Small Clone mod

[ratrod]

I modded my Small Clone with a vibrato/chorus switch. In vibrato mode it seems to cut some treble, which I like. I'd like to mod it to cut even more highs to get into that wooly woozy zone.

Can any of you electronics wizards tell me what components to change to achieve this?

[eatyourguitar]

can you start by giving us a schematic of what you did before we can tell you what you did?

[ratrod]

All I have done is lift one leg of R18(22k resistor) and put it on a switch for the vibrato mod.

It's a reissue big box Small Clone, I'll check what circuit board revision when I get home today.

[eatyourguitar]

R18 on what schematic? I want to be sure before I waste time trying to guess if we are both looking at the same thing.

[ratrod]

Got it, I didn't use a schematic for the mod, I just followed this: http://www.offsetguitars.com/forums/vie ... 11&t=79873

I'll check the pedal when I get home and I'll try to find the correct schematic.

[eatyourguitar]

ok I see it now. it looks like you are lifting one side of the 22K resistor from pin 2 and pin 3 of the CD4047. the CD4047 is the clock generator that gets an LFO input at pin 2, 3 from the LFO connected to the FET. lifting this resistor increases the resistance on one side of the range of the LFO. instead of 22K now it can go to 1M. This increases the depth of modulation I think. Your post asks how to make it darker though so I think that is doable but unrelated to the other mod. The clock is not audible therefor no matter the speed of the clock it would not affect the brightness directly. What you are hearing might be a side affect of clocking a BBD very slow. They can lose brightness that way. However this is just an adjustment that can be made if you have enough time left in the BBD. It depends on a lot of things. You might want to go another route and just add a simple RC low pass filter on a switch. leave the other mods if you like them. maybe put the vibrato mod on the same footswitch as the RC lowpass mod. you can do it on one pole of the same switch by grounding the new cap through the switch. The resistor in series can be something that is already there. Half of an RC low pass filter is just a resistor. defeating the low pass filter is as simple as lifting one side of the new cap.

http://www.experimentalistsanonymous.co ... MN3007.jpg

[Scruffie]

That's the Clone Theory, not small clone... and the schematic's wrong any way.

When you lift the dry signal by taking R18 out of circuit, you're only running the wet signal which has an input low pass filter, BBD (which has inherent high roll off) and output low pass filter, ignoring the pre & de-emphasis which is meant to be neutral regarding tone, although isn't quite.

Are you saying you want to make the chorus darker or just the vibrato? For the vibrato it'd be a (relatively) simple case of lowering the filter cut offs which are a standard sallen-key topology, for the chorus too (so your dry signal would also have high roll off) you could add a high roll off cap in the feedback loop of the pre and/or de-emphasis circuitry.

There's also the other option of splitting the wet mixing resistor in to a pot and resistor and using something like the 'stupidly wonderful tone control' for a variable low pass on the output of the wet signal.

[ratrod]

Yeah that's the stuff! Would you be so kind as to point me to those filters??

I just want to make the vibrato darker.

[eatyourguitar]

I think I got the right schematic now it says small clone but it is a tonepad clone of a clone. the last opamp has a cap and a resistor in series in the feedback loop of the opamp. it would be trivial attach a 10K trimmer on the vibrato footswitch and run two wires back to both sides of the resistor. 0 to 6K gives a good range with a 10nf cap in the feedback loop.

[ratrod]

Thanks for the info guys! Super excited to fool around with the filters this weekend.

Also, looking at the Tonepad schematic, do you think I could tack in some clipping diodes between pins 6 and 7 of IC1b to get some mild overdrive? Looking to add to the lofi tapey vibe.

[Scruffie]

Personally, instead of altering the cap that's already in series with the 6k8 and changing the de-emphasis, i'd add a cap (try starting at 10n for ~5kHz roll off and shifting up and down to suit) in parallel with pins 6 & 7 and yes you could add clipping diodes as well but you will cut the volume for which you can compensate by reducing the value of the 22k wet mixing resistor (the resistor that still connects to pin 6 after you lift the dry resistor for vibrato).

[eatyourguitar]

Personally, instead of altering the cap that's already in series with the 6k8 and changing the de-emphasis, i'd add a cap (try starting at 10n for ~5kHz roll off and shifting up and down to suit) in parallel with pins 6 & 7 and yes you could add clipping diodes as well but you will cut the volume for which you can compensate by reducing the value of the 22k wet mixing resistor (the resistor that still connects to pin 6 after you lift the dry resistor for vibrato).

there is exactly 10nf from pin 6 to 7 already there. turning the trimmer down to 0 Ohms would accomplish the exact same task as adding another 10nf cap from pin 6 to 7. you could argue that there is a difference but it is less than a 3Db per octave difference in slope to the low pass filter depending on how you make it. I also do not think a steeper slope to the low pass is going to sound as good as a little darker at the right frequency. the trimmer gives you the ability to dial it in fast and precisely. the cap change everytime to test it out is hit or miss. you could however change the cap anyway to something like 22nf to shift the entire range of the trimmer on both ends more darker. I think it is possible that my way has adjustable slope more than it has adjustable frequency. That might be one reason to just do it the way scruffie says.