SmashDrive problems

[docz]

I'm trying to build a SmashDrive pedal that I found here on this forum. My first attempt I tried using veroboard and built the simple version. I did substitute the drive pot for a 10k instead of 5k, and the 47uF for a 33uF because that was what I had. I got sounds out of it, but not the sweet drive from clean to hard distorted that I was expecting, I got russian radio mixed with a low guitar signal. So I thought I'd get myself a breadboard to try and build it again in case I did something wrong or the layout was wrong.

On the breadboard I did this, I got it working without russian radio, but it only has loud harsh distortion, drive pot totally off makes some sort of "blip" noises, and at full it mellows the distortion out, but the amount of distortion sounds pretty fixed through the whole range. The sustain is also cut short with a quick fade out after a while - almost like a gate. If driven hard (high guitar ouput - playing hard), signal drops out. I also hooked up a LED to the power supply (9V battery), that will dim / light in sync with the guitar signal.

The only modifications made to the circuit is the drive pot is 10k instead of 5k, and the 47uF cap is a 33uF. I also tried different cap values here, I had a 10uF and a 100uF none of those gave me any difference in function. I tried swapping chips/pots no difference.

DocZ

[aron]

Not sure. I mean it IS named the smash drive so sweet distortion is not the forte of this pedal. Maybe I need to look at this circuit so more since I now have LM386 chips in the store.

[Electron Tornado]

When I build my OD386, which is based on the Smash Drive, I tried 10k, 5k, and 2.5k pots for the drive pot. I ended up using a 1k pot.

The drive pot doesn't have a smooth taper. Starting from min drive, there is little distortion until about 3/4 pot travel, and then you have pretty much full distortion for the last quarter travel.

The sustain could be better, and the very end of a note or chord does die out rapidly with a buzz, sort of like it gets gated at the end. Not sure why this is, whether the chip doesn't like to operate at high gain with a low input signal strength, or if there is a biasing issue.

Not sure why you're having the other problems.

The 386 does seem happier with an input buffer, like this:

http://runoffgroove.com/grace.html

[compuwade]

I have never built a smash drive, but I have built a Purple Plexi which is the same type of circuit. What I have found is that plugged into a SS amp I get that fizz at the end of a note which can sound very unnatural. However, plugged into any tube amp, the circuit sounds great and the fizz is gone. I'm not sure why that is, but it's what I've found. I too have the same issue with the drive control. It's not very responsive till about 1 O'clock. It does make some difference in the 1st half but not much. The purple plexi doesn't have a buffer and sounds just fine without one. However, add any pedal behind the circuit and it becomes a whole different animal. I recently built a TS808 and put that in front of it, and wow, what a sound. So instead of a buffer, I would add a fet booster if I ever built one again. Or even make a dual TS808/Purple Plexi pedal.

[docz]

I just followed Aron's thread on the build, and they mentioned the pedal would do from clean to hard overdrive. But min just does overdrive - I would say distortion... harsh metallic very unpleasant distortion. I just can't believe that what I've got is what it is supposed to sound like, the guys in that thread were raving about how sweet and good it sounds.  My idea was to use this as sort of a preamp and add another fixed gain version of the circuit to get an extra boost for a clean - crunch - higain setup. I guess I'll go back to the drawing board, maybe try an add a buffer to it and see what happens.

DocZ

[docz]

Here is a schematic showing my idea. Do I need to attenuate the input signal or something?

DocZ

[deadastronaut]

erm!.shematic!.....where!...

btw some peoples idea of a good distortion is way off what others think is great...

but hey some people like single coils..and others humbuckers...

i love hi gain pedals....dr boogie for one ..its a great proper hi gain pedal to build.....no hiss too...

also...ive been messing with the 386 chip for a while..and i know there is a very nice gain to be had out of it..

its in there somewhere.....ive just got to pin it down to suit MY ears!......

[docz]

Sorry, forgot to include it It is there now.

DocZ

[tiges_ tendres]

10k is too big for your gain pot.  5k is also probably too big.  1k is probably too small!  It's a funny chip like that.

I would think that this thing is going to have huge output!  1 386 by itself has massive volume.  Although your tone stack will tame a lot of that, I think this is still going to be too loud.  I think clipping diodes might help attenuate the volume a touch, and also provide you with more of the distortion you are looking for.

Another thing to try is maybe trying the non-inverting pin and grounding the inverting pin (I think I have that right.  Either way, go in pin 2 and ground pin 3 on the first stage.

Are you going to use this in front of a guitar amp, or is this going to be the guitar amp?

[Electron Tornado]

I took a look at the data sheet again this afternoon:

http://pdf1.alldatasheet.com/datasheet-pdf/view/8887/NSC/LM386.html

Here are a few things that might be worth trying in the basic Smash Drive:

- instead of shorting the unused input to ground, try connecting a 0.1uf cap between the pin and ground

- try different cap values on bypass pin 7, or eliminate the cap to ground entirely, leaving pin 7 unconnected

- use a series cap and pot across pins 1 and 8 instead of capacatively coupled to ground

- the datasheet also discusses placing a seried RC between pins 1 and 5 which will boost the bass.

[docz]

The idea was to use this as a preamp, I have two bridged TDA2030s that will serve as a power amp. My hope was that I could get clean -> high gain. But now I just get weird high gain distortion with a gating/limiting effect.

DocZ

[Electron Tornado]

Not sure what you're trying to do in the schematic. The first chip is set up to provide a gain of about 200 or so, while the second one should only have a gain of 20. What's the point of the second chip?

I think you also need a cap in series between pin 5 on IC1 and the junction of R2 and C7.

[docz]

The idea was to give it an extra "boost" to go into hi gain territory.

DocZ