Voltage gain stage for Non-NFB MOSFET current amp

[gripracer]

I have a 2SK1530/2SJ201 class A/AB (adjustable) amplifier, that has unity voltage gain and no negative feedback.

I have attached the circuit for one mono side, power supply included.

What should I drive it with? I would like a discrete voltage gain stage, with as little feedback as possible.

Thanks!

[ra7]

How about that JFET BOZ?

[Steve Eddy]

Originally Posted by gripracer

I would like a discrete voltage gain stage, with as little feedback as possible.

How 'bout one with no feedback, highly linear, ultra low noise, outstanding common-mode rejection, can accept balanced and unbalanced sources, and has infinite PSRR?





se

[Gordy]

Try a single-ended parallel-feed 6H30 triode with a constant-current anode load. Bias at about -3 V and about 25 mA with about 80 V on the anode. Yes, honestly.

[gripracer]

@ Steve: I don't know if you're joking, can I seriously use a transformer as a voltage gain stage?

Originally Posted by ra7

How about that JFET BOZ?

Do I know you?

I do have a BOZ that I could use. I just wasn't sure if it was the right type of thing

Originally Posted by Gordy

Try a single-ended parallel-feed 6H30 triode with a constant-current anode load. Bias at about -3 V and about 25 mA with about 80 V on the anode. Yes, honestly.

Could I do the same thing with a 6N6P or 6N2P?

[Gordy]

Originally Posted by gripracer

Could I do the same thing with a 6N6P or 6N2P?

In theory I would suppose yes, however I've not used those tubes in practice. If I remember correctly the 6N6 is much like the 6H30 but for lower power duties. The main factors to consider are gain, internal resistance (R plate) and (perhaps the most important) the linearity. Check out the anode curves. The 6h30 is very good - notice how parallel the lines are. This leads to good open-loop performance which I guess you are searching for. When it is constant current source loaded the output impedance is roughly equal to the internal plate resistance, which is about 1350-ish Ohms for the 6H30. As long as your power buffer has reasonable input capacitance then they should match up fine. You will get a gain of about 14 from it as a single tube stage.

[Steve Eddy]

Originally Posted by gripracer

@ Steve: I don't know if you're joking, can I seriously use a transformer as a voltage gain stage?

Oh absolutely.

Of course you can't take just any step-up trannie and drop it into any circuit or any situation. But as long as you provide it with proper loading, drive it from a source which doesn't overload it or have too high an output impedance, absolutely you can use a transformer as a voltage gain stage. And a very nice one at that.

se

[Eli Duttman]

@ Steve: I don't know if you're joking, can I seriously use a transformer as a voltage gain stage?

Mr. Eddy was NOT jesting. While a trafo can't yield power gain, it most certainly can step a voltage up. Steve has put a considerable amount of resources into making trafo based voltage gain blocks work well.

Gripacer, what is the magnitude of the I/P signal and how much voltage gain do you need? If you are starting with the CDP "standard" of 2 VRMS, your best bet (IMO) is a vacuum triode. Why? Fact, vacuum triodes are the most linear amplifying devices ever made. If the gain structure works out, a 6SN7 section will require (sic) zero NFB.

[gripracer]

Originally Posted by Steve Eddy

Oh absolutely.

Of course you can't take just any step-up trannie and drop it into any circuit or any situation. But as long as you provide it with proper loading, drive it from a source which doesn't overload it or have too high an output impedance, absolutely you can use a transformer as a voltage gain stage. And a very nice one at that.

se

Cool! My source is the (+) outputs of a CS4397 DAC chip. It puts out 1.4vpp (avg) according to the data sheet, but I think it puts out a full 2v, as it gets as loud as a regular CD player output, and doesn't require a preamplifier. RL=1k min, CL=100pf max.

What do you think is a suitable transformer under $50 ea?

Originally Posted by Eli Duttman

Mr. Eddy was NOT jesting. While a trafo can't yield power gain, it most certainly can step a voltage up. Steve has put a considerable amount of resources into making trafo based voltage gain blocks work well.

Gripacer, what is the magnitude of the I/P signal and how much voltage gain do you need? If you are starting with the CDP "standard" of 2 VRMS, your best bet (IMO) is a vacuum triode. Why? Fact, vacuum triodes are the most linear amplifying devices ever made. If the gain structure works out, a 6SN7 section will require (sic) zero NFB.

Yes, I think that's a great idea too. After reading Lukasz Fikus' pages, I have been quite impressed by the triode as a voltage gain stage.

I'm not actually sure how much voltage I need...
- I am starting with around 2v
- The MOSFET stage is rated at 10w class A, 35w class AB.
- The supply voltage will be 18-0-18VAC

How much would be suitable?

I have 6N6P and 6N2P triodes on hand. Should I follow the Lampizator SRPP design (two triodes, self biasing)?

[Steve Eddy]

Originally Posted by gripracer

Cool! My source is the (+) outputs of a CS4397 DAC chip. It puts out 1.4vpp (avg) according to the data sheet, but I think it puts out a full 2v, as it gets as loud as a regular CD player output, and doesn't require a preamplifier. RL=1k min, CL=100pf max.

What do you think is a suitable transformer under $50 ea?

How much voltage gain are you wanting?

se