On Sep 6, 3:10*pm, John Byrns wrote:
In article
,
*Andre Jute wrote:
Time to return to tech-talk.
In a modest-sized room (by horn standards anyway) I want to rig up a
singleton of my modded semi-Fidelio bicor horns for Lowther PM6A. I
thought I'd do the monoing in a specially made 1 metre cable between
the CD player and the power amp.
The QUAD CD expects to see at least 10K impedance on its outputs.
Output of the CD player is 2Vrms and about 0.5Vrms of that is required
to drive the amp to enough power to handle the horns, so high value
resistors can be used in the monomaker if there is any advantage to be
gained.
However, the sound is NOT intended to be reprocessed as stereo
downstream (home installation, not studio); if I want stereo again,
i'll just plug in a stereo cable.
The pot on the integrated amp is probably (the board won't be here
until Tuesday and i can't read the spec on the piccie) 50K Alps but I
can replace it with a DACT of which I have a good selection of values.
So what value resistors would you use for monoing?
How many? Only two, or three?
With your choice of values, what can I expect to lose from the monoing
in bandwidth as distinct from gain?
Hi Andre,
I would use two 12k resistors, connecting one to each of the two outputs
of the CD player, with the other ends of the two resistors tied together
to feed mono amp. *I would place the resistors at the output end of the
cable to minimize phase shifts at the higher frequencies due to the
effects of cable capacitance, that is use a stereo cable right up to the
input of the mono amp where the mixing network is. *The loss with this
arrangement will be minimal, with a mono signal of 2Vrms from each
channel of the CD player, you will see 1.79Vrms across a 50k amplifier
input resistance.
--
Regards,
John Byrns
Surf my web pages at, *http://fmamradios.com/
Thanks, John. I have a couple of 15K resistors in my junkbox, so I
think I'll use them, at the power amp end of the cable -- good tip
that. I don't see that it matters if the output impedance is 7K5 as
there is no cable-length to drive. More on the amp when the
installation is finished.
Thanks to all who contributed.
Andre Jute
Visit Jute on Amps at
http://www.audio-talk.co.uk/fiultra/
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