Final 03 Electrostatic Hybrid Speakers

I completely missed these 2 posts.

yes the intention was to set the output voltage of the amp to around 1V (not the source connected to the amp).
Connect the output with 1V on it to the input of the speaker.
FWIR you set the source to 0.7V and the amp was driven to full power, unleashing probably well over 30V to the speakers.

Anyway... it seems like one of the audio trafos may be gone but most likely not by this experiment as the owner already mentioned 1 trafo was dead and probably didn't mean the 15V trafo.

Is your amp still O.K. after this beating ?


Next test:

Measure the DC resistance of the primary and secondary windings of both trafos.
No need to desolder the trafos.

The primary winding should give readings in the order of a few Ohm max (but way less than 10 Ohm)
If the defective trafo reads 10 Ohm the primary winding went open circuit (you are thus measuring the 10 Ohm resistor in parallel to the trafo).
This is unlikely though, but possible.

Then measure the secondary windings.
Each trafo has 2 windings connected in series.
So between the middle pin and each of the outer pins there should be the same amount of resistance which most likely is high (> 100 Ohm ?)

If any of the readings of the defective board differ from the working board then unsolder the trafo from the board.

IF the secondary winding(s) are open circuit check with a magnifying glass if one of the very thin wires has not been broken off the PCB pins.
When this has happened sometimes it is possible to repair the damage IF you can get to the broken wire.
If the primary winding is open circuit check to see if there is not a fuse in series with the primary winding and the board pins.
In that case you see a copper wire on one pin and a silverish one on the other pin. Somewhere under the trafo there might be another copper wire attached to a silver one, usually well isolated.
If there is a fuse (don't know if there is one)your are lucky and it is probably open and just needs to be removed or bypassed.

Getting a new audio trafo, if needed, is a difficult task when the manufacturer doesn't have replacements any more.
Perhaps they can tell you what the ratio was and if there are alternatives.

When that fails you can search the web for trafos voor stats.
I believe there are plenty that may come close.

For my DIY stats I used 6 x 220V-24V trafos in a similar way as you connected the small trafos.
All 24V in parallel and all 230V windings in series.
with 1V input I got around 50V out.

You can't use ordinary mains trafos as they generally don't go further than a few kHz.
The trafos I used can from Panasonic videorecorders and had collected tens of these as they needed to be replaced.
All of these had defective fuses inside the 220V winding.

It so happened that I experimented which trafos I could use as trafos I had bought in the past all shorted their high voltage sides in the past.
Surprisingly these trafo's reached 19kHz flat and so I bypassed the fuses and used these.

If you need a new trafo you may probably end up with a (dedicated for audio/stats) toroid or 'normal' trafo.
You would need 2, one for each speaker as this trafo will differ from the good one.
They may very well not fit in the speaker any more.

BUT measurements first.

No signals, no mains connected just resistance measurements.

Well you can still make some measurements before you head of to Spain.


primary = thin teflon wires = measuring leads connected to both pins of R1
Should read well below 10 Ohm, most likely around 2 or 3 Ohm.
If it reads 10 Ohm the primary is open circuit...

secondary has 2 windings in series.

Measure resistance between blue wire (back stator) and white wire (front stator)
There should be a resistance there.
Possibly in the kOhms ?

If you measure open circuit measure between blue wire (back stator) and small yellow wire (the one connected with traces to HV ground)

and measure between white wire (front stator) and small yellow wire (the one connected with traces to HV ground)


That black 'blob' appears to be some kit and does not seem to be related to damage.

Thanks for that Frans:  I did indeed have time to get some measurements.

On the 200 setting both pins of R1 measured:
L/Amp          R/Amp
00.3             00.3

On the 2K setting other mesurements were:

Blue wire & white wire            =    L/Amp  .757Kohm    R/Amp  1.174Kohm

Blue wire & small yellow wire  =    L/Amp  .376Kohm    R/Amp  .588Kohm

White wire & small yellow wire =   L/Amp  .380Kohm    R/Amp  .585Kohm

The black blob is not what I was trying to point out Frans, but the small blue wire (that looks purple).
The wire insulation has burned (see pic below), so I guess it must have been that smoking?

It will now be after holidays until we can progress a little further as I go to Spain tomoro @ 3am.

Thanks

Chris

O.K. on the XA200.
You are correct it was wired O.K....
The amp has connections for bi-wiring, I assumed it was a stereo amp (having 4 speaker connections)

Measurements suggest 2 different trafo's are used and one may already have been replaced in the past ?
It would appear as though the windings are still O.K. in the sense they aren't open circuit.

Possibly the transformer could still have a winding that short-circuited internally.
Doesn't entirely solve the riddle why one would have an output voltage and the other one doesn't at all.

This shorting was the same problem I had with the transformers I used before I started using the Panasonic ones.
I had blown up quite a few expensive trafo's in those days.
When this happens, the output voltage is very low and distorted and the transformer behaves more like a short than a transformer.
Still ... smoke from very high currents with just 1V is nearly impossible at 440Hz as the high pass filter already provides a 10 Ohm 'resistance' limiting the current.

Still puzzled about the 1V on the output.
I figure the XA200 will have a gain of around 40x and in that case the SM6 would have an output voltage of just 0.025V (25mV).

One way to test is by using an extra resistor of just a few Ohm but with a high Wattage.
That must be put in series with the speaker input of the board.

Then a test voltage must be applied again and voltages must be measured over the output of the amp, the resistor and the trafo.

By the time you get back from your vacation and start working on it again we'll be in contact again.

0.5V or any other voltage will also be fine.
As long as the input and output voltage can be measured you can determine the winding ratio.

Let me know when you want to get started again.

Maybe I can help real-time using skype or something.

This may be the most logical place to start:

www.sowter.co.uk/acatalog/E_A_Sowter_Ltd_ELECTROSTATIC_LS_TRANSFORMERS_28.html#a232

given the fact that 1V in delivers 130V which means 2x65V CT it would seem logical that a 1:70 transformer would probably be the correct one.
As this is a 2 way system and the xo freq is above 150Hz a trafo like 8758 ESL Transformer. 1:70 CT 150 Hz may probably do.

To get L and R to sound the same you will need 2 trafos (one for each side)

There are probably a few more manufacturers as well that can be found here and there.
Sowther is UK based.

As mentioned I too use 'abnormal' mains transformers as audio trafos.
Some trafo's do work well and extend far enough in the audio range.
These may be no exception.

What I found in the past (when using just 2 trafo's) that some trafo's simply short out their primary windings.
When you connect a trafo 6V secondary winding to an amp that can deliver 20V you get about 800V on the primary windings.
That's 800V AC = 2.6kVpp !!!
Some transformers may have problems with those voltages.

Another thing is you must reach 1:130 ratio because of the woofer's efficiency that must be matched.
A 6V trafo is about 1:38 so you will need 4 trafo's per channel.
that's 4x GBP 23.60 = about GBP 95 (excl VAT) per speaker which isn't that far removed from the physically much smaller and specialised single trafo from Lowther.

I reckon you don't have to parallel the 6V input windings and suspect connecting a single 6V winding can even be beneficial.

The trafo's I use were designed to deliver 18V and as my amplifiers could deliver around 22V this worked fine and all trafo's remained O.K. simply because they never reached 800V but max 300V (900Vpp)
This meant 8 trafo's per channel.
Since they were free to me this wasn't a problem.

So you could try 4 of these 50W toroids per speaker but you may need the same type/brand because other transformers may not even reach 10kHz.
Possibly 4 x 20W or 4x30W toroids could do the trick as well but again... not all power transformers do audio that well.