Sustain problem with Ross Compressor Clone

[lordoftears]

Hello,
I've just finish to make my first Ross compressor clone (the one sold an das musikding website). I've already made a linear booster and an overdrive without any problems.

The pedal works until the sustain pot is less than half, then the sound disappear and the guitar is just earable if the strings are pulled strongly.

I've already checked connection and solder points.

I've measured the voltage as suggested by most sites, here are the results:

IC
Pin1 = 0V
Pin2 = 3,71V
Pin3 = 3,71V
Pin4 = 0V
Pin5 = 0,7V
Pin6 = 0,62V
Pin7 = 9,40V
Pin8 = 0V

Tr (2N3904)
    Q1                 Q2               Q3             Q4           Q5

C    7,8V              9,24           8V             8,1V        8,5V
B    1,28V             0,6            0V               0V           8V
E    1,48V             0,1            0V               0V         9,4V

The sustain pot is a 500K rev log.

Can anyone help me?

[R.G.]

Pin6 = 0,62V

Whatever is causing this is causing your problem. That point should be up at a few volts. You didn't leave a link to a schematic or project file so I can't tell you more than that. There is a resistor divider that produces the voltage, and a resistor from pin 6 to there. Something is wrong with either the resistor divider or the resistor from pin 6 to the divider.

[lordoftears]

Thank you R.G. I'll check it.

Here is a link to the schematic: http://diy.musikding.de/images/stories/dyna/compschalt.pdf

[R.G.]

Thanks.

The bias voltage is generated by R21, R22, and C16. The voltage at the junction of those three should be about 2.9V with a 9.00V supply, and scaling up or down with the supply voltage.

That voltage is applied to pin 6 through R13 (150K). You should find very nearly 2.9V on both sides of R13. As it is you get 0.6V on the pin 6 end. So the questions are:
- is the bias voltage end of R13 still 2.9V? If not, why not?
- is R13 the correct value?
- is R13 soldered in correctly, and do the traces to pin 6 and the bias voltage show the correct continuity?

And I notice that your original voltages do show the voltages on Q2, which is where I was going next. The problem is that it's hard to tell whether Q2 is pulling pin 6 down or pin 6 and R13 are not providing for Q2. So pull out Q2 and see if pin 6 comes back up to 2.9V more or less. If it does, there's something wrong with Q2, R15, C10, or C31 pulling the emitter down.

[lordoftears]

Thank you for your answer and sorry for my late!

I redid some solder points, checked the R13 (150K and soldered correctly).

The problem now it that I cannot hear any sound when the switch is on. The led turns on but the audio signal is not passing with every pot or trim position.

The values measured now are the following:

IC
Pin1 = 0V
Pin2 = 3,95V
Pin3 = 3,95V
Pin4 = 0V
Pin5 = 8,3V
Pin6 = 2,43V
Pin7 = 9,23V
Pin8 = 0V

Tr (2N3904)
    Q1                 Q2               Q3             Q4           Q5

C    7,65V             7,0            8,11V          8,05V      9,23V
B    1,34V             2,44          0V               0V          8,10V
E    1,56V             2,19          0V               0V          8,67V

Than you again.

[lordoftears]

 
Hello, I replaced the IC and then I measured again all the voltages: alla are Ok except for:

pin6 of the IC: 6,97V instead of 3,2V

Q2:                E     B     C
                   6,3   7    6,3

instead of:     2,7  3,2  6,3

I also checked R20, R13 and R19, all of them are of correct values and well soldered.

Voltage between R21/R22 is 3,4V (should be 2,4V).

All measurements were taken with pots set on maximum values as suggested on the seller's instructions.

Please help me!