Sanity check on new MC phono stage.

[Tjj226]

So I wanted to learn how to design a phonostage from scracth. After learning how to use LTspice, this is what I was able to come up with.

Im using parts I have in my parts box. I have a ton of hammond 156cs to use as a plate load, so I can use 2 in series to minimize winding capacitance and double the inductance.

I am a complete noob when it comes to designing phono stages, so any ideas, thoughts, or pointers would be welcome.

 

[lcsaszar]

Do you use LED bias in the cathodes?
I would swap the EQ network of the first and second stage, so that the 75us pole will attenuate the noise of both stages.
Also, if the gain of two stages is sufficient, you can configure the 3rd stage as cathode follower (and spare the L4 choke).
I can't comment on use of 6BQ7A, because I've never used it. I use 6DJ8 (E88CC).

I am not sure it will low enough noise for MC. Use a step-up transformer or dedicated MC head amplifier so that the tube phono stage gets 5...10mV.

 

[Tjj226]

Do you use LED bias in the cathodes?
I would swap the EQ network of the first and second stage, so that the 75us pole will attenuate the noise of both stages.
Also, if the gain of two stages is sufficient, you can configure the 3rd stage as cathode follower (and spare the L4 choke).
I can't comment on use of 6BQ7A, because I've never used it. I use 6DJ8 (E88CC).

I am not sure it will low enough noise for MC. Use a step-up transformer or dedicated MC head amplifier so that the tube phono stage gets 5...10mV.

I am indeed using LEDs for the cathode bias.

I do need all 3 stages to get the full 70db for MC cartridges. I have thought about MC steup transformers. The catch there is that the step up transformers usually cost around 200 bucks for a half decent pair. I already have the parts to make this, so it wont cost me anything.

The neat thing about this circuit is that the first two tubes gives me 40db of gain for a MM cartridge, and the 3rd stage gives me 70db for MC. I could theoretically switch out the 3rd tube stage with a rotary switch to switch between modes.

I like your idea about swapping around the EQ network.