DIY Transistor Amp Using NVA Boards

For the three and more legged things
Post Reply
Cressy Snr
Social Sevices have been notified
Posts: 8887
Joined: Wed May 30, 2007 12:25 am
Location: South Yorks.

Re: DIY Transistor Amp Using NVA Boards

Post by Cressy Snr » Sat Jan 11, 2020 5:27 pm

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:
77C07E7D-48D1-43E8-B197-9E08FB505433.jpeg
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. :)
Hey Drooper! ....Take out the trash!

Cressy Snr
Social Sevices have been notified
Posts: 8887
Joined: Wed May 30, 2007 12:25 am
Location: South Yorks.

Re: DIY Transistor Amp Using NVA Boards

Post by Cressy Snr » Sat Jan 11, 2020 6:05 pm

Better layout after removing one of the partitions:
E0964937-E236-44E9-882A-5CAA8A7803F7.jpeg
Hey Drooper! ....Take out the trash!

User avatar
pre65
Amstrad Tower of Power
Posts: 18546
Joined: Wed Aug 22, 2007 11:13 pm
Location: North Essex

Re: DIY Transistor Amp Using NVA Boards

Post by pre65 » Sat Jan 11, 2020 6:11 pm

Personally, I like the first layout better.
Life is what happens to you while you're busy making other plans. John Lennon

G-Popz THE easy listening connoisseur. (Philip)

User avatar
Nick
Site Admin
Posts: 12554
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

Re: DIY Transistor Amp Using NVA Boards

Post by Nick » 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.
Resistance isn't futile it's V / I.

Cressy Snr
Social Sevices have been notified
Posts: 8887
Joined: Wed May 30, 2007 12:25 am
Location: South Yorks.

Re: DIY Transistor Amp Using NVA Boards

Post by Cressy Snr » Sat Jan 11, 2020 9:04 pm

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.
Hey Drooper! ....Take out the trash!

Cressy Snr
Social Sevices have been notified
Posts: 8887
Joined: Wed May 30, 2007 12:25 am
Location: South Yorks.

Re: DIY Transistor Amp Using NVA Boards

Post by Cressy Snr » Mon Jan 13, 2020 5:07 pm

Made up a base from black painted 3mm aluminium sheet, plus a couple of angle brackets for the heatsinks:
FEEE605C-56FE-4CB9-878A-30030BB2382D.jpeg
Power transistors temporarily mounted to check that positioning holes were drilled in the right places.

How it looks in the chassis:
FBA0F5CD-8644-4E7F-B96B-1120D2A6BED2.jpeg
Hey Drooper! ....Take out the trash!

User avatar
Nick
Site Admin
Posts: 12554
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

Re: DIY Transistor Amp Using NVA Boards

Post by Nick » Mon Jan 13, 2020 5:32 pm

I assume you will be isolating the transistors?
Resistance isn't futile it's V / I.

Cressy Snr
Social Sevices have been notified
Posts: 8887
Joined: Wed May 30, 2007 12:25 am
Location: South Yorks.

Re: DIY Transistor Amp Using NVA Boards

Post by Cressy Snr » Mon Jan 13, 2020 5:47 pm

Nick wrote:
Mon Jan 13, 2020 5:32 pm
I assume you will be isolating the transistors?
Oh yes indeed!
Hey Drooper! ....Take out the trash!

Neal
Needs to get out more
Posts: 1952
Joined: Fri Aug 03, 2007 10:57 am
Location: From the land of the Bodgers

Re: DIY Transistor Amp Using NVA Boards

Post by Neal » Mon Jan 13, 2020 9:13 pm

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

Cressy Snr
Social Sevices have been notified
Posts: 8887
Joined: Wed May 30, 2007 12:25 am
Location: South Yorks.

Re: DIY Transistor Amp Using NVA Boards

Post by Cressy Snr » Fri Jan 17, 2020 7:39 pm

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.
Hey Drooper! ....Take out the trash!

Cressy Snr
Social Sevices have been notified
Posts: 8887
Joined: Wed May 30, 2007 12:25 am
Location: South Yorks.

Re: DIY Transistor Amp Using NVA Boards

Post by Cressy Snr » Fri Jan 17, 2020 7:46 pm

OK, here is the progress so far:
7315937A-0EE9-42E4-8749-763C293384F1.jpeg
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.



9AD35500-9E43-4C17-A459-D85BF17F68CB.jpeg
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.



854C3CFE-A28D-4A58-8E94-83EE6CC39195.jpeg
Back panel.
Hey Drooper! ....Take out the trash!

Cressy Snr
Social Sevices have been notified
Posts: 8887
Joined: Wed May 30, 2007 12:25 am
Location: South Yorks.

Re: DIY Transistor Amp Using NVA Boards

Post by Cressy Snr » Fri Jan 17, 2020 7:47 pm

4C73B905-8541-4711-8E45-0874B07615EC.jpeg
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.
Hey Drooper! ....Take out the trash!

Cressy Snr
Social Sevices have been notified
Posts: 8887
Joined: Wed May 30, 2007 12:25 am
Location: South Yorks.

Re: DIY Transistor Amp Using NVA Boards

Post by Cressy Snr » Sat Jan 18, 2020 6:35 pm

I’ve ended the day utterly pissed off! :x

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?
Hey Drooper! ....Take out the trash!

User avatar
Mike H
Amstrad Tower of Power
Posts: 18725
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

Re: DIY Transistor Amp Using NVA Boards

Post by Mike H » Sat Jan 18, 2020 7:19 pm

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 Image
 
"Entrenched convictions cannot be changed by facts." – Dick Francis

User avatar
Mike H
Amstrad Tower of Power
Posts: 18725
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

Re: DIY Transistor Amp Using NVA Boards

Post by Mike H » Sat Jan 18, 2020 7:28 pm

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.
 
"Entrenched convictions cannot be changed by facts." – Dick Francis

Post Reply