simplest amplifier possible with BJT's?

[Upupa Epops]

Realy amazing schematic ! Now I know, what was start point by developement of Zen's and Aleph's! Realy good damping factor ! Are you doing joke ?

[TEXAS_OUTLAWS]

Great Work

[rmgvs]

Yes, I should have written 'almost all design criteria'. There is a feedback loop in this design.

If you have a better alternative that does fullfill the criteria mentioned please attach the circuit with appropriate component values.

[millwood]

maybe the difficulties with this whole effort is that the conditions are too stringent. For example, it would be hard to design an amp w/o global feedback to compete with amps that have global feedback (the Pass amps may be able to do that but they use mosfets, something you don't allow here).

with a few exceptions, the submitted schematics in this thread have global feedback.

so maybe if you can relax the conditions a little,

[Lars Clausen]

I think the 8 Ohms resistor in each of these designs is a really stupid pitfall. It's a waste of power, and will really giuve you no good-effects, unless you want to replace it with 12V Automobile bulbs, to make the whole amp look like a simulated tube amplifier.

How about taking one transistor out of the small signal chain (as you don't really need it), and make a push-pull output or at least a current mirror i n the output instaed......

Circlotron ... You contribution is the most innovative in my opinion so far ......

[Steve Eddy]

How 'bout something like this? It covers all the criteria except for the 33k ohm input impedance (what's that about anyway?).

[rmgvs]

Can you give some specifications and component indications for this design (where does it come from)?

The input-criteria (impedance and sensivity) come from the desire to be able to drive the amp straight from a cd-player and/or a highish output impedance tube pre-amplifier (that can not deliver any amount of current into low impedances: that's way the Zen amps can not be driven by simple tube-amps).

You have introduced a new element into this thread: the use of a transformer. I have nothing against it per se but these things are hard to find or very expensive or not sounding right..

[Steve Eddy]

Originally posted by rmgvs
Can you give some specifications and component indications for this design (where does it come from)?

I haven't given the all-BJT version a full workout (I've since abandoned it and opted for a JFET for Q1) so I presented it more as a conceptual circuit. But if you want to experiment, the component values are as follows (actually you can leave R3 out, I forgot to remove it from the schematic):

R1: 9.76k
R2: 39.2k
R4: 8 ohm, 50W
C1: 220pf
C2: 2,000-4,000uF 35V, non-polar
Q1: 2SC4793
Q2: 2SA1302
T1: Jensen JT-13K7-A

The input-criteria (impedance and sensivity) come from the desire to be able to drive the amp straight from a cd-player and/or a highish output impedance tube pre-amplifier (that can not deliver any amount of current into low impedances: that's way the Zen amps can not be driven by simple tube-amps).

Ok. Kind of figured tubes were behind it somewhere.

Though even your garden variety NE5532 opamp can drive loads as low as 600 ohms so the 1.5k ohm input impedance of this circuit wouldn't be a problem for most any solid state source.

You have introduced a new element into this thread: the use of a transformer. I have nothing against it per se but these things are hard to find or very expensive or not sounding right..

Well, "inexpensive" wasn't included in your design criteria so...

se

[millwood]

rmgvs:

since you seem to be interested in making an amp that sounds as good as the JLHs of the world, without global feedback, i would submit to you just the JLH without global feedback, .

it is identical to the JLH1969 (with four transistors, tho. But you can take out either the upper or lower output device if you truly want to make it a three transistor design). the only modifications: take out the lower feedback resistor (220ohm in the JLH design) and upside the DC blocking cap to as large as you can get (3300uf is good enough per my simulation). Here are some performance figures:

================================
JLH1969:

-3db: about 15khz;
gain: 750x;
THD: 0.79%

================================

If you a llow MOSFET, you can replace the output devices (2n3055x2) with MOSFET (I used irf540x2), and run the driver a little bit hotter (the 2.2k resistor on the phase splitter is downsized to 110ohm, as the lower resistor (560ohm down to 110ohm). Here is its performance for the MOSFET version:

================================
-3db: about 25khz;
gain: 2500;
THD: 0.53%
================================

Not bad, isn't?

[rmgvs]

Millwood,

thanks for the idea. In fact this idea crossed my mind before and I put a separate thread on the issue (JLH without feedback). I exchanged some ideas with Geoff Moss on this topic and he thought that the JLH without global feedback altogether would mean a complete redesign of the amp since the sensitivity is not workable and for some more points (see the thread).

Geoff thinks that a total amount of feedback comparable with that of the Hiraga is feasible though (to be continued). I have not heard of any people that fiddled with the amount of feedback in the JLH though.

Rudy