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Old 25th November 2009, 11:18 PM   #11
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Damn... Got a good tip to remove them... Luckily I havnt snipped them down.

Apart from the diodes error, got one almost complete.
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Old 5th February 2010, 04:46 AM   #12
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A couple of questions...

If I want to use one of the 2 LM4780 kits I have to power 2 channels (left midbass/right midbass), 4ohm impedance each, non-balanced input, which is the best configuration to run, will it require dual toroid transformers and what is the output power?



Thank you.
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Old 5th February 2010, 04:57 AM   #13
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It's best to use separate transformer per channel to power multiple amps.

The graph below shows power vs supply voltage with 4 ohm loads. It's for parallel configuration, but single amp will be the similar, although won't go as high due to current output limitation.
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File Type: jpg power.jpg (76.2 KB, 823 views)
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Old 5th February 2010, 01:07 PM   #14
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I think the terminology is confusing me.

Please correct me if Im wrong, and thank you for taking the time to answer my questions. This is great service !

Scenario 1:
One kit can be made to run "parallel" (also called dual mono?)which would give you two amplifier channels total, using both boards, one channel per board. This requires two transformers. Does not require balanced input.

Scenario 2:
One kit can be made to run "bridged" which would give you one amplifier channel total, using both boards. This requires one transformer, but you need to use a balanced input source.


Is that correct?

And then finally, IF that is correct than based on that power vs supply voltage graph for 4ohms, would it benefit me to use (2) 400VA 35v+35v transformers for that 2 channel parallel amp instead of the 400VA 18v+18v ?

Thank you.
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Old 5th February 2010, 03:32 PM   #15
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In case you are using only one kit, a single transformer is sufficient.

Also, please note that maximum allowable power supply voltage is 40V DC, so 35v + 35v transformer is out of question, as it produces DC voltage way over 40V.

With parallel setup and 4ohm speakers you'd be getting close to 160W according to graph. In such case a single 400VA transformer is sufficient for both channels. If you are adding mid and high freq amplifiers, then I would switch my recommendation to single 400VA transformer per channel.

In bridged mode, you have 2 options:

1) One kit produces two bridged channels (single amps in bridge)

2) One kit produces one channel (parallel amps in bridge).
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Old 16th May 2010, 04:40 AM   #16
ra7 is offline ra7  United States
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Peter,

I ordered your 4780 kit a few ago and am currently building it. I see that the 270R resistors are actually 220R. Is this on purpose? I didn't see it documented anywhere on the forum, hence I'm asking.

Thanks!
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Old 20th May 2010, 01:47 AM   #17
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There is no difference between using 220R and 270R input series resistors and I currently supply 220Rs. You will see a difference though, when you omit those resistors completely
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“Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC
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Old 14th April 2011, 01:07 AM   #18
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I just realized that location of mute resistor (Rm=10K) might not be clear, so here it is, in a bottom layer:
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File Type: jpg Rm.jpg (185.1 KB, 529 views)
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Old 20th August 2012, 04:45 PM   #19
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i have 25-0-25 Vac (250VA) rated toroidal transformer. after rectification it will give 35.35Vdc. will this be ok for LM4780 amp in any of the mode?
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Old 28th April 2014, 05:48 PM   #20
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So, I've got my boards populated for parallel configuration, hooked up to to the PSU board (which is also populated) and I'm making the input and output connections...

Is the input ground common to the output ground?
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