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Old 13th May 2009, 02:32 PM   #1
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Default Markaudio CHR-70: Amplifier options?

Hi guys,

I`ve been lurking a while, and I now need your help - please!

I`m looking for a bit of advice regarding amps for use with the Markaudio CHR-70. I`m building a set of speakers using this driver, but have become quite lost trying to match it to an appropriate amplifier. The low impedance (4 ohms) and sensitivity (85db) seem to be the main obstacle to finding a good amp....

I had previously settled on the LM1875, but I am worried it won`t supply enough power (only 20w/channel), given the low sensitivity of the CHR-70. I had then moved to consider the LM3886, but some comments made by AndrewT in another thread seemed to suggest it is more appropriate for 8 ohm loads, where the CHR-70 is 4 ohms. He also suggested that chipamps generally are not suited to low impedance loads due to their current handling.

Any advice on options to power this driver would be greatly appreciated. At this point I am becoming a little frustrated in the search, and am open to any suggestions.

Thanks in advance!

-- Mike.
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Old 13th May 2009, 04:27 PM   #2
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The LM3886 should be fine. It can be optimized for ~50 watts into an 8 ohm load, or 68 watts into a 4 ohm load. It has more current capabilities than the LM1875 or LM3875, though most folks think the LM1875 or 3875 sound better (depending on which camp they're in).

Regardless, I don't think you can go wrong with any of them. The LM1875 can do 25 watts into 4 ohms, and that will probably push the CHR-70 well beyond where it still sounds good

I'm planning on juicing my CHR-70's with an old BrianGT/Peter Daniels LM3875 amp myself.

Good luck!
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Old 14th May 2009, 12:47 AM   #3
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Default Thanks!

Thanks motherone, that`s exactly what I was looking for

Considering the room these speakers will be going in (8` x 12`), and the fact that I only intend to listen at lower volumes anyway, I see the output of the LM1875 will be suitable. The relative simplicity of the design also appeals to me.

As mentioned, I had initially settled on the 1875, so thanks for confirming my suspicions. It is easy when in the design stage, to get carrried away with specs and datasheets, and lose sight of the real-world application of the design.

One of the goals with this project is to keep things simple (or at least try to!), so I`ll save the 3886 for something to rattle the bones later

Good luck with your CHR-70 build. I`m sure they`ll sound great!
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Old 14th May 2009, 02:57 AM   #4
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One thing to keep in mind is whether you are going to PTP the design, or get a PCB. There are far more PCBs available for the LM3875/3886.

The component count for all three chips should be similar -- I think the only difference between them will be the addition of a muting resistor on the LM3886.

Good luck with whatever route you choose! I've built all 3 and I'm satisfied with all of 'em
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Old 17th January 2010, 07:30 AM   #5
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Sorry to bump an old thread but I'm about to build a gainclone / mark audio chr70 combo but I can't decide between the lm3875, lm1875 or lm3886 - anyone care to offer an opinion - in all cases I'd be using the kits available on audiosector.com & chipamp.com
cheers
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Old 11th March 2011, 05:56 PM   #6
jemraid is offline jemraid  United Kingdom
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Dear Rob,

I have the same dilemma, I have an LM3875 gainclone with real cheapo components, I made it about 6 years ago and it sounded great with my Needles and FRS8's.

Last week I went to Colin's [toppsy] house to listen to his Frugel Horn Mk3's, I thought the pair with the CHP-70's were the best, to my ears that is [of course :-] My GC was not up to Colin's 300B valve amps but not that far off it.

However, like the CHR-70's they are 4 Ohm and I asked about GC's and 4 Ohms in another place and got the answer that chipamps are no good at all with 4 Ohm speakers!

Despite that I am going to go ahead with the LM1875 build after reading the advice in this thread.

I would also note that Dave [Planet 10] also prefers the LM1875 over the LM3875 and the LM3886.

Warmest wishes - Jim
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Last edited by jemraid; 11th March 2011 at 06:21 PM.
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Old 11th March 2011, 06:02 PM   #7
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When making a gain clone, one can optimize for the impedance. Lower rails for low impedance (25 VDC for the 3875 (i think the same for the 1875) up to the limit (or even slightly over) for 16 ohms

dave
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Old 11th March 2011, 06:20 PM   #8
jemraid is offline jemraid  United Kingdom
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Thanks Dave, really nice of you to contrbute to this little thread :-)

When I've made my FH Mk3's I will make an LM1875 GC and report back to this thread.

It may take some time though, I've got to make a cold frame for Eileen first.

Warm wishes - Jim
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Old 15th March 2011, 02:09 PM   #9
jemraid is offline jemraid  United Kingdom
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Hi all,

Just been reading this about TDA2050 "Thanks to its high power capability the TDA2050 is able to provide up to 35W true rms power into 4 ohm load"

The PDF goes on to say that 100w instantaneous has been verified.
http://www.st.com/stonline/books/pdf/docs/1461.pdf

Hmmmmmm interesting!! :-)

Jim
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Old 31st May 2011, 10:45 AM   #10
jemraid is offline jemraid  United Kingdom
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Hi all,

TDA2050 vs LM1875 resolved by Ashok in this thread;
Another TDA2050 amp built and tested..............

I have ordered the parts to make the LM1875 version and will post some pics here when I have.

Jim
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