|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
120.156.166.71
I was told (by someone whom I have always thought knew what he was talking about) that a gain stage - whether tube or ss - inverts phase.So you need an even number of gain stages in a component, if it is to preserve phase. (Unity-gain buffers don't count.)
But someone recently posted on a site I visit that gain stages which use jfets ... do not invert phase?
Would anyone like to comment? (Is the statement true ... or rubbish?)
Thanks,
Andy
Edits: 02/20/21Follow Ups:
The way I teach it is that the emitter, source or cathode is the common of the device. It is how you put it in the circuit.
Now taking an N-channel, NPN or a tube, when the input goes positive at the gate, base or grid the plate, collector or drain goes negative, actually less positive because it has a dummy load of sorts and pulls against DC applied to that in all these cases +DC.
Then PNP and P-channel while the opposite in DC voltage applied it is all negative it still inverts. Mostly they use two stages to get rid of that.
Other configurations like using the other terminals ads the common result in no inversion but also with common grid, gate or base do not invert. However they either have too much voltage gain or none, making it all current gain.
In effect in both other cases you are putting the output with the input either the same polarity or not.
I can't teach this whole thing in one post, but if you want non-inverting voltage gain then you need two stages.
" but if you want non-inverting voltage gain then you need two stages " confirms to me that the guy who posted the comment I read recently (that jfets don't invert) ... is seriously confused! :-))
Andy
One can't help wondering if it makes a difference whether or not a gain stage inverts polarity or whether the system itself is in correct polarity since many recordings are in reverse polarity. Wouldn't it all even out?
Recordings are an overall mess. I wouldn't worry about my amp / pre/ inverting or not.
I did some experiemtns when I had gear with a phase switch and it made a difference on a VERY small number of recordings......And than I had trouble determining a 'preference'.
Too much is never enough
Yes, ignore it and it will go away. Kinda like aggressive compression.
Can't do anything about recordings unless YOU do it all yourself. From wiriing the studio and board, to making certain all the microphones are in phase to even the speakers in the control or mixing areas.
And what about the recording which has tracks made in different studios which are later made into a single tune?
Nope, sorry. Recordings are a mess and I've never been informed of a single standard to which all are made....at least ensuring all tracks obey the same phase rules.
Too much is never enough
Neither answer is correct. It depends on the circuit.
However to make a general statement that jfet stages don't invert is even further from the truth.
Example - common source (FET); common emitter (bipolar trans) and common cathode (tube) gain stages all invert phase.
Dan Santoni
That makes more sense to me than the blanket statement which I read about jfets! :-))
Now to find out what a 'common source jfet' circuit looks like!
Andy
A JFET is just a transistor, though a different way to fabricate than bipolar or mosfet. Some steps will be the same (implant and metalization, for example) while the sequence of steps may not be identical and certainly differences in what the mask layers (photolithography) look like.
Might be differences in Start Material, too......We make Hexfet (IR Proprietary design) using Epitaxial Silicon to start......
Too much is never enough
Here you go.
Dan Santoni
.
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: