Fet 6Gk5 ECC88 mc phono stage

[velvetsunrise]

Hi Just built this phono stage and sounding really good, thought i would share it.

Comments welcome


Cheers.

[Wavebourn]

Looks nice!

[velvetsunrise]

Thanks, bearing in mind it was only a knock up from my scrap box, its sounding really good.

Very quiet with a Denon DL103, and very smooth, but detailed, dynamic and natural sounding

[Stephen R]

Did you try self bias with unbypassed cathode on 2nd stage? You shouldn't lose any significant gain by doing so and you could lose the battery in the grid. I favour battery grid bias but only when needed and in this case, you might not.

cheers,

Stephen

[velvetsunrise]

H Stephen,

Thanks for the sugestion, no i didnt try that, there is plenty of gain, so as you say loseing the grid bias battery in favour of a cathode reistor is probably a very good idea. I shall try it.

Heres a pic of the thing, as i say it was quickly constructed from parts i had on hand, you will notice the blown electrolytic cap i snipped out from the heater regulator! WOOps i put it in the wrong way round.

Despite the makeshift prototype construction, it sounds supriseingly good, and no hum.

Maybe it would be worth rebuilding, with better components/layout. and perhaps seperate VR tubes/CCs for each channel.

[SY]

Nice construction work as well. I wish my makeshift prototypes looked half as good.

[analog_sa]

Qute nice indeed. I would replace the shunt portion of the regulator with "Salas simplistic" - less noise and better sound.

[velvetsunrise]

Hi, The preamp was built to try out the hybrid fet/valve cascode, and i have to say i am impressed.

Yesterday i tried cathode bias resistors in place of the grid bias batterys, i didnt notice a drop in gain, though perhaps the bass seeemed a little less tight, going to listen to it a while longer, not a huge difference at all though.

And any simplification is always welcome.

I did consider a more complex shunt regulator, such the the very highly regarded "Salas simplistic" shunt reg, but i had the VR tubes on hand, and was curious as to how they would perform in a sensitive high gain phono amp.

Certainly from a noise perspective, they appear invisible.

I think this is a far as i wish to take this project at the moment as i have an all valve mc compatable preamp on the drawing board, something i have been considering for a long time.

[Eli Duttman]

Velvetsunrise,

Your implementation of a JFET/6GK5 cascode is of considerable interest to me. I badly want to do something along the same lines. I'm inclined to keep your 1st gain block and EQ network intact. However, I'll stick with the grid leak biased 2nd gain block in the attached tweaked version of RCA's venerable design.

[analog_sa]

Originally Posted by velvetsunrise

I think this is a far as i wish to take this project at the moment

Your decision of course. After replacing the reg tubes with Salas shunt i have sworn to never ever use such tubes in my designs. I also use a cascoded CCS - another nice improvement.