Yet Another Phono Stage Suggestions Thread

[revintage]

What's odd about the operating point of the 6GK5?

Another odd thing is that it does not show the working point of your amp that you said where 120V, 12mA!

100V, 10mA is good but does it take CCS loss and load in consideration?

So assuming the CCS isn´t lossless and that you have a frequency depending load I still consider your initial figures odd.

When adding the current sink as I suggested, maybe you could add a low-DCR choke and a cap on top for filtering to get less voltage loss. But your CCSd shunt will of course work.

[dsavitsk]

Originally posted by revintage
Another odd thing is that it does not show the working point of your amp that you said where 120V, 12mA!

100V, 10mA is good but does it take CCS loss and load in consideration?

So assuming the CCS isn´t lossless and that you have a frequency depending load I still consider your initial figures odd.

Not sure I follow you exactly. B+ is about 155V or so. The CCS sets a current and the bias resistor sets a plate voltage. The CCS drops the volts it needs to. The curves for the second tube suggest it should be at around 100V. In actuality, it is closer to 120V. But, this still gives a 35V drop across the CCS which is plenty.

One point of the CCS is that the plate voltage, and in fact B+, can be largely ignored other than being sure it is reasonable. B+ of up to 300V would be fine here -- 300V is the limit of the transistors I used. (The other advantages are the high load for the tube, the drastic reduction in ripple which makes the raw power supply almost incidental, the easy control over the circuit, the reduced B+ requirements, and that the PS caps are isolated form the signal current path.)

Originally posted by revintage
When adding the current sink as I suggested, maybe you could add a low-DCR choke and a cap on top for filtering to get less voltage loss. But your CCSd shunt will of course work.

I think the CCS works better here. The PS is really noisy so the regulator does a world of good.

[dsavitsk]

Finally got this in a usable way. I replaced that final cathode resistor with a CCS. Not sure I am enamored with the change, but I'll listen for a while. Overall, seems to work pretty well. Most of the parts in the build were scavenged, or left overs from other projects -- I bought the 6GK5's (at Eli's suggestion) and the filter caps.

The PS is a generic CLC. It uses a toroid in Poinz's clever configuration for HT. The heater supply is a basic LM317 (LT1084 actually) with a switch to swap between 6.3 and 12.6V operation. It gets used as a raw supply for various lowish voltage projects.

A final schematic and a few pictures:

[felixx]

Nice.How it looks the ccs's exactly?

[SY]

It will not surprise you to know that this is extremely close to the phono stage I use.