Since you have a good alternative for the weak NoDAC as output stage, I suggest you don't go modify the 6V6 to noNFB max gain before you install in it a good quality volume pot so you also test it as a line preamp for all your sources first. Has proper gain for line preamp use as it is with NFB resistors.
Hi, I've just finished making the preamp with AZ1 as rectifier tube and final stage on the power supply as suggested by Elvee. The sound that comes out is wonderful but from the beginning I came across a perpetual hiss that grows when turned on and then tends to stabilize.
I tried various tricks but they didn't work: I didn't take measurements but it doesn't seem like ground loop noise or insufficient PSU filtering.
The noise seems to increase with the potentiometer (power amp) and with the shorted inputs it doesn't change, any suggestions about it? I thought it might be D.H. rectifier (used in hybrid mode with pair of diodes).
I tried various tricks but they didn't work: I didn't take measurements but it doesn't seem like ground loop noise or insufficient PSU filtering.
The noise seems to increase with the potentiometer (power amp) and with the shorted inputs it doesn't change, any suggestions about it? I thought it might be D.H. rectifier (used in hybrid mode with pair of diodes).
Trouble shooting is one of two things:
1. Troubleshooting with a correct schematic in hand.
Please post your schematic, Some of us are not going to read through 4,604 posts in order to find what version of that preamp you are using.
Thanks!
2. A Blindfolded Archer shooting arrows and trying to hit the target.
1. Troubleshooting with a correct schematic in hand.
Please post your schematic, Some of us are not going to read through 4,604 posts in order to find what version of that preamp you are using.
Thanks!
2. A Blindfolded Archer shooting arrows and trying to hit the target.
My experience says most hiss like you describe is caused by oscillations. See if the hiss goes away if you short the input grid to ground? The other time I've encountered that type of noise, it was caused by heater cathode leakage.
See if and what kind of noise is in the B+ line before and after that series reg. A 20MHz bandwidth limited scope will help you do that.
Looks like the regulator oscillates. Stable is a continuous featureless line as a goal. The channel output looks noisy for 50mV vertical. Random noise, that's the hiss.
Hi Salas, you are right. Beyond other hypothesis I had this suspect me too, and you confirmed.
In fact just replacing the regulator with a plain R-C filter (1k-220uF) the preamp is silent. What was wrong with the SSR suggested by Elvee? I followed his schematic, I changed only the Zd (I had that value) and the lower resistor network...
In fact just replacing the regulator with a plain R-C filter (1k-220uF) the preamp is silent. What was wrong with the SSR suggested by Elvee? I followed his schematic, I changed only the Zd (I had that value) and the lower resistor network...
I don't know the inner workings of his circuit. I could try guess but better not since the author is a reachable member. You let him know and he probably has a solution.
Yes, it's just as you say. Being not me the creator of that circuit I don't know actually what's wrong.
Waiting for Elvee's reply meantime, since I have Maida populated PCB set in a drawer could be fine to re-use it in the preamp?
Waiting for Elvee's reply meantime, since I have Maida populated PCB set in a drawer could be fine to re-use it in the preamp?
Maida has been applied before in the 6V6 preamp with success. Mosfet Maida version it was. Try it since you have it, why not. Compare the sound and background noise to your silent enough simple RC filter solution too.
By the way how much headroom you have for regs? Vin-Vout I mean. Also, got a picture of your build? Lit up AZ1 rectifier is nice to look at especially if mesh plate.
The ΔV between the regulator and the previous LC filter is about 70V (from 375 to 305-310).
Ok gladly, as soon as I post the picture although is not fully completed (it lacks the 3P4T rotary switch to be wired and assembled).
Ok gladly, as soon as I post the picture although is not fully completed (it lacks the 3P4T rotary switch to be wired and assembled).
Can you show the modified schematic, and post a picture of the physical build?
This regulator has been tried by a number of members, and is normally not very demanding
