Behringer B300 parallel LM3886's

[diydidi]

Hi All.
The Behringer B300 powered speakers use 3x parallel conected Lm3886's for the woofer, and 1x Lm3886 to drive the tweeter.
The outputs of the three driving the woofer are linked via 0,1Ohm resistors.
My question is this: Should those lm3886's be matched, or have the same batch numbers?
This would be a PITA as I have a couple half dozen of these, all with diff batch numbers.
I have replaced all of them in one unit. Haven't put a signal through it yet, but there is little/no offset voltage present- a good sign thusfar.

[J M Fahey]

For me, the whole idea is flawed, but yes, they *should* work.
Measure output to output pin offset, straight by the chip, and point to having the least.
5mV across .1 ohms means 50mA error and should be the maximum acceptable; 1º or 2 mV even better.
More than that, pull the stray chip and try another.
Remember waiting at least 15 minutes after soldering or you *will* have guaranteed offset, as in any junction.

EDIT: just checked. Funny they claim "300W" which is impossible with that chip configuration.
Optimum would be one of them driving 40/50W into an 8 ohm horn and the other 3 , say, 130W into 2 ohms .
They would definitely not stand a 1 ohm load.

[Jazz P Bass]

Not to defend good old Behr, but the cabinet is rated at 300 watts (Peak).
Woofer amp: 230W
Tweeter amp: 70W
I do not understand the 'adding the amplifiers together' power rating.
(or the Peak rating)

[Steve Conner]

The power rating is calculated as follows:

Think of the biggest number you can get away with
Double it

[MarkusBass]

Here: http://www.ti.com/lit/an/snaa021a/snaa021a.pdf you can find information about using LM3886 in parallel. The ICs should be matched, or there should be a servo circuit used (see pdf for details).

Mark

[diydidi]

The notes mention that the gain setting resistors should be equal 1% res, but nothing about the IC's being matched......

[tedmich]

no need to match ICs as you can trim the DC offsets or use a servo as stated

pot is for DC offset adjustment in Jeff Rowland's 6 x2 parallel LM3886's sold for $15k !


http://www.shine7.com/audio/jeff.htm

[J M Fahey]

Well, the guy is a genius.
If he can extract $15k from customer's wallets, I congratulate him.
I bet it's a KILLER amp, unlike a lot of the audiophool sh*t.
I notice 2 things:
1) he uses a multi turn precision trimmer for each
2) his series resistor is 0.5 ohms, not 0.1 .
both points show me he's not a fool at all

[tedmich]

Beautiful CNC massive metal is also what costs!



He made one version that used a Jensen input transformer ($$) and he also developed a whole series of HUGE SLA DC power supplies for his amps, before moving to sophisticated SMPS designs.

[diydidi]

VERY NICE!!!!!!!

[J M Fahey]

Incredible !!
Are they carved out of a solid block of aluminum?
WOW!!!!