Spectra 1100 10M resistor & parts replacement
Just got my hands on a mint and near stock pair of Spectra 1100 (final version); happy to join the team of Acoustat lovers
After much reading up in this great thread and elsewhere, I'm ready for some interface modding - which leaves me with some questions:
Audio section:
- On the HV side of the tranformer's center tap, the 10M resistor was swapped by a previous owner to 14M. Any reason to change it back to the original value?
- would a non-inductive type be an upgrade for the 330k resistors? If so, any take on power and voltage rating?
Bias section:
- I plan to replace the 47uf & 470uf electrolytics with higher values & solder cap between IC pins 6&2 bobwire and the Acoustat Spectra 11 - bobwire - Planar Speaker Asylum
Any sense in changing the 220uF to higher value, while I'm at it, or vice versa retain all original values?
TIA!
Simon
Just got my hands on a mint and near stock pair of Spectra 1100 (final version); happy to join the team of Acoustat lovers
After much reading up in this great thread and elsewhere, I'm ready for some interface modding - which leaves me with some questions: Audio section:
- On the HV side of the tranformer's center tap, the 10M resistor was swapped by a previous owner to 14M. Any reason to change it back to the original value?
- would a non-inductive type be an upgrade for the 330k resistors? If so, any take on power and voltage rating?
Bias section:
- I plan to replace the 47uf & 470uf electrolytics with higher values & solder cap between IC pins 6&2 bobwire and the Acoustat Spectra 11 - bobwire - Planar Speaker Asylum
Any sense in changing the 220uF to higher value, while I'm at it, or vice versa retain all original values?
TIA!
Simon
Servo Amp questions
It seems that many people who have had the Acoustat X with the servo amps claim much better sound quality than using the standard interface. First, is the sound improvement using the servo amps that significant? If so, how does it sound better. Also can the Spectra series of speakers be adapted for the servo amps and how many panels can the amp drive. Thank you for any input you can provide.
Regards
gwho
It seems that many people who have had the Acoustat X with the servo amps claim much better sound quality than using the standard interface. First, is the sound improvement using the servo amps that significant? If so, how does it sound better. Also can the Spectra series of speakers be adapted for the servo amps and how many panels can the amp drive. Thank you for any input you can provide.
Regards
gwho
Apparently with modification, I've read that the servos can be made to drive the Spectras. Should they? Heck yeah! I have both Monitor 3 and Model 3. Ime, there really is no comparison. I have red medallion interfaces and they sound great with the Model 3 but the Servos with the Monitors are in a different league. The panels of both are identical. So yes, the King was dead when Acoustat discontinued them; very bad move imo. Others are apparently glad they converted theirs to interfaces. I don't get it. Theirs lots of upgrades and tweaks for the servos too. Mine have been stone reliable and I use them a lot. Mind you I bought them with upgraded parts. I have several pairs and the ones I bought with the Monitors were also upgraded parts versions which were stored outside in a shed for 15 years and filthy, looking like they survived a flood almost. I cleaned them up, plugged them in and they ran like a champ, no noise or any adverse behavior. Some say reliability is questionable. I have to disagree. However, the upgrades could very well be responsible for that.
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Servo Amp questions
Discopete
Thanks for the reply. Interesting that you have both an interface and servo amp on the same type of Acoustat array. You as others I have read say things like "night and day" etc... . How can it sound so much better. Is the bass better? Transparency (interface acoustats are very transparent)?
Do you have any idea how one would adapt a Spectra to use the servo amp. I know that different panels cover different frequency ranges. With the servo amps do you drive all the panels full range. Would this defeat the advantages of the Spectra version having a wider sweet spot?
Regards,
gwho
Discopete
Thanks for the reply. Interesting that you have both an interface and servo amp on the same type of Acoustat array. You as others I have read say things like "night and day" etc... . How can it sound so much better. Is the bass better? Transparency (interface acoustats are very transparent)?
Do you have any idea how one would adapt a Spectra to use the servo amp. I know that different panels cover different frequency ranges. With the servo amps do you drive all the panels full range. Would this defeat the advantages of the Spectra version having a wider sweet spot?
Regards,
gwho
There's just more of everything. The interfaces just sound constrained in comparison. The starkest difference I hear is depth/low level resolution, big/open/effortless sound. Transient performance is second to none. Bass is also fuller. I won't say it's better defined, though. But it's more present.
I can't speak to why they differ in these ways as it's obviously subjective and I am not technically knowledgeable except to point out that the servos are direct drive and so lend insight into their superiority. All 3 wire panels of which the Model 3 and Monitor 3 consist are driven full range. Since the Spectra panels are crossed over, you would obviously need to implement a dividing network into the servo system to benefit from segmentation. You would need to consult with a knowledgeable tech.
The Monitor 4 are driven by the same servo as the 3 but I have read the servos can handle 6 panels but they may need modification for that.
I can't speak to why they differ in these ways as it's obviously subjective and I am not technically knowledgeable except to point out that the servos are direct drive and so lend insight into their superiority. All 3 wire panels of which the Model 3 and Monitor 3 consist are driven full range. Since the Spectra panels are crossed over, you would obviously need to implement a dividing network into the servo system to benefit from segmentation. You would need to consult with a knowledgeable tech.
The Monitor 4 are driven by the same servo as the 3 but I have read the servos can handle 6 panels but they may need modification for that.
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My pr of Acoustat Xs had the all stock servos tube amps...this was in 1985-6...
Jim still had his shop here in south Fl...I was working in the Audio biz an called Jim….Frist thing he said to me.. was to get the servos out an get Mk 121 interfaces...I thought it was funny...I had been into tubes for years ....to my ears... the interfaces ...sound just like all the great solid state amps if used to drive any ESL speaker... to my ears...Bad hehe...But the servos Amps sound well....like nothing I had ever heard, less be real!
But it was the sound of... Tubes Tubes Tubes....Big, Fat,Full, Rich, a little dark rolled off...why.. the Xs frames put the bottem of the panels on the floor..an the frame was made like a box...with a back to hide the amps....these amps were all stock with the tube that came with the amp.... but worket great...I could not get a nuf of there sound...But I had let them go..I move on to the Apogee ribbons..an on an on...as it goes...
I see Servo Amps come up for sale time to time...$1500-2k...I think Disco has ran his servos with the ML CLS panels...if that works well, I think that would be what I would like to hear.. Today with my Schiit Freya+'s an ML CLS with a Cary CAD 120s MK2 amp with the 8, KT120 tubes an my old CJ pv2-5 magic tone eqs….sound a little closer to the sound of a ESL panel that I like more than any other ...Acoustat 1+1s are great fun.. like Sound labs, quad 57s all good sound
Jim still had his shop here in south Fl...I was working in the Audio biz an called Jim….Frist thing he said to me.. was to get the servos out an get Mk 121 interfaces...I thought it was funny...I had been into tubes for years ....to my ears... the interfaces ...sound just like all the great solid state amps if used to drive any ESL speaker... to my ears...Bad hehe...But the servos Amps sound well....like nothing I had ever heard, less be real!
But it was the sound of... Tubes Tubes Tubes....Big, Fat,Full, Rich, a little dark rolled off...why.. the Xs frames put the bottem of the panels on the floor..an the frame was made like a box...with a back to hide the amps....these amps were all stock with the tube that came with the amp.... but worket great...I could not get a nuf of there sound...But I had let them go..I move on to the Apogee ribbons..an on an on...as it goes...
I see Servo Amps come up for sale time to time...$1500-2k...I think Disco has ran his servos with the ML CLS panels...if that works well, I think that would be what I would like to hear.. Today with my Schiit Freya+'s an ML CLS with a Cary CAD 120s MK2 amp with the 8, KT120 tubes an my old CJ pv2-5 magic tone eqs….sound a little closer to the sound of a ESL panel that I like more than any other ...Acoustat 1+1s are great fun.. like Sound labs, quad 57s all good sound
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Hi Andy.
Listening to my Monitors 4 again, I wondered what kind of coating was used. it is surprising that after 40 years they maintain a good sensitivity. So I would like to recreate on the cells that I am creating the same type of coating. In the "Acousta Factory tour" the lady smears a dark graphite-based substance with a brush (I think) ... Do you know what it was made of?
Listening to my Monitors 4 again, I wondered what kind of coating was used. it is surprising that after 40 years they maintain a good sensitivity. So I would like to recreate on the cells that I am creating the same type of coating. In the "Acousta Factory tour" the lady smears a dark graphite-based substance with a brush (I think) ... Do you know what it was made of?
tyu, I have come across Xs a couple of times now. First set I used for spare panels to fix my Monitor 3. One speaker had punctures in all three panels while in storage and the X had one speaker with huge burn holes so that worked out well. I have a full set of good panels from another set of Xs. Those frames are well.. junk. Very poorly made imo. The Monitor series is a huge improvement. No, I have not run servos with ML CLS, but that would be interesting.
See post #2297, where I answered this question to the best of my ability. The rest is lost to history.
Just got my hands on a mint and near stock pair of Spectra 1100 (final version); happy to join the team of Acoustat lovers
Audio section:
- On the HV side of the tranformer's center tap, the 10M resistor was swapped by a previous owner to 14M. Any reason to change it back to the original value?
- would a non-inductive type be an upgrade for the 330k resistors? If so, any take on power and voltage rating?
Bias section:
- I plan to replace the 47uf & 470uf electrolytics with higher values & solder cap between IC pins 6&2 bobwire and the Acoustat Spectra 11 - bobwire - Planar Speaker Asylum
Any sense in changing the 220uF to higher value, while I'm at it, or vice versa retain all original values?
TIA!
Simon
View attachment 813340
The 10-Mohm resistor is not a critical value, so 14-Mohm would work just as well. That might have even been a factory substitution.
The 330-kohm sector resistors are special high-voltage types, and I see little value in changing them to non-inductive types in this audio-frequency application.
You can increase the value of the 470-uF and 47-uF in the power supply if it would make you happy. That this is a sonic upgrade is questionable.
I don't much care for the idea of soldering a capacitor directly on the pins of the IC. This may damage the chip, which is no longer made and very difficult to find. Again, that this is a sonic upgrade is questionable.
DO NOT change the 220-uF. It's value is critical to the operation of the bias oscillator.
I agree that any modification that could compromise an unobtainable component is questionable - this one doubly so since the cap isn't really in the signal path. That said, it looks like there are plenty of references to an LM13080N IC, with currently available stock in a few places. If I understand, the "N" refers to the 8-pin DIP package (as opposed to the "P" version 11-pin SIL.)
Would this be a replacement for a damaged IC?
None of the caps you mention are in the audio path: both 47-uF and 470-uF are in the power supply for the bias oscillator. Hence my questioning as to their sonic impact. Regardless of the availability of the chip, soldering to the IC pins is just dumb. This mod is just adding more capacitance to the power supply, which, especially if you've already increased the 470-uF, is just gilding the lily. Just because you read it from someone on the internet, who may or may not have the required technical background or understanding of the particular circuit, does not mean it's a good idea even though they claim to hear an improvement. (We call this Expectation Bias: expecting to hear a change because you made a change.)
My recommendation is to not fix what ain't broken, and to take all advice (even mine!) with caution unless YOU fully understand the implications of your proposed modifications. But having worked at Acoustat, and specifically having worked on the Spectra series and the Ultrasonic Bias Power Supply, I would hope my advice carries a little more weight than the average well-intentioned audiophile with a soldering iron. There's an awful lot of bad information out there regarding Acoustats, and I've spent hundreds of hours battling it.
If I had any piece of gear already on the bench, I wouldn't hesitate to replace all electrolytic caps over 10 years old as a matter of course. I agree that modifications to the power supply for the bias circuit are highly dubious such as different power cords, but I see "audiophile" power cords recommended for that application which I can't possibly see any benefit in.
Hey there, I got some new panels for my 33's so that issue is resolved, but another has now cropped up with my tnt-200....
I figured since I had everything apart I would zero the offset and adjust the bias current on my TNT-200 before I put everything back together...Offset was nominal in both channels, but I am reading 0ma on both channels when measuring bias current (?) Adjusting either channels bias trim pot doesn't affect the reading. I tried on two different multimeters, with the same result....Am i missing something easy or is there an issue with my amp now? It was passing audio fine when I pulled it.... are there any other test points for bias I can check besides the fuse holders, or an alternate procedure for checking the bias that I'm not aware of?
I figured since I had everything apart I would zero the offset and adjust the bias current on my TNT-200 before I put everything back together...Offset was nominal in both channels, but I am reading 0ma on both channels when measuring bias current (?) Adjusting either channels bias trim pot doesn't affect the reading. I tried on two different multimeters, with the same result....Am i missing something easy or is there an issue with my amp now? It was passing audio fine when I pulled it.... are there any other test points for bias I can check besides the fuse holders, or an alternate procedure for checking the bias that I'm not aware of?