Hello everyone.
I am looking for schematic for low gain tube preamp. I need it for inverting chipamp. I've built cathode follower,running from 180v, and I dont want to change feedback/input resistors for chipamp, so I think I could use grounded cathode -> my cathode follower. Or any other design, that can be used to feed inverting amp. I have only two 6n1p's left, so I think I could just use one double triode for a channel. As I understand, I cant use only grounded cathode stage, because it is not capable to drive low impedance load.
I am looking for schematic for low gain tube preamp. I need it for inverting chipamp. I've built cathode follower,running from 180v, and I dont want to change feedback/input resistors for chipamp, so I think I could use grounded cathode -> my cathode follower. Or any other design, that can be used to feed inverting amp. I have only two 6n1p's left, so I think I could just use one double triode for a channel. As I understand, I cant use only grounded cathode stage, because it is not capable to drive low impedance load.
Whether or not it can drive a low impedance load depends entirely on the tube chosen to do the job. 6DJ8/ECC88, ECC99, 5842, 5687, etc can do the job in anode follower configuration and will drive 10K loads if designed to do so.
If you are concerned about the phase inversion you can always swap the speaker connections to correct the inversion in the amplifier. Depending on the material being played the difference may be inaudible or not.. (And it's often arbitrary from recording to recording.) Something I would not worry about too much.
Well still I am not sure about the best way to set gain so low. Resistor dividers? Or maybe I could use some kind of "feedback resistor", from grid to output?
EDIT. I attached two schematics. 6n1p buffer which I am using at the moment, and second one I found I've made some time ago. As I remember, It had low gain, I am just unsure how appropriate it is.
EDIT. I attached two schematics. 6n1p buffer which I am using at the moment, and second one I found I've made some time ago. As I remember, It had low gain, I am just unsure how appropriate it is.
Attachments
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Ok, I found this one, with gain = 22 DIY 6922 / E88CC Tube preamp
As I have 180V power supply I have to recalculate anode and cathode resistor values, but to decrease gain I have to reduce plate load resistor, and to increase a cathode resistor? I am a bit confused with setting gain for tube preamps.
As I have 180V power supply I have to recalculate anode and cathode resistor values, but to decrease gain I have to reduce plate load resistor, and to increase a cathode resistor? I am a bit confused with setting gain for tube preamps.
What is the purpose of this stage? A chip amp will typically have a gain of 10-20 (20-26dB) so needs no voltage amplification before it. A chip amp is likely to have an input impedance of 10-20k, so doesn't need current amplification.
If you're trying to add distortion, then use a very low plate load resistor, which will also drop the voltage gain.
If you're trying to add distortion, then use a very low plate load resistor, which will also drop the voltage gain.
Well I wanted to reduce chipamp's distortion, so it haven't enough gain, and as this LM4780 is point-to-pointed, changing feedback resistors is not so easy now. So now I need a little voltage amplification, and I have heard that inverting gainclones sound better if fed with higher current signal. I could use simple opamp stage, but well, tubes look better, and they sound nice too.
Well I have nothing against "tube distortion" 
. Well lets just say I cant (dont want to) change amplifier gain settings, so I have to use preamp to amplifiy input signal. Also tubes introduce 2nd harmonics. I plan to use this just after music source. Just like common preamp. As I have 3 more LM4780 chips, with next one I plan to try http://www.tubecad.com/2011/02/06/Super Triode GKA.png
. Well lets just say I cant (dont want to) change amplifier gain settings, so I have to use preamp to amplifiy input signal. Also tubes introduce 2nd harmonics. I plan to use this just after music source. Just like common preamp. As I have 3 more LM4780 chips, with next one I plan to try http://www.tubecad.com/2011/02/06/Super Triode GKA.png
Ar4,
I don't want to rain on the parade, but if want to use inverting chipamp, you may just find it easier to use J-FET based buffer, like Pass (firstwatt) B1. If you really want make a hybrid amp, I see a tube being much better suited as a voltage gain element, and a solid state as a current buffer, (i.e. a follower, like Pass F4 amp).
I don't want to rain on the parade, but if want to use inverting chipamp, you may just find it easier to use J-FET based buffer, like Pass (firstwatt) B1. If you really want make a hybrid amp, I see a tube being much better suited as a voltage gain element, and a solid state as a current buffer, (i.e. a follower, like Pass F4 amp).
Maybe replacing the CF with an anode follower would do the trick. I took the OP to be saying that the gain of his chip amp is set lower to reduce the distortion of the chip amp and so now he needs a bit of gain to make it up. AF can set the gain pretty much anywhere below mu by varying the amount of FB and Zout should be pretty low too if any significant amount of FB is used.
Yes, plate follower could be uset for voltage gain, and I just think that I could use something like this Signal source -> Plate follower -> Cathode follower -> Chipamp
Cathode follower for low output impedance to feed chipamp. Still wondering if they (inverting ones) sound better with buffer or not.
Edit: I think I just failed at my previous statement, as plate follower also provide low output impedance. But in most of preamp circuits I've seen, there is cathode follower after voltage gain.
Cathode follower for low output impedance to feed chipamp. Still wondering if they (inverting ones) sound better with buffer or not.
Edit: I think I just failed at my previous statement, as plate follower also provide low output impedance. But in most of preamp circuits I've seen, there is cathode follower after voltage gain.
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