I was wondering if it is possible (and not extremely complicated) to build a pre amp that could be switched from a normal pre amp with gain to a simple buffer depending on the amplifier its feeding.
Some complication is inevitable. If you are willing to tolerate a 10 Kohm I/P impedance (which happens to be IHF "standard"), the problem is (IMO) relatively easy to solve.
A 10 Kohm log. taper control is cap. coupled to either a common cathode gain stage or a cathode follower. The cathode follower always drives the downstream load. The cathode follower is switched between the volume control and the common cathode gain stage.
A 10 Kohm log. taper control is cap. coupled to either a common cathode gain stage or a cathode follower. The cathode follower always drives the downstream load. The cathode follower is switched between the volume control and the common cathode gain stage.
Is a cathode follower really called as passive pre? I thought passive pre is volume potentiometer only, no active parts at all.
The OP asked for switching between just buffered and with gain. You are correct about true passive being either via potentiometer or "autoformer".
Passive preamp is a terrible name to begin with. I guess my house is a large passive automobile then.
Forgive me. I can build from a circuit but im far from an expert when it comes to the technical. Is there a disadvantage to using a 10k I/P ?
You can do it guitar amp style and just switch a bypass capacitor on the common cathode stage cathode resistor in and out of circuit. Advantage is clickless and popless switching and just a DPST switch for stereo; disadvantage is the resulting gains might not be what you are looking for.
A lot of tube equipment can't deal with a load that awkward. OTOH, any commercially distributed SS component, like a CDP, will do just fine.
The reason for the 10 K I/P is adhering to the 1:10 rule. To avoid HF info. loss from an interaction with the Miller capacitance of a common cathode triode, the grid to ground resistance is best kept <= 100 K. The wiper of the 10 K volume control is coupled via a 0.47 μF. cap. to either the common cathode gain stage or the cathode follower.
https://www.transcendentsound.com/slider.html
I just stumble across this. Unfortunately out of my price range.
I just stumble across this. Unfortunately out of my price range.
watch your mouth boy.
is not for sale , and is in topic.
is merlins book for sale and for profit , and is protected .................
What is the gain of a 12B4A common cathode stage with bypassed Rk?
What is the output impedance of a 12B4A common cathode stage with bypassed Rk?
What is the gain of a 12B4A common cathode stage with unbypassed Rk?
What is the output impedance of a 12B4A common cathode stage with unbypassed Rk?
What is the output impedance of a 12B4A common cathode stage with bypassed Rk?
What is the gain of a 12B4A common cathode stage with unbypassed Rk?
What is the output impedance of a 12B4A common cathode stage with unbypassed Rk?
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I never bothered to "run" the numbers. The 12B4 datasheet says the plate resistance is 1030 Ω and the μ is 6.5, which I find to be highly satisfactory.