I am trying to construct an audio device that will split a stereo
incoming signal in two so that I can have "quadrophonic audio," IE the
left signal coming out of two speakers and the right signal coming out
of two speakers.

In the interests of protecting my pre-amp I want to insert a diode
into the signal path to prevent current from returning to the pre amp.
 My question is if I insert a diode into an audio signal path what
happens to the audio signal.  It is my understanding that diodes have
about a .7 volt drop even when the signal is flowing from the cathode
to the annode.  Will this voltage drop cause my music to be reproduced
'flat?' or will it just result in a slight volume drop.

Thank you.

Hello Sam,

I wrestled with answering your question, but decided I might be better
able to help with unqualified and unresearched comments, especially
since no researcher has yet fielded the question for you.

Note, I have 30 years in the consumer and pro audio business.

1. As a general rule, you can Y out of almost anything (power amps are
an exception) but almost never Y into something. Therefore, for what
you describe, a diode is not needed. The input impedance of your power
amps will not load the outputs of your pre-amp unduly and there is no
risk of current returning through the input of the power amps to the
output of the preamps.

2. This will not resemble either quadraphonic nor surround sound.
Surround uses rear channels for effects and ambience - to add the
sound and reflections of the environment something was recorded in.
what you will have here is two stereo systems which may not sound as
good as just two speakers due to room cancellations that may occur
with identical signals front and rear.

The only time I ever used a system such as this was to "wash" a dance
floor for disco so that there was a stereo effect almost anywhere on
the dance floor.

3. All electronic components have a sound. Whether you would be able
to hear a diaode in the signal path or not depends a great deal on the
associated equipment and just how good your ear is.


4. Although I do not know for sure, I would be very sursprised if the
voltage drop across the diode was as agreat as .7 V. That seems very
high to me.

5. If you REALLY want to do what I think you do, there were two pieces
manufactured for just this purpose. One was by Dynaco and the other
Carver. They were intended to create phantom rear channels from stereo
systems. The Dynaco unit was only $35 retail and I have forgotten
details on the Carver. You might check Ebay.

I hope this is somewhat helpful for you.

Regards,

-=clouseau=-
Google Answers Researcher

At best, diodes will radically change how music and speech sound. My
guess is your audio peak voltage is less than .7 volts, so a diode
will not pass a significant amount of audio. Even if the peak is 2
volts, the softer parts of the music will be lost. You might put two
diodes back to back in parallel across the source. This will prevent
the peak to peak voltage from exceeding .7 volts, otherwise diodes are
not useful for audio splitting. Instead of diodes try a 100,000 ohm
variable resistor in each input line. Start at maximum resistance and
measure the input voltage both ac and dc as you reduce the resistance.
Anything over about 1/2 volt may damage the input circuit. Most
amplifiers are protected and can tolarate lots more input without
damage, but you may have an exception. You will probably find you do
not need any kind of splitter net work as clouseau suggested.
 Some kinds of diodes drop only .2 volts at low current, but these
will also  be unsatisfactory in my opinion. Most diodes drop about .5
volts at one micro amp, .6 volts at one miliamp and .7 volts (or more)
at one amp. The input to your preamp is likely somewhat less than one
milliamp ac. There should be negligible dc voltage or current, but
small amounts may not be harmful.
 clouseau is correct; splitting will not produce true 4 channel sound,
but you may find the results pleasing. You can adjust the effects of
room cancelling with tone controls and by moving one or more speakers
and/or adding drapes and other sound absorbing material. Some (most?)
people find some room cancelling sounds good.   Neil