Home |
Search |
Today's Posts |
#1
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
Hello!
My friend just sent me this circuit that is designed by an Italian builder called Bartolomeo Aloia. The circuit BA211 (see link), I've discussed with my friend this morning about the driver section of this 211 circuit, it acts like a mutivibrator (pulse generator) for old tube computer. I wonder why they choose a pulse generator for a driver stage of the SE amplifier. Any benefits? What is the features from such driver circuit? http://www.audiodesignguide.com/ba/ Have Fun! |
#2
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
On Dec 1, 6:42*pm, Fai C wrote:
Hello! My friend just sent me this circuit that is designed by an Italian builder called Bartolomeo Aloia. The circuit BA211 (see link), I've discussed with my friend this morning about the driver section of this 211 circuit, it acts like a mutivibrator (pulse generator) for old tube computer. I wonder why they choose a pulse generator for a driver stage of the SE amplifier. Any benefits? What is the features from such driver circuit? http://www.audiodesignguide.com/ba/ Have Fun! "multi" just means it comes with various attachments. Nothing to do with valve circuits, one hopes. The circuit probably has a name. Maybe Alex knows? The purpose is to provide gain and a low impedance output, so it can drive a low impedance input...maybe triodes in AB2. There are umpteen ways its operation could be described, depending on how you untangle it. The first stage, comprising the left-most two valves, is an anode follower with an active high-impedance load, resulting in a gain of around the mu of the bottom valve, and a high output impedance. The two valves of the second stage operate in push-pull, or you might prefer to see it as a cathode follower riding on top of an anode- follower, operating in antiphase. The output impedance is the same as an ordinary cathode follower AFAICS. The bottom valve is driven directly by the input signal, and the top half is driven by the first stage. Altogether, it seems to me to operate like a mu-stage. Note the two halves are identical, such that the signal on the first stage's bottom anode should be the same as that at the same point of the second stage. If the grid of the second stage's cathode follower were driven by the anode of the valve underneath it, would that amount to the same thing as driving it from the first stage? Wouldn't that make the first stage redundant? Except for one thing. One way of looking at output impedance is to consider the effect of driving a signal into the output. As the circuit is, such a signal would see a cathode above, with an impedance of a couple of hundred ohms perhaps, in series with the power supply which should be of negligible impedance. In parallel, looking downwards, is a resistor and anode, together amounting to several k ohms. Now, if there were a connection from the anode of the bottom valve to the grid of the top, then that signal into the output would also find its way after some attenuation to the grid of the top valve and drive it. The effect of that would be to increase the impedance of the cathode, thus increasing the output impedance of the stage. All in all, it's a mu-follower with the output impedance of a plain cathode follower. Could be wrong. A mu-follower is one of several similar circuits with four-letter acronyms that I forget. I'm easily confused. Ian |
#3
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
On Thu, 1 Dec 2011 10:42:29 -0800 (PST), Fai C
wrote: Hello! My friend just sent me this circuit that is designed by an Italian builder called Bartolomeo Aloia. The circuit BA211 (see link), I've discussed with my friend this morning about the driver section of this 211 circuit, it acts like a mutivibrator (pulse generator) for old tube computer. I wonder why they choose a pulse generator for a driver stage of the SE amplifier. Any benefits? What is the features from such driver circuit? http://www.audiodesignguide.com/ba/ Have Fun! It's not a multivibrator. The first two (vertical) triodes (of each stage) are an SRPP amplifier and he's buffering it with the second two triodes. The top second triode is just doing "the same thing" as the previous triode grid it's connected to and so is the second bottom triode. The idea is to isolate the load from the signal (first) stage. Notice at the bottom of the schematic he calls it a "supertotem." It's also called a Gomes. See here for more than you probably want to know http://www.tubecad.com/2004/blog0015.htm |
#4
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
"Ian Iveson" wrote in message ... On Dec 1, 6:42 pm, Fai C wrote: Hello! My friend just sent me this circuit that is designed by an Italian builder called Bartolomeo Aloia. The circuit BA211 (see link), I've discussed with my friend this morning about the driver section of this 211 circuit, it acts like a mutivibrator (pulse generator) for old tube computer. I wonder why they choose a pulse generator for a driver stage of the SE amplifier. Any benefits? What is the features from such driver circuit? http://www.audiodesignguide.com/ba/ Have Fun! "multi" just means it comes with various attachments. Nothing to do with valve circuits, one hopes. The circuit probably has a name. Maybe Alex knows? The purpose is to provide gain and a low impedance output, so it can drive a low impedance input...maybe triodes in AB2. There are umpteen ways its operation could be described, depending on how you untangle it. Alex: ----------- I do not know what this circuit is called, as I am not an expert in tube circuits. But this one can be probably called a "mu/2 amplifier". Let me explain. To achieve gain = mu one needs to load a triode with an infinite load resistor -- for example, a CCS on MJE340 so loved by Patrick. But signore Bartolomeo uses a different approach. As a loading, he uses exactly the same triode with exactly the same cathode resistor (1.82K). As a result Ra of the loading triode equals Ra of the amplifier triode. Thus gain = mu/2. Perhaps there is some sweetness in having the load identical to drive. My gut feel, it reduces even harmonics (because of sort of symmetry), but would not help odd harmonics. It is only a gut feel, I am not sure. SPICEd people, go ahead and simulate! Patrick, warm up your soldering iron! (Ooops, I think Patrick's soldering iron is never switched off anyway, even while he is on a bike ride.) Regards, Alex |
#5
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
AFAIK, group of my friend is interested in revised this Supertotem
driver circuit designed Bartolomeo Aloia to drive the GM70 instead of 211. Don't you think the possibility having DHT type for the first stage that consists of 2 x Emission labs 20A and the second stage have 2 x PX25 invloved per channel rather than 6922 all the way? Or you guys can think of a better option. |
#6
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
On Dec 2, 12:02*pm, "Alex Pogossov" wrote:
"Ian Iveson" wrote in message ... On Dec 1, 6:42 pm, Fai C wrote: Hello! My friend just sent me this circuit that is designed by an Italian builder called Bartolomeo Aloia. The circuit BA211 (see link), I've discussed with my friend this morning about the driver section of this 211 circuit, it acts like a mutivibrator (pulse generator) for old tube computer. I wonder why they choose a pulse generator for a driver stage of the SE amplifier. Any benefits? What is the features from such driver circuit? http://www.audiodesignguide.com/ba/ Have Fun! "multi" just means it comes with various attachments. Nothing to do with valve circuits, one hopes. The circuit probably has a name. Maybe Alex knows? The purpose is to provide gain and a low impedance output, so it can drive a low impedance input...maybe triodes in AB2. There are umpteen ways its operation could be described, depending on how you untangle it. Alex: ----------- I do not know what this circuit is called, as I am not an expert in tube circuits. But this one can be probably called a "mu/2 amplifier". Let me explain. To achieve gain = mu one needs to load a triode with an infinite load resistor -- for example, a CCS on MJE340 so loved by Patrick. But signore Bartolomeo uses a different approach. As a loading, he uses exactly the same triode with exactly the same cathode resistor (1.82K). As a result Ra of the loading triode equals Ra of the amplifier triode. Thus gain = mu/2. Perhaps there is some sweetness in having the load identical to drive. My gut feel, it reduces even harmonics (because of sort of symmetry), but would not help odd harmonics. It is only a gut feel, I am not sure. SPICEd people, go ahead and simulate! Patrick, warm up your soldering iron! (Ooops, I think Patrick's soldering iron is never switched off anyway, even while he is on a bike ride.) Regards, Alex If grid and cathode were driven by the same small voltage signal, then the impedance would be the same as if the same signal were applied to the anode, it seems to me, so the bottom valve would then see a load of ra. However, in the SRPP, the grid is driven more strongly than the cathode because of the resistor at the cathode of the top valve, which senses current. Consequently the active resistance is greater, but it can't make a very good CCS because there's not enough gain, as Kimmel pointed out. ***Kimmel mu-stage: http://bit.ly/uL9G86 Develops mu-follower from SRPP, and ends up with a MOSFET on top, because it makes a stiffer current source than a BJT for the same reason a pentode would be better than a triode. Since first published, I think the circuit became commercial and this document was withdrawn. My criticism of the article is that it condemns SRPP merely on the grounds that it has a poor current source, without considering that the top valve, by the same token, must make a contribution to the quality, as well as the quantity, of distortion. The SRPP offers endless possibilities for golden-eared tube-rollers. ***SRPP distortion analysis: http://bit.ly/tai8te cheers, Ian |
#7
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
"Ian Iveson" wrote in message ... On Dec 2, 12:02 pm, "Alex Pogossov" wrote: "Ian Iveson" wrote in message ... On Dec 1, 6:42 pm, Fai C wrote: Hello! My friend just sent me this circuit that is designed by an Italian builder called Bartolomeo Aloia. The circuit BA211 (see link), I've discussed with my friend this morning about the driver section of this 211 circuit, it acts like a mutivibrator (pulse generator) for old tube computer. I wonder why they choose a pulse generator for a driver stage of the SE amplifier. Any benefits? What is the features from such driver circuit? http://www.audiodesignguide.com/ba/ Have Fun! "multi" just means it comes with various attachments. Nothing to do with valve circuits, one hopes. The circuit probably has a name. Maybe Alex knows? The purpose is to provide gain and a low impedance output, so it can drive a low impedance input...maybe triodes in AB2. There are umpteen ways its operation could be described, depending on how you untangle it. Alex: ----------- I do not know what this circuit is called, as I am not an expert in tube circuits. But this one can be probably called a "mu/2 amplifier". Let me explain. To achieve gain = mu one needs to load a triode with an infinite load resistor -- for example, a CCS on MJE340 so loved by Patrick. But signore Bartolomeo uses a different approach. As a loading, he uses exactly the same triode with exactly the same cathode resistor (1.82K). As a result Ra of the loading triode equals Ra of the amplifier triode. Thus gain = mu/2. Perhaps there is some sweetness in having the load identical to drive. My gut feel, it reduces even harmonics (because of sort of symmetry), but would not help odd harmonics. It is only a gut feel, I am not sure. SPICEd people, go ahead and simulate! Patrick, warm up your soldering iron! (Ooops, I think Patrick's soldering iron is never switched off anyway, even while he is on a bike ride.) Regards, Alex If grid and cathode were driven by the same small voltage signal, then the impedance would be the same as if the same signal were applied to the anode, it seems to me, so the bottom valve would then see a load of ra. However, in the SRPP, the grid is driven more strongly than the cathode because of the resistor at the cathode of the top valve, which senses current. Consequently the active resistance is greater, but it can't make a very good CCS because there's not enough gain, as Kimmel pointed out. ***Kimmel mu-stage: http://bit.ly/uL9G86 ---------------------------- Alex: You are right -- a triode with a relatively small Rk still is not a great current source. But being more accurate, an equivalent impedance of an "active" load, comprising a triode with Rk=1.82K is *exactly* the same as the output impedance of a common catode stage with Rk=1.82K unbypassed! That is why, gain is exactly mu/2. To get used to this concept you might do other mental experiments, e.g.: 1) Assume temporarily that your tubes are say 12AX7s with Rk=0. In this case the bottom triode will have its cathode literally grounded, and the top loading triode will have its grid hard soldered to cathode (it will work as a diode). Would you agree in this case that Ra of the "active" load equals Ra of a bottom "gain" triode. and consequently, gain=mu/2 ? Obviously you can not disagree with that. 2) Temporarily imagine that Rks for both tubes are hidden inside the tube bases or inside the tube envelopes, so you have no access to them. Then this case will be equivalent to case 1). 3) Imagine that the tubes are weak or poisoned so much, that the resistance of their cathode coating is 1.82K which just degenerates transconductance. Then you do need external Rks and the case again resembles case 1). Regards, Alex |
#8
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
On Dec 2, 11:02*pm, "Alex Pogossov" wrote:
"Ian Iveson" wrote in message ... On Dec 1, 6:42 pm, Fai C wrote: Hello! My friend just sent me this circuit that is designed by an Italian builder called Bartolomeo Aloia. The circuit BA211 (see link), I've discussed with my friend this morning about the driver section of this 211 circuit, it acts like a mutivibrator (pulse generator) for old tube computer. I wonder why they choose a pulse generator for a driver stage of the SE amplifier. Any benefits? What is the features from such driver circuit? http://www.audiodesignguide.com/ba/ Have Fun! "multi" just means it comes with various attachments. Nothing to do with valve circuits, one hopes. The circuit probably has a name. Maybe Alex knows? The purpose is to provide gain and a low impedance output, so it can drive a low impedance input...maybe triodes in AB2. There are umpteen ways its operation could be described, depending on how you untangle it. Alex: ----------- I do not know what this circuit is called, as I am not an expert in tube circuits. But this one can be probably called a "mu/2 amplifier". Let me explain. To achieve gain = mu one needs to load a triode with an infinite load resistor -- for example, a CCS on MJE340 so loved by Patrick. But signore Bartolomeo uses a different approach. As a loading, he uses exactly the same triode with exactly the same cathode resistor (1.82K). As a result Ra of the loading triode equals Ra of the amplifier triode. Thus gain = mu/2. Perhaps there is some sweetness in having the load identical to drive. My gut feel, it reduces even harmonics (because of sort of symmetry), but would not help odd harmonics. It is only a gut feel, I am not sure. SPICEd people, go ahead and simulate! Patrick, warm up your soldering iron! (Ooops, I think Patrick's soldering iron is never switched off anyway, even while he is on a bike ride.) Regards, Alex Barto's driver circuits don't work like multibibrators, but uses SRPP gain stages stages with following cathode follower buffer stage with active cathode load. See http://www.audiodesignguide.com/ba/ba211c.jpg See also the easier to understand http://www.audiodesignguide.com/ba/vtalast.jpg The driver stages to PP 211 OP stage does not have balancing, and the rather high THD of the SRPP gain function would affect final THD measurements, and 6922 would not be optimal IMHO. Better would be 6SN7, and instead of SRPP, bootstrapped follower or mu-follower would give less THD and be less at risk of arcing etc when used to produce high drive voltages for 211. His input stages use a pair of cascaded SRPP, with divider from the two phases of the two cathode outputs taken to a the grid of second SRPP; it is a paraphase phase inverter. Anyway, our Italian Tinkerer uses many more tubes to do what I would using 1 parallel input tube, and 2 x EL84, and a choke with CT, see sheet 1 at top of page at http://www.turneraudio.com.au/300w-1...tput-jan06.htm Nothing wrong with 211 ( or 845 ) based PP OP stages. I believe the main sonic character is generated in OP stages, and my feeling is that such high powered stages offer excellent audio sound. Patrick Turner. |
#9
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
"Patrick Turner" wrote Barto's driver circuits don't work like multibibrators, but uses SRPP gain stages stages with following cathode follower buffer stage with active cathode load. See http://www.audiodesignguide.com/ba/ba211c.jpg See also the easier to understand http://www.audiodesignguide.com/ba/vtalast.jpg Alex: My understanding is that there is a NFB applied to the cathodes of V5a and V3a, and a slight positive feedback into the cathodes output tubes. If this is correct, then I found odd that the feedback is applied to the cathodes of the amplifier triodes V5a and V3a, but not to the cathodes of dummy triodes V3b and V5b. (Perhaps it is a drawing mistake or even a deliberate error intended for those who want to reproduce the design get bad results.) This ruins the whole intrinsic symmetry of this "mu/2 amplifier". If the NFB is deep enough, then the dummy tubes V3b and V5b will be overdriven and create distortion. I would connect cathodes of V3a, V3b and V5a, V5b together. Oh, those tube designers... Regards, Alex |
#10
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
On Dec 4, 4:41*pm, Patrick Turner wrote:
On Dec 2, 11:02*pm, "Alex Pogossov" wrote: "Ian Iveson" wrote in message ... On Dec 1, 6:42 pm, Fai C wrote: Hello! My friend just sent me this circuit that is designed by an Italian builder called Bartolomeo Aloia. The circuit BA211 (see link), I've discussed with my friend this morning about the driver section of this 211 circuit, it acts like a mutivibrator (pulse generator) for old tube computer. I wonder why they choose a pulse generator for a driver stage of the SE amplifier. Any benefits? What is the features from such driver circuit? http://www.audiodesignguide.com/ba/ Have Fun! "multi" just means it comes with various attachments. Nothing to do with valve circuits, one hopes. The circuit probably has a name. Maybe Alex knows? The purpose is to provide gain and a low impedance output, so it can drive a low impedance input...maybe triodes in AB2. There are umpteen ways its operation could be described, depending on how you untangle it. Alex: ----------- I do not know what this circuit is called, as I am not an expert in tube circuits. But this one can be probably called a "mu/2 amplifier". Let me explain. To achieve gain = mu one needs to load a triode with an infinite load resistor -- for example, a CCS on MJE340 so loved by Patrick. But signore Bartolomeo uses a different approach. As a loading, he uses exactly the same triode with exactly the same cathode resistor (1.82K). As a result Ra of the loading triode equals Ra of the amplifier triode. Thus gain = mu/2. Perhaps there is some sweetness in having the load identical to drive. My gut feel, it reduces even harmonics (because of sort of symmetry), but would not help odd harmonics. It is only a gut feel, I am not sure. SPICEd people, go ahead and simulate! Patrick, warm up your soldering iron! (Ooops, I think Patrick's soldering iron is never switched off anyway, even while he is on a bike ride.) Regards, Alex Barto's driver circuits don't work like multibibrators, but uses SRPP gain stages stages with following cathode follower buffer stage with active cathode load. Seehttp://www.audiodesignguide.com/ba/ba211c.jpg See also the easier to understandhttp://www.audiodesignguide.com/ba/vtalast.jpg The driver stages to PP 211 OP stage does not have balancing, and the rather high THD of the SRPP gain function would affect final THD measurements, and 6922 would not be optimal IMHO. Better would be 6SN7, and instead of SRPP, bootstrapped follower or mu-follower would give less THD and be less at risk of arcing etc when used to produce high drive voltages for 211. His input stages use a pair of cascaded SRPP, with divider from the two phases of the two cathode outputs taken to a the grid of second SRPP; it is a paraphase phase inverter. Anyway, our Italian Tinkerer uses many more tubes to do what I would using 1 parallel input tube, and 2 x EL84, and a choke with CT, see sheet 1 at top of page athttp://www.turneraudio.com.au/300w-1+2-schem-input-driver-output-jan0... Nothing wrong with 211 ( or 845 ) based PP OP stages. I believe the main sonic character is generated in OP stages, and my feeling is that such high powered stages offer excellent audio sound. Patrick Turner. Dear Pat, I probably pressing a wrong button and my resppnse didn't show, hopefully they didn't send my post as email. From this link: http://www.audiodesignguide.com/ba/ What they call it a BA211 - the 211 Single Ended Power Amplifier by Bartolomeo Aloia. So this is a SE but you said this is a push pull, now I confused. Thanks! |
#11
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
On Sun, 4 Dec 2011 02:11:08 -0800 (PST), Fai C
wrote: On Dec 4, 4:41*pm, Patrick Turner wrote: On Dec 2, 11:02*pm, "Alex Pogossov" wrote: "Ian Iveson" wrote in message ... On Dec 1, 6:42 pm, Fai C wrote: Hello! My friend just sent me this circuit that is designed by an Italian builder called Bartolomeo Aloia. The circuit BA211 (see link), I've discussed with my friend this morning about the driver section of this 211 circuit, it acts like a mutivibrator (pulse generator) for old tube computer. I wonder why they choose a pulse generator for a driver stage of the SE amplifier. Any benefits? What is the features from such driver circuit? http://www.audiodesignguide.com/ba/ Have Fun! "multi" just means it comes with various attachments. Nothing to do with valve circuits, one hopes. The circuit probably has a name. Maybe Alex knows? The purpose is to provide gain and a low impedance output, so it can drive a low impedance input...maybe triodes in AB2. There are umpteen ways its operation could be described, depending on how you untangle it. Alex: ----------- I do not know what this circuit is called, as I am not an expert in tube circuits. But this one can be probably called a "mu/2 amplifier". Let me explain. To achieve gain = mu one needs to load a triode with an infinite load resistor -- for example, a CCS on MJE340 so loved by Patrick. But signore Bartolomeo uses a different approach. As a loading, he uses exactly the same triode with exactly the same cathode resistor (1.82K). As a result Ra of the loading triode equals Ra of the amplifier triode. Thus gain = mu/2. Perhaps there is some sweetness in having the load identical to drive. My gut feel, it reduces even harmonics (because of sort of symmetry), but would not help odd harmonics. It is only a gut feel, I am not sure. SPICEd people, go ahead and simulate! Patrick, warm up your soldering iron! (Ooops, I think Patrick's soldering iron is never switched off anyway, even while he is on a bike ride.) Regards, Alex Barto's driver circuits don't work like multibibrators, but uses SRPP gain stages stages with following cathode follower buffer stage with active cathode load. Seehttp://www.audiodesignguide.com/ba/ba211c.jpg See also the easier to understandhttp://www.audiodesignguide.com/ba/vtalast.jpg The driver stages to PP 211 OP stage does not have balancing, and the rather high THD of the SRPP gain function would affect final THD measurements, and 6922 would not be optimal IMHO. Better would be 6SN7, and instead of SRPP, bootstrapped follower or mu-follower would give less THD and be less at risk of arcing etc when used to produce high drive voltages for 211. His input stages use a pair of cascaded SRPP, with divider from the two phases of the two cathode outputs taken to a the grid of second SRPP; it is a paraphase phase inverter. Anyway, our Italian Tinkerer uses many more tubes to do what I would using 1 parallel input tube, and 2 x EL84, and a choke with CT, see sheet 1 at top of page athttp://www.turneraudio.com.au/300w-1+2-schem-input-driver-output-jan0... Nothing wrong with 211 ( or 845 ) based PP OP stages. I believe the main sonic character is generated in OP stages, and my feeling is that such high powered stages offer excellent audio sound. Patrick Turner. Dear Pat, I probably pressing a wrong button and my resppnse didn't show, hopefully they didn't send my post as email. From this link: http://www.audiodesignguide.com/ba/ What they call it a BA211 - the 211 Single Ended Power Amplifier by Bartolomeo Aloia. So this is a SE but you said this is a push pull, now I confused. Thanks! It is a simple common cathode triode amplifier. It has no DC feedback resistor in the cathode, so its operating point will be unstable, not only during the warm-up period, but over the life of the tube. This looks to me not so much like a work in progress as a "where shall I start?". d |
#12
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
On Dec 4, 9:11*pm, Fai C wrote:
On Dec 4, 4:41*pm, Patrick Turner wrote: On Dec 2, 11:02*pm, "Alex Pogossov" wrote: "Ian Iveson" wrote in message .... On Dec 1, 6:42 pm, Fai C wrote: Hello! My friend just sent me this circuit that is designed by an Italian builder called Bartolomeo Aloia. The circuit BA211 (see link), I've discussed with my friend this morning about the driver section of this 211 circuit, it acts like a mutivibrator (pulse generator) for old tube computer. I wonder why they choose a pulse generator for a driver stage of the SE amplifier. Any benefits? What is the features from such driver circuit? http://www.audiodesignguide.com/ba/ Have Fun! "multi" just means it comes with various attachments. Nothing to do with valve circuits, one hopes. The circuit probably has a name. Maybe Alex knows? The purpose is to provide gain and a low impedance output, so it can drive a low impedance input...maybe triodes in AB2. There are umpteen ways its operation could be described, depending on how you untangle it. Alex: ----------- I do not know what this circuit is called, as I am not an expert in tube circuits. But this one can be probably called a "mu/2 amplifier". Let me explain. |
#13
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
On Dec 3, 1:18*am, "Alex Pogossov" wrote:
"Ian Iveson" wrote in message ... On Dec 2, 12:02 pm, "Alex Pogossov" wrote: "Ian Iveson" wrote in message ... On Dec 1, 6:42 pm, Fai C wrote: Hello! My friend just sent me this circuit that is designed by an Italian builder called Bartolomeo Aloia. The circuit BA211 (see link), I've discussed with my friend this morning about the driver section of this 211 circuit, it acts like a mutivibrator (pulse generator) for old tube computer. I wonder why they choose a pulse generator for a driver stage of the SE amplifier. Any benefits? What is the features from such driver circuit? http://www.audiodesignguide.com/ba/ Have Fun! "multi" just means it comes with various attachments. Nothing to do with valve circuits, one hopes. The circuit probably has a name. Maybe Alex knows? The purpose is to provide gain and a low impedance output, so it can drive a low impedance input...maybe triodes in AB2. There are umpteen ways its operation could be described, depending on how you untangle it. Alex: ----------- I do not know what this circuit is called, as I am not an expert in tube circuits. But this one can be probably called a "mu/2 amplifier". Let me explain. To achieve gain = mu one needs to load a triode with an infinite load resistor -- for example, a CCS on MJE340 so loved by Patrick. But signore Bartolomeo uses a different approach. As a loading, he uses exactly the same triode with exactly the same cathode resistor (1.82K). As a result Ra of the loading triode equals Ra of the amplifier triode. Thus gain = mu/2. Perhaps there is some sweetness in having the load identical to drive. My gut feel, it reduces even harmonics (because of sort of symmetry), but would not help odd harmonics. It is only a gut feel, I am not sure. SPICEd people, go ahead and simulate! Patrick, warm up your soldering iron! (Ooops, I think Patrick's soldering iron is never switched off anyway, even while he is on a bike ride.) Regards, Alex If grid and cathode were driven by the same small voltage signal, then the impedance would be the same as if the same signal were applied to the anode, it seems to me, so the bottom valve would then see a load of ra. However, in the SRPP, the grid is driven more strongly than the cathode because of the resistor at the cathode of the top valve, which senses current. Consequently the active resistance is greater, but it can't make a very good CCS because there's not enough gain, as Kimmel pointed out. ***Kimmel mu-stage: *http://bit.ly/uL9G86 ---------------------------- Alex: You are right -- a triode with a relatively small Rk still is not a great current source. But being more accurate, an equivalent impedance of an "active" load, comprising a triode with Rk=1.82K is *exactly* the same as the output impedance of a common catode stage with Rk=1.82K unbypassed! That is why, gain is exactly mu/2. To get used to this concept you might do other mental experiments, e.g.: 1) Assume temporarily that your tubes are say 12AX7s with Rk=0. In this case the bottom triode will have its cathode literally grounded, and the top loading triode will have its grid hard soldered to cathode (it will work as a diode). Would you agree in this case that Ra of the "active" load equals Ra of a bottom "gain" triode. and consequently, gain=mu/2 ? Obviously you can not disagree with that. That should be obvious because it is the same point I made, except you confusingly use the term "Ra" in two different senses in the same senses. I use Ra for the anode load, and ra for the effective resistance of the anode. So when you wrote "Ra of the loading triode equals Ra of the amplifier triode" I took you to mean that the anode load of the bottom valve is ra. That is what I corrected. 2) Temporarily imagine that Rks for both tubes are hidden inside the tube bases or inside the tube envelopes, so you have no access to them. Then this case will be equivalent to case 1). Equivalent in some ways but not others...you just put resistors in the cathodes! I guess all you mean is that the impedance of the top valve/ Rk combination is the same as the bottom. Consequently, if you perceive the bottom valve/Rk as a voltage source with internal resistance, then the output voltage will be halved when loaded by an equal resistance. Thus if the gain were mu with no load, it would be mu/2 when so loaded. 3) Imagine that the tubes are weak or poisoned so much, that the resistance of their cathode coating is 1.82K which just degenerates transconductance.. Then you do need external Rks and the case again resembles case 1). I don't know if I want to agree with "just", but otherwise OK The key question is whether cathode resistance degenerates mu. If it doesn't, then your mu/2 is correct, with the proviso that mu, ra, and gm are not actually constants and all the common equations relating them seem to me to be shortcut approximations. Now, if an anode load is a current source, then the gain of the valve is mu, and Rk has no effect because under constant current conditions it cannot generate a signal at the cathode. It therefore appears that the cathode resistor does not degenerate mu, and you are correct. Actually, the load seen by each valve is quite high, being the sum of ra, Rk, and Rk(mu+1). This is only true for the second stage if it has no output load, which could be criticism of the circuit detail because a significant load would unbalance it. So if we use mu=33 and ra=2.7k for 6DJ8, then the load for each valve = 2.7k + 1.82k + 34*1.82k = 66k. That is better than 20 to 1, and gain for each valve would be fairly close to mu, were the gain not reduced by its cathode resistor. As ever, I could be wrong. My initial post didn't point out that the gain of valves is reduced by their unbypassed cathode resistors. Apart from that my explanation of the working of the circuit remains correct. Some clowns have since muddied the waters. The Butcher in particular has, as usual, poisoned the thread with nonsense, and misled and discouraged the OP. I find that behaviour simply too disgusting to witness, so I shan't be hanging around here much. cheers, Ian |
#14
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
On Dec 5, 12:46*am, Ian Iveson wrote:
On Dec 3, 1:18*am, "Alex Pogossov" wrote: "Ian Iveson" wrote in message .... On Dec 2, 12:02 pm, "Alex Pogossov" wrote: "Ian Iveson" wrote in message .... On Dec 1, 6:42 pm, Fai C wrote: Hello! My friend just sent me this circuit that is designed by an Italian builder called Bartolomeo Aloia. The circuit BA211 (see link), I've discussed with my friend this morning about the driver section of this 211 circuit, it acts like a mutivibrator (pulse generator) for old tube computer. I wonder why they choose a pulse generator for a driver stage of the SE amplifier. Any benefits? What is the features from such driver circuit? http://www.audiodesignguide.com/ba/ Have Fun! "multi" just means it comes with various attachments. Nothing to do with valve circuits, one hopes. The circuit probably has a name. Maybe Alex knows? The purpose is to provide gain and a low impedance output, so it can drive a low impedance input...maybe triodes in AB2. There are umpteen ways its operation could be described, depending on how you untangle it. Alex: ----------- I do not know what this circuit is called, as I am not an expert in tube circuits. But this one can be probably called a "mu/2 amplifier". Let me explain. |
#15
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
On Dec 2, 3:40*am, flipper wrote:
On Thu, 1 Dec 2011 10:42:29 -0800 (PST), Fai C wrote: Hello! My friend just sent me this circuit that is designed by an Italian builder called Bartolomeo Aloia. The circuit BA211 (see link), I've discussed with my friend this morning about the driver section of this 211 circuit, it acts like a mutivibrator (pulse generator) for old tube computer. I wonder why they choose a pulse generator for a driver stage of the SE amplifier. Any benefits? What is the features from such driver circuit? http://www.audiodesignguide.com/ba/ Have Fun! It's not a multivibrator. The first two (vertical) triodes (of each stage) are an SRPP amplifier and he's buffering it with the second two triodes. The top second triode is just doing "the same thing" as the previous triode grid it's connected to and so is the second bottom triode. The idea is to isolate the load from the signal (first) stage. Notice at the bottom of the schematic he calls it a "supertotem." It's also called a Gomes. See here for more than you probably want to know http://www.tubecad.com/2004/blog0015.htm Having written of clowns, I feel I should exclude you from the list. I think it's best to see this as a single, compound SRPP stage in which the feed from bottom anode to top grid is isolated from the output. It could be seen in lots of ways though...including a paraphase splitter and PP stage. SRPP and mu-follower are essentially the same circuit, but the mu- follower has a larger current-sense resistance for the current source, with a tap for the bias, which then calls for AC coupling from bottom anode to top grid. I'm quite looking forward to experimenting with my emerging headphone amp, but I'll likely end up with just a single generous triode and a beautiful output transformer. Gomes? Somewhere in my search for Kimmel I seem to recall a Gomes. The Great Revival of valve audio split into camps and many became commercial, or at least tried. I notice Jones deals with the mu- follower but doesn't mention the SRPP AFAICS. Too continental, perhaps. Ian |
#16
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
On Sun, 4 Dec 2011 11:38:57 -0800 (PST), Ian Iveson
wrote: On Dec 2, 3:40*am, flipper wrote: On Thu, 1 Dec 2011 10:42:29 -0800 (PST), Fai C wrote: Hello! My friend just sent me this circuit that is designed by an Italian builder called Bartolomeo Aloia. The circuit BA211 (see link), I've discussed with my friend this morning about the driver section of this 211 circuit, it acts like a mutivibrator (pulse generator) for old tube computer. I wonder why they choose a pulse generator for a driver stage of the SE amplifier. Any benefits? What is the features from such driver circuit? http://www.audiodesignguide.com/ba/ Have Fun! It's not a multivibrator. The first two (vertical) triodes (of each stage) are an SRPP amplifier and he's buffering it with the second two triodes. The top second triode is just doing "the same thing" as the previous triode grid it's connected to and so is the second bottom triode. The idea is to isolate the load from the signal (first) stage. Notice at the bottom of the schematic he calls it a "supertotem." It's also called a Gomes. See here for more than you probably want to know http://www.tubecad.com/2004/blog0015.htm Having written of clowns, I feel I should exclude you from the list. I think it's best to see this as a single, compound SRPP stage in which the feed from bottom anode to top grid is isolated from the output. It could be seen in lots of ways though...including a paraphase splitter and PP stage. SRPP and mu-follower are essentially the same circuit, but the mu- follower has a larger current-sense resistance for the current source, with a tap for the bias, which then calls for AC coupling from bottom anode to top grid. I'm quite looking forward to experimenting with my emerging headphone amp, but I'll likely end up with just a single generous triode and a beautiful output transformer. Gomes? Somewhere in my search for Kimmel I seem to recall a Gomes. The Great Revival of valve audio split into camps and many became commercial, or at least tried. I notice Jones deals with the mu- follower but doesn't mention the SRPP AFAICS. Too continental, perhaps. Ian You wouldn't need to search for Gomes if you simply read the link I provided. |
#17
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
On Dec 5, 4:21*am, flipper wrote:
Gomes? Somewhere in my search for Kimmel I seem to recall a Gomes. The Great Revival of valve audio split into camps and many became commercial, or at least tried. I notice Jones deals with the mu- follower but doesn't mention the SRPP AFAICS. Too continental, perhaps. Ian You wouldn't need to search for Gomes if you simply read the link I provided. I didn't search for Gomes. I didn't need to. Ian |
#18
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
Ian scribed........
SRPP and mu-follower are essentially the same circuit, but the mu- follower has a larger current-sense resistance for the current source, with a tap for the bias, which then calls for AC coupling from bottom anode to top grid. Well, SRPP and mu-foll do have "totem pole" config but that's where the similarity ends. The SRPP can only be really called PP when there is substantial work on the load done by BOTH top AND bottom tube, and the load is such that the top Rk generates enough load current from bottom tube to give Vgk applied to top tube which is nearly equal to the Vgk applied to the bottom tube from a signal source. Suppose one had a pair of EL86 in triode ( similar to EL84 in triode, but Ra = 1k2 ) in SRPP circuit, and for each tube Ea = 150V, Ia = 60mAdc, and phones of 32 ohms were connected to top cathode, then one probably could get about +/- 50mA peak Ia change in load to give 39mW of power into 32 ohms which to the tubes looks like a short circuit, because an ideal class A load would be 1k2, with each tube "seeing" close to 2k4, or R x Ra. EL86 has u = 10 approx, and gain with EL86 is low with load of about 64 ohms, and THD is high, so you'd need a shirt&trouser load of NFB to straighten out the mess you have without an OPT. But suppose you had a mu-foll, with say 6AS7/6080 with Ea = 100V and Ia 200mA, with choke between cathode and 0V. The cathode voltage would have a cap to keep Idc from the phones, say 2,200uF. The driver tube can be set up like a normal common cathode gain stage except that its dc RL is a pair of resistors to B+ with junction bypassed to 6AS7 cathode with say 470uF, ie, top of choke, and also the signal output for the phones. This means the output voltage from "top" tube 6AS7 is in series with bottom tube anode supply resistance, and this resistance is barely aware there is any load connected; and in fact the load resistance is "bootstrapped" and appears to the drive tube as a much higher R than it actually is, so the driver tube provides low THD drive to the OP tube. With 200mA in the 6AS7 at idle, load current can be maybe +/- 150mA giving 0.35 Watts which is enough to deafen our Ian if the Rolling Stones is played that loud. So the mu-follower has very little load current produced in its bottom tube and this is also true in a preamp situtation such as at http://www.turneraudio.com.au/Line-preamp-2003.htm The use of mu-foll as opposed to SRPP is to AVOID load current sensing between top and bottom tubes and to promote the top tube to being an almost pure cathode follower, and then have the bottom tube operating with a very high effective RL which its THD becomes much lower than SRPP, or a normal tube with non bootstrapped resistance for dc to anode. I'm quite looking forward to experimenting with my emerging headphone amp, but I'll likely end up with just a single generous triode and a beautiful output transformer. In the last headhone amp I used EL84 in triode with OPTs taken from a Fisher AM/FM receiver. The load was about 5k : 16, and for headphones, ANY load is about OK, you'll have enough power/voltage headroom. I used 1/2 6CG7 to drive EL84 with 12dB NFB. The customer is extremely happy. Noise is the main problem to overcome, so I suggest all trannys are potted, and DC is applied to all heaters; an external PSU is a good idea. Even then, tube noise can be present. One should aim for noise to be less than 0.05mV, or 50uV. You may find this impossible achieve, but you get say 0.25mV. Well, a simple resistance divider across the 16 ohm winding, say 39 ohms plus 8.2 ohms will give mean the tube signal level will have to be about 6 times higher, but the R divider divides the noise down so SNR is improved by 6 times. Most headphone outlets on power amps and receivers have such a divider which allows tubes or transistors to see a high value load and hence give low THD, while being able to still give oodles of voltage for headphones. The phones amp I built for my customer in 2009 is fully integrated, has hi & low level outputs, and can be used as a normal preamp with superb performance. A lot of ppl try to avoid OPTs in phone amps while insisting on tubes to give OTL type of power. Its not good practice, but a pair of complementary source follower mosfets could easily be used with a +/- 12V supply and Ia at 0.5 amps, and then one drives both gates from a C&R coupled triode of some sort. The secret is to have the voltage amping done linearly, and also the current amping, and class A mosfets in source- foll mode will be remarkably linear, even if the phones are 4 ohms. 6AS7 with a PP OPT would also be OK. But once you go to tubes and OPT, the OPT allows a normal amp to be made, and loading and linearity becomes much better than without OPT. Patrick Turner. |
#19
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
On Dec 8, 10:31*am, Patrick Turner wrote:
Ian scribed........ SRPP and mu-follower are essentially the same circuit, but the mu- follower has a larger current-sense resistance for the current source, with a tap for the bias, which then calls for AC coupling from bottom anode to top grid. Well, SRPP and mu-foll *do have "totem pole" config but that's where the similarity ends. The difference is as I have described it. The difference in how you envisage the operation of the two circuits is up to you. Alex has already pointed out that the gain of a symmetrical SRPP must be mu/2 and I have agreed with him, giving supporting analysis. I provided a link to Kimmel's original paper which develops the mu- follower from the SRPP. Do keep up. The SRPP can only be really called PP when there is substantial work on the load done by BOTH top AND bottom tube, and the load is such that the top Rk generates enough load current from bottom tube to give Vgk applied to top tube which is nearly equal to the Vgk applied to the bottom tube from a signal source. Suppose one had a pair of EL86 in triode ( similar to EL84 in triode, but Ra = 1k2 ) in SRPP circuit, and for each tube Ea = 150V, Ia = 60mAdc, and phones of 32 ohms were connected to top cathode, then one probably could get about +/- 50mA peak Ia change in load to give 39mW of power into 32 ohms which to the tubes looks like a short circuit, because an ideal class A load would be 1k2, with each tube "seeing" close to 2k4, or R x Ra. EL86 has u = 10 approx, and gain with EL86 is low with load of about 64 ohms, and THD is high, so you'd need a shirt&trouser load of NFB to straighten out the mess you have without an OPT. It would be easier for you to simply link to Kimmel's paper. Except it's already been done. But suppose you had a mu-foll, with say 6AS7/6080 with Ea = 100V and Ia 200mA, with choke between cathode and 0V. The cathode voltage would have a cap to keep Idc from the phones, say 2,200uF. The driver tube can be set up like a normal common cathode gain stage except that its dc RL is a pair of resistors to B+ with junction bypassed to 6AS7 cathode with say 470uF, ie, top of choke, and also the signal output for the phones. This means the output voltage from "top" tube 6AS7 is in series with bottom tube anode supply resistance, and this resistance is barely aware there is any load connected; and in fact the load resistance is "bootstrapped" and appears to the drive tube as a much higher R than it actually is, so the driver tube provides low THD drive to the OP tube. With 200mA in the 6AS7 at idle, load current can be maybe +/- 150mA giving 0.35 Watts which is enough to deafen our Ian if the Rolling Stones is played that loud. So the mu-follower has very little load current produced in its bottom tube and this is also true in a preamp situtation such as athttp://www.turneraudio.com.au/Line-preamp-2003.htm The use of mu-foll as opposed to SRPP is to AVOID load current sensing between top and bottom tubes and to promote the top tube to being an almost pure cathode follower, Had you read my original post on this thread, you would realise that the the circuit under discussion does exactly that. and then have the bottom tube operating with a very high effective RL which its THD becomes much lower than SRPP, or a normal tube with non bootstrapped resistance for dc to anode. I'm quite looking forward to experimenting with my emerging headphone amp, but I'll likely end up with just a single generous triode and a beautiful output transformer. In the last headhone amp I used EL84 in triode with OPTs taken from a Fisher AM/FM receiver. The load was about 5k : 16, and for headphones, ANY load is about OK, you'll have enough power/voltage headroom. Yes. In my case 5k : 62R I'm still dithering on the sec. 4 x 4R or 1 x 62. If only I could predict the effect on leakage. I used 1/2 6CG7 to drive EL84 with 12dB NFB. With 6CH6 in triode I would have more or less unity gain, and enough headroom. It would be nice to try a proper triode though. If I can do without feedback, that's what I'll stick with. The customer is extremely happy. Lots of headphone amps are rubbish. Not many ppl used to care because even poor headphones can sound much clearer than a poor room system. There's a huge market for headphones now, although much of the top end is functionalist rather than functional. Within that market, a new generation of discerning audiophiles is emerging. Noise is the main problem to overcome, so I suggest all trannys are potted, and DC is applied to all heaters; an external PSU is a good idea. Even then, tube noise can be present. One should aim for noise to be less than 0.05mV, or 50uV. You may find this impossible achieve, but you get say 0.25mV. Well, a simple resistance divider across the 16 ohm winding, say 39 ohms plus 8.2 ohms will give mean the tube signal level will have to be about 6 times higher, but the R divider divides the noise down so SNR is improved by 6 times. Most headphone outlets on power amps and receivers have such a divider which allows tubes or transistors to see a high value load and hence give low THD, while being able to still give oodles of voltage for headphones. Noise is indeed the biggest...actually the only...problem to be overcome. I'll start with as much as possible and then reluctantly add bits until the noise is gone. That way I'll know what I can't hear. The phones amp I built for my customer in 2009 is fully integrated, has hi & low level outputs, and can be used as a normal preamp with superb performance. A lot of ppl try to avoid OPTs in phone amps while insisting on tubes to give OTL type of power. Its not good practice, but a pair of complementary source follower mosfets could easily be used with a +/- 12V supply and Ia at 0.5 amps, and then one drives both gates from a C&R coupled triode of some sort. The secret is to have the voltage amping done linearly, and also the current amping, and class A mosfets in source- foll mode will be remarkably linear, even if the phones are 4 ohms. 6AS7 with a PP OPT would also be OK. But once you go to tubes and OPT, the OPT allows a normal amp to be made, and loading and linearity becomes much better than without OPT. That's why I'm using an OPT. Otherwise, Nat Semi does a very nice headphone buffer chip and I wouldn't need valves at all. Ian |
#20
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
On Dec 10, 7:22*am, Ian Iveson wrote:
On Dec 8, 10:31*am, Patrick Turner wrote: Ian scribed........ SRPP and mu-follower are essentially the same circuit, but the mu- follower has a larger current-sense resistance for the current source, with a tap for the bias, which then calls for AC coupling from bottom anode to top grid. Well, SRPP and mu-foll *do have "totem pole" config but that's where the similarity ends. The difference is as I have described it. The difference in how you envisage the operation of the two circuits is up to you. Alex has already pointed out that the gain of a symmetrical SRPP must be mu/2 and I have agreed with him, giving supporting analysis. I provided a link to Kimmel's original paper which develops the mu- follower from the SRPP. Do keep up. I have my own views, and will state them independantly to other websites if I see fit. I might say that regardless of how a triode is used, if the loading gives gain = µ/2, then that load is TOO LOW. Take a pair of EL84 in triode. µ = 20, and for nice clean class A gain might be 17. But your saying for SRPP, gain could be 10, and I would say that is preposterous, ie, stoopid, and to be avoided at all costs. The SRPP can only be really called PP when there is substantial work on the load done by BOTH top AND bottom tube, and the load is such that the top Rk generates enough load current from bottom tube to give Vgk applied to top tube which is nearly equal to the Vgk applied to the bottom tube from a signal source. Suppose one had a pair of EL86 in triode ( similar to EL84 in triode, but Ra = 1k2 ) in SRPP circuit, and for each tube Ea = 150V, Ia = 60mAdc, and phones of 32 ohms were connected to top cathode, then one probably could get about +/- 50mA peak Ia change in load to give 39mW of power into 32 ohms which to the tubes looks like a short circuit, because an ideal class A load would be 1k2, with each tube "seeing" close to 2k4, or R x Ra. EL86 has u = 10 approx, and gain with EL86 is low with load of about 64 ohms, and THD is high, so you'd need a shirt&trouser load of NFB to straighten out the mess you have without an OPT. It would be easier for you to simply link to Kimmel's paper. Except it's already been done. But suppose you had a mu-foll, with say 6AS7/6080 with Ea = 100V and Ia 200mA, with choke between cathode and 0V. The cathode voltage would have a cap to keep Idc from the phones, say 2,200uF. The driver tube can be set up like a normal common cathode gain stage except that its dc RL is a pair of resistors to B+ with junction bypassed to 6AS7 cathode with say 470uF, ie, top of choke, and also the signal output for the phones. This means the output voltage from "top" tube 6AS7 is in series with bottom tube anode supply resistance, and this resistance is barely aware there is any load connected; and in fact the load resistance is "bootstrapped" and appears to the drive tube as a much higher R than it actually is, so the driver tube provides low THD drive to the OP tube. With 200mA in the 6AS7 at idle, load current can be maybe +/- 150mA giving 0.35 Watts which is enough to deafen our Ian if the Rolling Stones is played that loud. So the mu-follower has very little load current produced in its bottom tube and this is also true in a preamp situtation such as athttp://www.turneraudio.com.au/Line-preamp-2003.htm The use of mu-foll as opposed to SRPP is to AVOID load current sensing between top and bottom tubes and to promote the top tube to being an almost pure cathode follower, Had you read my original post on this thread, you would realise that the the circuit under discussion does exactly that. Reading your waffle is difficult. You are a great waffler which few ppl understand, and now you complain ppl don't read you right, or fully. BE CLEARER using less words. and then have the bottom tube operating with a very high effective RL which its THD becomes much lower than SRPP, or a normal tube with non bootstrapped resistance for dc to anode. I'm quite looking forward to experimenting with my emerging headphone amp, but I'll likely end up with just a single generous triode and a beautiful output transformer. In the last headhone amp I used EL84 in triode with OPTs taken from a Fisher AM/FM receiver. The load was about 5k : 16, and for headphones, ANY load is about OK, you'll have enough power/voltage headroom. Yes. In my case 5k : 62R If you had a 5k0 : 16 OPT, and the sec load was 62 ohms, the primary load is 19k4, and the two EL84 see a pure class A load of high value and their gain approaches 20, or µ, and you get excellent fidelity. So in your case, and I guess, because you ain't supplied enough details, that you should have said "in my case 19k4 : 62r." I'm still dithering on the sec. 4 x 4R or 1 x 62. If only I could predict the effect on leakage. The loading of 16 ohms may give a -3dB pole due to LL at say 50kHz. With loading = 62 ohms, or near enough to 4 times the load ohms, the -3dB due to LL is raised to 200kHz. But the primary shunt C may possible prevent any such -3dB HF at 200kHz, and in fact shunt C and LL will form a seond order filter of some sort and give a peaked response unless some sort of a zobel is used to provide the LC circuit with a critical damping R value. The R&C values may be estimated, then tried out when you make the amp, then altered to whatever flatttens response, without adversely loading the amp at HF or provoking HF instability. I used 1/2 6CG7 to drive EL84 with 12dB NFB. With 6CH6 in triode I would have more or less unity gain, and enough headroom. It would be nice to try a proper triode though. If I can do without feedback, that's what I'll stick with. The customer is extremely happy. Lots of headphone amps are rubbish. Not many ppl used to care because even poor headphones can sound much clearer than a poor room system. Indeed. Headphone loadings usually cause the amp output devices to work in class A and increase their gain thus boosting effective NFB and reducing all forms of distertion. Because only a tiny poofteenth if a an output voltage is required with phones, even with a noise reducing R divider present, phones can give a cleaner signal than any supplied to a speaker. There's a huge market for headphones now, although much of the top end is functionalist rather than functional. Within that market, a new generation of discerning audiophiles is emerging. Yeah, but ppl are crammed close to a PC in a bedroom, and room sound is always going to be worse, and then there are neighbours close by in small dwelings. And the vast majority are listening to MP3 crap and programme is pop, and much processed digital sound, and the number of audiophiles conceived in this process of crapology is very small indeed. Phone uses have always "been emerging" for 100Years, but real audio nutters want good room sound where the source is an analog recording of an acoustic instrument of singer, all without much processing. That ideal is virtually never the case, and whatmost ppl use for source recordings is digital in origin, so audiophiles then have to discern between crap digital and good digital, and its a never ending search for the perfect sound. Noise is the main problem to overcome, so I suggest all trannys are potted, and DC is applied to all heaters; an external PSU is a good idea. Even then, tube noise can be present. One should aim for noise to be less than 0.05mV, or 50uV. You may find this impossible achieve, but you get say 0.25mV. Well, a simple resistance divider across the 16 ohm winding, say 39 ohms plus 8.2 ohms will give mean the tube signal level will have to be about 6 times higher, but the R divider divides the noise down so SNR is improved by 6 times. Most headphone outlets on power amps and receivers have such a divider which allows tubes or transistors to see a high value load and hence give low THD, while being able to still give oodles of voltage for headphones. Noise is indeed the biggest...actually the only...problem to be overcome. I'll start with as much as possible and then reluctantly add bits until the noise is gone. That way I'll know what I can't hear. Say you have a typical 2mV of noise across the 16 ohm winding from a pair of EL84 in triode. If you just connect phones to speaker terminals, that 2mV is clearly audible. In fact, strapping headphones across speaker terminals of any amp is a good way to monitor noise from a power amp and discern what it might be, ie, mains harmonics, or just hiss, or rectifier pulses, or all 3. I like to see less than 0.05mV of phone noise, so noise at 16 ohms should be reduced to 0.5mV, then a 10:1 resistance divider used. The audible noise within the measured 2mV may be a lot less than 2mV, typically 0.5mV at 16 ohms. So you can usually get way with a lower R diver ratio. The phones amp I built for my customer in 2009 is fully integrated, has hi & low level outputs, and can be used as a normal preamp with superb performance. A lot of ppl try to avoid OPTs in phone amps while insisting on tubes to give OTL type of power. Its not good practice, but a pair of complementary source follower mosfets could easily be used with a +/- 12V supply and Ia at 0.5 amps, and then one drives both gates from a C&R coupled triode of some sort. The secret is to have the voltage amping done linearly, and also the current amping, and class A mosfets in source- foll mode will be remarkably linear, even if the phones are 4 ohms. 6AS7 with a PP OPT would also be OK. But once you go to tubes and OPT, the OPT allows a normal amp to be made, and loading and linearity becomes much better than without OPT. That's why I'm using an OPT. Otherwise, Nat Semi does a very nice headphone buffer chip and I wouldn't need valves at all. Opamps OPA234 plus a couple of source follower mosfets in class A and a loop of NFB will also sound well, but it could be argued the SS will omit the spirit of the music....... Patrick Turner. |
#21
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
"Patrick Turner" wrote in message ... Opamps OPA234 plus a couple of source follower mosfets in class A and a loop of NFB will also sound well... Alex: Are you serious? OPA234 with only 350kHz unity gain bandwidth and only 0.2V/us slew rate is simply not suitable for Hi-Fi audio. LM358 which costs under 10c will "sound" even better. |
#22
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
On Mon, 12 Dec 2011 23:05:24 +1100, "Alex Pogossov"
wrote: "Patrick Turner" wrote in message ... Opamps OPA234 plus a couple of source follower mosfets in class A and a loop of NFB will also sound well... Alex: Are you serious? OPA234 with only 350kHz unity gain bandwidth and only 0.2V/us slew rate is simply not suitable for Hi-Fi audio. LM358 which costs under 10c will "sound" even better. Alex, could I ask a favour? Will you restore your newsreader's attribution settings to their default. The way you have it right now threads are screwed and impossible to follow the moment you post. Thanks Don |
#23
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
"Alex Pogossov" wrote in message ... "Patrick Turner" wrote in message ... Opamps OPA234 plus a couple of source follower mosfets in class A and a loop of NFB will also sound well... Alex: Are you serious? OPA234 with only 350kHz unity gain bandwidth and only 0.2V/us slew rate is simply not suitable for Hi-Fi audio. LM358 which costs under 10c will "sound" even better. Hi Alex: Patrick must have meant OPA2134. Best Regards: Doug Bannard |
#24
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
"Doug Bannard" wrote in message m... "Alex Pogossov" wrote in message ... "Patrick Turner" wrote in message ... Opamps OPA234 plus a couple of source follower mosfets in class A and a loop of NFB will also sound well... Alex: Are you serious? OPA234 with only 350kHz unity gain bandwidth and only 0.2V/us slew rate is simply not suitable for Hi-Fi audio. LM358 which costs under 10c will "sound" even better. Hi Alex: Patrick must have meant OPA2134. Best Regards: Doug Bannard This op-amp is a really good one! |
#25
Posted to rec.audio.tubes
|
|||
|
|||
Bartolomeo Aloia BA211
Someone said, in my defense......
Patrick must have meant OPA2134. Best Regards: Doug Bannard This op-amp is a really good one!- Indeed. I did in fact mean the OPA2134PA. I used some to make a very low THD oscillator this time last year. I got 0.001% at 5Vrms at 1kHz, an improvement over what I had been using. I spent a month being unwell then, and I used that unwell time to farnarkle with non pay dirt activities such as re-making a wien bridge oscillator. The OPA2134PA is listed at Jaycar electronic stores for $8.95. Its described as a "Audio high performance op-amp". But I cooked two to death very easily. But ya gotta let smoke out sometimes, even though smoke won't go back in, to be able to learn by doing. Patrick Turner. |
Reply |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
WTB Neve T1530 or BA211 | Pro Audio |