1st build problems - help required.

[Rodders]

OK, I've made myself an audio probe.

I've also realised that I have a Behringer XV-amp which I can use as a small testing amp.

So, this evening I shall do some audio testing......so I need some info- Do I need to put some kind of signal into the input, or should I just be looking for some 'static noise'?

Getting a signal in could be tricky...hmm.....although I could use my drum machine if I've got a suitable cable. maybe?

[Rodders]

UPDATE

Removed the CA3080. Installed DIL socket and fitted a new CA3080.

Plugged her in and...............



BINGO!

This is insane. I am extremely happy. I'm happier than a happy thing on happy juice. My 1st build works, and it didn't take much to get going. That's a confidence boost and a half.

Now I need to get it into the box so I can try it properly. At the moment I keep losing the signal because all the bare metals shorts against itself.....very undesirable. There's also a dodgy connection somewhere - I think it's the +9v but I'll check it all over when I'm putting it in the box.

But, it frigging works!

[oskar]

Wow, great going!   

It never keeps amaze me when it works...

[bassmasta17]

such a relief inst it?

just wait until you try to put it into a box that's too small.

[Rodders]

I'm especially amazed because it's my first time and, in truth, I haven't encountered many big problems.

I've also just finished populating a board for an MXR Blue Box (octaver) clone. Didn't realise I needed a 14-pin DIL socket so I'll need to pick one up over the weekend. This time, I'll do the off-board wiring slightly more carefully too. In fact, I'll start a thread asking for tips on that.

[Rodders]

such a relief inst it?

just wait until you try to put it into a box that's too small.

Hey, we'll have none of that! 

I'm fairly confident it'll go in, but I won't try and get a battery in there too. I'm hoping my mate wants this one because he's got a pedalboard with a suitable power supply so batteries are not needed.

[bassmasta17]

i always try to buy a box that i think will be too big. Even if it fits i have broken some solders trying to fit things into boxes.

[Rodders]

I'll continue my plans for a test rig on the other thread that I started.

Going back to this little circuit, it appears to not be working again.

I've got my audio probe hooked up and doing some investigating, but I don't really know what to expect. What I'm doing is trying to follow the signal path and hear what is happening at each point.

What I've noticed is that I seem to get no signal on the ground side of Cb - I assume that's correct. I also get no signal on the ground side of the 4M7 resistor, I assume that's correct too. I'm guessing, but is it pretty much correct to say that I don't want any signal going to ground?

I get a few loud pops when I first touch some components too - is that because they are charged up caps and I'm getting the full whack of charge from them the instant I touch?

And, I should avoid the +9v points too I assume?

Where should I be looking first in terms of most likely faults? I'll check voltages on the IC again, and also do an audio test on the useful legs of that.

Here's the layout again:

[Rodders]

OK, further notes:

Pins 2&3 of the IC are getting signal.

Pins 5&6 aren't. That seems wrong.

So I checked voltages - Pin 6 gets 2.65V as before. Pin 5 seems to be oscillating between about 20mV and 42mV. That doesn't seem like a huge variation so perhaps that's normal.

My 500k linear pot (sustain) may be dead. I can't get any reading for the resistance across it, whereas the 50k pot goes from 0-50k exactly how I'd imagine it to.

Is it possible that it's the dead pot that's causing the trouble. Or, maybe my trim pot needs setting properly. I'm getting signal on all of its legs though. I've used a multi turn trim pot here, but it seems to turn for ever and ever. Is that right?

[oskar]

Yes, if the 500k pot is broken this could cause pin 5 voltage to drop. Measure the voltage on the wiper at various settings instead of the resistance. There are capacitors in there that will disturb the measuring process.

[Rodders]

OK, my latest findings are that there's no volts getting to the 50k pot anyway.

There's a 0.05uF cap just before the input end of the pot and that has some volts at the input end, but not on its output to the pot (via a 10k resistor)

So, I suspect that cap might be fried.

Got some other readings (I may be wrong, but all the transistors seem to be reducing the signal):

Q1
b-2.0V
c-7.4V
e-1.5V

Q2
b-2.7V
c-6.8V
e-2.1V

Q3
b-0V
c-8.9V
e-0V

Q4
b-0V
c-8.8V
e-0V

Q5
b-8.9V
c-8.9V
e-8.43V

IC
1-X (not used)
2-4.65V
3-4.65V
4-0V
5-40mV (seems to wobble a little)
6-2.65V
7-8.92V
8-X (not used)

[oskar]

OK, my latest findings are that there's no volts getting to the 50k pot anyway.

There's a 0.05uF cap just before the input end of the pot and that has some volts at the input end, but not on its output to the pot (via a 10k resistor)

That's in order. In fact, that caps big mission in life is to block the DC potential.

Do you read any voltage on the 500k pot? All lugs, different wiper positions...

[Rodders]

I definitely have to bow to your far superior knowledge, but I don't understand why that cap is supposed to block any DC potential. Surely, the best way to block would be to just not have it wired up? And, if it's blocking the DC potential then why does it need the 10k resistor in series with it?

Anyway, the 500k pot seems to not be right either:

Full tilt c/w AND full tilt a/c/w both give these readings:
1- 1.04V
2- 1.04V
3- 8.34V

In between each end it's difficult to get a steady reading....but 2 & 3 stay constant but 1 dips to ~0.8V-1.0V

[oskar]

I definitely have to bow to your far superior knowledge, but I don't understand why that cap is supposed to block any DC potential. Surely, the best way to block would be to just not have it wired up? And, if it's blocking the DC potential then why does it need the 10k resistor in series with it?

Anyway, the 500k pot seems to not be right either:

Full tilt c/w AND full tilt a/c/w both give these readings:
1- 1.04V
2- 1.04V
3- 8.34V

In between each end it's difficult to get a steady reading....but 2 & 3 stay constant but 1 dips to ~0.8V-1.0V

Wrap some stripped wire between the pot lugs 2 and 3 to short the pot and behold...

[Rodders]

Cool, I'll have to do that tomorrow.....I packed up the kit already  In the New Year, I'll have a permanent workspace rigged up.......so, can you spoil my surprise? Will it suddenly burst into life?

[oskar]

Will it suddenly burst into life?

It'd better! Or I'll look quite a bit like a fool.

Full tilt c/w AND full tilt a/c/w both give these readings:
1- 1.04V
2- 1.04V
3- 8.34V

In between each end it's difficult to get a steady reading....but 2 & 3 stay constant but 1 dips to ~0.8V-1.0V

At full on you should have thoose 8.43 volts at the wiper right?...

I definitely have to bow to your far superior knowledge...

  -And maybe you should wait till that compressor really works.

but I don't understand why that cap is supposed to block any DC potential.

After Q2 you have an audio signal with a DC component. If you don't have a cap at the output you would also be sending a DC current across to the next pedal (  ..noise, hum, life in misery )

And, if it's blocking the DC potential then why does it need the 10k resistor in series with it?

To pad down the signal to the same level as the input signal?...   Don't know, don't care...   


I wan't a new smiley. This   --->    with theese question marks above --->     The "Ignorance is bliss" smiley...

ps. I'm off course not 100% sure about the pot.

[Rodders]

OK, just did a very quick test on your suggestion. It's definitely an improvement because some sound got through!

I didn't have time to check if the effect is really noticable or not but will do later.

What I did notice was that after a few seconds the sound seems to drop of suddenly with a bit of distortion too. I suppose that's part of the purpose of a compressor.

So, does this suggest that my 500k pot is indeed faulty? I can replace that tonight.

Now, presumably I need to work out what the trim pot is meant to be doing. Any ideas folks?

[mdh]

I think the standard answer on that trimmer is to set it dead center and forget it.  If you search for Ross Compressor or Dynacomp and trimmer, you will find many threads that conclude just that way.

[oskar]

OK, just did a very quick test on your suggestion. It's definitely an improvement because some sound got through!

I didn't have time to check if the effect is really noticable or not but will do later.

What I did notice was that after a few seconds the sound seems to drop of suddenly with a bit of distortion too. I suppose that's part of the purpose of a compressor.

So, does this suggest that my 500k pot is indeed faulty? I can replace that tonight.

Now, presumably I need to work out what the trim pot is meant to be doing. Any ideas folks?

Yeah it's the pot. We shorted it so the OTA was going full on for a while and then the 10u cap between Q4 was discharged.
Two fun errors in one build.     

[Rodders]

I don't know what OTA means

And by errors....you mean that the pot is dead and.....?