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Old 5th September 2005, 06:32 PM   #1
scottw is offline scottw  United States
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Default dual mono grounding options

Greetings,

I did a rebuild on my "chimpamp" to allow room for more capacitance and move the tx's to a separate case. Amp is the original briangt PCB for the LM3875. Currently running one large ground wire from the PSU for both amps, and a smaller wire just for the amp case ground. Left and right amp PCB grounds are joined by a single 16ga wire and the large ground wire is attached to this wire at the center point between the amps(I think this is 'similar to' what carlosfm has used/recommended re. grounding).

Nearly no hum at the speakers(~94dB). But, while the left-right channel effects are present, the sound stage lacks the focus at the center of the image(compared to before the rebuild).

I'm wondering about the effect of crosstalk through the ground because the amps, otherwise separated, have the grounds tied together in the amp case? What effect would you notice if you were getting crosstalk?

One possible option is to float the amps. My tx's have dual "center tap" secondaries. So, is it possible to ground the center taps for a ground reference and then float(not ground) the amps?

Any other suggestions?


Thanks,

scottw
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Old 5th September 2005, 10:20 PM   #2
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Are you talking about a stereo amp, with a single power source, or a dual monoblock, with two rectifier boards and possibly two toroids?

If the former (single PS stereo setup), search for posts containing star and ground by carlosfm. He posted some really nice pics about six months ago. IIRC using BrianGT 3875 boards and his own single PS.

If the latter -- dual monoblock design -- you took the post right out of my mouth. I'm getting ready to build a dual LM3886 setup with dual PS boards and a single toroid. Any grounding insights would be useful -- particularly whether or not PG or SG should be joined between the amps, and whether this will matter in a bridging configuration or not.

BTW, if you post a pic, you may get some extra neurons firing on your problem.

Wes
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Old 6th September 2005, 12:30 AM   #3
scottw is offline scottw  United States
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Quote:
"Are you talking about a stereo amp, with a single power source, or a dual monoblock, with two rectifier boards and possibly two toroids?"

Dual mono: two tx's, each with two center tapped secondaries; two diode boards(8 diodes each), one for each tx; umbilical includes two twisted pairs for each amp(V + , Neutral + , Neutral - , V - ). The PSU is in one case and amps and some large caps are in another case.

The tx's are big, homely, silent, cool running, industrial, under rated, non-audiophile, $5.00 at the hamfest EI's.

Quote:
"If the former (single PS stereo setup), search for posts containing star and ground by carlosfm. He posted some really nice pics about six months ago. IIRC using BrianGT 3875 boards and his own single PS."

Seen it. I think that's what I mentioned at the end of my first paragragh. This is similar, I think, to the grounding arrangement I'm currently using(see link below) and I have very faint hum. From what I've seen, carlosfm would be using the LM3886.

Hum with Brian 3886 kits

Quote:
"Any grounding insights would be useful -- particularly whether or not PG or SG should be joined between the amps, and whether this will matter in a bridging configuration or not."

Good luck with that. Most of the specific grounding recommendations are for a single tx powering two amps.

Quote:
"BTW, if you post a pic, you may get some extra neurons firing on your problem."

Pictures of my mess, I fear, would only confuse the issue. There is a lot of extra stuff(bypass and RC snubberettes) hanging off the little original briangt PCB. And I don't have the software to draw a decent schemo. I'll see if I can't post a pic.

scottw
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Old 6th September 2005, 07:35 PM   #4
scottw is offline scottw  United States
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Join Date: Feb 2004
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My first attempt with CircuitMaker.

Bypasses and snubberettes are only on the chip at this point. I'll get used to the sound before further bypassing at the big cap.

So, any obvious screwups, or thoughts on grounding crosstalk?


thanks,

scottw
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