I suspect the amp is oscillating at supersonic frequencies producing a continuous current capable of frying the resistors in a high pass tweeter filter.
The burning smell can't now return as the path for this continuous current has been broken by the fried resistors which have become open circuit.
N.B. I wouldn't risk using this amp on a new or refurbished pair of loudspeakers.
If the tweeters have a DC resistance of 4.6 ohm, this is consistent with a nominal impedance of 6 ohm and shows that the voice coils are not open circuit.
Although encouraging, this does not mean that the cylindrical voice coils have not been distorted by excessive heat - only by applying a music signal as detailed in post #2 can you eliminate that possibility.
Having made sure the tweeters are working properly, I would be tempted to replace both of those "side by side" resistors with the same 2.7 ohm 5 watt resistor value simply to note the result. Try it on just one speaker for now until we see where that gets us. Oh, and use another amplifier for testing!
I`ll get some 2.7R 5W. It did look VERY feint to me that the other was 3.9 ???? but really cant be sure.
I`ll grab another amp from the museum when I`m there on Friday/
I`ll grab another amp from the museum when I`m there on Friday/
Thanks tuantran.
An observation - your schematic shows 3 inductors while only 2 are visible on the physical board shown in post #1.
If you look at the twisted wires of the inductor (2 inductors in one bobbin). I have never seen this before
Did you draw the schematic by looking at the board pictured in post #1, or have you had prior experience with this speaker?
next question..
capacitor next to the resistors. I assume damaged due to excesive heat.
They are NP 15uf, 63v Caps.
The closest I can find is 10uf or 22uf.
Which would be better?
capacitor next to the resistors. I assume damaged due to excesive heat.
They are NP 15uf, 63v Caps.
The closest I can find is 10uf or 22uf.
Which would be better?
There is typically a manufacturer's tolerance of +/- 20% on these capacitors, meaning that the actual value of the 15 uF capacitor could be anywhere between 12 uF and 18 uF. The same tolerance of +/- 20 % applies to each of the replacements. I'll let you work out the better match from that angle!
Given the non-critical task that these speakers are being asked to perform, I'd be greatly tempted to remove the damaged crossover board by disconnecting it from the speaker input terminals.
I'd simply connect the mid/bass driver directly to the input terminals then also connect the tweeter to these terminals, but via a series 4.7 uF NP capacitor. https://wilmslowaudio.co.uk/monacor-mkp-polypropylene-capacitors/47-fd-monacor-mkp-capacitor
There would be no harm in trying it, Simon!
P.S. You could use the 6.2 uF that's on the board in a preliminary test.
Thanks for that idea..
As for the 15uf Cap, it states to be +/- 5%, so not sure what I can do.
I now have another Amp - that I`ll connect up tomorrow night (bit late in the Uk to play
As for that
Another idea..
The Warfdales - could I use the cross over from those on the Tannoys do you think? I`m not sure why they sound bad yet though - but the crossover boards look unharmed.
As for the 15uf Cap, it states to be +/- 5%, so not sure what I can do.
I now have another Amp - that I`ll connect up tomorrow night (bit late in the Uk to play
loudish music to test!)As for that
simple connection idea... Would that be ok, with the system playing music on about 3rd volume on the Amp, for about 6 hours each weekend day?Another idea..
The Warfdales - could I use the cross over from those on the Tannoys do you think? I`m not sure why they sound bad yet though - but the crossover boards look unharmed.
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To be certain, we would connect a 3.3 uF capacitor in series with the positive tweeter terminal and a 0.22 mH air core inductor across the positive and negative tweeter terminals.
I would need more information before commenting. Which Diamond? Photos of crossover board?
N.B. Repairing the original Mercury crossover is obviously the best course of action provided you can find the correct components to replace the damaged ones and can patch up the damaged PCBs. I was merely suggesting a a simple fix to get the speaker up and running in a way adequate to its application.
"Missing Mids" was the original topic of this thread.
Note that we moved on to a new scenario when Simon joined us at post #9.
