3-knob Manny's/Orpheum/Halifax/etc Fuzz

[mdcmdcmdc]

Ah, interesting - with the boost on full the volume reads 255K.

[Rob Strand]

Ah, interesting - with the boost on full the volume reads 255K.

Oh, something funny might be going on.

The 254K Boost pot measurement is too much like the 255K measurement.    What I think has
happened is when you measured the Boost pot the Boost pot wiper set to the wrong position.
You probably need to measure the Boost pot again.

Position the Boost pot to one extreme and measure the Boost pot across the outside terminals.  Then position
Boost pot to the other extreme and take the same measurement.    One of those measurements will be
254K/255K and the other should be higher.

In-circuit measurements are a bit tricky.

[mdcmdcmdc]

1:
Vol (full cw): 30.7 ohm
Boost (full cw): 22.7K
Tone (full cw): 525K

2:
Vol (full ccw): 251K
Boost (full cw): 252K
Tone (full cw): 525K

3:
Vol (full ccw): 22.5K
Boost (full ccw): 531K
Tone (full cw): 525K

4:
Vol (full ccw): 22.5K
Boost (full ccw): 531K
Tone (full ccw): 21 ohm

5:
Vol (full cw): 43 ohm
Boost (full ccw): 531K
Tone (full ccw): 12.5 ohm

6:
Vol (full cw): 34.5 ohm
Boost (full cw): 22.7K
Tone (full ccw): 8.5 ohm

7:
Vol (full ccw): 251k
Boost (full cw): 252K
Tone (full ccw): 8.5 ohm

8:
Vol (full cw): 32 ohm
Boost (full ccw): 531K
Tone (full cw): 525k

[mdcmdcmdc]

If any of those seem fishy I can double check - I started getting a bit crosseyed trying to keep track of the perms/coms.

[Rob Strand]

If any of those seem fishy I can double check - I started getting a bit crosseyed trying to keep track of the perms/coms.

Awesome effort.  Those measurements are above and beyond what most people would do.
There's no doubt about what's going on now.

2:
Vol (full ccw): 251K
Boost (full cw): 252K
Tone (full cw): 525K

3:
Vol (full ccw): 22.5K
Boost (full ccw): 531K
Tone (full cw): 525K

8:
Vol (full cw): 32 ohm
Boost (full ccw): 531K
Tone (full cw): 525k

From those, measurements we can work out,

Tone pot:      500k      (exact 525k)
Boost pot:     500k     (exact 531k)
Volume pot: 500k      (exact 457k)

Very interesting result as the pots have different values to some of the other similar units.
I guess one motivation for change is the addition of the Tone pot.


EDIT:
Your tests also confirm:
- when the Boost pot is on fully clockwise the wiper is at the C4 end.    I mentioned that before but your measurements confirm it.
- when the Tone pot is on fully clockwise the Tone pot opens, which gives more treble.

[Rob Strand]

If any of those seem fishy I can double check - I started getting a bit crosseyed trying to keep track of the perms/coms.

It's optional but if you want to work out the pot tapers.

1) Set Tone pot to mid position, other pots anywhere - no effect.
    Measure between ccw lug (pin 1) and wiper (pin 2) of Tone pot.

2)  Set Volume pot to mid position.  Set Boost pot fully clockwise, Tone pot anywhere. 
    Measure between ccw lug (pin 1) and wiper of Volume pot.
     Measure between cw lug (pin 3) and wiper of Volume pot.

3) Set Boost pot to mid position, other pots anywhere - no effect.
    Measure between ccw lug (pin 1) and wiper of Boost pot.
    Measure between cw lug (pin 3) and wiper of Boost pot.

[mdcmdcmdc]

Tone mid, vol ccw, boost ccw
Tone = 313K

Vol mid, boost cw, tone cw
Vol = 148K

Boost mid, vol cw, tone cw
Boost = 165K

[Chillums]

Looks to me from your measurements
Tone = B500k
Boost = A500k
Vol = A500k

[Rob Strand]

The volume pot 50% point needs to be calculated.     We take the raw measurement then remove the rest of the circuit taking into account the pot settings for the test.

I'm assuming all pot taper measurements were measured across pin 1 (ccw) and pin 2 (wiper).

Volume taper measurement = 148k
Rest of circuit is 831k
True volume taper @ 50% = 180k

                  exact pot       50% rotation (1,2)     %taper
Tone         525k             313k                            60%
Boost        531k             165k                            31%
Volume    457k              180k                           39%

Tone pot taper likely to be linear, 500kB
Boost pot taper is probably a 20% to 30% audio taper, 500kA.
The volume pot is a little ambiguous because within tolerances is sits between 30% audio taper and a linear (50%).

We might guess the audio tapers were nominally 30%.    Remember tapers weren't as standardized in the 60's.

As far as building clones, I've found most modern audio taper(A taper) pots end-up with a taper of about 15% to 20%,
but in some cases it's lower. Given that, a linear volume pot is likely to be closer to the original taper than an audio taper.

[mdcmdcmdc]

Oops, I read your previous post too quickly and didn't take 2 measurements - I'll recheck those numbers later today...

[Rob Strand]

Oops, I read your previous post too quickly and didn't take 2 measurements - I'll recheck those numbers later today...

No problem.  It's probably more important to be certain which measurements are between ccw (pin 1) and wiper (pin 2) and which are between cw (pin 3) and wiper (pin2).   Since that would flip the taper from log to anti-log.

The two measurements are a cross-check (which can't be done for the Tone pot).

[mdcmdcmdc]

Tone mid
Tone 1-2: 333K

Vol mid, boost full cw
Vol 1-2: 3.0 ohm
Vol 2-3: 150K

Boost mid
Boost 1-2: 22.2K
Boost 2-3: 228K

[Rob Strand]

Tone mid
Tone 1-2: 333K

Vol mid, boost full cw
Vol 1-2: 3.0 ohm
Vol 2-3: 150K

Boost mid
Boost 1-2: 22.2K
Boost 2-3: 228K

Not sure what's happened there.  Something has got out of whack.
Especially on the 1-2  measurements on the Vol and Boost pots.

The Tone looks fine and consistent with the previous measurement.

The Vol 1-2 measurement  (3.0 ohm) is like a short during the 1-2 measurement.  It shouldn't be possible to get a value like that if the Volume pot is set to the middle.   The Vol 2-3 measurement (150k) is roughly OK for a linear pot but something is off.

Boost 1-2 (22.2) looks off.   Boost 2-3 measurement implies more of a linear taper sort of in the ball park.