Best Chip amp for this 4 Ohm speaker

100db · 21st September 2006, 05:41 PM

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.

jackinnj · 21st September 2006, 05:47 PM

you can parallel the LM4780 quite easily --

pinkmouse · 21st September 2006, 06:36 PM

The LM4780 and OPA549 both work well with 4ohm

100db · 22nd September 2006, 01:57 AM

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.

pinkmouse · 22nd September 2006, 09:07 AM

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?

100db · 22nd September 2006, 10:13 AM

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

pinkmouse · 22nd September 2006, 10:23 AM

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?

100db · 22nd September 2006, 12:50 PM

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

v-bro · 23rd September 2006, 10:23 PM

this one can drive heavy loads too (1 ohm!) , and can be parallelled...

v-bro · 23rd September 2006, 10:25 PM

sorry........:
http://www.tripath.com/pb4100A.htm

21st September 2006, 05:41 PM	#1
100db diyAudio Member Join Date: Dec 2005 Location: Bangkok, Thailand	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.

21st September 2006, 06:36 PM	#3
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	The LM4780 and OPA549 both work well with 4ohm __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

22nd September 2006, 09:07 AM	#5
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	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? __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

23rd September 2006, 10:23 PM	#9
v-bro diyAudio Member Join Date: May 2006	this one can drive heavy loads too (1 ohm!) , and can be parallelled... __________________ Max. cone displacement can be several foot on any speaker!Too bad it can be done only once......

23rd September 2006, 10:25 PM	#10
v-bro diyAudio Member Join Date: May 2006	sorry........: http://www.tripath.com/pb4100A.htm __________________ Max. cone displacement can be several foot on any speaker!Too bad it can be done only once......


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21st September 2006, 05:47 PM	#2
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	you can parallel the LM4780 quite easily --

22nd September 2006, 01:57 AM	#4
100db diyAudio Member Join Date: Dec 2005 Location: Bangkok, Thailand	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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