My studio Mic compressor build

[jfrabat]

Man, that's weird.

Well we need to fix the voltages around D5 first.  If the voltages are bad there the whole circuit following won't have any hope of working.

Yup.  As soon as you mentioned what I should find, and I measured, I knew this was an issue...

One oversight on my part is your multimeter might be 1M ohm input impedance and not 10M ohm.   That's going to mess with the voltage on cathode side of D5.  Even then I can't make sense of the measurement because you get a positive value.

Is there any way to measure this?  Maybe with a second MM?  I have 2...

When you measured the D5 cathode voltage did you have the multimeter -Ve lead connected to ground and the multimeter +Ve lead connect to D5.?      Most of the time you want the multimeter -ve leads connected to ground so we can make sense of the sign of the measurement.

I grounded the MM to the sleeve of the output jack, so yes, GND (and not V-)

The next tests would be,
- measure the DC voltage on the anode side of D5 with an without signal.
- maybe recheck the sign of the voltage on the cathode side of D5 with and without signal

Re-measuring D5, I am getting:

D5 (no signal):
Anode: +12.18V
Cathode: +13.78V

D5 (signal):
Anode: +14.49V
Cathode: +14.08mV

- measure the voltage on pin 6 of IC5b with and without signal.

IC5 Pin 6:

And just to be sure this one I did trace correctly (I have two IC's with the polarity inversed in the board!):

IC5 Pin 4: +15.34V
IC5 Pin 11: -15.00V

Also, some others I figured could be important:

Oh, and there was no solder bridge; checked it after I took the video.

I also took one of the empty boards, to check the copper traces.  D5 is connected to R74, R73, and C18 (as it should be).  R73 and C18 are connected to Pin 11 if IC5, so they SHOULD be getting V- (we already checked that above).  I am not sure where the positive voltage is coming from, but it is not only affecting D5...  And it seems it is the source of the issue here!  Any idea on how to narrow it down?

[11-90-an]

Error in the pcb itself?

There's a small possibility... try to reflow just the diode legs...

[jfrabat]

I don't know...  I will continue tomorrow.  Almost midnight here, and I got to work tomorrow, so I am off to bed.  If you have any other ideas, post them, and I will try them tomorrow.

[Rob Strand]

I don't know...  I will continue tomorrow.  Almost midnight here, and I got to work tomorrow, so I am off to bed.  If you have any other ideas, post them, and I will try them tomorrow.

OK.   IC5c pin 8 (ie. the anode of D5) is being driven to +12.4V by the opamp IC5c and that's stuffing up the rest.

We haven't gone back far enough in the circuit to find something which is working normally.  When when get that far we will know what part of the circuit is broken.

So the next step is to check the input voltages of IC5c.    At this point stick with the multimeter.
Also try with an without signal.


Signal          pin 14 IC 5d                        pin 9 IC 5c            pin 10 IC5c***                         

no                 near 0V                               same as pin14     approx 0V to -12V
signal                                                       IC5d                      from one extreme of pot
                                                                                                  RV6 to the other

with              negative voltage                 same as pin14    approx same as without
signal           maybe -3V (not -15V)        IC 5d                     signal


*** Also check the wiper of RV6 follows the voltage on pin 10 IC5c

If those measurements are off then move back to IC5d and IC5a.   At this point just check with no signal.

All these should be close to zero volts:    IC5 a pin 1 might be inside of +/- 0.5V.

IC5d pin 13, IC 15d pin 12
Cathode of D3 (where it connects to R65 and R67)
IC5a pin 1, IC5a pin 2, IC5 pin 3

At some point we will find something that makes sense.

[PRR]

>> your multimeter might be 1M ohm input impedance
> Is there any way to measure this?

It is usually not a big secret. It is in the specs. But I can not read your model number from here. Maybe you can?

[jfrabat]

>> your multimeter might be 1M ohm input impedance
> Is there any way to measure this?

It is usually not a big secret. It is in the specs. But I can not read your model number from here. Maybe you can?

Found the manual, but no mention of impedance.

So the next step is to check the input voltages of IC5c.    At this point stick with the multimeter.
Also try with an without signal.


Signal          pin 14 IC 5d                        pin 9 IC 5c            pin 10 IC5c***                         

no                 near 0V                               same as pin14     approx 0V to -12V
signal                                                       IC5d                      from one extreme of pot
                                                                                                  RV6 to the other

with              negative voltage                 same as pin14    approx same as without
signal           maybe -3V (not -15V)        IC 5d                     signal

OK, this is where we are at:

IC5 Pin 14:
No Signal: -12.27V
Signal: -12.3V (a bit of fluctuation; -12.27~-12.4)

IC5 Pin 9:
No Signal: ~ 18mV
Signal: -12.13V

IC5 Pin 10:
No Signal: -11.88V
Signal: -11.88V

These readings are with the wiper at -12.11V (I can turn it down to 0V).

If those measurements are off then move back to IC5d and IC5a.   At this point just check with no signal.

All these should be close to zero volts:    IC5 a pin 1 might be inside of +/- 0.5V.

IC5d pin 13, IC 15d pin 12
Cathode of D3 (where it connects to R65 and R67)
IC5a pin 1, IC5a pin 2, IC5 pin 3

At some point we will find something that makes sense.

Obviously, we are at the "measure other values" stage.  So here we go:

IC5 Pin 1: Around -0.245 (it fluctuates around that value)
IC5 Pin 2: +1.4mV
IC5 Pin 3: 0V
IC5 Pin 13: -4.14V

D3 Cathode: Around +3.1V

[Rob Strand]

Obviously, we are at the "measure other values" stage.  So here we go:

IC5 Pin 1: Around -0.245 (it fluctuates around that value)
IC5 Pin 2: +1.4mV
IC5 Pin 3: 0V
IC5 Pin 13: -4.14V

D3 Cathode: Around +3.1V

IC5 pin 14 and the cathode of D3 show something is wrong.

You missed, IC5 pin 12.  Check if IC5 pin 12 is at about -4.1V.
If pin 12 and pin 13 are at about the same voltage then IC5d is probably OK.

It would be wise to check the voltage on the C8 side of R64 is at 0V.

So here's the key weird things.   

1) D3 cathode at +3V. 
This voltage is inconsistent with a lot of surrounding voltages, in particular:
  - pins 2 and 3 of IC 5a look OK, and 
  - pin 1 of IC5a is at -0.25V.
  It's like there is a short on the cathode of D3, or on R65 or R67.

2)  Depending on voltage on pin 12 IC5d.
      The voltage on pin 1 of IC5a points to pin 12 IC5d at about  +0.4V,
      but the voltage on pin 13 IC5d points to pin 12 IC5d at about -4.1V.

How the positive voltage is getting on the cathode of D3 is really strange.

[Rob Strand]

Obviously, we are at the "measure other values" stage.  So here we go:

I'm a bit confused about those last set of measurements.

Did you take the measurements with no-signal or with signal?

IC5 Pin 14:
No Signal: -12.27V
Signal: -12.3V (a bit of fluctuation; -12.27~-12.4)

IC5 Pin 9:
No Signal: ~ 18mV
Signal: -12.13V

The reason I'm confused is pin 9 changes with signal/no-signal.
But what's also confusing is IC5 pin 14 has not changed.
If IC5 pin 14 doesn't change it's doesn't make sense that IC5 pin 9 can change!

[jfrabat]

I will re-measure today.  I think it was without signal, but I am not 100% on that, so I will do both today when I come back from the office.

[PRR]

The same meter is sold under dozens of brands with several editions of the manual and I did not find the input resistance.

Measure a 9V battery, note the result.

Put a 1Meg resistor in series with the meter. Repeat.

Report.

[jfrabat]

OK, second time around (to double check and make sure I have this right!):

IC5 Pin 14:
No Signal: -12.89V
Signal: -12.78

IC5 Pin 9:
No Signal: -12.80V
Signal: -11.86

IC5 Pin 10:
No Signal: -11.84V
Signal: -14.95

IC5 Pin 1:
No Signal: MM does not measure (I assume 0V with some fluctuation; it keeps trying to lock in the V range)
Signal: MM does not measure

IC5 Pin 2:
No Signal: +1.4mV
Signal: +1.4mV

IC5 Pin 3:
No Signal: 0V
Signal: 0V

IC5 Pin 13:
No Signal: -4.24V
Signal: -4.24V (there is some fluctuation of about 40mV)

D3 Cathode:
No Signal: MM does not measure (I assume 0V with some fluctuation; it keeps trying to lock in the V range)
Signal: MM does not measure

These readings are with the wiper at -12.11V (I can turn it down to 0V, but left it at -12.11V).

The reason I'm confused is pin 9 changes with signal/no-signal.
But what's also confusing is IC5 pin 14 has not changed.
If IC5 pin 14 doesn't change it's doesn't make sense that IC5 pin 9 can change!

Looks like you were right; I took a wrong reading there...  I mean, it changes A LITTLE, but not as much as I had stated!

The same meter is sold under dozens of brands with several editions of the manual and I did not find the input resistance.

Measure a 9V battery, note the result.

Put a 1Meg resistor in series with the meter. Repeat.

Report.

1M Resistor (measured 0.975M on MM)

Voltage (w/o resistor): 9.72V
Voltage with resistor: 8.85V

[Rob Strand]

IC5 Pin 1:
No Signal: MM does not measure (I assume 0V with some fluctuation; it keeps trying to lock in the V range)
Signal: MM does not measure

IC5 Pin 13:
No Signal: -4.24V
Signal: -4.24V (there is some fluctuation of about 40mV)

D3 Cathode:
No Signal: MM does not measure (I assume 0V with some fluctuation; it keeps trying to lock in the V range)
Signal: MM does not measure

So the voltage on IC5 pin 13 is like before and it's not right.

For the problem voltages on D3 cathode and IC5 pin 1, try turning off auto ranging.  What you do is turn off auto ranging then if them display shows overload you can normally press a button to change the voltage range to the next higher setting.

You missed IC5 pin 12 and the voltage at the point  R64 and C8 join.

At this point I'm suspecting these possibilities,

- some sort of short around R65, R66, R67, D3, D4

- the circuit is oscillating.

It might be easier just to buzz out all the connections with the multimeter, double check your resistors values and double check the diodes are in the right way.

[jfrabat]

For the problem voltages on D3 cathode and IC5 pin 1, try turning off auto ranging.  What you do is turn off auto ranging then if them display shows overload you can normally press a button to change the voltage range to the next higher setting.

Not sure how to take it out of auto, but tried my other voltmeter.  Took all of them again because I noticed I had the signal connected to the output (DUH!):

IC5 Pin 14:
No Signal: -12.37V
Signal: -13.44V

IC5 Pin 9:
No Signal: -12.22V
Signal: -13.27

IC5 Pin 10:
No Signal: -11.79V
Signal: -11.75V

IC5 Pin 1:
No Signal: 0.294~0.304V
Signal: -1.95V

IC5 Pin 2:
No Signal: +1.3mV
Signal: +1.3mV

IC5 Pin 3:
No Signal: 0V
Signal: 0V

IC5 Pin 13:
No Signal: -4.15V
Signal: -4.84V

D3 Cathode (I also measured anode before! Sorry!):
No Signal: 3.72V
Signal: 4.03V

You missed IC5 pin 12 and the voltage at the point  R64 and C8 join.

Sorry, here you go:

IC5 Pin 12:
No Signal: -5.78V
Signal: -8.54V

R64/C8:
No Signal: 0V
Signal: 0V

At this point I'm suspecting these possibilities,

- some sort of short around R65, R66, R67, D3, D4

- the circuit is oscillating.

It might be easier just to buzz out all the connections with the multimeter, double check your resistors values and double check the diodes are in the right way.

What do you mean buzz out the connections?  Continuity check?

I just double checked the diodes, and they are correct.  For the resistors, which ones do you mean?  The ones mentioned above?

[Rob Strand]

Thanks for re-doing the voltages.

I can't think of anymore than this,

Quote from: Rob Strand on Today at 08:08:27 PM

    At this point I'm suspecting these possibilities,

    - some sort of short around R65, R66, R67, D3, D4

    - the circuit is oscillating.

What do you mean buzz out the connections?  Continuity check?

I just double checked the diodes, and they are correct.  For the resistors, which ones do you mean?  The ones mentioned above?

Yes, buzz-out means do a continuity check (sorry it's kind of slang).     

The resistors to check are R65, R66, R67.     Check values and also check the resistor leads are connecting all the way to the IC pins.

I had a look at the oscilloscope waveforms you posted a few posts back.   The waveforms look like there's definitely something wrong around the area of "R65, R66, R67, D3, D4".

Once we get that fixed the whole thing is likely to come back to life!

[Rob Strand]

Check values and also check the resistor leads are connecting all the way to the IC pins.

Oh, and check the diodes connect back the resistors and the IC as well.

[11-90-an]

Why do I think this is a case of "reading resistor values forwards and backwards are different" 
Try checking component values too...

Good luck! 

[jfrabat]

Thanks for re-doing the voltages.

You are thanking me?  THANK YOU for putting up with me! 

The resistors to check are R65, R66, R67.     Check values and also check the resistor leads are connecting all the way to the IC pins.

I had a look at the oscilloscope waveforms you posted a few posts back.   The waveforms look like there's definitely something wrong around the area of "R65, R66, R67, D3, D4".

R65:
Resistance: 46.5K (within 2%)
One side has continuity to D3 and R67
Other side has continuity to R64, R66 and IC5 Pin 2

R66
Resistance: 45.4K (not perfectly 47K, but within 5%)
One side has continuity to anode of D4 (it is so in the schematic)
Other side has continuity to R64, R65 and IC5 Pin 2

R67
Resistance: 46.0K (not perfectly 47K, but within 5%)
One side has continuity to D3 and R65
Other side has continuity to R68 and IC5 Pin 13


D3
Facing the right way
Anode has continuity to IC5 Pin 1
Cathode has continuity to R67 and R65

D4
Facing the right way
Anode has continuity to IC5 Pin 12 and R66
Cathode has continuity to IC5 Pin 1

All of the above I tested touching the upper side of the resistor/diode/IC lead, so it should be testing tracing and soldering.

Once we get that fixed the whole thing is likely to come back to life!

I sure hope so!  I am looking forward to having my own home-made studio!  It is kind of stupid, but it gives me great pride to have something I made, even if the digital stuff you can download is cheaper and sounds better/has more options!

I am going to re-flow all the solder for D3 and 4, and R64 to 68, and re-measure, just to be safe, as I cannot find any short.

[11-90-an]

It is kind of stupid...

What do you mean?!?

If I were to describe your builds and such, it would be any positive word FAR from stupid.    👉 👉

[Rob Strand]

If you want to check in-circuit measurements you could also measure the circuit around IC6b and IC6c.  It's virtually identical.

One obvious thing we haven't done is simply replace IC5!   I mean it's easy to do and maybe save a lot of headaches.

Another thing to try is to solder a small cap, say 10pF,  across pin 1 and pin 2 of IC5a.  If you don't have 10pF anything upto 33pF.   And if you don't have 10pF to 33pF, even 100pF is OK for a test.

I sure hope so!  I am looking forward to having my own home-made studio!  It is kind of stupid, but it gives me great pride to have something I made, even if the digital stuff you can download is cheaper and sounds better/has more options!

I don't think it's silly either.    Having a real box means you can use it with other "real" equipment.

[jfrabat]

OK, re-measured values:

IC5 Pin 14:
No Signal: -12.41V
Signal: -13.46V

IC5 Pin 9:
No Signal: -12.14V
Signal: -13.32V

IC5 Pin 10:
No Signal: -11.82V
Signal: -11.77V

IC5 Pin 1:
No Signal: 0.52~0.55V
Signal: -1.99V

IC5 Pin 2:
No Signal: +1.3mV
Signal: +1.3mV

IC5 Pin 3:
No Signal: 0V
Signal: 0V

IC5 Pin 13:
No Signal: -4.31V
Signal: -4.87V

D3 Cathode:
No Signal: 3.90V (there is some small fluctuation)
Signal: 3.68V

D3 Anode:
No Signal: +0.24~0.38V (fluctuates around there)
Signal: -1.96 (fluctuates a bit)

D4 Cathode:
No Signal: -1.98V
Signal: +0.625V

D4 Anode:
No Signal: -6.0V
Signal: -8.55V

IC5 Pin 12:
No Signal: -5.98V
Signal: -8.55V

R64/C8:
No Signal: 1.3mV
Signal: between 1 and 2mV (fluctuates)

Have not tried listening to it, but the LED is not showing anything, so I think there has been no progress so far, so no need to do it.

It is kind of stupid...

What do you mean?!?

If I were to describe your builds and such, it would be any positive word FAR from stupid.    👉 👉

Thanks, man.  Really appreciated.  But I cannot take 100% of the credit.  I may be hard headed, and difficult to throw the towel, but if not for the help of this forum (especially you and Rob, but many others as well!) I would have thrown the towel long ago.  Kudos to you guys!  I just wish I could understand electronics better (and I feel I am progressing, but there is still SOOO much I do not understand!).  At least I try to pay it forward by helping noobs here and trying to get my friends involved in pedal building.  Already got one building an electra...  talk about the blind leading the blind!  LOL!