Boss PH-1R --- TOO BRIGHT!

[rundgrenrules]

I scored a Boss PH-1R cheap ($50) because it had been returned to a seller due to it being "weak" sounding.  After a little troubleshooting I determined that the trimpot needed to be replaced and adjusted to bias the transistors, and the depth knob needed to be replaced.  Turns out someone had superglued the depth knob to the pot shaft so trying to remove it pulled the shaft out of the pot.  So... all new pots and knobs.

I have re-capped with new electrolytics and tantalums and replaced C1 (.047uf) with a .082uf cap to get the same perceived amount of bass when in bypass and engaged.  Stock value cut a decent amount of bass.  This larger value doesn't seem to cause any ugliness or extra distortion and just adds fullness.  The phasing is strong and the pedal sounds great...BUT...

The issue is that the phaser is BRIGHT when engaged.  Its not extreme but it makes me want to reach for the tone knob on the guitar to roll it down each time its engaged.  I dont see where in the circuit the top end can be tailored.  I dont mind losing a little white noise in the process too, if such a circuit exists here for noise suppression.

Any suggestions on where to look?  Schematic attached.
Thank you!

[Rob Strand]

There's nothing *making* it bright in the circuit.

Are you sure it's not the Resonance (RES pot) causing it?   Try setting it to zero, not 12 O'Clock.

Another possibility is the BIAS trimpot (VR4) is off and just happens to make the pedal sound bright.

You can take some of the high end out of the phase-shift path.   An easy way to roll-off some highs is by increasing the cap C3 to say 560p.   Another way is to add a cap across R9, say 39n.   While these filter the highs they don't remove noise.  A better filter would be to lift one end of C14 and insert a low-pass filter (or shelving filter), say 2k2 and 15n.   The cap values I've given are subtle you could be more aggressive and use larger caps.

I've purposefully not messed with the clean path.  I'm assuming you can dull down the signal enough by messing with the phase-shift path.

[PRR]

C2 C17 could have lost uFds over the decades.

[Rob Strand]

C2 C17 could have lost uFds over the decades.

He's already re-cap'ed.

[rundgrenrules]

Are you sure it's not the Resonance (RES pot) causing it?   Try setting it to zero, not 12 O'Clock.

Another possibility is the BIAS trimpot (VR4) is off and just happens to make the pedal sound bright.

It happens even with the Resonance pot wound all the way down as well.  The Bias trimpot I have adjusted for strongest sweep and the pedal also happens to have the most full frequency response from lows to highs at this point as well.

You can take some of the high end out of the phase-shift path.   An easy way to roll-off some highs is by increasing the cap C3 to say 560p.   Another way is to add a cap across R9, say 39n.   While these filter the highs they don't remove noise.  A better filter would be to lift one end of C14 and insert a low-pass filter (or shelving filter), say 2k2 and 15n.   The cap values I've given are subtle you could be more aggressive and use larger caps.

Earlier I had tried adjusting C3 to a larger value and it seemed to affect the bypassed signal as well, dulling both the effected and bypassed signal.  So I went back to stock there.  I tried paralleling R9, even going as far as 100nf and it didn't seem to remove it either so that is back to just the stock resistor.  Its some 6-8kHz spiky frequencies that pop out along the top of the sweep and recess in the bottom of the sweep.

I have adjusted the trimpot, tweaking the RES and DEPTH knobs to make sure I am accounting for higher and lower resonance settings and the frequency response remains the same in the narrow range of the trimpot where the bias gets a good strong phase happening.

There is a good bit of white noise anywhere above noon on the RES pot.  I am wondering if there might be a connection between the higher resonance noise and the peaky treble response.  It seems like more noise than would have been deemed acceptable when the pedal was fresh out of the factory.  I wonder if these 4558s could use some socketing and swapping, potentially with lower noise alternatives.  I assume the TL022 is providing LFO timing.

I also put C1 back to the stock 47nf since it is part of the input buffer and not the actual input cap.

[Slowpoke101]

Sorry to have to ask this but did you test the replacement capacitors to make certain that they were the correct value and were correctly labelled? It is possible to be supplied with incorrectly labelled parts.

[Rob Strand]

arlier I had tried adjusting C3 to a larger value and it seemed to affect the bypassed signal as well, dulling both the effected and bypassed signal.  So I went back to stock there.  I tried paralleling R9, even going as far as 100nf and it didn't seem to remove it either so that is back to just the stock resistor.  Its some 6-8kHz spiky frequencies that pop out along the top of the sweep and recess in the bottom of the sweep.

I get C3 affecting the dry signal, a silly oversight by me, the clean tap is on the output of that inverter.   It weird that the issue is still present with a cap across R9.   It's starting to smell like some kind of fault.

Something else you could try is to change R32 to 27k to see if it takes the sting out of it.

There is a good bit of white noise anywhere above noon on the RES pot.  I am wondering if there might be a connection between the higher resonance noise and the peaky treble response.  It seems like more noise than would have been deemed acceptable when the pedal was fresh out of the factory.  I wonder if these 4558s could use some socketing and swapping, potentially with lower noise alternatives

It's quite possible it is related but it's difficult to judge if the noise is normal or not.   That unit opens itself up to noise since it divides the signal by 2 before the 4xall-pass opamps then boost the level up again.  That effectively amplifies the noise from 4xopamps.  The have done this to handle larger signals.  There's a subtly in the feedback connection as well in that the first opamp boost has a gain of just under 2 for the RES signal.

There's so many opening for mods to reduce noise:
- pull R9, short R8
- change R7 to 12k  ; maybe increase C4.
- change R32 to 47k

Further mods would be to add pre-emphasis at the first opamp at R4 and de-emphasis at the last opamp at R33.   Sort of like the CE-2 structure.  The problem is that much isn't complete.  You need to add a step EQ to the RES path to put de-emphasis on the feedback.

The noise issue solution here is separate from the high frequency issue.

[GibsonGM]

TLDR, but If you recapped, you sure you put the right values in?  I know, I know, but gotta ask. Ignore if already asked, not enough coffee yet.

[Mark Hammer]

It is a frequent practice for phasers with more than 4 stages to include a cap in the feedback loop of the last stage, in order to reduce the cumulative noise of recirculated signal.  So I'll suggest tacking a 390pf cap in parallel with R26.  That rolls off above 3.4khz, but it's a shallow rolloff.

The other thing to bear in mind is that this, and many other, Boss circuits do not bypass anything.  They merely cancel the effect produced when wet and dry are combined by turning off Q6.  So normal clarity of the dry signal means one shouldn't monkey with anything in common to both wet and dry.

Rob is correct in suggesting R32 as a potential locus of improvement.  I will suggest swapping the 22k of R32 for a 10k+12k series pair.  That preserves the relative balance/mix of wet and dry, but offers a place of tonal intervention to address the problematic brightness.  Running a 330pf cap from their junction to ground will roll off highs for the wet path alone.  That will also help with the cumulative hiss.

[ElectricDruid]

Both halves of IC1 and C3 and C16 are all in the "dry" path, so if it sounds ok when bypassed, those parts must be at least reasonably good. These old Boss pedals have a lot more in the "bypassed" path than typical modern stuff, but that's normal for them.

If the noise and brightness only appears when the effect is switched in, it must come from the phase shift stages based around IC2 and IC3. Like Rob, I might suspect a fault in one of them. Perhaps something is oscillating or distorting? Can you post a sound sample somewhere so we can hear it?

Mark's suggestion of splitting R32 to provide a place where another smoothing cap can be added is a good one, but I'd want to be sure that the signal there was the signal that *should* be there before I started trying to fix the symptoms of a problem rather than fixing the problem.
Lifting one end of R31 would give you a wet-only signal when on (and nothing when bypassed!) but this might make it easier to hear if the phase shift stages are working correctly. You should get a basic vibrato like that, with no extra brightness or distortions.


PS: Incidentally, C1 definitely is the input cap, as well as being part of the input buffer, so put whatever value suits, but it will affect both bypassed and effected signals.

[Mark Hammer]

Both halves of IC1 and C3 and C16 are all in the "dry" path, so if it sounds ok when bypassed, those parts must be at least reasonably good. These old Boss pedals have a lot more in the "bypassed" path than typical modern stuff, but that's normal for them.

If the noise and brightness only appears when the effect is switched in, it must come from the phase shift stages based around IC2 and IC3. Like Rob, I might suspect a fault in one of them. Perhaps something is oscillating or distorting? Can you post a sound sample somewhere so we can hear it?

Mark's suggestion of splitting R32 to provide a place where another smoothing cap can be added is a good one, but I'd want to be sure that the signal there was the signal that *should* be there before I started trying to fix the symptoms of a problem rather than fixing the problem.
Lifting one end of R31 would give you a wet-only signal when on (and nothing when bypassed!) but this might make it easier to hear if the phase shift stages are working correctly. You should get a basic vibrato like that, with no extra brightness or distortions.


PS: Incidentally, C1 definitely is the input cap, as well as being part of the input buffer, so put whatever value suits, but it will affect both bypassed and effected signals.

Good strategy!

[rundgrenrules]

Sorry to have to ask this but did you test the replacement capacitors to make certain that they were the correct value and were correctly labelled? It is possible to be supplied with incorrectly labelled parts.

I tested the capacitance with my DMM, but I also have a Peak ESR70 on the way so i can test ESR going forward.

TLDR, but If you recapped, you sure you put the right values in?  I know, I know, but gotta ask. Ignore if already asked, not enough coffee yet.

Yep!  I used some bipolar 1uf electrolytics that I had on hand from a recent hifi receiver re-cap and a bit on the large size 100uf from the same hifi re-cap but it fits.  The only thing that is different really is that I used a 100nf MLCC in place of the tantalum that was there for C21.  I have read that tantalum might have better performance in certain areas like filtering.  Coming of the center lug of the bias trimpot to ground, it would seem that this might be a place where that might matter?

Something else you could try is to change R32 to 27k to see if it takes the sting out of it.

There's so many opening for mods to reduce noise:
- pull R9, short R8
- change R7 to 12k  ; maybe increase C4.
- change R32 to 47k

I tried all of these, as well as...

Rob is correct in suggesting R32 as a potential locus of improvement.  I will suggest swapping the 22k of R32 for a 10k+12k series pair.  That preserves the relative balance/mix of wet and dry, but offers a place of tonal intervention to address the problematic brightness.  Running a 330pf cap from their junction to ground will roll off highs for the wet path alone.  That will also help with the cumulative hiss.

...this suggestion.

In all cases the spikey harsh treble is there when engaged.  More and more it appears taht the filtering remedies might not be addressing the harshness because it might be coming from some type of distortion causing the harsh harmonics to pop out.  I have gone back to stock values throughout.

I also socketed the opamps and just quickly swapped in some other 4558s I had on hand, no change there either.  Still the same issue.  I am about to go through the entire Service Notes manual and make sure that all the cap and resistor values match up, and that there isnt some type of wrong value placed in there from the manufacturer all those years ago.

[ElectricDruid]

Good strategy!

Credit where it's due: it's *your* idea for the best/easiest way to find the right bias point in BBD pedals, but it works for this too!

[Rob Strand]

In all cases the spikey harsh treble is there when engaged.  More and more it appears taht the filtering remedies might not be addressing the harshness because it might be coming from some type of distortion causing the harsh harmonics to pop out.  I have gone back to stock values throughout.

Distortion is a whole different issue.   All the recommendations upto now are linear and only modify the frequency response.

Perhaps there is an issue with the switching JFET Q6.   Try temporarily shorting  out D and S with a wire.   Try both bypass and effects mode (although they both should sound like effect). It's better to remove the JFET as well but shorting might do it.

Check the zener voltage D3.  That can mess with the JFET switching if the JFET parameters are extremes.


Something else to check would be the DC voltages at the outputs of each of the opamps.

[rundgrenrules]

Looks like Q5 was soldered in reverse at the factory (I suppose):



Its flipped now.  I think the frequency when engaged is much more balanced now, but theres a definite volume boost when engaged.  Still a little noisy at higher resonance settings too.  I dont know how it was phasing before with one of the transistors in reverse.  Would it have been a 3-stage phaser?

Anyways, I went through the whole schematic and service manual.  Every single component is of correct value.

Here are the voltages I measured:

IC1   1-5v   5-9.23v
   2-5v   6-5v
   3-5v   7-5v
   4-0v   8-4.97v
      
IC2   1-5v   5-9.23v
   2-5v   6-5v
   3-5v   7-5v
   4-0v   8-4.97v
      
IC3   1-5v   5-9.23v
   2-5v   6-5v
   3-5v   7-5v
   4-0v   8-4.97v
      
IC4   1-Variable   5-9.23v
   2-Variable   6-Variable
   3-Variable   7-Variable
   4-0v           8-Variable

Q1      E-3.86v
        B-9.23v
        C-4.3v

Q2      D-5v
        S-2.9v
        G-5v

Q3      D-5v
        S-2.9v
        G-5v

Q4      D-5v
        S-2.9v
        G-5v

Q5      D-5v
        S-2.9v
        G-5v

Q6      D-5v
        S-0v
        G-5v

Q7      B-0.641v
        C-0.45v
        E-0v

Q8      B-0.616v
        C-0.017v
        E-0v

[Mark Hammer]

Sorry to have to ask this but did you test the replacement capacitors to make certain that they were the correct value and were correctly labelled? It is possible to be supplied with incorrectly labelled parts.

I tested the capacitance with my DMM, but I also have a Peak ESR70 on the way so i can test ESR going forward.

TLDR, but If you recapped, you sure you put the right values in?  I know, I know, but gotta ask. Ignore if already asked, not enough coffee yet.

Yep!  I used some bipolar 1uf electrolytics that I had on hand from a recent hifi receiver re-cap and a bit on the large size 100uf from the same hifi re-cap but it fits.  The only thing that is different really is that I used a 100nf MLCC in place of the tantalum that was there for C21.  I have read that tantalum might have better performance in certain areas like filtering.  Coming of the center lug of the bias trimpot to ground, it would seem that this might be a place where that might matter?

Something else you could try is to change R32 to 27k to see if it takes the sting out of it.

There's so many opening for mods to reduce noise:
- pull R9, short R8
- change R7 to 12k  ; maybe increase C4.
- change R32 to 47k

I tried all of these, as well as...

Rob is correct in suggesting R32 as a potential locus of improvement.  I will suggest swapping the 22k of R32 for a 10k+12k series pair.  That preserves the relative balance/mix of wet and dry, but offers a place of tonal intervention to address the problematic brightness.  Running a 330pf cap from their junction to ground will roll off highs for the wet path alone.  That will also help with the cumulative hiss.

...this suggestion.

In all cases the spikey harsh treble is there when engaged.  More and more it appears taht the filtering remedies might not be addressing the harshness because it might be coming from some type of distortion causing the harsh harmonics to pop out.  I have gone back to stock values throughout.

How hot a signal are you feeding the pedal?  The FETs used as variable resistors will clip when pushed hard.  There are adjustments that can be made to the FETs that will make them less susceptible to clipping.  However, Mike Irwin told me that, with such adjustments, the threshold for clipping moves up, but clipping comes on suddenly and is ugly.  He preferred the circuit without these adjustments because the distortion was gradual rather than sudden.  But then MIke was working with synths, that would normally have MUCH hotter signals than guitar.

The PH-1R uses that "adjustment".  In the first phase shift stage, you can see it with C7/R13, and C9/R18 in the next, and so on.  It's not"wrong", and Boss used it for all the right reasons.  This is why I ask how hot a signal you're feeding it.

[Rob Strand]

Looks like Q5 was soldered in reverse at the factory (I suppose):

Its flipped now.  I think the frequency when engaged is much more balanced now, but theres a definite volume boost when engaged.  Still a little noisy at higher resonance settings too.  I dont know how it was phasing before with one of the transistors in reverse.  Would it have been a 3-stage phaser?

I haven't checked the actual traces to confirm Q5 is reversed.  However you can see on this 1984 unit that it is like yours was,



All that aside those JFETs are supposed to be symmetrical (meaning D and S can be interchanged) so it shouldn't make a difference.   However, since JFET based phasers are sensitive to the matching of the VP parameter, which is why those parts are "Selected" on the schematic, it's possible the JFETs aren't matched as close as they could be.  It's all speculation really without measuring VP in forward and reverse to confirm how much difference it makes on VP.

Here are the voltages I measured:

All the voltages look good normal except some minor points:

- S and G are reversed.

- Q7 and Q8 voltages are not consistent with the flip-flop being
  in bypass or effect.   In both cases Q7 or Q8 are on.
  I think it's probably something trivial like the footswitch was pressed between measurements.


It's normal for the level to increase a bit.   Some people expect it, some people don't
The only easy way around it is to increase R32 as a compromise.  Ideally R33 needs to decrease, or, R31 and R32 need to increase but for this pedal those solutions are not suitable as they will drop the dry level.

[ElectricDruid]

Q5      D-5v
        S-2.9v
        G-5v

Q6      D-5v
        S-0v
        G-5v

Why is Q6 Source so different from all the others? (2.9V)

[rundgrenrules]

Here are a few more online photos I could find of the transistor orientation from other PH-1R units:





And here is Q5 on mine after the reversal:



Diode Voltages:
             (+)           (-)
D1     0v             9.23v
D2     4.59v        9.23v
D3     0v             5v
D4     .036v        5.64v
D5     0.44v        0.01v
D6     Removed & jumpered along with R56 for 12v-9v conversion

Q5      D-5v
        S-2.9v
        G-5v

Q6      D-5v
        S-0v
        G-5v

Why is Q6 Source so different from all the others? (2.9V)

Q6 is well separated in the circuit from Q2-Q5.  I think it is performing a different function entirely than those 4 others.

How hot a signal are you feeding the pedal?  The FETs used as variable resistors will clip when pushed hard.  There are adjustments that can be made to the FETs that will make them less susceptible to clipping.  However, Mike Irwin told me that, with such adjustments, the threshold for clipping moves up, but clipping comes on suddenly and is ugly.  He preferred the circuit without these adjustments because the distortion was gradual rather than sudden.  But then MIke was working with synths, that would normally have MUCH hotter signals than guitar.

Just a tele with slightly overwound single coils!  Nothing intense signal-wise.

[rundgrenrules]

Im not too sure what diode they used in D1 position instead of the RD11EB3 that was called for.  This doesnt look like one or a 1N4001 equivalent:



Probably grasping at straws and not too important if its just for polarity reversal protection.