Parasound A51 buzz/hum

[MichiganMike]

Currently with only speaker outputs and power cord plugged into the amp there is no noticeable hum present on any of the other channels.
However with my ear right on the front of the speaker i hear a hiss from the tweeter and what sounds like a very low hum from the mid ranges. (THIS IS NOT LIKE THE PREVIOUS PROBLEM AND IS A HECK OF A LOT QUIETER). This is on all channels.
Is this normal? I am using polk rt800i speakers. Is this just cause they are highly efficient?

I have a Parasound A21 and A51 connected to Von Schweikert speakers. With my ear very close to drivers I also hear low level hiss from the tweeter and hum. I agree with Glen B that this appears normal with reasonably efficient speakers.

[thejck]

I have a Parasound A21 and A51 connected to Von Schweikert speakers. With my ear very close to drivers I also hear low level hiss from the tweeter and hum. I agree with Glen B that this appears normal with reasonably efficient speakers.

thanks for all your help guys...
is there any way to clean this very low level noise up with some kind of power conditioning?

what causes this hiss? will it be different at different times of the day depending on what is found in your electricity? Does the presence of DC voltage in your electricity do anything to aggravate lessen this hiss?

[Glen B]

I mentioned the cause of the hiss in post #43 above. What you're hearing is thermal noise, caused by the thermal agitation of electrons. It is a natural phenomenon. This noise will be present to some degree in the finest amplifier designs and cannot be entirely eliminated. It is not DC offset related. DC only causes transformer core saturation and mechanical noise. I reiterate, as long as you can only hear hiss with your ear right up to your speakers it is NOT a problem.

The hum is likely some residual 60Hz supply noise, again not really an issue if you have to place your ear right up against your speakers in order to hear it. I run my main system on balanced power and found that it has all but eliminated such extremely low level hum. The thermal noise remains, as I expected it would.

[Peter Nielsen]

I mentioned the cause of the hiss in post #43 above. What you're hearing is thermal noise, caused by the thermal agitation of electrons. It is a natural phenomenon. This noise will be present to some degree in the finest amplifier designs and cannot be entirely eliminated.

All but one: TacT Audio solves this problem by letting the volume control alter the output rail voltage. Sure, if you turn up the volume to max, the hiss is there just like in any other amp, but as you gradually reduce volume, the hiss is reduced by the same extent as the output voltage goes down. A great solution to an old problem, but it only works for digital amps.

[Glen B]

That's interesting. I am not intimately familiar with the TacT Audio products, but yes, I am aware that thermal noise can be reduced in the digital domain. My comments above though were in reference to your typical analog amp.

[Peter Nielsen]

That's interesting. I am not intimately familiar with the TacT Audio products, but yes, I am aware that thermal noise can be reduced in the digital domain. My comments above though were in reference to your typical analog amp.

You could view the residual background noise as a voltage "leak". The higher the output rail voltage is, the harder it is to keep the "leak" at low, inaudible levels. Yet, the rail voltage determines the maximum peak power of the amp. This is why it's more difficult to make high-watt amps quiet.

TacT solves this by letting the volume control alter the voltage of the output rails. They simply let their DAC operatate at full "volume" and full bit depth all the time, and the voltage set at the output rails will determine the final power output. In effect, the volume control will adjust the output wattage of the amp.