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  1. #1

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    Default New SS power amp in 2 channel system has introduced hum

    I sure could use some help.

    I just swapped out a tube amp from my 2 channel rig and with a SS amp. I doing so noticed I now have a humming noise coming out of my speakers. The new amp is a ModWright KWA-100SE. I have it paired with a ModWright LS-100 tube preamp. ICs are MIT S1.3s and speaker cables are MIT S1.3s. Amp, preamp, CDP are all run through a PS Audio Power Plant Premier.

    I have experience ground loop hum in my HT system before, but never in my 2 channel rig. In the case of my HT system, I traced the hum to one of three external amps and fixed the problem with a cheater plug. I have used many different amps in my 2 channel rig and have never had any issues with hum (including when using tube amps). I have checked all my all connections and they all appear correct.


    Is it possible that the KWA-100SE is the culprit? This ss amp is supposed to be dead quiet. Therefore, I am stumped. I was going to run over to home depot a pick up a cheater plug to see if that has an impact. Before I did that, I am hoping someone might have a suggestion. Any help or thoughts would be greatly appreciated. Thank you!

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    Just to be clear, are you saying the only thing different in your system is the the new amp? Everything else is the same?

    I also have the MIT S1.3 ICs (XLR), but when I tried to add the S1.3 speaker cables my system went berserk with all kinds of bizarre noise. The problem was my amps were in bridged mono and the MIT speaker cable electronics did not like that at all. I went to stereo mode and they seemed okay, but that was a 5 second test.

    Anyway, it is amazing how many different variables there are in a system. It is amazing that anything works. Try the cheater plug, but there is some underlying issue that should be fixed. Maybe the amp is bad. Have you tried it in another setup?

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    The only change is the amp. Just a single ss 2 channel amp.

    Swapped out my PS Audio AC-5 power cord with the stock power cord, hum still persists. Added the cheater plug to the stock power cord, hum still persists. Frustrating....

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    Try different speaker cables. Lamp cord is fine for this test.

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    I sure hope it's not the speaker cables. I have really enjoyed the synergy between the S1.3 ICs and the S1.3 speaker cables via many different amps and preamps (both tube and ss).

    The hum isn't overly loud. Not like the hum I had in my HT system when I had a ground loop issue. Nonetheless, it's there and it shouldn't be there.

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    I use S1's with a dual mono (absolutely not common ground) amp with no problems, but you never know. The amp may simply have an issue.
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    Maybe drop Dan an email and ask his input too. He has always been helpful to me in the past, even if I bought his gear used. I recall my first ModWright SWL 9.0SE pre introduced a hum in my system. The guy I bought it from had used a cheater plug and said he forgot to tell me about it. I was comfortable with cracking the case, so Dan suggested I look to ensure they had ground the powdercoat off the inside of the rear panel where the ground attached. They didn't, I did and all was well (dead quiet) after that.
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    Quote Originally Posted by F1nut View Post
    The amp may simply have an issue.
    Geeze, I hope this is not the case. It was manufactured in May of 2011 and it does not have so much as a scuff on it. It was shipped to me in its original packaging and then with bomb proof packaging around the original packaging.

    The hum is only audible when music is not playing. It's very similar to a tube amp hum. Nevertheless, I would think the ss design of this amp would make it dead quite. If I turn off my source, the hum does not increase or decrease whatsoever, no matter how much I turn up the volume. Any other thoughts? Thanks!

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    If you haven't, maybe take a look at his forum over at AudioCircle.

    http://www.audiocircle.com/index.php?board=14.0
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    It was manufactured in May of 2011 and it does not have so much as a scuff on it. It was shipped to me in its original packaging and then with bomb proof packaging around the original packaging.
    C'mon man, that doesn't mean squat when it comes to electronics. Anything can happen at any given time.

    The hum is only audible when music is not playing. It's very similar to a tube amp hum. Nevertheless, I would think the ss design of this amp would make it dead quite.
    Is this a hum or a slight hiss only heard when you are right on top of the speaker?
    Last edited by F1nut; 10-14-2012 at 02:36 AM.
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    Quote Originally Posted by F1nut View Post
    C'mon man, that doesn't mean squat when it comes to electronics. Anything can happen at any given time.

    Is this a hum or a slight hiss only heard when you are right on top of the speaker?
    I agree....

    With my source off, I can hear a slight hum from my listening position. The best way I can describe it is that it is similar to the hum I have heard with some tube amp set ups.

    If I get closer to my speakers, a hear a slight hum coming out of the woofers and a slight hiss coming out of the tweeters. It's not loud, but it's there and probably shouldn't be.

    It's not audible with music playing. Even at relatively low volume.

    Could this possibly be related to the fact that my speakers are extremely efficient (Klipsch)?
    Last edited by Beta; 10-14-2012 at 03:16 AM.

  12. #12

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    Ok, a slight hiss from the tweeter(s) isn't uncommon, but a hum from the woofer(s) indicates an issue regardless if it's a tube or SS amp. Try what Bluefox suggested to see if the cables are involved.
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  13. #13

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    Quote Originally Posted by F1nut View Post
    Ok, a slight hiss from the tweeter(s) isn't uncommon, but a hum from the woofer(s) indicates an issue regardless if it's a tube or SS amp. Try what Bluefox suggested to see if the cables are involved.
    I have a pair of Kimber 8TC speaker cables. I'll try those in the morning and report back. Appreciate the help!

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    Beta, try the cheater plug on the pre amp too. Switching around cables is a good idea also, sometimes stuff doesn't gell well with other stuff. You could also try adding a small wire from an amp screw to a ground somewhere else. Pop the top and take a look see as Rich suggested about the powdercoating, could be as simple as that too.

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    Quote Originally Posted by tonyb View Post
    Beta, try the cheater plug on the pre amp too. Switching around cables is a good idea also, sometimes stuff doesn't gell well with other stuff. You could also try adding a small wire from an amp screw to a ground somewhere else. Pop the top and take a look see as Rich suggested about the powdercoating, could be as simple as that too.
    I use PS Audio AC-5 power cables throughout my entire system. The grounding pins on these cables are removable. Would removing the grounding pins on the power cables to my power amp my preamp render the same result as using a cheater plug? I thought I might try this before swapping out my MIT speaker cables. However, if I don't want to try this if there is inherent risk with this test. Any thoughts would be appreciated! Thanks!

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    The cheater plug basically does the same thing, removes the ground, so by removing the pin from the plug.....seems the same to me though there may be some inherit benefits of doing so at the PC plug itself. Doesn't hurt to try anyway, as long as you can replace the pin.

  17. #17

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    Quote Originally Posted by tonyb View Post
    The cheater plug basically does the same thing, removes the ground, so by removing the pin from the plug.....seems the same to me though there may be some inherit benefits of doing so at the PC plug itself. Doesn't hurt to try anyway, as long as you can replace the pin.
    Thanks Tony....

    I removed the grounding pins (they screw in and out) to the power cables to both the amp and preamp. Hum still persists. I am swapping out the MIT speaker cables with a pair of Kimber 8TC speaker cables. It will be interesting see if this has any impact.

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    I notice Dan added a GND lift switch on the back of the amp. That switch just lifts signal GND from chassis GND. Since it wasn't mentioned have you tried that?


    http://www.modwright.com/cms/resourc...nual-final.doc

    Since it hasn't been asked yet, your mains/ground all proper on the wall outlet? I have had gear that was not particular to swapped hot/neutral and some that was.

    I use one of these to find out and it is the first place I go when checking for problems.



    One other thing is try plugging the amp direct into a wall outlet. I've had issues with some gear and regenerators.
    Last edited by SCompRacer; 10-14-2012 at 04:16 PM.
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    Well....

    It's not the MIT speaker cables (gotta say I am quite happy about that). Same hum issue with the Kimber cables. I'll try some of SC's recommendations above. Gotta love this forum. Best out there IMP. Thanks everyone for your help. I can't tell you how much it is appreciated!

  20. #20

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    Quote Originally Posted by SCompRacer View Post
    I notice Dan added a GND lift switch on the back of the amp. That switch just lifts signal GND from chassis GND. Since it wasn't mentioned have you tried that?


    http://www.modwright.com/cms/resourc...nual-final.doc

    Since it hasn't been asked yet, your mains/ground all proper on the wall outlet? I have had gear that was not particular to swapped hot/neutral and some that was.

    I use one of these to find out and it is the first place I go when checking for problems.



    One other thing is try plugging the amp direct into a wall outlet. I've had issues with some gear and regenerators.
    SC,

    Yes. Flipping the ground switch on the back of the unit actually increases the volume of the hum. Tried plugging the amp directly into the wall. Same issue. Appreciate your thoughts.

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    Interesting problem. Have you tried putting the other amp back, and verify that the hum is gone? It almost seems as if the amp is the problem.

  22. #22

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    Quote Originally Posted by BlueFox View Post
    Interesting problem. Have you tried putting the other amp back, and verify that the hum is gone? It almost seems as if the amp is the problem.
    Agreed. At this juncture, it seems to me to be the amp. No issues with hum with any of my other amps (both tube and ss). Thanks BlueFox....

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    I'm a big fan of Dans gear. Still happy with my SWLP 9.0SE and ModWright Sony 9100ES, both with tube regulated power supplies. They feed two SS amps in a horizontal bi-amp, active crossover configuration. I am obsessed with having a low noise floor and that is just what I have. If he could achieve that with tube gear, I would think he could do that with his SS amp.

    Anyway, aside from the issue, how do you like the amp and his LS-100 pre? Something came up at the time and I missed out on the demo he had going at AudioCircle when the amp was released. I am on the list to host a Polk LSiM floorstander demo and may ask if I can get a demo amp from him.
    Last edited by SCompRacer; 10-14-2012 at 06:08 PM.
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    Beta, I feel your pain. At least you can't hear the hum while playing music, but I know the feeling of wanting, and expecting, perfection with our gear. Swapping stuff is a pain, and sometimes you break something else while pulling and pushing the rack in and out. Then sending something in for repair is just another hassle, especially when all you want to do is listen to music. I just sent my right channel amp in for repair after it just died one night.

    As I mentioned earlier, when I hooked up the MIT S1.3 cables, the amp did not like it, and all sorts of popping noise came from the speaker. Now I wonder if that incident a couple of years ago didn't weaken some part, and it finally failed. Oh we'll, there is no way to tell. I'm glad your problem was not a cable/amp mismatch. Good luck.

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    Quote Originally Posted by SCompRacer View Post
    Anyway, aside from the issue, how do you like the amp and his LS-100 pre? Something came up at the time and I missed out on the demo he had going at AudioCircle when the amp was released. I am on the list to host a Polk LSiM floorstander demo and may ask if I can get a demo amp from him.
    SC,

    I've had the LS-100 preamp with Dan's DAC upgrade for a few months now. By comparison, I recently had a Peachtree Audio GrandPre preamp. These two units are not even in the same league. Prior to that, I had a Parasound JC2 coupled with a Wyred 4 sound DAC 2. In my opinion, the LS-100 is a major step up from that combination. I rolled out the stock GZ34 rectifier with a NOS Mullard from the mid 60s. I rolled out the stock 6SN7s with a pair of Psvanes. I experienced significant improvement rolling in these tubes.

    The KWA-100SE arrived Friday and I only inserted into my rig last night. Given I have been trouble shooting this noise floor issue, I have not had much time for critical listening. However, other than the noise floor, I am very pleased with what I am hearing thus far. With my source playing, I cannot detect the hum, even at low volume listening. I moved from a tube amp to the KWA-100SE. My first impression is how warm sounding this solid state amp is. I suspect I will be very happy with this piece once I resolve the noise floor concern. Thank you for your help!

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