It is most likely the heat sinks heating up and cooling off. Being aluminum and most likely fastened to a steel chassis they have different thermal expansion rates. You might check any screws that fasten the heat sinks, side panels, or any others you can easily get to.
That is intriguing. What is the qualitative or quantitative difference in the sound between the 700ās and the BHK? Are the BHKs just more tube-like because they have a tube-based stage? Not interested in technical details, would really just like to hear what differences people have heard and the equipment they are using.
The BHK do have a more tube like sound but not in that way that a ALL tube amp normally present. But the BHK sounds smoother in that you hear is. more detail or the noise that the BHK makes in being a AB amp style is more of the kind that your brain ignores because it is more like sound you hear in nature also because of the way it is dealing with harmonics that your brain feels is normal. The M700 are very similar in sound to the BHK but the M700 have a way that presents the sounds in a way that the control of the speakers is very tight/high precision. But there something that you hear with the M700 but your not sure what is the cause when listening to the music critically between the BHK VS M700. But if you werenāt switching back and forth you would possibly never hear or even notice. I was listening to them on a ALL PS Audio system DMP, Directstream DAC SR, BHK preamp with Focal Grande Utopia EM EVO speakers. My only comparison was between the M700 and a BHK 250 switching back and forth to listen for the differences between them. Iām going to get a set of M700 this year for my 2 channel system. Until I can upgrade my Speakers and then get BHK 300 for my front three channels and then use the M700 for my surround speakers for my 2ch/HT system. The M700 VS BHK is like a high performance car say a Ferrari 458 VS Koenigsegg Agera R. One leaves you amazed while the other leaves you speechless. Both are amazing but just one is 1% percent better and if the cost to have that difference is worth it. Iām interested to see what my system will sound like with the Addition of the M700. I have Directstream DAC and it sounds so much better even though my 20 yr receiver. Iām waiting to sell one of my homes I had before I meet my wife to upgrade. It canāt get here soon enough.
Nice. Ha ha ā¦ priorities, always good to have them.
I just canāt bring myself to shell out the money for the preamp when I like the sound of the DAC and amp combo so much as it is. Just canāt wrap my brain around how another āboxā in the signal chain could do anything other than color the sound or negatively impact it. However, I know that the DAC is putting out its best S/N ratio at full āvolumeā (100 on the display) so a preamp could probably help take advantage of that, but again itās that price issue and my innate skepticism coupled with my love of the way the system sounds right now.
The comparison I might have used is the M700 as a Tesla in Ludicrous mode (class D) and the BHK as the Ferrari (tube and transistor biasing), but then I havenāt heard the latter. Heh.
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Yep, priorities. Got to have them. 
It will sound better with the preamp but From what I heard. You be fine with direct to amp for the time being and saving for the BHK preamp and get it when you can or keep looking for a deal on the marketplace here or upscale audio or underwood hifi. Iāve heard you can get a great deal from underwood Hi-fi but you need to be sure what you want when you buy from them. I bought a open box new from upscale audio and was very happy with the service I got. Iāve found mine sounded best when about 90 or so. Be able to adjust both preamp and DAC Iāve been able to find a sweet spot I love.
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old but fitting topic.
8 weeks ago my BHK 250 arrived. i told myself to wait, take you time burning in, then listen critically and take some time just enjoying before submitting some sort of review. since iām not a native speaker, i hope that my thoughts and explanations are āunderstandableā.
i have to give a warning right here: if you are interested in the sound quality aspects between M700 and BHK 250, just scroll to the last two segments of my post.
it has been 35 year journey from the first ārealā stereo system, an all Sanyo hifi rack with double cassette deck, simple tt and three way air suspension stand mounts to my current setup. back then hifi racks in Germany were in my school and at that age at least for the guys what the smartphone meant to teenagers in the 2010s.
todays system is a 4.0 setup with Dynaudio Contour 20 on front, Nubert nuvero 3 on back and a front channel fed Sub Nubert 1300 with DSP, Cambridge AVR 200, an CXU UDP, Chord Qutest DAC and Kimber interconnects.
by coincidence i stumbled two years ago upon Pauls videos on youtube, dived into PS Audios website and had a good laugh reading 99% true. what a refreshing, non elitist community with a lot of humor, compared to my experience here.
back then i already had mono power amps for the main channels from a small german company. great 80W class A/B amps called āigelā (hedgehog), due to the looks of heatsinks and size. they are still working and great, but after 8 years i was looking for something more gripping and dynamic.
why not give the stellar S300 a try, about 500 dollar more than my igel, would it make a big difference? it did. the color saturation was less (good!), dynamics and bass grip improved a lot. the instruments were nailed firmly to the floor across the stage, 3D a bit better.
i was happy.
in the coming months i started to notice that i listened less to music and was more in a evaluating/ testing mode. why? i read a lot about the difference in the PS Audio amp line up and began to compare the noted differences between the S300 and the M700. I asked myself, am i missing something? yes, i`d like more dynamics, my Dynaudio are a bit power hungry, and i thought the mid to top end could benefit as well, regarding detail and smoothness.
it helped getting a good deal on trading in the S300.
everything i hoped for got even better, especialy the mid and top end of the spectrum opened up and groundshaking bass with more grip showed what my speakers are capable of. once more i was very pleased, was listening to more music and found much more joy in live concerts and action movies. regarding the price/performance ratio, i can highly recommend both amps.
during the pandemic with most days in home office my thoughts began circling round which upgrade would promise the biggest step for system improvement. i would stick to the loudspeakers, but changing the AVR would be the next promising upgrade path. the market for high quality AVR with a really good preamp part and all the fancy other features (still, i feel no need for more than 4.0) is kind of a mixed bag. many features, a lot of reported sw bugs and still a noise intensive environment for the delicate task of a pre amp. a lot of stuff, most of that not relevant for me. a step up, so my conclusion, would be very expensive and not attractive at the moment.
meanwhile in the back of my head a long forgotten curiosity found its way into conciousness. should i try a tube based solution?
having some good memories listening to a DIY speakerset and a tube receiver in my dads system from in the late 70s to 80s ā¦
then my dealer came up with an anniversary offer on BHK amps. from what i read about the amps sound signature i thought that it fitted with what i strived for in my system. i told myself, i could resist that offer.
after two months i decided to contact my dealer and see if we could make a deal, trading in M700 for the BHK 250 and reverse transaction if iām not fully convinced and satisfied. the price gap was very close to my personal limit. 2 weeks later the 37kg monster arrived.
now what changed (burn in time 70-80h)?
yes, the M700 are better ā¦ a tiny bit, regarding tightness in bass and a little bit less disturbing/puzzling when listening to beloved but really bad recordings.
looking for power and cranking up rock or pop? stick to the M700 and be happy ever after.
with the BHK 250 in my system everything else is a lot closer to what i call reality.
due to a short career as a teen in a big band, iām familiar with the complexity of sounds emerging from a drum kit, e.g. with brushes on a cymbal or the sound palette of a kick drum played from soft to hard. what an eyeopener and a big fat smile on my face every time!
voices, piano and acoustic guitars are much more lifelike, 3d sculptured and feel at ease. which describes also what i am now, much more at ease when listening.
throughout the frequency spectrum each acoustic instrument have more nuances. the instruments are much easier to differentiate, still my feet start tapping unintentionally because it adds up to much more than the sum of its parts and feels like āoneā performance.
and for the the first time, i think i understood, what is meant in the english speaking world by āsweetā. there is an airiness without any emphazising the top end that makes orchestral works more enjoyable.
the most important part for me is, iām relaxed and attentive at the same time, immersing in the music within a few seconds without effort.
i had many upgrades over the years, approxim. one every 3-5 years, not counting S300/M700/BHK250 upgrade path. most of them on a small budget, luckily more often than not worth their extra money, so this one was my biggest investment to date, close to the Dynaudios and for me it is worth every cent.
one reviewer once wrote: this may be your last amplifier. although iām very far from retirement, i sense that this statement could me true for me.
thank you Paul and all at PS Audio, what an excellent product!
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I made the same S300/M700/BHK250 journey. Couldnāt be happier. I gave the stock tubes 6 months before rolling just yesterday.
Enjoy!
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I do!
Any first or second impressions or still in burn in mode?
What kind of tubes did you install?
I plan rolling tubes when experiencing sound degradation, so maybe a long way to go.
I have it for 6 months and listen about 8 hours a day. Itās full burned in.
Donāt wait for the tubes to sound bad. Try others, you just might like the differences.
Iām running NOS Matsushita/National 7DJ8 currently.
Theyāre a bit more lively than the stock Gold Lions in a good way. The Gold Lions are fine tubes though.
I also have the BHK preamp so itās tubes contribute too.
I just switched PSVANE-S tubes (better than stock MK2 ) from BHK Pre to a pair of Radiotechnique 1956 12AU7. It has only been a few hours but they show a lot promises.
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