Change from PS Audio S300 Stereo Power Amp to PS Audio M700 Mono Amps

I have had the S300 Stereo Amp and a Stellar GCD for about two years driving Vandersteen Treo floor standing speakers and have been very happy with the overall sound quality and never disappointed but have had the itch for a change so recently picked up PS Audio’s M700 Mono Amps.

After about thirty minutes of listening on the M700’s at a moderate level of about 60 dB I start to feel pressure in my ears. Over the past three days stopping and starting at different times of the day I get the same ear pressure after a short time listening. To note everything else in the system is exactly the same and the new amps are in the same position as the old amp. I am going to give the new amps more time but am thinking that the M700’s are possibly not a good match for the Treo’s where the S300 was a very good match.

Does anyone have a similar experience trying a new amplifier or have suggestions as to why this may be happening?

First of all—welcome.
I too have M700s and LOVE 'em
When you say 60dB, are you guessing, or is it based on measurement?
You state, “everything else in the system is exactly the same and the new amps are in the same position as the old amp” by that do you mean the volume level readout? if so, I don’t believe those numbers are the same thing/comparable.

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If you don’t visit an Ear Dr. regularly, it could easily be a build up of ear wax causing your problem.

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I own the M700 pair. They’re a lot more wattage into your 6 ohm Treos than the S300. I’m with @Palouse, did you try using the same volume on the M700 as you did S300? That might be too much volume for your space, and thus your ears. If the S300 sounded good with your Treos, I’d argue the M700 would sound better. Did you wire the M700s to the Treos as you did the S300? Just curious.

Thanks for the reply and questions. When I stated sound level seems to be similar to the S300 I was referring to setting the GCD at volume level 20. I should have been more clear about the dB level. I am using a dB meter and the max I hit was 60 bB. The average was more in the 40 to 50 dB range so not very loud.
Also, yes the speaker wiring and interconnects are correct as per the M700 connectors.

Sometimes with particular speakers, less is more. A friend of mine ran into that with a pair of B&W towers. Sounded like butt with his high-end amp, but a moderately priced Rotel made them sing. A good thread on Treo pairing: Audiogon Discussion Forum

Note the S300 is recommended there.


Thanks for the link jazzophile. I do want to add that the M700’s sound great and am speculating here but thinking the M700’s may be driving the bottom end of the Treo’s to a lower level than I am used to. I haven’t given up on them yet and am hoping everything will improve over the next week or two. Thanks.

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I had a similar situation a few weeks ago. I had for 18 months or so, the S300 connected to my Amphions, BUT connecting a new pair of M700’s, wow, a slightly different sound and far far better. I never play them loud tho, about 12 on the SGC Pre


This may be a silly question, but have you since switched back to the S300 to confirm the problem doesn’t still occur?


I too upgraded from the s300 to m700’s. I have only good things to say about the mono’s. I hope you get this sorted out.

The M700s need time to settle down and deliver their best.

Craig, I have not switched back to the S300 yet but intend to later tonight or tomorrow as soon as I get the time. I have never had this issue with the S300 in the past but one never knows.

I am going to reconnect the M700’s after testing the S300 again and will give them some time to break in to see if that resolves the issue. Thanks.

The M700s do take a bit of time to settle in so that could definitely be it. I find the 700s to be a much more listenable amp as far as fatigue goes so I’m sure they just need more time.

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I reconnected the S300 last night and it sounded as great as always and I did not experience an ear pressure issue like I was getting with the M700’s. I will say that the S300 might possibly have somewhat of a less bass response than the M700’s but it is not lacking at all and is punchy and very well defined and drives the Vandersteen Treo’s beautifully.
I am going to give it another day before I switch back to the M700’s. I understand that electronics require a break in period to reach their full potential but I wouldn’t think that is impacting what I am experiencing.

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I saw your mention of the Vandersteen Treos, which have always been on my acquisition list. Are you using the Treos or Treo CTs?

tgilb, you describe a curious situation. I don’t know the Treo speakers, but from what I’ve read see that they are especially sweet in the midrange and midbass. I have recently purchased the M700s after auditioning the S300. My speakers are modest and fit my space: Polk Reserve R500s with dual Definitive Technology ProSub 800s. (Less than a year ago, in another space, I used a Bryston 3B with Vandersteen 2CEs) What I noticed about the S300 was that while the bass was full and sweet, and the soundstage was clean and well defined, the midrange was under presented: it was thinner than I like and not present enough in the soundstage. When I got the M700s, the first thing I heard was the improved midrange–vocal harmonies were richer and fuller. Additionally, I am impressed by how well the M700s sound at lower volume–early morning or workday levels. They present a fuller balance that, especially with the subwoofers, give a warm depth to the music that my Bryston/Vandersteens could not at low volume.
I wonder if the midrange boost that I’ve heard reviewers speak of with the M700s and that is so welcome in my system might be what is causing the pressure you’re hearing.
I am interested to learn what you hear when you reconnect the S300.
Good luck!

My 700’s took quite awhile to break in. I observed harshness in the mid / top range and one day after about a month it just smoothed out and was great.

Thanks for the comments. I have the original Treo’s without the carbon tweeter upgrade but completely enjoy their sound. A friend of mine has the Vandersteen Quatro Wood CT’s that sound fabulous but he is always impressed with the sound of my Treo’s.
I definitely intend to give the M700’s more time and will focus on the mid range between the two amps. I hadn’t thought of that so thanks for that note.

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By the time my M700s had broken in the soundstage had expanded greatly and the system benefitted greatly from new speaker placement (I have Maggie LSRs). That helped smooth out the response at all frequencies.

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I wonder if Paul has seen the new NCOREx class D stuff.

Hypex Announces New and Improved NCOREx Class-D Amplifier Technology | audioXpress.

I would like his opinion on those.