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What is a "switched mains plug"? The interface provided is a 3-prong 120V input, so I plugged them into a standard powerstrip using MIT Terminator2 power cables. Is there a special power supply that is required to these?

Do you mean that you should never try to drive the panels from the amp without the speakers plugged in? This makes sense and I doubt I made that mistake in setting these up. By having a switched plug, are you also suggesting that while the amp is driving them, that the speakers could be accidentally switched off--damaging the transformer?
 
I mean a switched outlet - like a wall switch that switches a wall outlet.

If you are plugged into a Surge Protector and all else connected to this surge protector is working (getting power) than you should have power going to interface... but just check...I hate that these ML interfaces do not have a power LED showing power to the interfaces... Quad ESLs go one further and provide a Neon Bias lamp showing the pulses of Bias Voltage to the panels - really helpful in determining if panels have an issue... simple Neon lamp, and parallel capacitor in series with bias feed wire (see attached)...rapid neon lamp flashing indicates panel bias voltage leak somewhere, while a simple flash every 8 - 10 seconds indicates properly working panel with no leaks. I put these Bias Indicators in on some of my interfaces just because its a great idea...

Do you mean that you should never try to drive the panels from the amp without the speakers plugged in?
Yes, never do this. It doesn't take much time to bias up the panels...but the panels need to have that bias voltage before you have your amp driving the stators.
 

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Jeff, Thanks for your reply--seems like you are the only one who read my post and had some useful insight. I did vacuum the panels, but the problem increased the longer I had them plugged in. Now, I get about 10% out of 1 panel and nothing out of the other. Switching panels with the electronics, the problem follows the electronics.

I believe I have a bad T1 low-profile transformer and a potential grounding issue on one board and the other is on it's way out. I'll see if my local tech has a high-voltage probe and can work on these, which should be a very cost effective fix as compared with replacing the panels!

Why retire to Indianapolis??? Likely a very long answer, but either way, you are free to DM me once you get here and I will either still have a project or a set of CLS's that I can demo for you.

Thanks,
Doug
Doug,
Well, I am in California, but my kids have left long ago. It is just me and my dog so there is really nothing keeping me here. My daughter lives in in the Indianapolis suburbs. I have visited her and seems like a nice place to retire. I was raisied in the Mid-West so I am familiar. :)

As far as getting someone to work on the electronics I think that is a good idea. I did replace a capacitor and I think an inductor on mine. I did replace the panels about 10 years ago. I believe the new panels are about $3500.00 now. ouch!
Good Luck!
Stay in touch

Jeff
 

Leporello,​


Roger Sanders has an old writeup on driving ESL stators right off the plates of a tube amp (eliminating the step up transformer) to satisfying sound levels... the output tube plates were "only" around 500v, but worked... I have some old Acoustat and Quad panels laying around and my have a try one day with my Quicksilver amps...

I will have to look for that writeup...

EDIT - Found it
Thanks for sending that. I am almost sure I read that article, and am positive I read Hermayer's original (which used a very scary direct coupled transmitting tube based amplifier and very exposed stator elements). Probably the two things that turned me off about Sanders' direct coupled scheme from a stock amplifier is the lower than optimal bias voltage, and the fact that by loading the secondary of the transformer with a resistor you're burning up most of the power the amp is capable of. But if you have the amps and have the panels--I too have some Acoustats, though unsure what kind of shape they're in now, as well as the Latino monoblocks--it's worth doing the experiment. Maybe I will some day.

Plitron used to make toroidal transformers for tube audio applications and advertised they would manufacture custom transformers. I once tried contacting them about my plates to ESL transformer idea, but never heard back. They have since merged with someone, and gotten out of the audio transformer business. I don't yet know enough about transformer design and construction to attempt it myself.

AFAIK Sanders never got into tubes for his commercial products.
 
Leporello,

Yes, you would still need to "load" the secondary of the tube amp transformer, but here you just put a woofer, while HF on to the panels driven by plates...I would imagine quite a bit of EQ'ing would be neccesary...but for a simple test?

I talked to Roger a few times - he s a nice guy and is really approachable...he doesn't do tubes as he says he "needs" the power...he credo is if you have more power you will ever need, your amp will never clip. OK. I can agree...to a point...his amps are at least 300w@8 ohm, [email protected], would anyone ever need that much power??

On DIYAudio, there is a group of us that used basic Antec Toridal transformers for 75:1 Step up (model AS-1206)...they were pretty cheap too (used to be $12 ea 10 years ago, now $26 ea)... you need four (two per channel) wired in series-parallel to get the correct step up. Schematic below...

I used these homemade interfaces to experiment - drive a set of three Acoustat panels and an original CLS panel...tried full range first, but the low frequency - was saturating the transformer (hence why newer CLS have separate transformers for LF and HF), but as long as I just ran 150hz and higher thru this interface, worked very very good, and ear piercing loud! The Bias voltage supplied by 18V laptop power supply, and pot was able to dial in the final bias voltage...some pics

(Apologies - I don't mean to hijack this thread)

1675730676901.png

1675731061677.png



1675731097826.png



1675731555477.png
 
For anyone following my original post and who may appreciate the steps in trouble shooting your CLS speakers without knowing too much about ELS speakers, here's where I've landed.

I found a schematic online and there's a simple writing on the top that says "Approx 280 volts at X former pins 5 and 8". Probing pin 8 on the transformer required me to remove (lift up) the circuit board, but when plugged in, I only read 107VAC between pins 5 and 8 on this transformer. There is the start of my problems. I'm going to replace this transformer and keep going.

I noticed the power resistors R1 and R2, 27K ohm/15K ohm look burned up on the board. I want to see what I should measure across those. They definitely got hot, but not sure they are bad yet. That's next.

I'm also looking to measure V+. Any ideas of what V+ should measure and the best place to measure it?

Finally, I want to probe the output to the panel with a high voltage probe. I'm not sure what exact measurement, but I understand it should be about 3800V. If all works in the electronics, these all should check out.

Doug
 
For anyone following my original post and who may appreciate the steps in trouble shooting your CLS speakers without knowing too much about ELS speakers, here's where I've landed.

I found a schematic online and there's a simple writing on the top that says "Approx 280 volts at X former pins 5 and 8". Probing pin 8 on the transformer required me to remove (lift up) the circuit board, but when plugged in, I only read 107VAC between pins 5 and 8 on this transformer. There is the start of my problems. I'm going to replace this transformer and keep going.

I noticed the power resistors R1 and R2, 27K ohm/15K ohm look burned up on the board. I want to see what I should measure across those. They definitely got hot, but not sure they are bad yet. That's next.

I'm also looking to measure V+. Any ideas of what V+ should measure and the best place to measure it?

Finally, I want to probe the output to the panel with a high voltage probe. I'm not sure what exact measurement, but I understand it should be about 3800V. If all works in the electronics, these all should check out.

Doug
The approximately 280 volts is at the secondary of the power transformer where it feeds the voltage multiplier stack, correct?

First question: do both speakers exhibit the same problem? A bit of a coincidence, no?

Second question: Does the CLS 1 have circuitry that senses the presence of an input signal and turns on the bias? There might be an LED inside that lights when the bias is energized. Does it light?

The bias voltage isn't zero when not energized, it's at a "standby" value that's supposed to minimize dust collection when not listening. That 107 volts you measured might be the standby value.

The schematic I've seen, which doesn't seem to correspond exactly to my CLS II, throttles back the bias voltage with a voltage divider, with one leg shorted with a triac. If memory serves me, it is such that the bias is in standby when the triac is turned *on*. In either case, you probably need to be feeding the speaker a signal to get valid measurements. Be careful, because you will then have a second source of high voltage in the box which, unlike the bias supply with very low current capacity, could be lethal.

As far as what the bias voltage should measure, the theoretical value is 280 volts times the number of sections in the multiplier stack times 1.4 (square root of 2, the "crest factor"). But due to the aforementioned low current capacity/high impedance of the bias supply, even with a high impedance high voltage probe, you may not get that.

When I used to work on CRT monitors, I was pretty confident that the voltage I measured with a Fluke high voltage probe and a Fluke multimeter it was designed to work with was correct. But there, the current capacity was enough to knock me on my ass, even kill me.

A standard safety precaution is to work with one hand, with the other kept out of the way or in your pocket. It would behoove you to observe that. That means when you do something like measure the voltage between pins 2 and 5 of the bias step-up, you really should use something like a "grabber" clip or alligator clip. While the bias voltage itself is about the same as the annoying shock you get from walking on a carpet in winter and touching a doorknob, there is plenty inside that box to mess you up, including the 280 volts from that transformer and, with music playing to actually activate the bias supply, the music signal itself.
 
While the bias voltage itself is about the same as the annoying shock you get from walking on a carpet in winter and touching a doorknob

This is true, but only on the downstream (ESL) side of the high mega-ohm current limiting bias resistors, correct?

The amplifier to stator (step up transformer secondary) voltages are definitely lethal, be very careful if you are poking around the interface while amp is driving the interface
 
The approximately 280 volts is at the secondary of the power transformer where it feeds the voltage multiplier stack, correct?

First question: do both speakers exhibit the same problem? A bit of a coincidence, no?

Second question: Does the CLS 1 have circuitry that senses the presence of an input signal and turns on the bias? There might be an LED inside that lights when the bias is energized. Does it light?

The bias voltage isn't zero when not energized, it's at a "standby" value that's supposed to minimize dust collection when not listening. That 107 volts you measured might be the standby value.

The schematic I've seen, which doesn't seem to correspond exactly to my CLS II, throttles back the bias voltage with a voltage divider, with one leg shorted with a triac. If memory serves me, it is such that the bias is in standby when the triac is turned *on*. In either case, you probably need to be feeding the speaker a signal to get valid measurements. Be careful, because you will then have a second source of high voltage in the box which, unlike the bias supply with very low current capacity, could be lethal.

As far as what the bias voltage should measure, the theoretical value is 280 volts times the number of sections in the multiplier stack times 1.4 (square root of 2, the "crest factor"). But due to the aforementioned low current capacity/high impedance of the bias supply, even with a high impedance high voltage probe, you may not get that.

When I used to work on CRT monitors, I was pretty confident that the voltage I measured with a Fluke high voltage probe and a Fluke multimeter it was designed to work with was correct. But there, the current capacity was enough to knock me on my ass, even kill me.

A standard safety precaution is to work with one hand, with the other kept out of the way or in your pocket. It would behoove you to observe that. That means when you do something like measure the voltage between pins 2 and 5 of the bias step-up, you really should use something like a "grabber" clip or alligator clip. While the bias voltage itself is about the same as the annoying shock you get from walking on a carpet in winter and touching a doorknob, there is plenty inside that box to mess you up, including the 280 volts from that transformer and, with music playing to actually activate the bias supply, the music signal itself.
Would wearing rubber gloves help any?

When I was about 8 years old,I thought it would be fun to open up my Polaroid camera. I took the batteries out and opened it by removing all of the screws. I ended up touching something and got shocked really bad! I bet it was a capacitor for the flash? The batteries had been out for about 10 minutes. I learned then that electronics can be dangerous. That hurt bad.

Nowadays I have a defibrillator. I'd hate to find out what might happen to me now if I did that.
 
This is true, but only on the downstream (ESL) side of the high mega-ohm current limiting bias resistors, correct?
I would not recommend taking a risk by assuming that is not true. Always be careful when poking around anywhere inside the box.
 
I found a schematic online and there's a simple writing on the top that says "Approx 280 volts at X former pins 5 and 8". Probing pin 8 on the transformer required me to remove (lift up) the circuit board, but when plugged in, I only read 107VAC between pins 5 and 8 on this transformer. There is the start of my problems. I'm going to replace this transformer and keep going.
Don't you have the other side's transformer to try? I had one of these T1 go out on my old ML SL3, and for months I ran both speakers off the same transformer until I could install a new T1 from ML (~$16 back in 2012).
 
Don't you have the other side's transformer to try? I had one of these T1 go out on my old ML SL3, and for months I ran both speakers off the same transformer until I could install a new T1 from ML (~$16 back in 2012).
You may be talking about something different. Some ML speakers, especially those intended primarily for home theater, use a low voltage "wall wart" type transformer, and the HV bias is generated by electronics inside. The CLS is old school, with a line cord going directly into the box. It would be pretty hazardous to feed the speaker from the 280 volt secondary of the other one. That's not what you did, is it? I'm pretty confident of my electrician skills, but I would not go there.

In any event, we haven't heard from Indiana in a while. I hope what I posted above is useful to him, because I've had experience trying to figure out whether each panel of a CLS is getting proper full bias, and have been down the road he is going. I'm fairly certain the 108V he is measuring would turn into the 280 with an audio signal input, so buying a new transformer would be a waste. I posed the other side question but didn't get an answer.
 
I think Tosh meant to jumper the Secondary of the Bias transformer to the other non working speaker bias transformer...I agree, not very safe, and would require removing the questionable bias transformer all together to try....

But I am still trying to understand if both speakers have same issue? - Both speaker secondaries of the Bias transformer are reading low? Odd...

I remember that schematic (I had original CLS many years ago), and I do think it had a Input Sense circuit that turned on the full bias voltage...has the OP tried this?
 
I think Tosh meant to jumper the Secondary of the Bias transformer to the other non working speaker bias transformer...I agree, not very safe, and would require removing the questionable bias transformer all together to try....

But I am still trying to understand if both speakers have same issue? - Both speaker secondaries of the Bias transformer are reading low? Odd...

I remember that schematic (I had original CLS many years ago), and I do think it had a Input Sense circuit that turned on the full bias voltage...has the OP tried this?
My thoughts exactly. Haven't received an answer to either question. Hopefully OP has resolved his issues.
 
Found the CLS Bias / Sense circuit...yup, that whole Op Amp and Triac based circuit is the signal sense...

Don't really know why ML bothered, as the total draw from wall is tiny... wattage - wise...
 

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Found the CLS Bias / Sense circuit...yup, that whole Op Amp and Triac based circuit is the signal sense...

Don't really know why ML bothered, as the total draw from wall is tiny... wattage - wise...
Maybe to attract less dust while they aren't being used?
 
So, the schematic doesn't show pin 8, but it's presumably the top of the secondary, and it doesn't specify whether the 280 volts is in the presence of a music signal or not, implying it may not make much of a difference. There will definitely be a difference at the junction of R1 and R3, depending on whether the triac is turned on or not. There will be a difference in loading on the transformer, but that's not knowable without more information. So my question to dougstratch, if he were still around, is after moving the circuit board, if he's sure he was really on pin 8. It's possible--shorted windings or something--a transformer could measure low, but my experience has always been either they work or they're open circuit. 105volts sounds a lot like what you should have at the R1-R3 junction in the absence of music signal.

Less dust attraction is indeed ML's official explanation for throttling down the bias voltage. I've wanted to implement a 12 volt trigger turn-on instead, but haven't acquired the proper tool (round tuit). It's slightly annoying to have the first half second or so of music ramping up if they haven't been played in a while. With the hybrids that I used (Ascents) the turn-on seemed instantaneous, but that was probably due to the smaller panel area and capacitance. Most likely, removing the triac and replacing it with a 12 volt normally closed relay would do it. But I leave the stereo on a lot when not using it, so theoretically it would collect more dust. On the other hand, when I vacuum the panels off periodically, after leaving them unplugged overnight, there really isn't a lot of dust there.
 

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