Hey all,
Just picked up a pair of Model 3's locally. They have the 121-MK-2A interfaces and do not believe they have the Medallion trannies (brown paper wrapper on trannies).
Previous owner said he couldn't test the speakers, as he did not have a suitable amp to drive them. I took the gamble and purchased them. Took them home and noticed one of the speaker inputs was open. Replaced the blown 3A fuse and got around 1 ohm, just like the other. Hooked up my Icepower 1000ASP monoblocks and took a listen.
Sounded a bit different from my DIY CLS, but had some pretty deep base that I was not expecting from any ESL. The KSA-50 Clone sounded equally as good, if not better (clearer highs, etc). Pretty impressed.
I then tried a friends Acoustat TNT-200 I happened to have (he has Acoustats, loves them and told me about the local sale). He dropped off his TNT-200 last week as he could not get one channel to work (replaced a fuse and she fired right up).
Anyway, as soon as I turned on the TNT-200, I got a power "pulsing" and one of the audio fuses blew on the same speaker that had the bad fuse initially. I checked all the schematics for 121-MK-2A and noticed 5A instead of 3A audio line fuse. I changed both to 5A and tried again, but on the TNT-200, it still get the "pulses" for a few seconds with no sound from the speakers, and I shut off the amp. The amp continues to work perfectly fine with other cone speakers, and my CLS (although crossed over at 125hz and higher)
The Icepower play fine as does the Krell, but at certain high-ish volume, I get speaker cut out on both, where I just lower volume and all is OK (amp protection at work?) I tried the Aleph 5 I have and it also pulsed like the TNT-200....
I, later, did the C-Mod as shown on the Acoustat thread. I thought maybe the 10 ohm resistor across the speakers inputs / step-up trannys would give something the amp could work against, but still get the pulsing.
Don't know what the issue is...Am I saturating the LF cores? Whyis it just these certain amps? And the TNT was specifically designed to run these amps...
Or could it be that the panels are not yet fully charged when I connect the problem amps? I did give it a few minutes to charge the panels before turning on the TNT amp...do these require a longer time to charge?
Just picked up a pair of Model 3's locally. They have the 121-MK-2A interfaces and do not believe they have the Medallion trannies (brown paper wrapper on trannies).
Previous owner said he couldn't test the speakers, as he did not have a suitable amp to drive them. I took the gamble and purchased them. Took them home and noticed one of the speaker inputs was open. Replaced the blown 3A fuse and got around 1 ohm, just like the other. Hooked up my Icepower 1000ASP monoblocks and took a listen.
Sounded a bit different from my DIY CLS, but had some pretty deep base that I was not expecting from any ESL. The KSA-50 Clone sounded equally as good, if not better (clearer highs, etc). Pretty impressed.
I then tried a friends Acoustat TNT-200 I happened to have (he has Acoustats, loves them and told me about the local sale). He dropped off his TNT-200 last week as he could not get one channel to work (replaced a fuse and she fired right up).
Anyway, as soon as I turned on the TNT-200, I got a power "pulsing" and one of the audio fuses blew on the same speaker that had the bad fuse initially. I checked all the schematics for 121-MK-2A and noticed 5A instead of 3A audio line fuse. I changed both to 5A and tried again, but on the TNT-200, it still get the "pulses" for a few seconds with no sound from the speakers, and I shut off the amp. The amp continues to work perfectly fine with other cone speakers, and my CLS (although crossed over at 125hz and higher)
The Icepower play fine as does the Krell, but at certain high-ish volume, I get speaker cut out on both, where I just lower volume and all is OK (amp protection at work?) I tried the Aleph 5 I have and it also pulsed like the TNT-200....
I, later, did the C-Mod as shown on the Acoustat thread. I thought maybe the 10 ohm resistor across the speakers inputs / step-up trannys would give something the amp could work against, but still get the pulsing.
Don't know what the issue is...Am I saturating the LF cores? Whyis it just these certain amps? And the TNT was specifically designed to run these amps...
Or could it be that the panels are not yet fully charged when I connect the problem amps? I did give it a few minutes to charge the panels before turning on the TNT amp...do these require a longer time to charge?
Last edited:
![MK-121C_Xovr_changes[1].gif](/community/data/attachments/269/269915-74652b29d1431bf8c12baebaa99d5ca2.jpg)
![MK-121C_Xovr[1].gif](/community/data/attachments/269/269922-835ef1b9282f67e5ab2c15b797326720.jpg)
The DCR should be higher than 1 ohm.
It should be the DCR of the bass transformer windings plus the series resistor (1 ohm).
The impedance of the IIIs are about 6 ohms minimum.
I would suspect that the Acoustat TNT has a problem.
Easy to check.
Play the good channel on each of the speakers - if it works, then there is an issue with
the amp.
Could be some bad electrolytics, they are old. Or other problems.
The "medallion mod" moved the LF point that the HF xfmr gets signal higher in freq.
The main thing is to have polypropylene caps and NO electrolytics in there.
You can't tell which transformers are which by looking at the paper on the outside, afaik.
Or iirc.
So, check the good amp channel on both speakers... that will tell you where the issue is, amp or speakers. Check the DCR looking in, should be (guessing) around 3-4ohms minimum...
You can compare the DCR of the two channels, LOW DCR on ONE channel indicates a shorted primary on that speaker.
There was somebody in Florida selling replacement transformers... a search here might reveal that, or Google.
Also the IIIs have substantial bass - distance from the rear wall will effect that.
About 3-4 ft seems a good range... The Acoustat TNT has nicer lower mids than most SS amps on them, and the best is a non-pentode higher power tube amp. >100watts required for decent output power.
_-_-bear
It should be the DCR of the bass transformer windings plus the series resistor (1 ohm).
The impedance of the IIIs are about 6 ohms minimum.
I would suspect that the Acoustat TNT has a problem.
Easy to check.
Play the good channel on each of the speakers - if it works, then there is an issue with
the amp.
Could be some bad electrolytics, they are old. Or other problems.
The "medallion mod" moved the LF point that the HF xfmr gets signal higher in freq.
The main thing is to have polypropylene caps and NO electrolytics in there.
You can't tell which transformers are which by looking at the paper on the outside, afaik.
Or iirc.
So, check the good amp channel on both speakers... that will tell you where the issue is, amp or speakers. Check the DCR looking in, should be (guessing) around 3-4ohms minimum...
You can compare the DCR of the two channels, LOW DCR on ONE channel indicates a shorted primary on that speaker.
There was somebody in Florida selling replacement transformers... a search here might reveal that, or Google.
Also the IIIs have substantial bass - distance from the rear wall will effect that.
About 3-4 ft seems a good range... The Acoustat TNT has nicer lower mids than most SS amps on them, and the best is a non-pentode higher power tube amp. >100watts required for decent output power.
_-_-bear
Thanks Bear,
There is only the single 1 ohm resistor in series with the LF transformer. But the DCR of the low and high transformers audio side windings are usually quite low - less than 1 ohm a piece, correct? So series 1 ohm with the LF transformer and paralleled resistance of the HF transformers should be close to 1 ohm (btw - my voltmeter resolution at low resistance is crap). What should the DCR be at the speaker inputs?
My DIY interfaces I built for the CLS has a single 1 ohm resistor in series with the two Toroids stepups and it only shows 1 ohm DCR too.
If the trannies were bad, why would they work for the two amps (Krell and Icepower)?
It is the impedance that is 6 ohm min, not DCR, correct?
There is only the single 1 ohm resistor in series with the LF transformer. But the DCR of the low and high transformers audio side windings are usually quite low - less than 1 ohm a piece, correct? So series 1 ohm with the LF transformer and paralleled resistance of the HF transformers should be close to 1 ohm (btw - my voltmeter resolution at low resistance is crap). What should the DCR be at the speaker inputs?
My DIY interfaces I built for the CLS has a single 1 ohm resistor in series with the two Toroids stepups and it only shows 1 ohm DCR too.
If the trannies were bad, why would they work for the two amps (Krell and Icepower)?
It is the impedance that is 6 ohm min, not DCR, correct?
the bad channel - if it is bad - may not like the load.
You should do the things I suggested.
One ohm is way too low on the primary of that transformer, imo.
At minimum there is a one ohm in series...
You can add another resistor in series and measure the whole thing, measure the resistor alone, subtract. Pretty accurate.
Krell is a very high current amp, will drive almost to a dead short.
Icepower? Dunno.
impedance 6 ohm min, not DCR, but DCR should not be far behind.
I am not near my Acoustats, so I can't just do a quick measurement.
Regardless, if the "good channel" drives each of the two speakers the fault is in the amp.
CLS is a different animal.
You should do the things I suggested.
One ohm is way too low on the primary of that transformer, imo.
At minimum there is a one ohm in series...
You can add another resistor in series and measure the whole thing, measure the resistor alone, subtract. Pretty accurate.
Krell is a very high current amp, will drive almost to a dead short.
Icepower? Dunno.
impedance 6 ohm min, not DCR, but DCR should not be far behind.
I am not near my Acoustats, so I can't just do a quick measurement.
Regardless, if the "good channel" drives each of the two speakers the fault is in the amp.
CLS is a different animal.
"do these require a longer time to charge?"
just a comment here about the panel charging time. I have always used power strips to plug in any of my electrostats (I don't like the possible risk of transformer failure with older vintage equipment when I'm not around), and they all play just fine basically immediately. This is not to imply that they won't improve with a longer charge time.
just a comment here about the panel charging time. I have always used power strips to plug in any of my electrostats (I don't like the possible risk of transformer failure with older vintage equipment when I'm not around), and they all play just fine basically immediately. This is not to imply that they won't improve with a longer charge time.
so this was interesting-
for some reason I expected 3-4 ohms also, but I guess I never measured. I have several models available, so here is a list. Also, in the original Acoustat owners manual, they are all listed as "Nominal Impedance:4ohms". After I had the first unexpectedly low number I decided to get a bit more serious.
So these numbers are straight resistance numbers at the speaker input banana jacks hot and ground, and on 2 of the interface units I was able to get directly to the low frequency primary taps. I checked both channels of each Model and left and right channels were all basically the same.
All these numbers are pretty much at my measurment limits using an old 4 1/2 digit meter. I did check it against a 3.92 ohm 0.1 percent resistor and my meter reads 3.90 so hopefully I am fairly close, but don't bet any money on these numbers.
so here goes:
Model 3 with MK-121-2A (no Medallion labels) (each tap setting measured at input jack hot to ground) (brown paper transformers)(interface appears unmodified with a blue 220uf EL cap and yellow 0.01 uf and 10uf film cap and, and a monster cable label, and corroding internal monster cable)
At input banana jack. Red tap = 1.22 ohm
At input banana jack. Orange tap = 1.3 ohm
At input banana jack. Yellow tap = 1.33ohm
yellow to brown = .38 ohm (Directly across the low frequency transformer primary at tap terminal strip)
HF transformer alone = 0.07 ohms (red lead lifted to common)
I resoldered the red lead and again measured at the output jack and unplugged the low frequency tap lead and measured 5.99 ohms, so that is the resistance of the HI FREQ balance control in series with the HF transformer and without the low frequency transformer in parallel.
Model 1+1 with MK-121-B with Blue and Red Medallion labels. (Set at yellow tap)(black paper transformers)
At input banana jack. Yellow tap = 1.62 ohm
yellow to brown = .55 ohm (Directly across the low frequency primary at tap terminal strip)
Model 2+2 MK-121-2A no Medallion labels (I recall these having brown paper but did not confirm at this time)
At input banana jack. = 1.3 ohm (did not open box to see what tap)
Maybe you could try a 1 or 2 ohm resistor in series, at least to see if your amps then function properly. I'm going to try just that with my PP tube amp to see if anything changes for the better. It never sounded good on the 8 ohm tap and the bass is fairly fat even on the 4 ohm tap.
hope this helps-
Dave
for some reason I expected 3-4 ohms also, but I guess I never measured. I have several models available, so here is a list. Also, in the original Acoustat owners manual, they are all listed as "Nominal Impedance:4ohms". After I had the first unexpectedly low number I decided to get a bit more serious.
So these numbers are straight resistance numbers at the speaker input banana jacks hot and ground, and on 2 of the interface units I was able to get directly to the low frequency primary taps. I checked both channels of each Model and left and right channels were all basically the same.
All these numbers are pretty much at my measurment limits using an old 4 1/2 digit meter. I did check it against a 3.92 ohm 0.1 percent resistor and my meter reads 3.90 so hopefully I am fairly close, but don't bet any money on these numbers.
so here goes:
Model 3 with MK-121-2A (no Medallion labels) (each tap setting measured at input jack hot to ground) (brown paper transformers)(interface appears unmodified with a blue 220uf EL cap and yellow 0.01 uf and 10uf film cap and, and a monster cable label, and corroding internal monster cable)
At input banana jack. Red tap = 1.22 ohm
At input banana jack. Orange tap = 1.3 ohm
At input banana jack. Yellow tap = 1.33ohm
yellow to brown = .38 ohm (Directly across the low frequency transformer primary at tap terminal strip)
HF transformer alone = 0.07 ohms (red lead lifted to common)
I resoldered the red lead and again measured at the output jack and unplugged the low frequency tap lead and measured 5.99 ohms, so that is the resistance of the HI FREQ balance control in series with the HF transformer and without the low frequency transformer in parallel.
Model 1+1 with MK-121-B with Blue and Red Medallion labels. (Set at yellow tap)(black paper transformers)
At input banana jack. Yellow tap = 1.62 ohm
yellow to brown = .55 ohm (Directly across the low frequency primary at tap terminal strip)
Model 2+2 MK-121-2A no Medallion labels (I recall these having brown paper but did not confirm at this time)
At input banana jack. = 1.3 ohm (did not open box to see what tap)
Maybe you could try a 1 or 2 ohm resistor in series, at least to see if your amps then function properly. I'm going to try just that with my PP tube amp to see if anything changes for the better. It never sounded good on the 8 ohm tap and the bass is fairly fat even on the 4 ohm tap.
hope this helps-
Dave
I put a .649 Dale resistor in series with speaker input and now my Aleph 5 with a 600VA toroid plays just fine. Without the series resistor it pulsed...
The TNT-200 still pulses and the series resistors get pretty hot.
It is strange how the TNT plays fine on other speakers including my CLS (which also has a 1 ohm resistor and two very low DCR Step up transformers.
The TNT-200 still pulses and the series resistors get pretty hot.
It is strange how the TNT plays fine on other speakers including my CLS (which also has a 1 ohm resistor and two very low DCR Step up transformers.
Hi,
There is no reason that should be the case. Same as if you measure
the DCR of a valve amplifiers output windings, they are much lower.
DCR of transformer windings are much lower than designed impedance,
otherwise they would be at best 25% efficient, clearly not the case.
rgds, sreten.
I put an inline amp meter that reads the amps and watts off the mains plug and with normal speakers or no speakers the TNT pulls just short of 300 watts from the wall, but when I have the Model 3 plugged in I read it pulsing from 300 watts up to 900+ watts, back to 300 watts, and all the while the room lights dim as it peaks to 900+ watts.
My Krell pulls the normal 750 watts from the wall with the Model 3, as always.
Clearly something not right with the amp, or the combo.
My Krell pulls the normal 750 watts from the wall with the Model 3, as always.
Clearly something not right with the amp, or the combo.
I would suggest the Acoustat amplifier has some sort of marginal stability issue. Normally, the Acoustat amp should be able to drive the speakers with ease.
The DCR of the speaker will be on the order of only a few ohms. If your ohmmeter does not have good resolution or accuracy in that range, your measurement could easily be in error by an ohm or three.
The speakers require only a few moments to reach playing charge, but improvements in sound and dynamic capacity will be noticed during the first 24 hours of being energized. I suggest the speakers be left energized at all times unless you are expecting a long period of non-use.
The choice of 3-amp or 5-amp slo-blow fuses is personal one. For moderate sized power amps and most listening conditions, 3-amps should be fine. If you have a large amp, and like playing loud music, a 5-amp fuse may be a better choice. The idea is to use as small a fuse value as possible without 'nuisance' blowing, while still affording some protection to both speakers and amplfier.
The DCR of the speaker will be on the order of only a few ohms. If your ohmmeter does not have good resolution or accuracy in that range, your measurement could easily be in error by an ohm or three.
The speakers require only a few moments to reach playing charge, but improvements in sound and dynamic capacity will be noticed during the first 24 hours of being energized. I suggest the speakers be left energized at all times unless you are expecting a long period of non-use.
The choice of 3-amp or 5-amp slo-blow fuses is personal one. For moderate sized power amps and most listening conditions, 3-amps should be fine. If you have a large amp, and like playing loud music, a 5-amp fuse may be a better choice. The idea is to use as small a fuse value as possible without 'nuisance' blowing, while still affording some protection to both speakers and amplfier.
I suggested that to measure the DCR place say a 10 ohm resistor in series with the meter, measure the 10ohm + transformer. Now measure the 10 ohm, subtract the two, that is much closer to the actual DCR. The meter is more accurate at 10 ohms than at 1ohm.
Seems that something is up with the amp.
Do both channels do the same thing?
Just one channel, right?
I'm suspicious of the cap that is in the feedback network - which I think is there, it is an unusual feedback network - intended to pull the DC gain to unity... might be unhappy. Could be something else, but I'd have to look and see if I have the schematic on this laptop or not, don't think I do.
_-_-bear
Seems that something is up with the amp.
Do both channels do the same thing?
Just one channel, right?
I'm suspicious of the cap that is in the feedback network - which I think is there, it is an unusual feedback network - intended to pull the DC gain to unity... might be unhappy. Could be something else, but I'd have to look and see if I have the schematic on this laptop or not, don't think I do.
_-_-bear
Thanks Bear, I will re-check the DCR tonight, but suspect it to be around 1.5ohms.
As far as the amp is concerned, it is both channels, and I think it is likely a spent electrolytic that goes a bit haywire once a low DCR speaker is connected, as I have no issues (noise, etc) driving other speakers. Since it is not my amp and owner is not using it on his accoustat speakers, I will let him decide what he wants to do.
As far as the amp is concerned, it is both channels, and I think it is likely a spent electrolytic that goes a bit haywire once a low DCR speaker is connected, as I have no issues (noise, etc) driving other speakers. Since it is not my amp and owner is not using it on his accoustat speakers, I will let him decide what he wants to do.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.