This is a tough one and it would take a book to explore all the possibilities but let me tell you what I do in these cases. I pull the equipment off the rack and set everything on the floor. Then I put the most basic system together. Amp, speakers, source, etc. Then I use my ground breaking RCA interconnects or a ground breaking power cord/device to isolate the problem. My toughest case so far was an ungrounded preamp that would hum. Turned out if I reversed the two prong plug, the hum went away. Drove me nuts but I was totally relieved when I solved the problem.
So...good luck and just get down and dirty and work the issues until you can with certainty identify the offending hook-up or component.
I’ve fretted over hum a time or two...one was when my 2 subs weren’t grounded the same (how that happened is still a mystery, clearly operator error), and recently when moving some things around I mistakenly swapped power supplies between a Schiit Loki EQ and a Magni 2 headphone amp...the Loki was not happy as it requires 16 VAC and the Magni 14, so the Loki pointed out this issue by adding a nice low end hum...noticed the power supply swap after some hair pulling checking of every damn thing. Man...
loud enough to hear at the listening position, but just barely. Quite noticeable when standing at the rack.
I have about this same amount of noise, at least. Every time I think it might be worth trying to eliminate it I think how much time and effort that can eat up, and for how little, and balance that against how likely it is I am even able to find it, and say naw not worth it. Then I read one of these stories and say to myself, good man miller, pick your battles. The improvements made the day I spent tweaking my turntable are monster, and instead could have had naught but frustration to show had I spent that time tracking down noise instead.
Then I drop the needle and whatever the volume even extremely quiet vinyl is more groove noise than the other, so what really would be the point?
Anyway, the one fact that stands out to me is
Hums with any source, not volume dependent, still hums with no source components attached (I even tried unplugged them from the wall too). But the hum stops if preamp is disconnected from amps.To me the simple fact the volume does not change tells me this hum is not coming FROM the pre-amp, because then it should increase when the pre-amp volume is turned up. Only thing I can think of is its an interaction WITH the pre-amp.
Since you have already tracked down and eliminated everything there then the only thing left seems likely to involve a rather detailed technical knowledge of your amplifier. And with that I can only punt and hope Ralph is there to make the catch and run out the play for a touchdown.
Thanks for all the responses!
noromance: Wifi routers etc can't affect the system if their AC circuits are turned off, or can they? I tried turning all breakers off except the sound system, and the hum persists.
russ693: I think I tried reversing plug polarity when I tested cheater plugs, but will try again to be sure. I have disconnected everything except the preamp and amps and it still hums. I've swapped interconnects. No difference.
petg60: Regarding checking with multimeter, would you clarify exactly what should be connected and what I should measure? I'm a bit ignorant of electrical stuff so just want to make sure.
millercarbon: Hilarious... and agree with everything you said. At year end I said to myself "Hey why don't I frustrate the cr%p out of myself again and try to solve the hum again?" Yes, it does not seem to be the preamp per se, but the interaction with it. And the only things it can be interacting with are the power supply or my amps... assuming this is not coming from the air in terms of RF or something.
slaw: As I noted, unfortunately I can't, at this point, remember when the darned hum began. I realize that would be very helpful.
erik_squires: Never thought to check if one amp only relieves the problem! I will check.
ozzy: Interconnects are all RCA. I have not run the sources straight to the amps but I have replaced the preamp with a preamp section of a cheap receiver, and the hum goes away.
To me the simple fact the volume does not change tells me this hum is not coming FROM the pre-amp, because then it should increase when the pre-amp volume is turned up. Only thing I can think of is its an interaction WITH the pre-amp.
I would say Bingo! on this explanation and perhaps there is something inherently wrong with either component that only comes up when the two are connected. The issue may be masked with different components.
Stick with your cheater plugs that remove the AC ground at first, and then find some nice thick copper wire and run it between the pre-amp and amp chassis as short as you can. You may need to use a screw on each one and make sure you have an electrical connection to the chassis. Do not make the connection to an RCA connector.
Of course my next question is whether the RCA on either are electrically connected directly to the chassis.
Audio2design: I set up a star grounding system and grounded all the components to the Ground Zero unit, including wires from the amplifier chassis to it. No effect. I did not try a wire from the preamp ground to the power amplifier chassis by itself, But I assume if this would work then the star grounding would have worked right? However I don't think I did that in conjunction with cheater plugs. Why would I do those two things together? I am interested to know!
Ground zero claims that their system negates the AC ground connection impact. That assumption is based on the assumption that their ground connection is much better than the one via the AC plug. That is not guaranteed, so for test purposes to start let's ensure it is gone
I am concerned that perhaps you didn't have strong ground connections to the equipment. Hope you have a meter. Take a measurement between a ground wire and a few screws to make sure.
I would be inclined to try the preamp on a small isolation transformer. Perhaps there is a ground path or common mode noise path we are missing.
Check the voltages in the main panel. Measure phase A to ground (120 vac) and phase B to ground (120 vac). Then across A and B (240 v). If phase A and B are not the same, call an electrician. There may be a loose neutral in the meter pan and the voltage is not seeing a low impedance back to the panel and the imbalance causes a voltage on the neutrals in the house. This can cause hum in transformers. There’s always a voltage on the neutral, but it’s usually less than 2 volts. Anything more and it’s a problem.
Before that, tighten all the breaker lugs and neutral lugs in the panel. They do come loose. This alone may solve the problem.
If it was me and the voltages are correct at the panel, I would go to the panel and install a temporary circuit. Install breaker and connect a 10 ft wire (romex or armored) to a receptacle in an enclosed electrical box, plug in the preamp and see if it still hums. If it doesn’t then the problem is the wiring in the house (e.g. the neutral wires have a long run back to the panel, creating a voltage across them). If it still hums, then I’m at a loss.
It’s a tough call because that preamp has no problem outside the house and the problem is replicated on other circuits inside your house... and isolating the circuit is of no help. A voltage imbalance can cause dc to offset the ac waveform, as can fast switching loads inside the house — which can be ruled out because you turned everything off except the audio circuit.
...Or the utility power itself may be a problem. That’s why an electrician should analyze the power into the house. It’s possible that preamp is more susceptible to power issues than your other equipment. My guess is that dc is finding it’s way into your electrical system.
I think checking the main a second time is a good idea. Neutral and grounds. Do I think there is a problem in the main? NO. If your confident with you’re electrician.
Electricians and mechanics are NOT in short supply in my family, my brother retired as the local BA in Martinez CA. 12-15 last count. 4 HD local 3 mechanics.. No shortage of skilled labor, or muscle :-)
ALL of them learned what "tight" is from Uncle Scotty..(ME)
ALL were taught how to torque properly..
I use a Variac when I run into things like this.. Most electricians DON’T have them. Most old audiophilers DO.. You have a voltage difference between a "piece" of equipment and usually ALL the rest. or You have an old piece that need to percolate for 10-40 hours to tighten up the old caps.. So they just don’t leak all over..
Tube rectified in a preamp? MATCHED and checked for noise. NO excuse, on that one... You have to make sure it's not noisy at YOUR house... Not the Tec....Your house.
audio2design, mentioned an isolation transformer. A variac is, with the added feature of being able to VARY the voltage.
I suggest (only for a test) to very the voltage from 110 all the way to 122 VAC, SLOWLEY, and see if the noise goes away.
1. I would recheck MY main. I don’t trust anyone more than me.. NO
ONE. Check for 120 (A) 120 (B), 240 between. To ground less than 1% of the total being checked..
2. I would make sure I had a good PC going to my Pre amp. I’d change the PC no matter what. Just to test... I would pull the fuse clean the pocket with Isopropyl, LET IT DRY and inspect the HECK out of the fuse holder look for carbon trails.. LOOK close.. Reinstall a new fuse, a busman will do. NO fancy fuses for now...
3. The valves for the PS you know where the noise is coming from.. those valves would be changed (just for a test) MATCHED and checked for noise. NO EXCUSE on that one for sure. The pins and pockets on ALL the valves need to be cleaned and reseated, and pin pockets need to be checked for tightness and brushed and cleaned.
All this takes about 1-2 hours, from the mains to cleaning everything..
I would test NOW, did you get lucky, no luck go to # 4
4. I’d smoke a little weed about now.. :-)
Mind you, after everything you did THINK.
Clear your ears and
5. Hook up the Variac a DMM and turn it to 100 volts and go from there up to 122 or so.. You have to have a DMM, (no analog). LISTEN.
If it goes away, because of a voltage difference, LOL don’t be surprised.
If it doesn’t go away don’t be depressed.. Closer than you think..
You have already tried many things and gotten a lot of good advice so I will offer a few short items.
First, did David Berning offer you another pre amp? For starters, it would be interesting to see if the problem continues with an identical model. If it doesn’t, then you could make some sort of deal with him about swapping your current one for the replacement.
Second, I don’t know what a cheater plug is, but I have had a few hum problems many years ago. One was solved by a PSAudio device that turned hum into a light (nightlight). It was the size of a match box, attached to the power strip, and the first hum problem that I had disappeared completely. A few years later with changing components a nastier hum wasn’t defeated by this some I bought something called a “Humbuster” from Sweetwater. This required plugging the problem component in to the humbuster and then plugging that into the power strip and was entirely successful. I couldn’t tell if the SQ from the component in question was affected
Oh buddy, your Spidey Senses are tingling are they?... LOL
It’s always what you haven’t done... the way of the mechanic...
Worse yet, or done WELL and correct..No reason to doubt your own work.
No reason NOT to recheck others. I NEVER trust anyone... Brothers in all, that is the difference between a professional, and (NOT). Don’t assume stuff... Especially trouble shooting.. CRC, Check RE Check!!
You’ll get it figured out EVEN if you don’t stop the noise... BUT so you know, I’ve always figured out what caused the noise. EVEN if the person didn’t want to, OR couldn’t afford to fix it..
The issue for me is simple. I WON’T put up with it.. there is a difference... My stuff is BLACK. Almost spooky it’s so quiet..
Valve, SS, Class A, AB, D. Mix and match. Quiet a church mouse.
I have a buddy that says he doesn’t like it... YUP... Too quiet.. :-)
Most Variacs are not isolated.
I didn’t mean to imply that, JUST this is an option, a single coil, autoformer.. It is a great trouble shooting device, in lue of isolation.. cheaters, GF isolators, and a few others...
It will serve MY purpose..
The more you type, the more I learn..about you.. You related to Donald Trump. by chance?
Watch and LEARN... let the mechanic give it a shot.
I’m the one doing the bragging, ALL right.. LOL Let’s see if I can HELP... If not pick it apart AFTER that, ay... Just saying.
OP... excuse me, I had to make an adjustment, left cheek sneak? Romp..
Time to feed the chickens..
It’s the Preamp as you already know.
Both channels is a clue, perhaps a good one.
Some more investigation. Is the hum present at both low level inputs and high level inputs?
Connect only 1 high level source, one input at a time? Is it present at each input?
repeat with low level inputs.
Have another system, i.e. office, shop, to move the preamp into? Good? If good, then there is some unholy combination of interconnects/speaker wires/crossover component. If ok on the other system, you can in good faith sell it to someone who lives in Lake Woes Be Gone
My McIntosh SS Preamp C28 had a faint hum on low level inputs only. I bought a box, sent it to McIntosh factory, it came back ’fixed’. Same low level hum, low level inputs only. How the heck can I sell it knowing that?
I took it apart, gave the evil eye to the internal ground connection to the chassis. Unsoldered it, stripped end of wire, removed paint from the area, replaced with bolt and lock washer. Gone.
Days gone by, FM antennas were like the plague.
@montaldo you posted...
- Hums with any source, not volume dependent, still hums with no source components attached (I even tried unplugged them from the wall too). But the hum stops if preamp is disconnected from amps.Since the hum appears with the preamp only connected - try this...
Take a piece of wire with a small piece of insulation trimmed at each end
- touch one end to the neutral collar of any RCA or XLR jack
- touch the other end to a ground point
IF the hum disappears then the neutral side of the pre-amp is not at ZERO volts.
This is common with components that have a two pin mains plug or a wal-wart power supply.
- build a ground lead by attaching a piece of wire to the GROUND PIN ONLY of a mains plug
- attach the other end to the NEUTRAL ONLY of an RCA or XLR plug of the pre-amp
- plug the RCA/XLR end into any unused socket
- plug the mains plug into any outlet
Hope that helps - Steve
Could it be something else interfering with your pre amp like a nearby light? Something metallic? Proximity to another component? Did you blow out/clean pre amp especially all tube connections?
Before any more hair pulling could you get a loaner pre amp just like the one you have and try that?
Did you pray to St. Jude?
Did you try not plugging pre into the Shunyata T6000?
Apropos of nothing, with my gear, I found a Fuhrman reference to be a sound diminisher and switched to another power conditioner.
If you hold the pre amp and the hum goes away or decreases there’s proof positive of a ground issue as you are acting as a ground.
Have you ever given your pre amp a light to medium smack/tap? Seriously.
Did it ever work without hum?
There is no way in the world I would live with hum.
You have a temporary spare, I would ship that thing back to David, get him to give you a very good deal on a new one if you love his stuff so much.
So many knowledgeable members have offered great suggestions. I doubt that I have much more to offer. In light of all the great suggestions relating to ground loops, critical components and I/Cs near house 120v/60Hz lines, and the like, ... I assume that grounding and ordinary 60 cycle hum issues are not the problem. But here are few other simple ideas:
1. Are you sure the preamp is working properly. You posted that:
I had my local tech hook up the preamp on his bench and it is quiet as a mouse. I've also corresponded with its designer, David Berning, who has been very responsive and helpful. But no luck solving it.Ok, but have you sent the preamp back to the factory for a complete check-up. I own ARC gear and some of my pieces were getting long in the tooth. Even though I do not like shipping my gear to anyone ... period ..., one of my ARC pieces had a problem so I sent everything back to the factory for a check-up. What a nightmare. To my total surprise, all the tubes (almost new) in one piece were toast. ARC replaced all the tubesin the unit. Go figure.
2. Incompatibility? Let assume that your pre is in proper working order, is there some oddball incompatibility with your amp and pre? Have you tried swapping out your preamp with a temporary borrowed pre and then checked to see if the hum went away. If you still have the hum problem, same with the amp.
3. Upstream Issues? I assume you already isolated upstream source gear so you are satisfied that the hum is sourced to only the pre or amp.
I apologize in advance if the above suggestions were already offered by others. Just seems to me that a rig should not pass a hum unless (1) there is an external 60Hz signal that is inducing the hum in your rig, (2) there is a grounding issue, or (3) there is a problem with your gear.
Good luck and keep us informed. Happy New Year.
I have found that most elusive hum is due to DC components that tide on AC. Unfortunately it can come from just about anywhere in your local grid - basically anyone connected to your shared power utility transformer. It can come from your next door neighbor that is using an electrical wall heater (half-wave rectifier), hot tub heater, microwave, clothes dryer, dimmers with an SCR... too many sources to list here. Unbalanced AC lines just are evil. You can also check your cable or satellite grounds. They don't have to be in circuit to cause hum issues. Installation techs just look for the easy way, not necessarily the proper way to find earth. Then again, I once found a persistent system hum due to an interconnect pair that had telescoped grounds with one connected in opposition to its brother.
Hums suck. Big time.
You received good advice to "process of eliminate" the possible 60 hz hum and possible narrow this to the preamp.
One of my other hobbies is amateur radio and after reading your trails, this reminded me of what I have been doing for my stereo system, which like you, I did all the same recommendations you did to no avail.
In amateur radio, we use common mode chokes (CMCs) to eliminate man made noise. These are VERY VERY easy and cheap to build (buy the right toroid donut, wind your coax (for antennas) or your power cords (as in your preamp power cord around the toroid donut....plug and play...you will either solve it or not.
I had a LOT of man made noise entering my ham radio receiver (noise signal 7 to 10)...it was ridiculous...but I have have solar panels over my garage (where my ham gear is; and also close to my music room with the stereo gear, btw), over 75 computing / wireless devices in my house (I am in AI neural research for Alzheimer’s and build a lot of stuff).
I first replaced 7 shops lights in my garage that had the old ballast and replaced with LED non ballast shop lights. Ballasts transmit a LOT of noise into all radio gear. Man made noise reduced to signal 5 to Signal 7, but still very unacceptable. I then installed mu metal covers over my solar convertor boxes and EV vehicle transformer boxes (located in the garage). Not much help.
I then asked for help on eham.net (my ham radio Internet club); the older guys told me to try building inexpensive toroids for my antenna coax (transmission line) and my power cords that power all my ham gear.....this made a big difference...i am now down to normal atmospheric noise with Signal 1 to 3....more than acceptable.
After going through these experiments, I decided try using my spare toroid donuts with my stereo gear (which happens to share an adjacent wall to my garage...go figure).
SOTA turntable / ET2 tone arm / Shelter 901 mk3 ---> Wavestream Kinetics phono tube preamp --> Wavestream Kinetics line tube amp --> Nelson Pass passive analog crossover (bi amp output):
--> Nelson Pass full range / mid crossover outputs --> Moore Franklin Associates (MFA) 200Cs tube amps --> Linkwitz LX Mini full range speakers
--> Nelson Pass low/mid crossover outputs --> Audio Research D100Bs solid state amp ---> Linkwitz LX Mini mid/low driver.
Experienced the 60 cycle hum occurred as you have experienced.
Like you, I narrowed down the equipment issue and eventually all data pointed to the Audio Research D100a amp as the "possible cause". I eventually turned the D100A into Scott Frankland (of MFA fame and now Wavestream Kinetics fame...he still actively building and repairing gear in San Jose, Ca...not far from me). He changed some of the power supply filter caps and didn’t get any more 60 cycle hum noise on HIS bench...except when I put the D100A back into MY house/system...like you, I experienced the 60 cycle hum.
After performing my ham radio ferrite donut noise reduction experiments, I thought, what the heck, I have two spare ferrite donuts...I am going to wind the D100A power amp cord around one of the ferrite donuts.
Sure enough...I reduced about 60% of the 60 cycle hum = my power amp cord is acting like a receiving antenna and picking up noise either from all my research equipment, wireless devices, or computers in the house/garage or other stereo gear.
The ferrite donut is a common mode choke (CMC); these have been around for a LONG time and are used in many of the power supply conditioners.....
Below is the pdf link to common mode chokes (this is an amateur radio piece so you will read colloquialisms pertinent to two way (transmit /receive) equipment; don’t be scared or concerned). Document is on what, why, where, and how to build common mode chokes.
Read page 7
Why Use Common-Mode Chokes? The most common reasons for using common-mode chokes are: (1) to reduce the fraction of the RF power that is fed to your antenna from your transmitter, but then is conducted back to your shack via common-mode current on your feedline, causing RFI trouble in the shack or elsewhere in your house; (2) to keep the transmitted RF power that 60-Hz power, telephone, TV, and other cables in the field of your antenna pick up, from bothering susceptible devices connected to these cables in your own and neighbors’ houses; and (3) to keep the RF noise that all the electronic devices in your house generate, from being conducted via 60-Hz power, telephone and other cables to the outer shield of your radio, and from there along your feedline(s) to your antenna(s), in common-mode.
(more info in the document...but the point is your preamp power cord "may" be picking up the 60 cycle transmitted noise from other household devices....in YOUR environment and not in the shops where you had your gear tested/serviced.
Read page 9 where to install common mode choke
Best part....you can build this for about $25 in parts and 10 minutes of your time. If it doesn’t work....well it is much cheaper then other next options like hiring an electrician or replacing your power conditioner, which you already know is not likely going to solve this issue.
The best price for ferrite toroid donuts is here:
Yes, an amateur radio site, but cheaper then the mouser / digikey.
I specifically purchased the "Monster toroid mix 31" for $25.
You basically wrap your preamp power cord around this ferrite donut...as shown in the pictures.....I recommend about 16 winds if you have enough preamp power cable length....YMMV and you many need to experiment...but it is cheap!
My Audio Research D100 did not have a long enough cable, so I purchased a good quality extension cable and wrapped this around the ferrite donut. One end of the power cable donut went into the wall outlet. The other end went into the D100A power cord = 60% reduction in 60 cycle hum.
My next experiments
a. increase the number of winds around my existing donut for the D100a
b. I have another monster ferrite donut mix 31...and I will probably wind the power supply cord driving my Sota turntable.
c. observe 60 noise...and continue adding donuts to other stereo gear...especially anything with a walwart like device... until I reach diminishing returns.
Google photo link to some of my ferrite "donuts"
The "donut" on the carpet with the black power cord picture is what I am experimenting with for the D100A amp.
You may need to start hunting and unplugging other household devices (walwarts, computers, lights with transformers, etc.) as you listen to your stereo system (scientific method, one by one approach)....experimenting is fun!
The issue is the ferrite toroidals are not very effective at 60hz. More likely they take out the effects of 120Hz events, like dimmer turn on but do little about 60Hz fundamentals. Hence a small isolation transformer on the preamp as a better test. Attenuation at 60hz with that ferrite toroid will be near 0.
2 items I haven't seen mentioned:
1-Did you move your system to a new room? I know it's not easy to say the least. You could run a really long extension cord from another side of the house? Not sure it will help.
2-Did you try different amps. It might just be a compatibility issue. Don't use that junk receiver but borrow a nice high output power amp.
Your system has great components but that doesn't mean the kids will all get along well.
Couple more thoughts and experiments:
* I did a brief read on Shunyata and their power distributors. I might have missed it, but they did not call out specifically how their internal distributors actually work and corresponding components. It might be worth doing a YouTube search to see if someone has opened up a T6000 to actually see what components Shunyata is using in your distributor. The website refers to toroids, transformers and capacitors, but it is really unclear what actual parts are used in this device. If no one has opened up their T6000...be the first to do it and see if they have transformers, caps, toroids or if this is merely a "power strip"
* Cheap and easy....borrow an AC line conditioner, regenerator, etc. from a friend to see if it makes a difference, for your preamp. As usual, scientific method (plug this borrowed line conditioner into same outlet that your preamp is currently using and only plug the preamp into this device. If no difference, then one by one add more of your stereo components. You are trying to see if another device (close proximity) is creating the noise.
* Remember....as I found, multiple number of man made /house appliance and device RF noise sources could exist and no silver bullet. As audio2designs reminded me, even devices such as dimmer switches can be a source of noise transmission that is picked up and amplified by your preamp.
* The torroid I specifically used (and was recommended), mix 31, is designed to trap man made noise low frequency such as transformers, walwarts, etc. If you do a quick google search to see what other people have done and their results, you will see pretty good results. Not a 100%, but again like insurance, you have to have layers of filtering for pesky noise inducing situations. That is why I could easily hear reduction in noise in my music room. Will I have to explore other possible capacitors, transformers, toroid mixes? Yes. Will only one component solve all MY issues....nope. Hence, keep an open mind to the different possible noise trap solutions and the different sources of noises...which leads me to....
* A cheap and easy way to "hunt" for man made / house noise is using an old battery operated pocket AM radio. Go outside away from your home and away from household noise inducing devices. Set the AM radio to the top of the band, 1600 (1600 kilohertz), or something close to that range that does not have a broadcast signal. Listen and learn for the speaker noise and pitch on that non broadcast signal. Now go back into your stereo room and put the radio near each transformer, device, light switch, light, computer, etc.. Your going to use this device as a noise transmission detector.
Slowly turn the radio 90 degrees relative to the device and within 6 inches from each household device, switch, power strip, walwart, etc. If you hear a change in pitch/noise.....your on to something. If it is a light dimmer, for example, maybe it is an old dimmer that needs to be replaced. If it is a new device, then you will need to get creative on how to eliminate the noise transmission from that device. In my garage I have a battery tender for my car. The battery tender is relatively new but it is located near my ham gear. I A/B tested (before toroid / after toroid) with the toroid and noticed a small but perceivable reduction in noise. Again, you may have several different devices that contribute to the noise so you have to prepared to hunt for different noise sources and use different techniques to suppress / kill noise.
Happy hunting, Mr. Wick.
BTW, use the power extension cord technique (cheap and easy).. and use it with your Cardas...screw how much you paid for Cardas...go to home depot and get a 12 foot 12 guage extension and wind a donut. If this partially solves the problem...do you really care how much you paid for the Cardas but got rid of the annoying noise? Or do you want a rich warm sound with an annoying 60 cycle hum underlying everything?
By "Mix 31" they mean Fair-rite 31 ferrite material. It really does not work that great at low frequencies.
Here is the material data sheet: https://www.fair-rite.com/31-material-data-sheet/
Here is an example ferrite with it: https://www.mouser.com/datasheet/2/150/2631803802-1666141.pdf
How well it works is a factor of cross-section, so the big one you listed is better, than the one I linked above, but not much better. It only has 2x the cross-sectional area. As you can see the attenuation at 100KHz is quite low. At 60Hz, there will be virtually no attenuation. The hum improvement and hence why you only got partial attenuation in your application is it attenuates the bursts of noise that typically happen every 120Hz with most electronics. It would not have attenuated 60Hz.
An isolation transformer will provide huge common mode attenuation at 60Hz. There are very high permeability common mode cores, but the listed type 31 ferrite is not one of them.
Picking up on the last several comments, take a look at the Google search I did on Faraday cages:
https://forum DOT allaboutcircuits.com/threads/holes-in-a-faraday-cage.69512/
If a simple metal screen mesh can attenuate ambient 60Hz noise, that might be a simple way to solve your problem. It seems that the posters to the thread thought that an aluminum screen might not be conductive enough. Perhaps winding copper wire around the cage might augment its effectiveness. Think Occam's razor!
Techies, please weigh in.
I reiterate my suggestions that you should send your preamp back to the factory for a thorough check-up. For all you know, a cap used to filter out low frequencies might be leaking.
I would also swap out your preamp and your amp to check for compatibility issues.
No arguments with the specs and not operating at low frequencies (60 to 120 specifically); but at the same time THESE reduced man made noise in my stereo amp music environment. YMMV regardless of the Fair rite specs. More investigation on why, in my environment, noise reduction with mix 31....TBD..and curious to find out why.
I have 6 Nest powered cameras, whole house alarm with some walwarts, 6 Orbi Wifi mesh satellites, 15 SunPower panels (that each have its own micro inverter per panel, an EV transformer (adjacent the the music room and mounted in the garage, a big screen TV in the music room, a dimmer powering 6 recessed lights (house was built in 2015), 2 mac workstations in the music room. Fast and easy calculus... I wanted to test and hear if the toroid would solve my noise issue to get a North Star solution. I am not including the other 50 plus workstations, servers, ham gear, etc. that I would have to test in my environment.
We can say with high certainty: I have a 60 cycle transmission emitting in my house and that is received and amplified through the D100A and NOT the MFA amps or the WaveStream preamps.
Bottom line...my donut reduced 60 cycle noise for the D100A when no source music played, similar to Montaldo’s situation. Did it go away completely. No. Do I need to experiment more? Yes. I had these Fair rites on hand, so I used what I had. Was it cheap and easy? Yes.
If I just used the Fair-rite specs, I would agree with you....but because I had these readily available and tested it...the donuts are staying put until I can hunt and kill the other noise sources in my house. Maybe my house is the exception with all the gear I am running despite the house being newly built in 2015.
Jim Brown did a very extensive writeup on RF and discusses Fair-rite’s Mix 31 for 1500 cycles to 30 megahertz.
Pages 21 on provide very insights and how you could modify the chokes.
He also provides cook book recipes for transformer, cap, and toroid filtering solutions in this doc.
stuogawa22 posts01-03-2021 3:39pm
This one is easy @stuogawa. If you look at things like dimmers, linear amplifiers, and linear power supplies, most USB chargers, etc. they draw power in bursts at 2x the line frequency, i.e. 120Hz or 100Hz. When they make that current draw, it is a burst of high frequencies. The noise spectra ends up being 120Hz mixed with high frequencies, and harmonics of both. When those high frequencies that are harmonics of the high frequency mixed with 120Hz enter your equipment, it modulates back down to 120Hz in your audio equipment.
The ferrite will take out the high frequency harmonics so that they cannot modulate back down to 120Hz. It cannot remove common mode noise at 120/60Hz that is transferring from the pre-amp to the power amp if that is what is the cause.
"I reiterate my suggestions that you should send your preamp back to the factory for a thorough check-up. For all you know, a cap used to filter out low frequencies might be leaking."
No push back on this idea..and expanding on your approach....
Montaldo should just take his preamp to a friends house and test it. No shipping charges. Safer. No minimum bench cost to open up the preamp. If preamp has noise at friend's house, then send preamp for sure. No use spending money if you can do a quick and easy test at friend's house.
If preamp has no noise, then Montaldo has to hunt and kill the noise source....or suppress the noise.