Compressor Problems

[mattlee0037]

I used the layout from here http://www.sabrotone.com/?p=1331

It works kind of. The problems: to get unity volume I have to have the pot set up at about 90% clockwise and the LED doesn't currently light up. This might possibly be due to my 10k limiting resistor (only one I had on hand and too impatient to wait for a 4.7k) or something else I'm not sure. Another strange anomaly is that when turned fully counterclockwise the volume pot measures about 9.7k resistance, but the compression pot (also a 10k audio pot) measures about 3.3k so I'm not sure if this was because it was in circuit or what?

Anyways, thoughts are welcome, I will try to post pictures and voltages tomorrow.

[GibsonGM]

Yup, gonna need the voltages ;o)  Many things could be wrong; but the good news is, it is probably only 1 or 2 errors causing the malfunction!  You just have to track it (them) down....debugging......read the thread at the top of the forum about that.    Take your time, and you'll find the trouble!

[samhay]

The compression pot (10k) is parallel to a 5.1k R15, so at max you should have 10k||5.1k = 3.4k, so that is not the problem.

What LED? I don't see a 4.7k resistor in that layout.
I would not expect the LEDs in the feeback loop of the op-amp to light up unless you put a lot of signal through it.

[mattlee0037]

Sorry I meant the status LED. I always forget to be clear about that! I promise I will have pictures and voltages tomorrow!:)

[mattlee0037]

So I didn't have much time to check voltages so I will be more thorough later, but D1 had about 8.8v D2 and D3 had about 0

Pin 1 of IC had 1.4
Pin 2 had 4.8

I think I saw a solder bridge, but I'm not sure if it would cause all those voltage problems! I'll try cleaning it up soon to see what happens.

[mattlee0037]

Ok so here are my voltages
Just a note that I fixed the status LED, but now the volume control has no effect
DC jack: 9.54 (good start haha)
Status LED anode is getting 1.86 (and lighting up)

D1 cathode is 8.91
Q1 has 0 on G,S, and D.... hmmm I don't think that's supposed to be like that...
D2 and D3 cathodes have 0

IC is 1- 3.63
2- 4.84
3- 2.40
4- 0
5- 8.84
6- 4.84
7- 4.84
8- 2.39

D5 and D4 all points are about 4.85

So this is very befuddling. Maybe some bad contact with sockets or something? I'm not exactly sure. Thoughts?

[mattlee0037]

Bump

[Kipper4]

If the op amp is being used in a normal way i'd have expected most pins to be around 4.5 v except pin 8 which should be around the same as your 9v source and pin 4 which goes to ground so 0volts
IF?
google up lovesqueeze voltages you just might find something.

[bluebunny]

Not help for your problem, per se, but I think you're counting your chip pins in the wrong order.  You start at the dot (or "bite mark") and go anti-clockwise:



Otherwise your pin 8 (2.39V) is completely wrong - it should be close to your 9V supply.  Which is what you have on your pin 5.  I think you've counted down one side, then down the other (and thereby reversed 5, 6, 7, 8).

[mattlee0037]

  I did count them wrong.

Real voltages are
IC is 1- 3.63
2- 4.84
3- 2.40
4- 0
5- 2.39
6- 4.84
7- 4.84
8- 8.84

I'm going to try and see where the voltages are dropping from the input  9.54 to the diodes 0 tomorrow.

[PRR]

> I used the layout

Layouts are good for building.

Schematics are very-very-very helpful when *debugging*.

It is a kindness, when asking for help, to point to the schematic.

http://2.bp.blogspot.com/-oBz_XMAZSd8/T-jvPvJdWTI/AAAAAAAABk0/pF9SOGcl8PI/s1600/ROTH.png

Yes, at idle all pins of Q1 are zero. Also D2 D3.

All pins of opamp should be at +9V, zero V, or +4.9V.... except depending on your meter, pins 3 and 5 will read 10% low (or lower). Hmmmmm.... you report 3 and 5 way low. What kind of meter?

[mattlee0037]

I use a cheapie digital multimeter, although I've A/Bed the results with a very very expensive multimeter, and they're normally the exact same. I rechecked just to be sure and I got about 2.40 again for pins 3 and 5

[PRR]

Short FET drain-source. That should be LOUD. Is it?

If so, but not when the FET alone is there, re-re-examine FET type and pin-out.

[mattlee0037]

No it's at about unity volume and the volume will not adjust when rotating the potentiometer. And I just looked at the type and it's a bj26 or bj28 2n5457 which I couldn't find any datasheets for so I assume a regular pinout? Potentiometer resistance does still vary as the pot is rotated.

[mattlee0037]

Edit: it get's a *slight* volume boost when engaged.

[mattlee0037]

Second Edit: I'm an idiot :facepalm: I hooked up the LED to the circuit wrong because the PCB is a tad odd, so it currently lights when the effect is off, so there is a *slight* volume drop when engaged.

[Pojo]

I'm wondering about the bias supply voltage....what measurement do you get at the positive lead of C6?

[duck_arse]

assuming and pinouts don't go together.

the 2N5457 is the same pinout as the j201, but that's off the top of my head ......

[mattlee0037]

To Pojo, 4.73V was measure at the positive lead of C6

And to duck arse, are you suggesting I sub in a j201 for it to see how that goes?

[duck_arse]

sub a 2N5457? NEVER! j201 is a different beast altogether.

no, I was just pointing out their pinouts is all.