Weird Rat Power Issue

[nickbungus]

He guys, this one seems weird to me but I'm sure someone here can explain it to me.

I built a Rat using the following layout:


All works absolutely fine is isolation.  I then stuck it in an enclosure with a Deep Blue Delay.  Still all works just as it should.

I've got a gig tonight and I usually just use my Digitech multi effects thing.  (Sorry purists)   But I've decided to start using my analog stuff that I have mostly made.  So I built a board last night using a DC power brick.  Heres the chain

Wah -> Tuner -> Overdrive -> Rat /Delay -> Chorus -> Pitch Shifter -> Eq (for level boost).

Everything works fine including the Delay except the Rat.  I only get a signal when the volume is maxed, and it is maxed and loud.  If I power the rat with another DC supply it works,

Any ideas as to what is causing the issue and how I can resolve it?

[GibsonGM]

Does this only happen with the effects in the order you've drawn?  Like, take out the chorus - what happens?  Put Rat after Wah, what happens?

Do they all work 1 at a time?  Is the OD on when you're trying to turn the Rat on?    Need more info, you have to 'shake things up' by moving things in the chain...weird issue.

[anotherjim]

Maybe DC blocking issue - check in and out coupling caps are actually working (not shorted) and correct polarity if electro's.
Make sure jack sockets or inter-board connections either side are wired correct polarity.

Don't ignore possibility of a double fault (as it's tennis season), a bad out cap in one circuit can cause no trouble if the next circuits in cap is good, but if both are bad, it's game, set & match.

[nickbungus]

Thanks Mike

I haven't tried changing the ordering but the Rat is exhibiting the issue when its the only effect on as well as if I turn on other effects. 

The OD is a Digitech Bad Monkey and it doesn't matter if its on or off, the problem remains.  I'm swapping this for a Tube Screamer when I get mine back off a friend.  I'll try taking it out of the chain too.

[nickbungus]

Thanks Jim

I'll try and net this fault and grab it by the balls.  I'd love to get this sorted and dont want to let it get the better of me. 

Would probing it in situ be the way to go?  I can't understand why it works when I max the volume?  Its unusable at the high volume as it just makes too much of a racket.

[anotherjim]

You can often catch a bad cap or polarity problem by looking for DC volts on the in/out side of the coupling caps.

"Its unusable at the high volume as it just makes too much of a racket."
You mean Racquet surely?
New balls please.

[nickbungus]

Jim, of course thats what I meant.  I laden the last post with poor tennis puns

[nickbungus]

I'm just reading on what a coupling capacitor is .  Which caps am I looking at in the PCB layout?

Also, how do I look for DC?

I may have used a NP cap somewhere if I remember rightly.

[duck_arse]

find your blocking caps - follow the input in until you come to a cap in series, that's one. follow the output until the last cap before the vol pot, that's another.

to check for DC on yr caps - put the red probe "circuit-side", it'll read some volts, whatever. put the red probe "out-side", the end connected to ground thu a pulldown resistance of some description, and it should read 0V. unless it's bad, leaking current and showing a DC voltage.

and not a single tennis pun.

[anotherjim]

Yep, as per Stephen says/

Don't know specifics of what you built, but in this one...

C1 is input coupling aka DC blocking. Stops the 4.5v bias getting back out. Here, it's not a polarised type, and unlikely to be leaky. If you measure any DC across R1, then it's more likely the DC is coming from what comes before - or there's a path in the RAT that shouldn't be there due to a short/crap. A DC fault here can make the op-amp gatey, because it's input is pulled - usually to a lower voltage than bias.

C10 is output coupling. A DC fault here won't harm the Rat, even if it's name is Ben, it can harm what comes next, but usually only if it's input blocking is faulty.

[GibsonGM]

You can just measure for DC on the input and output jacks, they mean      Black probe to ground, red probe to "tip" of jack which connects into/out of the circuit.  The presence of more than a few mV DC there indicates bad ("leaky") caps... millivolt level crap is spurious...more than .5V or so could be real.

DC getting where it does not belong causes all kinds of bad side effects!  What you report is one of them.

[duck_arse]

yer, like gibbo says, the easiest way is the black box method. just bung in a lead each side, measure tip to sleeve each end and work the bypass. and if you get DC measures, your caps are wallaby bob's brother^*.

and because it's expected of me, bungus:
your volley of puns in the ^ post has really set the baseline. it would be rude of me to just lob in and try and string this out, I'd soon run out of djuice.


* roo ted^#

# NBG, RS, rotten sausage or ratchet in polite company