I keep hearing about AC and DC coupling and I'm not sure what they mean? I was reading parts of Morgan's Jones book and he was talking about direct coupling the phase splitter to the input stage. What does this mean? I was thinking about splitting the signal inside all my sources rather than in the power amp itself. Is this possible or does it go against the definition of direct coupling because of the capacitance in the wires?
David
P.S. I'm not sure what an input stage is good for? Is it like a mini-pre inside to boost voltage? or a buffer stage to change impendance? Mr. Jones doesn't go into input stages much and I'm not really sure what their function is
David
P.S. I'm not sure what an input stage is good for? Is it like a mini-pre inside to boost voltage? or a buffer stage to change impendance? Mr. Jones doesn't go into input stages much and I'm not really sure what their function is
It's a simple thing- it means getting the signal from one stage to the next. If you just transfer the AC component of the signal, that's "AC coupling." If you also transfer the DC on which the signal is riding, it's "DC coupling," normally accomplished by "direct coupling."
Stray capacitances are irrelevant to this definition.
I don't have Jones's book, but normally what one means is that the plate of the first (amplifying) stage is wired directly to the grid of the phase splitter. See, for example, the schematics for any of the Dynaco tube amps.
Stray capacitances are irrelevant to this definition.
I don't have Jones's book, but normally what one means is that the plate of the first (amplifying) stage is wired directly to the grid of the phase splitter. See, for example, the schematics for any of the Dynaco tube amps.
AC coupling means capacitor coupling between stages. DC coupling means there is DC voltage present on the following tube's grid - ie. the plate of the first tube is tied directly to the grid of the 2nd tube. The 2nd tube is biased via a large value Rk, to offset the relatively high B+ voltage on its grid.
Any first stage of voltage amplification could rightly be called the "input" stage. It's job is to take line level (usually 1V) and jack it up to the levels needed by the power amp stage.
Any first stage of voltage amplification could rightly be called the "input" stage. It's job is to take line level (usually 1V) and jack it up to the levels needed by the power amp stage.
Hi,
Coupling is used to transfer the signal (= AC) from one stage to another.
Usually this is done with a capictor which by its' nature blocks off DC and lets the signal through so it is then passed to the next stage.
Direct coupling requires more skill since you will have say the B+ and the AC signal directly on the grid of the next tube.
For that tube to function properly it will need its' input voltage rendered more negative to negate the difference.
The function of the phase splitter is to present two equal signals,each in opposite phase from each other to each half of a push-pull amplifier.
Again this can be done in a number of ways.
Although technically possible there are a number of factors against this.
Are you sure it is not something else you had in mind?
Splitting up the signal in various bands for a biamplified setup perhaps?
If you mean the inputstage (first stage) on an amplifier it is usually there to lift the voltage (amplify) so it can be of usable magnitude for the next stage(s).
Cheers,
Coupling is used to transfer the signal (= AC) from one stage to another.
Usually this is done with a capictor which by its' nature blocks off DC and lets the signal through so it is then passed to the next stage.
Direct coupling requires more skill since you will have say the B+ and the AC signal directly on the grid of the next tube.
For that tube to function properly it will need its' input voltage rendered more negative to negate the difference.
The function of the phase splitter is to present two equal signals,each in opposite phase from each other to each half of a push-pull amplifier.
Again this can be done in a number of ways.
Although technically possible there are a number of factors against this.
Are you sure it is not something else you had in mind?
Splitting up the signal in various bands for a biamplified setup perhaps?
If you mean the inputstage (first stage) on an amplifier it is usually there to lift the voltage (amplify) so it can be of usable magnitude for the next stage(s).
Cheers,
Re: RE:What does coupling mean?
I ment a phase splitter at the source that would go out to a differential amp. Can I direct couple the phase splitted source to the first stage of the power amp ie. (input stage).
I guess the question I wanted to verbalize was, "Does length of wire prohibit or make difficult direct coupling?"
For example: Phase split source ---(1~2 meters silver wire)---> Input power amp stage
fdegrove said:Hi,
The function of the phase splitter is to present two equal signals,each in opposite phase from each other to each half of a push-pull amplifier.
Although technically possible there are a number of factors against this.
Are you sure it is not something else you had in mind?
Splitting up the signal in various bands for a biamplified setup perhaps?
Cheers,
I ment a phase splitter at the source that would go out to a differential amp. Can I direct couple the phase splitted source to the first stage of the power amp ie. (input stage).
I guess the question I wanted to verbalize was, "Does length of wire prohibit or make difficult direct coupling?"
For example: Phase split source ---(1~2 meters silver wire)---> Input power amp stage
For SY
An except from Jones' book on phase splitting so you know where I'm comming from.
""High u valves, such as the ECC83, are not really suitable for the concertina, ECC88 amd E182CC are good, but 12BX7 and 12B4-A are better. It is usual to direct couple to the anode of the imput stage, and let that determine the Cd conditions of the concertina, resulting in the saving of a coupling capacitor and a low frequency time constant. Alothought the concertina is often criticized for its lack of gain, when directly coupled to the input stage, the two valves together give considerably more gain than the same two valves used as a phase splitter based on the differential pair."
David
An except from Jones' book on phase splitting so you know where I'm comming from.
""High u valves, such as the ECC83, are not really suitable for the concertina, ECC88 amd E182CC are good, but 12BX7 and 12B4-A are better. It is usual to direct couple to the anode of the imput stage, and let that determine the Cd conditions of the concertina, resulting in the saving of a coupling capacitor and a low frequency time constant. Alothought the concertina is often criticized for its lack of gain, when directly coupled to the input stage, the two valves together give considerably more gain than the same two valves used as a phase splitter based on the differential pair."
David
BANANA SPLIT?
Hi,
Wait a minute....
A differential amp can be used in balanced mode or in single ended mode.
Provided the input of the first stage of your amp is wired in balanced mode it will accept a signal out of phase on either input.
It will be amplified to the next stage in a balanced mode again and so on 'till it reaches the push-pull arrangement where each half (push + pull) will receive those out of phase signals again.
So,in your case you would either drive it from a balanced source (since these by nature carry two opposing phases as with a phase splitter)
If you start from a single ended source the easiest way two obtain two out of phase signals is to use a xtransformer.
An example of a tube preamp that is designed that way is the Euridice that is discussed here on page 8-9:
ECC88/6DJ8 PREAMP
The same can be achieved with a pair of triodes as well but this would unnecesarily complicate matters such as output impedance,loss of balance with age and the mere fact that designing a perfect active phase splitter isn't always simple.
Most of the time differential long-tailed pair stages are used in balanced preamps and studio gear preceded or followed by...a xformer.
Not really,just don't forget you'll have high voltages on the outputs so this can be dangerous.
In the real world I can't think of any product that uses this technique but technically it could be done.
With a transformer you do not face this problem and on top of that you have the added advantage of galvanic isolation.
Low output impedance so the cable impedance is less critical.
Complicated at first I know....
Cheers,
Hi,
Wait a minute....
A differential amp can be used in balanced mode or in single ended mode.
Provided the input of the first stage of your amp is wired in balanced mode it will accept a signal out of phase on either input.
It will be amplified to the next stage in a balanced mode again and so on 'till it reaches the push-pull arrangement where each half (push + pull) will receive those out of phase signals again.
So,in your case you would either drive it from a balanced source (since these by nature carry two opposing phases as with a phase splitter)
If you start from a single ended source the easiest way two obtain two out of phase signals is to use a xtransformer.
An example of a tube preamp that is designed that way is the Euridice that is discussed here on page 8-9:
ECC88/6DJ8 PREAMP
The same can be achieved with a pair of triodes as well but this would unnecesarily complicate matters such as output impedance,loss of balance with age and the mere fact that designing a perfect active phase splitter isn't always simple.
Most of the time differential long-tailed pair stages are used in balanced preamps and studio gear preceded or followed by...a xformer.
Not really,just don't forget you'll have high voltages on the outputs so this can be dangerous.
In the real world I can't think of any product that uses this technique but technically it could be done.
With a transformer you do not face this problem and on top of that you have the added advantage of galvanic isolation.
Low output impedance so the cable impedance is less critical.
Complicated at first I know....
Cheers,
High voltages
If all sources are outputing 1 Volt to the power amp.... How is 1 Volt high or dangerous?
I know what I want in my head just not used to all the terminology yet. Bear with me, I'll get there.
Let's try this again.
Balanced source material outputting at 1 Volt to the input stage of the power amp. Power amp out put stage is push-pull configuration.
Too complicated? Or stupid sonically?
David
If all sources are outputing 1 Volt to the power amp.... How is 1 Volt high or dangerous?
I know what I want in my head just not used to all the terminology yet. Bear with me, I'll get there.
Let's try this again.
Balanced source material outputting at 1 Volt to the input stage of the power amp. Power amp out put stage is push-pull configuration.
Too complicated? Or stupid sonically?
David
SPLITTING.
Hi,
What devices are you going to use that put out 1 VDC ?
Maybe you mean 1V AC for the signal??
You did say direct coupled,right?
In which case you have think in termes of AC output + DC voltage of the source.
Let me guess...you have a CDP with a single ended output with semi-conductors that you want to convert to balanced?
If so what devices do you wish to use to accomplish this?
If you want to direct couple tube circuitry we're talking at least 100 VDC here.
And that input stage has a balanced input already as well so you want to get rid of what?A pair of coupling caps?
If so,the xformer would be the best option since without them the input stage of the amp wouldn't work anymore with DC on its' input.
Not unless you can adjust the whole circuitry anyway.
I am afraid I'm a bit at a loss of your objective here.
Just put it into plain laymans' wording and I may see the
Cheers,
Hi,
What devices are you going to use that put out 1 VDC ?
Maybe you mean 1V AC for the signal??
You did say direct coupled,right?
In which case you have think in termes of AC output + DC voltage of the source.
Let me guess...you have a CDP with a single ended output with semi-conductors that you want to convert to balanced?
If so what devices do you wish to use to accomplish this?
If you want to direct couple tube circuitry we're talking at least 100 VDC here.
And that input stage has a balanced input already as well so you want to get rid of what?A pair of coupling caps?
If so,the xformer would be the best option since without them the input stage of the amp wouldn't work anymore with DC on its' input.
Not unless you can adjust the whole circuitry anyway.
I am afraid I'm a bit at a loss of your objective here.
Just put it into plain laymans' wording and I may see the
Cheers,
I'm not familiar with the term "concertina," but it sounds (from context) like you're talking about a split load inverter. If so, a high u triode can work very well, contrary to the book you cited. What one needs to be careful about is that the output stage is either isolated from it or has very benign drive characteristics. The load impedance MUST be absolutely symmetrical to maintain high frequency balance.
There are much better (IMO) circuits out there, though the split load has the virtue of a very low parts count. Since it is a less-than-unity gain circuit, the voltage driving it will be considerably more than 1 volt!
There are much better (IMO) circuits out there, though the split load has the virtue of a very low parts count. Since it is a less-than-unity gain circuit, the voltage driving it will be considerably more than 1 volt!
TO THE CONCERTINA
Hi Sy,
One of Julius Futtermans' favourite phase splitters for his OTL designs.
I need to look it up but I think you're reasoning is correct,it has virtually no gain so it relies on the previous stage for that.
Often a penthode was used in that position.
IMHO,Futterman used it since in the OTL circuits you often have to drive an asymmetrical load and it allows for some trickery.
Other than that,there definitely are better phase splitters for common PP designs.
Cheers,
Hi Sy,
One of Julius Futtermans' favourite phase splitters for his OTL designs.
I need to look it up but I think you're reasoning is correct,it has virtually no gain so it relies on the previous stage for that.
Often a penthode was used in that position.
IMHO,Futterman used it since in the OTL circuits you often have to drive an asymmetrical load and it allows for some trickery.
Other than that,there definitely are better phase splitters for common PP designs.
Cheers,
Guess I have a lot to learn. LOL confusing myself
ok, layman's term.
I want a completely balanced system from source to speaker.
So if I have say, a CDP and I modify it to put out a balanced signal, I don't have to do it in the power amp. I'm reading about how direct coupling has some advantages and solves several problems at the same time, so I was trying to find out how I could do away with the phase splitter in the power amp but still have in direct coupled to the input stage. Inside amp versus outside I guess. Since I didn't know what direct coupling meant, I was unsure if that was possible since I've never heard of it done in any "classic" ammp designs.
SY, Jones is talking about the Concertina phase splitter as oppsed to the long tailed diffential phase splitter. He says gain is ~1 but it has the advantages of not being dependent on the u of the valves and determined by passive components. Determined by the modulation of grd voltages and the anode and cathode loads are equal...implying perfect balance.
I must admit that not all of the previous verbose statement made much sense. I just keep cramming into my head. It'll get sorted out eventually.
P.S. fdegrove and SY, In your opinion, what other circuits would be better?
David
ok, layman's term.
I want a completely balanced system from source to speaker.
So if I have say, a CDP and I modify it to put out a balanced signal, I don't have to do it in the power amp. I'm reading about how direct coupling has some advantages and solves several problems at the same time, so I was trying to find out how I could do away with the phase splitter in the power amp but still have in direct coupled to the input stage. Inside amp versus outside I guess. Since I didn't know what direct coupling meant, I was unsure if that was possible since I've never heard of it done in any "classic" ammp designs.
SY, Jones is talking about the Concertina phase splitter as oppsed to the long tailed diffential phase splitter. He says gain is ~1 but it has the advantages of not being dependent on the u of the valves and determined by passive components. Determined by the modulation of grd voltages and the anode and cathode loads are equal...implying perfect balance.
I must admit that not all of the previous verbose statement made much sense. I just keep cramming into my head. It'll get sorted out eventually.
P.S. fdegrove and SY, In your opinion, what other circuits would be better?
David
I SEE..
Hi,
So...seems I wasn't too far off after all.
That is going to require major surgeory.
1/Direct coupling has it's pro and cons,it does away with a coupling cap and the problem is than transferred to the next stage.
2/Balanced operation has also its' pros and cons and in your case the easiest way it using xfromers at both ends.
The last one would then be wired for single ended operation at the secondorary.
3/Well,most classic amps use single ended topology but point 2/ makes sense to me especially for a CDP.
4/A phase splitter is balanced by its' very nature so without knowing the entire amps' circuit diagram it's very hard to tell what you can do.
Hope this helps,
Hi,
So...seems I wasn't too far off after all.
That is going to require major surgeory.
1/Direct coupling has it's pro and cons,it does away with a coupling cap and the problem is than transferred to the next stage.
2/Balanced operation has also its' pros and cons and in your case the easiest way it using xfromers at both ends.
The last one would then be wired for single ended operation at the secondorary.
3/Well,most classic amps use single ended topology but point 2/ makes sense to me especially for a CDP.
4/A phase splitter is balanced by its' very nature so without knowing the entire amps' circuit diagram it's very hard to tell what you can do.
Hope this helps,
To fdegrove
I haven't made an a power amp yet. Just reading and trying to understand the different circuit types. I'm trying to go about in a modular fashion. take the best of each circuit topology add connect in all together. Perhaps not the best way to go about it. But I have no time to experiment with anything hands on. A pity because hands-on is one of my strengthens. Fortunately I'm good at reading and understanding large amounts of information too. So this is how I choose to go about it.
So basically I was jsut reading some books on valve amp design and I wanted you guys/gals to clarify some things.
I know I have a long way to go as throwing around things such as Futterman's circuit, that or this circuit equals one totally clueless guy.
Thanks for the replies so far. I'm getting a handle on this stuff.
Fantastic, keep it coming so I can learn more crazy audio stuff.
david
P.S. What do you mean by "Point 2 makes sense especially for a CDP"? Why is that? What's different from say a tape reel or LP.
I haven't made an a power amp yet. Just reading and trying to understand the different circuit types. I'm trying to go about in a modular fashion. take the best of each circuit topology add connect in all together. Perhaps not the best way to go about it. But I have no time to experiment with anything hands on. A pity because hands-on is one of my strengthens. Fortunately I'm good at reading and understanding large amounts of information too. So this is how I choose to go about it.
So basically I was jsut reading some books on valve amp design and I wanted you guys/gals to clarify some things.
I know I have a long way to go as throwing around things such as Futterman's circuit, that or this circuit equals one totally clueless guy.
Thanks for the replies so far. I'm getting a handle on this stuff.
Fantastic, keep it coming so I can learn more crazy audio stuff.
david
P.S. What do you mean by "Point 2 makes sense especially for a CDP"? Why is that? What's different from say a tape reel or LP.
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