You can use 1 to 5 channels. It`s not neccessary to cap the unused inputs.
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That's what I'm doing at the moment. I have a pair of speakers biamped with a 5 channel power amp, with the full blessing of the manufacturer. You simply don't use what you don't need. No need to cap anything.
Also, if the multichannel amp uses a single power supply, particularly if it is not especially large, the amp might actually sound better the fewer channels you use. You would have fewer channels drawing the available power from the common power supply.
A long time ago all amps liked to see a load connected. Maybe more true with tube amps than SS. Today seems to be a different story. I sometimes use a HT receiver with an external amp so that none of the receiver's amp channels are in use. Some think it sounds best when the power supply isn't taxed so heavily. Makes sense to me. And it neither urban nor legend.
For optimum results, unused channels should have their inputs shunted with a reasonably low value resistor ( 100 - 500 ohms or so ). The unused output stages of those channels should also be shunted. You can use the same value resistors as you used on the inputs, so long as they are at least 50+ ohms ( at minimum ) and rated for a minimum of a 1/4 watt of power.
Shunting the input resistively shuts down the potential for the input stage to pick up RFI and / or EMI based noises. Otherwise, once these noises were picked up, they would be fed into other stages of the amp. Not only could such noise cross-contaminate the channels being used, such an occurance could either send the "unused" channel into oscillation and / or produce output power. By "closing" the input via the shunt resistor, that path into the amplifier via the unused channel is effectively stifled.
Shunting the output with an impedance much higher than what the amp would normally see with a speaker presents a load to the amp whether it needs it or not. Many amps DO produce low level leakage with / without a signal present. As such, the resistor acts as a load and helps to stabilize that channel and potentially extend the life of the associated circuitry. By using a higher value resistor, current flow is minimized and a high powered resistor isn't necessary.
From an electrical standpoint, one can only gain from such an approach. From a sonic standpoint, the benefits will vary with the environment that the gear is in and the design of the gear / system itself. From a monetary standpoint, it may help to preserve your investment in a multi-channel amp.
If you are even reasonably handy and not afraid to do basic DIY, shunting both the inputs and output stages of quite a few unused channels of an amp shouldn't set you back more than $10 at most. This is based on RCA / single ended shunts, as XLR / balanced connectors cost significantly more. In most designs, shunting either the RCA / XLR inputs will achieve similar results, so there's no need to do both at the same time. Sean
Tripper, this has ZERO to do with having a load connected. The inquiry was about the efficacy of capping unused inputs.
Sean, the only input that will benefit from a shunted input is a phono input. The RFI/EMI interference often posited has as much scientific grounding as a Santaria ritual. The only missing ingredient is the chicken blood.
How much of a difference is either audible or measurable will depend on the design of the amp, how much internal cross-talk it demonstrates from channel to channel ( primarily due to poor circuit layout and / or internal cable routing ), the ability of the circuit to reject extraneous noises ( due to poor shielding and / or microphonics ), etc... These are all real factors that are both audible and measurable. Resistively shunting the input can only help this situation and lessen the potential for them to occur.
IF any of the above were to take place within the amp i.e. signals being induced into the early gain stages of an amp, it is the very nature of the circuit to not only amplify these signals, but to try to output them to a load. If there is no load, the output devices themselves and any loading circuitry inside the amp would have to absorb that energy and dissipate it as a slightly higher level of heat.
The level of heat and / or "abuse" that the output circuitry has to undergo in such cases is typically minimal with most well designed SS gear, but many circuits aren't "well designed" and / or built with quite as much precision as we would like to think. This goes for both inexpensive and quite costly products alike. Having said that, the mass majority of tubed gear should never be run without a load on it.
As such, using the approach that i mentioned above can only help the situation / put one's mind at ease / help the longevity of the gear / potentially improve sonics. NO, it is not "necessary" by any means and NOT following this procedure won't destroy your multi-channel amp beyond usability should you choose to not shunt the inputs and / or the outputs.
Having said that, i've always thought that the goals of most people frequenting this forum were to achieve the highest levels of performance from their gear / installation that they can. As such, i tried to provide some simple and reasonably inexpensive tips that i thought might apply to the subject at hand. Sorry if i offended anyone and / or presented my opinion as being anything other than my opinion. Sean
I tried to explain how signals could enter the unused channel(s) through extraneous and / or internally generated sources. I also tried to explain that most amps do generate "leakage" from their output stage on their own, albeit very small quantities most of the time. This is why i suggested resistively shunting both the inputs and the outputs as it completely isolates and protects the unused channel(s).
As a side note, using a resistive shunt on the input will not have any potential side effects compared to simply shorting the unused inputs. Using this method of resistively shunting unused inputs on a preamp can also be used to varying levels of success. In some cases, directly shunting or "shorting" the unused inputs on a preamp and / or power amp can result in sonic degradation. This has to do with poor isolation of each input i.e. higher than desirable levels of cross-talk, etc... Sean