help for tentomushi - 5-knob compressor

[MAO]

"Hey mao, nice work, i made the layout that mirosol posted with with a few tweeks that you pointed out. im also having problems with the ratio pot, fall clockwise is silent and ccw is the comp which is working well, dead quiet for this type too. I will be most grateful if you had any pointers, i have checked the areas you pointed out to the chap before, I'm a bit stumped.. everything looks how it should and i can't find any bridges, maybe its a resistor like the other chap?"

Hi tentomushi,

Couple basic things to doublecheck: The clean signal travels through these circled components and links. Make sure none of those are shorted to ground or shorted to the Ratio pot lug 2. Also check IC2 pins 1 & 2, make sure neither is shorted to ground or to Ratio pot lug 2 (or to each other).  

Also, check the cut under the circled 100k and the cut on the top row.

Can you post IC2's voltages?

Do you have an audio probe?



 

[tentomushi]

Thanks mao, sorry its taken me a while to get back to you, really appreciate your help and time. i have replaced all the components you outlined and i have gone over the the vero with a microscope and have found no bridges. I dont have an audio probe, maybe i acan make one...

i have taken the voltages from IC2 which i think looks normal but thats just a guess.

4.39,pin1  /pin8, 8.87
5.79,pin2  /pin7, 4.37
4.00,pin3  /pin6, 4.39
0.00,pin4  /pin5, 4.20

something must be going to ground somewhere, just cant get my head round it.

[MAO]

Hey tento, glad you are still on it.

Pin 2 seems a bit high, and pins 3 and 5 should be exactly the same.

That might be a clue.

Have you tried swapping out IC2?

Which IC are you using? TL072?

An audio probe will be a big help at this point. There is a real easy way to make one.

Take a standard 1/4 inch jack and solder one end of a 100nf cap (or larger) to the tip connection. Preferably a 100nf cap with thicker legs and a higher voltage rating (25V or better). You will use the other cap leg as your probing tip.

Use an alligator clip (or solder a long wire) from the ring of the jack and connect to the pedal's ground.

This picture shows the idea  

And this video shows a similar approach

Then plug an extra guitar cable into this modified jack, and the other end of the same guitar cable into your amp...with the amp volume turned low.  

Attach the alligator ground clip or wire to the compressor's ground. It's a good idea to tape this ground wire coming off modified jack the to the guitar cable to be sure it doesn't get in the way or short the cap to ground.  

Plug the cable coming from your guitar to the input of the compressor as usual.

Then, with power applied to the pedal and the amp on (turned down low) carefully probe with the capacitor leg to trace the audio path.

EDIT: you'll need to strum the guitar (or feed the pedal with a constant audio source, like the output of your phone or iPod or something)

In this case, you can start probing at the junction of the circled 470n and emitter of the transistor. This will give you an idea of what you should be hearing through the probe as you move through the rest of the clean path.

EDIT. You should hear you guitar (or other audio source) as you touch the end of your capacitor to this junction.

Let me know if you get to this point and I'll walk you through the rest.

Once you get the hang of it, you'll wonder how you ever got along without an audio probe.

NOTE: be careful when probing with the capacitor leg so that you don't slip off a component and short something to the 9v supply.      

[tentomushi]

Thanks so much mao, hopefully I will have the time to crack on with this tonight, will let you know how it goes, cheers mate

[tentomushi]

I forgot to mention that i am using tl072 for IC 2 which i have replaced.

I have made the audio probe using my phone as the audio source and have tested from the 470n cap connected to the collector and im getting signal all the way up to the 15k connected to pin 1 of IC2 when the mix pot is at full clockwise, no signal from the top rail that the 15k is connected to lug 3 of the ratio pot. I only get signal when the ratio pot is not at full clockwise.

[MAO]

Nicely done!

so far so good, that is what should be expected. When you have the ratio pot full CW, the straight signal is shorted to VB (pins 3&5). So you would only hear your straight signal when that control is not full CW.

Can you check Ratio 1 lug and see if the opposite is true? You should not hear your compresses signal on that lug with the control full CCW, but should when you start rotating it CW.

If all good, compare the volume of lug 1 and then lug 3 with the ratio control midway, are they close in volume? (Sustain and clip full on)

If that checks out, something is getting lost at pin 6.

, make sure pin 6 isn't shorted to 3 & 5. Or shorted to pin 7.

Let me know

[tentomushi]

The only signal i am getting is from lug 3 when ccw, no signal from lug 1 at any position so im guessing the problems round there.

[MAO]

Yes, lug 1 is actually the compressed signal. Sounds like your straight signal may be fine.

So probe the emitter of the bottom right transistor, if nothing, then probe pin 6 of IC 1.

Report findings on those two probings

[tentomushi]

yep, im getting nothing off pin 6 or the emitter of the bottom right hand.

[MAO]

ok, we are getting there...

How about pin 2 or pin 3 of IC1?

Also, check emitter of top left transistor.

[tentomushi]

Im getting signal from all three.

[tentomushi]

think i have found the issue, will report back soon with a working comp with any luck.

[tentomushi]

Thanks mao, that really helped and i learnt something thats definetly going to come in hand lots im sure.
I found a couple schoolboy errors, both quite well hidden. The 22uf cap above ic1 was in the wrong hole and was grounding out on the rail going underneath the IC and the biggest issue was the bottom right transistor was a row to high, I dont know how i did'nt see that. Its working perfectly now and really makes my reverend warhawk sing, lovely clean sustain and very quiet, i also swapped the tl072 for an op2314. I may look into the jangle switch mod as put for the time being, im really happy with the outcome thanks again to you and mirosole. Cheers!

[MAO]

Excellent!

Nice job working through it.

How cool is that audio probe?

You can test the jangle option out 1st by simply swapping in a 100k resistor for the 15k at pin 3 of IC1. That will dump a good bit of the bass frequencies on the compressed side, leaving it much brighter/crisper.  Then if needed, you can dial in a bit more of your straight signal to compensate if it sounds to thin.

Might be any easy way to test it out before going through the hassle of wiring up a switch or tone control.

Mike

[tentomushi]

Ah cool, i will definitely try that, thanks for the tip. I do a bit of chicken picking and have been learning from one of greg koch's book "guitar gumbo". The jangle mod will definitely add to the flavour.

Yeah really dig the audio probe, also using a sine wave generator from my phone is really cool. To be honest Im amazed how i managed for two years without one. I have built a load of stuff including a couple of univibes, an analog chorus and phaser.'s and a mountain of fuzz and overdrives without a hitch.. never had to debug mutch because when i make a mistake, its tends to be quit obvious so it must be dumb luck that i got this far. Its definitely going to make things a lot faster to figure out when things do go wrong. Thanks again mike.

joe.