I own a pair of quad 63s. I bought a 90 wpc tube amp and the sound is fantastic except....the clamp board now activates at high frequencies, sopranos singing for example, and at what was previously moderately loud volume.
Is there a reason why my ss amps don't activate the clamp but the tube amp does?
Is there a reason why my ss amps don't activate the clamp but the tube amp does?
My guess would be that your tube amp may be unstable driving capacitive loads at the higher frequencies resulting in peaking or oscillation that is triggering the clamp circuit.
What tube amp are you using?
Do you have the ability to run a frequency response curve on the output while it is driving the ESL?
If the 63s do not have the latest protection boards in them OneThingAudio can supply them. I've no affiliation, just a happy customer with some 63s in as-new condition...
Like bolserst says, instability may be triggered by low input impedance at high (or supersonic) freqs. Try putting an inductance in series with speaker leads, just to test. Almost any old coil, even a cone speaker voice coil (in situ) might be about right, from one of those old fashioned crossovers, or wind your own .1mH. Long term, you might see if .05mH sounds OK and removes harm.
It might simply be cutting input to speaker, but worth a try to test.
Adding a 1-Ohm resistor might work as well but screw up the freq response... so not good for permanent application. 100 watt light bulb cold might be in the ballpark.
Ben
It might simply be cutting input to speaker, but worth a try to test.
Adding a 1-Ohm resistor might work as well but screw up the freq response... so not good for permanent application. 100 watt light bulb cold might be in the ballpark.
Ben
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From memory (terribly unreliable) I think the 63s hit about 2 ohms at about 10KHz... That can be challenging for an amplifier.
There are two different clamp board designs as noted above. Sometimes the older unit can be pretty touchy, and can clamp early. The later stacked diode bridges and zeners seem to be more rugged and less likely to trigger early.
Is it one speaker or both? I've had speakers in for repair that one clamp board triggers early. The arcing protection portion of the board (that uses an antenna to sense arcing) can get pretty sensitive. It uses an NPN transistor which is biased up by a diode, and as the diode and transistor age, the circuit seems to get quite sensitive occasionally. I have never dug into the mechanism for why the transistor turns on so early, I just replace the parts...
Sheldon
Is it one speaker or both? I've had speakers in for repair that one clamp board triggers early. The arcing protection portion of the board (that uses an antenna to sense arcing) can get pretty sensitive. It uses an NPN transistor which is biased up by a diode, and as the diode and transistor age, the circuit seems to get quite sensitive occasionally. I have never dug into the mechanism for why the transistor turns on so early, I just replace the parts...
Sheldon
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