2nd 100v Amp blown :( Help needed to troubleshoot.

[devs]

Result! Found a 100w lightbulb. I knew there was a reason why I have a hoard of old lightbulbs.

 

[oldbutnotdead]

Always do the easy jobs first- so go round all the volume controls and check for whiskers, rewire etc. While you are doing the OUTPUT pairs you can use your new meter to check the impedance of the loudspeakers (while you have them disconnected from the volume control). For 1 speaker you'd be looking for 8 ohms ish, 2 speakers 4 ohms, 3 speakers 2.3 ohms. Your meter will be able to test this value

 

[devs]

Hello mate, the meter has arrived this morning and I've just started to go round the controls and test the readings.. I just wanted to double check that I've got the meter setup correctly before continuing as the readings on the two that I have tested so far differ from when you suggested.

1 - Kitchen / Dining room - 3 x speakers / one twist vol. control - Reading = 1.21


2 - Downstairs Hall - 1 x speaker / one twist vol. control - Reading = 3.51

Attached is a photo of how the meter is set..

Is this correct and shall I carry on.

Many thanks,

Devs.

 

[oldbutnotdead]

Morning. Better off having the meter set to 200 rather than 2k (for the low impedance you're measuring). Those readings imply that the speakers are 4 ohm impedance rather than 8 ohm which is odd and may not be helping with your problems (presenting too high a load to the amplifier).....

 

[oldbutnotdead]

Have you got an exact model number on one of those twist volume controls. Just checked again on Apart's website, the speakers you quoted are meant to be 8 ohm. Intriguing

 

[oldbutnotdead]

And just to confirm- those readings are with the output cables disconnected from the volume control aren't they?

 

[devs]

Morning mate, yes the readings are via the outputs whilst disconnected. The bulk of the controls are these: https://www.avsl.com/product/952.461UK-100v-volume-controls-relay-fitted

However there is one thats different upstairs. I'll go and check what that one is now and report back

 

[devs]

The odd ball control, appears to be one of these: https://www.commercialaudiosolutions.com/apart-e-vol120-100-volt-line-volume-control.html

I trust that the system was never designed to have all speakers running at the same time and that I've been blowing the amps by cranking the music up on all zones?

 

[oldbutnotdead]

Hmmm. Most of the controls are to handle 12 w- that's reasonable for 1 speaker. The odd one (if on the zone with 3 speakers) makes sense- that'll handle 100w. The interesting bit is there are 2 variants on those controls. The ones without relay appear to have an onboard transformer (so you'd connect your 8 ohm speakers direct to the control). The ones with relay appear NOT to have said onboard transformer fitted (what passes for a drawing implies that the line transformer is separate to the control). Can you get at any of the loudspeakers to see if they have transformers attached? (An easy one is always better to start with)- and if they have got transformers (they should have) whether they've been wired to use the transformer or bypass it?

 

[devs]

The odd ball control is for the upstairs hall, that powers only on speaker. I've just double checked a speaker and attached a photo of one here. I can confirm that they are all the same as this one without anything additional attached as I've had them all out previously whilst painting.

 

[oldbutnotdead]

OK and all good so far. Might be an idea to swap the odd one to the zone with 3 speakers on it. And no you shouldn't have blown the amp up by having all the speakers on full- there's only 8 speakers on the system, with them at full chat that's still only 50 watts. Those controls you have are the proper ones for the job so not a design issue, I still suspect a low impedance fault from a whisker on those chunky cables at the volume controls. The speakers have been wired sensibly (decent sized terminal block so less likely to be a wiring fault there). Those resistance readings intrigue me- they are quite high for DC through a transformer. Shame I don't have any 100v line kit here any more to do some testing of my own.

 

[devs]

Morning mate and sorry for the later reply. The in laws have descended and consumed my time. That’s good to hear, I’ll continue around the controls and meter the readings and report back with what they are, I’ll also swap out the upstairs control so its where the 3 speakers are attached.


Many thanks

 

[devs]

Okay I’ve been round the controls and checked for any stray wires and metered the outs. I’ve also swapped the more powerful control to the 3 speaker location.



The readings are as follows:



1 - Kitchen / Dining room - 3 x speakers / one twist vol. control - Reading = 1.21


2 - Downstairs Hall - 1 x speaker / one twist vol. control - Reading = 3.51


3 - Living Room - 1 x speaker / one twist vol. control - Reading = .359 (meter set to 2k)


4 - Upstairs Landing - 1 x speaker / one twist vol. control - Reading = .359 (meter set to 2k)


5 - Master Bed / ensuite 2 x speakers / one twist vol. control - Reading = 181.5



I’m hoping the new amp will land today so should be in a position to do further tests soon..



Do I still need to do anything with the 100w bulb?

 

[sparkymarka]

As advised above ....could it be some strays shorting ....

 

[devs]

Thanks for the input sparkymarka, I've been round all the controls now and rewired them so any strays should now be out of the equation. I've also meter read the outputs for each of the controls and come back with the following readings..

1 - Kitchen / Dining room - 3 x speakers / one twist vol. control - Reading = 1.21


2 - Downstairs Hall - 1 x speaker / one twist vol. control - Reading = 3.51


3 - Living Room - 1 x speaker / one twist vol. control - Reading = .359 (meter set to 2k)


4 - Upstairs Landing - 1 x speaker / one twist vol. control - Reading = .359 (meter set to 2k)


5 - Master Bed / ensuite 2 x speakers / one twist vol. control - Reading = 181.5

Do they seem right for the setup?

Many thanks,

Devs.