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TKO956  
#1 Posted : Wednesday, August 15, 2018 2:00:34 PM(UTC)
TKO956

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Hello all,

I've searched and can't seem to find the information I'm looking for:

Is it possible to run the LM4780 in parallel mode with these PCBs?

Thank you in advance!
Brian Donegan  
#2 Posted : Wednesday, August 15, 2018 3:11:47 PM(UTC)
Brian Donegan

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Do you mean running multiple boards in parallel?

To that, the answer is no.
TKO956  
#3 Posted : Wednesday, August 15, 2018 3:26:26 PM(UTC)
TKO956

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Hello Brian,

Thank you for the reply. Actually I wanted to run each LM4780 in parallel mode therefore making it easier for these to run 4ohm speakers. Then having 2 PCBs per channel: 1 for pos., 1 for neg.

Is this something that would work?

Thank you
Russ White  
#4 Posted : Wednesday, August 15, 2018 5:13:20 PM(UTC)
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Actually because of of the fully symmetrical nature of the whole circuit - you won't have any trouble driving 4ohms as long as you respect the maximum power of the LM4780.

I am currently driving 4ohm speakers myself - and I am confident even a speaker that dipped into 2ohms would be just fine as long as you did not try to play them too hard.

Unfortunately there really is no practical way to parallel the 4780s with that PCB - it would really require a whole new design.

Cheers!
Russ

Edited by user Wednesday, August 15, 2018 5:13:52 PM(UTC)  | Reason: Not specified

TKO956  
#5 Posted : Wednesday, August 15, 2018 6:11:37 PM(UTC)
TKO956

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Hello Russ,

Thank you for the reply. My speakers are the ER18mtm thstdrop to 4 ohms in the bass region but are a nominal 6ohms. Should I spec the transformer at the 22V I've seen recommended for 4ohms or the 25V I've seen for the 8 ohm?

I was thinking that anywhere in between would work OK. Also, I was planning on 600VA unless you think that a lower VA rating would be sufficient to get the best Sonics out of the amp.

Thank you
Russ White  
#6 Posted : Wednesday, August 15, 2018 8:32:29 PM(UTC)
Russ White

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Either choice is just fine - I would probably go with the 25V trafo myself since you are really operating between regions. 600VA is definitely adequate - I would use one per channel. In my office setup I went a bit overkill and have 24V 1000VA per channel - but I could go small without any problem.

Cheers!
Russ
TKO956  
#7 Posted : Wednesday, August 22, 2018 12:02:36 PM(UTC)
TKO956

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Hello Russ,

Thank you very much for all of the information. I had a couple of the LM4780 chips laying around so I only ordered the PCBs. I have been looking over the BOM and have a couple of questions:

C13,C14 - obsolete - will Panasonic LGY series LGY1H153MELC50 work as a replacement or is something "better"
CF1 - obsolete - will Kemet PHE820MB6100MR17 be OK
Faston connectors - having a hard time finding 2.54x1.1 (mm correct?) Can you please point me in the right direction?

Thank you!
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