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Old 23rd August 2005, 02:37 PM   #1
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Default Brian GT LM4780 Bridging

Hello Everyone,

I have a pair of the Brian GT LM4780 kits, awsome kits by the way, and I would like to know if I can bridge them mono for a subwoofer? My HT sub is 4 ohms. I plan on building 5 channels of Mr. Ed for the other speakers, or possibly 5 LM4733 and doing a bridge/parallel configuration. Can anyone help me bridge the two kits? Has anyone ever worked with the LM4733 before? And one last question, I love how the Mr. Ed has the ps on board, could I adapt his ps to work with the LM4733??

Thank you very much,

John
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Old 23rd August 2005, 11:05 PM   #2
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You should be able to bridge those, but not with your sub -- each amp will see a 2 ohm load.

I suppose you could always parallel them if you need more oomph.

BTW, who is Mr. Ed? I take it somebody other than the horse?

Wes
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Old 23rd August 2005, 11:47 PM   #3
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Default Mr Ed

Quote:
Originally posted by wes-ninja250

BTW, who is Mr. Ed? I take it somebody other than the horse?

Wes

Mr. Ed is a simple NI chipamp design utilizing the LM3886.

You can read about it here:
My NI chipamp Mark-II - Mr. Ed :)

Cheers!
Russ
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Old 24th August 2005, 01:01 AM   #4
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you mean this?

Click the image to open in full size.

there's no creativity in the design -- i just used national's circuit diagram, modified it for somewhat better components -- i have boards if you care (and parallel boards as well).
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Old 24th August 2005, 02:33 AM   #5
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Would not each amo see a 4 ohm load? Those LM4780 kits are 2 3886 amps in parallel.
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Old 24th August 2005, 11:40 AM   #6
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Quote:
Originally posted by Tweeker
Would not each amo see a 4 ohm load? Those LM4780 kits are 2 3886 amps in parallel.
the 3886 "dies" are attached to separate pins (i.e. not in parallel -- including separate mute functions) -- so one amp is configured as inverting, the other non-inverting. the LM4780 can be bridged or paralleled.

The bridged amp is a great performer as long as you are driving a nominal 8 ohm load:
Click the image to open in full size.

note the performance between the prototype (dotted lines) and finished boards -- this is entirely due to dressing of the power supply leads -- and is the reason that I am somewhat skeptical of the performance of "Mr. Ed" with the power supply caps and diodes immediately adjacent to a high power, high gain opamp.
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Old 24th August 2005, 12:03 PM   #7
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Quote:
Originally posted by jackinnj


note the performance between the prototype (dotted lines) and finished boards -- this is entirely due to dressing of the power supply leads -- and is the reason that I am somewhat skeptical of the performance of "Mr. Ed" with the power supply caps and diodes immediately adjacent to a high power, high gain opamp.

It is good to be skeptical, I was indeed skeptical of Mauro Penasa's "My Ref" design for the same reason. It seems to be a bit taboo to approach the PS on board as he did. But I was dead wong, as you are. Reward your skepticism with a test, and see for yourself. Naturally any amp rewards you with lower noise and distortion with good cable dressing.

Do us all a favor and comment more on the PS noise subject after you have actually measured "Mr Ed" I would really like to see that. In fact I will send you two PCBs if you like to do the test. Without that it just appears as if your are pushing your design over another without any basis in fact, only opinion.

Cheers!
Russ
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Old 24th August 2005, 04:05 PM   #8
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I also can get an 8ohm sub so each amp will see a 4ohm load instead of a 2ohm. wes-ninja250 do you have a wiring diagram? Russ_White, you have been posting some of the more interesting implementations I have seen lately and am building several Mr. Eds right now as well as a yardbird and a freebird. Have you ever experimented with the LM4733? I was thinking about trying your PS section from the Mr. Ed and using it on the LM4733?

Thanks for your input.
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Old 24th August 2005, 05:21 PM   #9
Tweeker is offline Tweeker  United States
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I took Juan as meaning he had two Brian GT 4780 chips and was intending to bridge the two. In the Brian GT 4780 pcb the two 3886 chips are configured paralelled. Giving a 3886 BAP arrangement- 2 sets of 2 paralell 3886 bridged. If this is the case they should be able to handle a 4 ohm load, providing there is sufficient heatsinking, especially if a higher voltage is used.
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Old 24th August 2005, 06:11 PM   #10
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Thanks again for the response. I was just checking and I was thinking it is very similar to the BPA200 also. Do you think a 48v ct transformer with a 2 amp rating will be enough? Do you have any suggestions about connecting the two lm4780 kits together?

Thank you,
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