Power amplifier 130w

[aguantesoda]

Hello, I found this power amplifier in a book; and I want to know a little about it, before make it.

What is R7 - R8 - C8 doing?

What is R13 - R11 - C7 doing?

PD: I write in spanish too, because I dont speak very well in english. Thanks!

In Spanish:

Hola, encontré este amplificador en una revista, y voy a armarlo, pero antes de eso me gustaría aprender un poco acerca de él.

¿Que función cumple R7 - R8 - C8?

¿Que función cumple R13 - R11 - C7?

PD: Perdón por escribir en los dos idiomas, pero no hablo mucho inglés, y por temor a equivocarme y por las dudas lo agrego. Gracias!

[aguantesoda]

here are the components

[teemuk]

Originally posted by aguantesoda
What is R7 - R8 - C8 doing?

What is R13 - R11 - C7 doing?

Those are "bootstraps". Consider them as constant current sources. AC bypassing R8 and R13 will keep the DC voltage drop over the resistors constant regardless of signal voltage swing. Constant voltage drop over constant resistance results to constant current. The voltage amplifier operates in more linear manner when it's loaded by a constant current source.

R13-R11-C7 is an addition I'm a bit unfamilar with. Perhaps someone can explain the difference between this and the conventional arrangement?

[destroyer X]

A double bootstrapp.....symetrical and complementary...hehe....very different.

Do you have more informs?

Someone had constructed?

regards,

Carlos

[aguantesoda]

I have the pdf....

[destroyer X]

Very interesting,

Carlos

[teemuk]

I have seen some guitar/bass amplifiers from the 70's that used this symmetric bootstrapping arrangement. SPICE sim shows that in comparison to conventional topology this one can swing about 1 volt closer to negative rail (which is not much). Clipping of the negative rail also introduces a strange "glitch" so this symmetric configuration doesn't look too stable either. The arrangement never seemed to catch success so I wonder does it have any significant benefits over the conventional one with single bootstrap/active CCS? Are there any particular reasons why it isn't used that much?

[destroyer X]

Adjustment suggested into the text was made over 2 ohms load...and made to allow the protective transistors to hold maximum of 7.5 Volts over 2 ohms in the output...this is a problem.

Was made to protect the output, but will disturb hardly sonics.

This will protect, as a single transistor is used into the output, ...a single pair...but will kill all musical dinamics when using real speakers.

There are many speakers, that despite having 8 ohms specified, that has very lower values, depending on frequencies..sometimes 4 ohms and lower impedances can be found....in this moment the over current protection will start to limit.... say, into frequencies where a deep of impedance happens...the protection will feel over current and will reduce power...hummmmm, not a good idea for quality sound reproduction during dinamic musical reproduction

Better idea is to keep this protection off, not to construct it, or adjust it not to enter during normal work.... so, 280 watts (4 ohms) will be sent to the speakers since the protection will not operate (mis adjusted or removed)

Of course, at least, three pairs will be needed in the output, each one using it's own emitter resistance (colector resistance into the negative rail unit) and tweaking a little R25 and R27.

Different values into those two bootstrappers seems reasonable because the output arrangement.

I could not understand those D3 and D4...i am hardly afraid of them, as i do not know if they will disturb the Vbe multiplier..i hope not.... i am confused with that...please, if someone knows why those diodes are there....as they could be removed, inform details please.

Very interesting...and provided as Kit in Argentina i think.... very good, keep me informed please.

This is a South American design for sure, i am interested to follow your progress Aquantesoda.

I have not simulated yet.

regards,

Carlos

[aguantesoda]

Do you think it work well?

I marked the part of circuit I understand... correct me If I´m wrong...

This is the Power amplifier, and Zobel circuit.

[aguantesoda]

Differencial pair