Peachtree Audio Nova125 & sensitive speakers

I wanted to inform any potential buyers of the Peachtree Audio Nova125 (Class D, 2x125W) its inherent incompatibility with high sensitive speakers. I learned this the hard way.

I own a pair of the excellent Klipsch Reference RF7 Mk.ii floorstanding speakers. They are horn loaded and have a very high sensivity (101db); you could practically run them on a clock radio. They used to be powered by a top-of-the-line Rotel pre+power combination. I sold this combo and bought the Nova125 instead because I wanted something simpler and/or more pleasing to the eye.

To my horror I noticed the Klipsch speakers produced a very loud hiss when connected to the beautiful Nova125. I had never heard this before with the Rotel combination. The hissing was clearly noticeable from 8 meter away (30 feet)! When the amp was switched on and nothing was playing, my living room was actually immersed in this horrible noise. The hissing was present and unaltered even when no source was connected and the volume knob was turned down to zero.

I contacted my dealer, who offered a new Nova125 and power conditioners. The hiss remained exactly the same.

I thus contacted Peachtree Audio directly. They simply stated that Class D amplifier tend to have a higher noise floor than typical Class A/B amplifier and that high sensitive speakers should be avoided in combination with an amp like the Nova125.

I am currently selling the Klipsch speakers and will buy the PSB Imagine T2 speakers, which are rated at 90db sensivity. I hope the hiss will not be present with these speakers.

All in all not a very pleasant experience.

I hope this will be helpful to anyone considering Peachtree Audio products (or any other Class D amp).
Two comments.

I used to have a Bel Canto S300 amp and there was no hiss whatsoever, even with my ear to the tweeter. It was dead silent. I don't buy the explanation that class D has an inherently higher noise floor.

Second, is there a source connected and on (but not playing) when you hear the hiss? If so, the origin of the hiss could be the source and a gain mismatch between it and the amp.
Hi Mlsstl

The explanation came directly from Peachtree Audio HQ. I don't actually buy it either, but what can I say?

Like I said: hiss was unaltered, even with no source connected at all and/or the volume knob turned down to zero. It's just there...
I would have kept the speakers and ditched the amp.
@Stereo5: Actually, that crossed my mind also. Yet I quickly grew to love the form factor, ease of use and energy efficiency of the Peachtree Audio Nova 125, despite it being a 'noisy' amplifier. Switching my system on in the morning is literally one push on the remote away; no separate DAC, no extra remotes...

Anyway, I got really excited about the PSB Imagine T2 speakers now (hedonic adaptation anyone?). The Klipsch RF7 II speakers have always seemed a bit overkill in my home. I do hope they will be quiet with the Nova125... Fingers crossed.
Probably a long shot, but have you tried the "tube" button on the remote to see if there is any change? This switches the tube buffer in and out.
@Tls49: Yes, I did try tube on or off. No difference.

I also asked Peachtree Audio if the gain could be lowered somehow, but I don't think it can be done. No answer yet.
After reading the other responses, I suspect the noise has nothing to do with the class D amps but is more likely coming from a noisy preamp section. Since you've had 2 different units that sound the same and someone else also has a noisy unit, it appears some hiss is just inherent to this model.

(I looked at the specs and they are a bit odd - Peachtree states the S/N ratio is 96 dB but then claims a dynamic range of 121 dB. Strange.)

Not sure what's going on w your set up, but Peachtree works fine on high sensitive speakers w no noise. Something is wrong w/your unit if there's an audible hiss, even w your ear to the speaker. I have a pr of excellent Zu Omen @ 101dB and 0 noise is present w the 125 or the novaPre/220 for that matter, although the 220 is way over-kill.
Also not sure whom you spoke w/at Peachtree, but if someone told you that our class D amps inherently produce more noise than a standard A/B, they were simply wrong.
Please send your unit in and we'll get it tested.

Best wishes,
David Solomon
Peachtree Audio
Its a common problem with efficient speakers. There's too much gain. Your old Rotel preamp was acting as a buffer between your amp and your sources. I don't know a lot of technical details regarding your Peachtree but it almost certainly doesn't have a traditional type line stage inside to preform this function. The DAC section probably goes directly into the amp. Given the other post, it doesn't look like you have a global gain setting for your DAC. That would fix the problem. There's nothing wrong with your Peachtree, it just doesn't have that feature. If you still have your Rotel pre, go from the preout on the Peachtree to a line level input on the Rotel and the hiss will go away.
I should have mentioned in my 1st post. The blame lies with the dealer. As long as you told them what components you had in your system, they should have seen that one coming. Its a pretty easy call (for someone like a dealer that is "supposed" to know what they are doing).
From what I've read class D (switching) amps are inherently noisier than traditional class A/B amps due to the high frequency switching. Read any of JA's measurements of class D products and you'll find that the noise is so high that it swamps the measuring equipment. A special low pass filter has to be used to make the measurements. I believe that most (maybe all) manufacturers of class D products utilize an output low pass filter. It may be that the Peachtree product's filter doesn't attenuate enough for high sensitivity speakers.

It would be interesting to see if the hiss persists with the speaker cables disconnected from the speakers.
"It would be interesting to see if the hiss persists with the speaker cables disconnected from the speakers."
Bob Reynolds, That's a good one...
Bob Reynolds wrote: "It may be that the Peachtree product's filter doesn't attenuate enough for high sensitivity speakers."

By definition, ultrasonic noise in an amp does not create audible hiss - its beyond the range of hearing. At worse, if unfiltered, it is going to create an intermodulation problem in the audio band, but that only exists when music (an audible signal) is being played. In that case, you will not hear hiss, but rather some type of distortion in the music.
I have a pair of Tekton Lores (98db) and a novaPre/220.
Overkill yes but sound great together. No problems whatsoever.

I wasn't kidding about the speakers picking up the high frequency noise from the switching amp.
I thought you were kidding too. The 1st paragraph I can follow easily enough, but in the 2nd when you say to unplug the speakers, it doesnÂ’t make sense. If you unplug the speakers, how will you here the noise?

Also, when you talk about the measurements from Stereophile, it looks like they used the filter just to take the measurements. I could be mistaken, but if you don't need the filter for regular listening, it may be relevant to this discussion.
Mlsstl, your comment makes perfect sense about not being able to hear ultrasonic noise. Thanks for correcting me. I should think, at least, 4 or 5 times before typing.

And your comment about ultrasonic noise intermodulating an audible signal, I assume, is what I recall reading when early class D amps were interfering with tuners.

Thanks again.
Bob Reynolds,
Got it now. It was kind of funny, though
Zd542, what I was thinking about is that if the switching noise being high enough in level, the amp is effectively a high frequency transmitter and that the speaker's voice coil could act as an antenna. But, as Mlsstl pointed out, it would be beyond our hearing.

I'm pretty sure that all class D amps have a low pass filter on their output. They need to reduce the signal so that, as Mltssl noted, it doesn't intermodulate other signals nearby.

My reference to JA's use of an additional filter was just to backup the idea that class D amps are inherently more noisy than class A/B.
I own Zu Definition speakers and Wyred 4 Sound electronics (mAMPS, STP/SE, DAC2). Black background, absolute silence. In fact, one of the things that sold me on W4S is the total silence and black background. Agree with others, something else is wrong here.
Thank you all for your considerations, comments and analysis. I have since received an email from David (Peachtree Audio) in order to investigate the matter further. In due time I will post an update here.
Must be something wrong with your amp. I have the Nova 125 with a pair of 89db speakers and while that is not as
sensitive as yours, I cannot hear any hiss even with my ear
against the speaker. Excellent amp!!
I'm just trying to figure out who on this site (supposedly the high end) would actually buy one of those things.
Abrew19 wrote: I'm just trying to figure out who on this site (supposedly the high end) would actually buy one of those things.
I don't own one (I'm more of an old fashioned tube guy) but I have owned a Bel Canto class D amp (S300) in the past. It was a very nice sounding amp that I easily could have lived with if I hadn't decided to go back to tubes.

Not everyone has a ton of money to throw at high end gear and Peachtree gear has had excellent reviews in several audio publications and many nice user comments on the forums. We've got one fellow here with a specific problem that seems to be unique to his situation.

If I were shopping for an integrated amp in this price range, I wouldn't hesitate to audition one.
What complete idiots some people are! Never ceases to amaze me. But it is what makes the world go around I guess. :o)
"07-15-13: Abrew19
I'm just trying to figure out who on this site (supposedly the high end) would actually buy one of those things."

Why not just start a new thread and ask?
I would like to report the same issue with my Nova 125. I got it to power a set of Ascend Acoustics tower speakers. I contacted Peachtree as well and got a similar response about noise floor. Have you sent your unit back for warranty repair?
Ran a Decco 65 with Zu Def4s for about a month while my Mac60s were being refurbished. Dead quiet.