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I recently purchased the Teac AP701 power amplifier. The Hypex modules it uses, while not SOTA, appeared to have audibly transparent performance. The Teac is connected to the pre-out of my Yamaha Integrated (RN800A) with a no-frills RCA cable. I noticed that when nothing is playing, there is a low level hissing and buzzing noise coming from the mid-range/tweeter (KEF uni-Q) driver. It is not terribly loud, but clearly audible if I put my ear about 6 inches from the tweeter. The combination of hiss and buzz makes it sound a bit nefarious. Here are a few observations and things I tried to identify the source of the noise:
- In order to disentangle the effect of the Yamaha preamp, I disconnected the Yamaha and tried listening with only the power amp connected to the speakers. This reduced the overall volume level of the hiss so that I needed to be about 3 inches away to hear it well. Also, the noise consisted mostly of a low level hiss and the buzzing was either no longer there or very very faint.
- I tried listened to the speakers connected directly to the Yamaha (using the Yamaha's internal power amp) and now the hiss was so low that it was only faintly audible with my ear right up against the tweeter.
- I tried plugging the Teac and Yamaha into different sockets and different surge protectors, but this had no effect.
- Changing the volume level (when testing Yamaha->Teac->speakers or Yamaha->speakers) did not affect the noise level. I did hear a faint clicking noise that occurred when I changed the volume level up or down, but assume this is normal.
- Changing the inputs from CD to USB DAC (when the Yamaha was in the chain) did not affect the noise level.
- Changing the RCA cable to another (slightly less cheap) cable did not affect the noise level.
- Is the relatively loud hiss + buzz I hear when I drive the Teac with the Yamaha harmful in any way to the speakers?
- If the answer to 1 is no, and I can't hear any noise from my listening position (given that the noise does not seem to increase with volume), do I have nothing to worry about?
- Given that the hiss is louder when the speakers are connected solely to the Teac compared to when the speakers are solely connected to the Yamaha, does this indicate that the Teac has a higher noise floor than the Yamaha? If so this is a bit surprising to me as I expected the Teac to perform better. Or is it possible that my unit is defective?
- Given that the noise is at its worst when the Teac is plugged into the Yamaha, does this indicate that the two are not a good pairing (assuming the Teac is not defective)?
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