I have a bit too much gain in my system, so I need to reduce the output of my pre. I'm new to tubes, so I was thinking I'll just ask. Is there any way to successfully add NFB to this circuit?
NFB??? Why?
BTW this stage "gain" about 0.6, so if you want to decrease its would be better do it in the previous stages ... or use resistor divider on input (if it possible: depends of previous stage).
BTW this stage "gain" about 0.6, so if you want to decrease its would be better do it in the previous stages ... or use resistor divider on input (if it possible: depends of previous stage).
Because this design's gain is quite more than just 0.6!
One could increase the value of R23 and put a resistor from the output to pin 7. This also would cure the issue of the lacking 1st triode grid leak.
Best regards!
One could increase the value of R23 and put a resistor from the output to pin 7. This also would cure the issue of the lacking 1st triode grid leak.
Best regards!
Increasing R25 value decrease the output volume.... if the previous stage hasn't DC on its output, but has resistor as grid leak of V1b.
Is the problem the too high gain or the hiss?
If the later, try to temporarily remove R23 and shorting V1b grid to ground.
If the hiss ceased, the problem is in the previous stage.
If the hiss remains, possible the V1 tube "hissing".
BTW both channel hissing?
If the later, try to temporarily remove R23 and shorting V1b grid to ground.
If the hiss ceased, the problem is in the previous stage.
If the hiss remains, possible the V1 tube "hissing".
BTW both channel hissing?
Yes, both channels hissing. I don't have hiss with my ss preamp with similar gain, so I assume it's the tube. The hiss is the main issue. Lower gain will just be an added benefit. Reducing the gain with -10 dB would be good.
The problem is that my speakers are 110 dB/W and the power amp is 29dB gain. I reduced the output voltage from my dac IV so it works with overall volume. But any noise from the pre will be very audible.
The problem is that my speakers are 110 dB/W and the power amp is 29dB gain. I reduced the output voltage from my dac IV so it works with overall volume. But any noise from the pre will be very audible.
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Try to swap V1 and V2.
If you don't eliminate the problem at the source, but -for example- decrease gain, you are only making a pretence.
If you don't eliminate the problem at the source, but -for example- decrease gain, you are only making a pretence.
It's not a faulty tube. I tried switching them. Same hiss. I also switched from the standard tube to NOS Siemens tubes, and it helped a little. The Siemens tubes are less noisy, but it's still too much.
If I add a feedback resistor, that would also reduce hiss on the output, right?
If I add a feedback resistor, that would also reduce hiss on the output, right?
Please put the voltage on each electrode
Just to understand the working point
Walter
Eliminating C18 & C17 should drop the gain a couple dB. Don't know why C17 is there anyway? R24 isn't needed either.
jeff
jeff
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To calculate the NFB, one first has to guesstimate the open loop gain, which mostly is defined by the 1st triode's gain. Sorry, but I don't have spare time to do that ('cause it isn't my own project, obviously...). Then you need to calculate the voltage divider resistor values accordingly. Anyway, remember that as in any inverting amplifier design the previous stage's output impedance needs to be as low as possible, optionally the input resistor needs to be matched.
Best regards!
If the values are correct in the schematic (pF), then they do nothing for the audio range.
To use the feedback you need to take the signal form anode of second stage , so this means that you need to change the configuration completely. The FB signal must be in phase with input and sent it to Rk that it isn't bypassed.
But you haven't sent the voltage reference on each electrode
The two cap in input do nothing in audio band, can be omitted
Walter
