Thoughts on how to reduce 60 cycle hum coming through Rythmik a370 and Super V

danvprod · « **on:** 23 Apr 2017, 05:11 pm »

I'm looking for some brainstorming ideas on how to deal with a couple of issues I am running up against with the A370 amps and Super V 2x12 subwoofer arrays namely:

1) Transformer Hum coming from the transformers on the plate amps. (This is not being transmitted through speakers and even is audible if I stick my ears up to the amps when the are plugged in and in the 'off' position).
2) Audible 60 Hz hum coming through my MiniTorii tube amp line out through the plate amps and out the 2x12 GR research speakers (really can't be heard through the p-audio co-ax).

I just added this power conditioner, which has helped greatly, but I am still wrestling with these two issues.

I am using blue jeans for interconnects, so I don't think it's a shielding issue and everything is plugged into the same outlet. This happens with both my digital and analog sources so I don't think it's that.

Couple of other things I was thinking of trying:
1) Could use the high-level inputs of the plate amps vs. the line level.
2) Could make a splitter to route the line level input to the plate amps before going to my tube amp (sub-optimal because I am using two line sources). Advantage: could put in a line level HP filter for the P-audio drivers).
3) Could try running a ground cable to each of the plate amps somehow.

Anything else simple I am missing? Here is how I am wiring this.

Source 1 (Analog) -> Line In 1 of MT.
Source 2 (Digital) -> Line In 2 of MT.
Line Out to a370 amps.
Speaker outs to P-audio drivers.

I should also check to see if I am getting the ground loop when the Amps are on but no sources are plugged into the line inputs. I haven't tried that yet...

Captainhemo · « **Reply #1 on:** 23 Apr 2017, 06:41 pm »

Pick up a couple of ground lift, cheater plugs to TRY on the A370's, this will at least tell you if it's a ground loop issue. these aren't ideal for long term use as thy eliminate a direct path to ground anda safttey aspect if the chassis should ever beco energized

The Blue Jeans LC1's are usually a nice tight fit but just be sure they are snug onthe outside of the RCA inputs on the amps

jay

avahifi · « **Reply #2 on:** 23 Apr 2017, 06:58 pm »

A DC Blocker may take care of your transformer hum.

If there is low level DC (direct current) floating on your Ac power line this will make power transformers very unhappy.

This can be generated by a number of devices such as a plasma TV or a dimmer or power level adjustment on something else in your home.

A DC blocking device has only one task and that is to pass your AC power while blocking that ugly DC component that upsets the power transformer.

Available inexpensively from us and others.

Frank

Early B. · « **Reply #3 on:** 23 Apr 2017, 07:02 pm »

Check everything in your house. I get an annoying hum through my A370's whenever I have a heater plugged up upstairs. Got any dimmer switches in your room?

Shakeydeal · « **Reply #4 on:** 23 Apr 2017, 09:00 pm »

Why don't you try using the high level inputs on the sub amps?

Shakey

corndog71 · « **Reply #5 on:** 23 Apr 2017, 09:45 pm »

I've struggled with a similar issue with my A370 amps. When plugged in but turned off I can hear a sound coming from the transformers that comes and goes and repeats about every 4 seconds. It's low enough that I only hear it when everything else is off. I have a Blue Circle DC blocker in the power line path which quieted a lot of transformer hum but can't seem to kill that weird fluctuating hum.

I chatted with one of the guys from Blue Circle and he seemed to think it was an amp issue more than a power issue.

Nick77 · « **Reply #6 on:** 23 Apr 2017, 10:04 pm »

That's starting to sound common???

danvprod · « **Reply #7 on:** 24 Apr 2017, 01:14 am »

Thanks @Captainhemo -- I had a couple of cheater lying around so I tried them. Tried with both A370s, no difference in transformer hum or hum through speaker and tried on main amp with no improvement in hum either in transformer or through the speakers.

Thanks @Frank -- I had tried an Emotiva CMX-2, which was billed to block DC if it was on the line, but that didn't improve it any. The HumDinger looks like a good option as well here.

Early B -- I have a dimmer switch in my room, which could be causing some issues. I had a heater during the winter, which caused horrible issues on the line. We've switched to an oil heater, which is much better.

@Shakey -- yes, I'll try the high level inputs tonight and see if that improves it any.

@corndog -- thanks for the details on your amps too as well as the feedback on the BC DC blocker.

Got a new rack today, which cleans things up quite a bit. Unfortunately the power issues remain...

avahifi · « **Reply #8 on:** 24 Apr 2017, 01:31 am »

Our HumDinger works In many cases where others don't. 30 day satisfaction guarantee too. $140.

Call us at 651-330-9871 to order. In stock for quick delivery.

Frank

gregfisk · « **Reply #9 on:** 27 Apr 2017, 08:39 pm »

I have one amp that makes a loud hum when it is either in standby or off which comes through the 12" servo subs. I called Brian and he said I needed to send the amp in for repair, If I keep it on all is fine so that's what I have been doing with one amp. If I turn it to standby or off it gets really hot, much hotter than the other one. I don't know if this is at all related but thought I would mention it.

Good Luck,

Greg

SoCalWJS · « **Reply #10 on:** 27 Apr 2017, 10:25 pm »

Have you checked to see if the wall outlets are wired correctly? I'd still swap my RCA's around and see if the problem is there. As a minimum, check and see if the wiring on the woofers still look good.

Have you experimented in the wee hours of the morning? Less likely that something else in the house is on and causing issues.

Folsom · « **Reply #11 on:** 27 Apr 2017, 11:17 pm »

My modification to the 370 stops ground loops through it.

The cheater plug may work to but isn't safe.

Circuit ground connected to safety ground is the most common way to have a loop. If you have a multimeter just touch the ground on an RCA then touch the other test lead to the chassis somewhere and see if you have a low reading, like under 10ohm. Once you know this you can figure out what's going on often.

danvprod · « **Reply #12 on:** 27 Apr 2017, 11:52 pm »

The Ohm reading of the Left RCA ground to the safety ground of the power cord is .7 Ohm. Other amp is .9 Ohm.

Folsom · « **Reply #13 on:** 28 Apr 2017, 01:21 am »

Source?

You got any DIY skills for solder/crimp?

danvprod · « **Reply #14 on:** 28 Apr 2017, 01:12 pm »

I took the measurements with my multimeter on the resistance measurement setting. I unplugged the amp from the wall and placed the test lead on the ground pin of the power cable and the other lead on the ground sleeve of the input jack to get my reading. I am not sure if that is a reasonable way to do this measurement.

I have a reasonable amount of DIY skills...

Speedskater · « **Reply #15 on:** 28 Apr 2017, 05:36 pm »

Get a little "Kill-a-Watt" meter.
Your AC power line voltage may be a lot higher than the amps are expecting.

Folsom · « **Reply #16 on:** 28 Apr 2017, 06:18 pm »

That can be a problem on tube amps.

Also you can put this between the ground from IEC input and whatever connection it makes to the circuit/chassis. Just use a little electrical tape to make sure it doesn't touch. I use a zip tie and zip tie anchor to hold them.

Mark Korda · « **Reply #17 on:** 28 Apr 2017, 07:07 pm »

Hi Danvprod,
I have a 2 tube amps that were doing what yours is doing. Frank VanAlstine and fellow expert Wayne offered me the return offer on the Hum Dinger. A friend lent then gave me something simular to Franks Humdinger from Motiva. It takes the small amount of DC out of the AC wall outlet that might sneak thru to your transformers. Not to argue with anyone but the Emotiva really did not make a difference that I could say (problem solved), so I'm kind of glad I did not take Frank and Waynes offer.....I would have to send it back and I don't like doing that kind of thing.
When I looked at your tube amp something caught my eye that solved my hum problem. Before I solved it I had a light dimmer switch on my bedroom wall. I replaced that from info from a master electrical guy I paint for and Waynes idea too. Not much difference.
My preamp was a passive rig I made myself 20 years ago. I used silver plated toggles for my switching ability between sources. When I was experimenting around I noticed there was some noise I never heard before when I switched the toggle, which look just like yours on your tube amp. The switch had become loose where it is connected to the chassis. With the nut end of a 6 and 1 hardware special screw driver there was plenty of tightening up to do that I had not noticed before........all hums from amps to cd player vanished!
It might not be your problem but might be an easy thing to check on your trouble shooting....check those toggles for tightness to the chassis...good luck...Mark Korda

Folsom · « **Reply #18 on:** 28 Apr 2017, 07:57 pm »

Almost forgot... check the continuity of all your RCA cables. A broken RCA cable can cause hum in both channels.

avahifi · « **Reply #19 on:** 28 Apr 2017, 09:20 pm »

Don't be so sure our HumDinger won't help just because the Emovita did not. We tested it here and it did not work anywhere near as well as the HumDinger did. Same with the PS audio humbuster.

Frank