Homebuilt pedal woes......again......

Kalimna

Having a spare hour or two last night, I wired up the enclosure (6 pots, 2 LEDs, 2 jack sockets, footswitch and a power socket) with a veroboard build of Madbeans Gravity Wave (their copy of EarthQuaker Devices Sea Machine chorus pedal).

For me, it's a fairly busy build with 4 chips and a lot of wires in a smallish space - experienced builders will probably have not too much bother however.

So fire it up - rate LED constantly on, power LED on when engaged. No audio whatsoever in engaged or bypass. Grrrrrr. Check connections, and swap the active and ground on the output jack. I now have sound on bypass, but nothing at all when engaged. The modulation rate LED is on constantly still, which suggests a problem anyway with the build, and the complete lack of audio suggests a grounding problem - a short somewhere.

Problem is, I had to resolder a few wires and components which makes the back of the build rather messy. I'll have a look at it tonight, knife the tracks etc, but if it doesn't work I'll pull out another piece of stripboard and re-build the circuit...

Grumble over.

Adam

Adam_MD

Did it work out of the enclosure? 

Kalimna

Ahhh, well, I haven't quite gotten around to testing prior to boxing any of my pedals yet - a habit I should really grow out of.... I could undo all the hardware bar the power jack and have the board hanging free, and see what happens.

cheers,
Adam

Adam_MD

Always rock it before you box it dude.  Make a testing rig it's super easy Mirosol on tagboard effects has a good guide

http://tagboardeffects.blogspot.co.uk/2014/09/test-box-20.html?m=1

Kalimna

Thanks for the link. Thing is, i know what I *should* do. But always too much of a rush to get to the finish line!
I'll try a couple of things tonight on the faulty build, and get stuck into a test rig the next time i have a free afternoon. Tagboard is a fantastic resource and where i have acquired most of the layouts and knowledge so far - mirosol especially.

Out of interest, do you think my reasoning is sensible regarding a short somewhere? Theres obviously a constant voltage (will also check over with DMM too) going to the 'rate' LED, when it should ve oscillating.

Cheers,
Adam

Adam_MD

I'd knife the tracks as you said and check to make sure everything is in the right place with no missing cuts etc.  Then check voltages at the ICs etc and post the results on tagboard asking for help.  

Kalimna

Well, tracks re-knifed, track-breaks re-drilled, solder re-flowed and as far as i can tell, components and leads correctly placed.

Interestingly, with cable plugged from pedal to amp there is no buzzing at all if the tip of the jack plug within the pedal (am using open sockets) is touched. Again, leads me to think that there is a short to ground somewhere in the audio path that isnt a solder bridge. Maybe there is a misplaced component after all.

Adam

Adam_MD

Take a break and come back to it tomorrow you might notice something obvious with a clear head I've had that happen loads of times.  The worst was when I finished a honey bee clone and couldn't get any life out of it I checked and rechecked all the components, the cuts then checked for solder bridges and eventually gave up in frustration.  The next day I realised I forgot to put the opamp in the socket :-)

Kalimna

2xTL072, 1xPT2399 and a LM324 all socketed
I suppose its possible one of them is faulty, and i have spares for each, so thats something else to try.

Taking a break tonight is a good idea though.

Adam_MD

I'm not suggesting the ICs are faulty checking the voltages might help pinpoint errors in the build.  Do you have an audio probe?  

Kalimna

I was just thinking out loud regarding the ICs - just something else to check.
An audio probe is next on my list before the test rig. Thing is, its rather dependent on knowing what makes up the audio path, is it not? Fine for a simple overdrive, less so for a filtered, split and delayed, LFO'd signal in a chorus pedal.
And I completely agree about checking the voltages - just didnt have it in me tonight

Adam

Adam_MD

Here's the schematic in case you don't have it.  The tagboard site never has them listed.  

Kalimna

Thats fantastic, thank you.

lasermonkey

I have to admit, when I'm feeling lazy (which is most of the time), my "audio probe" consists of me holding something pointy and metal. It'll usually make a buzzing noise which does the job.
Once I've given the circuit the once-over for shorts, dry joints and obvious errors and checked the voltage rails, I'll start at the end of the circuit, working backwards. In this case, I'd touch the probe on IC4 pin 7 and if I could hear the click of the probe touching, If so,  I'd go to the input of that IC! namely pin 6. If that's ok, work backwards. At some point, you should find somewhere that you can't hear the probe.
The fact that there's no signal at all when engaged suggests that the fault is either a supply issue or associated with the TL072s, as the dry signal is routed through three op-amp stages.
Good luck!

Kalimna

A quick question - given that there is no sound at all when i touch the tip of the jack which has been inserted into the 'out' socket (back not attached to enclosure), is a short to ground not more likely somewhere? 
Cheers,
Adam

Alvin

I recently bought 10 ic's  out of those only 3 worked  , if i had only  bought one i would have presumed i had a fault in the build  so they can definitely have faulty batches . Lesson learnt there , always worth buying a few if they are cheap ones.   Easy enough to swap if they are socketed and as in my case could be an easy fix .

lasermonkey

Thinking back on it, I probably shouldn't have used the word "buzz", as it's not always a good indicator, especially in non high-gain circuits. Try holding the shaft of a screwdriver, touch the tip of the jack repeatedly and listen for a click as it makes contact. If you can hear it, you know you have continuity.

Sporky

Kalimna said:

A quick question - given that there is no sound at all when i touch the tip of the jack which has been inserted into the 'out' socket (back not attached to enclosure), is a short to ground not more likely somewhere? 
Cheers,
Adam

It's certainly possible.

Check resistance to ground there, and then back through the circuit. Then check voltages back through the circuit. You do need to be methodical about these things - it's actually quicker than randomly poking at stuff.

Kalimna

Thanks for the advice folks - i shall give it another looking over tonight. I do have a set of pin voltages which i can post up if thats of any use, and they were *almost* identical whether the pots were full on or off. A fresh set of ICs (072 from a different batch, the LM324 and PT2399 from the same order) didnt have any obvious effect.
I shall try to be a bit more methodical, and work the problem which is perhaps easier when you know what you are looking for

Cheers,
Adam