Author Topic: Phaser not phasing, but there is a clean signal  (Read 2201 times)

spargo

Phaser not phasing, but there is a clean signal
« on: October 19, 2010, 02:24:10 AM »
I just breadboarded the BYOC Phase Royal.  When the pedal is engaged, it doesn't seem to do anything...I still get a clean sound coming through but I can't hear any difference, no matter what position the knobs or trimpot are at.

I subbed a 2N4125 for the 2N5087.  I also removed the 4/6 stage switch (as well as the last 2 stages - so it's only the original 4).  With the help of another thread, I also measured the voltage at the LFO point, and I can see it sweeping back and forth between about 1.5v and 1.7v when the sweep is at the slowest speed.

Any idea what may be happening?  I've never built a pedal only to have it sound just like the clean signal before.

Mark Hammer

Re: Phaser not phasing, but there is a clean signal
« Reply #1 on: October 19, 2010, 08:13:42 AM »
Is the bias set right?  Mis-set bias means no phasing.

earthtonesaudio

Re: Phaser not phasing, but there is a clean signal
« Reply #2 on: October 19, 2010, 10:10:17 AM »
One quick check you can do:
Measure the resistance across R6/9/12/15.  It should be modulated by the LFO voltage.  If this resistance is varying with the LFO then the JFETs are biased correctly and the problem is elsewhere.

spargo

Re: Phaser not phasing, but there is a clean signal
« Reply #3 on: October 19, 2010, 12:52:24 PM »
Are you speaking of the bias trimpot?  It doesn't seem to make any difference where the trimpot is set, it's still the same.  Or are you referring to matching the transistors?  Because I didn't do that, and don't really know how.  But I did find the article at geofx, which I assume is the way to go. Would that be the issue?

Mark Hammer

Re: Phaser not phasing, but there is a clean signal
« Reply #4 on: October 19, 2010, 02:34:09 PM »
Double-check the pinouts for all transistors.  There is a possibility they might be the opposite of what you think.

spargo

Re: Phaser not phasing, but there is a clean signal
« Reply #5 on: October 19, 2010, 04:00:16 PM »
Call me crazy but I've double and triple checked the transistor pinouts via the fairchild semi spec sheet for the 2N5952 against the schematic and they seem to be correct. Drains connected to pin 5 or pin 3 of the opamp, gates connected to the LFO point, and sources connected to vref.

Is it possible to fry a transistor if you put it in backwards or should I try that?  If they're reversed is it possible for a signal to still come through?  Thanks for the help!

Mark Hammer

Re: Phaser not phasing, but there is a clean signal
« Reply #6 on: October 19, 2010, 04:03:37 PM »
Is it possible to fry a transistor if you put it in backwards or should I try that?  If they're reversed is it possible for a signal to still come through?  Thanks for the help!
An earlier Tonepad layout had the 5952s shown backwards and eventually corrected it.  I soldered mine in the way they were shown in the earlier drawing, and after meeting with failure, stumbled onto the newer drawing and re-installed with no problems whatsoever.  So, living proof.  Just make sure you don't overheat.

And no, you're not crazy.  I just wasn't sure if it was done yet, and wanted to be able to at least rule that out as a cause.

spargo

Re: Phaser not phasing, but there is a clean signal
« Reply #7 on: October 19, 2010, 04:11:44 PM »
And to respond to earthtonesaudio, I did measure the resistance across each of those resistors and the resistance was rising and falling with the LFO.

Looking at the Tonepad layout for the Phase 90, the transistors do seem to be different, but it's not as simple as flipping them around is it, because of the pinout?  They seem to show the source connected to pin 3 or 5 of the op amps while the BYOC shows the drain connected to these locations.  Am I correct?

Mark Hammer

Re: Phaser not phasing, but there is a clean signal
« Reply #8 on: October 19, 2010, 04:28:48 PM »
When used as a variable resistance, drain and source are essentially interchangeable.  Of course, when the gate pin is not the middle pin, how you orient the transistor has implications for whether the gates are in the right spot.

earthtonesaudio

Re: Phaser not phasing, but there is a clean signal
« Reply #9 on: October 19, 2010, 04:31:20 PM »
If the JFET resistance is varying according to the LFO, you can stop looking at the transistors.  Now would be a good time to take an audio probe and listen at various points along the audio path.  I would bet that either the audio never enters the phase shift stages, or else the output of the phased audio is shorted to Vref.

This is of course assuming you've wired your bypass switch correctly.  You did check that first, right?

spargo

Re: Phaser not phasing, but there is a clean signal
« Reply #10 on: October 19, 2010, 04:51:31 PM »
Bypass switch is fine.

Probably the best help I've found so far: the mix knob (which I believe blends the clean signal with the phased signal) works more like a volume knob...When fully clockwise it sounds normal and clean, but as you turn it counterclockwise the signal fades out to nothing.  So I'm assuming there is no phasing coming through?  If so, where would be a good place to start?  How would I check to see if it's shorted to vref?

spargo

Re: Phaser not phasing, but there is a clean signal
« Reply #11 on: October 19, 2010, 05:06:18 PM »
Ok, I get the first stupid of the day award. :)

I made 3 missing connections between the phasing op amps.  But still no phasing.  On the plus side, the mix knob now gives a clean signal throughout its full range.  I tried fiddling with the trimpot again, but no luck.  Depth is at max, speed is slow, mix is middle, and resonance middle also.

spargo

Re: Phaser not phasing, but there is a clean signal
« Reply #12 on: October 19, 2010, 05:48:31 PM »
Got it figured out! After the wiring snafu, I messed with the trimpot some more.  Turns out there is a much smaller ranger than I was expecting for phasing to occur, but I got it to work.

Now this is more of an EQ question: is there a way I could make it have less mids at the low end of the phase and less highs at the high end?  At the high end of the phase ideally it would sound just like my clean signal (but it's VERY harsh right now), but at the low end of the phase I want it to sound really hollow with the mids heavily cut.  Any idea?