Didn't take time to look at the circuit. You are correct in that there is no control on the output. My mistake...
My advice to the thread poster is this....either use the circuit as designed or scrap the line stage and add a VC to the input of the amplifier.
Quote:
Some people only listen, not test or measure anything. That is their way to do amplifiers, but I would not call such process as developing.
artosalo
At one time I was anal like you are. I believed only in the distortion reading on my analyzer. I have two analyzers on my shelf. I would buy an amplifier (blown Up as a project) and rebuild it. Check its distortion and continue to work on it doing everything to lower its distortion even getting it lower than factory specifications. I finally realized there is a point where one cannot hear a difference even thou it is seen a a change in distortion on the analyzer. It took a while to realize that tubes will not deliver the lower distortion figures that SS equipment does. To me now days the ear is probably more important than the analyzer is is assessing how good a circuit does sound. I don't really know at what point a person can hear that distortion is present but have been told that its around 1% distortion. I would have to say after playing with tubes the last 9 years or so that that figure is probably correct for most people. If it sounds good then use it.
My advice to the thread poster is this....either use the circuit as designed or scrap the line stage and add a VC to the input of the amplifier.
Quote:
Some people only listen, not test or measure anything. That is their way to do amplifiers, but I would not call such process as developing.
artosalo
At one time I was anal like you are. I believed only in the distortion reading on my analyzer. I have two analyzers on my shelf. I would buy an amplifier (blown Up as a project) and rebuild it. Check its distortion and continue to work on it doing everything to lower its distortion even getting it lower than factory specifications. I finally realized there is a point where one cannot hear a difference even thou it is seen a a change in distortion on the analyzer. It took a while to realize that tubes will not deliver the lower distortion figures that SS equipment does. To me now days the ear is probably more important than the analyzer is is assessing how good a circuit does sound. I don't really know at what point a person can hear that distortion is present but have been told that its around 1% distortion. I would have to say after playing with tubes the last 9 years or so that that figure is probably correct for most people. If it sounds good then use it.
I do not look my distortion analyzer only. I make many other tests too. Including listening test, which is ofcourse the most important and gives the final answer.
Hello,
This is strictly my opinion.
The 6SN7 sounds better drawing more current than set up in the original circuit.
Also the 6SN7 plate resistor converts a change in current (due to grid input) to a voltage output. Lower the value of plate resistor and the gain decreases with it.
To get the current up to about 5 ma change the gain stage 6SN7 cathode resistor to about 600 ohms. To drop the gain to about 10 change the plate resistor to 25 K ohms. These changes also increase the gm and reduce the noise of the circuit.
A gain of about 10 is on the low side with a pot on the input works well.
If you are using a CD player or some other device with a output of near 2 volts I am with others here a passive or buffer (my prefrence) line stage is all that is needed.
DT
All just for fun!
This is strictly my opinion.
The 6SN7 sounds better drawing more current than set up in the original circuit.
Also the 6SN7 plate resistor converts a change in current (due to grid input) to a voltage output. Lower the value of plate resistor and the gain decreases with it.
To get the current up to about 5 ma change the gain stage 6SN7 cathode resistor to about 600 ohms. To drop the gain to about 10 change the plate resistor to 25 K ohms. These changes also increase the gm and reduce the noise of the circuit.
A gain of about 10 is on the low side with a pot on the input works well.
If you are using a CD player or some other device with a output of near 2 volts I am with others here a passive or buffer (my prefrence) line stage is all that is needed.
DT
All just for fun!
Arto,
Those are some very nice distortion figures. I would be curious as to the performance of your circuit when set to zero feedback. What is the gain and distortion of your circuit at zero feedback and Uo=10V?
Those are some very nice distortion figures. I would be curious as to the performance of your circuit when set to zero feedback. What is the gain and distortion of your circuit at zero feedback and Uo=10V?
With zero feedback this circuit is an ordinary differential amplifier or long tailed pair. The gain is then half of one triode. In this case some 23 dB.
The output impedance without NFB is essentially higer and thus same 10 k or 22 k load resistance can not be used, or if used, the distortion becomes quite high. If the load resistance is some 47k...100 kohms, then the distortion would be about 0,3...0,4 % with 10 Vout.
The output impedance without NFB is essentially higer and thus same 10 k or 22 k load resistance can not be used, or if used, the distortion becomes quite high. If the load resistance is some 47k...100 kohms, then the distortion would be about 0,3...0,4 % with 10 Vout.
OK. So according to your figures, if everything else was reasonably the same, the long tail pair at zero feedback has slightly less distortion (at same gain) than the simple amp, which already has some stage feedback from the unbypassed cathode. That sounds reasonable.
A typical long tailed pair phase splitter gives some 30 Vrms to 150 kohms load with 0,3...0,4 % THD. This with 350...400 V supply voltage.
With single triode amplifier the THD is higher.
However, some triodes with CCS at the anode will give even lower THD.
For example, russian 6S45P gave in one of my tests only 0,16 % THD when output voltage was 30 Vrms and Rload = 220 kohms.
With single triode amplifier the THD is higher.
However, some triodes with CCS at the anode will give even lower THD.
For example, russian 6S45P gave in one of my tests only 0,16 % THD when output voltage was 30 Vrms and Rload = 220 kohms.
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