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Hissing buzzing noise from Hypex based power amp

Symphoniac

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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.
Given all this, I would love to pick resident experts' brains on the following questions:
  1. Is the relatively loud hiss + buzz I hear when I drive the Teac with the Yamaha harmful in any way to the speakers?
  2. 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?
  3. 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?
  4. 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)?
Thank you in advance for your comments and insights.
 
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XLR connections often carry a higher voltage signal then RCA connections, up to 4 volts against typically the 2 volts on an RCA connection. For the Yamaha to provide acceptable sound level you are turning the Volume up? If that is the case you are simply raising the noise floor from the Yamaha when connected to the Teac. Ideally you want a source with XLR output, or a source device that is quieter than the Yamaha.
The Buzz is most likely can be solved by moving the Teac away from the Yamaha and a different mains outlet. Maybe a DC blocker for the Yamaha
 
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.
Given all this, I would love to pick resident experts' brains on the following questions:
  1. Is the relatively loud hiss + buzz I hear when I drive the Teac with the Yamaha harmful in any way to the speakers?
  2. 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?
  3. 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?
  4. 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)?
Thank you in advance for your comments and insights.

My guess - the hiss is the inherent noise floor of amplifier - either TEAC or Yamaha. As you point out the hypex module isn't SOTA, and one area of improvement in more recent designs has been in internal amp noise.

The buzzing (since it disappears when you disconnect the preamp) is most likely to be ground loop noise picked up across the unbalanced RCA interconnect (not a fault of the lead - just inherent to unbalanced connections if there is ground current). Also nothing to do with compatibility/pairing of devices. If you have a balanced option, using that will eliminate it. You could also play around with system earthing (including whatever source is in place) but that is a frustrating and often unsuccessful exercise - not worth bothering with for such low level noise.


Neither are dangerous to the speakers.


And if the noise is inaudible at listening position, you can safely forget about it. Most systems will have some noise if you put your ear next to drivers.


EDIT: I note your power amp has XLR in - you can make a pseudo balanced RCA to XLR cable as explained by @staticV3 here ("a better way")

 
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XLR connections often carry a higher voltage signal then RCA connections, up to 4 volts against typically the 2 volts on an RCA connection. For the Yamaha to provide acceptable sound level you are turning the Volume up? If that is the case you are simply raising the noise floor from the Yamaha when connected to the Teac. Ideally you want a source with XLR output, or a source device that is quieter than the Yamaha.
Actually, the noise level does not seem to be affected at all even when I crank the volume on the Yamaha preamp. Which runs counter to my newbie intuition, as I would have expected the noise "floor" to rise with increased volume. Would love it if someone can explain why this is the case. Is it because the noise when nothing is playing is different compared to when music is actively playing? For example, when I play a track that has tape hiss in the recording, I can definitely tell the tape hiss getting louder when I increase the volume, but I attribute this to hiss sound that is embedded in the recording, not the noise floor of my amp.

The Buzz is most likely can be solved by moving the Teac away from the Yamaha and a different mains outlet. Maybe a DC blocker for the Yamaha
By "different mains" do you mean a different outlet in the room? Just due to the way things are set up, I'm afraid I can't physically relocate the Teac too far from the Yamaha, but I can try testing it in a different/far location temporarily to see if that helps. I'm not too familiar with DC blockers, so will do a search here to read up on it.
 
My guess - the hiss is the inherent noise floor of amplifier - either TEAC or Yamaha. As you point out the hypex module isn't SOTA, and one area of improvement in more recent designs has been in internal amp noise.
I'm afraid you're probably right that what I'm hearing when the Teac is decoupled from the pre-amp is the inherent noise floor of the Teac, which is pretty disappointing given that the Teac is 3x more pricier than the Yamaha integrated, and the noise is so much quieter when the speakers are directly connected to the Yamaha. When I look at measurements of similar Hypex modules such as this Buckeye and compare it to measurements of the Yamaha RN1000A (assuming amp section is similiar or identical to the RN800A), the Hypex seems to have as good if not better SINAD... or perhaps I'm misunderstanding the data? Is there still a chance that my Teac is a lemon? I guess it also won't hurt to reach out to Teac to make sure what I'm hearing is expected behavior.

The buzzing (since it disappears when you disconnect the preamp) is most likely to be ground loop noise picked up across the unbalanced RCA interconnect (not a fault of the lead - just inherent to unbalanced connections if there is ground current). Also nothing to do with compatibility/pairing of devices. If you have a balanced option, using that will eliminate it. You could also play around with system earthing (including whatever source is in place) but that is a frustrating and often unsuccessful exercise - not worth bothering with for such low level noise.
Maybe one of those RCA to XLR cables will help? See my comment below.

Neither are dangerous to the speakers.
Thank you, this is my number 1 concern, so very good to know! The combined hiss and buzz just sounds pretty nefarious, so was worried it would damage the tweeters over a long period of time even though you can only hear it up close.

And if the noise is inaudible at listening position, you can safely forget about it. Most systems will have some noise if you put your ear next to drivers.
Yes, definitely inaudible at listening position, and music sounds great. Just a bit disappointed that I spent extra $$$ to get worse performance than the Yammie... but hey, VU meters! :)

EDIT: I note your power amp has XLR in - you can make a pseudo balanced RCA to XLR cable as explained by @staticV3 here ("a better way")

Thanks for sharing this link. I see that @staticV3 recommended this monoprice cable in that thread, which I understand is still not ideal, but is better than some other off-the-shelf alternatives, so I will give that a quick try. I'm not too handy/technical, so I'm a bit wary of trying to build my own cable, but may eventually try it.
 
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Which runs counter to my newbie intuition, as I would have expected the noise "floor" to rise with increased volume.
It means the noise you are hearing is inherent in the gain and output stage of the amplifier - after the volume control. It doesn't matter what the input signal is, or what the volume is - the noise is generated in the power amplification.
 
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
You normally need to short the inputs to the power amplifier to test for noise.
 
You normally need to short the inputs to the power amplifier to test for noise.

Thanks for pointing out. Does this mean that if I conduct a proper test with the inputs shorted, I might find different results, ie, more hiss with Yamaha compared to the TEAC? If so, does this help from a practical standpoint given that I won’t be permanently shorting the inputs for normal usage?
 
Ok... mate... The noise is low level that you can't hear unless you put your head next to the speaker. You're not going to be doing that for normal usage either.

Forget about it, and enjoy the music. ;)
 
Ok... mate... The noise is low level that you can't hear unless you put your head next to the speaker. You're not going to be doing that for normal usage either.

Forget about it, and enjoy the music. ;)

LOL, good point... I believe I was just hoisted by my own petard. :p
 
Thanks for pointing out. Does this mean that if I conduct a proper test with the inputs shorted, I might find different results, ie, more hiss with Yamaha compared to the TEAC? If so, does this help from a practical standpoint given that I won’t be permanently shorting the inputs for normal usage?
Sorry, I should have been much clearer.

But yes, it is quite possible that you "might find different results, ie, more hiss with Yamaha compared to the TEAC". I'll explain a bit later. But first I need to explain why you aren't quite right when you state "given that I won’t be permanently shorting the inputs for normal usage"...

Impedance Bridging is how modern HiFi is connected. The rule of thumb is that the input impedance of a device needs to be 10x higher than the output impedance of the device feeding it. For example, your TEAK has a stated input impedance of "64kOhm (in STEREO mode), 32kOhm (in BI-AMP mode). So in stereo mode, the output impedance of your (source) Yamaha Integrated (RN800A), must be 6.4kOhm or less. In practice, the specs seem to suggest it's 1.2kOhm which gives a ratio of 1:53, which is obviously several times better than 1:10!

The thing is, although 1.2kOhm is not zero, compared to the 64kOhm input impedance, it's much closer to zero! So we are very close to "permanently shorting the inputs for normal usage"! In other words, a short is very similar to a plugged in device and very unsimilar to an input with nothing plugged into it, which is why noise is always measured with the input shorted.

But what if you plug in nothing? Well the "output impedance" of thin air is a very large number of MegaOhms. This is way too high and completely breaks the impedance bridging rule: not only does it fail to meet (output to input) 1:10, it's not even 1:1, 10:1 or 100:1! You should NEVER plug thin air into a power amplifier! In practice, all designers put some impedance across the input of their amplifiers to handle inputs with no devices connected.

But clearly, they can't put a very low impedance across the input, otherwise the output impedance of the preceding device would have to be too low (see Impedance Bridging). So they compromise. That compromise is design dependent since it's a combination of this "protective" impedance and the input impedance of the first gain stage. And this is where things get tricky. Resistors at room temperature generate noise. The noise they generate is proportional to their resistance. A 1kOhm resistor has less noise than a 100kOhm resistor. So your 1.2kOhm output has less "resistor noise" than your 64kOhm input. In other words, as soon as you plug your Yamaha Integrated into your TEAC, you make the TEAC quieter! How much quieter depends on how the input of the TEAC is designed. Which is another reason why we always measure noise with inputs shorted.

But the consequence of all this is - two different amplifiers with nothing plugged in, may have very different noise behaviours. However, these differences will normally become significantly less when the inputs have a low impedance source plugged into them. The best way to reliably test this is with a short!
 
I don’t know if it is the same problem as something I experienced, along with some others, but I had a unique thing happen with my Hypex Amps.

I’ve heard this seemed to affect a group of folk also using a Speaker with an AMT, however this happened to me on a 2-way standmount design with a Morel Silk Dome Tweeter.

Upon power-on, a hum-whistle-buzz would occur, starting at a low frequency, then rising. It would settle at a high frequency: one channel would be just barely audible while the other channel was completely audible.

It has been suggested that installing ferrite chokes on the negative lead at both ends of the Speaker cable might eliminate the problem.

For me and my DIY Amps, after deciding that my test Speakers didn’t blow up, I proceeded to connect them to my real Speakers which worked without any sound occurring.

For the folk using that particular Speaker with the AMT, the ferrite chokes fixed their problem.

Hypex is aware of the problem I describe but seemingly not interested in addressing it.

Ferrite chokes are pretty inexpensive. May be worthwhile buying a set and trying out. *shrugs
 
Wanted to follow up on @antcollinet's suggestion to try replacing my RCA cable with an XLR-to-RCA cable. I purchased these from monoprice (mentioned by @staticV3 in a separated thread linked above) and it worked like a charm. All the buzzing is gone and the hiss is now comparable to what I heard when the speakers were connected directly to the Yamaha integrated. So grateful for your knowledge and help!

Not to rain on my own parade, but I noticed yet another issue (will I ever just be able to just enjoy my system??) having to do with popping noises... I will post it in another thread so we can close the loop on this specific issue with a nice bow.
 
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Wanted to follow up on @antcollinet's suggestion to try replacing my RCA cable with an XLR-to-RCA cable. I purchased these from monoprice (mentioned by @staticV3 in a separated thread linked above) and it worked like a charm. All the buzzing is gone and the hiss is now comparable to what I heard when the speakers were connected directly to the Yamaha integrated. So grateful for your knowledge and help!

Not to rain on my own parade, but I noticed yet another issue (will I ever just be able to just enjoy my system??) having to do with popping noises... I will post it in another thread so we can close the loop on this specific issue with a nice bow.
Thanks for the follow up. It's always nice to hear a good result.
 
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