Muju-amp

[Vaum]

Hello,

What, if anything, is wrong with this schematic/idea? Anything I should consider?



Modified from the ROG Supreaux. 

Thank you for your help.

[petemoore]

  You have bipolar transistors in what otherwise looks like a Mu Amp?, I don't think it'll bias unless you put Jfets in.
  Otherwise you have 3 Mu gain stages [kind of like BSIAB], I tried 3 and found 2 to provide plenty,,,about as much grind and drive possible without having misbehaviour and noise problems...perhaps dial the gain down somehow...who knows.

[Vaum]

I'm pretty sure it's possible to run bipolar transistors in a mu-amp configuration. What I'm not sure of is the details on how to do so.

[Vaum]

Bump.

http://www.diystompboxes.com/smfforum/index.php?topic=39796.0

Found that, seems pretty relevant but the images are dead.

[Vaum]

 

[brett]

Hi
There are many BJT amp designs with active loads, if that is what you are after.
 
The Bosstone is one of the more common one.  The schematic is somewhere around here (geofex.com?).  In that case, an NPN device is loaded by an active PNP device.  Gain of Q1 is doubled (the 18k/18k or 22k/22k resistor split does this), which was very handy back in the days when hFE was more likely to be 100 or 200 than 400.  Maybe you could use something quite similar in reverse polarity (PNP germanium loaded by an NPN silicon would seem logical).
cheers

[slacker]

Here's another way of doing a mu amp using transistors. http://www.diystompboxes.com/smfforum/index.php?topic=52011.0

[earthtonesaudio]

I would bias like Slacker's link shows.  The way you have it right now won't work well for BJT's, I think.

Maybe also of interest:
http://web.telia.com/~u43200663/blocks/bootstrapping.htm (second schematic, toward the bottom of the page).

[B Tremblay]

FYI: http://www.diystompboxes.com/smfforum/index.php?topic=44909.0

[wampcat1]

see the boss md-2 schematic for a mu-amp with trans
http://www.indyguitarist.com/schematics/boss/bossmd2.jpg

[Vaum]

I apologize, B Tremblay. I really did not know and only used them as a time saving measure, with the base being your Supreaux schematic. Could a moderator remove it from my first post, please?

Thanks very much everyone, I think I will go with slacker's method.

[brett]

Hi
maybe I didn't look well enough but the schematic mentioned here

see the boss md-2 schematic for a mu-amp with trans http://www.indyguitarist.com/schematics/boss/bossmd2.jpg

has a complimentary pair in it (Class AB ?), but I don't see a loaded amp. 

I'm no expert, but I think that the two concepts are different.  In the complimentary pair, each device carries a little more than half the signal.  In the mu amp and other designs with active loads, one device (Q1) does the majority of the voltage gain and the other device (Q2) acts as a variable resistor (load), turning off as Q1 turns on, and vice versa.  The mental model that I use is to think of a spring that is in phase with the "spring" that is Q1.  (? have I got the phase thing wrong here somewhere?  Old-timers has got me.)

In the case of the Bosstone that I mentioned above, the gain availabe from Q1 is doubled, and the output impedance is greatly  reduced.

cheers