Award Sessions "Blues Baby"

[mckayprod]

Just stumbled onto this british SS amp today.  Not sure what chip he uses for the final (TDAxxx, I think, can't confirm) but somewhere on the site he references TL072 opamps.  Quite a thoughtful design, IMO.  Anyone on the forum ever see or play through one?

http://award-session.com/index.html

Good reading on this site for design philosophy, etc.

[mike45]

Hi,
the powerampchip is a LM3886. I have a BluesBaby at home and i'm modding it a the moment. Yesterday i changed the powerramp pcb to a dual-parallel LM3886 and inserted a new toroid tranny with 120VA 2x22V AC. So that my Bluesbaby will have 100 watts insteed of 22w output. I am not yet ready with it so i can't say how it sounds. With 22w output it is a little bit weak for playing in a band. But its a very nice amp for Bedroom players.  :dbtu:

mike

[mckayprod]

I wondered if the amp might be a little low-powered.  So the idea is to bridge the outputs of two LM3886?  What speaker did you get with yours?

[J M Fahey]

Hi,
the powerampchip is a LM3886. I have a BluesBaby at home and i'm modding it a the moment. Yesterday i changed the powerramp pcb to a dual-parallel LM3886 and inserted a new toroid tranny with 120VA 2x22V AC. So that my Bluesbaby will have 100 watts insteed of 22w output. I am not yet ready with it so i can't say how it sounds. With 22w output it is a little bit weak for playing in a band. But its a very nice amp for Bedroom players.  :dbtu:

mike

Not sure what you´ll achieve, in any case I doubt the 100W improvement.
If you keep original speaker and very little or nothing the power rails voltage, power will stay the same.

And Award makes a big fuss about their power amp design, so if you replace it with anything else, you lose that.

Doubt the schematic is available but maybe some old/new pictures might give us a better idea.

[teemuk]

One can read between the lines and make few deductions:

They call the "Restricta (TM)" circuit a "power amp driver", so it's not neccessarily a power amp at all, it could be just a stage that drives it. "Restrictor" sounds a lot like limiter.

They call it a "logarithmic driver", so I guess the stage has a logarithmic gain function instead of linear one. Hmm... "The early stages of its PA distortion really just compresses the sound a little, giving it a fatter tone as the volume is turned up. This also progressively reduces the dynamic range, the louder you play until, finally, the brain interprets it as distortion."

Sounds suspiciously like ordinary "soft clipping". Hmmm... Even generic diode clipping actually introduces a said logarithmic gain function: Small signal levels do not forward bias the diode but at higher signal levels dynamic impedance of gradually forward biasing the diode attenuates overall gain in logarithmic manner. Instead of linear gain function that abruptly turns to hard clipping the diode introduces a round "knee" to the transition area from linear operation to full clipping. Basically, the transisition to distinct clipping distortion becomes less abrupt at the cost of increased overall signal distortion.

Basically some power amp headroom is sacrificed to achieve softer transition to clipping distortion. You can find many examples of such guitar amp designs. Without soft clipping the power amp would generate higher output power within the quoted THD spec but transistion to clipping would be equally more abrupt.

I'm not sure if the power amp stage features the "Dynamic Feedback" of their "RetroTone" mods, but that is basically just generic current feedback. It's been somewhat a "standard" feature of SS guitar amps for a few decades.