Sheldon - I don't disagree with anything you said, but you are discussing thermal stress in power transformers. Thermal stress can be a factor in Acoustat's high-voltage step-up transformers, but I think the bigger factor here is high voltage breakdown. In the MK121 low frequency transformer (the most common one to fail) voltages of 10 kV or greater can be encountered due to both phases of the push-pull audio signal being in the same transformer. The original MK121 LF transformers had the highest failure rate. The later Medallion versions had improved high voltage insulation, though still not bulletproof. One of the advantages of the step-up transformers in the later Spectra series is that the 'push' and 'pull' signals are on separate transformers. This cuts the potential high voltage stress in half.
That's a very good point. I was talking about tube amp output transformers, but voltage breakdown isn't a big deal there either. doubling up the step-up transformers is a good idea and one that Quad did as well starting with the ESL-63's. The original ESL's have three separated windings on a core which is another way to try to solve the HV breakdown problem and still keep tight small windings.
Sheldon
Sheldon
Hi Audio Fans,
i‘ve got the opportunity to buy a 2+2 in good shape. Thanks to AAM and this thread i was able to bring my 1+1 to another level (cleaning, tensioning membran, new parts in the HV supply and replacement of the elco with Mundorf PP). They‘ve got Red medaillion interfaces.
The 2+2 I could buy, are older modells non Medaillion, with the bigger electronics box. They‘ve no serial number on them. It was a demo modell for the german market.
I can‘t open the interfaces, they are fare away and seller won‘t open them.
I have to drive 450 km to buy them.
So it could be that they have the old coating.
I‘m quite unshure if i jump on this train and buy them.
I could do the C-mod to the 2+2, but what about the coating and the older Interface-box?
Does the new coating formular a big difference to the sound?
Or could it be, that they have the new coating?
About the interface box;i could use the boxes from the 1+1 for the 2+2, right?
Thanks for your input
BR
Olaf
i‘ve got the opportunity to buy a 2+2 in good shape. Thanks to AAM and this thread i was able to bring my 1+1 to another level (cleaning, tensioning membran, new parts in the HV supply and replacement of the elco with Mundorf PP). They‘ve got Red medaillion interfaces.
The 2+2 I could buy, are older modells non Medaillion, with the bigger electronics box. They‘ve no serial number on them. It was a demo modell for the german market.
I can‘t open the interfaces, they are fare away and seller won‘t open them.
I have to drive 450 km to buy them.
So it could be that they have the old coating.
I‘m quite unshure if i jump on this train and buy them.
I could do the C-mod to the 2+2, but what about the coating and the older Interface-box?
Does the new coating formular a big difference to the sound?
Or could it be, that they have the new coating?
About the interface box;i could use the boxes from the 1+1 for the 2+2, right?
Thanks for your input
BR
Olaf
These speakers will absolutely not have the improved coating and may even have the older 3-wire panels. The improved coating's advantage was improved dynamic range - meaning the speaker can play louder without "crackling" on bass notes. I've never had the opportunity to compare 3-wire to 5-wire panels. They supposedly do sound better, but how I don't know, and I suspect the difference is subtle.
Electrically speaking, the interfaces from your 1+1 can drive the 2+2 by simply changing the bass tap from red to yellow. However, because the box also provides support for the panels, some (or a lot of) modification will be necessary to make it work mechanically.
If these speakers were indeed "demo models", that means they are very early models. Proceed with caution and audition thoroughly.
Electrically speaking, the interfaces from your 1+1 can drive the 2+2 by simply changing the bass tap from red to yellow. However, because the box also provides support for the panels, some (or a lot of) modification will be necessary to make it work mechanically.
If these speakers were indeed "demo models", that means they are very early models. Proceed with caution and audition thoroughly.
Sorry for those of you that may have seen my posts on other sites about this.
I came across a pair of Acoustat The Monitor speakers that were at an estate sale after being called by a friend that was there. I had no intentions of keeping them only hoped to find them a good home with someone yet unknown to me.
They sounded great so I made them a minimally researched offer of $800 thinking at the time they were Monitor 4 speakers.
The Monitor, I have sense found out is the second model made after the original X.
They didn't have the servo amps any more but a pair of MK121-2A interfaces.
I started disconnecting the interface from one speaker while my nephew worked on the other. As I took off the wire nuts connecting very dirty wires I know I saw one of the wire groupings was 3 wires in a wire nut. Unfortunately the wires dropped away and I then had no idea which 3 were together.
This makes no sense as I have owned enough speakers with interfaces that there are 3 wires and 2 are for the signal to the panels and 1 is the bias feed. My terms may be different from other descriptions so, sorry.
When I got the dust light blown off the grill cloth and panels from the back side along with what was in the interface I moved them to another room connected to my work shop. I cleaned the wires and cut and stripped the ends coming from the collection blocks at the panels and the interface. Everything was back together and ready for a test run again.
I only had a old Marantz 2245 in my shop for the test so I approached it with caution. They did make music but it was garbled at best. Now I am puzzled about why. I will probably take an Argon 2004 amp from our HT to the shop and see if that makes any difference.
I'm looking for the schematic for the MK121-2A interface to see if anything has been played with.
Any suggestions you might have as to my wiring issue or good sound one day and not the next please let me know.
If anyone know of someone that might want these I only hope to get my purchase price back. They are currently located just north of Tampa Fl.
Thanks in advance for any help offered.
I came across a pair of Acoustat The Monitor speakers that were at an estate sale after being called by a friend that was there. I had no intentions of keeping them only hoped to find them a good home with someone yet unknown to me.
They sounded great so I made them a minimally researched offer of $800 thinking at the time they were Monitor 4 speakers.
The Monitor, I have sense found out is the second model made after the original X.
They didn't have the servo amps any more but a pair of MK121-2A interfaces.
I started disconnecting the interface from one speaker while my nephew worked on the other. As I took off the wire nuts connecting very dirty wires I know I saw one of the wire groupings was 3 wires in a wire nut. Unfortunately the wires dropped away and I then had no idea which 3 were together.
This makes no sense as I have owned enough speakers with interfaces that there are 3 wires and 2 are for the signal to the panels and 1 is the bias feed. My terms may be different from other descriptions so, sorry.
When I got the dust light blown off the grill cloth and panels from the back side along with what was in the interface I moved them to another room connected to my work shop. I cleaned the wires and cut and stripped the ends coming from the collection blocks at the panels and the interface. Everything was back together and ready for a test run again.
I only had a old Marantz 2245 in my shop for the test so I approached it with caution. They did make music but it was garbled at best. Now I am puzzled about why. I will probably take an Argon 2004 amp from our HT to the shop and see if that makes any difference.
I'm looking for the schematic for the MK121-2A interface to see if anything has been played with.
Any suggestions you might have as to my wiring issue or good sound one day and not the next please let me know.
If anyone know of someone that might want these I only hope to get my purchase price back. They are currently located just north of Tampa Fl.
Thanks in advance for any help offered.
Attachments
For a speaker of this vintage, there will be 3 wires for each panel. One for the front stator (white), one for the rear stator (blue), and one for the diaphragm bias (red). If the color coding has faded over the years or is otherwise not apparent, you'll need to trace them individually. Once identified, all four blue wires should connect to the blue terminal on the interface, all four white wires should be connected to the white terminal, and all four red wires to the red terminal.
You may have low bias voltage - a common problem for speakers of this vintage. Do you have a high-voltage probe you can check the voltage at the red terminal (with panels disconnected)? It may be necessary to replace the five diodes and five capacitors in each interface. Let me know what you find and I can provide further guidance. I can send an MK-121 schematic later (at work now).
You may have low bias voltage - a common problem for speakers of this vintage. Do you have a high-voltage probe you can check the voltage at the red terminal (with panels disconnected)? It may be necessary to replace the five diodes and five capacitors in each interface. Let me know what you find and I can provide further guidance. I can send an MK-121 schematic later (at work now).
Looks like all the wires go into a clear junction box on the back. From there, it looks like a black wire with all (3) different color of wires, comes back out and goes down through a hole to the bottom? Looks like it terminates into a 3-prong banana plug? Could you please take a picture of the inside of the interface? I see single wires coming out from it.
You are correct mrAG that the wires are encased in the black wire casing. The 3-prong plug was abandoned and 3 wire nuts were substituted.
On a brighter note. I took a descent amp to the shop and used the pre-out of the Marantz and was able to play fuzzy FM signal through the speakers after making an FM antenna out of a piece of zip cord. We live in the country and I have never found an antenna I could get a decent FM signal. That said the sounds that came through the Monitors sounded healthy, or as healthy as a bad FM station could sound.
In my shop I use an HP laptop with Qobuz and it connects to the Marantz receiver and a pair of small speakers. This works fine.
When I used the pre-out to the Aragon amp the Marantz would not play the laptop-Qobuz signal out to the amp. It made no sense at all. The FM signal went to the amp but not the laptop signal. Something internal in the 50 year old Marantz topology. Now I'm trying to figure out how to play a decent signal to the amps so I can hear how good the speakers sound. Difficult to sell a pair of speakers without a reasonable demo.
I'm still not sorry I'm trying to get them to a good home but a glass of wine will help think through it.
I will post pictures of the interfaces to see whether anyone sees something that doesn't look right.
I guess I will do a search for Pre-Amp rentals-R-us while enjoying my wine.
I'll update with any news but it sounds like they will be up for sale sooner than I had thought.
Thanks, Brad
I did find a MK121 schematic. Is the 121-2A different?
It's possible but I don't think I could leave my ML CLX with ARC 40th Anniversary pre and 610T amps.
I would never say never without hearing them though.
This really was about finding a home for them. Not letting them set in a warehouse, which is what they said was the next move. It may take a while but I will find one for them.
I would never say never without hearing them though.
This really was about finding a home for them. Not letting them set in a warehouse, which is what they said was the next move. It may take a while but I will find one for them.
I think it's great what you're doing!
I found my 2+2's in a barn. They had been there for over 25 years. Next stop was the dump. Took awhile, (my journey is on here somewhere), but they turned out REALLY, REALLY NICE!!!
Based on the appearance of the hi and low frequency transformers (shiny black wrapper), I believe you already have the Medallion Transformers. And the resistor near the group of capacitors would suggest these interfaces have the C-Mod. All good news, which should increase the value of these speakers.