Variable Bounding-Saturation Control

[chunkitup]

I am looking for help implementing a saturation control/variable bounding circuit. The amp is a straight up JCM 800 50w clone. I have Tut#1 and I am reading about the var bounding and I want to try it out. I would print the illustration but I did that before and some people were not happy about copyright infringement.
The circuit uses a dual pot with the middle lugs as Vref but shows a V+ and a V- also and I dont know where that is coming from. If anyone has a variable bounding circuit that I can implement into this amp please give me some pointers.

[chunkitup]

Anyone have Kevin O'Connors number then?

[loudthud]

Kevin has been on diyAudio alot lately. His ID there is Struth. You can email him, PM him here or on diyAudio, or find an email at londonpower.com

Give me the chapter and illustration number and I'll look over the subject in TUT 1.

[chunkitup]

It is on page 5-17 Fig 5-22. Thanks loudthud for taking a look.

[loudthud]

The plus and minus supplies connected to the pots are low voltages such as might be used for opamps. Kevin suggests that the current through the pots be ten times the current in the diodes, so 5 to 10mA is needed. With +/- 15V or +/- 12V you'll need 1K or 2K pots. This will make a nice square wave. You could use higher value pots for a more rounded wave or add resistance like the Compliance pots does. If you don't have low voltages supplies available, you'll have to use zener diodes.

[chunkitup]

Thanks loudthud! All I have that low are 5k pots. The prpose of the var bounding is to go from rounded wave to square wave and anywhere in between correct?
Also, are the zeners for the supply +/- voltage?

One other question. The dual pots are ganged correct?

[loudthud]

The zener diodes like in figure 5-19B just provide a way to clip the input without having a negative supply. The disadvantage is that the clipping point is not variable. The value of the pot depends on how sharp you want the clipping and the value of Rin (figures 5-20, 21 and 22). So 5K pots would work if Rin is made big enough. Experiment with a trim pot in place of Rin to find what works.

A dual pot is indicated on a schematic by the dashed line between the center terminals. You don't see many pots that are not ganged these days but if you can find one, it's ok to use. I don't think there is much value in having a pot, at most I would have a switch with two different levels of clipping, and maybe a center off position. Symmetrical clipping tends to sound hollow, so having equal clipping on plus and minus might not sound good. You should experiment because there are a lot of things that effect the result.

[chunkitup]

yea the variable bounding sounds more of a hassle than its worth. I had an extra hole in a amp that I gutted. I will have to find something else to make variable.

Thanks again.