Motional feedback amplifier based on Philips 40 wats amplifier 1970s

[sanbadgujar]

Hi all
I fond Motional feedback amplifier when i browsing it make some changes in original Philips 40 wats amplifier lat 1970s

 

[troystg]

Are you going to build it and if so what driver / box is it designed for?

 

[sanbadgujar]

Hi am build the old version a philips 40 WATS 1970s but this one is better because very low distortion original is also very good i used 10" woofer 1" tweeter shield enclosure

 

[troystg]

So you used it full range? Why not bi-amp and use only on the low section? Is there any benefit to the tweeter / HF section?

 

[sanbadgujar]

HI i prifard to use tweeter & woofer because this amplifier don't need passive filter with tweeter hi frequency response is very good can you give me some suggestion about this amlifier

 

[troystg]

I don't know what you mean by suggestions, but to me a motional feedback amplifier would be used in the LF section of a bi-amped speaker.

I use a negative feedback electronic suspension system designed by Mr. Erath.

 

[dw1narso]

HI i prifard to use tweeter & woofer because this amplifier don't need passive filter with tweeter hi frequency response is very good can you give me some suggestion about this amlifier

I know that this is old thread...

but could you elaborate why/how this amplifier don't need passive filter with tweeter hi frequency? is it because you have two seperate amp for low and hi part? (bi-amping with active x-over or passive network in front of the amp?)

 

[Zero D]

Originally Posted by dw1narso

but could you elaborate why/how this amplifier don't need passive filter with tweeter hi frequency

Maybe he's using a piezo HF ?

 

[dw1narso]

piezo HF? hm... don't really like it except for filling the air with really high frequency spectrum...

or I suspect that he use another capacitor coupled tweeter in parallel with the woofer? Which is actually doing 1st order filtering...

 

[geraldfryjr]

This basically a schematic of a simple (typical) Class AB amplifier design that uses current feedback instead of voltage feedback via the .47ohm resistor in series with the output load to ground and the 470ohm resistor going back to the input transistor.

It appears that the motional feedback section had not been implemented yet.

FWIW

jer 🙂

 

[chicks]

That's not the Philips MF design, just someone's imitation using a current-sensing resistor vs Philips MF sensor...

Motional Feed Back Amplifier Electronic Circuit

 

[troystg]

I didn't see an author of that article, do you know who wrote it?

 

[sanbadgujar]

Hi

My Motional Feed Back Amplifier making sound like MOTORBIKE like THA.... tha... please help me

 

[Ian Finch]

"Motorboating" is caused by spurious feedback from ouput to input. Clean up your layout and connection wiring, assuming the circuit is otherwise correct.

 

[forr]

It's an amp providing a negative output impedance through positive feedback by bootstrapping the input node between the two 150 kOhm resistors.
The idea is very ancient, see Werner and Carell, JAES October 1958, for example, Thiele also details it in his BR papers.