guv'nor...lack of gain

[Miracle Man]

Anyone?!  I'm really bummed out by this as it was my first pedal build and I can't get it to work properly.

[Gus]

Have you measured the DPDT switch.  Make sure the switch is still working correcly. 

Have you checked the input and output jacks?

  Check the loop jack.

[Ronan]

I have a Crunch Box and a Crunch Box clone converted to a Guv'nor, the input stage of both pedals is identical to a Guv'nor, tomorrow I will open them both up and measure the voltage at pin 3, and see what it is. Hope I don't get a nasty surprise, anything is possible...

[Ronan]

Genuine MI crunch box
batt 8.69V
pin 8 8.15V
pin 3 4.08V

Joyo copy crunch box
batt 9.04V
pin 8 8.47V
pin 3 4.07V

[Mike Burgundy]

Sorry, I lost track of this thread. Pin3 is definitely wrong, pins 1-3 and 5-7 should be at roughly 4.5V.
The + input pin sets that DC voltage at the output, so without an IC in only 3 and 5 should be at that voltage.
The weird thing is that with pin 3 low, pins 1 and 2 should follow that and be low as well. Are you sure the measurements are ok? I can't see how 1 and 2 could be correct without 3.
What is your measurement technique, and what is your meters internal resistance? It could be the meter is interfering with a correct reading if it's resistance is something like 1M..... You could replace R3 with a 100k, just to rule out meter interference.

[Gus]

When an effect with a DPDT etc switch and jacks loses volume IMO the first things to test are
the DPDT switch
the loop jack
input jacks, did the contacts lose their "spring"
Remove the battery set the meter to Ohms and test the connections.

Install the  battery set the DMM etc to volts and install a 1/4inch plug to power up the effect.
Not knowing what the meter specs are
Here is a trick for testing a high input resistance reference to 1/2 the power supply voltage with a meter that has a low input resistance in a circuit like this.
Check pin 3 to ground and pin 3 to +9VDC.  If they both measure about the same voltage the meter is loading down the reading.  Pin 3 has 1meg to 1/2 voltage

My guess is it is the loop jack having resistance from corrosion.  

[Miracle Man]

I really appreciate the help guys!

...so without an IC in only 3 and 5 should be at that voltage.

Correct, without an IC I only see voltage at pins 3, 5 and 8 (9v).

The weird thing is that with pin 3 low, pins 1 and 2 should follow that and be low as well. Are you sure the measurements are ok? I can't see how 1 and 2 could be correct without 3.

What is your measurement technique, and what is your meters internal resistance? It could be the meter is interfering with a correct reading if it's resistance is something like 1M..... You could replace R3 with a 100k, just to rule out meter interference.

I'm not sure about the DMM's internal resistance. It's an older one and I can't find any data online. I've ordered a new one a few days ago and it should be here at the end of the week.

However, I did replace R3 with a 100k as per your suggestion and it did make a difference. 2.12V with 1M and 3.8V with 100k. The R3 change only affects pin3 while pins 1 and 2 read 4.3V either way.

Here is a trick for testing a high input resistance reference to 1/2 the power supply voltage with a meter that has a low input resistance in a circuit like this.
Check pin 3 to ground and pin 3 to +9VDC.  If they both measure about the same voltage the meter is loading down the reading.  Pin 3 has 1meg to 1/2 voltage

I also tried this (with 1M for R3) and get 2.11V and -2.11V. So... does this mean the DMM is the problem?

Again, Mike, Gus and Ronan, I really appreciate the help! Thank you!! 

[ashcat_lt]

Yup, must be the meter has low impedance compared to R3.  Evidently even low compared to 100K, but quite large compared to the output impedance of a TL072.  The reading between Vref and 9V comes up negative because you moved the black lead, which the meter expects to sit at a voltage lower than the red.

BTW - when you were measuring resistance between pin 3 and ground you were actually reading R3 plus the bottom hals of the Vref divider. 

[Mike Burgundy]

Okay, that unclutters the mystery somewhat.
Lets consider voltages and IC ok.
Have a go at Gus' excellent suggestions, those are your best bet.

[qtws]

bump....again...

ok, last weekend, I replaced the IC, pulled up the ends of R3 and C5 - all good, 1M and not shorted, respectively.  Still 2.21V on  pin 3.  Said sod it, and rebuilt, and the thing works....fair amount of gain, but not quite as much as I remember (or would like). Seems to be fairly stable, but the sustain on top GBE strings isn't that great - you really have to work for those notes. Picked lightly, they are almost clean.
I have no idea why this might be: the overall tone is not bad - although it seems to emphasise string buzz.

This evening, I breadboarded a guvnor circuit, minus the tone controls. Used 68k for R4 and R5 as I didn't have any 47k to hand. VR1 substituted with a 100k for max gain initially. Kept C14 (470pf to gnd).

Now....I measured the voltages. 1, 9.56; 2, 4.82; and, on pin 3, 2.35V  Pin 4, 0.0;  Pin 5, 4.83; pin 6, 4.84; pin 7 5.31; pin 8, 9.6.

Same low voltage on pin 3, but bliddy 'ell, this thing sounds great! Loads of gain, almost uncontrollable pouring into feedback, no problem slurring on the top strings, but still plenty of attack and definition. And the low string pinch harmonics a la Zakk Wylde -they there   This is more like it (and how I remember the original pedal thru a PA20/4x12), although the treble is nearly too sharp.  It set off my tinnitus very nicely    Only one of the leds glows with signal - both do in the original.

The breadboard version is much much louder - which is presumably due to no tone controls, which probably explains the relative sharpness. Time to build a tone stack.

Any suggestions? Box the original up and enjoy it? Is it worth trying to get pin 3 up to 4.5V?.....Oh! just did the trick mentioned by Gus  above - pin3---gnd, and pin 3---9V:  2.21V in both cases, suggesting its the meter which is giving the odd reading....

On the upside, the breadboard circuit worked first time! Yay!   

[Mike Burgundy]

Like Gus said: have you tried measuring pin 3 to ground, and then +9V to pin3? If these voltages are the same, there is nothing wrong but your meter is low impedance enough to load your measurement. If this is the case, circuit is fine.
It would seem (with the partial rebuild fixing problems) that it was indeed a connection problem somewhere - see Gus' post.

[Mike Burgundy]

Oh, and yes, the tonestack drops quite a lot, which accounts for both the level and sound difference.

[qtws]

Cheers Mike. I have put it all back together and that's that. I have no idea where the problem lay, but it seems to be fixed now and I have learned loads thanks to you guys. 

Current experimentation involves a 12V 12AU7 powered jcm800-style valve boost into the first half of the breadboarded guv'nor (FB resistor 50k) running on 9V.  This is very pleasing....very responsive to touch, if lacking a little in outright gain.  This hobby is good clean fun!