LM3875 audiosector kit - Optimum DC cable length - power & amp PCBs? - diyAudio
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Old 24th August 2009, 04:43 AM   #1
GAH is offline GAH  Fiji
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Default LM3875 audiosector kit - Optimum DC cable length - power & amp PCBs?

How critical is the length of cable (DC power) between the Power and Amp PCBs of a LM3875 or LM4780 audiosector kits?

I'm building one these kits and wish to include a separate chassis each for the amp and power supply. Would 1.5 metres be ok?
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Old 24th August 2009, 12:16 PM   #2
Nuuk is offline Nuuk  United Kingdom
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1.6743 metres would be optimum!
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Old 24th August 2009, 12:31 PM   #3
AndrewT is offline AndrewT  Scotland
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0.6m would be OK, 0.3m would possibly be better.
The speaker cables also fall into a similar length compromise.
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Old 25th August 2009, 10:08 PM   #4
GAH is offline GAH  Fiji
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Quote:
Originally Posted by Nuuk View Post
1.6743 metres would be optimum!
Thanks. Nuuk, your reply is so precise!
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Old 28th August 2009, 09:43 AM   #5
Atilla is offline Atilla  Norway
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1.6743 metres of which wire gauge ?
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Old 28th August 2009, 10:07 AM   #6
mrevie is offline mrevie  Australia
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Three strands of precisely braided 17.98 guage cadmium wire.

N.B. Best results obtained if braiding is done by rare south americian mountain gerbils.
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Old 28th August 2009, 03:27 PM   #7
H3nry is offline H3nry  United States
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Serious answer: as long as the chips are bypassed well on the amp board, which means put your big electrolytics there, and maybe bypass them with small high quality film caps, you're covered. Then the only concern is the voltage drop / current carrying capacity of the cable. With a meter or more cable, I'd probably put something larger than the 10 uF filters that come in the kit on the rectifier PCB.

My own amps have 3300 uF + 10 uF on the rectifier board and 4700 uF + .047 uF on the amp board. I like solid bass, so I go for lots of energy storage in the power supply. Peter Daniel prefers a lighter supply, I believe. That's a nice feature of chip amps. The circuit is so simple it's easy to tune to your own taste.
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Old 28th August 2009, 03:43 PM   #8
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Quote:
Originally Posted by H3nry View Post
Serious answer: as long as the chips are bypassed well on the amp board, which means put your big electrolytics there, and maybe bypass them with small high quality film caps, you're covered. Then the only concern is the voltage drop / current carrying capacity of the cable. With a meter or more cable, I'd probably put something larger than the 10 uF filters that come in the kit on the rectifier PCB.

My own amps have 3300 uF + 10 uF on the rectifier board and 4700 uF + .047 uF on the amp board. I like solid bass, so I go for lots of energy storage in the power supply. Peter Daniel prefers a lighter supply, I believe. That's a nice feature of chip amps. The circuit is so simple it's easy to tune to your own taste.
The shorter the better!.and I am also using big caps on the power supply
10000uf on the rectifier and 1000uf on the amp board.Nice bass!
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Old 28th August 2009, 04:02 PM   #9
H3nry is offline H3nry  United States
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Originally Posted by lanchile View Post
Nice bass!
Indeed! My amps are DC coupled and my preamp is flat to 1 Hz, and the bass is incredibly natural, smooth and alive. My previous amps were decent JBL pro studio monitor models, and the Audiosector amps are amazingly better. Not only bass - mids and top are much clearer, more relaxed and natural.
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Old 28th August 2009, 04:18 PM   #10
AndrewT is offline AndrewT  Scotland
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Lanchile,
please stop posting in that almost illegible colour.
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