marshall speaker simulator

[siafu12]

i recently built this pedal and i am having problems with the sound.  when play through it, it distorts alot and when i roll the volume back a little it does fine.  this cicuit uses two TL072 chips that scavenged from an old satellite receiver the rest of the parts are brand new. the address is www.diystompboxes.com/pedals/schems/msim.jpg

[gez]

Sounds like op-amp clipping.  Either sub amps that swing rail-to-rail (CMOS output), or perhaps reduce the 47k feedback resistor in the first stage.

[Prive]

What voltage are you using to supply the op amps??? you must have at last +/- 12 or better 15 volts to have a decent headroom, if you use just a 9v battery it will distort a lot, the JMP-1 speaker emulator need 30v between pins 4 and 8 in the op amps, it means +/- 15 V.

I hope it helps, if you understand my english...  :wink:

Saludos Marcelo.

[siafu12]

thanks guys!


siafu12

[Ed Rembold]

Do not use a bi-polar power supply with this "circut snip-it" that I drew. use a wall wart.  18-30 volt Dc. make sure your caps are so rated. Don't forget to add an output cap. and use a pot as suggested in place of the 47K.
Ed R.

[Ed Rembold]

Do not use a bi-polar power supply with this "circut snip-it" that I drew. use a wall wart.  18-30 volt Dc. make sure your caps are so rated. Don't forget to add an output cap. and use a pot as suggested in place of the 47K.
Sorry guys, I don't know why this is in here twice!
Ed R.

[Yazoo]

The Marshall speaker simulator sounds good. Would you plug your guitar straight into it, or can/do you need to use a preamp to drive it?

:?

[gtech]

I normally use it with an effect before it.

I made a stereo version of it because I use it only to record my guitar with the stereo line input of my computers.

But I had to add a gain pot at the input op-amp because there was some distortion, even with a + /-12V power supply.

Gilles

[Marek]

Do not use a bi-polar power supply with this "circut snip-it" that I drew. use a wall wart. 18-30 volt Dc. make sure your caps are so rated. Don't forget to add an output cap. and use a pot as suggested in place of the 47K.
Ed R.

Few questions:

1. Why not use a bipolar power supply? I found a wonderful  compact -+15V in an Elektor book. It gives max 25mA, but I guess that's enough?

2. How big should a cap @ the output be? Around 47nF?

3. If I use a pot in place of 47K resistor, is there a need to put 27K in series with this pot? (Or simply discard 47K and put 250K pot?)

3a. What happens when the pot is in the position around 1K or 5k or 10K? Is the input gain stage then attenuating? I'm too lazy to experiment... :-)

Greetings,
MM

[Marek]

I just don't understand what's wrong with this topic?

It seems to be too heavy, it keeps sinking on the bottom of the forum all the time... :-)

Marek