Digital Amplifier Questions

Almarg,

That's good news. And, yes, I agree that I would have noticed any combo of static, noise and buzzing. None was present even at a fairly high (1/2 of max) volume.

Thanks for your assistance and verification,

Tim

I did initially try your recommended method (tuning to an area low on the AM band with no station present) but found it difficult to determine when RF interference was present.

Good! That provides further confirmation of your conclusion. If significant RF was being radiated it's pretty much inconceivable to me that you would not have perceived it under that condition, as some combination of static, noise, and buzzing, most likely at any reasonable setting of the volume control.

Best regards,
-- Al

Hi Almarg,

I did initially try your recommended method (tuning to an area low on the AM band with no station present) but found it difficult to determine when RF interference was present. Tuning to a station with only decent reception (not an overly strong signal with very good reception) made it obvious to me when RF interference was present; the signal strength would decrease (sometimes going out completely), static would increase and a buzzing sound would begin.

Your method may work better for some than it did for me but I wanted you to know I appreciate your input.

Thanks,
Tim

For something that has absolutely nothing to do with the sound of your system, RF interference/leakage testing is sure a pain in the butt; mainly since I'm handicapped and walk with a cane.

RF itself is way above our hearing range but different frequencies can mix on any non-linear element in the system, producing new frequencies that might be audible. Al mentioned it many times. Keep your system clean from interference (shielding, keeping things apart, using different outlets etc.). Anything can be the gateway, including speaker cables.

Good news, Tim, and thanks for undertaking the effort.

To others who may wish to perform similar tests in the future, though, I would repeat one of my earlier statements:

03-31-15: Almarg
... the test will be most sensitive if you tune to a frequency at which no station is present. If a station is present the radio's AGC (automatic gain control) circuit will reduce its sensitivity, especially if the station's signal is strong.

Best regards,
-- Al

All,

For something that has absolutely nothing to do with the sound of your system, RF interference/leakage testing is sure a pain in the butt; mainly since I'm handicapped and walk with a cane.

As I stated I would in my last post, I bought a $15 Craig portable AM/FM radio that runs on 4 AA batteries (I also bought a new hairdryer I've needed so this whole thing already has been worthwhile).

Having completed a somewhat lengthy and definitely aggravating process, I want to complete it here by documenting my findings thoroughly. What follows is probably overkill but I hope to never need to duplicate this little experiment on my system and would like it to be of benefit to others wanting to test for RF interference/leakage.

My audio rack is 5ft wide and 2ft high and is located directly below my wall mounted 5ft wide and 3ft high HDTV. The rack has a solid walnut top shelf that holds a D-Sonic mono amp on each end, with an Oppo 105 located between them. Below are 2 compartments that are accessed via 2 swing-down doors and hold my sub, center and surround amps. All system amps are class D except the class A/B sub amp.

I assigned the amps as follows:

Amp#1: D-Sonic M3-600M class D mono pair on top shelf.
Amp#2: ClassD Audio SDS-440-CS class D stereo amp located in left lower enclosed compartment.
Amp#3: Dayton Audio SA-1200 mono class A/B sub amp/controller located in left lower enclosed compartment.
Amp#4: Emerald Physics EP-100.2-SE stereo amp located in right lower enclosed compartment.

I began the testing by tuning the Craig to the lowest station on the AM band that had decent reception. The lowest range station was unfortunately mid-band at '1070 KHZ' but this setting proved to be good for testing purposes. My process was to move the radio, set at half volume and tuned to 1070KHZ, from a few feet away to a few inches away from each amp on all sides and top. I did the following tests:

Test#1: All amps off.

Result: No loss of signal, static or buzzing near any of the 4 amps. However, there was some loss of signal and buzzing between the amps as I walked from the right mono amp to the left. I was able to pinpoint the source to the small Directv satellite tv 'client server' box located just to the right of my Oppo. This box was off but the signal loss and buzzing got worse when I turned it on. The RF was emanating from the small box as well as the power cord leading to my multi-outlet surge protector power strip.

Test#2: Amp#1 (mono pair) on only with all others off.
Results: Same as above with no RF leakage detected from any amp but buzzing and loss of station when near Directv client box and power chord.

Test#3: Amp#2 on only with all others off.
Results: No RF leakage detected from any amp just from Directv box and power chord.

Test#4: Amp#3 on only with all others off.
Results: No RF leakage from any amp just from Directv box and power chord.

Test#5: Amp#4 on only with all others off.
Results: No RF leakage from any amp just Directv box and power chord.

As you can see, the results were clear that none of my amps had RF leakage but the small satellite tv client box and power chord did. I'm not going to take any action since, as Guido correctly stated, there are no adverse audible affects of this RF leakage on my system.

Tim

My feeling is that a portable battery powered AM radio would be preferable. Not only for the obvious convenience factor, but because it may make it possible to more accurately locate the source of any RFI, and to more accurately assess its relative amplitude as a function of distance. With an AC powered radio there may be ambiguity as to whether what is being picked up is being picked up by the built-in antenna, or by the long power cord acting as an antenna, or that is perhaps being routed into the radio via the power wiring itself.

Just my opinion. Best regards,
-- Al

Bombaywalla,

You're right, I could do as you suggested but I don't want to be tied to a cord and handheld portable radios aren't expensive.

Guido,

Okay, I'll keep an open mind and see if I can pinpoint the leakage point if RF interference is detected.

Rookie Midwest RF Interference Technician,
Tim

03-31-15: Noble100

Thanks for the info Bombaywalla and Kijanki.

I tried the test again using the AM radio. I couldn't even find an AM station that was tunable. There was too much buzzing on the whole range. I'm thinking this is caused by RF leakage from my 3 class D amps, all located within a 5ftx 2ft area.

I plugged the radio into an outlet in my adjacent dining room (less than 20ft away) and the buzzing (hash?) went away and I was able to tune in a station in the low AM band.

why do you need to get a new AM radio?
Why can't you repeat the test (where you cannot even tune into any AM station due to the supposed RF interference from one of your class-D amps) with the existing AM radio & simply switch off one class-D amp at a time until you can tune into a AM station using Almarg's suggestion for the AM freq?
isn't this equally valid (as Guidocorona's suggestion of switching on the class-D amps one/2 at a time)?
thanks.

Tim, if you use a battery powered radio, and you find that one of the amps seems to leak, try sliding the radio along/around the amp case, and then along the power cord, the speaker wires, and the input ICs.... There is no telling from where the leak might originate... It might even come from a totally different device... Make no assumptions, as reasonable as they might seem.

G.

Guido and Al,

Both good ideas; I'll get a battery powered portable radio (I've been needing to buy a new hair dryer, anyways) and set the dial to a low frequency on the AM band that lacks a strong station signal. Next I'll test with the various amps on/off according to the permutations Guido listed.

This amateur RF interference technician will report back on results soon.

Thanks,
Tim

Hi Tim, I recommend that you repeat test walking around with the radio as follows....

Amp 1 on, 2 and 3 off;
Amp 1 off, 2 on, 3 off;
Amp 1 and 2 off, 3 on;
Amp 1 and 2 on, 3 off;
Amp 1 on, 2 off, 3 on;
All three amps on.

G.

Hi Tim,

If you are going to get another AM radio, consider purchasing a portable one that is battery powered. Also, the test will be most sensitive if you tune to a frequency at which no station is present. If a station is present the radio's AGC (automatic gain control) circuit will reduce its sensitivity, especially if the station's signal is strong.

Best regards,
-- Al

Thanks for the info Bombaywalla and Kijanki.

I tried the test again using the AM radio. I couldn't even find an AM station that was tunable. There was too much buzzing on the whole range. I'm thinking this is caused by RF leakage from my 3 class D amps, all located within a 5ftx 2ft area.

I plugged the radio into an outlet in my adjacent dining room (less than 20ft away) and the buzzing (hash?) went away and I was able to tune in a station in the low AM band.

I then moved the radio as close to my amp rack as the cord would allow (about 10ft away) and there was no interference; the station continued to be clearly audible without hash/buzzing. I was thinking the interference would increase as I moved the radio closer to my amp rack (from about 20 feet to about 10 feet way) but it did not.

These somewhat mixed results have me a bit confounded. I think further testing is called for, perhaps with a better AM radio, before conclusions are drawn. My current thought is that at least one of my amps is producing RF interference but I don't know for certain at this point.

I'm going to get a better AM radio, plug it in in my dining room using a 20ft extension chord, tune in a station on the lower AM band and retest by walking toward my amp rack in the adjoining living room. I'll post again with results.

If anyone has a better idea, please let me know.

Thanks,
Tim

03-29-15: Kijanki
My class D amp switches at 500kHz. This square wave is filtered by the Zobel network at about 60kHz. Harmonics are most likely filtered out and main problem is about 1% residue of 500kHz switching frequency present on the speaker cable.

makes sense Kijanki - 500KHz is 3.05 octaves away from 60KHz. Zobel network/filter is most likely a 2nd order filter which is 12dB/octave implying 36.6dB of attenuation of the 500KHz. That works out to 1.48% of residual 500KHz on the speaker binding posts.

My class D amp switches at 500kHz. This square wave is filtered by the Zobel network at about 60kHz. Harmonics are most likely filtered out and main problem is about 1% residue of 500kHz switching frequency present on the speaker cable. This 500kHz frequency represents wavelength of 600m. Antenna below 1/10 of the wavelength becomes very ineffective - and that is 60m. Typical 3m cable is practically non-radiating. It is still a good idea to keep cables apart to avoid capacitive coupling.

I Don't know why but I thought any RF leakage from class D amps would be closer to the FM band range.

Thanks,
Tim
Noble100

Noble100, don't know why you were thinking this???
FM operates in the 88MHz - 108MHz range i.e. 88 million cycles per second --> 108 million cycles per second.
the class-D switching amp is probably running at 1MHz switching freq (if that high at all. more likely in the 500KHz region). I.E. 500,000 cycles per second --> 1 million cycles per second.
As you can see, 500,000 --> 1 million cyc/sec is far away from 88 million --> 108 cyc/sec.
Let's say that the class-D amp was switching at 1MHz, then the 89th harmonic of this 1MHz switching freq would be 89MHz but it's power would very, very low to the point that even if it interfered with the FM radio station tuned to 89MHz it would produce a very low amplitude distortion that would most likely be un-hearable.
(Just wanted to point out that the switching waveform of the class-D amp is most likely a square wave & square waves have only odd harmonics).

Like Almarg pointed out the AM freq would be right in the vicinity of the class-D switching frequency & much more likely to create interference.

Al and Guido,

I'll test again using a station low on the AM dial and report back on the results. I Don't know why but I thought any RF leakage from class D amps would be closer to the FM band range.

Thanks,
Tim

Thank you Al, I conducted the test with an ancient tuner a few years ago.... Device is a rather low end NAD from approx. 1979. The tuner has a button that causes it to reject interference in FM... If the switch is in the off position, the device picks up very significant statics whenever tuned to weaker stations, and in some days, FM is plainly unlistenable, regardless of station or switch setting... or amp connected to the system. Call it a hyperdistractable/ADD FM tuner... Or just a plainly crappy tuner.

But I might have conducted the test in AM... I just can't remember.

G

Guido & Noble100,

Why an FM radio? I would expect that an AM radio would provide a much more sensitive and potentially more meaningful test.

As you probably realize, FM is inherently vastly more immune to RF interference than AM, since the audio that ends up being reproduced corresponds to frequency variations in the airborne signal rather than to amplitude variations. Also, in contrast to the AM broadcast band the 88 to 108 MHz frequencies of the FM band (and even its 10.7 MHz IF frequency which follows down-conversion within the radio) are vastly higher than the bandwidths of any audio component, and are therefore much less likely to be relevant.

I suspect that if an FM radio audibly responds to airborne RFI generated by an audio component it is likely not what is picked up by its built-in antenna that results in the audible interference, but rather what is picked up by downstream circuitry within the radio that operates at much lower frequencies. That response probably being much less sensitive than an AM radio's response would be to interference picked up by its antenna.

FWIW, my guess is that you'll hear significant interference when an AM radio, preferably tuned near the low end of the band (e.g. 540 kHz), is placed close to the amp. But what will be of interest is how quickly the interference drops off as the distance increases.

Best regards,
-- Al

Guido,

Well, I finally tested my amps for RF interference today; sorry it took so long.

The only FM radio I had for testing was my bedroom alarm clock. I tuned it to an FM station that had very good reception and then positioned it within 2 inches along each amp's sides, top, front and back. I then increased the distance, to a distance of about 6 inches and then multiple distances trying to find any location where the signal was affected. I even tested my class A/B bass system amp even though I knew there should be no RF interference/leakage on a non-class D amp.

The results indicated there was absolutely zero affect on FM radio reception on any of my amps at any position or distance I tested. I understand your comment that, even if there was some RF interference/leakage from an amp, it would not affect the sound quality produced by the amp.

I was still pleased with the lack of RF interference, however, since I consider this a validation of the amps being well designed and the designers' attention to details. As a reminder For anyone interested, the 3 amps I tested were the following:

D-Sonic M3-600-M mono-block amps
ClassD Audio SDS-440-CS stereo amp
Emerald Physics EP-100.2-SE stereo amp

I highly recommend all 3 of these amps for sound quality. Not having any apparent RF leakage issues is just a bonus for those concerned.

G.,

There are a few things that were obvious from the beginning that I can address:

Overall stage and image sizes: compared to the A21, image size appears to be the correct height/size with the M525...the A21 is relatively flat and images appeared below eye level, as if I was looking down. One of the most significant difference is the overall stage...this is where the M525 really shines, outstanding separation of instruments, with the best front to back placement of instruments that I've ever heard in my system

Authority-very hard to explain because the A21 and M525 are very different, I need more time to provide honest feedback

Transients distortion and speed- M525 has a lower noise floor, where music emerges out of a completely dark background

treble sweetness in complex passages-the A21 was closed in and lacking detail compared to the M525, cymbals sound so real and natural with the M525

That's exciting Richard.... You basically got an essentially brand new M525 for the priced of a used one! Let us know how things develop. G.

G.,
The M525 is used; however it only has approximately 60 hours on it. In a couple of days I will post my thoughts.

B_limo, if you live around the Springs, there is a Rowland dealer with vast experience in JRDG gear -- My friend Ron of Black Forest Audio keeps a super selection of new and pre-owned gear in his stash, ranging from late 1980s classics to Jeff's latest amps and preamps for you to listen to... 719.475.7501.

G.

Not of real importance, but Jeff Rowland gear is absolutely beautiful. I saw his gear at RMAF a few years back and if I remember correctly, the chassis is machined out of solid billets of aircraft aluminum. Jeff also lives in the same city as I do, probably less than 20 minutes away from me... maybe someday I will be able to afford some of his gear :)

Could you also give us initial comments on other Rowland M525 parameters compared to Parasound A21....

Overall stage and image sizes;
Authority;
Transients distortion and speed;
Macro and microdynamics;
Harmonic complexity;
treble sweetness in complex passages;
Sense of the recording venue surrounding instruments.

Saluti, G.

Hi Richard... Congrats for M525!!!!

Is the unit new or used? If used, how many hours on it? Overtight bass is likely to relax with more playing time.

G.

I never thought changing from an Parasound A21 to the 525 would yield so many improvements...the most noticeable is spacing between instruments.In my system the highs are musical,real,great tonality, and the mids are even better. The bass compared to the A21 is very different...A21 sounds bigger, 525 tight and detailed. I don't know how much better the 525 will get, but I'm already satisfied. I've reached a point that I'm enjoying music and done buying for now.

Thank you Tim, keep me posted... But do not worry too much if you hear a bit of increased hash on the tuner... IMO the impact of a little bit of RF leakage from a class D amp does not necessarily translate into a perceivable degradation of overall system performance. E.g. ICEpower modules seem to leak a bit... Yet, Bel Canto REF1000M and Rowland M312 remain marvelous sounding amps in their own rights. G.

Gabdx,

You replied:

"I prefer Class D left disconnected at all times."

I consider this both funny and sad; funny because it's a humorous and good line but sad because your fairly obvious bias against class D amplification will likely prevent you from giving them an honest audition in your system.

I assume you currently use another competing amp topology that your allegiance to has resulted in closing your mind to possible better performance. Your choice and your loss.

Tim

Hi Guido,

In an earlier post, you asked if I would perform your FM radio test on my D-Sonic M3-600M class D mono-blocs. Yes, I will test them and report back results on this thread when done.

I'm currently use 3 class D amps in my combo 2-ch and 5.1 ht system:

D-Sonic M3-600M monos for R+L mains

ClassD Audio SDS-440CS stereo amp for rear surrounds

Emerald Physics EP100.2SE stereo amp, bridged to mono, for center channel.

So, I will test them all soon (including the Dayton Audio SA-1000 950 watt class A/B amp that now powers my 4 sub bass system.

You remain the class D Guru in my estimation. Like you, I have a strong interest in class D happenings and its evolution. Now that I've heard 3 class D amps in my system, although only 2 were compared on my mains with music, I can say they all have similar traits:

Extremely low noise floor- music and sound emerge from a dead quiet background. Without an input signal, I've turned the volume to near maximum and listened with my ear an inch from the speaker and it's still dead quiet.

Very detailed and neutral- the low noise floor is probably at least partially responsible for the high level of detail. All of these amps impart no particular sound of their own and present a clear and honest portrayal of recordings as well as the quality of upstream components. This results in great system performance when recordings and upstream components are of good quality. If either recordings or upstream components are subpar, however, these amps will make it obvious.

Very good bass response- muddy or loose bass is never an issue; as Mapman stated, the high damping factor typical on class D amps results in clean, taut bass without exaggeration that easily enables differentiation of the instruments producing it.

Relaxed and effortless- these amps never sound strained, overtaxed or restricted. This could be a function of high power, since they range from 440 to 1.200 watts into 4 ohms, but it may be a result of the topology, I'm not sure.

As others have mentioned, the other benefits of class D include small size, light weight, low heat and very low wattage at idle so they can be left on 24/7.

Mapman,

In a prior reply, you asked:

"Any familiarity with the Class D audio amps? These seem like they must be a great bargain. If the noise isolation is up to par with the latest and greatest as well, that might just be the icing on the cake."

Prior to buying the D-Sonics, I used a ClassD Audio SDS-440CS amp to power my mains for both 2-ch and ht for over 6 months. I would definitely classify this amp as a great bargain. For about $650 you get 220/440 watts into 8/4 ohms, respectively, along with all the virtues mentioned above. The 440 and the D-Sonics are similar in that they both are very neutral, detailed with solid bass and smooth midranges and trebles that are never harsh or fatiguing. The D-Sonics are more detailed with an even more effortless presentation and better dynamics. Since the price difference is about $1,200, I'd say that makes the ClassD Audio an excellent bargain. I'll report back on whether they have rf interference/leakage issues.

Tim

back to the Op - W4S manual said to leave the ST1000 on all of the time.

Hi Bcgator! I have been enjoying the Nova pre/220 combo. It sounds pretty good but I still prefer my last setup (Classe CA-200, Paradound Z Dac, Lightspeed attenuator) more. The Volume control on the Lightspeed was way better, especially at low volumes.

I haven't heard a difference really with power cords on the Peachtree gear either, that's partly why I asked that question. I could definitely hear a difference when I upgraded my power cords on my last set up so I was wondering if it was because the Class D amps draw less current.

Anyhow, thanks again to everyone who's responded! I appreciate it.

Hi Richard, if a single M125 created a great stage and images in your large room, M525 is sure to be amazing for those parameters.... In addition, M525 is known for inducing a great bass experience.

G.

Hi B_limo,

I've got the Peachtree Grand Integrated X-1, which combines the pre, amp and dac, so questions 2 and 3 won't apply.

For question 1, I honestly don't hear sound difference between sitting down to listen after the unit has been powered for 10 minutes vs. 5 hours, so I shut mine down most of the time when not in use just to save electricity.

For question 4, before I bought the Peachtree I called them up with some questions. I don't remember whether I asked them, or they asked me what my plan was for the power cord, but the question came up and I said that I was just planning to use the stock cord it came with. Their answer, and I'm only paraphrasing minimally, was "good, don't waste your money on a power cord, the one it comes with is all you need". That's just what they told me, so use that information however you like.

Just for kicks, I have tried the power cord from my Audio Research integrated and I can't hear a difference so I just use the stock Peachtree cord. For what it's worth, the Grand X-1 sounds as good as the Audio Research - my wife and I can't tell them apart sonically.

I hope you're enjoying your Nova Pre/220 combo as much as I enjoy the Grand X-1. Peachtree makes some good gear.

Guidocorona,

I agree it was just a lack of overall power(my room is 20'x26'). The image size and stage was the best I've ever heard. We had this conversation privately. My plans are to get a 525. I really love the Jeff Rowland sound.

Hi Richard, I suspect that the perceived lack of bass impact with Rowland M125 in your system might have been a meer lack of overall power rather than an architecture issue in the device... Assuming that the overall size of images and stage was not too far from desired when using a single unit, If you used a pair of M125s in bridged configuration you would likely to achieve correct base response, and overall excellent imaging and staging proportions. G.

Kijanki...what a great response. Hearing and tech analysis agreeing on something. What a concept!

B_limo,

I had a Peachtree 220, 220se, and Grand Integrated. The 220se has the best overall sound. With the exception of the Grand, initially I enjoyed the sound of both the 220 and 220se... I never liked the Grand. After a couple of months, to my ears the Peachtree had a thin sound and something just never sounded right.
Recently I've listened to a friends Jeff Rowland 125 and with the exception of bass impact, it was one of the best amplifiers I've ever heard. I confess that's the only amplifier that I've had in my system that presented a three dimensional image.

RF leak thru power cord depends on the type of power supply. Rowland's supplies have zero current switching and power factor correction presenting load similar to resistive. No narrow current pulses. Ref1000m, a second generation uses also power factor correction. In contrast linear power supplies are, in reality, a very primitive switchers operating at 120Hz. They produce a lot of electrical noise since switching is done at max voltage (producing narrow current spikes of high amplitude). Higher switching frequencies of SMPS are easier to filter. Linear supplies in power amps require a lot of capacitors not only to filter out 120Hz but also to reduce voltage drops since they aren't regulated (line or load). For that reason Jeff Rowland uses zero current switching (+PFC) supplies operating at 1MHz, even in class AB amplifiers (Models 625, 725).

One comment on Damping Factor. Speakers are mostly resistive meaning that 4ohm rated speaker will measure likely 3ohm with DC ohmeter. This resistance is in the circuit limiting effective DF to less than 3. Adding 1/10 (0.3ohm) equivalent to DF=27 should not affect the sound. Above that it is only spectmanship. In class D amps very high DF, especially for low frequencies, is caused by the fact that one of the output switchers (Mosfets) is always connected to low impedance point (GND or Vs), making low output impedance to start with. Feedback reduces it even further.

Also, transition from A to B in class AB is audible - it is only matter of extend. It is because trans-conductance (Iout/Vin) is different for one transistor (class B) operating at given time vs two transistors (class A). It is called "gm doubling" and it adds to distortions in class AB amplifiers. It is also the reason why extending area of class A operation (increasing bias) increases distortions.

My experience has taught me that there is a vast difference in the approach that some manufacturers have taken with Class D technology versus others. An example would be Rotel vs Jeff Roland. Albeit, that we are talking about two companies targeting different market segments, but spending time with each has caused me to love one and despise the other. I'll let you guess which is which!

And yes, it loves to be kept on all the time.

Also with Bel Canto, newer ref1000m and ref500m include teh BC custom power board internally as well as custom input board with higher input impedance to work better with tube preamps. These make a difference and go for a premium accordingly. PRior ref1000 and ref500 models were basically stock Icepower modules in a nice box and can be had for much less accordingly. Also I believe 500m uses a newer version of Icepower than 1000m last time I checked about a year ago FWIW.

If you look at second hand OHMS, be sure to identify what version/generation drivers on them. They all tend to look similar on teh outside but each version will sound differnet with the most current ones being the most refined. Mine are series 3 which is one generation old now (current sereis are designated X000) and superceded original X series (including Walsh 4's) and mkII series. Also custom mods to all of those have been done over the years. So unfortunately it can be very difficult to know for sure sometimes unless the source is trusted or maybe John Strohbeen at OHM can help confirm.

Guidocorona,
Have you had any experience with the Peachtree 220? If not, maybe you could pull up the specs and let me know what you think?

Mapman, Guidocorona, Timlub and Xti, thank you all for your helpful and informative posts! I appreciate it and hopefully others will benefit from this also.

Ps, Mapman, I researched Bel Canto last night and a pair of the Ref500m monoblocks and a Dac 3.7 or Dac 2.7 looks like that be an awesome system. You've got me interested in Bel Canto now :)
There's also a pair of Ohm Walsh 4's for sale local to me; if I had the $ for them I'd go listen to them.

Yep... Worth pointing out that my old Rowland M7 monos, which were almost class A amps, reached best performance after one week (yes, that is 7 days) of operation... Tried that one fine Christmas break... The creatures sucked up 720W per side for some three weeks... By the end of the first week they did sound really golden... When wifie received the AC bill she almost threw me out of the house.

May Gaia bless class D... Rowland M925 monos are on 24/7, and I never heard one peep of complaint from Mrs. Better Half.

G.

Every component that I've ever had, preamp, amp, dac, etc, has benefited sonically by leaving it on. Even tubes, I eventually turned off my tube gear to save on life, but on long lasting pre amp tubes, I did experiment over a few weeks never turning them off and you could hear it.

Hi Mapman, no I have never had an amp manufactured by Class D Audio in my system.

Guido,

Any familiarity with the Class D audio amps? These seem like they must be a great bargain. If teh noise isolation is up to par with the latest and greatest as well, that might just be the icing on the cake.

That's interesting to hear.

I know the technology continues to evolve and noise isolation is an important part of the overall equation.

I find with the BC ref1000m, with just a little physical isolation from other components, as seen in my system picture, the only noise issues I encounter is with unshielded ICs. The DNM Reson ICs are my preferred ones in my main system and I am able to use those to good effect from pre-amp to amps, but I do have to play with the physical location/path of teh wires to avoid RF noise. With other more common shielded ICS, it is not an issue. I With things set up properly, I can put my ear up to the isotar tweeters in the Dynaudios and hear nothing with no music playing. So its just a matter of proper setup to provide teh extra touch of isolation needed, which is never a bad thing to consider doing.