Unecpected and not understood tweek - help?

Contact Musical Fidelity with the same question you posed to us. They may be able to give you a better answer or at least a faster one.

If I understand correctly, you are saying that the sound when listening via speakers is affected by the connection of the V-CAN to the Krell's tape outputs.

Does that occur with the V-CAN turned on, or turned off, or both? I would not assume that its input impedance is 25K when it is turned off, and conceivably when it is turned off its input impedance might vary somewhat with signal level, leading to unpredictable effects.

Also, are you sure that the output impedance of the Krell's tape outputs is 47K? That sounds very high for an output impedance, and sounds typical of an input impedance. If the output impedance were really that high I would think it would tend to minimize or eliminate any effects on the amp's main signal path of what is connected to the tape out jacks.

I don't think it is possible to say much more than that without having more information on the design of the Krell's tape output circuit and how it relates to its main signal path.

Regards,
-- Al

Al, thanks. Yes, when listening through the speakers the sound is affected with the V-CAN connected to the tape-out. The V-CAN does not have a power switch and is on constantly. As far as the the Krell's impedance goes, I know the input is 47K but as far as the tape out I guess I'm not sure. This I do know, powered on or off, with the V-CAN connected to the Krell, the amplifiers hyperactive nature seems to be a bit calmed down.
Rpg

OK, well then I would suspect that the output impedance of the tape outs is much less than 47K, and also that the tape outs are not driven by separate buffer stages that would isolate the main signal path from what is connected to those jacks.

So perhaps the cable capacitance and/or the 25K loading are interacting with the main signal path to produce the effects you are describing. Cable capacitance, to the extent that it may have any effects at all, would figure to affect mainly the upper treble, and to attenuate it slightly, which would seem to correlate with your mention of reduced edginess.

It's hard to formulate a more precise explanation without having detailed information on the design of that part of the Krell's circuitry, but it does seem very conceivable to me that the effects you are perceiving are real.

Best regards,
-- Al

Al,

If the front end source is a CDP, and basically the tape out jacks of the amp are connected in parallel with the CDP output, would that be causing the difference in sound Rpg is hearing? The output of the CDP is being affected.

Al, thanks. I guess potential flaws with the Krell tape-out and the impedance of IC's and V-CAN ended up as a good thing. In the end, I now have a headphone amp and a better sounding system to boot!
Rpg

If the front end source is a CDP, and basically the tape out jacks of the amp are connected in parallel with the CDP output, would that be causing the difference in sound Rpg is hearing? The output of the CDP is being affected.

Hi Jim,

Yes, that's a possibility if there is no active circuitry or significant resistance between the Krell's cd input and its tape outputs. That is the case with at least some designs (I believe that my Mark Levinson ML-1 has nothing between its inputs and tape outs other than wires and switches), but I suspect that most designs are not like that.

Rpg -- Enjoy!

Best regards,
-- Al

Jea48,
Yes, the source is a CDP and occasionally a Tuner. Regardless of my input source, primarily CDP, the positive affects of having the V-CAN connected can be heard. Mind you, it's not Earth Shattering, but it does calm down a bit the trademark Krell sound, it's less hyperactive and a bit warmer. Even if I didn't listen to headphones, the inexpensive (and sounding inexpensive) Musical Fidelity connected to my tape-out turned out to be an affective tweak.
Rpg