HiFi Subjectivist ¦ Audio Forum ¦ NVA User Group

I was watching tv last night when everything went dark. I thought it was a dry run for the upcoming "winter of discontent" but investigation, following the smell of cooking electronics, found that the cause was a cooking A30 I bought as part of the NVA starter kit in 2007. I use it to run the HF in my vintage Doc mod Goodmans Dimension 8 speakers.
I was not listening to anything it seems the amp just got really hot and blew. I have opened it up and tested the transformer. The primary is broken but secondary seems fine, as far as I can tell.
Does anyone know how it could happen this way and if any other components could be affected.
I normally turn off my amps when not listening but I had recently decided to try to follow the Doc's instruction; to leave everything on all of the time.

Are your speakers ok?

The bass drivers are fine. I have A80s driving the bass and they are ok but yet to check the tweeters. I am not sure yet how to do that until I fix/ replace the A30.

floydfan wrote: ↑Sat Oct 16, 2021 10:43 am The bass drivers are fine. I have A80s driving the bass and they are ok but yet to check the tweeters. I am not sure yet how to do that until I fix/ replace the A30.

Remove the tweeters if you can and disconnect them from the wiring. If you have a multimeter then check them for continuity and if they are blown then they will be no reading. They will be usually be somewhere between 3.5 ohms and 8 ohms.

If you don't have a multimeter then just swap the A80 on to the tweeters and listen for any sound. You don't have to have the other drivers connected. the other way is to briefly connected a small 1.5V battery to the terminals and watch if the tweeter dome moves. Just connect it for a moment though.

Swapping the good amp to the tweeters is probably the easiest.

I was a bit wary of connecting up the A80s in case it was a fault with the drive units that was causing the transformer overheating. I am still not sure why the transformer should suddenly decide to overheat. Anyway, my other half is calling me to head out, so will come back to this later. Thanks for the reply.

Fair enough. Don't connect the A80.

Removing the tweeters is the only way as you can't measure their resistance through the crossover and the series cap will block the DC from a 1.5V battery.

Tweeters usually blow open circuit ie there is no continuity. If they have blown then that tells you that probably the whole amp needs sending back to NVA HQ.

3 common causes of overheating...

Component failure
Inadequate ventilation
Inappropriate use

Ruling out the last 2, please contact Tomasz at mail@hfsaudio.co.uk

Overheating to the point of failure is not normally 'sudden' - heat builds over a period of time. Tomasz will tell you more, though.

Sounds like the transformer as given up .

14 years is not bad, it's not good but it's not bad. Sometimes parts just fail.

I managed to move the speakers across the room, which is not easy due to the large amount of steel plate in them, and plugged them into an old Cambridge Audio amp installed in a hi fi unit and the tweeters seem ok. I intend to try replacing the transformer which I happen to have from my external PSU project, thanks to D.Quinn, and see what happens.

Replaced the transformer and it all seems fine. I will keep an eye on it for overheating and will go back to turning off when not listening.