His Master's Noise: A Thoroughly Modern Tube Phono Preamp

Not sure what you mean, Sheldon.

The high Miller capacitance of the input tube means that, first, the transformer will not be easily de-ringed with a 47k load, and second, the cartridge will not be happy because of the high input C. Dropping the 47k resistance to get the ringing out will make the cartridge even unhappier.

Moving coils are much better about load capacitance and resistance.
 
I see the problem now. I was referring to the strategy of applying various loads to either side of the transformer. I've seen some discussion of that before. However, that was with MC step up transformers and may not be useful at 1:1. But, maybe with a modest step up. And maybe playing with series resistance?

Sheldon

On further reflection, and fiddling with the numbers, I see the problem more clearly. Already in the range of typical load capacitance with just the input grid and other connections. Adding in a transformer will be tough. On the other hand, the higher output of most MM cartridges makes the balanced input less significant, as far as noise goes. I guess one could use an FET based balanced to single ended converter, but I'm not sure it's justified.
 
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Very nice SY ;) I see your comments that you made on a thread here came to fruition (might have been the bybee thread) where you mentioned a way of getting around the input noise issue. I can see how did it now. In fact in just the same way as has been mentioned in an article on "Grounding" i was reading earlier. Balanced - unbalanced, thus one input device & lower noise, neat!

Now if only my MC cartridge worked on both channels....
 
Thanks for posting this SY, great article and you are dead right about balanced line for the cartridge signals. Most arms have that anyway - with a separate earth lead for the arm. One just needs an isolating RCA socket on the pre-amp and most setups would not need modding.

Except mine as it is an old RB300, but that needs modding anyway!
Useful to see the current sources too with the 1k resistor - they should be good for 400V I think which makes them useful perhaps in my Sweet Peach FU50 driver circuit too....

Now to save up for the input transformers ;)
 
".... a common-mode choke will make things even better, but I just didn't have one. If you do, feel free to use it."

I stumbled across this sentence and I'm wondering whether you mean:
"... use the common-mode choke instead of the dual regulator heater supply" or else: "... use the common-mode choke with the dual regulator supply, and if so where in your heater power supply?"

Well thought out indeed!
 
The spec sheets I have don't give much info about triode operation. It does look like the gain is lower, as is the transconductance. Since the source impedance of the first stage is critical to getting the RIAA right, you'd want to measure the plate resistance and adjust the 20k build-out resistor accordingly. For an operating point, I'd probably start with 10mA and 1.2V on the cathode.
 
Thanks SY, sounds like it may be worth trying then. Some triode data is here:

Tube Tester Files - 6J51P

6j51p_vah15.GIF


I'm still collecting the bits - I'll post back later when I've got a bit nearer!