HiFi Subjectivist ¦ Audio Forum ¦ NVA User Group

I’ve ended the day utterly pissed off!

Two power supplies all wired in. Fire up to check it functions and the large transformer goes beserk, drawing massive current, yet voltages on its associated caps check out fine, then smoke wisps, so switch off. Small psu is fine. The large transformer is also fine; until it is in circuit.

Can’t find any shorts, but something is causing the large current draw. All I can think of is either a duff cap or bridge rectifier; there’s nothing else, unless I’ve somehow created a shorted turn with the fixing bolt. Either way the fault has got to be found or I’m going to have to abandon the dual power supply idea.

Is there some kind of black art with multiple bipolar PSUs that I’m not in on?

SteveTheShadow wrote: ↑Sat Jan 18, 2020 7:29 pm
Is there some kind of black art with multiple bipolar PSUs that I’m not in on?

Nope, not that i know of. Only the 0V arrangement caused any chin scratching.

I would be trying different rectifiers and caps to rule them out.

Hope you get it sorted.

Thanks Stu,
I’ll have a look in the morning.

Here was the problem:


Sharp edge on the inside of one of the cap clamps on the larger power supply, had cut through the plastic insulation, and caused a high resistance ground fault to the earthed chassis, via the can of the offending cap. This must have been enough of a short, to pull excessive current through the large transformer. Anyway I’ve replaced the whole rectifier/transformer/capacitor network and everything fires up properly without incident.
I also binned the offending cap clamp.

Now we can put in the wires to the boards etc.

Power supply all done; double pole switching (with fuse in the live side of course)
Chassis divider repositioned as a heat shield between caps and heat sinks.

Such a simple fault- was it easy to spot.
When’s the switch on?

SteveTheShadow wrote: ↑Sun Jan 19, 2020 4:11 pm
Sharp edge on the inside of one of the cap clamps on the larger power supply, had cut through the plastic insulation, and caused a high resistance ground fault to the earthed chassis, via the can of the offending cap. This must have been enough of a short, to pull excessive current through the large transformer. Anyway I’ve replaced the whole rectifier/transformer/capacitor network and everything fires up properly without incident.
I also binned the offending cap clamp.

Now we can put in the wires to the boards etc.

Obviously very annoying. Good luck with the rest of the build.

I use acrylic cases and glue in caps with Bison kit so avoiding issues like that.

Alfi.

Latteman wrote: ↑Sun Jan 19, 2020 5:32 pm Such a simple fault- was it easy to spot...

No it fecking well wasn’t!

Richard must be up there p*ssing himself laughing

The story so far: Just the power rails and the input sockets to do tomorrow.
Then it’ll be, throw the switch, shortly followed by..... KERBLAMM!.... then,
“Darling..where’s the dustpan and brush?...er...don’t come in the kitchen just yet.

Hats off to you Steve, that looks to be a fine and time consuming project. I hope it sounds sweet when it's finally connected