[R-390] OT: Transistor Amplifier Question

[Alan Victor]

Adding C from base to emitter will significantly reduce the unity current
gain crossover frequency or F_tau.

So, yes, if the desire is to roll off high frequency gain for whatever
reason, this added C in that location will do it. Curious if you can read
the device p/n or is it an internal number and not a 2N or MPS, etc...

Alan

On Sun, May 17, 2020 at 6:45 PM Barry <n4buq at knology.net> wrote:

> Okay, Roger.  Given that Marantz had/has a reputation for sounding great
> (and I tend to agree with that), if there was a way to enhance the sound,
> especially with such a small part like that, I'm sure they didn't hesitate
> to include it and I will restore it the same way it was.
>
> Thanks!
> Barry - N4BUQ
>
> ----- Original Message -----
> > From: "Roger Ruszkowski" <flowertime01 at wmconnect.com>
> > To: r-390 at mailman.qth.net
> > Sent: Sunday, May 17, 2020 7:38:34 PM
> > Subject: Re: [R-390] OT: Transistor Amplifier Question
> >
> > Barry,
> > The problem is complex and common.It is a bias stabilization method that
> > works.In an audio pre amp any thing better is OK.
> > We were looking at some 7805 or 7905 or 7812 voltage regulators.The
> comment
> > was why the pf cps on the input and outputs of theregulators. What is +
> / -
> > 50 pf going to do for the DC voltage andcircuit bias.
> > It is not the exact value.At different device sizes, different pop corn
> > noises get trapped insidethe specific device not the specific capacitor
> > value.The science of what is going on in the circuit is complexand why
> RF is
> > real squirrely compared to DC and Audio.Different cap types, silver mica,
> > foil, ceramic, different dielectrics, and packaging all have different
> > characteristics relevant to audio amplifiers.
> > However the discussion of why the extra caps are includedwith three
> terminal
> > voltage regulators explains it all the circuit science in nerd.
> > The 50 pf caps do change the linearity of the amplifier stageeven if the
> > improved nuisance misses your ears.The idea is that neutralizing the
> > hysteresis on the transmission linebetween active amplification
> junctions is
> > to retain signal fidelity.
> > The caps self resonate and this effect extends or boosts the high
> frequency
> > response in the amplifier stage giving better detail to lower audio
> > frequencies. (Richer harmonic content)Those little caps just let the
> circuit
> > sound better when the signal is more than just a simple sine wave.
> > Roger AI4NI
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