Preamp Noise with High-Efficiency Speakers

The OP is going to have a hard time sorting out the noise issue with 104 dB speakers. I do not think line conditioners or isolation transformers are going to solve the issue. He has already said going direct with his CD player has worked. Maybe this is the solution. Based on this if he feels he needs to insert something in between I would have to recommend something that will not add gain. I would recommend either the LSA or a very good TVC (Bent Audio and Music First come to mind), and if there is a need to increase flexibility to have longer cables or to have peace of mind regarding impedance matching then something like the Pass B1 or Burson Audio buffer could work. An MP-3 set up as a tube buffer could work as well.

An isolation transformer can indeed fix or sort out the noise issue mentioned by the poster. I have used them with good results.

Yes, the LS passive attenuator is easily one of the best buys in audio history. It does sound very nice and if I had a very low budget it would be high on my list. Both Charles and I are talking about best in class active tube preamps that cost many times more.

I, like Charles, simply wish George would stop saying we like Voodoo etc..That simple.

I also thank George for his unselfish DIY giving. I am a very active DIY guy and kind folks like George make it possible for me to play.

George's Lightspeed is IMO one of the best PVCs made, but-

If then you don't like this, by all means colour it to your liking with a active preamp of your choice, this is why ALL active preamps sound different as they are not a strait wire with gain, as Nelson Pass alludes to in his statement. And if other can't see this they cannot see the forest through the trees and believe in voodoo.

this quote is rendered entirely fictitious by the last sentence. IME PVCs usually have more coloration, not less, than a competent line section (although as I have pointed out in the past it is because the math of the situation goes against you when trying to use an outboard PVC, Nelson Pass or no; I am sure if he ran the math he would come to a similar conclusion). Try running 30 feet of cable between the PVC and the amps and you will see what I mean.

I find that the better a line stage is, the more they sound like real music.

Now if you really want to make a PVC work, the thing to do is install it in the amplifier so you don't have the math issues associated with the cable.

Don_s, you were correct- I meant 'without'.

The original purpose of the thread was to discuss noise abatement using a very high efficiency speaker (one which I own). George, I have great respect for what you do, but I think the proselytizing is a bit much since many of us have a variety of experiences using different sorts of set-ups, passive and active. I'm not sure this is the place to debate the merits of passive preamps.
And I say this without being condescending. I just recognize that there are many ways to get to the end result, which is music.
No disrespect intended, either to you or to Mr. Pass.

It's virutes are transparency and lack of coloration. It's shortcomings are timbre and dynamics but you have to spend perhaps 10X or more $ to substantially improve on the LSA.

I would say I can agree if the second half of your statement was attributed to passive preamps (a well designed TVC the exception) in general. I find in my system the LSA does not lack in timbre and dynamics. For reference I use the LSA with the Music Reference RM-10. My other system is Atma-Sphere MP-3 and S-30 amp. Sources are the same for either as are speakers. I could live with either of these amp/pre combinations, one costing about 5x less as the other. Sure there are differences in the sound, but they are much more similar than different. Ironically I found a combination of the LSA and S-30 to be less satisfying, although still enjoyable. It tided me over just fine while I waited on my MP-3.

Swampwalker,
There`s no arguement,and I`ve said his component has gotten much praise and compliments(Grannyring for example). My point is don`t be condescending and dismissive to those listeners who chose an active component rather than his.All components have their sonic compromises(to some degree) including his Lightspeed.

Charles & George- Rather than argue about this, one could very easily conclude (and I think Grannyring and others, including myself who have compared the Lightspeed to active linestages have concluded) that the Lightspeed is one of, if not THE best values in high end audio. It's virutes are transparency and lack of coloration. It's shortcomings are timbre and dynamics but you have to spend perhaps 10X or more $ to substantially improve on the LSA. And George, you should be very proud of that!

George it`s interesting how you dismiss the results of others who don`t agree with you. Grannyring and others on this site have put their money where their mouth is and actually purchased your component.Most of them thought highly of it but ultimately found short comings when directly compared to an active linestage in their systems.

Rather than graciously acknowledge their honest opinions, you claim they just prefer the added colorations they hear.A bit defensive and disingenuous don`t you think? Why can`t you admit they have discovered a few sonic flaws with your component when it was out performed by another component? there`s no shame in that, nothing is perfect,and some will prefer your device(it goes both ways,subjectivity).Do you believe you have superior hearing or that the others don`t know what live performing musicians truly sound like? Are they all wrong and you`re right? true to the source(as you claim) is a pale alternative to those components that reach deeper and further and provide the closer to real live music criteria/sound.Why would someone settle for less,tone,body,dynamics and vibrant timbre/harmonics(what Grannyring and others found lacking with the Lightspeed) in the name of "true to the source" which is less convincing in direct comparisions.Humility is a virtue.

Charles1dad Quote:"Anything inserted into an audio system signal path will make its presence known."

That's right, one of the best open/transparent sounds lately I have heard was from a old Musical Fidelity A3/24 dac that has such a beefy output stage (standard) that can give 6watts!!!, (modified output resistor from 47ohm to 1ohm)
This dac was directly attached to a pair of highend 108db horns from Italy (no power amps, no preamps), directly from the dacs output rca's to the speaker terminals.
The more active junk in the signal path the worse/electronic the sound becomes.

Cheers George

It seems some prefer a more realistic sound thus the preference for high quality actives.Everything sounds different(not just actives) including passive devices(they have their signatures also) and even going direct the sound varies. Anything inserted into an audio system signal path will make its presence known.So you might as well go with what sounds most real and enjoyable to the individual listener.

Germanboxers, glad to see you get the meaning of my username! Cycle on!

Like I keep saying.

"By all means you can change the sound to your liking with a active preamp of your choice, this is why ALL ACTIVE PREAMPS SOUND DIFFERENT, as they are not a strait wire with gain"

But if you want to hear the source as it is, go direct this is, a straight wire with no gain.

Cheers George

Grannyring - just kick it up to the big ring, get out of the saddle, and power
over that voodoo!! Maybe it'll work for you?

In my case, I made the mistake of wearing a Tiki Talisman around my neck
and I too have had to live with a voodoo curse. Incredibly, having a
Concert Fidelity Linestage in between my DAC and amps actually sounds
more real, more live, and more enjoyable than running DAC-direct to amps.
Rather than fight it, I've resigned to just live with it...with a smile on my face.

Bill.
We have a piano in our that sounds beautiful. I attend the local jazz clubs frequently and love them. Any audio component that strips or dilutes that tone,body,weight and dynamics that I hear"always"in live music is a flawed component. If this is voodoo or coloration, I`ll have more please.You tried the Lightspeed "three" times, once would have done it for me.

Charles I am on the same Voodoo vibe as you. Enjoy the spell you're under! I am...

Any component that preserves the full tone,harmonics, body, scale and dynamics that are so obvious with live music is closer to the truth.Most listeners 'long term' won`t be happy with a device that`s incapable of maitaining this vital signal information. How the attributes of fuller tone,saturation and dynamic vibrancy can be a "coloration" when their presence is so very obvious with live performances? It would seem the passive(or active in some cases) component is subtractive of the complete audio signal if it doesn`t maintain these mandatory and honest aspects of the music, this is why music has emotional power and involves us.If these nautral and intrinsic features of live music are not lost or diluted then the component is doing its job,be it active or passive.
Regards,

Roscoeiii and Grannyring,
I know others who patiently tried various passive components in their system based on the predicted advantages. Ultimately they returned to high quality active linestages as they provided a more realistic and natural sound that more closely mimics live instruments and human voice, just as you two discovered.No theory will ever substitute for the personal experience of direct listening with your own ears.Nothing.
Regards,

Not apologizing to you at all, just correcting your misinterpritation of Nelson Pass's statement, as you also did with my post.

Cheers George

No need to apologize George. I have found what works best for me in my system and am quite content. That happened to be an active pre in my case. Please do not take it upon yourself to put down what I have found to work best for me in my system.

Also just to let you know that Nelson Pass originally designed the B1 buffer back in May 2008
http://www.diyaudio.com/forums/analog-line-level/80194-lightspeed-attenuator-new-passive-preamp-137.html#post1521766
to be on the output of the Lightspeed Attenuator so it could then drive low input impedance amps of 20kohms or less that some of his amps have that people want to use the Lightspeed with.
You can read all about it on the Lightspeed thread on diyaudio.
After that he released it in diy form with a passive pot for diyer's who wanted to use just a potentiometer as the volume control.

Cheers George

Sorry Roscoeiii, you need to read Nelson Pass's quote more carefully.

"just an input selector and a volume control.Hardly any noise or distortion added by these simple passive parts"
His B1 buffer is active

"no worrying about what type of capacitors – just musical perfection."
His B1 buffer is also capacitor coupled.

Cheers George

My active voodoo sounds more like music. My voodoo ways confirm my active sounds more like the instruments sound live. Oh well, live music cast a spell on me causing me to enjoy great active, tube preamps!

Tried passives and George's LS on three different occasions! Purchasing the unit on two of those occasions..... Installed in passive friendly systems it was very good, but missing the cues that equate to the sound of live instruments and voice. Nice for sure, but the overall tone, natural weight and scale of music was simply absent. No voodoo at all, just reality to my ears.

Others will have a different experience and I say great! You're not a victim of voodoo, but just a different opinion and preference. Enjoy

But it should be noted that the passive preamp offered by Pass is no mere volume control. It is a buffer design that attempts to eliminate impedance issues that afflict many passive designs, IIRC.

I will also add my 2 cents:

Cent #1: I agree that attending to the gain structure of a system is a very important part of achieving system synergy. With speakers like the OP's, too much gain is likely to be an issue.

Cent #2: I have also never found a passive preamp that doesn't impact dynamics and oomph, compared to an active pre. Of course to get both the drive of an active and the level of detail of a passive you need to spend a good deal. So for some budgets you may need to choose one or the other. I found my perfect balance in the Musical Fidelity kW linestage.

YingtonggaoI am not sure the DP-777's output impedance (at more than 100 Ohm) and the FL-100's input impedance (57k Ohm) is a match made in heaven.Yingtonggao

100ohms into 57kohms
This is a great/perfect match end of story, especially that you have more than enough gain. And if you look at internals the DP-777 the volume control is not a tacked on potentiometer on the output rca's, it is a analog domain volume control that is after the dac yet before the tube output buffers. This will be the most transparent/perfect way you can get the signal from your dac to the FL100 amp. If then you don't like this, by all means colour it to your liking with a active preamp of your choice, this is why ALL active preamps sound different as they are not a strait wire with gain, as Nelson Pass alludes to in his statement. And if other can't see this they cannot see the forest through the trees and believe in voodoo.

Cheers George

just read this quote from Nelson Pass, I think we could all aggree that we all here with our combind wisdom pale into insignificance compared to him.

Given the fact that Ralph from Atmasphere is among the contributors to this thread I certainly do not agree with the above. :)

Regarding the preamp vs. no preamp issue my experience is that it also depends (very much in fact) on the component used (maybe on how transparent these components are). I have recently upgraded my power amp from the Accuphase A-45 to Accuphase A-65. Except for the power ratings and price the two amps are almost identical on paper, in fact, the cheaper amp has better specs in some cases (though maybe those are typos in the manual). In reality, A-65 + cd player sounds better than the A-45 + pre-amp + cd player. Putting the pre-amp between the A-65 and cd player has brought some improvements. Whether or not these improvements justify the price of my pre-amp is debatable.

I too have very efficient speakers, i.e. Avantgarde UNO G2, and luckily I had no "noise" problems.

Paul

Wow, I did not know my thread can attract so many responses in days! It looks like noise is more attractive than music.

Georgelofi, I currently do exactly what you say: set the input impedance at max (57k Ohm on RCA) and run DP-777 directly. I normally listen at -30 dB on my DP-777, so you are right, modern electronics have too much gain and we are throwing the signal away. And I have to either throw it away at DP-777's internal volume control, or at an external preamp. I don't know which way is better because the noise issue doesn't allow me to evaluate preamps.

I appreciate your (and Nelson Pass's) belief on the preamp-less approach, but I am not convinced that the volume control inside the DP-777 is a world beater; and I am not sure the DP-777's output impedance (at more than 100 Ohm) and the FL-100's input impedance (57k Ohm) is a match made in heaven.

When I use conventional speakers (85-92 dB), having a good preamp is a clear winner. Audia's own Flight Pre actually worked much better than Cary SLP-05 due to impedance matching, and running AMR DP-777 direct sits somewhere between these two preamps. With a Cary V-12R power amp the results is totally reversed in favor of the Cary SLP-05.

I don't want to turn this thread into another arguement over preamp/preamp-less comparison, but we all know system matching is key and there's no way better than all others. At one point I bought an all Audia system (CD/Pre/Pwr), and an all Cary system to reduce the hassle of system matching. But at the end of the day it is still not simple. Now I am thinking about buying a Devialet D-Premier and sell everything else.

Cheers!

Atmasphere,

Did you mean to say "without" instead of "with"? If not, then I am confused by the statement.

"A simple solution is a buffered volume control. This offers proper volume control performance with it acting as a mild tone control or hindering dynamic impact."

George, you can't count on a preamp having a 47K input impedance- that is for phono, not a line section, which might often be more like 100k.

Amplifiers frequently have 100K input impedances too. When you run impedances that high and then introduce a high impedance (passive volume control) between the source and the amplifier, the result will be that the system is going to be extremely sensitive to cable colorations. There will also be a loss of bandwidth as capacitance in the cables take their toll. In addition, if there is any input capacitance in the amplifier it will not matter if the source is direct coupled- you will loose bass impact.

There is no 'blasphemy'. As much as I respect him (I think of him as one of the top ten designers worldwide) Neslon Pass is simply wrong about this although I agree that it makes no sense to have a lot of gain and then burn it off. There are more elegant ways to do it than passive controls though.

A simple solution is a buffered volume control. This offers proper volume control performance with it acting as a mild tone control or hindering dynamic impact.

Neat post, German B. And that guide book is pretty clearly written. Nice contribution!

Hi Ying - I highly recommend buying the Jensen noise troubleshooting kit. It is inexpensive (or you can make the devices yourself - they give you the directions) and will come in handy for years to come as equipment, rooms and homes change.

I have 101dB/m speakers and recently installed a new and quite expensive Linestage and immediately noticed the buzz that was always present, but low in level, grew in volume to where it was annoying at the listening seat during quiet passages. With the help of Jensen's troubleshooting guide, I tracked it down to noise being induced in the 3m unbalanced IC's I run from Linestage to amp. With IC's plugged into the amp, but not plugged into the Linestage, the noise was loud and variable depending on how the IC was moved around. Isolation transformers on the IC's won't fix this and I couldn't move IC and equipment that significantly. My solution: my Audion amps have a gain control knob. I turned the gain down on the amps and use more gain in the Linestage. Noise has vanished.

Get the troubleshooting guide with special RCA couplers ($12.50) or print out the guide at the link below and make your own. You'll then be able to unequivocally identify the source of the noise. Dave and Bill from Jensen are also great and very helpful if you need help.

Jensen Noise Troubleshooting Guide

Good luck. You shouldn't have to live with noise nor should you have to settle running DAC direct if you don't want to.
Jordan

It is a banaid fix because his AMR has to drive the input of a preamp through the same interconnects and pre amp inputs are usually 47kohm (industrie standard), his FL100 is acually higher and easier to drive at 57kohm through the same interconnect and 1 pair less as well.
And gain doesn't even come into it as he has an abundance. and as a bonus it's all direct coupled, no "masking" capacitors in the signal path as it would be with many preamps.
A preamp in this case in the path can only add colouration/distortions that some may like because it's masking a problem elsewhere.

Like I said Nelson Pass's quote says it all, to contradict it is almost blasphemous. read again carefully.

Cheers George

A Quote from the master Nelson Pass

We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.
Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.
Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.
What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.
And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp.

Cheers George

Amen Atma!

If after that you still prefer an active preamp, then it's the colouration/distortion of it you like, which is a bandaid fix for something else that's wrong.

Its not a bandaid- an active line section can control an interconnect cable and reduce its artifact. A passive cannot.

Yingtonggao, just set the input impedance of your FL100 to the max, which is 57kohm and feed your AMR DP-777 straight in and use it's volume control, which quote is a "Direct-Coupled Analogue Volume Control." No extra caps in the signal path.
This will be the most transparent/dynamic sound you will get PERIOD! As it is basiclly then a straight wire from the 777 to the fl100 then (no impedance mismatches). And you will have bags of gain left over still on the AMR's volume control.
If after that you still prefer an active preamp, then it's the colouration/distortion of it you like, which is a bandaid fix for something else that's wrong. Remember it is impossible for an active preamp to extract any more music than what is on the disc and being presented by your DP777, it can just add artificial things, as it does not make music itself.

Cheers George

Just got an email from the maker of the FL100 and your amp is also dc coupled. No caps in the signal path from your DP777 volume control all the way to the speakers, that is a big plus always.

If it sounds like white noise, then the signal to noise ratio on your preamp is not high enough to use with the AG horns. If it sounds like 50/60Hz harmonics, then it may be due to your power supply/transformer saturation/DC offset etc.
Finding high quality pre and power amps to run with ultra high efficiency speakers like the AGs is hard. I have a pair of Duos and run mine with TRON amplifiers (www.tron-electric.co.uk).
TRON amplifiers have been specifically designed to work with ultra high efficiency speakers. The designer, Graham Tricker, is the Uk distributor for Avantgarde and has a pair of Trios in his listening room. Ralph Cessaro uses TRON as his preferred amplifiers for his Liszt speakers.
TRON are distributed by Jeff Catalano at Highwater Sound in NYC. Thomas Woschnick (TW Acustic turntable designer) uses TRON for his own personal system.

Wow, lots of good suggestions on possible cause of, and solutions to, the noise problem. I personally had a problem with hum and buzz that came from a different source. Although my audio system and video system are separate, they share the same branch of power from the main panel. When my system seemed to suddenly develop a noise problem, I looked at the usual suspects and then tried something else. I cut the 75 ohm cable feed to the video system. That completely cured the problem. It appears that the cable feed managed to contaminate the power line even though the buzz/hum was not that big a deal with the video system (audio system is relatively high in efficiency, and thus, more susceptible to noise issues). Even though the entire video system was itself on a Furman power conditioner, the noise managed to infect the power feed to the audio system. I tried isolation transformers on the cable feed, but that did not work. The problem had to be cured by the cable company.

Worth seeing if changes in location of preamp (and associated ICs, especially if not shielded) relative to surrounding gear and any other electric gear, power cords or appliances results in any change in the buzz level. If so, take note of where noise level is minimal and use that to help identify what the external source of the noise might be. Repositioning gear alone might be a practical solution. The further each piece is away physically from each other and other potential noise sources, the better. Flourescent and halogen lighting as well as dimming devices are also often culprits for causing noise and interference with other devices, as are many digital devices and devices with large power transformers, like many power amps for example. Use of mu-metal sheets to provide additional isolation is another cost effective option to help in many cases. I use mu metal as an external barrier around my phono step up transformer device. Low level phono sections/gear are the most noticeably sensitive usually to external sources of noise.

No doubt very high sensitivity speakers like Avantegarde up the ante in terms of need for that feeding them to keep noise levels minimal.

The problem with a passive is that it can act to functionally reduce the value of the coupling cap that might be in the source, such as a DAC. In doing so this is how bass impact can be lost. The other problem is that the system will be a lot more sensitive to cable artifact. This is likely the why of Nelson Pass' comment.

In a high efficiency system, it is more elegant to simply not have the gain. Power amps typically have about 30 db because speakers might only have 87db efficiency. But what if the speaker is a good 15-20db more efficient? Then it makes sense to have less gain in the amp, so the preamp or source can have the volume control in a reasonable (higher) position.

If you think about it, amplifier and preamp manufacturers have a difficult dance; to have enough gain to work with lower efficiency speakers but be quiet enough to work with higher efficiency speakers too.

We solve the problem by offering a jumper plug for our amplifiers that replaces one of the voltage amplifier tubes, thus reducing the gain (and the noise floor) of our amplifier.

With regards to grounding: If your equipment is built correctly there should be no need to resort to exotic grounding solutions like a copper stake in the yard. 'Built properly' means that the chassis and the circuit ground are two different things. This has been challenging for a lot of high end audio designers; but if you are going to meet the directives for the CE mark or similar, this is a problem that will have to be dealt with.

Yingtonggao, just read this quote from Nelson Pass, I think we could all aggree that we all here with our combind wisdom pale into insignificance compared to him. Remember your FL100 takes 1.4v input to clip. Your AMR DP777 gives out more than 2v and you have 104dB sensitive speakers.

A Quote from the master Nelson Pass

We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.
Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.
What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.
And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp.

Cheers George

Ying: Just keep in mind that the Granite Audio thing is not really a total solution, but in some ways a 'band-aid'- and i had mixed results with it; on some system configurations with different amp and preamp it seemed to work better than others. Just sayin'. And, you really need two people to work it successfully- one to throw the various switches (exponential combinations, when you add in what gear you join on the same 'path') and one to listen to results. You also may have to order more of their grounding cables and longer lengths to get it to connect to various components. (and yet another variable is not connecting to some components). I bought mine back in 2007 or so, it is far cheaper than some of the esoteric external grounding solutions available today, but imagine if you are handy, you could come up with a DIY solution. ( Ralph or Almarg might chime in here), you may be fighting potential grounding problems within the components themselves. None of this is easy, but it's more labor than anything to get it sorted.
Let us know what you come up with. I hate hum!

Whart and Triode: I may have to go through the lengthy process like yours to eventually get rid of hum/noise. I was thinking about Granite Audio Ground Zero yesterday.

Georgelofi and Atmasphere: There are pluses and minuses using an active preamp, and endless threads/debate about going preamp-less. I am fully aware that in recent years digital front ends have better and better output stages capable of interfacing power amp directly; and before I fix everything I have to live with the AMR DP-777 driving my power amp (Audia Flight 100) directly. But you never know what you are missing, and I've witnessed many times a good active preamp can do wonders to a system.

Passive volume controls and digital controls offer their own colorations. You are certainly not throwing the money away if the active preamp delivers on its promise. They can be plenty quiet on high efficiency speakers if the system is set up correctly.

What's wrong with just using the AMR DP-777 with it's volume control or just use a passive preamp like Lightspeed Attenuator or similar with just a pot in a box, no noise with passive pre's. And as you have such high sensitive speakers you are throwing money away using an active preamp, unless you like the colouration they can give.

Cheers George

I too have super sensitive Avantgardes (107 dB Duo Omegas) and run a tube pre and tube amps (as well as an AMR tube CD player, and analog with tube phono stage) with virtually zero noise - one must put their ear right up to the tweeter horn to hear the slightest hint of tube rush with no music playing, even at "generous" volume settings.

I would definitely check for ground loops first, and ensure that you have clean power (I run dedicated 20A circuit for my amps/sub amps and dedicated 15A circuit for my pre and sources, the latter through a Shunyata Hydra).

A tube pre with separate L&R gain controls will allow you to dial in the sweet spot of gain for your rig, as well as providing a de facto balance control, handy in asymmetrical rooms.

I transitioned from electrostats to the Avantgarde Duos almost seven years
ago. Quieting the system was a major effort, but yielded enormous
rewards. I agree with the above remarks about trying to find the source of
the hum. At a certain point, mine was not pronounced, but I wanted the
system to be dead quiet and worked further on the following things, some
of which you have done:
1. dedicated AC and subpanel
2. running a noisy compressor for my tonearm into an isolation transformer
3. identifying noise inducing appliances that contribute to low level hum on
the system- even dedicated lines don't really 'isolate' the system power
from the rest of the household electrical system. For example, a hi-
intensity, low voltage spotlight over a kitchen sink 3 floors away will induce
hum. Solution- when I am listening, we don't turn on that light. Ditto on a
room humidifier in one of the bedrooms. Finding the source may thus not
even be 'in the system' in my experience.
4. Cable and equipment layout, as others have mentioned.
5. Playing with grounding solutions- for a while, I used that Granite Audio
Ground Zero- a sort of external star grounding system that allowed you to
change impedence on various grounds (these are not a substitute for the
ground to power receptacle but in addition to it). It worked for some system
set-ups, but I'm now at a point in my evolution where I don't need it.
6. Others with more technical experience can weigh in here, but as I
understand it, different components may have different internal grounding
set-ups. That may contribute to the problem.
7. Alot of this is simply time consuming and mind-numbing, frustrating
experimentation and fiddling.
8. Positive note: it can be done! My system is extremely quiet. And the
results are worth it, not just for avoidance of hum, but to yield more
information coming through the system.
9. Anecodotal observation: The Avantgarde Duo is tricky in the extreme to
really nail. A lot of folks critical of it have heard it set up badly. I'm not
suggesting that it is the 'best' or 'better than' anything, but I can get an
extraordinary amount of music out of my system.

Thank you all for the very insightful suggestions. I'll do some experiment early next month. I will try removing the ground pin (on power cord) one by one, and then try a passive preamp to see if it's a gain issue. I've had a Benchmark DAC-1, even at 0DB setting (10 volt output on XLR!) it is dead quiet with the same pre/amp. Will report later.

This could be caused by a ground loop. A ground loop can exist if your equipment is built without a proper grounding scheme.

If you float the ground pin of the amplifier power cord from the wall (using a hardware store ground cheater) and the buzz is solved then it is the amp. If this works best on the preamp than the preamp could be at fault. In either case it is not recommended to operate the system without the equipment being properly grounded- there is the risk of shock or fire hazard if a component develops a fault.

If you are able to sort out which component is the culprit, you will have to come up with a solution. The best solution is to have a proper grounding scheme installed in the defective equipment. If the manufacturer gives you pushback on this have them give me a call (seriously- setting things up right is not that hard).

Otherwise an isolation transformer for the problematic unit could sort things out.

It is encouraged to have low-gain low-power amplifier for high efficiency horns and same applies to the preamp that should be minimalistic. I belive hat Wyred4Soun preamp may surprise you, but I'm not sure what amplifier(s) you're currently using

Good comments by the others. One additional thought:

By any chance have the preamps you have tried been located close to the DAC or the source, perhaps just above or below it or them in a rack? While is the power amp located several feet or more away from those components?

If so, it could be that the DAC and/or source are radiating digital noise into the preamp. If that seems like a possibility, try locating the preamp a few feet away from the other components.

Regards,
-- Al

I assume that you've tried all the different amps, preamps, and cables using your AMR dac as the source. If you are getting the exact same problem with all of that equipment, the dac may be the problem. I know the problem doesn’t happen when you run it straight into the amp but that doesn’t rule it out. Aside from the volume control on the dac, it may have global gain settings as well. The gain from your dac plus the gain from your preamp may be too much. I can have the same problem with my Wadia. When I use it with my Wilson speakers, I have to open it up and lower the global gain using a row of dip switches Wadia gives you just for this reason.

I'm not saying this is definitely the case, but its definitely worth looking at. If it turns out that you don't have any global gain settings, try going from the fixed out to the variable out on your dac and lower the volume manually.