charvey,
Two brands that go deep and are probably tight enough to keep up with Acoustats are REL and Rythmik (sealed enclosures). Audio people often say a good sub is "fast", but "tight" is a much more accurate term. It needs to respond quickly and accurately and end notes quickly. The cabinet design (stiffness) is a major factor. A less than excellent cabinet muddies the bass. I have studied the subject a lot and built good subs.
You need a way to roll off the lows to the Acoustats. A line level high pass network is small and cheap. Some preamps do this, especially home theater models.
From what I have read most Acoustats can be crossed over between 50-100 Hz (cycles) depending on the model.
Two brands that go deep and are probably tight enough to keep up with Acoustats are REL and Rythmik (sealed enclosures). Audio people often say a good sub is "fast", but "tight" is a much more accurate term. It needs to respond quickly and accurately and end notes quickly. The cabinet design (stiffness) is a major factor. A less than excellent cabinet muddies the bass. I have studied the subject a lot and built good subs.
You need a way to roll off the lows to the Acoustats. A line level high pass network is small and cheap. Some preamps do this, especially home theater models.
From what I have read most Acoustats can be crossed over between 50-100 Hz (cycles) depending on the model.
I have a pair of Acoustat Monitor 3 with dual panels isobarically mounted on either side of the frames and 4 direct drive servo OTLs driving them, one for each set of three panels. I have 1/2" felt in between the panels covering the entire area. This yields a very well damped presentation free of resonance for the most part. With this a pair of Linn 5150 subs crossed at 58hz. They are "tight" as you say so the bass is well defined over all.
Thanks for your reply. Sorry it took me a while to respond but here is a picture. I got one of the three remaining screws out. If these are similar to my old 1+1s anyway it’s only the screws around the perimeter holding the transformer chassis in place.
That appears to be an MK-121 B or C enclosure, and you do NOT want to remove any of the screws on the top of the enclosure. Those are for attachment of internal parts.
You want to remove the screws on the sides of the chassis. This will allow removal of the L-shaped interface chassis. There are large screws inside the side plates (visible after removing the interface chassis) that attach the panel array to the side plates, and also the side plates to the base (the base-attachment screws generally do not need to be removed).
If you are having difficulty removing the screws, I suggest a small drop of your favorite penetrating oil (WD40 or similar) on the screw, and then it soak a while. A loss of volume is typically caused by a defective bias supply: rebuilding the bias supply is covered elsewhere in thus thread. Parts are cheap and generally readily available.
You want to remove the screws on the sides of the chassis. This will allow removal of the L-shaped interface chassis. There are large screws inside the side plates (visible after removing the interface chassis) that attach the panel array to the side plates, and also the side plates to the base (the base-attachment screws generally do not need to be removed).
If you are having difficulty removing the screws, I suggest a small drop of your favorite penetrating oil (WD40 or similar) on the screw, and then it soak a while. A loss of volume is typically caused by a defective bias supply: rebuilding the bias supply is covered elsewhere in thus thread. Parts are cheap and generally readily available.
Yes, but only if your amplifiers have been equipped with a bridging module. This converts a stereo amp into a higher-power, mono amplifier. I think Roy Esposito in Florida is still offering this service, but that's not much use to you considering shipping costs. I've never been a fan of bridged amps on Acoustat speakers. Their already low impedance will be seen as only half that value by their connection to a bridged amp. Also, the TNT-200 provides enough power for any model Acoustat, so unless great care is used, you have the potential for over-driving and damaging the speaker.
I'd say there's a pretty low chance of success. Due to the speaker's low impedance at some frequencies, the relatively high output impedance of most tube amps will create anomalies in the frequency response. And since the weak point of the Spectra 11 is the woofer, I think any reduction in damping factor would only make matters worse. And even though you listen at close range, the power requirements are still considerable. I think anything less than 50 WPC would tend to disappoint. Buy your requirements may be different - I would strongly suggest auditioning the combination before laying down your cash.
I picked up as set of acoustat model 3 today. The guy I bought them from said he hooked them up and they were no louder then a set of headphones (he found them at a goodwill). So I brought them home and wired em up to my audio research d-110b. They actually do work but you can tell they are not right and one is much louder then the other. I could clearly see they were taxing my amp (by looking at the meters) to get not much volume out of them. I pulled the im interfaces off and measured voltage. One has about 600v and the other about 1200v. So I figured a rebuild is due on the HV supply. These dont look like they were ever even opened imo. After doing some research there seems to be a lot of variables to these interfaces. It appears I dont have the medallion xformers or the "c mod" I'm reading about. Basically I want to get these functional without going crazy to make sure the panels are good. I'm pretty sure I know the ceramic caps and diodes I need but looking at the schematic I cant seem to find the value of the two bigger caps. It looks like they are .01uf on the schematic (I might not be looking at the right one) but these would be big for that value. I dont completely yet understand fully how these interfaces work so maybe they are that big because there high voltage. I will post some pictures, if anyone has any advice or recommendations I would really appreciate it.
Attachments
I'm thinking the caps and diodes at a minimum. When I tested the interfaces they were on my bench and not wired to the panels at all. I would agree it's just the diodes but il definitely recap while there. Ceramic caps are cheap and there is only one electrolytic in there. The big ones I'm guessing are film caps but I'm really not sure. There is no markings or anything on them wich is pretty strange to me.
It does sound like both the bias supplies are putting out a low voltage. This is most commonly solved by replacing the (5) ceramic disc capacitors and (5) HV diodes in the voltage multiplier. Below are suggested replacements. There is no sonic advantage is replacing the ceramic caps with something "better". The ceramics are designed for the task, and anything "better" would not fit the board. Be careful in using the speakers with a malfunctioning bias supply - it's very easy to overdrive/damage them in this state.
Vishay 564R30TSD33 capacitor, 3300 pF, 3000 volts
Mouser p/n 75-564R30TSD33
GP02-40-E3/54 Vishay Semiconductors | Mouser (http://www.mouser.com/ProductDetail...=sGAEpiMZZMtbRapU8LlZD0HbIjlpuZ44XerUncvtHjs=)
As for the two large tubular .01 uF capacitors on the board, those are special high-voltage types, which explains their large size. These rarely fail, and replacements are hard to find due to their 6kV rating. The originals were custom-made for Acoustat, which is why they are unmarked. I'd say leave them alone unless you have determined one or more are defective. If defective and you can find replacements, replace all four.
The 500M-ohm resistor is not wirewound, but a special high-voltage type. These also rarely fail, and replacements are hard to find. It is rated at 2-5 watts with 5-10 kV voltage rating. I'd say leave them alone unless you have determined one or more are defective.
Once you get the speakers working properly, I would recommend the "C-Mod", which is easy and cheap to do, and parts are readily available. Medallion transformers are no longer available, and even if you could find the (2) LF transformers and (2) HF transformers, their price would likely be beyond what you are willing to invest (probably more than you paid for the pair of speakers). Good luck!
Since I wasn't around in the early days of Acoustat, when the decision was made to fuse both sides of the bias transformer, I cannot say for sure. But I would suspect the dual fuses would protect in cases of a short to chassis from either hot or neutral (which could occur either internally or externally to the bias transformer). Although the speakers were supplied with 3-prong plugs, it's always possible someone might remove the plug's ground pin and insert the plug backwards. This could mean either side could be the hot side, and the dual fuses would protect in either scenario. And of course, there's always the possibility that the wall outlet is wired backwards. Just one man's opinion. When it comes to electrical safety, more safeguards are better.
Gotchya. I'm not running the speakers at all. I just had to figure out if they worked or not before disassembly. I also plan to do the c-mod and I figured out what it entails so no help needed there. I do have one question before I order parts. How long do those 4kv rectifier diodes live in these hv supplies seeing as there is more then 4kv going through at least the last one? I understand how the caps take it as none are really seeing the full voltage.
If you look at the voltage traces at the circuit nodes, you can see that each diode in a Cockcroft–Walton voltage multiplier must withstand 2x the peak input voltage.
In the case of the Acoustat HV supplies, this is about 2kV, so about half of the 4kV rating.
None of the diodes experience the full output voltage across their terminals.
See also posts #1310 & 1311 here: https://www.diyaudio.com/community/threads/acoustat-answer-man-is-here.183168/post-4296930
In the case of the Acoustat HV supplies, this is about 2kV, so about half of the 4kV rating.
None of the diodes experience the full output voltage across their terminals.
See also posts #1310 & 1311 here: https://www.diyaudio.com/community/threads/acoustat-answer-man-is-here.183168/post-4296930