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Old 20th June 2009, 08:00 PM   #1
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Default gainclones single chip vs parallel config

Hi there!

I'm planning to build a gainclone as soon as my university exams end but meanwhile I'm doing some research.. (noise filtering, psu design, best pcb design, etc).

Well, in fact, I'm thinking of designing my own PCB's, unless I find anything that fit my specs..
But let's get to the point..

a 90-100W per channel with LM3886..
It is perfectly doable with a single chip per channel!

But some folks (based on national ap. notes http://www.national.com/an/AN/AN-1192.pdf) use a parallel configuration with 2 IC's per channel in order to get this kind of power.
Just like we can see at http://www.shine7.com/audio/pa100.htm.
The difference is that "shine7" uses TF package..

So, I'm just wondering.. single chip vs two parallel chip's..

Well, from what I can see/understand at the moment, at least theorically, with the 2 chip config I guess each chip would be less "loaded" and will give better performance.. like a car: it runs better when carraying less weight.
(Is this right or am I sounding crazy? )

So, anyway, I would like to hear you people..

Thanks!!
RJ
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Old 20th June 2009, 08:21 PM   #2
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Default Re: gainclones single chip vs parallel config

Quote:
Originally posted by ruijorgemoreno

a 90-100W per channel with LM3886..
It is perfectly doable with a single chip per channel!

It is? Even parallel chips won't give you this power with 8ohm loads.
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Old 20th June 2009, 08:48 PM   #3
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I'm sorry I forgot to mention that my speakers are 6ohm each so my whole system will be designed according to this.

By the overture design guide, an LM3886 running on 36V would deliver about 87W into a 6ohm load and running at 38V about 98W. ( 'T' package, of course!)
That's just about what I need.. Anything between 90-100W would be great for my Technics speakers...

RJ
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Old 20th June 2009, 09:20 PM   #4
Minion is offline Minion  Canada
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Your calculations might be correct but the problem is that the Chip can not dissapate the needed heat at those power levels ....

for a 6 ohm load the max Voltage I would use would be +/- 32v , much higher and the thermal protection will kick in .....

A TDA7293 will put out close to 100w into 8 ohms with a +/-40v supply and are quite easy to paralell ...

http://www.datasheetcatalog.org/data...08fj3sqq3y.pdf

I actually like the sound of these chips more than the LM38XX chips but they sound better at lower voltages ...... I use one in a Guitar amp playing through a 4x12 and it is Extremely loud as in things start falling off shelves and pictures fall off walls ....


Cheers
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Old 20th June 2009, 09:49 PM   #5
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Quote:
I actually like the sound of these chips more than the LM38XX chips but they sound better at lower voltages ...... I use one in a Guitar amp playing through a 4x12 and it is Extremely loud as in things start falling off shelves and pictures fall off walls ....
Minion I don't want (at all!) to tell you are wrong in any way but.. I would not compare a guitar amp with a stereo amp..
Plus I don't think TDA's could be compared to LM's in sound quality.. I could be worng though...

See?! This is why I've been planning my amp for almost 3 months!!
I first began to think in TDA's.. Then a couple of experieced guys told me: "For the money? TDA! For quality? gainclone!! " ...
And here you come talking about TDA's again..
I just don't know what to think!


RJ
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Old 20th June 2009, 09:49 PM   #6
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Anyway, a fast reading at TDA7293's datasheet shows me it's not that bad...
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Old 20th June 2009, 09:57 PM   #7
Minion is offline Minion  Canada
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I only mentioned the TDA Chip because you wanted close to 100W ... I also have used them in Stereo amps and I like them ....

the do sound considerably different , the TDA Chip has a Mosfet output compared to the BJT of the LM series ... the LM sound very crisp and clear and has a tight soundstage but can sound a bit sterile the TDA to me sounds more musical with more defined Bass .....

just throwing out info , do with it as you will ....

Cheers
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Old 20th June 2009, 10:11 PM   #8
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And I appreciate that kind of info!! I truly do!
You see, everyone talks so much about gainclones but honestly I don't know anymore if it is the right stuff for me...

I'm beginning to think that it's a matter of taste. Maybe I could only decide after listening to both of them.. :s

RJ
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Old 20th June 2009, 10:56 PM   #9
kscharf is offline kscharf  United States
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The National spreadsheet gives a hint at what is possible, but maybe not what
is practical. Some combinations I've extracted...

60w @ +-25v / 4 ohms single chip
30w @ +-25v / 8 ohms single chip
60w @ +-30v / 6 ohms single chip
60w @ +-35v / 8 ohms single chip (actually more like 55w) The LM3886 is limited in power output at 8 ohms by the voltage rating.

120w @ +-35v /4 ohms two chips parallel
120w @ +-25v /8 ohms two chips bridged

240w @ +-25v / 4 ohms 4 chips parallel/bridged
240w @ +-35v / 8 ohms 4 chips parallel/bridged

360w @ +-30v / 6ohms 6 chips parallel/bridged
480w @ +-35v / 4ohms 8 chips parallel/bridged

The LM3886 can run the 4 ohm combos at +-28v with a bit more power (NOT TF packages)
if your heatsink is up to the task. A fan will help. The LM4780 or the LM3886TF should be
limited to +-25v at 4 ohms. The LM4780 is actually WORSE in thermal resistance with a non-insulated package than the LM3886TF with the insulated package. That's why National doesn't make the LM4780 in a 'TF' package. They also derated the LM4780 to +-25v at 4 ohms. The LM3886TF is marginal at +-28v / 4 ohms, the LM4780 is toast under those conditions.
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Old 21st June 2009, 12:11 AM   #10
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That was the answer I was waiting for!
thank you so much!
your answer is what I though I would hear in the first place..

So, even if possible, it's more pratical and reliable to have chips in parallel to achieve this kind of ratings, right?

And, having two 3886 in parallel, how much amps are needed from the power supply? How can you tell? I was told 2-3A each chip is enough...but I don't know...

And by the way, (example: 3886 @ 30V) the 3886 vs 3876. I noticed the difference between them (when in parallel) is not that much.. (about 16W) which one should we choose in this case?

I'm sorry for making so many questions, I really want this thing to be as good as I can make it... Plus, I'm very curious!

Thanks!
RJ.
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