I have a few single 12AX7/ECC83 tubes from various manufacturers, so I was wondering if there are any good designs than use only one single tube for a stereo preamp. I don't need a lot of gain, if any, just a simple circuit with one triode system per channel.
A search didn't bring up much, and the only circuit I know of that does use a single 12AX7/ECC83 for stereo is the Grundig CS200 tuner's output stage. There must be more. I attached a pic of said output stage and the pdf with the full circuit.
Can anyone point me to other schematics using a single 12AX7/ECC83 for a stereo preamp?
A search didn't bring up much, and the only circuit I know of that does use a single 12AX7/ECC83 for stereo is the Grundig CS200 tuner's output stage. There must be more. I attached a pic of said output stage and the pdf with the full circuit.
Can anyone point me to other schematics using a single 12AX7/ECC83 for a stereo preamp?
Attachments
I did post a design using a pair of 12AX7A/ECC83 for a line stage here sometime in the not too distant past. Might try searching for it. (Line stage thread or similar)
Low gain and single ECC83 do not go together too well, as it is a high gain valve. There are basically two ways to get low gain from this valve:
1. use a low anode load, and accept the distortion you get - maybe OK for a guitar effects box.
2. use lots of negative feedback, so you will get low distortion until you get near the clipping threshold - a carefully designed anode follower might work quite well.
1. use a low anode load, and accept the distortion you get - maybe OK for a guitar effects box.
2. use lots of negative feedback, so you will get low distortion until you get near the clipping threshold - a carefully designed anode follower might work quite well.
It also depends of your amplifier.. If it have low input impedance, you may need buffer, so it means one double-triode per channel.
I don't think that the amp's input impedance will be a problem, my mini Aleph has around 220k I'd guess.
Distortion I can live with, since I'm simply looking for a fun project for these unpaired 12AX7 tubes.
I'll dig out some tube literature, maybe I can cook up something...
Distortion I can live with, since I'm simply looking for a fun project for these unpaired 12AX7 tubes.
I'll dig out some tube literature, maybe I can cook up something...
I followed this schematic from a K-5 tube preamp.
Swap some resistors and stuff since this is a 5670 tube. Also, remember C5=22uF otherwise you`ll get no stereo. Dont ask me why, it`s just the way it is.
An externally hosted image should be here but it was not working when we last tested it.
Swap some resistors and stuff since this is a 5670 tube. Also, remember C5=22uF otherwise you`ll get no stereo. Dont ask me why, it`s just the way it is.
With high output impedance this is a good example of how not to design a line stage. Simply changing the cathode resistor to change gain is rather crude, as it will also significantly change the bias point - with a range from 100 to 8.2k they can't all be near optimum. Omitting C5 gives a little cross-talk between channels.
I don't quite get the logic of single tube. Is it because you don't have pairs of tubes from the same manufacturer? You can do multiple tubes with each tube doing left and right rather than separate tubes for each channel.
Hi
What changes to the schematic are required if I use tube 5670 instead of the tube ecc82?😕
The output impedance of the preamplifier to be <1kOhm and gain <10dB.
thank you and cheers!
You need to use two triode halves. With only one, your specification can not fulfilled.
First triode could be normal voltage amplifying stage and the other cathode follower.
The gain and low output impedance can be achieved with negative feedback from the cathode follower to the grid of first triode.
First triode could be normal voltage amplifying stage and the other cathode follower.
The gain and low output impedance can be achieved with negative feedback from the cathode follower to the grid of first triode.
Can someone tell me why it is essentiall to have C5 present? If it is removed I have no stereo. I dont understand that.
C5 creates a solid DC/AC rail. Without it both channels modulate through R7 voltage drop resistor and it needs to be considered in the gain calculations of both sides.
Recommend 2 dual triodes for more flexibility cathode follower, SRPP etc... with lower output impedance.
Recommend 2 dual triodes for more flexibility cathode follower, SRPP etc... with lower output impedance.
With only one tube you can use mosfets. TubeCad is a great program to sim preamp stages. An 12ax7 anode follower might sound pretty good, I have to experiment with anode followers. Not enough time.
C5 and R7 are part of the supply voltge filtering and both components can be omitted if the supply voltage is already clean.
If you omit just C5 you still have stereo amplifier, but with slightly reduced crosstalk between channels, still more than sufficient.
Hi, I’d like to build model L stereo tube preamplifier using one 5670 tube. I heave question about biasing. I see on schematic that it is using gain resistors R3, R6 from 100R to 82k. I wonder if I could use variable resistors (2w) instead and than bias it? My suply voltage is aprox. 211VDC. If a’m corect plate dissipation on 5670 should be 1,35 watts? I could measure plate voltage and voltage drop across "gain" resistor and then calculate value of "gain" (bias) resistor? Does that sounds right? What do you think gain resistor should be aprox?
Classic Valve Design - Dynaco Clone and Original Design Boards
This is a single tube line stage. You can make a stereo line stage with just
one 12AX7.
If you prefer octal tubes, you can also use 12SL7 instead of 12AX7.
Just one 12AX7 is reguired.😕
( but also two bibolar transistors, two NFETs and 5 zener diodes plus huge amount of resistors and capacitors )
That circuit has nothing in common with any Dynaco.
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