| Jason Watts |
Which of the three designs listed below should produce the best performance. What would be the preferred design?
1. Common-cathode stage, fully-bypassed cathode:
2. Common-cathode stage, unbypassed cathode:
3. Single-stage inverting feedback amplifier:
See the link below.
http://www.aikenamps.com/Equations.htm
|
|
|
| leadbelly |
| quote: | Originally posted by Jason Watts
Which of the three designs listed below should produce the best performance. What would be the preferred design?
1. Common-cathode stage, fully-bypassed cathode:
2. Common-cathode stage, unbypassed cathode:
3. Single-stage inverting feedback amplifier:
See the link below.
http://www.aikenamps.com/Equations.htm
|
Even a newbie like me knows you can't just compare tube stages on a philosophical basis like that. What is the application? What is the gain and output impedance required? What surrounds that stage, active loading, passive loading, regulation, etc. |
|
|
| EC8010 |
Which is the preferred method of breaking open atoms?
1 A hammer, fully shrouded rubber handle:
2. A laser, paid for by somebody else:
3. A star, not paid for, but quite a long way away:
As a physicist, you owe it to yourself to frame questions better. ;) |
|
|
| EZ_Angus |
| Oooh Oooh, I know this one, its the hammer, innit?? |
|
|
| Jason Watts |
| A neutron is the preferred way to split an atom. By the way I get paid to prevent neutrons from splitting atoms. It’s a great job if you like high stress and high liability one calculation screw up and large quantities of atoms get split. Very ugly. I am sorry for asking such a vague question. My intent was to eliminate the need to do a large quality of research and rapidly eliminate a few of the possibilities. I will be more specific next time. |
|
|
| EC8010 |
| Not to worry. Having avoided splitting atoms, what did you want to do with your gain stage? |
|
|
| Jason Watts |
| What are they advantages and disadvantages between a fully-bypassed and unbypassed cathode? What is the typical input impedance of an off the shelf tuner or CD player? What is a nominal voltage gain typical desired during amplifier construction? Why are they two different outputs for the unbypassed cathode amplifier? Should I try to design the amplifier such that the output impedance is equivalent to my driver impedance? |
|
|
| leadbelly |
| quote: | Originally posted by Jason Watts
What are they advantages and disadvantages between a fully-bypassed and unbypassed cathode? What is the typical input impedance of an off the shelf tuner or CD player? What is a nominal voltage gain typical desired during amplifier construction? Why are they two different outputs for the unbypassed cathode amplifier? Should I try to design the amplifier such that the output impedance is equivalent to my driver impedance? |
You're still missing our point. You've told us what comes before, tuner or CD, but what comes after :) |
|
|
| tubelab.com |
| quote: | | Not to worry. Having avoided splitting atoms, what did you want to do with your gain stage? |
Avoid splitting ears! Sorry I just couldn't help it.
The answer to the question obviously depends on the application, which determines the required amount of gain. Once this is known then some choices can be made. |
|
|
| EC8010 |
| quote: | Originally posted by tubelab.com
Avoid splitting ears! Sorry I just couldn't help it. |
With your avatar?
Back on-topic: In the absence of anything else, I'll make some sweeping assumptions, pronounce a few edicts, then go to bed before the fur flies.
A standard CD player produces a maximum output of 2VRMS. That's quite a handy sensitivity for a power amplifier. Ergo, all power amplifiers should have a sensitivity of 2VRMS for full power. Oh, there are other sources? All digital sources tend to produce 2VRMS. Analogue? What do you mean, analogue? LP? Make the RIAA stage produce 2VRMS. Tape? I'm biased against the stuff. FM tuner? In the unlikely event of you having an FM station that doesn't hammer the Optimod multiband compressor, its future is short-lived and obsolescence beckons (dastardly digits).
Well, that made everything easy. All you need for a pre-amplifier is unity gain. Have a look at SYs Heretical stage.
I'll run away now. |
|
|
| audiohead |
| With all due respect, all CD players @ 0dBFS have 1 Vrms output not 2! |
|
|
| EC8010 |
| I think you'll find it's 2V. I don't have the "Red Book" standard, but that's the accepted figure and I've measured a number of players that corroborated that number. |
|
|
| SY |
| quote: | Originally posted by audiohead
With all due respect, all CD players @ 0dBFS have 1 Vrms output not 2! |
Checking three at random, I find:
Quad 99- 2.4VRMS
Cyrus - 2.1V
Ayre CS-7 - 2.25V |
|
|
| EC8010 |
| Oh yes, we shouldn't forget the players that were designed to sound better in AB tests by virtue of being louder. |
|
|
| Miles Prower |
| quote: | Originally posted by Jason Watts
Which of the three designs listed below should produce the best performance. What would be the preferred design? |
It depends...
1. Common-cathode stage, fully-bypassed cathode:
Highest voltage gain, highest THD, and lowest possible input Vp-p.
2. Common-cathode stage, unbypassed cathode:
Trades off voltage gain for improved THD, and more input Vp-p.
3. Single-stage inverting feedback amplifier:
Trades off lots of voltage gain for very low gains and enhanced distortion performance. Most often used as a "plate follower" to invert a signal at or close to unity gain. (Cathode followers produce an in phase signal at close to unity gain.
As for your situation, what do you need so far as voltage gain, distortion performance, input Vp-p? Decide that, and you have your answer. |
|
|
| lndm |
And then there's the swamped common cathode stage (partially bypassed). Using an unbypassed cathode resistance of 1/gm, on its own or in combo with some bypassed resistance or an LED, will linearise the transfer curve.
About Zo, it should be low compared to the load, generally speaking. |
|
|
|
