Amplifier Bass

[aguantesoda]

hello, I am Guido, I live in Argentina, and I was looking for an aid with my amplifier. them story the problem:

I was arming this simple amplifier, and the truth that works enough good, but the power does not reach to me. I have a band and I touch the bass, but count with little money like buying an amplifier. Pre amplifying already arms it and works well. Then I would to know if you can help me to elevate the amplification, with making little changes to him, since the armed equipment this and working. My idea is to leave tip him 142 and 147 that it has when coming out, but to change the feeding, and to take it +45 0 -45V. I would to knowledge you thinks, and what changes I would to make so that this works correctly.

Jeje my inglish is too bad! I translate the document to spanish, if somebody don´t understand me!!

Thanks for that can help me! below is the circuit!


hola, me llamo guido, y estaba buscando una ayuda con mi amplificador. les cuento el problema:

Estuve armando el amplificador mas sencillo que encontre, y la verdad que funciona bastante bien, pero la potencia no me alcanza. Tengo una banda de musica y yo toco el bajo, pero cuento con poco dinero como para comprarme un amplificador. El pre amplificador ya lo arme y funciona bien. Entonces queria saber si me pueden ayudar a elevarle la potencia a la amplificacion, sin realizarle muchos cambios, ya que el equipo esta armado y funcionando. Mi idea es dejarle los tip 142 y 147 que tiene a la salida, pero cambiar la alimentacion, y llevarla a +-45V. queria saber que opinan, y que cambios deberia realizar para que esto funcione correctamente.

Gracias para quien pueda ayudarme! aca va el circuito.


R11 = 330 ohms
R12, R13 = 0.47 ohms
Power Supply= +25 0 -25

[clem_o]

'Ola Guido,

I understand you are hoping to get more power from your amplifier, by bringing up the supply voltages.

Firsthand look at the circuit - I think it's not safe to bring up the power, those are very small transistors in the input and voltage amplifier stage - replacing them will not necessarily work, since bringing up the supply voltages that much will increase the currents into the stages significantly. The bias to the output transistors will probably run wild as well.


Cheers

ps: and that's about as far as my Spanish can get me... :-) Good luck with your band - and bass guitar playing...

[richie00boy]

As he said it's not that simple. Also, if your speaker is 4 ohms, raising the supply to 45 volts will blow the amp up when it is used loud.

[destroyer X]

But those transistors will not hold that voltage increase.

You will have to replace the differential transistors for others that can hold the increased voltage.....2N5401 or something alike will be needed there.

Also the voltage amplifier transistor will need replacement...try a 2sc2238 with a heatsink.

The current, that is supplying this voltage amplifier may need some increase too..but you can try without it.

The output transistor will need more two or three pairs in parallell, each one with its own emitter resistor...and your heatsink will need to be three times bigger.

The VBE multiplier transistor...the bias adjustiment transistor will hold the small voltage there...but if something burns...it will burn too, because the voltage over it will be more than it can hold...maybe a replacement for a bigger voltage unit will be better

All your electrolitic condenser will be needed to be replaced for high voltage units.

The input capacitor need to be increase as you want more bass

Also C2 and C4 will be good if increased.

This will produce enormous power....i do not know if your 45 plus 45 supply will feed the little monster....maybe some adjustment will be needed in th R9 abd R6...they will need to be reduced...both of them...around 30 percent...to increase the current to the voltage amplifier transistor.

Too much modifications to have a better amplifier.

regards,

Carlos

[destroyer X]

You will need big electrolitic condensers...at least 15000uf each one.

In the schematic the transistor number was corrected..the one that is NPN is the 2N5551

R6 os 470 ohms...and the new series resistor included is 1K

The bootstrapp condenser must be a 100 volts unit....220uF that can hold 100 volts...or.... 100uf that can hold 100 volts.

The heatsink size may force you to give up..also the transformer size... a good power will be reached in 4 ohms....i am not sure, but maybe more than 200 watts.

Yes...the last transistor base is conected with the others...i forgot to put that line..connecting the last ones bases.

Here is the idea.

regards,

Carlos

[aguantesoda]

Hi! thanks for the idea,

If the speaker have a resistence of 8 ohms, they work well too, or I have to made any change to the circuit?

In the supply, the current is more than 3 amperios?,

The capacitors of the supply, if I put here two caps of 4700 uf x 100V, they will work well?

[Leolabs]

Wondering what is C2 doing out there?

[clem_o]

Originally posted by Leolabs
Wondering what is C2 doing out there?

Seems that they wish to couple the signal directly through the differential transistors. 470 ohms/2 is way too much emitter degeneration. Maybe the other thing is so that if the variable resistor gets 'scratchy' the otuput voltage won't be jumpy when it is being adjusted... ??

Cheers!

[Tony]

or said another way, the designer did not like to decrease the differential stage gain at ac anyway.