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Old 1st June 2018, 09:22 AM   #2001
morrism is offline morrism  United States
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I found a discrepancy between my board and the schematic. The board has a 4.7uF capacitor, the schematic shows 47uF. Perhaps a revision? What value should I use?
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Old 2nd June 2018, 11:04 PM   #2002
AcoustatAnswerMan is offline AcoustatAnswerMan  United States
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Quote:
Originally Posted by morrism View Post
I have removed the panel and interface from my spectra 11. The board has been cooked!. Is this from cranking them too much, or using the wrong type amplifier, or? The speakers still seem to be working OK.

1. As found. The 10ohm 20W has cracked open. It measured 11.9 ohms.
2. The backside of the board.
3. I re-mounted the inductor and glued the piece of broken ceramic with heatsink epoxy. The electrolytic caps are labeled for those that want to replace them.

Are there any recommended upgrades? I was thinking of bypassing the 2 crossover caps with some small (5uF ?) film caps.
Yes, it might be a good idea to ease-up on the applied power. The heat damage shown is fairly common on the Spectra 11: I had the same problem on my Spectra 1100. I replaced my resistors with metal-bodied resistors and bolted them to the inside of the chassis metal to act as heatsink. Short lengths of wire connected the new resistors to the board.

Unfortunately, there's not much that can be done about the coil. It has a specific inductance and resistance that would be difficult to replace unless you custom-wind one. (or used one of the same inductance and lower resistance, and made up the resistance with a series resistor).

There may be some value in bypassing the 100-uF and 150-uF electrolytics with a quality film cap. There'd probably be greater value in bypassing the 100-uF, as that's the one that feeds the ESL portion (the 150-uF is in the woofer crossover). Don't mess with any of the other caps unless they are faulty.
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Old 2nd June 2018, 11:10 PM   #2003
AcoustatAnswerMan is offline AcoustatAnswerMan  United States
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Quote:
Originally Posted by morrism View Post
I found a discrepancy between my board and the schematic. The board has a 4.7uF capacitor, the schematic shows 47uF. Perhaps a revision? What value should I use?
There were different revisions of the Ultrasonic Power Supply, and the value of that cap did change. Your schematic shows the final version. If you have the final version, it should be 47-uF. The final version can be identified by a wire wrapped around (not electrically connected to) the red wire exiting the air core high voltage transformer.

If you don't see that feature, leave it at 4.7-uF. As long as your speakers works okay, it doesn't matter which version you have. BTW, there were several changes involved between early and final versions of this circuit, not just the one capacitor.
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Old 9th June 2018, 12:19 AM   #2004
Daudio1 is offline Daudio1  United States
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Quote:
Originally Posted by morrism View Post
I have removed the panel and interface from my spectra 11. The board has been cooked!. Is this from cranking them too much, or using the wrong type amplifier, or? The speakers still seem to be working OK.
...
Are there any recommended upgrades? I was thinking of bypassing the 2 crossover caps with some small (5uF ?) film caps.

I scrapped out my old 1100's and have the 2 Interface modules and crossover assemblies available. I replaced my old burntout inductors with some massive Alpha-Core bobbins pretty close to original value. Worked out pretty well for a long time until the woofers burned out due to an unrelated problem.
The interface module is upgraded with big Solen PP caps on the input and a heavy speaker level input wire & binding posts, for bi-amping. Maybe more mods ? it's been a while
Think that might work for you ?
Dave
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Old 9th June 2018, 08:55 AM   #2005
morrism is offline morrism  United States
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My spectra 11 boards are working. I replaced all the electrolytic caps and the power resistors. The only mod was adding a bypass cap to the 100uF crossover cap.



Thanks for the offer for replacement boards, but I'm good for now.
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