Help with orange squeezer

[littlegreiger]

I just finished putting an orange squeezer together from the layout at GGG. However, it doesn't work and I think I fried the IC, a 4558.  When I measure voltage on the pins Pin 6+7 are the same at around 8.15v.  Which I don't think is right.  So I took out the opamp and measured the voltage on the socket and get something considerably lower at around 0.38v on pin 7 and 0v on pin 6.  Does this sound like I fried the opamp?

[j0shua]

did you check any soldering error?

[rubberlips]

When I measure voltage on the pins Pin 6+7 are the same at around 8.15v

Are you sure you're measuring pins 6+7? Pins 1&2 should be shorted together and would actually be reversed if you've put the IC in the wrong direction.

Actually I've got two circuit diagrams. One uses pins 1,2 & 3 for the circuit, but the other uses pins 5, 6 & 7 (which matches the layout for the GGG site)

Checks you've got the IC around the right way for a start and check the supply voltages

Pete

[David]

When I measure voltage on the pins Pin 6+7 are the same at around 8.15v

Are you sure you're measuring pins 6+7? Pins 1&2 should be shorted together and would actually be reversed if you've put the IC in the wrong direction.

Actually I've got two circuit diagrams. One uses pins 1,2 & 3 for the circuit, but the other uses pins 5, 6 & 7 (which matches the layout for the GGG site)

Checks you've got the IC around the right way for a start and check the supply voltages

Pete

Sorry, Pete.  Close but no cigar.  Look at the GGG layout again.  Pins 1 and 2 are not shorted together.  They connect to pads that don't go anywhere -- they aren't connected to anything.  Now, you could say that pins 3 and 4 are shorted together because they both connect to ground.  This grounds out the unused op-amp, thus preventing nasty things from happening to the chip.

LG -

Did you check the postings on "what to do when it doesn't work"?  Review those.  Also, we need voltage on pins 4 and 8, too.  Your readings on pin 6 and 7 appear fishy, as you have observed.

[rubberlips]

Pins 1 and 2 are not shorted together. They connect to pads that don't go anywhere

Actually they are shorted, but yes you're they don't connect anywhere else in the circuit. And I was thinking of pins 5+6, my bad   , but still check to see you've got that IC around the right way. Also check theres no a short from pin 8, that would give you a high voltage on pin 7

Pete

[littlegreiger]

I was getting voltages the other day and I realized that there were 0 volts on Q1 so I remembered the bias pot and changed that until i got some voltage.  Then I rechecked the voltages on 6+7 and they were the same as on Q1. So I thought I would try it to see if it works. Well it worked, so I decided to tighten everthing back in the box and then it stopped working.  Do you think I might have shortcircuited by FETs?

[bwanasonic]

Well it worked, so I decided to tighten everthing back in the box and then it stopped working.

http://www.diystompboxes.com/pedals/debug.html


Kerry M

[littlegreiger]

I built an audio probe and started using it. But first some information about my build. I'm using the layout from GGG with the external volume control http://www.generalguitargadgets.com/index.php?option=content&task=view&id=47&Itemid=79.
I'm using Tantalum Capacitors instead of normal electrolytics. I'm also using a regular 10k linear pot for the bias control instead of the trim pot. Now on to the audio probe results. Following the signal I got to C6 and the signal stopped, and yes I have it installed correctly. Following the signal another way I got to R6 and it stopped. The same with R10. Also I only have a signal on the drain of Q1 and nothing on the other pins of it. Any help is appreciated, and if you need more info I'd be happy to tell you.
Thanks.

[littlegreiger]

Bumping this up to the first page because I've run out of ideas.

[rubberlips]

hmmm, just on an off chance, did you put the jumped to the volume pot on the PCB?
If you have it in, I'd be checking that on the -ve side of C6 that it's not going to ground or something silly like that. Check the PCB around there and R11. You shoudl get an output sound even if the compressor part of it isn't working too well, considering you're getting some signal out of pin 7.

Pete

[littlegreiger]

Well I finally got it working. What happened was one of the wires on my volume pot was grounding out to the enclosure. Thanks for everyones help and ideas. I have to say it's hard to notice the sound it makes but once you realize it it's pretty cool.

[ptrx]

hey,

i got problems with my newbuilt OS as well, maybe you can help me out: voltages seem to be ok, but my audioprobe stops giving me signal past the 470k going to diode/100k/4.70cap (though the resistor itself measures right). Also: nothing on lugs 6 & 7 from the IC (volts yes, sound no).
Did your problems all have to do with the one potlug being connected to the box/ground? Any info would be very much appreciated,

pat

[littlegreiger]

Not all my problems were to do with the pot lug grounding to the enclosure. At first I had a problem with my bias voltage. I suggest you check that it is around half the supply voltage, which if you're only using a 9v will be around 4.5v.  This will be show up on pin 5 of the opamp. I suggest that you take voltage readings and post them on here. This will make it easier for people to help you.

[ptrx]

hmm...

well i got it working now, thanks for the info. Seemed i wrongly interpreted the pot lug order (me being in europe - A and B mixup), which caused the output tip being connected to ground via the output pot. A DMM with peeping thingy helped me find that out. Seems a good idea to always check the ground and what's not supposed to be connected to it when you're getting no sound or crap voltage readings.

I think i'd like to (try and) modify this one a bit though, anyone know any good ways to increase the compression, make it a bit more squashy? Cuz it's bearly audible now... mind: i used a linear 10k pot for the bias and i can't hear any change when i turn it. Should I increase the value of the pot? Use logarithmic?

cheers
pat

[cd]

hmm...

well i got it working now, thanks for the info. Seemed i wrongly interpreted the pot lug order (me being in europe - A and B mixup), which caused the output tip being connected to ground via the output pot. A DMM with peeping thingy helped me find that out. Seems a good idea to always check the ground and what's not supposed to be connected to it when you're getting no sound or crap voltage readings.

I think i'd like to (try and) modify this one a bit though, anyone know any good ways to increase the compression, make it a bit more squashy? Cuz it's bearly audible now... mind: i used a linear 10k pot for the bias and i can't hear any change when i turn it. Should I increase the value of the pot? Use logarithmic?

cheers
pat

You may have something else wrong with your circuit.  The effect is very squashy (well, it is with mine at least), it should be very audible.  Bash a chord with the pedal ON and the output should be clamped considerably compared to the pedal OFF.

The BIAS pot is a "set and forget" control - there should be a very very VERY tiny portion of the control where the effect is loud, then turn it the slightest bit and then there's no sound.  It's in that "sound to no sound" range that you should set the trimmer.  Once you've got it there, leave it, that trimmer biases the FETs.

Once you have the circuit working properly, then I'd dink with the circuit values - you can parallel more diodes to squish things more.  Check out this link to get you started:

http://www.generalguitargadgets.com/index.php?option=content&task=view&id=47&Itemid=79

[ptrx]

first, thanks for the tips,

i think the jfets aren't getting the right amount of current. I got these readings (with a slightly flat battery) (ggg schematic):

Q1:  
G: 2.6
S: 3.6
D: 8.2

Q2:
G: 0.02
S: 3.0
D: 1.6

comparing this to the GGG build instructions (at the end of that doc are some ref readings) these are a little bit pear-shaped no?

so i recon either my bias pot is wasted (though it seems to measure right, it just doesn't make any change to the sound while i have quadrupelchecked the connections) either some other component is not doing a very good job... ( by the way: the IC does show me accepteable voltages).

pat