What Does the Foxx Phase?

anotherjim · November 20, 2015, 11:13:40 AM

I can't see anything different in the 2 schemes around the feedback. Both lack the cap in series with the control that I'd added, but then Mr May's examples probably lacked it too. The cap would have changed things a bit, since it would have cut some of the bass in the feedback, and in the Foxx, both the phase shifted AND clean signal get fed back.
The feedback is positive, which, where the clean signal is involved, usually leads to uncontrolled howling, so you get quite a small range of adjustment between a useful feedback amount and rampant squeel. The cap I added probably gave a bit more useful range.
The original reason for adding that cap, was to isolate the first amp from any ground or DC voltage sneaking in from the output and changing the bias of the first amp. Normally, you would hope whatever it's plugged into would have a cap on it's input to stop this ever happening anyway. In the real world, you can't guarantee this is always the case, so I would add a cap in there anyway.

armdnrdy · November 20, 2015, 12:46:02 PM

Nick,

Without reading through this whole thread.....I'm not sure if it was ever outlined how to adjust the feedback path.

I'm assuming that you will "calibrate" TR1 (feedback trimmer) with a guitar instead of a signal generator.

The feedback control (P1) is connected one way....the correct way.
You should have less feedback (thinner sounding signal) when the control is CCW. You should have a "thicker" sounding phase when the control is CW.
Looking at the pot from behind, with the lugs facing down, the lugs are numbered 3, 2, 1, from left to right.
My drawing depicts the correct lug connections.

With the feedback control CW, the feedback trimmer set around the 50%, and the speed control around 50%, strum your guitar...sort of hard, to emulate the hottest signal that this circuit will see.

If the phaser starts to oscillate, adjust T1 CCW until the oscillation stops.
If it isn't to the point of oscillation yet....adjust T1 CW until it oscillates and then back it off a bit.

Check for oscillation at slower and faster speeds and adjust T1 accordingly.

With the feedback set correctly...you might achieve that "swampy" sound that you're searching for.

nickbungus · November 20, 2015, 02:17:20 PM

Cheers guys.

I've played with the trimmers to no avail on builds 3 and 4. I don't own these anymore though. I've only got my second build which is a mash up and this is the one with the nice swamp.

I'll do the build with the new board and then experiment with the feedback and the added cap to see if I can get a resolution. Perhaps just for testing omit the trimmer and have a temp 2M pot.

Thanks again Larry and Jim, the education is always appreciated.

nickbungus · November 22, 2015, 05:58:14 AM

Quote from: armdnrdy on November 20, 2015, 12:46:02 PM
The feedback control (P1) is connected one way....the correct way.
You should have less feedback (thinner sounding signal) when the control is CCW. You should have a "thicker" sounding phase when the control is CW.
Looking at the pot from behind, with the lugs facing down, the lugs are numbered 3, 2, 1, from left to right.

That is really interesting and I take it, it holds true for the trimmer. On my board, I've been using multi-turn trimmers and just putting them in without regard for CW/CCW.

Looking forward to my next build!

anotherjim · November 22, 2015, 06:21:57 AM

CW or CCW only matters for control panels where we want the common intuitive action of CW=More, CCW=Less. Also Log or Anti log pots will only give their intended sweep when CW=More, as in a Volume control.
In practice, with ordinary linear pots and trimmers, it makes no difference which direction More & Less is as long as YOU know.

It may be the 2 builds that didn't have a strong Q effect had a fault, such as one phase shift stage not working, but still passing clean audio. That would mean fewer notches - but still sounding like a working phaser.

nickbungus · December 01, 2015, 05:31:29 PM

Just a quick update on the Feedback control. I got my hands on one of the builds I wasn't happy with and played with the feedback trimmer some more.

This is what I did

1) Turned the pot to max Feedback
2) Adjusted the trimmer until I achieved squeal
3) Backed off the trimmer a tad

Much better. Getting a lot of control now.

lovetone · July 05, 2018, 06:07:12 PM

Hey

Can anyone re post the schematic please?

I know this is an old topic but it would be nice to see what your all talking about

nickbungus · July 09, 2018, 04:41:08 AM

I've got a newer board layout which is much neater. I've also verified it. I keep meaning to post it so give me a day or so and I'll get both the schematic and new board up.

njkmonty · July 09, 2018, 05:20:33 AM

nickbungus · August 16, 2018, 12:16:24 PM

Sorry - I promised this a long time ago and never got round to it.

Heres a PDF showing my final version and notes etc.

Any changes please let me know.

bcruzin2 · September 17, 2018, 01:04:13 PM

Hi Nick, I know this is an old post, but I have built the Foxx Phaser per your pdf. The only thing I had an issue with was it distorted quite a bit. I did change the R49 to 39K to reduce the distortion. I did not do the calculations what the gain is actually. Also it looks like it does not mention the jumper that goes on the board next to C21. other than that, it sound great, I might mess with some of the cap values mentioned earlier in this post. Great Job!

nickbungus · September 17, 2018, 02:34:21 PM

Hi. I'll have a look at the pdf and that jumper. The only time I've had distortion is because I've got a 10k or a 100k value wrong. Check you've got your component values correct and if you post your voltages I'll check with mine.

bcruzin2 · September 17, 2018, 06:32:32 PM

Wow that was fast, thanks I will check that tonight! I can see where a 10k or 100K could cause a mess. Also, earlier in the thread it talks about a 4 way rotary switch for different speed setting, do you happen to have a jpg of that handy, if not no biggie, I can experiment, I know where it goes. so I can figure out the layout.

nickbungus · September 18, 2018, 04:41:09 AM

Yes - Because its just a sea of 10k and 100ks, after I build one I now just quickly check them all before I even try it out.

I've added the jumper to the document - good spot. I've also added the wiring for the rotary switch - although I think its not necessary

Thanks

bcruzin2 · September 18, 2018, 06:15:29 PM

For the voltages I get
From the Voodoo Labs Power 9.35v
at pin 4 of the chips 8.55
at the D4 I get 1.86v
Z3 pin I get +6v
For the FETS
1= +6
2= +6
3= +2.5v
I did not have a 12 ohm so used a 18ohm and for the 560, it is a 580.

nickbungus · September 18, 2018, 06:36:25 PM

If you give me all the voltages on all pins on all chips we'll probably be able to see there the issue is

bcruzin2 · September 18, 2018, 06:47:00 PM

Found it! R46 and R47 need to be swapped on the board. Just the labeling needs to be changed so the correct values are used.

nickbungus · September 19, 2018, 07:40:05 AM

Brilliant - That is such a good spot. Much appreciated. I've amended the PDF

Thank you so much

DMgremlin · September 26, 2018, 02:53:35 PM

About to be repairing this Studio Model 7, thought I would share pics. Right now it has output signal with no phasing. Read the entire thread and looks like Larry's schematic with updates is no longer visible? I should be able to figure it out anyway, I think...

nickbungus · September 28, 2018, 02:05:59 AM

Oh wow.

If you could get some high quality shots of the top and bottom and also some side shots on the component side I'm sure we can figure it out

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What Does the Foxx Phase?