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Old 25th October 2011, 03:32 PM   #1
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Default High Power Amplifier with LM391-100

Any practical Hi Power low distortion amplifier circuit with IRFP240 & IRFP9240 MOSFET.
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Old 25th October 2011, 05:17 PM   #2
farjon is offline farjon  Brazil
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Lm391 N100

I know only this, with BJTs:

Power Amplifier 35W with LM391

It appears to be obsolete:

LM391 - Audio Power Driver [Discontinued]
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Old 28th December 2011, 05:38 AM   #3
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Default LM391N-100

Merry christmas
Hi i am nick from Greece and i am new to forum
I have an amp 2x 100w at 8Ω with LM391N-100....bd 139-bd140 as driver and the output transistor is MJ15003 and MJ15004 by Harries ..2 transformer 2x33voltAC secondary eatch ...2x10.000 mf 63 volt sic safco capacitor for eatch amp
And the sound Exelend very easy and Detail
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Old 28th December 2011, 06:41 AM   #4
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Wow! 100W/8R with BD139/40 drivers and 46V rails?
There must be some big transformers and special drivers there.
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Old 28th December 2011, 07:16 AM   #5
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Default LM391N-100

LM391 - Audio Power Driver [Discontinued]

buy from ebay or........ from BG electronics hear BG-Electronics LM391N-100, LM391N-80, LM391N80, LM391N100
The input impedance to my amp is 10k -gain and bandwidth is selectable for this IC
Give very good source and preamp (descrete) whith low output resistance ......and
This amp drive my loudspeaker JMLAB FOCAL PS5.1 Point Source at 4Ω
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Old 28th December 2011, 07:32 AM   #6
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Hi Ian
The transformer is 300va eatch and 4 bridges semicron 25A ..2 per amp
this amp drive my loudspeake JMLAB Focal PS5.1 point source at 4Ω
I bought some lm391n-100 from BG Electronics about a year ago
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Old 31st December 2011, 07:12 AM   #7
djk is offline djk
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With no thermal tracking on the bias, amplifiers using the LM391 frequently blew up, even the designs with class B output stages.

I keep a few LM391 around to repair the old PA amplifiers used in 70V systems that used this chip.

I would never use it in a new design.
Candidates for the Darwin Award should not read this author.
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Old 31st December 2011, 11:40 AM   #8
jaycee is offline jaycee  United Kingdom
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I was thinking that myself - where's the thermal tracking? With a CFP output stage as shown by Sam and in the datasheets it might be acceptable. I guess you could also wire up some external sensing diodes between pins 7 and 6.

The equivalent schematic shows that it's nothing special - a pretty standard current-sourced LTP, with current mirror loading, and a cascode VAS. You'd get better results with discrete parts.
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Old 1st January 2012, 06:22 PM   #9
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The amplifier is my possession since 1988 with excellent results
is about the same with (lm391pdf ) at page 11- and no sam circuit
The resistors Reb-Reb' -R1-R'1and Rf1 -Rf2-Cf want calculation acording the pdf
The voltage rail +/- is important for calculation to ( Reb-Reb' and to R1-R1')
Entry capacitor are 10mf mkp direct the pin 2
and input impedance is 10 Kohm- bias current is about 30- 40ma
at the pin 14 I think I have a capacitor 10mf
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Old 2nd January 2012, 08:11 AM   #10
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i presume that the amplifier is red and blue pcb and made by a company called ""hobby kits"" electronics .... Actually a very good Greek kit company that executed properly suggestions and schematics from National and/or other companies .

the good thing is that this company actually used the best available parts at the time ( nothing exotic ) just very good quality ....

Company is long time ago gone since prizes was 3 times up from any other available kit at the market , at the time .

As about the amp it shelf was a terrible amplifier ( with today's standards ) with probably terrible performance figures ....expect your amplifier to have mos of the capacitors dead as we speak..

things that went wrong with this amplifier is basically that the performance was based on the performance of the IC ...the bandwidth and speed was limited and for the people that didn't know enough the biggest mistake was the wiring between the board and the output transistors the use of flat cable that was included inside the kit ( that actually originated from PSU technology ) was the number one reason for oscillations and instability ...

other than the above it was just bellow average

kind regards sakis
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