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Old 23rd May 2005, 03:17 AM   #1
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Default Gainclone humming in new setup

I've completed my active crossover project, and my Gainclone. I moved them downstairs to my home theater room. Once I got everything together, powered 'er up... Massive. Humming. We're talking, earth loop hum-a-thon.

Both the active crossover, and the gainclone hum like crazy, but, only when connected to the pre-amp out on my receiver (Yammy RX-V1200), or DVD player (granted, haven't tried anything else).

The gainclone has the neg input grounded to the star ground, whilst the active crossover does not.

I'd like to focus on the gainclone for now, since if I figure that out, I bet the active crossover will fall in line. Both the search here, and google haven't helped, although you'll see my facts prove that I've read up on this a bit.

Ok, so, here are the facts:

1. Slight AC line noise, but 100x less humming then its previous location (bedroom). Used a CD player with varible output as a source (no safety ground on that source).

2. No humming at all when no input is connected. DMM shows input + is not bridging to chassis GND (when earth ground is disconnected).

3. Pre-amps tried (RX-V1200 and DVD player) each have no safety earth.

4. If I run a wire from the GND connection (for phono?) on the Yammy, to the chassis on the gainclone, the humming gets quieter, but, not nearly quiet enough.

5. If I ground the chassis on the Yammy to AC earth, and then ground the Gainclone chassis to that, humming is least of all, yet, still much, much too loud.

6. In all these examples, the pre-amp hasn't even been powered on (plugged into an outlet though).

7. All share the same outlet, tried different outlets as well, seperating equipment. Currenty using Monster cable line conditioner as well.

8. Tried different RCA cables, both grounded shield and ungrounded.

9. There is no COAX or antenna connected in the entire system. Just coax to TV, which doesn't run anywhere near the equipment.

10. My subwoofer plate amp doesn't hum at all, and it has an earth ground, so, maybe there is still hope left.

11. My commercial amp (which will be driving just the woofers), doesn't hum, and doesn't have an earth ground either.


To be honest, I don't understand how most commercial equipment, with metal chassis, get away without having a safety ground...


Ok, thats a long list. Sorry, but, better be too detailed than not enough. Keep in mind that there was acceptable levels of hum in the old setup.
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Old 23rd May 2005, 03:22 AM   #2
jleaman is offline jleaman  Belgium
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I can't use any gain clone amp with another manufactured amp at all only seperate to it's self.. It's weird that is why i have ditched all the gain clone stuff in my hifi setup..
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Old 23rd May 2005, 03:59 AM   #3
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Try inserting a 10 ohm NTC thermistor between each of the gainclone circuit grounds (i.e. two thermistors for stereo - you should already have a separate star for each chip) and the gainclone chassis ground. This includes the input RCA jack ground and the speaker ground - if they aren't already isolated from the chassis this could be the problem.

The normal cold impedance of the thermistor prevents circuit currents from flowing through the chassis ground, but still allows large currents through in a fault situation.
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Old 23rd May 2005, 01:41 PM   #4
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Here is some more information, that I forgot to mention. I'll try the 10 ohm thermistor idea, and verify the speaker posts as well.

This is BrianGTs 3875 rev 2 PCB kit. There are 3 grounds total. One from each PCB, and the AC earth ground. These are all connected at one common point, grounded to the chassis with a bolt.

Using my DMM, I can verify that the neg input is grounded to the chassis, but, only through the star-ground. I disconnected the star ground, and verified that both RCA inputs are not touching the chassis. I'm assuming this design is intentional.
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Old 23rd May 2005, 06:19 PM   #5
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Quote:
Originally posted by jleaman
I can't use any gain clone amp with another manufactured amp at all only seperate to it's self.. It's weird that is why i have ditched all the gain clone stuff in my hifi setup..


No problems here, and I can't see why a well made amp should not behave when connected to commercial components.
There's some problems in the layout there.

Quote:
Originally posted by drfrink24
This is BrianGTs 3875 rev 2 PCB kit. There are 3 grounds total. One from each PCB, and the AC earth ground. These are all connected at one common point, grounded to the chassis with a bolt.
A picture would help.
A lot.
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Old 23rd May 2005, 06:31 PM   #6
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I've attached the picture. A few changes that I've made since this was taken:

1. I re-routed the AC in, so that it goes around the trans, instead of directly over it.

2. I've since went to sheilded SG and IN for input.

3. I've added a .1 uf cap on the signal input, per the active crossover designers recommendation.

Keep in mind, this doesn't hum in my old setup. Its not dead quiet either, but, nothing noticeable at 5 feet from the speakers.
Attached Images
File Type: jpg amp 0041.jpg (71.6 KB, 551 views)
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Old 23rd May 2005, 06:35 PM   #7
jleaman is offline jleaman  Belgium
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drfrink24

Nice case.. Where did you buy it from ?
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Old 23rd May 2005, 06:43 PM   #8
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Thanks.

Par-metal. Under $50 shipped, all aluminum.
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Old 23rd May 2005, 06:45 PM   #9
jleaman is offline jleaman  Belgium
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Quote:
Originally posted by drfrink24
Thanks.

Par-metal. Under $50 shipped, all aluminum.

Got a link Please That would look good for my Pre-Amp.
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Old 23rd May 2005, 06:47 PM   #10
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Just for a test, disconnect the chassis ground and leave both wires from the amps floating, without touching anything.
The pic is not very clear because of the angle it was taken, but it seems you have two separate ground paths from the amp's boards: PSU and chassis ground.
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