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 |
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 |
B limo,
By 'digital amps' do you mean class d amps? 'digital amps' is a bit of a misnomer probably persisting because people believe 'class d' refers to digital, but it was just the next letter in the alphabet used to designate various types of audio amplifiers using different methods of amplification. Class A defines amplifiers that use a more traditional circuit that has input devices that constantly remain 'on', resulting in excellent sound but produce excessive heat as a byproduct. Class D amps use 'switch mode power supplies' (smps) that are able to switch on and off extremely quickly, which produces much less wasted heat as a byproduct. I use a pair of class d mono-blocks that sound very good, output over 1k watts and barely get warm to the touch no matter how hard they're driven. I leave them on 24/7 since they only require a few watts of electricity at idle.
I'm no expert on amplifier design, so others may need to answer your other questions. So, if by 'digital' you meant class d, then yes I would advise to leave them on constantly. I thought it would be useful to clarify your question before your thread progresses.
Let us know,
Tim |
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
|
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. |
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 |
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
|
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 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 |
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 |
