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Old 19th November 2006, 10:28 PM   #1
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Default Please check my chipamp with 2 x LT1210

Hello

after a long abstinence from the web and electronics (but while gardening a lot), I feel as if I have forgotten everything concerning electronics...
Anyhow, before I spent too much time reading and thinking, now I want more practice!
I have four LT1210, and from the datasheet it looks ok for a (low power) chipamp.
To feed 4ohms, it looks like I'd better parallel two of them.
As from the datasheet (and my spice simulation) it looks that a gain of 2 would be a good choice, so I'll put an op-amp in front.

It won't be very strong, but 16W at 4ohms should still sound ok.
Spice gives me the least distortion for the global feedback version. Maybe in practice distortion numbers may look different, but I tend to realize the version below.

About the op-amp in front, I'm not sure yet, but it's by far less important than the main amp anyway. Maybe I'll use an OP227 or an OP132, or even an AD8620 (ok, in this case I'll be aware of the supply voltage, it has to be less than +-15V).

I'll probably replace R5 with a pot for volume adjustment.
I think that R2 should be in the range of 1k to 10k, I think that 1k should give me less dc offset, but I'm not really sure, as the LT1210 is a current FB op-amp and if I remember well the offset isn't really calculable here.

Any objections?

Thanks for your interest,
Dominique

EDIT: oops, I've forgotten to put resistors in the signal paths just in front of both LT1210! How big should I make them, maybe 1k?
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Old 19th November 2006, 11:54 PM   #2
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... you might relabel your power supply voltages on the diagram ... all labeled +15 VDC (yes, I see the battery symbols are there, correctly, but I'm old school). ( http://www.linear.com/pc/downloadDoc...46,P1329,D2461 ) I know you are thinking the right way, but us old timers look at the drawings first, and the comments after.

" ... About the op-amp in front, .... but it's by far less important than the main amp anyway. ..."

Well, I would say just the opposite: The input stage (op-amp) is very important to the over all quality and results. This is the point where most noise can creap in, where wiring practices and impedence matching are most important ... Pick the best quality input stage possible and the rest of the parts will natually work better, sound better. (This is why so much attention is paid to pre-amps. No matter what the power output may be, it would not matter much if that power is simply amplifying a noisy signal. Garbage in = amplified garbage out.)

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Old 4th July 2007, 02:54 PM   #3
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http://yooree.narod.ru/homehoney.html
look this
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Old 6th July 2007, 07:06 AM   #4
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Is it sounding good?
I have some LT1210s and want to make a small amp with them.
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Old 6th July 2007, 07:17 AM   #5
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in the opinion of author it best sounding from the chip-amps.

But it low power (only 15W, L=4, Vcc=+/-15v)
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Old 6th July 2007, 07:55 AM   #6
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LT1210+MC33079 audio amplifier diagram are in archive
I recommend to repeat without change.
attention! check the power supply of chips !
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Old 6th July 2007, 08:05 AM   #7
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Its a current feedback op-amp. So that means;
- We should use lower value resistors in NFB line (like yours 680R)
- We cannot use high gain designs.
- If so, we must add a high gain preamp before it. (like your design)
All these true?
Thx
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Old 6th July 2007, 08:18 AM   #8
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you absolutely rights!

repeat, recommend to do on offered amplifier, without any change (particularly MC33079)


"Waft-HomeHaney" was made by many people, all of them are very complacent

Look yooree's site, it is author
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Old 6th July 2007, 08:20 AM   #9
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Ok guy.
Thanks a lot. I will try it (may be I cannot find that op-amp 33079) in Turkey. But I will find a equivalent one.
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Old 6th July 2007, 08:28 AM   #10
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MC33079 (ON semicon only! Not SGS-Thompson!!!) is unique for it design.
But if you not find it - recommend OPA404 (TI) , TLE2144, TLE2074 (TI) - it is free sample on www.ti.com
and LT1356 (is free sample on www.linear.com)
I has got samples from all it supplyer.
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