Build Your Own Clone Message Board

Hi all

Wondering where to start looking for fault for my first stripboard build.
Here is what it does

Effect off:
bypass works fine, no problemo

Effect on:
LED comes on
Volume pot works as expected
Tone pot works as expected
Drive pot works in that it acts like a second volume. Effect goes from off to unity gain at 100%

I'm expecting the clipped stage is going to ground somewhere.

I've checked the transistor pin outs 2n3904 and the op amp (RC4558P) orientation. Op amp was specified on the layout so the pin out should be good.

Built from a verified layout which I can link if that is ok? Can also post pics. Wanted to ask first as it isn't BYOC.

Any ideas where to start looking, or voltages to expect on the transistors etc?

Thanks

burst

Forgot to mention there is no drive on the drive control it just sounds clean :s

"Drive pot works in that it acts like a second volume. Effect goes from off to unity gain at 100%"
I'm not at all sure how you managed that because the drive control normally has a 51K series resistor that would stop it going to "off". I suppose it could happen if the anti-clockwise tag was connected to ground. In any case it does seem from your description that the problem is localised around the clipping stage. That's only a handful of components, I'd examine it through a magnifying glass under a bright light looking for bad joints or shorts. Also check that section of the circuit against the circuit diagram. I'm assuming you have referred to the circuit diagram and not been guided solely by someone else's stripboard layout drawing (which might contain errors).

drive pot doesn't completely kill the signal, just as the clipping appears to be going to ground it's just *really quiet.
I've checked against the schematic and can't see where I have gone wrong, but I'll go over the offboard wiring for the drive pot and the clipping section with a probe and see where I lose the signal.

cheers

Oh OK - well that sounds like either the diodes aren't connected properly or are faulty, so the op-amp is just acting as a variable gain stage. Or perhaps the op-amp is dead and the signal is just leaking past it through the feedback network and the drive pot.

Thanks for the help Tark

Easiest thing is to swap the opamp out and see if that helps before I start desoldering diodes.

Yup, certainly try that.
You could also check that the op-amp is biased properly. The output pin(s) should be sitting at approximately half the supply (about 4.5 V). They do this because the input is biased from a reference voltage produced by two (normally 10K) resistors wired as a divider across the supply lines. Each non-inverting input on each half of the op-amp is connected to this divider through another 10K.

As ever with vero, have a very close look track side for solder bridges using a magnifier of some kind, double triple check your track cuts (make sure that you have completely severed the track) and component placement. A link to the layout would help too.

Here we go guys.

I tested the continuity was broken with a meter before populating so unless there is solder bridge we are good.

Layout and schematic are here

http://www.aronnelson.com/gallery/main. ... v_special/

And a couple of pics.







I'll have a chance to look at this again this evening

Cheers

One more pic of the offboard wiring (plenty of potential for error here) and the voltages for the opamp.

V+ 9.3
V- 1.97
In/Out A/B etc (i.e the rest) ~3.75 give or take 0.2.

Sorry everything is green

Okay, so you noticed that the IC is upsidedown on this and are mounting it in your tray with IC dot to cut out?

Using your meter you should have 9v+ on pin 8 (Black lead to ground in all voltage readings)
9v+ on Q1&2 Collectors
4.5v+ at R5 and C3, and I think pin 2.

Check continuity of pin 4 to ground and check that those two leads in the middle on the left aren't touching at the solder posts, thsy look very close. Its all good learnin' built this one myself, its nice.

Yeah, the socket is notched south and the IC goes in facing south too so in the picture the pins are
5 4
6 3
7 2
8 1

I posted the voltages in the last post. I have a bit less than 2v on V- (Pin 4) which I'm guessing should be 0v so could be placement error or a solder bridge?

9v on Q1 and Q2 collectors.

The two posts are staggered, one soldered on the bottom, one on the top so they look a lot closer than they are.

I'll check I have 4.5v on pin 2 and R5 and post back.

Can confirm 4.5 v on r 5 and in/out pins of opamp.
Also checked collector / base / emmiter are 9 v 4.5 v 0 v

Pin 4 should be at signal ground so if you have any voltage relative to the jack sleeves / the case that is wrong. It would seem you have some resistance between pin 4 and ground.
In fact your ground wiring off the board seems a little messed up, you haven't implemented the power socket or jack socket power switching and I cannot see where the negative line connects to ground on the board.

I removed the LED as I wasn't sure how it should be connected.
I made certain that the board ground pin went to a jack sleeve.

I now have 9v on V+ and 0v on V- on the opamp.

So some success at least on that front.

I changed the pot as the vdc readings were a bit strange, and it was a salvaged pot so just to be sure I changed it for a new one.

I still have exactly the same symptoms as in my initial post.

I'm pretty sure it is on the board now and inclined to start over.