Building Three Band Guitar Distortion

[zonedout245]

Hello, everyone,

I'm building a three band guitar distortion pedal for a college lab project. I'm basing the design on a Yamaha MBD-100, which is currently out of production from what I understand (schematic in link below). The part that I'm having trouble with now is choosing the OpAmps for the active filters and buffers. I'm not able to find the model used in the MBD-100.

I'd like the bandwidth of the output signal to be similar to the bandwidth of the guitar's dry signal. Can any of you recommend any OpAmp that are common or that you know work well for this application?

Thank you.

https://www.dropbox.com/s/2ev8snvrm19b9bg/YAMAHA_MBD-100.png

[R O Tiree]

"Error 403 - Forbidden to access"

[zonedout245]

"Error 403 - Forbidden to access"

Sorry about the link. I fixed it.

[R.G.]

I'm building a three band guitar distortion pedal for a college lab project. I'm basing the design on a Yamaha MBD-100, which is currently out of production from what I understand (schematic in link below). The part that I'm having trouble with now is choosing the OpAmps for the active filters and buffers. I'm not able to find the model used in the MBD-100.

I'd like the bandwidth of the output signal to be similar to the bandwidth of the guitar's dry signal. Can any of you recommend any OpAmp that are common or that you know work well for this application?

Probably any modern dual opamp will work. The TL072 is quite common, and probably will work fine. That's a guess.

It's not clear that the bandwidth of the output signal can be similar to the guitar's dry signal, at least with that design. The low end of a guitar's signal in standard tuning is about 82Hz on the low E string, but the harmonics in the strings go considerably above the 1312Hz of the high E on a 24 fret neck. However, the inductance and self-capacitance of the pickups tend to cut off highs from any magnet/coil guitar pickup above about 6000 to 8000Hz.

That would be OK, but clipping/distortion stages create additional harmonics above this, not limited by the pickup characteristics, so you could well have products of the clipping in the octave-and-a-fraction above 8kHz in the audio band. You'd have to add a lowpass filter to the whole mess after the clippers are added together to cut this out. Actually, there is a simple version of this filter there, in C124/R126 in the feedback path of IC6; but this is a relatively slow 6db/octave filter, and doesn't do all that much cutting, only a treble rolloff.

[R.G.]

By the way, go look up Craig Anderton's "Quadrafuzz".

[Mac Walker]

Looks like the original used an NJM4558 (lower right hand corner), I would start with that one....





http://www.taydaelectronics.com/catalogsearch/result/?q=4558

[zonedout245]

Thanks everyone.

It's not clear that the bandwidth of the output signal can be similar to the guitar's dry signal, at least with that design. The low end of a guitar's signal in standard tuning is about 82Hz on the low E string, but the harmonics in the strings go considerably above the 1312Hz of the high E on a 24 fret neck. However, the inductance and self-capacitance of the pickups tend to cut off highs from any magnet/coil guitar pickup above about 6000 to 8000Hz.

That would be OK, but clipping/distortion stages create additional harmonics above this, not limited by the pickup characteristics, so you could well have products of the clipping in the octave-and-a-fraction above 8kHz in the audio band. You'd have to add a lowpass filter to the whole mess after the clippers are added together to cut this out. Actually, there is a simple version of this filter there, in C124/R126 in the feedback path of IC6; but this is a relatively slow 6db/octave filter, and doesn't do all that much cutting, only a treble rolloff.

I think I was a bit unclear in my explanation. I meant to say that I would like for the output to contain at least the bandwidth of the dry signal; that is it doesn't cut too much of the signal. I say that because there are some pedals that seem to have a rather "bright" sound, and I would like to have a flatter response from this pedal.