60dB is SPL - a loud speech sound level that at 1m distance produces ~1uV in ribbon motor.
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Yes, it does affect gain. The gain goes up, depending on the mu of the tube. The higher the mu, the greater the increase in gain.
removing bypass in LTSpice model decreased gain just a little bit. However increased noise by 30%. Because all AC current that previously went through bypass cap started to go through Rk. I am not sure though if bypass cap correctly models its noise in Spice.
The mu-follower gain is set by the valve mu. This is because the upper triode sets such a high load impedance for the lower anode that cathode degeneration can have little effect, apart from changing the output impedance of the stage.
The extra noise from an unbypassed cathode resistor probably comes from the resistor itself.
The extra noise from an unbypassed cathode resistor probably comes from the resistor itself.
Hi,
If the noise level of such a low value resistor is of such a great concern (and I know we all brainlessly rely on software sims, don't we) then replace it by something less noisy perhaps?
I'll repeat it once more: removal of the bypass caps linearizes the stage by means of degenerative feedback which in this case is by far more beneficial in the whole scheme of things than keeping them there.
So, I suggest to stop looking at minor details and start looking at the grander scheme of things.
The entire schematic is so full of basic errors that it begs questioning the validity of using a software program to concoct anything more than a boiled egg. Period.
Ciao, 😉
If the noise level of such a low value resistor is of such a great concern (and I know we all brainlessly rely on software sims, don't we) then replace it by something less noisy perhaps?
I'll repeat it once more: removal of the bypass caps linearizes the stage by means of degenerative feedback which in this case is by far more beneficial in the whole scheme of things than keeping them there.
So, I suggest to stop looking at minor details and start looking at the grander scheme of things.
The entire schematic is so full of basic errors that it begs questioning the validity of using a software program to concoct anything more than a boiled egg. Period.
Ciao, 😉
Also the bigger bypass cap is the less noise from Rk and the lower its frequency.
In my case with low ESR 220uF bypass, Rk 2.2k shows some little noise in 0-10Hz
With 10uF it shows much more noise and it spans above 100Hz.
So I'll keep both Rk "oversized".
In my case with low ESR 220uF bypass, Rk 2.2k shows some little noise in 0-10Hz
With 10uF it shows much more noise and it spans above 100Hz.
So I'll keep both Rk "oversized".
That's true for a normal grounded cathode gain stage but that's NOT what he's using now is it?
His latest circuit is just fine. Show and describe the exact errors he made, please, and why.
Hi,
Which goes to show how well a mu-follower stage is understood.
No one in particular but if the shoe fits...
Ciao, 😉
Which goes to show how well a mu-follower stage is understood.
No one in particular but if the shoe fits...
Ciao, 😉
What do you mean by "linearizes"? If FR then it is already linear, at 1Hz it is rolled down just ~2dB. Without bypass cap it is flat down to 1Hz. But, do we need this?
However flicker noise is a bit higher in this case. And we fight with noise, do not we? I'll try without bypass caps anyway, just to compare.
Hi,
To linearize: "Linearization is a linear approximation of a nonlinear system that is valid in a small region around the operating point."
To put it in plain words, to linearize a stage is to take action so it deviates less from its input, IOW it will show less distortion product at its output.
Tell me, why is the cathode resistor bypassed in the first place?
Ciao, 😉
To linearize: "Linearization is a linear approximation of a nonlinear system that is valid in a small region around the operating point."
To put it in plain words, to linearize a stage is to take action so it deviates less from its input, IOW it will show less distortion product at its output.
Tell me, why is the cathode resistor bypassed in the first place?
Ciao, 😉
In fact bypassing the bottom cathode of a mu follower is pretty much essential if you want to gain all its low distortion and low output impedance properties.
Cheers
Ian
for the first stage where plate V~ amplitude is just 7mV linearity is not an issue.
but the noise is. so it should be the priority.
I want this tube!
A New Low Noise Vacuum Tube
A New Low Noise Vacuum Tube
does anybody know what the tube is it and if it is possible to buy.
Hi,
Not sure you noticed but that invention dates from 1932.
You could replace the "noisy" resistor for one or more LEDs or diodes with the same voltage drop as R14.
Or, keep a resistor but rebias the stage so it uses lower value Rs. Or use battery bias.
Ciao, 😉
Not sure you noticed but that invention dates from 1932.
You could replace the "noisy" resistor for one or more LEDs or diodes with the same voltage drop as R14.
Or, keep a resistor but rebias the stage so it uses lower value Rs. Or use battery bias.
Ciao, 😉
So they had tons of time to produce this tube. What the tube it could be?
I tried LEDs in simulation, they produce similar amount of noise.
Lower Rk will increase current, and noise.
Battery? I am afraid that battery is a questionable conductor of variable current. Batteries are not designed to conduct any signal in sound diapason. Capacitors are.
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