Bridge amp config comparison

[panson_hk]

Originally posted by jerluwoo
Just noticed also that your first example ,both fed from the source, is unbalanced. Top amp has a gain of 10 and the lower 11. This will affect your distortion sims.

Gain unbalanced, you are right. R7 of the lower bridge amp should be changed to 10 k. Then both amps are of gain 11.

[djk]

Is this for a power amp, or a line driver application?

In a power amp the first type in your attachment may have better specs, but is more prone to oscillation.

The second type is less fussy, and is used in amplifiers like the Adcom GFA555.

[panson_hk]

Originally posted by djk
Is this for a power amp, or a line driver application?

In a power amp the first type in your attachment may have better specs, but is more prone to oscillation.

The second type is less fussy, and is used in amplifiers like the Adcom GFA555.

Hi djk,

Thanks for your sharing. Why is the first one pone to oscillation?

panson

[djk]

IIRC, the problem was related to current flowing through the load and the diff input of the other half trying to correct it. This would see-saw back and forth as fast as the amplifier would go (in excess of 1Mhz) and could cause common-mode conduction and destroy the amplifier. Many designs deliberately roll-off the HF response (above 200Khz or so, determined by experiment) of one side to help with this.

There was a real good two-part article on bridge amplifiers in Wireless World magazine circa 1980~81.

It would be worth a trip to the library (if yours has the magazine).

Designs for two amplifiers were presented, one was a 20W 12V design, the other a 200W design.