Reverb power supply

[Ben79]

I tried it with the headphone out of my Korg MS20 and it gave me an AC on the secondary that was 0.05 of the primary (unloaded) - I took that as working so I rebuilt the board with all new parts.

It works!

....sort of. The 9v regulated is fine but what's supposed to be 12v is reading 17v ish....The transformer says it puts out 11.8v. Could it be I DID fry my transformer but only a bit?

[crochambeau]

The transformer says it puts out 11.8v

Please forgive my insistence on the pedantic.

Does this mean there is printing on the transformer indicating a nominal design voltage across the secondary (if so: ignore that) or does this mean you have measured 11.8 volts AC across the secondary while the primary is connected to mains?

Typically when you damage a transformer windings will either open (rendering the object a paper weight) or short to adjacent turn on the same winding (essentially changing your turns ratio). I suppose it is possible that you could have shorted some of the primary winding and now you have essentially increased the turns ratio of the secondary - but I sort of doubt this. Burning windings is a smelly business, and requires either a fair bit of heat or exposure to moisture.

Rectified DC is going to be above measured RMS by a noticeable percentage (is it 30%? I forget off hand and am too lazy to look it up). Anyway, it does not sound like you're out of reasonable bounds on what you're measuring, unless that 17 is on the ass end of a 12 volt regulator.

If your regulator is running hot you can series string more diodes at your rectifier (in, before, or past), losing a half volt for each unit used, but this is a total bodge and can look ugly (not recommended for anything beyond personal use/experimentation). I would just rate the parts in the circuit up to meet a higher power supply rail (if possible) and enjoy life.

...unless you are correct in the concern that your PT has been stressed, as those may continue to degrade if compromised and you should have a backup handy.

[Ben79]

I welcome your pedanticity! I just got my rail polarities backwards, I need it!

The transformer says 11.8 on the label but i had a vague memory of having measured it when I found it and it reading around 12 but that's hazy.

Thanks for you advice. No 12v reg in there at the moment but I have one I could use. The seller recommendss a regulated supply.

Here's a little update....

I found a couple of karaoke mixers in the street and have used various bits for the build (and got a load of nice spares for future projects).

The Tripple Fuzz is in and I've started the wiring job.

[imJonWain]

So in Germany people just leave music related electronics in the street? Like all the time?

[Ben79]

Yes, today I found a vintage DDR 24v power supply (the Universe was trying to help but she doesn't really know electronics), and a 6v supply and little USB powered fan which I need to blow away the solder fumes.

I get almost everything off the street. I've decked out and equipped an apartment almost entirely with street finds or upcycled bits - (a lot of wood).
Found a hard shell tweed guitar case last week too.

[crochambeau]

Sounds like a nice place to be!

[imJonWain]

In Boston I used to find cool stuff on the sidewalk. Here in NC it's pretty much just mattresses and trash on the sides of streets.

[Ben79]

I've finished the reverb (the fuzz is still awaiting a 10k gain pot).

It doesn't work. The circuit passes signal but there's no reverbing.

One thing that puzzles me is that the kit supplied insulated rca sockets for the reverb pan connection but on the board, the shielding solder hole is marked 'ground'. My board ground is connected to the chassis (using the supplied self grounding metal jack sockets) so I don't see why the rca socket 'outers' should be insulated from it.....the Surfybear guy shows a photo in the instructions to make sure you don't get the RCA shielding washer/terminal the chassis side of the plastic insulating washer.....but then it's grounded at the board! Have I missed something?

[crochambeau]

I don't think the ground reference should give you any grief, unless there are disconnects making hum. Naturally, the signal aspect should be free and clear of it though.

If you tap the reverb pan, do you hear sound?
If you plug the driver output into something like a mixer, does it deliver?

You could have a bum pan, broken connection, or short. Just have to dig into it in a manner that allows you to isolate a problem section.

[eatyourguitar]

there are two rotational transducers. one going in one coming out. the signal coming out of a tank is weak like the signal coming out of passive single coils on a vintage strat. any noise that gets picked up through induction gets amplified along with the signal at the reverb recovery stage in the reverb circuit. this is why they ground the sleeve at the PCB. it is just rf drain. basic shielding.

[Ben79]

Thanks EYG and Crochambeau for your help.

I got it working!

Turned out the RCA leads were dodgy - I'd checked the soldering and it was all fine but I think the metal plating had tarnished as it was hard to get a good continuity reading between the outers. They were probably found in a rubbish pile. I could probably have just cleaned them up with a file thinking about it now but I sprung for some new ones and that did it.

The reverb sounds really nice, very pleased with it. As an intro I'd say the Surfybear kit is worth the expense for the work that's gone into it although I think they're discontinued now.

The fuzz part is still awaiting its 10k gain pot and I might paint the finished unit somehow - then I'll post some final photos.

I still have a 3 spring Accutronics tank that came out of a Marshall so I think I'll build a legit DIY reverb next with that. I found this schematic that corresponds to the tank I have....



It looks straightforward enough and I have a centre-tapped 15v transformer that came out of one the karaoke units I dismembered. Any advice before I jump into it? I'm not quite sure what they mean about the floating input.....do I just wire it up as shown through the resistor and cap to ground?

[eatyourguitar]

is the metal on the tank connected to anything else?

[crochambeau]

Here's a couple pics of a pan I have, notice that the output jack shield is connected to the pan via a conductive material whereas the input jack is not.

[Ben79]

Yes, same here - output sleeve is connected to the tank chassis.

And am I right in thinking this will do the job for the power?



And I'll go with 220uf 25V caps....?

[crochambeau]

That depiction of a rectifier looks good (have built the same myself). 220uf is a fair amount of capacitance, but really just a shot in the dark. Values are best arrived at while calculating current draw. Mind the polarity on the caps.

If supply ripple remains problematic, regulators or chokes can help tidy up your rails.