Home |
Search |
Today's Posts |
#1
|
|||
|
|||
Phase splitter w/ no name
Gentlemen,
here is a link to a corrected schematic and article using that "phase splitter with no name" (in German, though): http://www.jogis-roehrenbude.de/Roeh...unktechnik.pdf The 1M pot, according to the text, indeed is for adjusting the drive voltages to the output stage to get maximum 2H cancelation. Tom -- The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth. - Niels Bohr |
#2
|
|||
|
|||
Hi Tom ,
Looks like a Mullard paraphase splitter with an extra C to me .... Ronald . "Tom Schlangen" schreef in bericht ... Gentlemen, here is a link to a corrected schematic and article using that "phase splitter with no name" (in German, though): http://www.jogis-roehrenbude.de/Roeh...unktechnik.pdf The 1M pot, according to the text, indeed is for adjusting the drive voltages to the output stage to get maximum 2H cancelation. Tom -- The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth. - Niels Bohr |
#3
|
|||
|
|||
http://www.jogis-roehrenbude.de/Roeh...unktechnik.pdf The 1M pot, according to the text, indeed is for adjusting the drive voltages to the output stage to get maximum 2H cancelation. You could almost think of the inverter tube as a sort of op-amp circuit. The 100K resistor from the plate of the first triode feeds via the coupling cap the "inverting input" (grid) and continues on thru the 180K and the trimpot to the "op-amp output" (plate). The load on this plate is around the parallel value of the plate resistor, the feedback resistor, and the grid resistor of the output tube. About 25K. The open loop gain of this stage is around 21, with the cathode resistor of 1200 ohms. SO the "virtual zero" at the "inverting input" will see about -1/21 of the output signal. The trimpot can boost the gain a bit to compensate for this, to get a closer inversion of a gain of -1. |
#4
|
|||
|
|||
On Thu, 10 Feb 2005 05:31:42 +0000, robert casey wrote:
http://www.jogis-roehrenbude.de/Roeh...unktechnik.pdf The 1M pot, according to the text, indeed is for adjusting the drive voltages to the output stage to get maximum 2H cancelation. You could almost think of the inverter tube as a sort of op-amp circuit. The 100K resistor from the plate of the first triode feeds via the coupling cap the "inverting input" (grid) and continues on thru the 180K and the trimpot to the "op-amp output" (plate). The load on this plate is around the parallel value of the plate resistor, the feedback resistor, and the grid resistor of the output tube. About 25K. The open loop gain of this stage is around 21, with the cathode resistor of 1200 ohms. SO the "virtual zero" at the "inverting input" will see about -1/21 of the output signal. The trimpot can boost the gain a bit to compensate for this, to get a closer inversion of a gain of -1. So, is that why the 100k is there and why 0.5 has been chosen for the coupling cap? Low input impedence into the "virtual ground"? -- Mick (no M$ software on here... :-) ) Web: http://www.nascom.info Web: http://projectedsound.tk |
#5
|
|||
|
|||
"mick" So, is that why the 100k is there and why 0.5 has been chosen for the coupling cap? Low input impedence into the "virtual ground"? ** The "virtual ground" point is at the conjunction of the 100k, 180k and 1M trim. The 0.5uF simply cap drives a 1 Mohm load with a -1dB point at 1 Hz. ................ Phil |
#6
|
|||
|
|||
Tom Schlangen wrote: Gentlemen, here is a link to a corrected schematic and article using that "phase splitter with no name" (in German, though): http://www.jogis-roehrenbude.de/Roeh...unktechnik.pdf The 1M pot, according to the text, indeed is for adjusting the drive voltages to the output stage to get maximum 2H cancelation. The schematic above includes grid coupling cap. The pot isn't there to get lower 2H from the phase inverter stages themselves. That is impossible. Whatever 2H is produced by the first half of the phase inverter is fed into the second stage of the inverter. This second and entirely separate stage has a shunt FB loop of which the 1M pot is a part, and its purpose is to equalise or otherwise adjust the amplitude of the two phases. But by varying the drive to each PP output tube 2H of the output stage can be nulled to its low as possible level and inclusding nulling the 2H from the inverter/input stages. But you'd need thd meter and CRO to achieve all that, and I bet trying for maximum 2H cancellation at 1 watt wouldn't mean you'd get good cancelation at 3 watts, or 20 watts, because the rate of increase in 2H is quite different for the stages involved. The idea of driving one output tube harder than the other to cancel 2H isn't my cup of tea. A better solution is to use an LTP, with low 2H in the first place, and perhaps better output tubes, with lots of class A and 30 watt class A capacity, and UL or CFB or triodes, and with that sort of kit there is never any thd to worry over at normal levels. Patrick Turner. Tom -- The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth. - Niels Bohr |
#7
|
|||
|
|||
"Patrick Turner" But by varying the drive to each PP output tube 2H of the output stage can be nulled to its low as possible level and inclusding nulling the 2H from the inverter/input stages. But you'd need thd meter and CRO to achieve all that, ** Have you never done just with a 600 Hz frequency sine wave, a dummy load and tuned it by ear ?? I mean by listening to the faint OT sing and tuning the drive for least 2H. .............. Phil |
#8
|
|||
|
|||
On Thu, 10 Feb 2005 20:42:16 +1100, Phil Allison wrote:
"mick" So, is that why the 100k is there and why 0.5 has been chosen for the coupling cap? Low input impedence into the "virtual ground"? ** The "virtual ground" point is at the conjunction of the 100k, 180k and 1M trim. The 0.5uF simply cap drives a 1 Mohm load with a -1dB point at 1 Hz. Thanks. :-) -- Mick (no M$ software on here... :-) ) Web: http://www.nascom.info Web: http://projectedsound.tk |
#9
|
|||
|
|||
Phil Allison wrote: "Patrick Turner" But by varying the drive to each PP output tube 2H of the output stage can be nulled to its low as possible level and inclusding nulling the 2H from the inverter/input stages. But you'd need thd meter and CRO to achieve all that, ** Have you never done just with a 600 Hz frequency sine wave, a dummy load and tuned it by ear ?? I mean by listening to the faint OT sing and tuning the drive for least 2H. .............. Phil Not in hi-fi amps with FB. I don't claim to be able to hear 2H that is usually below the theshold of my hearing ability to detect such things, even with a speaker connected with a lot of series R and across a dummy load. But on the odd occassion when farnarkling with some amp and with biasing, I have had a speaker connected and plainly heard the distortion kick in when there has been some frightful fault. Most amps have NFB and any 2H (or 3H) present that is audible at any level means that the open loop 2H (or 3H) must be horrendous, and something must be wrong with the amp. I usually rely on the test gear to tell me all about what's wrong. Usually, the 3H is the most dominant harmonic in PP amps at all levels but there is always some 2H in a tube PP amp, unless the circuit is balanced throughout, and has no SE triode stages, and the balanced tubes, including the outputs, are matched fairly closely. In a pair of Quad II amps I worked on last year, I was able to get the thd down by up to 15 dB just by swapping positions of the KT66 and EF86. Finally at about 2 watts, the thd was about 0.05% or a lot less, and one doesn't hear such levels of 2H and 3H. And this was after biasing the tubes for class AB, with separate RC cathode bias networks. Full class A would have made only a marginal difference. Class AB amps can produce considerable 2H if the output tubes are old, or unmatched, and especially at high levels, and where the power in the +ve and -ve peaks differ considerably. Class A PP triode amps can be routinely made to produce 0.1% thd at 20 watts with a pair of KT88, and some NFB. At a watt, they usually measure 0.025%, since thd reduces approximately with output voltage. That's not something that hits you in the ear very hard. If it was 7th harmonic, then the amp might be in trouble, and the music....... Patrick Turner. |
Reply |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Using power triode or power pentode wired as a triode as a split-load phase splitter tube? | Vacuum Tubes | |||
Using power triode/pentode wired as triode as a split load phase splitter tube? | Vacuum Tubes | |||
Doppler Distortion - Fact or Fiction | Pro Audio | |||
Transient response of actively filtered speakers | Tech | |||
CCS for Mullard phase splitter | Vacuum Tubes |