Fuzzdog Phase 90 Clone - Ticking noise

[bettsaj]

Just finished my second Phase 90 clone, this time a Fuzzdog pedal parts build using GGG Jfets.

The pedal has come out perfect with lovely phasing, except for a ticking noise at the top and bottom of the sweep...... Any ideas what could be causing this?

[bettsaj]

I've just read on a review of this very pedal that a previous builder had the same issue, but his was cause by using the incorrect voltage Zener diode. Instead of the correct 5.1v he used 4.7v.... When he replaced his 4.7v with the correct voltage diode the ticking disappeared.

the issue here is I've used the correct voltage Zener diode. I suppose there is a small chance I could have killed the diode when I soldered it in place.... I have spares, i'll swap it out and see what happens.

[Rob Strand]

There's many ways that can happen.   I can only assume some people have got it to work.

One issue is the LFO IC, IC1B, shares common power pins with IC1A which carries the audio.  Good designs avoid using opamps common to the LFO and audio for that reason.  Basically IC1B is switching off and on and the pulses from that are coupling back into the audio.  I'd guess through the ground pins but it doesn't have to be that way.  Some opamps might be more prone to this than others.

Another possibility is related to the zener supply.

A good start would be to check all you solder connections especially the ground pins and power pins on the ICs and also C12 and C10.

So a sledge hammer approach to see where the problem *might* be would be to:
- Solder a 100uF cap right across the power pins of IC1.
- Solder a 100uF cap across the Zener/C12
The aim would be to see if there is any change/reduction at all.

Next is more to prove that IC1A has crap on it.  So lift C2 (side to Q1's collector) and wire that to pin 1 IC1A.
That would stop the phasing effect and only listen to the output of IC1A.   If the ticks are there then clearly source of the ticks related to IC1 (or the zener supply).

If the ticks aren't on IC1A then I'd restore the wiring of C2 and see if the ticks are present with R21 lifted.

Beyond that is kind of damage control in that we are trying to get out of a bad situation.   You might be able to use a different opamp IC1 which just happens to have less coupling between the halves of IC1A and IC1B.  Another would be to increase C8.

[bettsaj]

What I'll do is start easy first. I'll replace the zener to see if I fried it when I soldered it. Hopefully that will sort it.

If not i'll start going through the above.

[mickeybellinello]

Hi

I'm interested to..

Please write when You'll get updates.

Thanks

[bettsaj]

Will do...

[Rob Strand]

What I'll do is start easy first. I'll replace the zener to see if I fried it when I soldered it. Hopefully that will sort it.

It's worth trying.  You should measure the voltage on the zener.  If it's way off it could be damaged.


FYI: What you can find is *different* zener will produce different results even if the zener is not damaged.
Those MXR circuits run the zeners at low currents so 1W zeners are only just working.   You might
replace the zener and fix the problem even though there's nothing wrong with the original zener!
If you use a 500mW zener instead of a 1W zener the chances of success are higher.

[Mark Hammer]

I can't see that the zener would play any role in this.  Its purpose is to provide a stable voltage source that can be divided down by the trimmer to whatever voltage is usable for the JFETs.  Remember that the JFETs need a stable bias voltage/current, and the original design is predicated on being battery-operated, which meant that the divided-down bias could potentially drift as the battery aged.  The zener makes the circuit behave as if one is feeding the bias circuit with a 5.1V external power supply.  It plays absolutely no role in the functioning of the LFO.

The TL072 used for the input buffer and LFO is not an especially current-hungry op-amp, but neither is it modest in its current demands.  And usually audible LFO-rate ticking is a product of the LFO chip wanting enough current to affect the audio path.  Unfortunately the board/layout you are using employs one dual op-amp for both the LFO and input buffer.

The earliest P90s used 6 separate op-amp chips (741), and issues that followed used a trio of TL062 chips, which can be a little hissy, but are low current.  I'm going to suggest swapping the TL072 for a lower-current chip like a TL022, TL062, or LM358, just to see if that makes a difference.

[Rob Strand]

I can't see that the zener would play any role in this.

It's unlikely but I'm willing to see how it pans out (since there was one report).   The LFO has some resistors going to Vref.  They are quite large so the "glitch" current going into Vref is very small and is further fended off with the 22uF cap.

[bettsaj]

Just for info.... Here's a link to the product page. The 3rd review down details the issue with incorrect voltage on the Zener.... So I suspect there must be a correlation.

https://shop.pedalparts.co.uk/Phaze_90/p847124_13467433.aspx

I'll swap the Zener and go from there. I have about 6 or 7 spares. i've also emailed Lee at Fuzzdog to see if he has any experience with this issue.... If he responds obviously I'll post it for all to see. I've been busy the last 2 days so stealing even half hour to swap out the Zener and test the circuit has been near impossible. I'll endeavour to get it done tonight and report back ASAP.

[bettsaj]

I've had a reply back from Lee.....

Hi Andy,

Hmmm. that's pretty extreme.

It won't harm to try swapping out the zener, but you could just check your reading at VB first, a quicker change would be to try another chip in IC1.

does it change with the biasing adjusted?

I have a few more of the TL072 chips so that's an easy swap, only thing i'm concerned about is when I bought them i bought them all from the same supplier (NOT Ebay), so if one's bad they all might be iffy as they might be from the same batch. I'll try it anyway.

I'll check the reading at VB and see what that is... What should it be?? I'll try and do all this tonight.

[mickeybellinello]

The TL072 used for the input buffer and LFO is not an especially current-hungry op-amp, but neither is it modest in its current demands.  And usually audible LFO-rate ticking is a product of the LFO chip wanting enough current to affect the audio path.  Unfortunately the board/layout you are using employs one dual op-amp for both the LFO and input buffer.

The earliest P90s used 6 separate op-amp chips (741), and issues that followed used a trio of TL062 chips, which can be a little hissy, but are low current.  I'm going to suggest swapping the TL072 for a lower-current chip like a TL022, TL062, or LM358, just to see if that makes a difference.

If it can be useful, when I built my phase 90 I tried several Opamp and some of them added strange noise... With an OP2134 (in my circuit one opamp for input/LFO) it produced strange sound/noise. The TL072 works well but it's not the best for the LFO. I ended with the TL062 which is less Hi-Fi but it has a great "modulation".

[bettsaj]

Update:

Changed the diode... no change
Changed the chip (IC1)... No change

Voltage of Zener is bang on 5.1v

I've also taken voltage readings off each leg of both IC's, as I was there with my DMM

IC1
1 - 5.13
2 - 5.13
3 - 3.49
4 - 0
5 - 3.9 to 5.0 (varying between the two readings)
6 - 4.6 to 5.4 (varying between the two readings)
7 - 2.2 to 7.0 (varying between the two readings)
8 - 8.48 to 8.51 (varying between the two readings)

IC2
1 - 4.73 to 4.75 (varying between the two readings)
2 - 5.13
3 - 5.03 to 5.07 (varying between the two readings)
4 - 8.46 to 8.49 (varying between the two readings)
5 - 5.48 to 5.64 (varying between the two readings)
6 - 5.27 to 5.32 (varying between the two readings)
7 - 6.15 to 6.46 (varying between the two readings)
8 - 5.85 to 5.89 (varying between the two readings)
9 - 6.2 to 6.35 (varying between the two readings)
10 - 6.02 to 6.19 (varying between the two readings)
11 - 0
12 - 5.02 to 5.04 (varying between the two readings)
13 - 5.13
14 - 5.13

[Rob Strand]

Changed the chip (IC1)... No change

Changing the IC is only has a chance to work if you replace it with a different type.  Same IC type and same batch/brand is likely to produce similar results.  It's a grasp at straws solution in an attempt to try an opamp with less internal coupling ; at this point we don't *know* it's internal coupling.   It's also pot luck.

At this point I'd definitely be trying some of the stuff I mentioned in my earlier post.  That's more about narrowing down the problem.

[bettsaj]

That's next on the agenda

[abram]

I'd have to agree with Rob's take on it. The switching of the LFO is definitely coupling into the audio somewhere. Finding out where is the tricky part. Increasing C8 should smooth the transition between states in the LFO if added filtering doesn't help. You might also investigate C9 by switching it with a different cap and making sure that it's polarity isn't reversed. Since the LFO is oscillating, C9 seems to be doing it's job but it's worth a look. Good luck!

[bettsaj]

A good start would be to check all you solder connections especially the ground pins and power pins on the ICs and also C12 and C10.

So a sledge hammer approach to see where the problem *might* be would be to:
- Solder a 100uF cap right across the power pins of IC1.
- Solder a 100uF cap across the Zener/C12
The aim would be to see if there is any change/reduction at all.


Next is more to prove that IC1A has crap on it.  So lift C2 (side to Q1's collector) and wire that to pin 1 IC1A.
That would stop the phasing effect and only listen to the output of IC1A.   If the ticks are there then clearly source of the ticks related to IC1 (or the zener supply).

If the ticks aren't on IC1A then I'd restore the wiring of C2 and see if the ticks are present with R21 lifted.

Beyond that is kind of damage control in that we are trying to get out of a bad situation.   You might be able to use a different opamp IC1 which just happens to have less coupling between the halves of IC1A and IC1B.  Another would be to increase C8.

Right, I've actually got around to looking at this issue. Juggling too many things at the moment so this got put on the back burner.

I only have 100uf polarised caps for the first test...

[anotherjim]

Some trusted designs tick if the builder does something clever like add an indicator LED driven off the LFO.
But if you haven't done that, the LFO can sometimes be de-ticked  by adding a small capacitor to ground where the squarewave is which I think might be on pin5 of IC1B. Something like 1nF maybe or even 10nF? This slows down the fast edge as the LFO oscillator switches direction.
On the pcb, C11 (100nF) should be very close to IC1 power pins. If not, add another 100nF ceramic cap there. This will help filter the ticks. As it's in the nature of ticks to contain fast transients then (counter-intuitively) the smaller ceramic type capacitor is better for filtering them out.

[bettsaj]

So a sledge hammer approach to see where the problem *might* be would be to:
- Solder a 100uF cap right across the power pins of IC1.
- Solder a 100uF cap across the Zener/C12
The aim would be to see if there is any change/reduction at all.

Rob, I only have 100uf polarised caps..... Do you mean 100nf?? only asking as @anotherjim suggested pretty much the same as you but he recommended 100nf

[Rob Strand]

Rob, I only have 100uf polarised caps..... Do you mean 100nf?? only asking as @anotherjim suggested pretty much the same as you but he recommended 100nf

Nothing wrong with what Jim said.  IMHO it's best to be heavy handed when debugging.  For problems like this a 100uF is usually better since it provides a very solid supply rail.  I'd try that first then take it from there.   If it doesn't fix it I'd also try a 100nF.   That's kind of what you do in cases like this.