Chip amps against a tube amp.

[danielwritesbac]

Sorry that I forgot a reference for that comment. Here it is: Amplified music : Solid-state valve amp

 

[nicotin78]

Interesting, reference, especially the variable current drive.
Did someone already played with chip amps and variable current drive?

 

[danielwritesbac]

Interesting, reference, especially the variable current drive.
Did someone already played with chip amps and variable current drive?

Trans-conductance, emitter resistors/ballast resistors, padding resistor, BSC, base stopper and even output caps, can accomplish forms of current drive.

Current drive in the right locale will remove blare, but if done wrongly, will cause treble droop. If when it has gone wrongly, the terminology has changed, because that is called impedance mismatch. The most frequently reported inconvenience that way is the volume knob "sounding good" at only one spot, and when this is reported, I'd like to suppose that the good sounding setting is also impractical for use, thus yielding some vexation at the mystery. Well, the cause isn't a mystery, but the fix can get weird.

 

[danielwritesbac]

The decoupled input stage on a TDA 7294 is supposedly even better than the stock circuit though it needs protection to prevent it from being killed on a power up/down cycle.

... it is the quick OFF-ON that kills the TDA7294.

After eight years of flipping the power switch, I claim that the fault is at the inappropriate datasheet sample schematic that fails to promote stability.

If one had made it run better (more stable), even if only to reduce heatsink costs, then flipping the power switch doesn't break it.

In the field, the most common cause of breakage with TDA7294 chips include rail fuses and the slippery erratic screw terminals provided with kits--lose a rail = lose a chip. Please solder the power connections.

The killer with the TDA7294 is that the substrate is connected to the signal -ve pin, not the output stage -ve pin. So this means if you RC decouple the signal -ve pin from the power -ve pin, it's no longer the most negative potential in the circuit. Result is a quickly destroyed chip.

In relevant experiments (usually quad rail, aka separate front end power), adding a schottky bypass will save the chip, because a schottky has a smaller switch-on voltage than the chip substrate, thus the failure mode never turns on. That makes such experiments more convenient.