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Old 18th March 2009, 01:39 AM   #1
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Default Newbie project - LM1875 or LM3875

Hi,

First of all thank you to everyone here. You are such a great source of information for a total beginner such as myself.

I am considering building a chip amp and from what I can tell it seems like the LM1875 is the favourite of these two chips but I am concerned that it won't be enough to drive my speakers. I have Kef iq3's, 8 ohm, 89 dB. (spec - http://www.superfi.co.uk/index.cfm/p...roduct_ID/2490 )

Which chip would you recommend for my purposes?

Also, would It be correct to say that the LM1875 has a more laid back smoother sound? My KEF's are quite aggressive and trebbly as they are so I wouldn't want to emphasise that any further.

Any suggestions would be very welcome.

Thank you
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Old 18th March 2009, 03:38 AM   #2
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I would defenently use an LM3875 or LM3886.Between these two,I personally like the LM3875 better.
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Old 18th March 2009, 03:54 AM   #3
ttan98 is offline ttan98  Australia
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I have both LM3886 and LM3875, I prefer the latter, better clarity.
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Old 18th March 2009, 08:19 AM   #4
Nuuk is offline Nuuk  United Kingdom
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The LM3875 will be fine. Just because you read the LM1875 "has a more laid back smoother sound" doesn't mean that the LM3875 sounds in any way aggressive.
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Old 18th March 2009, 10:45 AM   #5
AndrewT is offline AndrewT  Scotland
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Hi,
I think those KEF speakers are 4 to 8ohm and not 8ohm.
See the spec for minimum impedance of 3.2ohms.

If these are using a 4ohm or 5ohm bass/mid driver with an 8ohm treble driver then you must design the amp as a 4ohm capable amplifier.

The 3875 has a current limit ~ 60% of the 3886. The 1875 has an even lower current limit.
I would recommend neither the 3875 nor the 1875 for this 4 to 8 ohm duty.
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Old 18th March 2009, 11:47 AM   #6
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I use the 3886 from chipamp.com with my B&W CM4's which are similar to your KEFs although a bit more efficient at 91dB...I like it a lot but I could use a bit more power - at high volumes the bass starts to clip a bit i think.
byron
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Old 18th March 2009, 12:19 PM   #7
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Thank you for your replies.

If I were to build a LM3875 amp from a kit then which do you recommend? Chipamp.com don't appear to offer one. I liked the look of the kit at audio sector (http://www.audiosector.com/lm3875.shtml) but it says its dual mono? Does that mean I would need two transformers? sorry If I'm being stupid.

Thanks again
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Old 18th March 2009, 01:04 PM   #8
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you could use two transformers but a dual-secondary transformer will work just fine...Peter has a guide to the build of his kit somewhere on the site (I think it's a sticky in the chipamp forum)
Byron
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Old 19th March 2009, 08:03 AM   #9
Francec is offline Francec  Australia
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I used a bridged 3886TF with one PCB for both amps and a balanced driver, Rod Elliot's P19 amp and P87B balanced driver. It drives my 8" Peerless woofer and doesn't have any problems even with high volume.

Frank
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Old 19th March 2009, 02:46 PM   #10
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Quote:
Originally posted by mantisory
you could use two transformers but a dual-secondary transformer will work just fine...Peter has a guide to the build of his kit somewhere on the site (I think it's a sticky in the chipamp forum)
Byron
Would this transformer be suitable for the audiosector kit (i think it is dual secondary)?
http://uk.farnell.com/jsp/search/pro...sp?sku=9532838

On the kit guide he recommends a transformer with 220VA. Would that be per secondary or overall?

Thank you
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