ROG Phoser build report

[RickL]

The new version, here: http://runoffgroove.com/phozer.html

I used the layout provided to build it using the 4ms/Commonsound CBCB technique. The only change I made was to use a 10k pot for the manual sweep with no parallel resistor.

It fired up perfectly from the start and sound good in both the  LFO and manual mode. The new LFO is great with a nice range of speeds available.

The real reason I'm posting is because I got a chance to try several different LED/LDR combos and I was surprised at the difference in sound I got. I first used a home brew red LED/CdS combo that worked reasonably well. VTL5C3's sounded about the same as did a single VTL5C3/2 with the common wire of the LDRs to ground. It really came alive with a couple of unmarked, small bodied optocouplers that I found somewhere. Wonderfully vocal wah/phase sounds. I got similar results using a 21L915 (I believe these are used for switching in Fender amps. I was given these by an amp tech who ordered them for someone who never came back). I also tried some CLM8500's that I had robbed of some junked circuit boards I had found somewhere. They worked but they sounded a little on the thin side. I think they were my least favorites (I think these are/were also designed for switching).

It would probably be worth adding a place on the layout for series and parallel resistors (or trims) to go with the LDRs. I wonder if the great vocal sound I got with the 21L915 could be achieved by getting any generic LDR to sweep through the right resistance range.

[Seljer]

I've always thought that in addition to the LFO and the manual control, adding envelope follower would even give even more cool options to the thing.

[B Tremblay]

Excellent!  Rick, you've built both versions now, correct?  If so, I believe you're the first to do so!

I still really like my homebrew dual vactrol for the most vocal sounds, but I wanted to make it a bit more user-friendly by not requiring builders to "roll their own."  I ordered a few different units from the VTL series to determine the best and there are significant differences among them in terms of performance.

I can't find any information for the 21L915 you mentioned.  Are you sure of that part number?

[RickL]

I double checked the part number. It says

21L915
9925
ASSM. IN RP

on the side opposite the VACTROL marking and it's dual - one LED and centre-tapped LDR.

I also agree with Seljer, I think an envelope follower would be a great addition.

I have built both versions but I can't believe I'm the only one. I love modulation effects like this. This version is great.

[B Tremblay]

Well, I don't know for sure if you're the first, Rick, but you're the only one who has reported doing so here.

Adding an envelope follower did cross my mind during its development, but I didn't want to overcomplicate the circuit.  However, the filter section can be used as a building block and nearly any LED driving circuit could be used to put the filters in motion.  I've thought about trying the Dr. Quack envelope follower section, but haven't tried it.

I should also mention that the Tremulus Lune LFO works incredibly well with those filters.