Salas, Good find.
That could very well be the cause, my raw capacitance in the LCLC is only 10+30 uF so it races down immediately with a current drain of 65 mA.
Would a diode work as well? Cathode to the plus, anode to C2&R9 node? That is how I would solve it. I must try it tomorrow.
albert
I added the pre-regulator. (Fet with a 180k/4 uF filter; guarded with a reverse diode over the 180k). That is absolutely silent. Dead flat.
Still some reg-output flutter.
I think the reason is there is a loose connection in an amplification stage: the output jumps once in a while and the regulator voltage drops a little as response, just a little later.
Oh my. Having to revisit all solder joints ..
albert
Still some reg-output flutter.
I think the reason is there is a loose connection in an amplification stage: the output jumps once in a while and the regulator voltage drops a little as response, just a little later.
Oh my. Having to revisit all solder joints ..
albert
I will test with external 10k, 20 watt types (no output): one or two parallel.
Then I will detach the stages one by one (though I know it is not the input stage) but the problem starts at the second one (6SL7).
As regards semi's, a joint with different solder type might also be a problem. I have Sn-Ag 2% solder (from China, I bought it my self at a main distributor), but I found it is excellent for first soldering, once you rework it, it breaks apart (no flux left or so). This is just mine conjecture and I have not heard others talk about this strange phenomenon.
I am listening now to the RIAA stage: nice, lively. The 'noise' is far in the background and more or less disappears referenced to normal listening after half an hour. I also note the voltage goes up a few volts in this time period.
albert
Yes, I have 2n7 (mica) rail decoupler caps on input board and I have 5 uF that is the point where all the power comes from.
- Should I take out all caps? Or put a 4 ohms on this point?
- Issue is that I saw that the noise spectum rises with a 20 kHz signal and no caps . .
A trace with 500 Hz out to show the regulation (a few days ago) just input stage. Regulation trace is on 2 mV/cm. 4 volts out pp. Not bad really!
So no 5 uF yet connected.
The the current situation (indeed with 5uF):
and non periodic it is:
It sags in a non-periodic timeline.
I took out tubes and it got better (that is: less frequent bumps). This is with only the first stage, one line is power out the other the preamp out, both 10 mV/cm. The noise comes from the regulator.
My board:
I am now replacing the jFET (went from BL to GR), and will take out the 5uF.
Update: Replaced the jFET
Last evening I stopped the vinyl, these background subsonic ticks were nerve-breaking!
I relistened today - worse in fact.
As the pictures show I had it all right at first, but while I readjusted for a higher voltage out, the problems started to occur: I tried various LCLC combinations, this must have caused some harm somewhere.
Oh well, after days of tinkering I'll go more traditional.Then next week I will recheck the shunt PCB on the lab supply.
albert
Salas,
I have 3,9 ohms and 1,2 uF. I thought this would be an adequate value. I understand the Zobel component values are very critical then. Probably it also depends on the shunt device transconductance (mine has a lower S - 3.9 versus 4.9 for the IRF840).
I have 3,9 ohms and 1,2 uF. I thought this would be an adequate value. I understand the Zobel component values are very critical then. Probably it also depends on the shunt device transconductance (mine has a lower S - 3.9 versus 4.9 for the IRF840).
- could I isolate the amp with an inductor, 200 ohms, 2 Henry, then 220 uF electrolytic and 5 uF MKP?
[/LIST
I tested it, it works, but I saw the electrolytic introduces its own noise spectrum!
Thanks for the support.
albert
I think I found out the reason for my persistent problems, problems that got worse and worse: one of my 6SL7's heaters was breaking down. It is now dead - though I measure a resistance on the tube, as soon as I apply a current it pops open and there is no current any more 
In fact not true 6SL7 but the russian 1578. I had them in series & with DC even though it was slow start.
I think: This caused the non-systematic drops in heater current and voltage sags.
I now have old ECC35 in the circuit, though a lot more noise, well sounding.
Have to revisit the heaters first of all though .... think I will go current source. Then restudy the Salas SSHV1
In fact not true 6SL7 but the russian 1578. I had them in series & with DC even though it was slow start.
I think: This caused the non-systematic drops in heater current and voltage sags.
I now have old ECC35 in the circuit, though a lot more noise, well sounding.
Have to revisit the heaters first of all though .... think I will go current source. Then restudy the Salas SSHV1
I am putting together a 26 preamp with transformers I have on hand, and I need to drop about 40V. Should I drop before the SSHV reg or use the reg to drop that much? Will it make the board too hot? Will a higher output impedance affect the performance of the reg?
Will order a better rated transformer but it would be nice to use what I have on hand for now.
Thanks
Charlie
Will order a better rated transformer but it would be nice to use what I have on hand for now.
Thanks
Charlie
Last edited:
