Unichannel Bi-amping
darrel...@yahoo.com
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Date: Mon, 24 Apr 2006 09:22:17 -0700 (PDT)
Subject: Re: "unichannel bi-amping"(?)
John,
The arrangement you describe is typical of
vacuum tube amplifiers with output transformers,
or the McIntosh transistor amplifiers with output
transformers. So a pair of custom transformers
with 8-ohm inputs and one 8 ohm output could also
accomplish the same thing for any exsting stereo
amplifier. They would work because two stereo
outputs from the existing stereo amp would excite
the input coils of the transformers which would
have to be in a combined core with one coil
output, your mono bi-amp output. It could also be
done, in a way, with a unity gain "power booster"
circuit where the input transistors feed into a
mono output transistor output, sorta like the old
car power boosters of 20-30 years ago but like
the transformer approach there would only be one
channel output, to suit the customers requirement
of course.
The bad news is that the music in both of the
above circuits would have to contain higher
distortion than the incoming signal, maybe
objectionable enough to not use it. Also there
are losses in both processes if input and output
must have the same frequency response.
The good news is that all the stereo power from
both channels would be converted into a single
channel can ALSO be converted into any desired
narrow frequency band for much greater gain.
Altho everyone focuses on the combined channels,
there is another advantage in gaining power
output this way, the output can be a narrow
frequency band like 20-150HZ. Since in a
transformer, the area under the curve of the
power input must equal the area under of the
curve of the power output, once the the frequency
is intentionally limited in the process itself,
then the gain or power must rise to a level to
equal it. That's how the coils in radios work. So
in this case, 50 watts of audio input at
20HZ-100K Hz might have 100 watts of output at
just 40HZ-100HZ even considering the losses. And
since distortion works by including a percentage
of frequencies/amplitudes not in the original,
having such a limited frequency response, like
40-100K, might actually have LOWER distortion
than the original. That's because there are so
few frequencies being amplified.
As you can see, good engineering is the good
excercise of compromises 'cooked' in such a way
as to produce a new result that we did not enjoy
before we started.
But really its much easier just to put a load
resistor of any kind across the speaker output
terminals of the undesired odd stereo channel. 50
ohms resembles a speaker's coil resistance that
would not produce much audible power if you had
such a speaker, say one or two watts. So a 5 watt
resistor suffices here, but many others would
work as well. Say 1000 ohms at 1/2 watt, that
sort of thing. The main reason is to prevent that
stereo channel from amplifying anything using
real electrical power. (Ohms Law)
Thanks for the info on the bi-amp 'converter you
described!!
Darrell Lakin
3174 South Shore Drive
Smithfield, VA 23430
.
--- John <jb...@ix.netcom.com> wrote:
> I seem to remember an external circuit that one
> could use to drive a
> stereo amp as a Bridges mono one. If I
> remember correctly you apply
> the same input signal to both channels and then
> wire the outputs
> together so that you take the Negative terminal
> of the A channel to the
> Positive terminal of the B channel. Then you
> attach your load to the
> positive and negative outputs that are left
> over. Now I have never done
> this. but I do remember reading about it a
> long time ago. I do not
> know if this will work with every amp on the
> market. I am sure that
> some one out there more knowledgeable than me
> can shed some light on
> this.
>
> HTH
> John
>
>
>
>
>
> Rodrigo VN wrote:
>
> >ALEX escreveu:
> >
> >
> >
> >>Theoretical question: Is there any danger
> of destroying a power amp
> >>if you only use one channel to drive a load
> (with NO load on the other
> >>channel)?
> >>
> >>
> >
> >No.
> >I'd like to put a shorted rca plug into the
> non-used input... paranoia...
> >
> >
> >
> >>Second question: Would there be any
> advantage to using just one
> >>channel (I can't mono this amp) of each of
> two identical power amps to
> >>drive a pair of Mag SMGas? Thanks, Alex
> >>
> >>
> >>
> >If the power supply is common to the both
> channels, you will have a best
> >reserve power to the music stronger peaks.
> >If there is two separated power supplies for
> each channel, no
> >differences at all.
> >
> >[]s
> >RVN
> >
> >
>
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> >
> >
> >
>
>
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