four transistor emitter follower (diamond buffer) as power output stage?

[thanh]

I can access geocities site .Please post up some photos!

[thanh]

I can access geocities site .Please post up some photos!

[Alme]

I have recently built an amplifier with output stage what is called here "diamond buffer", using FETs. I was sure this was not a new output FET concept although have never seen it before. I expanded my observations in the thread named {My 'parallel' amplifier}. I switched to another amplifier since then but plan to return to that one as soon as get good acoustic systems for listening (measured parameters were not that bad).

[Alme]

here is output stage of amplifier that was proposed around 1987 in 'Radio' magazine. It was entitled 'parallel' there that is where I took this name from.
I could mess base resistors value a little bit though (drawn without book). That amplifier was intended to drive 8 or 4 Ohm load.

[djk]

"djk, I've been messing around with this for a while. I'd like to read your posted links, but they are dead. Anything you can point me to?"

http://www.audiodesignguide.com/my/Cool_Follower1.GIF

http://www.audiodesignguide.com/my/Hot_Follower1.GIF

http://www.audiodesignguide.com/index_nobanner.html

Nice DC servo:

http://www.tnt-audio.com/gif/a18a.gif

[Upupa Epops]

To Alme : Clever !

[mtlin12]

I have open a new thread, using Marc Vi's sziklai-darlington
output stage instead of normal diamond buffer's NPN/PNP, so the
6-transistor output stage can be an huge AC current gain.

sziklai-darlington diamond buffer (SDDB) for power output stages


ULTIMA-SDDB CLASS-A POWER AMP CIRCUIT PDF

In this SDDB POWER AMP , the Vbe of Q13 about 0.7V is equal to
the stand-by current multiply (R25//R33+R26//R34), if R25//R33=
0.33 OHM, the stand-by current will be 0.7V/(0.33+0.33)=1.06A.
It is about a small power class-A amp's stand-by current .

It can be applied to either Class-A or Class-AB.

[ppl]

[QUOTE]Originally posted by lumanauw
[B]Hi, Wrenchone,

How much bias do you put in your amp? Will this DB works properly if the bias in the final stage only about 25mA?


You can read my mind. I'm thinking about using this output stage with no-global feedback frontend.

I think of 2 candidates that can do this. One is this DB, and the other is Hawks ford EC or NP-PMA by PMA. I think both can be driven without global NFB, but I still don't know which one is better.

This Buffer is intended for headphones in the 50-600 ohm range. The Schematic referenced to was my first attempt at error correction and the buffer as shown worked splendidly however what ever voltage was dropped across the 100 ohm resistors in the voltage divider was that much less voltages swing available than a conventional Diamond buffer. This also was dependent upon Bias current. As illustrated this is only 200-600Mv. Since this is a resistive divider as opposed to a more elegant voltage reference and current source the current will change thought these resistors making large signal swings clip earlier than expected in actual operation. This voltage divider is needed to maintain enough Vce on the driver transistors to sty turned on .If the collectors were connected to the opsing out transistors emitter only about 200-200 mV of VCE is maintained across the drivers. This as one would expect would have some strange stability issues and one would be correct as I have had this circuit do everything from reproducing actuate musical sounds to a perfect white nose generator. However once the Bias is adjusted and a stable input output connection is maintained it remains stable and works thereafter.

As a stand-alone unity gain feedback free Line or headphone driver this circuit’s high input impedance and symmetrical input bias currents make DC offset stable with in +/- 2 mV with source resistances from 100 to 50,000 Ohms. Most BJT Input op amps with lots of Feedback are nowhere near that precise unless input bias current compensation is used. The THD still measures superb on this buffer as shown @ 2 volts and 32 ohm real Headphones not a pure resistor as typically used.

OOps the White trace is the Sound card only the Green the Buffers open loop into Sony MDR-V700 Dj

[Ipanema]

Hi Alme,

May I know what is the function of capacitor C1 and C2 in your drawing?

Regards.

[Tim__x]

Alme last posted on DIYAudio.com in august of last year, so he's not likely to reply.

C1 and C2 are bootstrap capacitors, in short, they make the resistors look like constant current sources with a compliance voltage reaching into the negative. Try to analyze it thinking of the capacitors as voltage sources.

You should google "Bootstrap capacitor".