Axiom Home Page Forums General Discussion Technical Questions Axom A1400-8 amp hum from Denon AVR-4306...

Hello everyone,

I am having a humming issues with a Axiom A1400-8 using a Denon AVR-4306 as a source. I am currently using the included TRS to RCA adapters that are straight and am using quality coax (Bluejeans LC-1)with Canare RCAs to said adapter. I also removed each source/transport from the ins on the Denon to see if humming is produced with no devices input on the Denon but the hum is still there. I also tried powering up the A14000-8 with no inputs plugged it. This then produces no hum. I was curious if I used an XLR to RCA cable connecting pin one to pin three of the XLR or pin one to RCA sleeve this might cure the issue. The folling diagrams outline what I believe might solve my issues. My question is what pinout/method will work best as there is no real standard on how to pinout/crimp an XLR to RCA cable.





Justin

Using XLR-RCA adapters usually cures this. As for the pinouts, only an Axiom technician should answer to that. I am using adapters that I bought on the market (can't remember where!).

Thanks for the reply,

Do you mean a TRS 1/4 mono to RCA female like the included adapters that came with the A1400-8 as that's what I am currently using. Perhaps this is what you mean...



Those guys want 75 bucks a pair for those... what a rip off perhaps you know of a better source? I'm going to give Long and McQuade a call to see if they have such a beast.

Justin

No, I really mean a cable ended RCA (to plug into receiver) and XLR (to plug into A1400). The model I have is like this:
http://www.fullcompass.com/product/279398.html
(I did not buy from there, just did a quick google).

You might also simply contact Axiom. They are pretty good at troubleshooting this issue (finding the root cause) which is quite typical of separates not using balanced connections.

Yeah, I'd say contact Axiom in this case. It sounds (to my uneducated on this topic brain) like a ground loop hum.

I have to make the obvious comment that this problem from looking at it would be systemic with most any AVR using line level unbalanced out. I am rather surprised that Axiom didn't include those type of adapters but included TRS to RCA adapters that are useless for this application. At 4k for the amp I'm surprised they didn't include adapters that work properly by connecting pin1 to pin3. Here's hoping Axiom includes such adapters with future shipments as I think a lot of end users purchasing this INCREDIBLE amp are transitioning from integrated to separates and are using unbalanced ins.


Justin

That kind of problem is far from systemic. I do agree that a nice bundle of connectors like these should be made available for those of us who are starting like that, even if it means a slight increase.

It would be interesting to know how many went from separates-to-separates with A1400 and how many from integrated-to-separates (for the people I know on this forum, it is about 6-to-2 in favor of separates-to-separates, and I just counted you too!).

In any case, hopefully you will be hum-free soon and get to truly appreciate this beast!

Interesting. I too experienced a light hum when I used the RCA outputs of my pre-pro to the A1400-8. Same outputs from the pre-pro to a Yamaha receiver (used as the amp) did not produce any hum. I disconnected all sources, grounded the pre-pro to the amp but there was still a hum. By the way, I had the same LC-1 cables and no cablevision cable with a different ground in the system. Since the pre-pro also had balanced outputs, I finally exchanged the LC-1 cables for balanced cables and the hum went away completely.

In one of the reviews for this amp, I believe the reviewer used RCA-to-XLR adapters and successfully eliminated the hum. Those who sell these adapters simply assume that you know what you are doing. But do people really know what they are doing? There is a 3-6 dB difference in balanced lines; what about the need for an impedance matching transformer? Bottom line is that I would ask Axiom before going ahead with any wiring/connection unless you know what you are doing (though a name like SolidSate certainly suggests that you do )

John

Hi,

I quiz the ultimate authority (Tom Cumberland) on this one.

His answer is . . .

"I would suggest that he try connecting the hot to pin 2 of the XLR and the ground to pin 3 without using pin 1. This will make the RCA look balanced to the balanced input of the A1400. He should also try plugging the AC power lines of the Denon and the A1400 into the same wall socket so that they have the same neutral and hot lines.

Thanks so much for all the support guys. Such a fantastic Axiom community we have. With regards to the hum issues... In testing this afternoon I found that by populating each module with two speakers and not one (the system is 5.1) the hum went away!! In other words using an EVEN number of speakers with the A1400-8 seems to remove the hum. I discovered this by connecting just LR first no hum... connect LR SR SL hum... add center... no hum... use center LR and one rear... no hum... add rear again for 5.1 hum.... added a rear center for 5.1 ES and again no hum. It seems to me the hum is introduced when I am using an uneven number of speakers and one of the modules is only driving one speaker. I was thinking of testing again with a 8 Ohm high watt resister connect across the terminals of a module only populated with one speaker. I also confirmed the hum using just a single channel on the amp though the hum wasn't as pronounced and seemed to increase logarithmically when uneven speaker count was connected. In other words one speaker produced least hum while 5 speakers produced the most. I will get some shop speakers over to this customers house and confirm this by populating all of the channels. I have a feeling the SNR would be LEAST with all 8 channels populated and would get worse working back in even speaker counts whilst it's the opposite with uneven speaker counts where 1 speaker would have the least and 7 the worst. It's also interesting to note this is a non issue with a pre that has balanced out. I am going to run tests using my notebook with trueRTA and REW. I'll post the graphs with results using various numbers of even and uneven speaker counts... 1,3,5,7 and 2,4,6,8 . Thanks again for the responses guys!!! sure makes one feel great and is reassuring to see the designer/OEM/ODM and other end users so willing to come forward and help. It's a fantastic example of Axiom's dedication to it's customers and a great indicator of how happy other customers are that they are willing to come on here and help others out without any volition simply because they want to share with others these fantastic products.

Justin

PS By systemic I mean anyone that's using non balanced inputs... here's dreaming this customer (a relative) gets the AVP-A1HDCI as these two pieces would be a match made in heaven IMHO

OK I've confirmed the uneven speaker counts were causing this hum. I will run the trueRTA measurements and post them in the coming days but I will also try the various pinout/cable arrangements suggested by JC and Tom and also post trueRTA results cross referenced and matrixed.. though I don't have the gear to measure accurately on the highend of the spectra. It looks like my uncle is gunna just have to order a rear center and a couple of Algonquins to solve this issue Lucky guy...

You can confirm! And now it is time to turn the thanks to you!
I still a very, very light hum in a central channel (louder when my SACD player was ON, but before it had played once). I just hooked the unused channel to a dummy zone 2 cannel of my 805 and gone!

Hum... That's one for Mr. Tom!

I had actually hooked up in 6.1 before completly without hum! So it is pretty strong evidence now.

So, thanks SolidState for having done more testing (I am sort-of not confortable to play too much in the back of the A1400 as I accidentally shorted my first one moving the furniture to reach it... the spectacular firework sorts of sticks into your memory and makes you stay clear of it! So I am very happy you did it! ).

Hi EFalardeau!

Hey that's great to hear!!!

Hi JC,

With regards to Tom's suggestion, and again my knowledge is limited to Heathkits and highschool electronics but I do claim to be a "pro" HT installer ;), by connecting the hot to pin 2 of the XLR and the ground to pin 3 without using pin 1 would this not result in a 6 dB loss in signal? Would this not mean I'd have to set the volume knob to double on the Denon to achieve the same SPL?

Justin

PS How would this affect "gain structure" and "headroom" ?
Also I am curious what the affective pin out is when using a TRS 1/4 mono to RCA (included adapters) with the A1400-8's combo XLR/TRS Neutrik plug?

Justin,thank you for identifying a hum issue with the use of odd number(s) of channels using unbalanced inputs into the amp. How were you able to confirm that this is a "non issue with a pre that has balanced out"? I have 7 channels connected to the A1400-8 using balanced outputs from the prepro and can say that the background is absoultely dead quiet even when I tested by putting the volume on the prepro way up.

EFalardeau, I assume the dummy zone 2 output on your 805 had audio output? Did you not connect a speaker to that channel on the amp?

I had heard somewhere that using all eight channels would actually run the amp cooler. This hum issue with odd number(s) of unbalanced inputs is also interesting.

John

I did not connect a speaker to the unused channel. The audio is life (but without actual audio signal) as I use the "zone2 power ON" as 12V trigger for the A1400.

Preach it, brother!

Hi ihifi,

I determined the balanced had no hum by using an Aardvark Q10 pro soundcard for audio recording as a source.

Justin

PS I found using a PC with a pro sound card as the source produced the best sound I've heard yet from the A1400-8... Amazing one can get balanced output of a caliber competing with those very expensive pre/pro

This question has never been answered...

Justin - Just a suggestion... If you haven't already, send JC a PM (or e-mail him directly) to make sure he saw your response and question. I don't think he monitors each thread actively like some of the other Axiom employees do, so direct contact might be more effective.

Jason

Exactly, many of the technical support folks rotate via phone schedule and aren't regular on the boards, if at all. Your best bet is to email or call the 800#.

I thought you were gone for good?

We missed him too much, so he came back to soothe us.

... by reviving a 10 month old thread. Welcome back, my link obsessed, doesn't lead to much... acquaintance. Now....go away?

Hi,

I have quized Tom and fisrt he says that it is not a good practice to use XLR to RCA adaptors; secondly you are right it would be a 6dB drop. The adjustement on the Denon volume knob will depend on its gain structure.

Next time, you don't hear back from me, please, do not hesitate to email me at jc@axiomaudio.com

Professionally answered JC given the controversy with this poster. Good job.

Your high school must have a very robust electronics program.

Thanks for the response JC. I ordered some Mogami 2549 and 3173 as well as some Vampire copper base RCAs and XLRs at 6mm and 9.3mm OD. I intend to terminate using example 17 from this rane corp article. Rane Corp Termination Article
My question is if I pinout the XLR in that manner will the Ice module go into balanced +4 dBm mode? From my understanding placing a 1/4" TRS mono RCA adapter, came boxed, will connect -10dBV line level source to pin 2 and bridge pin 1 and 3 in a hybrid TRS/XLR as on the back of the A1400-8. This will also using a single ended source via single conductor COAX (90% of consumer line level cable) connect pins 1 and 3 to coax ground/braid. No wonder it's so horrible using coax with that adapter. What is needed is two conductor UTP cable with braid. The thing is if I use the Rane example 17 pins 1 and 3 won't be bridged. Is this how the Ice module determines what mode to go into? Basically if pin 1 and 3 on xlr A1400 end are bridge does this make it go into consumer line level -10dBV mode OR is it hot pin 2 that triggers balanced pro line level +4dBm ? Also why did you guys package those adapters because they just turn the coax 90% will terminate with into a bloody antenna? I guess if you used two conductor "balanced" RCA (oxymoron IMHO) with open shield on one end it would work right... other than that with those adapters your screwed.

Solid-State

-10dBV mode OR is it hot pin 2

should read

-10dBV mode OR is it hot pin 1

How is the XLR terminated on the A1400-8? is Pin 1 signal ground and pin 3 chassis ground with hot pin 2?

http://www.rane.com/note151.html

In particular this is of interest...

"The second column in Figure 5 shows unbalanced outputs driving balanced inputs. Again, only shielded 2-conductor cable is used. The best case here has both ends of the shield connected to units whose shield is chassis-grounded (Figure 5e). Some may argue that the induced noise on the signal conductors may be injected into the "sending" unit through the unbalanced output stage. This is a function of the system and output circuit, and is quite likely. Disconnecting the shield at the unbalanced output might reduce this problem. (affecting my uncle with LC-1 and included adapters)

When units with signal-grounded shields are encountered, disconnect the shield at the signal-grounded end (Figures 5f & 5g). This keeps the noisy shield currents out of the audio signal ground. If both units involved have signal-grounded shields, you've entered the twilight zone again (Figure 5h). Support your one-end-only political party (Figure 5l)."

I intend to terminal at the A1400-8 XLR, Hot pin 2, signal ground pin 1 and shield to pin 3. On the source RCA single ended I intend to connect hot pin 2 to RCA tip and signal ground to RCA ring AND leave shield open/unconnected at the RCA. Is this the best way to avoid noise and have the Ice module go into -10dBV mode? Also why would Tom direct me to connect to Hot 2 with nothing on pin 1 and signal ground to pin 3? From my understanding this would result in Ice module going into +4dBu mode no? Why direct me to do this with no balun? I didn't do it as it's bad advice considering I'm use -10dBV consumer line level. Other than the -6db result could this not damage the input and output stages on each device?

doh!

I have signal ground and shield mixed. Just to recap.

XLR male, hot pin 2, signal ground pin 3 and open shield to pin 1, On RCA hot pin 2 to tip and signal ground to pin 3. This is how I intend to terminate. Will this still result in the Ice module going into -10dBV mode?

Solid-State

PS I'm also curious why a module populated with only one in and out produces a hum in that channel? If you connect an in to the unused chan or in and a speaker the hum is completely gone... why?

?

SolidState, Axiom is not using the B&O Ice module. Axiom has evaluated it and decided to design its own digital module to overcome many shortcomings of the Ice module. Axiom not only has designed its amplifier modules in house it also manufactures it in Axiom's main Canadian facility.

To recap on the XLR pins :
Pin 2 is Hot + and Pin 3 is Hot – while Pin 1 is ground.

Hum :
The A1400 should not have hum either way. The only way this may happen is when Pin 2 is hot and Pin 3 is not connected or to a different ground than Pin 1. We do not recommend this as the A1400 has different circuitry for the unbalanced and the balanced inputs. The balanced inputs stay balanced all the way to the power stage.

Just to clear up for those of us playing along at home.

What makes the A1400 pick the different circuitry when it only has one physical set of inputs?

Hi ClubNeon,
The input jack used by Axiom on its A1400 amplifier models is a dual type configuration. The larger central hole of the connector is for the phono type connector and the outer three identical small holes are for the XLR connector. It is like using two separate connectors. Only when an XLR connector is plugged to it that the audio signal will be processed by the balanced circuits.

That was my guess.

So when using an unbalanced feed, one should always use the included adapters. They are not shorting two leads of a balanced connector together, they are in fact connecting to a different part of the input.

You are exactly right on all points !

I'm not sure about that guys! If you look at the included adapters they are MONO sleeve TRS 1/4" NOT Stereo/balanced sleeve! The entire length of the ring shaft connects to the female RCA sleeve! Just by looking at the thing one can deduce that sleeve will short pin 1 and pin 3. It depends on how that hybrid XLR socket is wired though. I don't believe the pins are discrete for the TRS socket from the XLR pins on a hybrid. The jack prongs are just physically connected to the same pins for XLR balanced as TRS balanced. Please tell me the part number for the hybrid XLR and I can determine if it's a special hybrid XLR with discrete pins for the XLR and the TRS sockets. I don't believe such a beast exists though I could be wrong.

I'm very curious as to how the single ended or balanced ins are wired on the TC Preamp-3 board. I wish to understand how the TC Preamp-3 board determines if it's receiving -10dBV or +4dBu AND singled ended or differential signals as they are NOT the same thing! Signal symmetry as in single ended or differential is DIFFERENT and INDEPENDENT from "balanced" as it pertains to interconnect pinout/pre circuit! I have tried open and closed shield on pin 1 XLR A1400 on the RCA sleeve. I found that open shield as in pin 1 XLR in is tied to Mogami 2549 shielding but open at the RCA end with RCA hot tip to XLR pin 2 and RCA single ended sleeve return to XLR pin 3 produced WORSE hum! than XLR pin 1 and 3 shorting at sleeve! I'm am starting to think that pin 1 on the XLR in on the A1400 is tied to signal ground and NOT chassis ground when TC Preamp-3 board is in -10 single ended mode!

Please axioms don't fluff this off! I know you installed a new grounding bar in later revisions of this piece! Is not pin 1 on that hybrid XLR pined to this ground bar! I sure hope it's not pined to signal ground! It seems to be guys when the TC Preamp-3 board is in -10 singled ended mode! All I need for a hum free singled ended source to work from RCA to XLR is the TC Preamp-3 board to go into -10 singled ended mode and for the hybrid XLR pinout to be pin 1 chassis ground (NOT SIGNAL GROUND!) pin 2 singled end hot and pin 3 return. If I then used a two conductor with shield cable like my Mogami 2549 and pinout the XLR pin 1 shield pin 2 + pin 3 - and at the RCA end pin 2 to tip and pin 3 sleave with the ground shielding OPEN it should work best. I think the problem is that pin 1 is signal ground and NOT chassis ground when TC Preamp-3 board is in -10 singled ended mode. Considering the unit is a true differential designed as Jc sorta alluded to I'd assume that the XLR in terms of the TC Preamp-3 +4 differential mode is pinned out as XLR pin 1 chassis ground, pin 2 "+" pin 3 "-" as in a true differential circuit with same impedance in both directions. Again it's important to note "quazi balacing" with balums, VERY common because 90% of amps with balanced ins are NOT true differential designs, has led to the practice of pinning signal ground to XLR pin 1 because in a non differential design chassis is signal ground right!

Please read these article from rane

Sound System Interconnection

Grounding and Shielding Audio Devices

Solid-State

PS If you really wanna take the red pill check out this article from Rane on the Linkwitz-Riley crossover
Linkwitz-Riley Crossover Brilliance
It really nailed it in my head for me this week working on my own speakers!

The XLR/TRS combo jack has discrete pins for XLR and TRS? If that is the case then nothing is connected to sleeve on the TRS? Why have some reported better results with a XLR to RCA cable two conductor not coaxial?

Solid-State

OK I'm wrong. I have it now in a catalog. On the back of the XLR/TRS combo jack is six solder points. Pins 1, 2 and 3 as well as tip, ring and sleeve as well as XLR jack ground. The included mono TRS adapters would still jump ring and sleeve though it sounds like nothing is soldered to the sleeve pad.

Solid-State

uhh!!!

This is the line card from Neutrik on "Combo" XLR/TRS chassis connectors.

http://www.neutrik.com/fl/en/audio/204_59540618/Combo_Series_productlist.aspx

They are all 3 pole on the XLR but some are 2 pole and 3 pole on the TRS.

Solid-State

http://www.neutrik.com/fl/en/audio/210_341930987/NCJ5FI-H_detail.aspx

This is what's used on the input board?

http://www.neutrik.com/fl/en/audio/210_1817827768/NCJ9FI-H_detail.aspx

and

http://www.neutrik.com/fl/en/audio/210_129149521/NCJ6FI-H_detail.aspx

on the TRS pins it shows T, R and S as well as TN, RN and SN what is this "N" about... please explain drawing if any of you understand. On the PCB version with TN RN and SN there seems to be six pins for the TRS alone! ugg it's way over my head

Solid-State

Solid-State

I would say they probably used something similar to the NCJ5FI-H.

There is no correct way to connect an unbalanced signal into a balanced input (without something to create the inverted signal). If you don't want to use the adapters, have an RCA to 1/4" mono phono cable made up.

The 'N' jacks are for use with things like headphones. Where inserting something into the jack breaks (or switches) the connection. When there is no plug in the jack the T and TN are connected so the jack can be placed before an internal amp. Inserting the plug opens the switch so the signal goes stops at the jack.

Owhh I get it ClubNeon. It's so a person can jack in say a guitar but prevent a momentary hum the instant the TRS is jacked in. I guess you'd use that model for a guitar amp. I'm now wondering if coax or two conductor "balanced" cable should be used.

From this new info, I take it the best cable for me to use would be a decent coax like Bluejeans LC-1 with Taversoe RCA on one end and a switchcraft 1/4" mono on the other. The tip shaft on the Switchcraft units are solid OFC copper as well as the sleeve with a silver plate. The included adapters are very poorly made and are hollow and the weight suggests they are made of aluminum or something with gold plate. No way they are made of brass they are simply to light.

Solid-State

OK I just took a hacksaw to the included adapters. They are made of aluminum with a VERY THIN coat of gold plate. WOW that's horrible man...

Man I wish Tom wasn't so obsessed with the piece's height. The long runs from PCB headers to the speaker terminals and input board sucks and you can't help but wonder about EMI/RFI on those and proper RCA jacks could have been used if it was made taller. Owh and no weird power plug on the bottom. Also looking at the preamp board it seems it has a series of through-holes unused (4pin header) and the ones that are (16 pin header) seem to have the pin header soldered in place that would put the header pins on the back of the PCB. I guess that's how the pre opamps connect to the amp boards? Some of the pins on that 16 pin header don't look like there is enough solder man. I haven't opened the thing up yet just using a flashlight and looking in there. I'm scared of opening the thing as I've never worked with any electronics with caps that HUGE. I'd be scared to bleed the thing. I can imagine the crack discharging them!

Solid-State

Since you're so very helpful in teaching us all about topography and stuff, do us all a favor so we know for future reference:

Power the unit up, let those caps just fill up, and stick a screwdriver in there while standing in a tub of grounded water.

We'll wait for your report.

That 16 pin header is of concern now. I've looked at it with my magnifier headset with very powerful light shinning into the chassis and I can see through hole pins on the header without a proper solder joint. Some are gray even and look cold! Others only have solder bead on one side of the through-hole! Perhaps 20% look right with a proper "dome" and shine. OMG I now am very upset again and feel HORRIBLE! Owhh and thanks for the comment Mark... Axiom if I open the unit to take photos of these solder joins will you void my warranty?

Solid-State

Board one for chan 1-2 looks ok with propper domes and shine. Board two is god awful with gray joints and a lot without enough solder or heat when made. You can literally see that the solder didn't bead around the pin as it's only on one side and you can actually see down into the PCB on one side of the pin where there is no solder! Boards 3 and 4 are 50% success rate pin to pin on the solder job! I'M SO UPSET AGAIN!

This is at least your SECOND promise to leave this board because what a waste a time you claim it is. You obsess, have obvious bipolar tendencies, and need assistance with it. How bout you make good on your statements, give us all a break and LEAVE?

Just email the Axiom staff directly and let the rest of the sane participants (somewhat ) enjoy the forum.

Damn.

Try a longer screwdriver. Really get in there. I'll wait.

I wish I had a schematic for the TC Preamp-3 board. I wonder what that 16 pin header is for? I can see the input into the board from the input PCB/XLR combo jacks. I can't see any other headers on the top so I assume that 16 pin header is the opamp into the amp board. I'm surprised you guys would use a header with such tight pin density and small pads. The unused 4 pin header through-holes have much larger pads that would be much better to send source to the amp boards. Also I notice the pins are steel. Why not use copper pins as this is a VERY important interconnect!

Solid-State

this is a great thread. Turn on "ignore" and just see the fun posts. Great tool Axiom, thanks.

Actually yeah this is a great thread and I hope it helps others that own the A1400-8! It's a great amp just a little rough around the edges. That solder job can easily be fixed but it is a major concern anyway. I think axiom will just let me fix it my self as I believe they have faith in my technical skills. It's a FANTASTIC amp with properties and power that no other amp on earth has! Please any prospective customers don't view this negatively. I'm 100% certain Axiom will remedy the situation.

Solid-State

Ah, see I can't read his response...this is beautiful. I bet he had some long bitter attack on smoking babies, but I don't know that, cause I'm ignoring him. Wow, I like this. I wonder if Axiom can make a version i can take to business meetings.

Wow, this guy's out of control. He has dreams of being some sort of lone warrior. Ya know what Zimm, you're right. It isn't worth it. Good luck SS. At some point in the future you'll realize you did need some help.

Ignore +1.

BTW...I notice as of this post that he edited one of his recent posts from threatening to post pics of "flaws" to a somewhat kinder post. I'm done.

Perhaps he just needs a hug.

top secret

I bet he agreed with the hug suggestion. Or not.