Gainclone humming in new setup

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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.
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.
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.
jleaman said:
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.

drfrink24 said:
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.
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.


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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.
carlosfm said:
Disconnect those two wires and test the amp.

Ok, I'm at work ;) I'll test when I get home.

What I do know is, the Neg of both output and input is grounded to the chassis thru those very same wires as well, as I assume is the PCB design.

So, basically, what I'm doing is "floating" the PCBs, while still retaining the Chassis ground, and since I've verified that the RCA jacks are not touching the chassis (still need to verify the speaker out), I should be ok.

If this works, what will I learn from it? What does it mean about my setup?
drfrink24 said:
Yeah, sorry about the quality of the picture. Here is a drawing, maybe this will help.

Maybe it's time for BrianGT/Peter Daniel/Vikash to make a good documention for in particular the grounding and in very particular the grounding for stereo!

It seems that most common trouble with those Gainclones is the grounding.

Grounding is easy if you know it but hardly common knowledge.
drfrink24 said:

If you want, they will countersink the faceplate screws, free of charge.

For the money, they are very nice cases. I've been told to stay away from anything but clear alondine finish though, others have had quality concerns with their gold/black/beige/gray colors.

I shal order one soon then.. I like them.
drfrink24 said:
This is a direct quote from the LM3875 construction manual:

"The chassis ground essentially go to what could be referred to as the star ground. There will be 3 wires tied here, one each channel, and AC ground connection."

I'm sorry to say, but this is hum for sure, with one PSU for two channels...
Less or more hum, depends on the distances and the wire used for the ground.
The main problem here is the separate (power) ground feeds that join on each board.
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