Philips 40/25/15 watts amplifier with Universal preamplifier circuit.

[Kay Pirinha]

There seems to be another issue of high value coupling capacitor with the speaker. There is a fear that this will lead to losses in low frequency .While this is true, it will be seen that the bass gain of Universal preamp is 20 db which is quite high and compensates for this loss .This is why the system did not seem to loose on bass.

This »Universal preamplifier« is the one shown in #14, isn't it? It may have some boost if the bass tone control is set to it's maximum, but in it's linear mode it doesn't. Otherwise it couldn't be called a »universal« preamp, btw.
The LF roll off of a 2.5 mF output capacitor at a 4 ohms load is about 16 Hz, hence this capacitor value may be sufficient. But it mustn't fall below that value even in smaller amplifiers for the reason that it isn't a matter of output power rather than LF roll off and load impedance.
Best regards!

 

[chaks]

Although the increase of output cap value increases the Bass response but it must be borne in mind that Caps also create frequency and phase distortions. Hence min use of Caps have been made in the circuits. A full treatise on this aspect is on P57 of the book.
Secondly, this amp has been designed keeping the Universal Preamp in view (440v/K ohm)and so also specified crossovers along with drivers for HiFi purposes .The output Cap in tandem with crossovers and drivers will have an effect on the overall performance although for audio purposes it may be marginal if the two are well matched.
Thirdly, even with a very large cap the Bass reproduction may not be very satisfactory .So, in case of sealed enclosures, to get a large Bass we used to place the enclosure in the corner of rooms which increased the Bass gain theoretically by 8 times otherwise practically it was around 2 to 4 times. Of course treble loses by that much .This is discussed on P 180 of the book.
Fourthly, the Bass response will also depend on Resonance frequency of the speaker and enclosure that is used. P 189 of the book refers.
Chaks

 

[chaks]

This »Universal preamplifier« is the one shown in #14, isn't it? It may have some boost if the bass tone control is set to it's maximum, but in it's linear mode it doesn't. Otherwise it couldn't be called a »universal« preamp, btw.
The LF roll off of a 2.5 mF output capacitor at a 4 ohms load is about 16 Hz, hence this capacitor value may be sufficient. But it mustn't fall below that value even in smaller amplifiers for the reason that it isn't a matter of output power rather than LF roll off and load impedance.
Best regards!

#14 does not show the Universal Preamp (UPA) ,rather it shows noise contours of BC 159 .For a detailed discussion on the Bass and Treble controls of UPA, you may please ref to pages 36 and 37 of the book.
As far as Bass Roll off at 16 Hz is concerned well I have not measured it .It seems to be quite adequate for the 2.2mF Cap.


Chaks

 

[chaks]

I just realized that you were ref to # 14 of this forum and not P 14 of the book.To that extent I stand corrected.

Chaks

 

[Mooly]

And

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[RMSharma]

my dear DIY brothers

this is regarding a circuit developed by Philips in 1970's. it is a 40/25/15 watts amplifier with Universal preamplifier circuit. it was very popular in DIY groups at that time. it use to give a very good quality of sound, eventhough it was a AC coupled amplifier. originally the output transistors are BD182. but most of the people used with 2n3055.

do anybody have the circuit diagram. i got some printed circuit boards without circuit diagram.

regards
renjish

Yes I have it. It is a super quality 40 watts rms push pull amplifier worth. Do contact for details on email rmilansharma@gmail.com. Vishal electronic Bombay sells these pcb even today

 

[chinoy]

40 watt philips amp

1. this amp really sounds great , i made this circuit in year 2005, and use the power 60v,10,ampere current,but i used 2n3773,but the problem i faced was at the near end of the volume , a hiss sound starts and the transistors becomes hot I do not know why.
2. I also have that books some photo copies printed by bombay.
3.I have made many amps,like stks,tip142/147,and many more but the quality i really felt is in philips 40w circuit,
4.this circuit is very famous in india and i think every hobbiest made this amp,
5. I even repaired 6-7 amp,but i really seen and observed that all those amps were made in 0-36v supply,not by 0-60 to draw actual power,
6.I used every care to maintain the actuality of the circuit,so i used 1% rated resistors and good quality components .
NOTE : IF anybody have the solution of that problem than help me or you have any other good circuit which sound like this 40w phillips,than please tell me ,
my email id : usualfellow@yahoo.co.in

Sir
I am looking for this schematic if you can help. I believe the Woodstock SA4000 used the same circuit.
If you could share or email it to rdchinoy@gmail.com
I am in the same boat i.e. I want to replace the 2n3055 with a 2n3773 but I know i will need to change the 2 watt 4 ohm resistor to at least 5 watt 10 ohms.