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Chip Amps Amplifiers based on integrated circuits

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Old 29th December 2012, 09:07 PM   #11
bcmbob is offline bcmbob  United States
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Here is the link I mentioned containing a balancing process. You might want to brows the entire thread to get a bigger picture.
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Old 29th December 2012, 11:57 PM   #12
JMFahey is offline JMFahey  Argentina
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It's bad Engineering to wire in parallel multiple *voltage* sources.
Even worse if gain and offset depend on yet more external parts, which have their own tolerance spread.
And , by the moment you need to accomodate **33** pins for the active parts, plus all the passives, you might very well build discrete.
All that complexity and troublesome matching for meager 150W/2.6 ohms?
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Old 30th December 2012, 12:24 AM   #13
bcmbob is offline bcmbob  United States
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JM, Do you have a link to a schematic or build thread supporting what you suggest, or are you saying to not use this type of chip (LMXXX/TDAXXX) at all and just move to a Pass type amp?
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Old 30th December 2012, 02:20 PM   #14
JMFahey is offline JMFahey  Argentina
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Dear bcmbob, you ask 2 questions in one, I'll answer both separate.

1) Don't get me wrong, I *love* chip amps, an old dream come true
Impressive sound and specs, simple and cheap, what's not to like about them?
But, of course, they have their ratings (like everything else).
So far, they easily provide *up to* 100W ; more realistically 50 to 70W. Perfect.
Someday they'll make larger ones.
But trying to go beyond that, you must resort to combining them, if possible.
And then they lose their charm, plus creating new problems.

a) parallelling voltage sources is bad Engineering.

Not specific to chip amps, applies to discrete amps too, regulated PSUs, etc.

Being a voltage source and low internal impedance to boot, any slightly higher voltage one will pump lost of amperes into another parallel one (instead of into the load) , trying to make it reach it's own designed voltage, usually both dying at the same time, or at least overheating and working with lots of waste.
Because the other amp will have its own ideas as to what the output voltage should be.
Paralleling 3 certainly won't minimize this, quite the contrary.

b) to prevent (or really, reduce) this, you must obsessively trim and match gain setting resistors, select parts within 1mV offset, etc.
Even so, you *must* add 0.2 ohms in series with each one (negating its high damping and tight control of output voltage) to reduce output-to-output wasted current.
And any part value error, perfectly acceptable anywhere else and well within tolerance, can spell disaster.

c) and even so, the "power increase" is nothing to write home about.
You still have your rail voltage limits, after all.
Stating "150W" on the label sounds good ... learning you'll need nonstandard 2.6 ohm speakers to achieve them is a cold shower.

d) I *do* agree with multiplying power by bridging (one chipamp per side, please )
There you double your effective rail voltage but much more important: you have voltage sources on opposite sides of the load.
In fact, if gain setting resistors on any (or both) of them vary by, say, 10%, nothing bad happens (they certainly do not go up in flames); worst case is that they do not clip at exactly the same time, and you may lose 10% peak voltage. Which anyway you just doubled
Nothing compared to what would happen to parallel amps, same parts tolerance.

2) Complexity.
Chip amps are beautifully simple . Did I mention they sound good?
But if you parallel 3 of them, each of which still needs its own external components as before , you, ... er ... triple the complexity
Plus adding 3 previously unneeded wirewound resistors, needing specially matched parts, being very careful with layout (nobody mentioned this before, but it's a point to be considered), etc.
They quickly lose their charm.

As of simple discrete examples? Tons of them.
Just to mention one, the popular Rodd Elliott P3 amp, if built with robust transistors and higher rail voltage, can easily provide 150W RMS into more useful 8 or 4 ohms loads, standard speaker impedance values, without requiring a 2.6 ohms load.

I have been building Musical Instrument Amplifiers since 1969, over 10000 (yes, ten thousand, not a typo) . Always a dyed in the wool minimalist
Have been using MosFets for 10 or 15 years now, here you have my popular Fahey B300 amplifier, +/- 70V rails, 4xIRFP250 (yes, I still use quasi complementary), 300W RMS/4 ohms.
Built and measured, not simulated.
This is a frame from a You Tube video, by an Argentine Heavy Metal band, who plays with them in Football (soccer in USA ) Stadiums and such.
They're using 3 x B300 into 3 x Ampeg 8x10" "fridges".
Yes, they sold their Ampeg SVT Classic tube heads to buy mine.
Here's the video it came from:
Almafuerte - Almafuerte (en vivo) - YouTube

*If* needed, I can draw and post the (very simple) schematic.
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Old 30th December 2012, 03:28 PM   #15
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Iirc, AlexM had a design up here maybe last year that was 3 chips, he was providing boards too... maybe you want to do a search and see what other people have already done. I think that was his name here, definitely Alex<something>...

Look into it via search...
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Old 30th December 2012, 04:43 PM   #16
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I had a thought after reading this thread. I have fancied paralleling chip amps and I realise that it's nowhere near as straightforward as simply building two circuits on one board and paralleling them.

Could one chip be a slave to the other chip? That way there'd be no "fighting" between the chips. Small tolerance differences wouldn't cause major problems with such a configuration.
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Old 30th December 2012, 05:29 PM   #17
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do a search Fast Eddie D... it's been done.

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Old 30th December 2012, 05:34 PM   #18
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Quote:
Originally Posted by Fast Eddie D View Post
I had a thought after reading this thread. I have fancied paralleling chip amps and I realise that it's nowhere near as straightforward as simply building two circuits on one board and paralleling them.

Could one chip be a slave to the other chip? That way there'd be no "fighting" between the chips. Small tolerance differences wouldn't cause major problems with such a configuration.
If you use two chips you could bridge them.
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Old 30th December 2012, 07:38 PM   #19
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Quote:
Originally Posted by nigelwright7557 View Post
If you use two chips you could bridge them.

Of course, but this thread is about more current, not more voltage.
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Old 30th December 2012, 07:52 PM   #20
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Quote:
Originally Posted by bear View Post
do a search Fast Eddie D... it's been done.

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I did a search and found discussions but no example circuit. I think I could figure it out on my own, though.

How about this- 2 x 3 or 2 x 4 3886 parallel/ bridged? If you used a slave circuit, you could skip the lossy output resistors. I can think of a few advantages to a circuit like this, like full bridged voltage swing into 4 ohms with 2 x 4 parallel/ bridged. There are some other advantages too.
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