Snail Phono Pre

[Mike H]

EDIT - Although having no experience of this, I would guess that the heater current/power must have an effect on the sound and that the greater the heater current, the more 'control' or 'aithority'.

I've never heard that theory before !

Me neither!

If it's the line amp you're talking about then ECC82's (or by whatever other number) would be ideal.



 

[Mike H]

FWIW this is my take on it.

Heater supply needs elevating 60V I would say

[Mike H]

Oh yeah has a Voltage gain of a little over X10.



 

[Nick]

I would try and make R1 and R3 the same so the supply see's a constant current draw.

[Mike H]

Could do that yes.

I admit the only reason I put 22k in is 'cause my phono pre does it like that.




 

[little eddy]

After Nick's post with link to the DIYAudio 10m45s CCS kit, I've seen reference in several places to a cascode CCS attangement including here:

http://www.kandkaudio.com/accessories.html

Has anyone an idea on the 'cascode' circuit or any experience as to whether it's worthwhile for just a couple of quid more?

[little eddy]

OK so taking on board Mike's passive proposal, a couple of comments by Nick and also a posts on DIYaudio regarding cascode CCS and CF protection diodes, I have the following two options for the line amp.

What do people think about the cascode CCS? Worth trying from the outset?

[andrew Ivimey]

I've used a few of Kevin Carter's CCS kits here and there - they are lovely and so simple ... but then so are most constant current source setups - v.useful!

[Mike H]

Looks alright to me, not seen 2 x 10M45S used like that but should work.


Personally I'd get the 10M45S and a bit of plain matrix board rather than shell out for someone elses kit. But that's just me of course


Cynical, moi




 

[little eddy]

Personally I'd get the 10M45S and a bit of plain matrix board rather than shell out for someone elses kit.

I'm not cynical - just tight. A stripboard design is being provisionally laid out at the moment but if it then looks pretty straightforward will elect to hard wire.

[Mike H]

I'm not cynical - just tight.

I know the feeling!



 

[little eddy]

While I now pull together a BOM and then get the bits for the line stage, my attention tonight has on the phono stage and how I am going to incorporate my changes in the donor enclosure.

What might be the simplest implementation would be to try and use a significant proportion of the 'mounting plate' that you can see in the previously posted photos.

But looking at the general layout, if I opt for Nick's recommendation of parallel ECC83s, CC gain stage and CF output, what would make this much simpler to build on the current platform would be if the gain stage and CF were of the same valve type because the current layout is basically dual mono.

If I take Nick's original recommendation for the gain stage as the 12AY7/6072a, AN often use this in their preamps also as the CF. Would this work well, or might there be a better valve if it were to share these duties? Or is this too much of a compromise and a separate CF such as the 5687 would be beneficial?

EDIT - Scanning MJ last night, he has a scheme with ECC88 for CC and CF stages. I also think in the basic ThorstenL design although only as CF in this instance.

[Mike H]

Is the input stage 2 x parallel ECC83? See elsewhere discussion about Miller capacitance effect and of ECC83's in parallel!

Say the Cag is 2pF (just looked it up), x 2, (2 triodes in parallel) x V-gain of the stage, I dunno X50? Miller cap = 200pF.

Would your cartridge be OK with >=200pF input capacitance plus strays plus that of the connecting cable?

You're talking of using CCS's and pushing the gain up even more, which will also increase the Miller cap.

Just another aspect that may need to be considered.



 

[Nick]

I think I will just stop publishing info about circuits I have build and listened to.

http://www.theanalogdept.com/sut.htm

"Example, a Shure V15VxMR has a recommended load requirement of 47K ohms in parallel with 250 pF"

[little eddy]

I think I will just stop publishing info about circuits I have build and listened to.

Sorry Nick - reference to your design removed from previous post.