TSSA - The Simplest Symmetrical Amplifier

[Joachim Gerhard]

I think JLH argued in the original article that the 0.22 Ohm resistor somewhat helps to suppress back EMF entering the feedback chain. The lower impedance of the feedback resistors in a CFA could have a similar effect.

[Lazy Cat]

Originally Posted by supernet

Hm...interesting question

hehe you know something I shoulda known too, please talk

[dadod]

Originally Posted by Salas

Meaning that amp? I got one still going strong. Using it for when everything else is under planning or cruel operations. Built on 80's L bracket modded PCBs that skip the 0.22R and speaker line fuse originals. I should add it and see what happens at a point I guess. Will reserve it for when the devil will find work for idle hands to do, and that is very British being a Morrissey lyric too.

Not that one but this one, and my moded one.
dado

[Esperado]

Originally Posted by Joachim Gerhard

A transmission line of cause does also not need a high damping factor because it has a quite flat impedance curve in the bass.

Yes, and transmission lines present a good acoustical charge to dump the speaker at the resonance too.
Transmission lines and 1/4 waves are probably the best enclosures for Bass, although not always possible (QTS of the boomer) and sooo complicated to build. :-)

On my side, I do not care too much about the influence of the serial impedance of the amp on the response curve, as my speakers are all compensated (motional and self) to present a near flat impedance on all the bandwith (6ohms +- 1 ohms).
So the influence of the damping factor of the amp is mainly on pulse response.
Having a flat impedance helps the amp, too, because it do not have to deal with disparate (word is correct ?) Voltage/Current ratios, depending on frequencies.

I will never understand why manufacturers do not care this aspect.

[Salas]

Originally Posted by dadod

Not that one but this one, and my moded one.
dado

Which one he published last, mine or yours with the Mosfet Vas?

[Lazy Cat]

I don't know what kind of music you guys listen to, but for me Jazz is the most revealing, true "acid test", since PRAT (Pace Rhythm And Timing) is everything at Jazz. Live Jazz performances daily in summer time offers major experiences, sound absorptions, tasting and learning how live instruments and Jazz band should sound. System must be capable to reproduce near live experience and that happens only when PRAT is OK. Musicians come together playing the same tune, they're tuned together, if not, complex Jazz takes sounds like tune's falling apart, musicians not playing in the same composition. To me Y axis correlations (phase, time, frequency) are the most important ones, amplitude related distortions are much more tolerable.

I could hear Jazz band from 1 km distance and I would immediately know it is live band playing: transients (speed), phase synergy, PRAT tells me that.

[dadod]

Originally Posted by Salas

Which one he published last, mine or yours with the Mosfet Vas?

It was published in EW-WW 1984 July to August, later he changed it a bit, but I do not have that magazine(I think it was 1989.)
I don't know yours, I see it first time.
dado

[Salas]

Mine is older after all. "Wireless World August 1982"

The Class-A Amplifier Site

[Jay]

Originally Posted by Salas

Which one he published last, mine or yours with the Mosfet Vas?

Salas, the later JLH with mosfet vas has transformed into a Fetzilla

The idea of matching P and N channels (by differing the gate stopper resistance) are also still adopted in Fetzilla, not in your older version of JLH (I think mosfet was still new for him then). Even in Dadod version of JLH, JLH used a series of 2 resistors for gate stopper. In later model JLH used only one resistor, and that is lower value than yours (330R for N, 270R for P. Yours are 680R for both). Go figure

[Esperado]

Originally Posted by Jay

The idea of matching P and N channels (by differing the gate stopper resistance) ...

.. look like squaring the circle, because gate capacitance are varicaps, depending on the gate voltage in a different way between the N-channel and P channel.
Paralleling a cap to reduce the C delta, playing with gate stopper to equalize the low pass filter (created with the capacitance holes) between the P & N devices ?
Never found a good enough response.
So, i believe the only thing we can really do is to allow the driver to never run out of current in the worse situation with the gate resistance little enough for keeping the desired bandwidth in the worse situation too and forget about matching... Am-i wrong ?
What are your experiences about this problem ?