Stupid question - re: Mark Hammer's Phase 100 mods

[Bucksears]

In the following archived quote, Mark Hammer is describing how to swap (part of) the 4-pos. rotary switch in a Phase 100 for a Depth control.

"The other function of the switch is to adjust sweep width.  Here, I am guessing as to the appropriate replacement of the switch with a pot, but let's say 1meg for starters.  When the switch is closed, you essentially have a zero-ohm resistor bridging R41 and R45.  The question is how much resistance is needed to mimic the effect of opening up that connection.  You may find that a 3-position toggle switch that either bridges it with one of two different resistances or leaves it open can provide enough sweep width options if it turns out that sweep width depends on a wider range of pot values than you can provide."

I guess my question is, in a nutshell, do you just place a 1M pot somewhere? Any help would be greatly appreciated.

Thanks!
- Buck

[Mark Hammer]

The only thing that 4-position switch can do is join things or separate them.  One of the things it does is take the junction of R41/R42 (using the schematic at Generalguitargadgets as a reference) and the junction of R51/R45 and either link them or separate them.  What we can extrapolate from that is that it is not disrupted or thrown into chaos by either very low resistances (like, say, zero ohms), or very high ones (like megs and megs).  So, subbing a 1M pot, wired as variable resistor, for those two contacts or points of contact, should in principle allow for some variation in sweep width.

Is 1M enough to get the "other" setting?  I have no idea.  There is obviously a lot of ground between 1M and infinity, so 1M may be insufficient to get as much variation in sweep width as you'd like.  I simply recommended it becasue it clearly did not exceed allowable resistance values, and was something you were likely to have in your parts bin, or available locally.  It may be that the territory beyond 1M is important for getting sufficient variation in sweep width.  In which case, a toggle or other switch that is able to invoke both open circuit (as the stock switch would), and resistances between 1M and open circuit (as well as closed circuit or zero ohms), may be the wiser and more practical choice.

Sweep width is one of those things that some people futz around with constantly, while other people are content with a couple of settings.  The popularity of the Phase 90 (which has one sweep width setting) and the Small Stone (which has two width settings) is testament to how many people can get along fine with something other than continuously variable sweep width.  YMMV.