Mixing Modes on the Hyped Fuzz with a Potentiometer

[debrad]

A friend of mine has asked if I can build him a Hyped Fuzz with a "Blend" or "Mixing" knob instead of the 3 way Mode toggle.

In my research, I came across a post from @Grubb (Hyped Fuzz Mode Blend) who was trying to do the same thing but didn't receive any answers to his questions so I will ask again with the hope that someone more knowledgeable than I will chime in with some words of wisdom (or maybe @Grubb ploughed ahead and can share the results...):

1) Can I replace the 3 way toggle with a potentiometer which would give me Fuzz 1 at one end of the rotation, Fuzz 2 at the other end, and a blend of the two in between (I realize that I may lose the boost function, he's OK with that, but I am also thinking that I could use a switch to toggle between the blended fuzz path and the boost path if he wants...).

2) Would it work to install the potentiometer where @Grubb suggested below (Scooped path goes from R26 to one outside lug of a pot, Full path goes from R27 to the other outside lug of a pot, and lug 2 connects to R28)?

3) What would be an appropriate resistance for the blend/mix potentiometer...something small (under 50k to minimize the impact on the values of R26 and R27), something between 100k and 500k, or something larger?

 

[jwin615]

I think using a MN or AC dual pot here could work. You could try a regular pot but I think you'll have adverse effects from the loading of the opamp output. I would stick to a low value pot for that reason. I don't think I've seen MN in less than 25k.
A dual linear pot may work as well.
I would cut the carbon trace on each wafer at the extreme(off) end of whatever dual pot you use. That way, when the wiper hits that position, there is absolutely no signal.

If that doesn't make sense, I can maybe elaborate some more to ight. A little busy this afternoon.

 

[Grubb]

@debrad I haven't tested it yet (due to the long and constantly-changing list of projects I'm working on), but my schematic did end up with a B10K pot blending both paths. The advice I got on another forum was that the proximity to the opamp stages was a benefit - but @jwin615 has pointed out a potential issue with that so I'd also be keen to hear more.

 

[debrad]

Back again to let you know that I finally got my Hyped Fuzz built now that Canada Post's strike is over and my parts were delivered.

I implemented a blend between the "Scooped" and "Full" paths by replacing the toggle switch with a 200k 100k MN dual pot as outlined by "WalterW" in this thread on the TalkBass forum:

https://www.talkbass.com/threads/ultimate-no-load-ungrounded-blend-pot-pics.1096449/

It seems to work in the sense that I definitely get Scooped at one end of the rotation, Full at the other end of the rotation, and a 0/50 combination of the two at the centre of rotation; however, I'm not really hearing much of a gradation in between...it's more like Scooped from 0-49%, both at 50%, and Full from 51-100%.

Do you think I've done something wrong, is this the "nature of the beast", or do you think I need a different pot value (higher, lower)?

 

[thunderaxe]

lower pot value. the lower the pot value, the less separation there will be between the extremes of the pot. remember that an M/N pot is actually two pots, with both being at 100% (or 0 resistance) in the middle. so if at 49% and 51% of the pot's rotation you can only hear one or the other effect, then those are the resistance values that you would want at the extreme ends of the pot. so i would go with the lowest-value MN taper pot you can find.

if you you can't find a low enough value MN pot you could look into R.G. keen's panner circuit as a way to have 100% of both signals in the middle. if you only want 50% of each signal in the middle, a simple wiper-outpot blend pot ought to do it.

 

[debrad]

Thanks @thunderaxe , I edited my note above because I had actually used a 100k MN taper pot rather than a 200k. I replaced that 100k with a 20k and there is a slight improvement but it's still mostly on/off (there is SOME blend between 11:00 and 1:00 on the pot rotation). I think 1k or maybe even 10k might help but I'll have to see if such a thing exists (I'd also like to look at the RG Keen "panner" you mentioned and the blend control I used to mix "wet/dry" on a compressor I built). Otherwise, the guy I'm building this pedal for seems OK with it working the way it does...

 

[thunderaxe]

Thanks @thunderaxe , I edited my note above because I had actually used a 100k MN taper pot rather than a 200k. I replaced that 100k with a 20k and there is a slight improvement but it's still mostly on/off (there is SOME blend between 11:00 and 1:00 on the pot rotation). I think 1k or maybe even 10k might help but I'll have to see if such a thing exists (I'd also like to look at the RG Keen "panner" you mentioned and the blend control I used to mix "wet/dry" on a compressor I built). Otherwise, the guy I'm building this pedal for seems OK with it working the way it does...

the panner can be found here:

http://www.geofex.com/Article_Folders/panner.pdf

if your browser is like mine you'll have to open it in a new window and then get a warning message saying it can't be downloaded securely (presumably because it isn't from an HTTPS server) and choose to save it anyway.

you can also find it in use in the pedalPCB bootleg overdrive (JHS moonshine V2) where it's used for the clean blend, and the pedalPCB caesar chorus (walrus julia) where it's used for the wet/dry blend. the caesar/julia uses slightly different resistor values to get a blend that's a little more than 50% of each in the middle. presumably that just makes for a more pleasant sweep. you can also play around with these values to get the ideal blend and volume in the middle.

 

[Bricksnbeatles]

What if you put a 33k resistor in parallel with each gang of the MN pot. That’ll give you essentially a 25k pot with a taper that has more gradual taper in the middle making the blend more subtle (essentially an MN pot that has a C taper in 50% of the rotation instead of a linear taper in 50% of the rotation)

Edit: not the greatest illustration since I don’t have graph paper on hand, but this is the taper you’d get

 

[thunderaxe]

^ ooh, i like this idea. adding a parallel resistor changes both the total resistance and taper of the pot, and this is a rare instance where both things would be useful to you

 

[debrad]

Now that I have replaced the original 100k MN taper pot with a 20k pot, would that give me 12k effectively and will the resulting taper match with what @Bricksnbeatles has drawn above? Is the trial and error the best way to find the appropriate parallel resistor or was there a specific reason why 33k was chosen above (i.e. my 20k pot and a 7k parallel resistor should give me 5.1k, correct)?

For my second question, by saying "a ?k resistor in parallel with each gang", do you mean one resistor across lug 1 and 3 of the top gang and a second resistor across lug 1 and 3 of the bottom gang or some other arrangement? Also, does the fact that I have cut the trace between the "ground" lugs and their carbon tracks have any impact on how I apply this parallel resistance?

 

[Bricksnbeatles]

No that I have replaced the original 100k MN taper pot with a 20k pot, would that give me 12k effectively and will the resulting taper match with what @Bricksnbeatles has drawn above? Is the trial and error the best way to find the appropriate parallel resistor or was there a specific reason why 33k was chosen above (i.e. my 20k pot and a 7k parallel resistor should give me 5.1k, correct)?

For my second question, by saying "a ?k resistor in parallel with each gang", do you mean one resistor across lug 1 and 3 of the top gang and a second resistor across lug 1 and 3 of the bottom gang or some other arrangement? Also, does the fact that I have cut the trace between the "ground" lugs and their carbon tracks have any impact on how I apply this parallel resistance?

I chose 33k just because of the shape of the taper it would result in, and I thought ~25k might be an appropriate value. Now that I see you tried 20k and still don’t have the taper you want, I’d say maybe a 6.8k to give you roughly the same smooth fine adjustment in the middle of the sweep down with the total pot resistance at 5k

 

[debrad]

I have some 6.2k resistors but I just tried them and I think that the steps I took in converting these MN taper pots to "no load" (i.e. creating a physical break between the ground lugs and their respective tracks) MIGHT present a problem.

For one set of lugs, when the pot is fully "off", I measure 6.2k between the wiper and the "output" lug where I used to measure "open". Once the wiper passes over the "cut", I measure almost 20k between wiper and "output" and that declines to approximately 2 ohms at the centre of rotation (and remains at 2 ohms from the centre of rotation to "fully open"). The same is true for the other set of lugs...just in the opposite direction of rotation obviously.

I put the 6.2 parallel resistors onto the 20k MN pot that I didn't modify for "no load" to see if the results looks more promising...and they did:

1 ohm between "input" and "output" at "max" setting, 3.5 ohm at the centre of rotation, and 4.7k at the "min" setting!

Now the real test will be whether that 4.7k is enough resistance to stop the "inputA" signal from bleeding into the "inputB" output when "A" is set to "min" and "B" is set to "max". If not, I guess I just tweak the parallel resistance value until I find the best fit...

 

[debrad]

Well...still not all that much blend but a little better than the 20k pot alone and the individual inputs appear to be well separated at the min and max postions (also DEFINITELY better than the 100k pot I started with)! Thanks everyone!!

Interesting side note...the parallel resistors do some strange things at the "max resistance" settings. I mentioned that it measures 4.7k at that point but, as you slowly turn the pot, the 4.7k jumps up beyond 5k then rolls off to the 3.5 ohm measurement at the centre point of rotation. Should I be grounding that "min" lug now that I'm not using the "no-load" cut in the trace?

 

[jwin615]

Well...still not all that much blend but a little better than the 20k pot alone and the individual inputs appear to be well separated at the min and max postions (also DEFINITELY better than the 100k pot I started with)! Thanks everyone!!

Interesting side note...the parallel resistors do some strange things at the "max resistance" settings. I mentioned that it measures 4.7k at that point but, as you slowly turn the pot, the 4.7k jumps up beyond 5k then rolls off to the 3.5 ohm measurement at the centre point of rotation. Should I be grounding that "min" lug now that I'm not using the "no-load" cut in the trace?

Not sure but that's probably the "no load " mod causing that. Not sure if that needed to be done. Reversed pan pot wiring should have worked but whatever works in the end.

 

[debrad]

I may not have been clear @jwin615 but this new strange behaviour (4.7k at max resistance and a higher resistance (5.2k) as I turn the pot towards "min") is happening with the un-modified pot (i.e. the one that I didn't cut the traces on) so, if anything, it would only be due to the parallel resistance I've added...just didn't want you to think I was still fighting with the "no-load" option...

 

[Feral Feline]

Some more fodder for your consideration...


I would look at the VFE Blueprint schematic, it's a delay, and other circuits that blend dry with wet signals.


I've been working on a Slapback Delay idea based on the VFE, and here's what I'm talking about, essentially:...






You can plug in values from the aforementioned VFE delay, right up at the top of the schem.










Electric Druid's slapback delay uses the same thing as well, but the wiper of the pot goes to VB not to ground.






Note the above blend would require a recovery op-amp stage of some kind. Have a look at JMK's Paralyzer.