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In Reply to: RE: MGIIIa's up and running posted by neolith on February 06, 2012 at 13:01:35
neolith wrote:
"Before going to an attenuator resistor, I would recommend the 10 uH choke. It may tame your tweeters and also give you better resolution.
I have an LP of Trevor Pinnock's Goldberg Variations on the harpsichord that was recorded in 1980 and it is one of my favorites."
I think 10 µH is not doing very much until above 40 kHz.
Roger Gustavsson
Follow Ups:
I applied the 5522 chokes and have to say that the effect is positive. It does tame the high end a bit. but without seeming to give up much if anything. Smooths the whole presentation offered by the IIIa's.
Also, prior to receiving the chokes, I experimented a bit with the jumper. When I first hooked them up I used a simple piece of 10ga copper wire. Switched to the 1.2 ohm attenuator resistor just to see what would happen, and that suppressed the highs too much. Then, I tried the Magnepan steel jumpers, they were less bright than the copper, and introduced what I would describe as "grit" - didn't like 'em. I also have some 5502's that I can monkey around with just to see what they will do. As some have observed, paralleling them provides more options.
With the chokes, I can run the system a bit louder which helps wake up the bass a bit. Overall, an improvement.
Thanks for urging me to try this!
In terms of attenuating audio frequencies, you are right, as the fc for a 10 uH coil into a 4 ohm load is ~63 kHz However as, the late Al Sekela pointed out, RFI seeping back into the amplifer can cause stridency and harshness to the upper end.
On the violin: "Heaven reward the man who first hit on the idea of sawing the innards of a cat with the tail of horse."
Edits: 02/08/12
In some cases the poweramp sees a very low impedance at high frequencies, the red line of this diagram, dropping to 0.25 Ohm at 10 MHz:
http://www.lts.a.se/pub/artiklar/hogtalarkabel/karimp.gif
In can be cured by a suitable loudspeaker cable, one with a caracteristic impedance that matches well. A RC link at the end of the cable (or inside the speaker) and the amplifer sees the impedance of the blue line. Many amplifiers have a similar RC link (Zobel network) at their outputs.
Roger Gustavsson
Yes, indeed. The choke should raise the impedance at high frequencies but because of self-capacitance the high frequency behavior is far from ideal and an RC network across the leads is the way to go. I believe that is what the Walker High Definition links are.
BTW, I couldn't get your link to work.
On the violin: "Heaven reward the man who first hit on the idea of sawing the innards of a cat with the tail of horse."
Edits: 02/09/12
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