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.
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.
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
Hello there! I recently purchased a pair of Spectra 11s, and am trying to get the bias set properly. After testing and replacing many of the big main resistors, I'm only able to max out bias at 55V on one speaker and 70V on the other with the pots at maximum. I used the test probe method of connecting the + to the red wire input, and the - on the ground lug attached to the outer housing, as you mentioned. The opamp and transistors seem to measure okay. Can't figure out whats going on with the low bias on the one speaker! Thank you very much for any suggestions!
Hi Andy I saw your other site -fantastic I just bought a used set of spectra 11s where do you think the best placement in a living room for these things is? (distance from wall walls etc-im going to use them for music and home theatre) I also have a good quality subwoofer and I have not read anything about calibrating subwoofers with electrostatics -what frequency etc I am running a modern Marantz pre amp which has the Audessy mic calibration function but I'm concerned the way it pumps the drivers when it calibrates the systems on setup might damage the speaker anyway any advice would be helpful
Room placement is often controlled more by the particular room and other furniture than it is by any hard and fast rules. Generally speaking, a good starting place is to place the speakers 2-3 feet from the rear wall. The distance between speakers should be approximately the same as the speaker-to-listening position distance. In other words, an equilateral triangle. Toe-in the speakers so that they face the listening position. After that, it's a matter of adjusting the final position to get the sound stage you like (making sure left and right speakers are positioned correctly). If the room is rectangular, try to have the speakers firing along the longer dimension. All of this is subject, of course, to other factors having more to do with Domestic Tranquility than sonics.
I have no experience with subwoofer calibration systems. If possible, do it at a low level to avoid any possible damage to the speaker from continuous tones. Crossing over at about 80 HZ would be a good start. Be patient with the process, as it often takes a while to get the proper balance between subwoofer and main speakers to suit all conditions.
Based on those voltage measurements, I assume you are using a multimeter to measure the voltage. Does your meter have a 10-Megohm or greater input impedance? If it's lower, you will read a voltage lower than the instructions specify, due to the meter loading the circuit.
You may need to upgrade the bias power supply. Early Spectras sometimes had an issue with the bias supply, which is easily remedied. I can post instructions if necessary.
To determine if you need the upgrade, look at the square-ish, air core transformer mounted on the PC board. A red wire exits the top of this transformer. Do you see another wire wrapped around the red wire? This wire is not electrically connected to the red wire - it serves as a feedback "antenna" for the bias oscillator. If you don't see the wire wrapped around the red wire, you need to upgrade the supply (easy to do with commonly available parts). Let me know if I need to post the instructions (which are not handy where I am right now).
If you DO have the antenna wire, you may have an issue with either the HV diodes or the HV caps in the bias multiplier. Report back and we'll go from there.
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Thanks for the reply! I've been dying to get these adjusted properly. Mine are apparently older and do not have the upgrade. I don't know what I need to do for it. I've been going through and testing parts, including solder joints, caps, resistors, opamp, transistor, but haven't found the problem. I had to replace the big power resistors on both. I haven't yet tested the small value resistors yet, or the section with multiple rectangular diodes and ceramic caps, but they look okay with no burn marks. My meter is 10Meg ohm impedance. I even tried a new trim pot, and that didn't work.
I wouldn't waste any further time in looking for bad components. Your bias supply needs to be upgraded. There is a 90% or better chance this will fix your problem. See post #1861 on page 187 of this thread, where I posted all the necessary documents to perform the upgrade. Please report back with your results!
Well, I did the bias supply upgrade. One turned out great. Easily adjusted to 75V measuring the way described. The other... Stuck at 59 maximum bias adjustment. Grrr! I don't know what to do next with the lowbias board. I even tried swapping opamps, no difference. What am I missing? I even tried a new trim pot. Didn't help. Thanks!!
I had a low bias issue with my Spectra 22's several years back. Here's a link to that thread, my summary is in post #34. Maybe something there will be of assistance to you.
