DIY Transistor Amp Using NVA Boards

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Dave the bass
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Re: DIY Transistor Amp Using NVA Boards

Post by Dave the bass » Sat Jan 18, 2020 8:06 pm

Ooo errr.

Where did the smoke come from Steve? If it was me I'd check TX phase and rectifiers.
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Re: DIY Transistor Amp Using NVA Boards

Post by pre65 » Sat Jan 18, 2020 10:04 pm

Dave the bass wrote:
Sat Jan 18, 2020 8:06 pm
Ooo errr.

If it was me I'd check TX phase
Many years ago I had transformer smoke and TX phase was the problem.
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Re: DIY Transistor Amp Using NVA Boards

Post by Nick » Sat Jan 18, 2020 10:45 pm

then smoke wisps
Where from?
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Re: DIY Transistor Amp Using NVA Boards

Post by Nick » Sat Jan 18, 2020 10:50 pm

If the caps are metal cased, make sure they are isolated from the chassis as the -ve terminal will be connected to the can of the transformer (this has caught me out before).
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Re: DIY Transistor Amp Using NVA Boards

Post by Cressy Snr » Sat Jan 18, 2020 11:49 pm

Thanks for the suggestions guys. The smoke came from the on off switch, just a small wisp. That was enough to trigger a hurried switch-off. I’ll have a look tomorrow.
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Re: DIY Transistor Amp Using NVA Boards

Post by pre65 » Sun Jan 19, 2020 8:45 am

Cressy Snr wrote:
Sat Jan 18, 2020 11:49 pm
Thanks for the suggestions guys. The smoke came from the on off switch, just a small wisp. That was enough to trigger a hurried switch-off. I’ll have a look tomorrow.
I've wired up DP on/off switches incorrectly in the past. :oops: :oops:
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Re: DIY Transistor Amp Using NVA Boards

Post by steve s » Sun Jan 19, 2020 12:17 pm

I'm sure will soon get the issue sorted Steve
You would think relatively simple solid state would be easy after valve amps.. but my first chip amp is going pretty crap... a simple tda 2030, but it just loves to ossilate.. after a month I still can't plug anything into it ! Although it seems ok untill I wave the phono cable anywhere near it
Best of luck..
Last edited by steve s on Sun Jan 19, 2020 1:00 pm, edited 1 time in total.
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Re: DIY Transistor Amp Using NVA Boards

Post by Cressy Snr » Sun Jan 19, 2020 12:55 pm

steve s wrote:
Sun Jan 19, 2020 12:17 pm
I'm sure will soon get the issue sorted Steve
You would think relatively simple solid state would be easy after valve amps.. but my first chip amp is going pretty crap... a simple tda 2030, but it just loves to ossilate.. after a month I still can't plug anything into it ! Although it seems ok untill I wave the phone cable anywhere near it
Best of luck..
Yes, SS at the moment, is a royal PITA . When Richard sent me the boards, he told me, in his email, that he wanted to see a valve bloke, try and do a transistor amp, and that he knew he would be p*ssing himself laughing at my attempts to get his boards going.
He’s definitely up there laughing at the moment. :)

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Re: DIY Transistor Amp Using NVA Boards

Post by Cressy Snr » Sun Jan 19, 2020 3:08 pm

Nick wrote:
Sat Jan 18, 2020 10:50 pm
If the caps are metal cased, make sure they are isolated from the chassis as the -ve terminal will be connected to the can of the transformer (this has caught me out before).
Here was the problem:
5788A691-7E69-4301-BFF5-A9ABC68637EB.jpeg
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. Sod’s Law of course ensured that said cap just happened to have its negative terminal as the power feed, with its positive as 0V.
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, plus I threw away the offending cap clamp, and everything fires up properly without incident.

Now we can put in the wires to the boards etc.
Last edited by Cressy Snr on Sun Jan 19, 2020 4:00 pm, edited 1 time in total.
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Re: DIY Transistor Amp Using NVA Boards

Post by Dave the bass » Sun Jan 19, 2020 3:48 pm

Well done on finding the problem Steve.
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Re: DIY Transistor Amp Using NVA Boards

Post by pre65 » Sun Jan 19, 2020 3:53 pm

Dave the bass wrote:
Sun Jan 19, 2020 3:48 pm
Well done on finding the problem Steve.
Yes, well done Steve.

I prefer to use non metallic capacitor clamps if possible.
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Re: DIY Transistor Amp Using NVA Boards

Post by Cressy Snr » Sun Jan 19, 2020 4:09 pm

Thanks chaps.

It’s non metallic clamps for me from now on.

Power supply all done; double pole switching (with fuse in the live side of course)
Chassis divider repositioned to serve as a heat shield between caps and heat sinks.
858ACBBA-6C13-47B5-8F76-324AEC5FC264.jpeg
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Re: DIY Transistor Amp Using NVA Boards

Post by Mike H » Sun Jan 19, 2020 5:30 pm

Cressy Snr wrote:
Sun Jan 19, 2020 3:08 pm
Nick wrote:
Sat Jan 18, 2020 10:50 pm
If the caps are metal cased, make sure they are isolated from the chassis as the -ve terminal will be connected to the can of the transformer (this has caught me out before).
Here was the problem:

Image

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.
Image

Image

Anyhow, that's alright then!

:thumbleft:
 
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Re: DIY Transistor Amp Using NVA Boards

Post by Cressy Snr » Sun Jan 19, 2020 7:22 pm

The story so far:
02F35BE6-0980-4F87-ADD3-556DD863DB68.jpeg
Just the power rails and the input socket wiring to install, then it’ll be switch-on, shortly followed by...KERBLAMMM!, then :sad2:...cough..splutter..then...”darling, where’s the dustpan and brush? ...No....don’t come in the kitchen just yet!”....”I know there’s a draught; I’ve got the back door open!” then.... “feck it I’ll stick with valves” :lol:
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Re: DIY Transistor Amp Using NVA Boards

Post by Cressy Snr » Mon Jan 20, 2020 2:03 pm

Board wiring and inputs all done:
874D6C1E-98DE-4B5B-945E-4FC2099F1B44.jpeg
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