does it for me.

[Mark Hammer]

The frequency of the clock generator is a function of both the timing cap AND the voltage it sees at the input.  The cap value is normally selected to produce a given clock range with the anticipated input voltage that will result in a given delay time from a BBD of known capacity.  So, if you were using an MN3008 (2048 stages) instead of an MN3007, you would need to use a 75pf timing cap to achieve the same delay-time range (and sonic effect) with that input voltage range from the LFO source.

Note that since the notch-filtering effect is considerably less noticeable once the delay range starts to move in an upwards direction (e.g., 6-16msec, as opposed to 1-10msec), there is little point in using very slow sweeps when designing a chorus.  As a result, while many choruses can sweep as fast as a flanger, most will not sweep as slow as one (i.e., they only use part of the overall speed range that a flanger might use).  In this instance (flangerizing a Small Clone), I doubt whether there is anything lost since the complete absence of regeneration/feedback will make the slowest speeds not particularly appetizing anyways.

Long story short, I doubt whether you will need to change anything in the LFO circuit.

Finally, since the SC is designed around an anticipated clock range, the lowpass filtering intended to reject clock noise from the audio path is set lower than it would if this were a flanger with a noticeably higher clock range (for a shorter delay time).  One of the unintended consequences of that is that some of the harmonic content that would normally be pleasantly notch-filtered at the shortest delay times will simply be absent here.  In other words, even with regeneration, the flange sound would not be as pleasing as it would in a unit designed explicitly for flanging.  That doesn't mean you can't get some damn fine sounds out of it that would normally require a flanger to achieve, but do not expect the full range of what a true flanger can deliver.  I imagine the same is quite true of the SC10 as well.

[Rayman]

Mark,

Thanks for the well explained answer.  I changed out the 150pf with a 30pf and it did what I wanted.  I also increased the 2.2uf to 6.8uf and there was little affect, as you mention above.  Appreciate it.

Ray