Wow - I'm genuinely impressed at the HP engineer so may years ago who designed that PSU to gracefully operate whilst being hooked up inside-out like that. (I have one of those, BTW, they are awesome... 🙂 )
Please attach your green wire to the INSIDE + and -, take your output from the outside + and -, and attach your ground wire to either of those inside posts with the green wire. Leave both of the posts marked GND alone, as you already are doing.
Thanks - it's producing + and - 28v, can you explain the difference?
I'll take a stab at this. (Someone will no doubt correct me if I've got the wrong end of the stick.)
If the two power supplies are truly floating (ie: they use separate transformers or separate secondaries on a single transformer) then it won't make any difference. However, if they're not (ie: they use a split secondary), then the middle -/+ are already connected and connecting the outsides will short out the secondaries.
Always doing it the way 6L6 suggests means that you don't have to know which it is.
All my supplies are fully floating, but I can't remember if I specifically looked for that when I bought them or not. (Or maybe non-floating were more common "back in the day"?)
If the two power supplies are truly floating (ie: they use separate transformers or separate secondaries on a single transformer) then it won't make any difference. However, if they're not (ie: they use a split secondary), then the middle -/+ are already connected and connecting the outsides will short out the secondaries.
Always doing it the way 6L6 suggests means that you don't have to know which it is.
All my supplies are fully floating, but I can't remember if I specifically looked for that when I bought them or not. (Or maybe non-floating were more common "back in the day"?)
Well the unit seems happy either way, but it's now connected per 6L6 recommendation. Using this until I get around to a more permanent solution.
Edit - I just looked at the schematic and it shows only one side, with a note at the bottom saying everything to the right of the transformer is identical.
Edit - I just looked at the schematic and it shows only one side, with a note at the bottom saying everything to the right of the transformer is identical.
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Ha! Great example.
The secondaries are centre-tapped, but to select different voltage ranges rather than for the two sides of the power supply. Each side has its own (centre-tapped) secondary. 😉
The secondaries are centre-tapped, but to select different voltage ranges rather than for the two sides of the power supply. Each side has its own (centre-tapped) secondary. 😉
Do you choose 3.3 uF for C3 of BA-3 preamp as this links?
I will try your Capacitor branch and Elna Cimic as JeffYoung said.
Thanks for kindly sharing.
In a push-pull design the voltage the coupling cap is blocking is only the DC offset (ie: the difference between ground and the centre point of your push-pull). In an ideal world that would be 0 (and there would be nothing to block), but in practice differences between components (and in particular between complementary P and N pairs) means it can be a few volts.
The other thing to consider is what happens if one of your output MOSFETs fails. Depending on the failure mode the DC offset could rise to your + or - rail voltage.
So, even though the cap will normally only be blocking a few volts, it's best to spec it at your rail voltage. Since that's still well under 150V, the mentioned cap would be fine.
Cheers,
Jeff.
Many thanks for your detail explain. I'm a newbie. And this is my first DIY preamp, before that, I finished my first +_15V PSU ( Salas UltraBiB V1.3 ) for Allo Katana DAC. I'm glad to joining you guys DIY world.
I like one of Zenmod's favs, the Philips MKC very reasonable and sound very nice. Just ordered a bunch off Ebay in 1.0 and .1 uf for bypass duty.
Russellc
I'd like to put these for my Fisher tube amp in .047uF but all they have is 2KV - is there any disadvantage to using a 2KV cap to replace a 400v?
Hi, I kindly ask for information, having available 2 matched pair of K170 / J74 for 10.5 mA (of an old project), can I get lost or I have to change the value of the resistance? Thank you very much
I'm planning to use a Silmic II in C3 with a .1uf film. How do I orient the polarity of the Silmic? There is a + on the output side on the PCB, but the Pearl 2 schematic has the + sign on the circuit side.
output node (inner side - pre cap) of BA3 FE is approx at 0V , if you set so ....
next stage potential ( amp input) is presumably on same level
so - how you are going to orient Silmic is irrelevant
next stage potential ( amp input) is presumably on same level
so - how you are going to orient Silmic is irrelevant