Hey friends -- I have a pair of Acoustat Model 2's that have "Mk 121 mod installed" labels on the interfaces. I'm not sure what exactly that means, but I can tell report that one speaker is significantly less efficient than the other. I will try to upload pics of what's inside, and it's apparent that one speaker has had the disc capacitors replaced while the other has not (or has, but with different caps). Agreed? The "older" (and bigger) looking caps are in the weaker speaker.
Is it safe to assume that these should be swapped out? If so, can anyone recommend a replacement? I am handy with a soldering iron, but do NOT know the ins and outs of components. I wouldn't know for a second what to order if I were looking at a catalog page.
THANK YOU IN ADVANCE to anyone who can lend a hand! I owned Acoustats back in college, and absolutely loved them. Can't wait to get these back to form; it's been 20 years or so since I've listened to Acoustats! (Well, properly working Acoustats, anyway)
Pics here:
https://imgur.com/a/PhIc6
Is it safe to assume that these should be swapped out? If so, can anyone recommend a replacement? I am handy with a soldering iron, but do NOT know the ins and outs of components. I wouldn't know for a second what to order if I were looking at a catalog page.
THANK YOU IN ADVANCE to anyone who can lend a hand! I owned Acoustats back in college, and absolutely loved them. Can't wait to get these back to form; it's been 20 years or so since I've listened to Acoustats! (Well, properly working Acoustats, anyway)
Pics here:
https://imgur.com/a/PhIc6
You have a very early vintage MK-121, as evidenced by the small "daughter" board installed on top of the main board. Early interfaces used a higher voltage bias transformer and three stages in the multiplier, which proved unreliable. Later interfaces used a lower voltage transformer and a five stage multiplier. Your interface has been upgraded with the newer bias system.
More than likely some of the capacitors have gone bad, and possibly the diodes, too. I suggest you replace all ten capacitors and ten diodes. I have information on replacement parts, but not where I am right now. Let me dig up my notes and I will make a second reply, along with some cautions about the process.
If any one else has info on suitable replacement parts, feel free to chime in. Somewhere in the thread "AcoustatAnswerMan is Here" there is information on the diodes (they are special high voltage types).
Thank you, sir!!! I very much appreciate the assistance! I'll look through the AcoustatAnswerMan is Here thread for that info as well and will try to get these parts ordered ASAP, as I am very anxious to get these back in proper shape. If anyone's got a good source for these parts, I'm all ears.
Thank you again. I certainly appreciate the help!
Andy, I found the following in the "AcoustatAnswerMan is Here" thread. Am I om the right track looking at these?
564R30TSD33 Vishay / Cera-Mite | Mouser
"A difference in volume between the speakers usually indicates a problem in the 5000-volt bias power supply. I would suggest first replacing all five of the capacitors in the voltage multiplier. These are 3300 pF, 3000-volt ceramic discs. A higher voltage rating is okay as long as they fit okay in the board. I also suggest replacing these parts in both interfaces. There's no point in using fancy "audiophile grade" parts in this application - plain ol' ceramic discs are fine."
564R30TSD33 Vishay / Cera-Mite | Mouser
"A difference in volume between the speakers usually indicates a problem in the 5000-volt bias power supply. I would suggest first replacing all five of the capacitors in the voltage multiplier. These are 3300 pF, 3000-volt ceramic discs. A higher voltage rating is okay as long as they fit okay in the board. I also suggest replacing these parts in both interfaces. There's no point in using fancy "audiophile grade" parts in this application - plain ol' ceramic discs are fine."
I'm not going to argue the pros/cons of ceramic vs. metallized polypropylene, except to say that all capacitors can fail with age, and that Acoustat's use of ceramic capacitors in the bias multiplier has not shown a significant rate of failure "for no reason". The caps in this particular speaker are probably in the range of 35+ years old.
Your first suggestion of ECW-HC3F392J is significantly larger (0.886" lead-space vs. 0.37" lead space) than the ceramic part I suggested in an earlier post, referenced again above. Due to the tight layout of Acoustat's bias multiplier, I think it would be very difficult, if not impossible and/or dangerous, to cram such a large part in the space provided.
Your second suggestion of B81123C1332M189 is rated for only 500V and would fail rather quickly if not immediately.
I say stick with the ceramic discs as originally spec'd by the factory that will easily fit the board. Now, if you were designing a new bias supply, with the freedom to lay out the board for larger parts, then the metallized polypropylenes might be a better choice, given a sufficient voltage rating for the application.
I recommend these replacement parts for the bias multiplier. Both can be purchased from www.mouser.com. You'll need ten of each to service one pair of speakers.
Vishay GP02-40 diode, 250 mA, 4000 volts
Mouser p/n 625-GP02-40-E3
Vishay 564R30TSD33 capacitor, 3300 pF, 3000 volts
Mouser p/n 75-564R30TSD33
Be sure the interface circuitry is completely discharged before work. This can be done by either waiting several hours after being unplugged, or you can use an insulated test lead to short the red pin plug to ground.
The capacitors are not polarity sensitive and can be inserted either way.
The diodes ARE polarity sensitive. Be sure to document the orientation of the original diodes by noting which end is marked (usually with a paint dot). These marks will correspond to the banded end of the new diodes.
Be sure all solder connections are good, and in particular watch for any stray whiskers of solder that might be bridging parts of the circuit.
If you lack the skills or confidence to do the work, any good electronics technician should be able to do the work if you supply the parts.
Vishay GP02-40 diode, 250 mA, 4000 volts
Mouser p/n 625-GP02-40-E3
Vishay 564R30TSD33 capacitor, 3300 pF, 3000 volts
Mouser p/n 75-564R30TSD33
Be sure the interface circuitry is completely discharged before work. This can be done by either waiting several hours after being unplugged, or you can use an insulated test lead to short the red pin plug to ground.
The capacitors are not polarity sensitive and can be inserted either way.
The diodes ARE polarity sensitive. Be sure to document the orientation of the original diodes by noting which end is marked (usually with a paint dot). These marks will correspond to the banded end of the new diodes.
Be sure all solder connections are good, and in particular watch for any stray whiskers of solder that might be bridging parts of the circuit.
If you lack the skills or confidence to do the work, any good electronics technician should be able to do the work if you supply the parts.
Thank you! My speakers have been unplugged for more than a week now, but I will be very careful nevertheless. Should be a good learning experience for me. I will try to post an update in the thread here once I am able to get these parts installed; I sure do appreciate your time!
Well, I swapped out caps only (for starters), and the result is like night & day. The volume levels are even now from one speaker to the other, and to my ear, both speakers are more "efficient," for lack of a better term. I did one at a time; I first recapped the "quieter" speaker, and fired both up. That resulted in an imbalance that was opposite for the previous condition: the newly recapped speaker was now noticeably louder than the other. I then recapped the second speaker as well (after taking care to ground the red lead), and now both speakers play at the same volume level. I was up far too late enjoying some old favorites. Thank you again for the assistance; I couldn't be more thrilled!
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