mre28m5
5 posts 12-05-2017 2:45pm
About a year ago I was experiencing system symptoms virtually identical to those the OP has described. At some point after much thought, frustration and experimentation, I replaced my speaker cables and the harshness disappeared.
30 feet of Monster Cable or 12 gauge TW cable from the hardware store will be an easy and inexpensive experiment. Hope this helps.
almarg
7,718 posts 11-27-2017 4:21pm
I don’t know what the capacitance per unit length of OCOS speaker cable is, but given that your cable is fairly long and given also that OCOS is a somewhat unconventional design a possibility that occurs to me is that its capacitance might be causing an ultrasonic oscillation in your amplifier. And perhaps the condition is sufficiently marginal that minor aging effects or perhaps even a change in AC line voltage have put it over the edge.
If so, the volume dependency you mentioned might result from the speakers being stressed to a greater degree when an oscillation and a high volume audio signal are both present.
So I would suggest trying different speaker cables, whenever that may become practicable.
Good luck. Regards,
-- Al
almarg
7,718 posts 11-28-2017 11:03am
Kosst, I assume that I was not included among those to whom your last comment was addressed, even though it mentioned cables. But to further clarify my comment about the OCOS cable (and Peter, thanks for the second): As you may be aware there are a few speaker cables which have ultra-high capacitance, such as Goertz and the old Polk Cobra cables. When used without a Zobel network, and especially when used with solid state amplifiers, those have been known to cause ringing and/or oscillations, and in some cases oscillations which have even resulted in severe damage to the amplifier.
After doing some research I have not been able to find an indication of the capacitance per unit length of OCOS, but it is an unconventional coaxial design having an extremely low "characteristic impedance" of about 8 ohms. That suggests a strong possibility that its capacitance is very high.
On the other hand, I would expect that the not especially extended 100 kHz bandwidth of the amp, and the relatively modest amount of feedback I believe it uses, lessen its susceptibility to that kind of effect. But it should be easy enough to rule this possibility in or out, perhaps even by using Home Depot or Radio Shack wire for purposes of the experiment, if the OP doesn’t have any other cables of suitable length on hand.
Your suggestions about the amp are of course also good ones, IMO.
Regards,
-- Al jwpstayman
248 posts 11-28-2017 4:44pm
OCOS cables are pretty old ( around 1997 or so). If I remember correctly, they were designed with OCOS standard terminators (Red), but when used with dome tweeters or a speaker with a rising impedance curve, they needed to have the HFC (Black - nobel) network installed on the speaker end in place of the Red ones. They also came in VERY specific lengths (9’10"/13’/16’6",etc) which I have to assume was a performance benefit or to correct a design/engineering issue. I would try and borrow some newer speaker cables and hear if that "fixes" the problem. Those OCOS cables might have oxidized over the years and/or the connectors might have issues. I also suspect that the Black HFC needs to be used for the Endeavor speakers. |
+1 Jim (Jea48). Although it may seem improbable, I would not by any means rule out the possibility that BOTH amps have succumbed to the very high capacitance of the speaker cables. Also, I would add the following to the quotes you provided, this one coming from a respected designer of highly regarded audio electronics and speakers: Pbnaudio 12-1-2017
My gut reaction to this is the very long, highly capacitive speaker wires are at least contributing to this. As someone stated above - try lamp cord. Best regards, -- Al |
Changing the amp made no difference. How about swap the preamp? |
At the risk of repeating myself, this appears to be very much a circuit focused group. It seems my earlier post intimating the problem of the “shrill top end” could be *something else entirely,” something out of the blue, was taken down hard. You know, the suggestion that the culprit could be unrelated to the audio system entirely, I.e., not (rpt not) the amplifier, preamplifier, cables, power cord, room acoustics, or even the house AC. It doesn’t have to be the amp or the preamp. And I am not referring to any of the issues in Vogue such as fuses, wire directionality, polarity, out of phase conditions, things of that nature. But something a little bit scarier. I’ll be watching with some interest to see how this thread plays out. 😀
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I am still surprised the OP has not at least tried swapping speaker cables with how cheap, quick and easy it would be to do....... |
