High Power Amplifier with LM391-100

[katiyar]

Any practical Hi Power low distortion amplifier circuit with IRFP240 & IRFP9240 MOSFET.

 

[farjon]

http://www.diyaudio.com/forums/solid-state/143043-lm391-n100.html

I know only this, with BJTs:

Power Amplifier 35W with LM391

It appears to be obsolete:

LM391 - Audio Power Driver [Discontinued]

 

[nicksonFM]

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
Regards

 

[Ian Finch]

Wow! 100W/8R with BD139/40 drivers and 46V rails?
There must be some big transformers and special drivers there.

 

[nicksonFM]

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
Important
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

 

[nicksonFM]

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

 

[djk]

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.

 

[jaycee]

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.

 

[nicksonFM]

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

 

[east electronics]

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

 

[consort_ee_um]

I agree with the thermal tracking issue. One way around this would be to use STD03N & P transistors. In a domestic environment I guess the amplifier is not too thermally stressed which is why it works for NicksonFM. The IRF's would have thermal tracking issues, I suspect, if you used high power.

My blog
Consort3′s Blog

 

[east electronics]

here is a set of pictures of one amplifier wired with similar cable and topology (IE flat thick parallel cable from board to output transistors ) most of the problems was solved after replacing the cables to few course non parallel ones and of course shorter distance ..

What actually makes the difference is the non parallel distance is also important but not that much .

enjoy a mess

 

[east electronics]

and picture of the amp UT

 

[nicksonFM]

SAKI BRAVO
The amplifier was from hobby electronics
does not have many capacitors electrolitics
i change all electrolitics
decouplin for +/- rails - 100mf over the board
The capacitor input are 10mf arkotriniks MKP
and the big supply capacitors 4x10000mf 2 for each amplifier is SIC SAFCO 63volt
I changed the resistors with metal film
I love the sound of
reason more tight bass I had but never mind.....
Very natural and that says it all
If he has something for this amp....i am here...thank you for this post
(I agree with the thermal tracking issue. One way around this would be to use STD03N & P transistors. In a domestic environment I guess the amplifier is not too thermally stressed which is why it works for NicksonFM. The IRF's would have thermal tracking issues, I suspect, if you used high power.)
Do you have any shematics for this Mr consort -ee-um
in the past I had some problems with it and LM391N-100 were burning
Thank you all

 

[consort_ee_um]

I had forgotten how tricky the STD03 were to set up. However this thread:
http://www.diyaudio.com/forums/chip-amps/143263-lme49811-sanken-std03n-p.html
shows the output circuit you could use and you substitute the LM391 for the LME49811.
The problem with the setup is to get 2.5mA in the diode chain while at the same time having say 40mA bias in the darlingtons.
A possible easy way to set the bias is to use a fixed 56 ohm in the diode chain and then adjust R12 for 40mA bias.

 

[AVWERK]

The Amber 70 used this chip also. It was a frequent blower of fuses but sounded decent for the era and price point of the time.

Regards
David

 

[east electronics]

there is no point working with an obsolete IC

 

[kimon]

I think that most opinions expressed in this thread are right.I built this amp in1986 and I faced current drifting and overheating problems(and had several blown transistors and ICs).The amplifier,once set, is good for domestic use,with sweet decent sound,no hum or hiss,but nowadays I would build something modern.

 

[wahab]

This circuit has a VBE multiplier that is used to set the power devices
quiescent current , as can be seen on NS application note.

The only problem is that to have a thermal tracking the LM391 should
be in thermal contact with the main heatsink but NS rate it at 70°C
maximum operating temperature , wich is not compatible with the max
temps that can be reached with power transistors.

 

[consort_ee_um]

Hi Wahab, the point of my suggestion was to move the thermal sense point from the IC to the transistors so you would not use the on chip Vbe multiplier. The string of diodes on the transistors would do the thermal compensation.