Is it better to use a tube instead of anode resistor in a grounded cathode amplifier?
I am trying to design a simple line amplifier with 6n6p and i am thinking if it is better to use a resistor for anode or a similar tube biased at the same point like an SRPP but instead of getting the ouput at top tube's cathode, taking it at bottom tube's anode?
Thanks!
I am trying to design a simple line amplifier with 6n6p and i am thinking if it is better to use a resistor for anode or a similar tube biased at the same point like an SRPP but instead of getting the ouput at top tube's cathode, taking it at bottom tube's anode?
Thanks!
Grounded cathode: plate output, circuit has voltage gain
Cathode follower with CCS in cathode: cathode output (CCS plate), voltage gain of 1
Is this what you are seeking?
Cathode follower with CCS in cathode: cathode output (CCS plate), voltage gain of 1
Is this what you are seeking?
I took a quick look and i think is CCS what i am talking about. I am going to check it thoroughly. I have seen the Aikido which uses something like what i want in the first stage(called the "half mu") which a lot of people think it is SRPP but it is not. Also i saw that lampizator is making the same circuit in his kit's and he calls it SRPP...
The only diference is that i am going to load the next stage with a capacitor interstage. It is still the same as the first stage of "standard" aikido? Do i get it right?
Thanks for all the answers, i am new to tubes and you are very helpful!
The only diference is that i am going to load the next stage with a capacitor interstage. It is still the same as the first stage of "standard" aikido? Do i get it right?
Thanks for all the answers, i am new to tubes and you are very helpful!
What you are suggesting is known as 'grounded cathode with active load'. It is not quite a CCS as it has somewhat lower impedance. If output is taken from the lower anode then it is not an SRPP, although many people wrongly call it that. Given that the upper valve is present, you might as well take output from the upper cathode - it will do little good if the next stage is a high impedance but it won't do any harm.
Given a high impedance load, you might get lower distortion by using a resistor from a suitably high supply rail voltage. This will also give you better PSRR. As always in engineering, it is horses for courses. There is not such thing as a 'better circuit', just a 'better circuit given certain constraints and requirements'.
Given a high impedance load, you might get lower distortion by using a resistor from a suitably high supply rail voltage. This will also give you better PSRR. As always in engineering, it is horses for courses. There is not such thing as a 'better circuit', just a 'better circuit given certain constraints and requirements'.
The next stage is a Pass D1 buffer... What i am trying to accomplish is a PCM1798 DAC with a small resistor for passive i/v and a simple clean tube stage before the b1 buffer. The B1 has input impedance of 47kohm (because of the volume potentiometer). I started by looking at lampizator's schematic and now i get that he calls every circuit with one tube on top of the other as SRPP which is wrong and that the SRPP stage is godd sounding but not so good for so high input impedance. So I thought of getting the output from the bottoms tube anode. The srpp circuit is optimized for a certain impedance while the grounded cathode is not, so i believe is a better choice. I am not sure if it is better to completely replace the upper tube with a resistance. I have checked the mu follower also and i would like a comment if in this setup would it be better than a grounded cathode. I am sure now that the SRPP is not too bad, but no good (it sounds nice although, not much different tha grounded cathode, it measures different - more THD the SRPP).
It will also be helpful if somenone could tell me if it is mandatory in such a setup to add a low pass filter before the tube.
Thanks everybody!
It will also be helpful if somenone could tell me if it is mandatory in such a setup to add a low pass filter before the tube.
Thanks everybody!
For your application, yeah, a LPF before the tube's grid would be important.
I would suggest that you consider 2 stages: a grounded cathode with solid state CCS DC coupled to a cathode follower that also has a solid state CCS, and then use loop feedback around all of it to control gain.
I would suggest that you consider 2 stages: a grounded cathode with solid state CCS DC coupled to a cathode follower that also has a solid state CCS, and then use loop feedback around all of it to control gain.
That depends on what kind of feedback you are talking about. There is local feedback, as in an unbypassed cathode resistor for example, and then there is loop feedback, which connects the output to the input in a predetermined ratio. Cathode followers have 100% feedback for example, so by the logic of folks here, they should be avoided, I guess.
If you want great stereo imaging, then you must have equal gain in each channel. The only way to insure that the gain is equal in each channel over the useful life of the tubes is to use feedback. I don't understand why the tube people on this message board seem to be allergic to loop feedback, or to think that going without it is "better", because it's not. But, do as you like. It's your HiFi.
What a CCS does is make the tube's gain maximum and present a nearly infinite impedance to the tube's plate, making it more linear, depending on what else is attached to the plate of course, as well as giving excellent PSRR. That does not mean that the gain between two tubes will be the same however, nor will it be the same over the useful life of the tube, or to put it another way, the useful life of the tube will be substantially reduced because the circuit fails to take into account the aging of the tube and the resultant degradation of it's characteristics. It's wasteful of tubes to not use global feedback, in other words, because as soon as they have less gain than when new, the stereo imaging will wander and you'll have to buy "matched pairs" of tubes to replace them. To me, this is completely stupid, but what ever, people do all kinds of stupid things in the HiFi world.
The SRPP and an active load stage have identical performance for an infinite load impedance. In addition, the SRPP can give lowish distortion into a particular (fairly low) load impedance, but this will often result in much lower gain too. For most audio usage of SRPP the optimum load impedance is not a design issue, as the SRPP is being used with a near-infinite load.nkostop said:
Hi,
Equal gain from both channels ensures that the stereo image is well centred. It does not per definition ensure good imaging.
In fact one could argue that global feedback distorts correct imaging...
No amount of global feedback prevents valves from aging. Feedback, especially global feedback is a corrective mechanism that is far from perfect. Why correct for errors that can be avoided in the first place?
And I still fail to see how global feedback will guarantee equal gain over the useful life of a valve.
Properly designed a valved stage can stay within 70% of its maximum performance for several thousands of hours. Especially so when we're talking input valves.
Rest assured, there's nothing wrong with a properly designed cathode follower. Even though it is often blamed by audiophiles for all kinds of sins it is an extremely useful topology.
Using a CF and a global NFB loop in a simple two stage preamp however?
Noise from what exactly?
Ciao, 😉
Equal gain from both channels ensures that the stereo image is well centred. It does not per definition ensure good imaging.
In fact one could argue that global feedback distorts correct imaging...
No amount of global feedback prevents valves from aging. Feedback, especially global feedback is a corrective mechanism that is far from perfect. Why correct for errors that can be avoided in the first place?
And I still fail to see how global feedback will guarantee equal gain over the useful life of a valve.
Properly designed a valved stage can stay within 70% of its maximum performance for several thousands of hours. Especially so when we're talking input valves.
Rest assured, there's nothing wrong with a properly designed cathode follower. Even though it is often blamed by audiophiles for all kinds of sins it is an extremely useful topology.
Using a CF and a global NFB loop in a simple two stage preamp however?
Noise from what exactly?
Ciao, 😉
As usual, you have completely mis-read what I wrote. The rest of what you wrote isn't really worth a reply.
Have a great day!
Hi,
Really?
It seems to me that once again this simple question has been misunderstood by some dragging it into never-neverland....
I'm sure it must be that avatar that once belonged to....Mr Feedback who at least had the decency to be more polite.
Have a nice day too, 😉
Really?
It seems to me that once again this simple question has been misunderstood by some dragging it into never-neverland....
I'm sure it must be that avatar that once belonged to....Mr Feedback who at least had the decency to be more polite.
Have a nice day too, 😉
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