The how and why behind the mix control for a Small Clone clone?

[skiraly017]

So I added the mix control mod to my Small Clone clone by replacing the 20k resistor with a 50k linear pot in series with an 18k resistor. Works great, absolutely love it. My question is why does it work? I would think that you would replace the 20k resistor on the board with a 20k pot (25k since I have not found a 20k linear). Instead, I've effectively replaced the 20k resistor with a 68k resistor (50k pot + 18k resistor). So why does this work? How did I get from A to B? What would happen if I increased the value of the pot or the resistor? Any thoughts on this would be greatly appreciated. Thanks.

[Processaurus]

I'm guessing because I haven't seen your mod, but I'm pretty sure the pot + series resistor replaced the 20K resistor that sums the wet signal with the dry signal (that also goes through a ~20K resistor and gets summed with the wet using the classic reistive mixing circuit).  By making the wet signal's summing resistor larger compared to the dry, you turn down the wet signal, and get less of the chorus effect, because the effect is strongest with a 50/50 mix of the two, which is what you get when the pot is turned so it is a 0 ohm resistor, and all that is left is the 18K. 

The same mod would work for a flanger or phaser (works good on the P45), to achieve a more subtle effect.  Its a good one, I'm planning to do the same thing with my polychorus sometime, because the effect is so strong.  Polychorus Lite...

[nelson]

I would do the mod to the opposite resistor. Attenuate the dry signal.



For the polychorus an active blend control would be my choice. The vibrato sounds would be amazing, especially for feedback noise making.

[Mark Hammer]

For echo/delay boxes, a balance control that can have more wet than dry or more dry than wet is a good thing, but not for a chorus or flanger.  Why?  Because vibrato is produced by having all wet and no dry, rather than just more wet than dry.  A mix which is, say, 20% dry and 80% wet, is not particularly interesting.

So why is a wet-level control "interesting" in  modulated effects like flanger, chorus, phaser?  Because it adjusts the subtlety of the effect so that one can use light touches of it and reduce its obviousness.  The added pot reduces the level of the wet signal below a 50/50 mix. In a perfect world, the nominal value of the stock mix resistors would absolutely nail a 50/50 blend, yielding maximum effect.  In reality, the resistors used are almost always 5% tolerance resistors, which could make one a functionally higher real value than the other.  As a result, it is advisable to use the next standard value down, and add a pot.  The combination will allow you to address the worst-case scenario (i.e., the mix resistor for the dry signal is actually more than the mix resistor for the wet signal).  So, if the stock values were, say 27k and 27k, it might be the case that the dry side actually measures 28.3k and the wet side measures 25.6k, which would mix down to something favouring the wet over the dry.  By pîcking the next standard value down from the dry fixed resistor, we would move to 24k or maybe 22k for the wet side.  That would assure that even if the wet-side resistor was 5% over its nominal value, it would still be a lower REAL value than the dry one.  By adding in the variable resistance, we would be able to absolutely NAIL a 50/50 balance in spite of any tolerance issues, plus we would be able to reduce the amplitude of the wet signal to achieve subtler sounds.  For people who like to crank up the regen but don't want to have it in your face, being able to dial the wet signal into the background a little more is very helpful.

I hope this makes it clearer for you.  The basic idea is that the altered resistor values and added pot permit obtaining a 50/50 balance in spite of component tolerances, plus providing a means of getting subtler sounds suitable for rhytm sounds or just providing light animation to a sound without being too "effect-ey".  Personally, I like to install a variable wet control and a dry cut switch so that both subtle sounds and vibrato can be achieved.

[skiraly017]

As always, Mark Hammer lays it down and I pick it up. But why the 50k pot? Why not 100k or 250k? Enquiring minds want to know. 

[Processaurus]

For echo/delay boxes, a balance control that can have more wet than dry or more dry than wet is a good thing, but not for a chorus or flanger.  Why?  Because vibrato is produced by having all wet and no dry, rather than just more wet than dry.  A mix which is, say, 20% dry and 80% wet, is not particularly interesting.

My feelings too, 80% wet and 20% dry was a poor sound from my phase 45.   But the economy of eliminating a switch and leaving just one pot to give you vibrato or any subtle slight mix of wet can be attractive.  How about a pot with a center detente, like pan knobs on stereos.  Or for the 0-50%, then an immediate jump to 100% wet, using a pot with the NC switch, wired backwards, so when you turn it down it mixes more wet, up to 50/50, until you click the switch, which then kills the dry signal and you leaves the 100% vibrato.  The dry kill switch does let you have two presets, though.

As always, Mark Hammer lays it down and I pick it up. But why the 50k pot? Why not 100k or 250k? Enquiring minds want to know. 

Maybe the original modder felt like the full series 50K pot and 18K resistor gave the subtlest effect mix anyone could be bothered to step on a switch to get, and had useful variation over the entire travel of the pot.  If the minimum setting isn't subtle enough for you, though, the bigger pot will get you there.  A different taper to the pot can help get the right feel in that case.

For the polychorus an active blend control would be my choice. The vibrato sounds would be amazing, especially for feedback noise making.

It'll be the real deal.  Not to hijack this thread, but I want to get medieval with that box... but I should whittle down the options before I start drilling, theres so many things it could do by adding some extra circuits I have laying around to the already interesting existing circuit: rand-o-matic, dc-2, hybrid digital/analog memory man, VB-2, TZF, etc.  Maybe a clipping amplifier like the MS-20 filter in the regen path so it doesn't bite so hard when it oscillates.

[Mark Hammer]

If the stock mix resistor is 22k or thereabouts, my own inclination would be to use a 100k pot as well, though 250k would be overkill.  The idea is to move the effect a little more to the background.  If you want to outright kill the effect, you step on the bypass switch.

In some respects, the builder might be advised to use 1% resistors for the mixing to nail a perfect 50/50 blend.  On the other hand, there are so many points before the mixing node where signal amplitude can be altered by 5% and 10% tolerances that depending on just those 2 resistors to do it for you is a little foolish.  That's why I opt for the wet-level pot. Ideally, the lowest setting on the wet-level pot should still permit some effect to be heard.

For choruses, I also like to be able to cut the bass of the wet signal for a gentler, less wobbly chorus sound.  Of course, when you cut the bass of the wet signal, sometimes you need to turn its level up to yield the same "thickness" to the chorus sound.  That's yet one more reason why a mixing resistor for the wet side should be replaced with the next common value down plus a pot.  That way you can get subtler sounds with full wet bass, yet still dial up the wet signal a little more when and if you chop the bass.  I have this (bass cut on/off and wet level) on the Zombie I made for myself.  I loaned it to a buddy who told me that he never realy liked chorus pedals and never used them.  When he returned it to me, he said it was the first time he's ever really liked a chorus.  That's only one person, but I'd say "MIssion accomplished".  I also have these features on my Tonepad Heladito SC-clone.

In truth, the vast majority of chorus pedals have pretty much the same design, largely because the requirements for using BBD chips which only come in fixed delay capacities (512 stages, 1024 stages, etc.) dictate a lot about the design.  The differences between one model and another seem to stem from deliberate choices the designer made with respect to which part of the delay range they would aim for and how they would address aliasing and clock noise, given their chip choice.  If a slightly shorter delay was selected by the designer/s, then the clock rate will generally be higher, the bandwidth a little wider due to faster sampling and the filtering needed to control noise a little gentler.  But it won't sound as "thick".  Make it thicker sounding by increasing delay, and because one is clocking the same chip a little slower to do that, the sampling will be at a lower rate, the wet bandwidth reduced, and the filtering more severe to control noise.  The effect will be more obvious in some ways, but also a little sludgier i others.  I find that being able to cut the bass, adjust the wet level, and shift the delay range over can buy me a tremendous degree of flexibility and emulation of a great many desirable chorus tones.  You can make almost any unit very quickly lose its characteristic "personality" and adopt others...up to a limit.  That limit will of course be whatever the onboard lowpass filtering dictates.  Readers will have likely seen a number of commercial chorus pedals in recent years, though, that incorporate a "tone" control to brighten or dull up the wet signal.

[sandro]

Hi everyone, I read all the post with attention and I understood what kind of mod to do on the wet-mixing resistor. Now, I'd like to locate the same resistor in the ARION SCH-1, because I like the pedal but in some cases I find the chorus too present. Thankyou guys!