Power Supply vs. Delay

[newfish]

Hmm, so ....

I've been using a 'Cherub' MD-6 delay for a few months now.

Nice piece of kit - 5 seconds of delay and 11 seconds of sample / hold.  It eats batteries, but it's digital...

Came to do an outdoor gig yesterday and all was not good.

The pedal now produces a rhythmic 'ticking' on the output, and the sample / hold function is somewhat erratic with its timings.

The pedal was powered by the usual 9v adapter (wall-wart) as it has been since I first bought it.

We were powered by generators, and I'm not sure if the mains adapter was regulated (d'oh!) - is it likely that some bad power has damaged / fried  something?

I'll have time to look inside tonight, but if anyone has any immediate pointers (oither than buying a regulated PS!), I'd be most grateful.

Cheers.

[axg20202]

First thing to do is rule out damage to pedal vs. damage to PSU - does the noise still appear with batteries?

[newfish]

Sadly, yes - with the existing battery.

Will try with a fresh-out-of-the-box battery this evening though.

Also with different (but equivalent) Adapter.

I'm not scared of opening the pedal up - would be quite intrigued to be honest - but given the complexity of features (tap tempo / reverse / ping pong / S&H) and the small case size, I'd expect to see a lot of SMD in there.

If nothing else, I hope this prompts people to be more careful with they use to power their kit.

Be ye Warned!

[R.G.]

I did a series of articles on the dangers of running from generators for my "Tech Views" column in Premier Guitar.

I think they make for useful reading ...before... doing an outdoors gig.

[newfish]

Ah.... Right.   

If I can *just* tweak my flux-capacitor and calibrate to 88bpm, I'll be able to pop back a day or so...

Hindsight really *is* 20 / 20.

Screwdriver and Scope at the ready...

FWIW, the DIY kit I was using performed magnificently.   

[axg20202]

In that case, the problem could be anywhere in the pedal, but I'd put my money on an IC in the delay portion of the circuit which was stressed somehow by a mains spike. If it's all obscure surface mount components in there, I see a new delay pedal in your future....I'd recommend getting stuck into one of the various BBD chip-based delay projects like the Rebote. Easy enough to build and sound great. No S/H function though.

[newfish]

Had a sneaky peek under the hood last night.

It's like a tiny City in there - vast majority of components were indeed SMD.

Scanned across the board a few times with a Jeweller's Loupe to see if anything had physically burnt up.
Then checked the Diodes with a DMM.  All looked fine.

Two relatively large chips with tiny gnat's-whisker legs on all four sides.

I do indeed see a new Delay in my future, and also the purchase of a proper regulated power supply.

I really like having a S/H function, so will probably buy the same pedal again as, compared to the likes of Line6 and Boss, ths one was reasonably priced for equal performance.

You lives, you learns, you buy better power supplies.

Nice case though - I can see it coming in very handy sometime soon.

[R.G.]

I have examined a number of digital delay-ish and processing devices which died mysteriously.

In most cases, there is a switching power supply right at the DC input port that changes whatever comes in to +2.5 or +3.3V and ground. This is what's known in the power supply biz as a buck regulator, chopping whatever comes in down to the output voltage in a PWM fashion and using an inductor/cap filter. This stuff has all been subsumed into a single SMD IC which contains all of it, including the switching MOSFET in many cases, leaving only the inductor, cap and a few Rs outside the chip. The switching frequency is up in the near-1MHZ range to run the inductor and filter cap sizes down to infinitesimal.

In the units I looked at, the power supply regulator chip has a spec of about 10Vdc absolute maximum; the presumption is that if you go over 10.000000V, the chip dies. It's not really that bad, I think, but I suspect anything over 10V leave cumulative damage and someday it dies. There are similar chips with an absolute max input voltage of 15 and up to 30V that for some reason were not used.

From an engineering standpoint, this is the sheerest folly. Anything that's powered from batteries and wall warts near to or around 9Vdc will eventually be given more than that. One of the silliest things you can do is design stuff that is reasonably certain to die early because you cut your margins too close.

I don't know that this is your problem, but it sure sounds like it.

Sorry, the units are essentially irreparable. I think that was your next question.

[Ice-9]

Sorry, the units are essentially irreparable. I think that was your next question.

Unless
If the "buck converter" is the problem and you can find out the output voltage (maybe from the datasheet of  the other digital chips in circuit) you could make up an equivelent voltage converter. Probs not an easy job but if its a pedal you really love then it  would be worth it. Look up SMPS and buck converter

[JKowalski]

Anything that's powered from batteries and wall warts near to or around 9Vdc will eventually be given more than that. One of the silliest things you can do is design stuff that is reasonably certain to die early because you cut your margins too close.

Yeah - I have found that 99% of unregulated 9v wall warts put out a typical 12-13VDC in reality. That is pretty ridiculous, what kind of designer wouldn't think of that?