audio-talk

The broken down Sony CD player has been gutted to give a nice, solid, heavy chassis for the next chapter in the evolution of the NVA clone. I don’t have to order anything for this project, just needed to do a bit of creative up-cycling of the CD player.

This new iteration of the NVA clone will have twin power supplies; one for the front end and the other for the driver/power stage. I’ve done a preliminary layout below: It’s quite a nice chassis, with partitioned off, screened sections. TBH, I’m not particularly enamoured with the layout above, but it does show the generous size of chassis available to work with.

Comments from the panel will be much appreciated.

Better layout after removing one of the partitions:

Personally, I like the first layout better.

pre65 wrote: ↑Sat Jan 11, 2020 6:11 pm Personally, I like the first layout better.

Probably because you like symmetry more than keeping the transformers further away from the PCB's.

Nick wrote: ↑Sat Jan 11, 2020 6:36 pm

pre65 wrote: ↑Sat Jan 11, 2020 6:11 pm Personally, I like the first layout better.

...keeping the transformers further away from the PCB's.

Aye, with the second layout, the transformers are as far away from the input stages as it’s possible to get them.
As soon as I’d done the symmetrical layout, I knew it was sub optimal, especially given the fact that there are two power supplies.

Made up a base from black painted 3mm aluminium sheet, plus a couple of angle brackets for the heatsinks: Power transistors temporarily mounted to check that positioning holes were drilled in the right places.

How it looks in the chassis:

I assume you will be isolating the transistors?

Nick wrote: ↑Mon Jan 13, 2020 5:32 pm I assume you will be isolating the transistors?

Oh yes indeed!

Given the layout you could build a Mu metal box inside the case to place them in...

Neal wrote: ↑Mon Jan 13, 2020 9:13 pm Given the layout you could build a Mu metal box inside the case to place them in...

Sounds like a plan if I can get the boards going in the first instance without blowing them up. I’m not holding my breath, but we’ll see if they stay in one piece first.

OK, here is the progress so far: Just the rectifiers to fit; one behind each pair of caps, plus the electrical safety earth wire needs bolting to the base of the case. This is being built to class 1 standard.



Output transistors fitted to heat sinks. Better fixing brackets for the heatsinks were made up, creating extra work, but the heatsinks are far more solidly connected to the black aluminium plate than they were.



Back panel.

Four 30mm holes punched in base to draw air through the heat sink fins. Fins are sitting 6mm above the inside of the base.
There will be four corresponding holes punched into the lid of the case, backed by an aluminium mesh.

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.

I don’t get it. I have put three power supplies on the OTL with zero issues. But solid state is proving a complete bastard. Is there some black art regarding multiple bipolar PSUs that I’m not in on?

Nick wrote: ↑Sat Jan 11, 2020 6:36 pm

pre65 wrote: ↑Sat Jan 11, 2020 6:11 pm Personally, I like the first layout better.

Probably because you like symmetry more than keeping the transformers further away from the PCB's.

That told you didn't it

Steve C, welcome to my world, that was me in the 1970's. Walking home from college Friday night I'd pop into Bi-Pre-Pak in West Road, Southend, and get four if not six power transistors for whichever amp prototype I'm going to be working on over the weekend, cos was a pretty safe bet I'd blown up at least two of them.

Have a break and get back to it later with a fresh pair of eyes.