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Old 16th August 2014, 05:39 PM   #1
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Default Refurbishing Acoustat 2123 interface, have ?'s

I have Spectra 22's and one speaker is generating a little distortion under certain circumstances. I checked and adjusted bias for both interface units but the one that is paired with the speaker that has the issue would not bias up to the recommended range. My tech has demonstrated interest in taking a look at the units (hopefully he'll jump in on this conversation) and while he has them I thought I might have the units recapped and/or perform any other proven and recommended mods/upgrades. I've done some searching on this but haven't been able to find much in the way of common mods for the 2123 like the "c-mod" and "air mod" for the earlier interface units. Any recommendations wrt this?

Also, I was hoping I could have him install a second set of binding posts to make each panel bi-ampable, but from what I've read the circuit design of the interface will not allow for this. Is that accurate?

Thanks,
Michael

Last edited by tinnitusintx; 16th August 2014 at 05:41 PM.
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Old 16th August 2014, 10:03 PM   #2
tyu is offline tyu  United States
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This Is the Spectra33...I have the Spectra 3...an there the same.....i think the 22 are the same with one less panel,an a diff wire setup....there are two trans.....but there wired to make one trans per speaker...
there was a sub made by Acoustat to work with the Spectra speakers you can see the setup that what the crossover is for....but there are know parts to upgread if there ran fullrang...the one ohm res. is all.... an it could be cook from over driveing....an making the noise..change that frist.....lot less $$ if that it...
take the 1ohm from the one 22 not making noise...put it in the 22 makeing noise... an see it it stops....
The Mixer parts .....Less a .1mf 5k cap is bad are a res..is...i would leve them AS is.....good luck hope it not one of the transfourmer....Killer ESLs

As for bi-wireing i gess you could but i well let other chime in on that......

Long live Acoustat
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Last edited by tyu; 16th August 2014 at 10:16 PM.
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Old 17th August 2014, 03:26 PM   #3
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I am doing the work on these Acoustat 2123 boxes for Michael. We made a quick visual assessment of them yesterday when he dropped them off with me. One of the two boxes had a PP film 10uF/100V cap in the input network where the other box had the original 1988 date code electrolytic in it. The box with the non-original 10uF film cap also had some bubbling apparent to the 1ohm (full range) resistor in the network. So I'm assuming this box has had issues in the past and was repaired. For now, the plans are to replace all of the old electrolytics in both boxes. On the input network I'll use PP films for both of the 10uF caps. I'll also install new 1 ohm resistors in both boxes as well. Any suggestions on the replacements for the 1 ohm resistors, is everyone replacing them with original ceramic wirewounds or have better input resistors been identified? We are also going to go back with better binding posts. In addition, I found the bias procedure for the 2200/3300. Those panels are biased at 4300V, so I'm assuming that the 22/33's are as well?

Looking at the schematic posted by TYU I see why its not possible to biamp these boxes, at least not in a simple manner, so we'll take that one off the table.
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Old 18th August 2014, 12:48 PM   #4
tyu is offline tyu  United States
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The Res....well unlike the caps....if the 22 are ran fullrang...the one ohm is in the path..better res...well sound better
Some use the gold dail....but the better Omite would sound better...the chep sand cast res....like ratshak an SL use sound bad....but as you know any well work...as long as there of the high watts..........i would use 3ea 3hom 20watt put to gather...to make a 1ohm..... sounds much better....

All just one mans o-pine........................Long live Acoustats
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Old 19th August 2014, 03:10 PM   #5
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A note on the schematic: the labels for the red and orange bass taps are reversed: my mistake when I drew it some 25 years ago.

The purpose of the 1-ohm resistor is to limit the minimum impedance at very low frequencies. It should always be present for maximum stability with your amplifier. As this resistor is bypassed with capacitors, thereby removing it from the circuit at high frequencies, its quality is not vital. However, if it needs to be replaced anyway, it's not much extra trouble or expense to replace it with a more robust part like a metal-bodied resistor, made by Dale/Vishay and others.

The bias voltage is the same for all Acoustat speakers, so any information about one model will apply to all. If you cannot get the voltage high enough in one speaker, you may need to perform a simple modification to the circuit. Let me know if you need more information (this mod applies only to the earliest Spectra models). Otherwise, you may have an issue with one of the voltage multiplier's diodes or capacitors.

The value of the capacitance bypassing the 1-ohm resistor is critical only if using the speaker in the 'Above 100-Hz' mode. If the speaker is being used full range (or is utilizing an external crossover) the total value of the capacitance can be dropped to around 20-uF. This greatly reduces the expense and physical challenge of stuffing a huge polypropylene cap inside the interface.

Bi-amping the Spectra series is not advisable, at least not in the usual sense of splitting high and low frequencies and driving with separate amplifiers. My advise is to leave that aspect alone and drive the speakers as originally intended.
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Old 19th August 2014, 04:06 PM   #6
tyu is offline tyu  United States
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Yes.... an we learn more about the be-loved Acoustat.s.....thanks for being there Andy



Long live Andy an Acoustats......
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Old 20th August 2014, 01:00 PM   #7
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Quote:
Originally Posted by AcoustatAnswerMan View Post
A note on the schematic: the labels for the red and orange bass taps are reversed: my mistake when I drew it some 25 years ago.

The purpose of the 1-ohm resistor is to limit the minimum impedance at very low frequencies. It should always be present for maximum stability with your amplifier. As this resistor is bypassed with capacitors, thereby removing it from the circuit at high frequencies, its quality is not vital. However, if it needs to be replaced anyway, it's not much extra trouble or expense to replace it with a more robust part like a metal-bodied resistor, made by Dale/Vishay and others.

The bias voltage is the same for all Acoustat speakers, so any information about one model will apply to all. If you cannot get the voltage high enough in one speaker, you may need to perform a simple modification to the circuit. Let me know if you need more information (this mod applies only to the earliest Spectra models). Otherwise, you may have an issue with one of the voltage multiplier's diodes or capacitors.

The value of the capacitance bypassing the 1-ohm resistor is critical only if using the speaker in the 'Above 100-Hz' mode. If the speaker is being used full range (or is utilizing an external crossover) the total value of the capacitance can be dropped to around 20-uF. This greatly reduces the expense and physical challenge of stuffing a huge polypropylene cap inside the interface.

Bi-amping the Spectra series is not advisable, at least not in the usual sense of splitting high and low frequencies and driving with separate amplifiers. My advise is to leave that aspect alone and drive the speakers as originally intended.
Good information, thank you Andy.
I had stated in my original post that one of the two boxes had a 10 uF electrolytic in it. Upon closer inspection this was incorrect. It was actually a PP film wrapped in an aluminum foil material. It looked liked one of those old silver axial electrolytics when I first saw it.
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Old 20th August 2014, 03:39 PM   #8
tyu is offline tyu  United States
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I have had a pr of the Acoustats Spectra 11....in the 2 interfaces one had one type of cap an the other had a diff cap...an thay were stock....that why when you saw diff i said nothing....but then again there only a crossover cap for none fullgrang....in your case....most run full...even with a added sub...
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Old 20th August 2014, 10:36 PM   #9
Atom666 is offline Atom666  Canada
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Andy
Just to make sure I understand this the correct transformer wiring should be
Spectra 3300 = RED
Spectra 2200 = Orange
Thanks
Andrew
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Old 21st August 2014, 12:46 AM   #10
tyu is offline tyu  United States
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121 bass tarn.................2red..........3org........... 4yelo....
Spectra...........2123..... 3-33-3300..org......2-22-2200.red.......i think Andy said the 44-66 had diff tran...my Spectra 3s are on org....................But Andy well say
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Last edited by tyu; 21st August 2014 at 12:51 AM.
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