Distortion Pedals into Tremolos..?

[Wighty]

A while back i did a mod on a DS-1 which made it into a very lofi tremolo with just a simple jumper between traces.

Now i have come to fix up an old DOD FX-55B distortion, but this thing seems to do it on its own!

Could anyone explain why this happens? Or how to control or stop it!?

Many Thanks.

[foxfire]

i can't help you as to why it happens but, take a look at this tread about dragonfly's whirlygig. i don't know circuits all that well yet so i'm not sure how much help it will be but, he came up with fuzz that you could get a lofi trem from and we talk a bit about how to get of it if you should want to. maybe you can apply the theory to your pedal? hope it helps.

http://www.diystompboxes.com/smfforum/index.php?topic=58782.msg458351#msg458351

[Wighty]

Wow! That Tremfuzz is awesome!

It seems like its some sort of oscillation causing the trem, which means it probably isn't that controllable..?

In my FX-55B the tremming comes from the distortion part of the circuit - could it be a dodgy op amp oscillating?

[chris_d]

A while back i did a mod on a DS-1 which made it into a very lofi tremolo with just a simple jumper between traces.

I would love to see details of that modification. I have a DS-1 here and find it to be one of the most useless pedals i have ever met. I have never heard  one, modded or not that didn't have a certain nastiness to its distortion that i hated.

If it can be made into some form a trem, i might give it another shot!

-chris

[Wighty]

This was the link for that mod:

http://www.effector13.com/GPA/effector13/index.html

from this thread:

http://www.diystompboxes.com/smfforum/index.php?topic=56038.msg432371#msg432371

but unfortunately they've gone. Someone may have the photo with the traces to join highlighted...

Anybody know why these distortions go tremolo?

[cheeb]

This is the DS-1 trem mod.

[chris_d]

This is the DS-1 trem mod.

Wow. Thanks! Is the mod simply that one jumper? What do the blue and red tinted areas indicate?

-chris

[Barcode80]

the coloring is just to make it clearer which traces to jumper. the jumper is all that is needed.

[chris_d]

the coloring is just to make it clearer which traces to jumper. the jumper is all that is needed.

Wild. Thanks a bunch! I am off to solder it together now and try it out!

-chris

[chris_d]

Hey, it is actually kind of cool. The "trem" speed varies with signal strength. Fast on hard attack, and then it slows as it decays.

Kind of a "square" on-off-on trem effect. If i can mod some nastiness out of the distortion, i might find use for this. The speed variation is cool.

If you set the distortion lower than max, the "trem disapears, until the signal starts to die, then the "trem" kicks in on the tail, almost like playing with a kill switch on the sustain.

Very interesting. Very simple. Neat.

Thanks very much for bringing this up!

-chris

[Wighty]

Thought someone may have it!

It is a simple and interesting little mod!

Does anyone actually know why this tremming happens though?

[chris_d]

What is especially cool is that at 5:00 on the distortion the trem is full and pretty much obscures chords, at 3:00 is it very pronounced but lets the most basic gist of notes through, at 1:00 it only kicks in on note tails, and at 11:00 it totally disappears. I would never use the stock DS-1 above 10:00 anyhow, so really instituting this trem hack doesn't actually alter the basic pedals functionality in any way, just adds a screwy noise dimension to certain settings i never would use before anyhow.

I haven't looked at the other side of the board to see what is getting jumpered(got to love a one wire mod that only requires that you take the back off the pedal and solder, not remove the board!) so the following is just straight up wild guessing from someone with very little real in depth electronics knowledge:

But it almost feels like voltage is feeding backwards through the circuit. If the regular forwards voltage is high enough(strong signal) then it overrides the reverse voltage. If the regular signal dies down, then the reverse voltage shorts the circuit out, killing the sound, almost, it seem until the caps refill from the battery, then it does it again, and again and again, making it "tremolo"?

Also interesting is that after a certain point, the trem stops and the tail end of the guitar notes are allowed to sustain into nothing un-tremmed. I would guess that this is because the reverse voltage that is killing the signal is being provided by the distortion knob, and at the tail end of the signal the gain dies down due to reduced input?

Really just wild unfounded guesses about what is happening. Maybe it is just a quirk of the op-amp? i.e. that it can only function with voltages between a certain specific range, and whatever is jumpered into its second(? or 7th) pin is causing it to go over/under that spec, and kill the sound until it returns to normal, kind of like a hard rev limiter in a car's engine management computer?

I, clearly have no clue! It is an interesting trick though!

-chris

[Wighty]

I think you may be close to what is happening.



I've located the traces on the schematic and marked them on and it seems like it may be C9 which is causing the trem.

Looking at the Whirlygig, it also bypasses with a capacitor...

Maybe we're on to something?

[Wighty]

So, i managed to fix up the problematic DOD FX-55B!



At first i tried putting a larger capacitor across the diodes. Any values above 1uF stopped the tremming, but i lost a lot of gain, ie. barely a boost with max distortion set.

Thinking about it, i decided to see what information i could find about circuits with similar designs. So, over to GEO and after a good look at the Tubescreamer Anatomy, especially the clipper section, i then had another prod around, but this time at the cap marked with the *. I removed it and then started "crocodile clipping" in different values. I found that larger values, such as 22uF gave a longer time between pulses. Then subbing in a poly 0.015uF cap i had lying around and, bam! No trem, normal gain! Fixed!  

I'm so glad i managed to get this thing working - not particularly for the effect itself but just because i've learnt a lot about how these clipping sections work. I've now modded various values to make it sound at least a little more pleasing!