Generally, if you have a 2-chassis construction, I would suggest that the chokes are mounted with the transformer, if possible. The chokes are unshielded, and can spill EM fields on to the signal parts.
The best way to check the 'umbilical' for risk of noise:
- model all of the power supply in PSUD2. The look at the peak-current into the capacitor on the signal-chassis. 100/120Hz capacitor-recharge current will cause coupling to other cables in the bunch.
1mA peak is probably OK, 20mA peak is probably enough to get some coupling, at a rough guess. You can try adjusting the balance of capacitance on the power chassis vs. the signal chassis, to get improvement.
If there are recharge-currents in the cable, twisting the +/- supply-pair is more effective than shielding, and twist the 'victim' cable-pair, too.
Shielding the cable pairs is needed, if there is voltage-noise (Ripple-voltage).
Signal Current:
Only A small capacitor on the signal chassis might mean that there is some signal-current in the B+ cable. A shunt-regulator is a good fix for this, since it makes the supply-current completely static dc.
But with low-current valves like the 26, this is unlikely to be a problem.
Peak? On HT I have min;max;diff;mean;RMS. Diff is 430.66n and RMS is 157.34n. So less than 1mA any way I read it?
1. Plot the value of (say) I(C3) if C3 is the cap on the signal chassis.
2. The current into this cap is the current in the cable.
3. Look at the plot of current I(C3), and check that it is stable - i.e. not still ramping up from power-ON. If not, increase the Reporting Delay.
4. Read the peak current as DIFF. (or just look at the plot to get a rough idea)
2. The current into this cap is the current in the cable.
3. Look at the plot of current I(C3), and check that it is stable - i.e. not still ramping up from power-ON. If not, increase the Reporting Delay.
4. Read the peak current as DIFF. (or just look at the plot to get a rough idea)
I've put the AZ1 meshplate back in, and somehow it reduces the annoying sibilance that the AZ31 seemed to emphasise. Oh well, I guess it stays then.I'm playing with the AZ31 now, and it's lively, but "splashy", if that makes any sense! Some people might prefer it, as some prefer pop over classical (for example, not a judgmental opinion), but not so much to my taste. Still, I'll leave it in for a bit and see if I appreciate it more when I'm sober!
I love valves, the way I can mess around with the sound. I just wish I was a bit cleverer and understood them more.
BTW, I should mention that this is with the 01A/gyrator, but I did experience very similar differences with the 26.
I wanted to build my preamp in one chassis only, but disregarding hum, the size and weight of it all was just too much. You need room to change parts and tweak the sound. I would say 2 chassis minimum or 3 smaller ones for signal, HT supply and Filament supply. You will not regret it if it is your first build. Trust me.
Thanks for the reply. I have the parts layed out
on a plywood board & it's not big & heavy. My only
concern is how to lay out the transformer & chokes
to prevent hum. What parts are you using that's making
it big & heavy ? Im going to use 3 chokes , first from
from rectifier then split Dc to 1 choke for each
channel. Will see how it turns out on the ply board
Thks again
on a plywood board & it's not big & heavy. My only
concern is how to lay out the transformer & chokes
to prevent hum. What parts are you using that's making
it big & heavy ? Im going to use 3 chokes , first from
from rectifier then split Dc to 1 choke for each
channel. Will see how it turns out on the ply board
Thks again
I use a mix of Weiss, Lundahl and Hammond. 3 power transformers and 5 chokes. Not that much but it takes up som real estate. At least mine does. The most important aspect in avoiding hum is the conctruction of the filament supplies, and that you have short leads from the rectifier to the first capacitor. I use choke input myself to avoid most of the hefty current pulsing.
Please load up some pictures when you are finished breadboarding so we can have a look at it.
Please load up some pictures when you are finished breadboarding so we can have a look at it.
You can trust me too! I now use 3 chassis for everything - signal, HT and filaments. Each to switch things around. We're all experimenters here.