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Old 21st September 2006, 05:41 PM   #1
100db is offline 100db  Thailand
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Default Best Chip amp for this 4 Ohm speaker

Hi All,

Would like to hear your opinion on this...
Between these popular chips... LM3875/3886/4780 and also OPA 541 / 549... which one should be the best suit to my speaker ?

MTM, 4 Ohm ~90db, using parallel 15w-8530 with Vifa XT25 tweeter

thx.
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Old 21st September 2006, 05:47 PM   #2
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you can parallel the LM4780 quite easily --
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Old 21st September 2006, 06:36 PM   #3
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The LM4780 and OPA549 both work well with 4ohm
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Old 22nd September 2006, 01:57 AM   #4
100db is offline 100db  Thailand
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Hi Jackinnj, Hi Al

I'm currently using inverted 549 with 10k input and 93.1k feedback... I wonder if this single unit enough for my speaker ?

I've tried to bridge them but can't away from Hum problem. Also when I turn the volume up and down, will be a "poke" sound come out from the woofer.

Will try the 4780 soon.
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Old 22nd September 2006, 09:07 AM   #5
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Well, for 4 ohm loads, you should be looking at parallel operation rather than bridged. As for hum, the 4780 will be slightly easier in this respect as it is all on one chip, but if you're careful, and trace all the wiring in your existing amp, then you should get rid of the hum. As for the noise when you alter the volume, have you tried changing/cleaning the volume pot?
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Old 22nd September 2006, 10:13 AM   #6
100db is offline 100db  Thailand
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Hi Al,

I did try parallel 3875, but I found that it didn't sound as good as a single one, the other thing is I need to turn the volume more ( from 11am to 2pm ) to get the same loudness. Out put resistor is Mills MRA 0.1 R, 5 watt.... I don't think this output resistor will kill down the quality that much, isn't it ?

Quote:
As for the noise when you alter the volume, have you tried changing/cleaning the volume pot?
Yes, I've tried a DIY Stepped atten', a fake ALPS step', Noble 31 steps... all of them having this problem, maybe from somewhere else ?


Ball
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Old 22nd September 2006, 10:23 AM   #7
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Quote:
Originally posted by 100db
I did try parallel 3875...
Bridging 3875s into 4 ohms wouldn't work that well, they are optimised for 8 ohm loads, and in your setup they would be seeing 2! Your Mills should be fine, though I would put two in series to get a little better current sharing with a bridge or parallel setup. What schematic did you use?
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Old 22nd September 2006, 12:50 PM   #8
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Quote:
What schematic did you use?
For 3875, all of them are inverted.
2.2uf Ci, 10k input, 220k feedback, 220k from + to gnd.

Toroidal 24-0-24, 20A through MUR1620/R, No snubber no regulated.

Ball
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Old 23rd September 2006, 10:23 PM   #9
v-bro is offline v-bro  Netherlands
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this one can drive heavy loads too (1 ohm!) , and can be parallelled...
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Old 23rd September 2006, 10:25 PM   #10
v-bro is offline v-bro  Netherlands
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sorry........:
http://www.tripath.com/pb4100A.htm
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Max. cone displacement can be several foot on any speaker!Too bad it can be done only once......
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