Do you(or a tech friend) have access to a signal generator you can hook up to the amplifier driving the speakers and a DMM(digital multimeter)? If so, I would recommend measuring the output of your HF & LF transformers and the mixer at 100Hz. Based on what you measure, the fault should be narrowed down to the mixer parts or a particular transformer.
With the interface unplugged from the wall and the wiring to the panels disconnected, apply a 100Hz signal @ 1Vrms to the audio input binding posts using signal generator and power amplifier. If possible measure the voltages on the “good” interface before the “bad” so you know what to expect. The voltage values shown in the attachment are ballpark numbers, but they won’t be far off.
Let us know what you find out.
With the interface unplugged from the wall and the wiring to the panels disconnected, apply a 100Hz signal @ 1Vrms to the audio input binding posts using signal generator and power amplifier. If possible measure the voltages on the “good” interface before the “bad” so you know what to expect. The voltage values shown in the attachment are ballpark numbers, but they won’t be far off.
Let us know what you find out.
Attachments
My 2200's crackled on one panel; turned off the transformer 24 hours , tapped on the corner it crackled at, blew it with my leave blower downward, plugged in the transformer and the dust particle had fallen to the bottom outside of the charged field. No Crackling. Now then, my 1100s could not be fixed as the gray magnetic coating painted on one side was delaminating; I replaced the panels with some from a Spectra 11, fixed.
High voltage connection to diaphram
Hello,
I moved about a yr ago and finally brought out my Acoustat 2+2's which were 2" too tall for my basement. So new frames made from steel. I removed and cleaned the panels in shower and dried them off and found that 3 of my panels had a ~.75" tear in the diaphragm right through the tab of conductive paint that connects to the red wire. 2 of the 3 have only a very thin crescent of conductive coated mylar going to the red wire.
I bought some copper adhesive tape and went over the hole with approx. 1 inch long piece ( more to ensure bias voltage to panel, than support against further tearing). The copper tape is no closer than about 3 mm from any of the stator wires.
Now I am afraid to plug them in for fear of corona discharge from the copper tape.
Should I remove the tape, leave it alone, or maybe cover it with silicone caulk.
The copper tape seems quite well "stuck " onto the mylar and its coating.
Thanks,
Paul
Hello,
I moved about a yr ago and finally brought out my Acoustat 2+2's which were 2" too tall for my basement. So new frames made from steel. I removed and cleaned the panels in shower and dried them off and found that 3 of my panels had a ~.75" tear in the diaphragm right through the tab of conductive paint that connects to the red wire. 2 of the 3 have only a very thin crescent of conductive coated mylar going to the red wire.
I bought some copper adhesive tape and went over the hole with approx. 1 inch long piece ( more to ensure bias voltage to panel, than support against further tearing). The copper tape is no closer than about 3 mm from any of the stator wires.
Now I am afraid to plug them in for fear of corona discharge from the copper tape.
Should I remove the tape, leave it alone, or maybe cover it with silicone caulk.
The copper tape seems quite well "stuck " onto the mylar and its coating.
Thanks,
Paul
Is the copper tape you are using the type with conductive adhesive? If not, you will most certainly generate corona/ozone between the edges of the tape and the conductive coating you have it stuck to. You will likely hear it (and see it if room is dark) as soon as you plug in the power cord. Over time, operating in this many will eat away at the coating around the tape and eventually cease to charge up the panels.
If it does have conductive coating, the other concern would be ozone generation from exceeding the voltage gradient for ionization between the insulated stator wires and the copper tape. You mentioned a 3mm separation distance which should be more than adequate for the voltages involved. The only way to tell for sure is to play some bass heavy music at high volume in a darkened room and look for purple corona glow around the copper tape pulsing to the music. If it does, I am skeptical as to whether silicone would help…maybe some corona dope.
If it does have conductive coating, the other concern would be ozone generation from exceeding the voltage gradient for ionization between the insulated stator wires and the copper tape. You mentioned a 3mm separation distance which should be more than adequate for the voltages involved. The only way to tell for sure is to play some bass heavy music at high volume in a darkened room and look for purple corona glow around the copper tape pulsing to the music. If it does, I am skeptical as to whether silicone would help…maybe some corona dope.
bias transformer mk-141
hello all
(i tried searching this thread but lost patience)
I'm in the process of restoring my old beloved model 1 MK-141C speakers
I have the schematics and part list. But one of the bias transformers is damaged.
Anyone know the specs (A) ??
... (I know they're 750 VAC)
Thanks... can't wait... haven't heard them in 25+ years
hello all
(i tried searching this thread but lost patience)
I'm in the process of restoring my old beloved model 1 MK-141C speakers
I have the schematics and part list. But one of the bias transformers is damaged.
Anyone know the specs (A) ??
... (I know they're 750 VAC)
Thanks... can't wait... haven't heard them in 25+ years
hello all
(i tried searching this thread but lost patience)
I'm in the process of restoring my old beloved model 1 MK-141C speakers
I have the schematics and part list. But one of the bias transformers is damaged.
Anyone know the specs (A) ??
... (I know they're 750 VAC)
Thanks... can't wait... haven't heard them in 25+ years
I don't know the ampere output on the bias transformer, and in any case, it's highly unlikely that you would find an off-the-shelf replacement. You really need to find a genuine Acoustat part. Any bias transformer from MK-121, MK-131 or MK-141 will work, unless it's from a very early 3-diode multiplier model (most use a 5-diode multiplier). The most recent part numbers assigned to these transformers are TTA-100 (100 volt mains), TTA-117 (110-120 volt mains) and TTA-240 (220-240 volt mains).
I'm in process of bringing a pair of Acoustat Model 3's back on line after 25+ years in storage. In my instance they worked for about a week and then one speaker went quiet. Likewise believe that it's the HV multiplier, but in my case the xformer is good. So I did search the entire thread.
In post 3631175 https://www.diyaudio.com/forums/planars-and-exotics/183168-acoustat-answer-75.html#post3631175 john65b generates an estimate that the xformer is "near 30ma - 40ma at best".
In post 3631175 https://www.diyaudio.com/forums/planars-and-exotics/183168-acoustat-answer-75.html#post3631175 john65b generates an estimate that the xformer is "near 30ma - 40ma at best".
Thanks!
I Think I'll have try these.... I have no idea wher to get original ones
274X Hammond Manufacturing | Mouser Sverige
I Think I'll have try these.... I have no idea wher to get original ones
274X Hammond Manufacturing | Mouser Sverige
Hey guys. I’m hoping for a bit of guidance on my Spectra 11s.
I bought them nearly 20 years ago, and I believe that they had some cap mods done prior to my ownership. I used them for many years as mains in my 2ch setup, then as I grew into home theater, they took on the role of mains in my HT fit quite some time. Then I retired them because I wanted a matched center and mains.
Anyway, I’ve recently pulled the Spectras out of storage to set up a new small 2ch room. That said, the high frequencies seem to be either slightly diminished or my hearing has faded a bit. Is there any way to compensate for this internally?
Ive downloaded some of the docs on adjusting the bias, i just haven’t read them yet.
Any help would be appreciated!
I bought them nearly 20 years ago, and I believe that they had some cap mods done prior to my ownership. I used them for many years as mains in my 2ch setup, then as I grew into home theater, they took on the role of mains in my HT fit quite some time. Then I retired them because I wanted a matched center and mains.
Anyway, I’ve recently pulled the Spectras out of storage to set up a new small 2ch room. That said, the high frequencies seem to be either slightly diminished or my hearing has faded a bit. Is there any way to compensate for this internally?
Ive downloaded some of the docs on adjusting the bias, i just haven’t read them yet.
Any help would be appreciated!
Yes, the is a way to increase the hi frequency output. The large 1-ohm resistor in series with the audio transformer may be decreased in value, all the way down to zero ohms. Since the Spectra 11 was designed as a "budget" ESL, the thinking was that it would typically be paired with less robust amplifiers. The 1-ohm was included to "ease" the high frequency impedance, which can otherwise dip quite low. Some amps don't like that (including, possibly, the amp you intend on using).
In the upgraded Spectra 1100, the Hi Frequency Balance switch was used to vary the value of that resistor. The Low position set the value at 1-ohm, the medium setting at 0.4 ohms, and the high setting at zero ohms.
And yes, checking the bias voltage is recommended. If low, it will reduce the volume of the ESL portion as compared to the woofer. Also make sure you have the speakers oriented properly, left/right-wise. For the single-panel Spectra 11 (and 1100), the high frequencies should be coming from the outer edge of each speaker.
WOW! great, thanks for the info. Im super excited that it may be as easy as a resistor change.
Im using an older Pioneer Elite receiver for the time being, and Im hoping it wont have issues.
I just verified the panel orientation is correct. So no worries there.
I'll work on the bias voltage testing which will give me a good chance to locate the resistor in question to confirm its value.
Thanks a million.
I might be looking at the wrong component. Here is a pic, can you help me determine which resistor is the 1Ohm?
An externally hosted image should be here but it was not working when we last tested it.
If anyone is looking for a full set of Medallion Transformers, I came across this smokin' deal on eBay. If all you get from this set is the transformers themselves, it's still a great deal (I am not connected with the seller).
Pair Acoustat MK-121-2A Interface Units, Medallion Transformers, Original Boxes. | eBay
Pair Acoustat MK-121-2A Interface Units, Medallion Transformers, Original Boxes. | eBay