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Old 8th November 2003, 11:06 AM   #1
Raka is offline Raka  Europe
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Default Grounding in a biamped buffered system

I'm designing a biamped system based on GC and buffered ala Rasmussen with an OPA627.
My question is about the grounding, as there will be THREE power supplies.
Should I just make a power star ground common for the 3 PS, an other star gnd for the 3 stages and join in only one point?
Should the GND of the OPA power supply go to the signal GND of the buffer, or to the main GND star power gnd?
Has anyone had a problem with the turn on/off of a LM1875? I've almost completed the poit to point- PCB for both 1875 and 3875, but maybe with the 3875 there will be no problems for the tweet (yes, I know it has to be protected)
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Old 8th November 2003, 12:09 PM   #2
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Raka, presumably you will be using four amplifiers to bi-amp a two-way speaker system. Will you be using seperate PSU's for each amp?

If so just build them as seperate amps.

For powering the OPA627 buffers, you could use one or two PSU's (I used one but it was only a two channel amplifier). Either way, connect the ground connections from each buffer to the signal ground star of the corresponding amplifer and you should be OK.

However, I think that if I was doing a bi-amped system, I would use an active preamp rather than four buffers!
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Old 8th November 2003, 02:39 PM   #3
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I'm not sure if I've understood well your post...
I'm not going to use four buffers, just one for each channel.
After the RCA's I'll fit the opa (one ps) that feeds the high and mid-low amps (two more PS's) each amp with a passive filter in it's input. Each amp will have it's own transformer and bridge.
Then I start thinking about the grounding scheme. Starting with the buffer, I'll have a neutral for the signal and a neutral from the ps.
The woofer amp has his own supply, so that means that there are two more grounds. There is also the tweeter amp, so two more gnds to consider...
Should I join all the power supplies gnd (tweeter+woofer+opa) in a star point (and take the speaker lead from here) and do the same with the signal gnds? Or should I join the power gnd of the opa PS with the signal gnd before going to the power amps?

I have the file with the wiring, but I don't know if the software allows to export as a jpg. I'll try a hand drawing if I can
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Old 8th November 2003, 03:59 PM   #4
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you could put a buf634 in the loop on the opa627.......
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Old 8th November 2003, 04:39 PM   #5
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What for, if it's going to be an integrated?
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Old 8th November 2003, 04:56 PM   #6
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how much are you loading the opa627....?
....and are you using a constant current source....?
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Old 8th November 2003, 06:22 PM   #7
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According to my simulations, the max current loading of the OPA will be a little bit more than 1 ma from 5KHz, more or less. I don't think this is a great effort for the OPA, is it?
What do you mean with constant current source?
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Old 8th November 2003, 07:00 PM   #8
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Ok, I see what you're doing now. I'm not sure what to suggest though as I have not yet done any IGC channel that wasn't separated from the other(s).
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Old 8th November 2003, 07:34 PM   #9
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http://www.tangentsoft.net/audio/opamp-bias.htm
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Old 8th November 2003, 07:42 PM   #10
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Thanks for the link but the document is not available!!

If I think as pre+powerX2 as separate, not integrated, I understand very well the grounding, but as integrated...

As maybe you are starting to think that actually I don't build anything, this is the speaker that is going to be biamped

Do you like it?
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