MXR Distortion+

[Bubesz]

Hi!

About a year ago I built a Dist+ using the Tonepad schematics. Everything was fine, except that I couldn't find rev.log pot in my town, well, I couldn't find a good pot in the whole country (in Hungary there's no Radioshack and I didn't want to order parts from the other side of the world...). Since then I disassembled it, but now I want to build it again.
I have an idea:
I read an article about diode-clipping which is used in Dist+ (http://www.instructables.com/id/Add-Diode-Clipping-Distortion-to-your-Guitar-Amp/). So: Can I do this? I omit the normal gain pot and put a jumper there. Perhaps also omit the 4.7k resistor and the 0.047uF cap, although I'm not sure about these. Then put the pot before a 2 diodes (and not a rev.log pot, but a linear)

What do you think?

[Mark Hammer]

You do NOT need a reverse-log 500k pot for the Distortion+ to work properly.  That pot was used so that people in the 1970's could go from very low gain and a tiny bit of clean boost to full distortion, using the same pot.  All the distorted settings occur in the last 50k of that pot.  A reverse-log taper pot was used to spread out that last 50k over a broader range.  Otherwise, all the diastorted sounds would be in the last few degrees of pot rotation, and people would have a hard time getting the same exact setting twice.

If you have no intention of ever using it for clean sounds, then a 25k-100k linear pot is perfectly acceptable, and will get you the full range of possible distorted sounds from the unit.

[solderman]

I assume you are referring th step 5 in the link. No you will not be able to omit the gain put and have a pot that controls the amount of clipping to do the same thing. The gain pot controls the amplification of the circuit and also the amount of op amp clipping you can get, of cause substitute that for a normal resistor or even a jumper is possible but then you will have no way of controlling the gain setting. The pot in step 5 controls the amount of clipping NOT the gain. Soubs the pot in pic 5 for a ON-OFF-ON SPDT switch and connect the two sides to diffeternt diode combinations and you will have both no diode clipping and two different types Eg. Ge diodes 2X1N34 and the ones you have now. 

[Bubesz]

You do NOT need a reverse-log 500k pot for the Distortion+ to work properly.  That pot was used so that people in the 1970's could go from very low gain and a tiny bit of clean boost to full distortion, using the same pot.  All the distorted settings occur in the last 50k of that pot.  A reverse-log taper pot was used to spread out that last 50k over a broader range.  Otherwise, all the diastorted sounds would be in the last few degrees of pot rotation, and people would have a hard time getting the same exact setting twice.

If you have no intention of ever using it for clean sounds, then a 25k-100k linear pot is perfectly acceptable, and will get you the full range of possible distorted sounds from the unit.

Oh well...At least I tried... I'll try a linear pot then.

[Mark Hammer]

Just so you know, it doesn't HAVE to be linear.  I just mentioned linear because that is often the easiest form to obtain.  If all you can get is log, that's fine too.

Keep in mind that taper usually does not change what the circuit does or is able to do.  What taper changes is how easy or difficult it is to find, and replicate, those possibilities.  If the relationship between some resistance, and what a circuit is able to do, places all of the "interesting" outcomes in a 5-degree arc of rotation, then it will be hard to set the controls to your satisfaction.  A perfect case of where taper is important is with modulation effects (tremolo, chorus, phaser, etc).  For phasers, the range of modulation speeds can often vary from .1hz (one full sweep every 10 seconds) to 5hz (5 full sweeps every second).  How easy would the pedal be to use if settings between 7:00 and 4:00 got you speeds from .1hz to .5hz, and everything above .5hz (one sweep every 2 seconds) was between 4:00 and 5:00 on the control?  It would drive you crazy!
The taper will "spread out" or compress resistance changes at one end or the other.  So, if by distributing the resistance differently speeds above .5hz were spread out from 12:00 to 5:00, it would be easier to find the exact speed you want each time.

For the Dist+, as I say, everything of interest happens in the last 50k.  That is, all possible settings between a total ground resistance of 54.7k (50k of pot and 4k7 of fixed resistor) and 4k7 (the fixed resistor alone).  Once that 50k is spread out over the entire rotation of the pot (instead of only being a segment of a 500k pot), taper matters very little since it will be fairly easy to find/achieve any setting.

[Bubesz]

Hmm, having a closer look, it looks like sth may be wrong with the PCB, too (a friend of mine designed a new PCB layout which is more "airy")  At the first glance the IC is wrong...Pin 7 goes to 9V and so on I'll have to make a new one using the original PCB.
I think I'll try to repair sth else first, which will be an Orange Squeezer Compressor.