I have lurked here for a long time and am posting for the first time. I hope you don't mind entertaining some very rudimentary questions. I have built lots of speakers over the years and a few electronics, both tube and solid state, from kits, but it has been a while. I have no EE background but I can solder and read a schematic and work on a circuit without going to the ER. I am working on educating myself on tube circuits, including reading Kevin O'Connor's book. I am hoping to build a preamp/phono from some off-the-shelf circuits I have already. I have both the preamp boards from Ken Stapleton. He specifies that the linestage requires 285/265/6.3 and the phonostage requires 285/245/6.3. I spoke with him fairly extensively over email (super nice guy, BTW) and he says for the 245 and 265 you can meet somewhere in the middle to power everything with one power supply.
I also have the tube rectifier power supply kit from John Broskie. I am not dead set on using this power supply, but I have it and it is much more approachable to me than building one from scratch. I'll attach his schematic below, but it is not my intellectual property to please let me know if that is against rules or etiquette. I am wondering if someone could please point me in the right direction of figuring out if this power supply would be appropriate and what transformer values I would need to get it there. I would like to use dc for the heaters, and I am very confused about how he is handling that since he shows considerably higher voltage for the heaters. Additionally, I'd like to know what to look for in a choke to use, but if appropriate that can be another thread. I still have some reading to do on that front.
Thanks, guys.
I also have the tube rectifier power supply kit from John Broskie. I am not dead set on using this power supply, but I have it and it is much more approachable to me than building one from scratch. I'll attach his schematic below, but it is not my intellectual property to please let me know if that is against rules or etiquette. I am wondering if someone could please point me in the right direction of figuring out if this power supply would be appropriate and what transformer values I would need to get it there. I would like to use dc for the heaters, and I am very confused about how he is handling that since he shows considerably higher voltage for the heaters. Additionally, I'd like to know what to look for in a choke to use, but if appropriate that can be another thread. I still have some reading to do on that front.
Thanks, guys.
I like John's thoughts but his products sometimes confuse me.
Since Stapleton's plan is based on the Marantz 7C why not steal the plan from the 7C?
Not, the B+ voltages are NOT critical. 200V would be increased THD. 400V would be increased heat. 250V-300V is the happy medium.
Since Stapleton's plan is based on the Marantz 7C why not steal the plan from the 7C?
Not, the B+ voltages are NOT critical. 200V would be increased THD. 400V would be increased heat. 250V-300V is the happy medium.
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I'm probably overstepping my valve expertise here, but doesn't the 100pF capacitor Grid to Cathode need to be changed to 47pF shunt to ground. Otherwise, won't the cartridge will only see a tiny fraction of that 100pF for its required load?
Cheers
Ehh .. now that I look closer at the feedback network, I'm probably wrong ..
Cheers
Ehh .. now that I look closer at the feedback network, I'm probably wrong ..
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Low pF grid to cathode is great at killing RF interference (because you are shorting a dangerous RF rectifier/detector diode) yet not loading source at Audio frequencies because it´s bootstrapped.
Grid to ground both loads source and does not guarantee avoidance of RF detection.
Grid to ground both loads source and does not guarantee avoidance of RF detection.
Doesn't the cartridge need/expect, have to have a capacitive load -- 47pF or 100pF or so -- for the proper, slightly peaked top-octave response?
Yes, the 100pFd cap is largely bootstrapped-out to maybe 10pFd.
No, we do NOT generally add capacitance. The design load of most phono is a few feet of coax (100pFd) plus the Miller of a high-Mu triode (about 100pFd). If the C is a little less than designed the error is usually benign: resonance a little high in F and Q a little low, both(?) going as square-root of C.