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Old 18th October 2008, 05:56 AM   #1
Luke352 is offline Luke352  Australia
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Default Which Chipamp to choose?

So I've got a speaker project which I'm about to kick off but I also want to start an amp build aswell, so I've been looking around for something cost effective and easy to assemble and have found. ChipAmp and AudioSector for chipamps, they all seem to be quality products with similar levels of pre assembly. So which to choose?

LM4780
LM3875
LM3886
LM1875

What are the advantages and disadvantages of each type, expected power, and are they all able to be bridged as the idea of bridgeing them together at a later date to get more power has crossed my mind.

So which should I chose and why, as I really don't now why I should pick one over the other.

Any help you could give me would be great.

Thanks

Luke
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Old 18th October 2008, 06:53 AM   #2
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Look here for a technical comparison.

LM4780 - advantage: two LM3886 in one, disadvantage: narrow pin spacing, limited heat dissipation
LM3875 - advantage: few pins to connect
LM3886 - advantage: mute function, highest possible power output, disadvantage: mute function must be connected
LM1875 - advantage: price, space requirements, few pins to connect, disadvantage: less power and current
Add LM1876 - advantage: two amps in one, price, space requirement, mute function, stand-by function, disadvantage: less power and current, PCBs difficult to find -> have to make your own or use breadboard or P2P

They can all be bridged and paralleled and bridge-paralleled. For the LM1875 and LM1876 that makes however little sense, because you can achieve the same result with the other ICs non-bridged and non-paralleled.

As for the sound, the differences from one IC to the other are much smaller than any differences their implementation will produce.
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Old 18th October 2008, 11:01 AM   #3
Luke352 is offline Luke352  Australia
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Thanks heaps for that, that' just what I was looking for!!! Something like that should be sticked so when people like me come looking to find out information like that it's in one handy area.

Thanks again

Luke
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Old 18th October 2008, 01:55 PM   #4
ratza is offline ratza  Romania
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Quote:
Originally posted by pacificblue

Add LM1876 - advantage: two amps in one, price, space requirement, mute function, stand-by function, disadvantage: less power and current, PCBs difficult to find -> have to make your own or use breadboard or P2P

Luke, I would choose LM3875 over LM3886 as you'll never use the mute function, trust me. The sound seems to be also better on 3875, although I was not able to make the difference between them on a double blind test.

Offtopic: From what I've seen until now, it seems like everybody runs away from a schematic whitout a PCB available. Is it really that hard to design your own, or there are some laws in your countries which doesn't allow to use home the chemicals needed to produce the PCB (FeCl2 or HNO3)? This is a question which came to my mind a long time ago while reading this forum but I always postponed it. I ask this because in Romania almost everybody creates their PCB at home.
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Old 18th October 2008, 06:37 PM   #5
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No law against using the chemicals, but laws about how to deal with them after use, which make the disposal more inconvenient than the actual use.
And then there is the point of avoiding the risks involved, like getting skin or eyes etched or clothes and furniture stained.
Ever heard of WAF? Stinking and etching chemicals rank even lower than wardrobe-sized speakers, when it comes to wife acceptance factor.

On the other hand P2P or breadboard is widely considered as ugly and unprofessional looking.
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Old 18th October 2008, 10:38 PM   #6
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fwiw, the LM3875 was supposed to be obsoleted -- well this is the case for the LM3875T, but not the LM3875TF (the insulated version) which is in current production.

the case adds a bit more to the thermal impedance compared to a mica washer -- but it is very good to see that the chip will remain in production.
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Old 19th October 2008, 08:07 AM   #7
ratza is offline ratza  Romania
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Quote:
Originally posted by pacificblue
No law against using the chemicals, but laws about how to deal with them after use, which make the disposal more inconvenient than the actual use.
I thought that this may be a reason.

Quote:
Originally posted by pacificblue

On the other hand P2P or breadboard is widely considered as ugly and unprofessional looking.
P2P is quite dangerous if the parts are not stiff enough, but if it's made properly it can be a work of art. Breadbors really looks ugly, but it's functional and sometimes it spares time and work.

P.S. I never take into consideration the WAF, although I'm married. Either she likes it or not, I'm still building.
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Old 19th October 2008, 08:20 AM   #8
lineup is offline lineup  Sweden
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anybody knows how LM3875 performs in 4 Ohm
and
is there any difference between LM1875 and LM3875
how to handle 4 Ohm speakers

the dataheet for LM3875 looks very strange
in the curve Power out, Watt vs. Load impedance
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Old 19th October 2008, 10:15 AM   #9
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Quote:
Originally posted by lineup
anybody knows how LM3875 performs in 4 Ohm
Like any amp -> more output power, more distortion, more heat dissipation with the same power supply.

Quote:
Originally posted by lineup
is there any difference between LM1875 and LM3875
how to handle 4 Ohm speakers
The max supply voltage, output power and current are different, so the LM3875 goes louder. In other words LM3875 has more headroom on the same listening conditions.

Quote:
Originally posted by lineup
the dataheet for LM3875 looks very strange
in the curve Power out, Watt vs. Load impedance
It is drawn for Ī35 V supply. Lower supply voltage will shift the peak downward to the left. For 4 Ohm operation you should not choose transformers with more than 2x18..2x20 V.
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Old 19th October 2008, 11:41 AM   #10
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Quote:
Originally posted by ratza

P.S. I never take into consideration the WAF, although I'm married. Either she likes it or not, I'm still building.
You obviously haven't been married long enough, or haven't pushed the edge of the envelope of domestic tranquility.
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