Best rbb transistor, for MM phono preamp

[peranders]

... mmm ... but his design was for MC cartridge.

[amplifierguru]

Clearly the 2SD786 is overkill for this - but isn't that some of what DIY is all about. Hell, the 3 you've nominated are all cheap enough, try them. Listen.

Proof of the pudding....


Cheers,
Greg

[jblmar]

Originally posted by claudio
Hello,
I am working on a MM phono preamp, a cascode configuration, which uses a Jfet 2sk389 as the low transistor and a NPN BJT for the upper one. For the noise issue, it's important to use an high Hfe and low rbb BJT, and I came up to these 3 options, which are easily available in my country:
2SC2240 datasheet
MPSA18 datasheet
BC550C datasheet

Now my question: which one has the lowest "base spreading resistance" (rbb)? Only the BC550C datasheet show this value.

Thanks,
Claudio

Hi Claudio,
My Marantz 3650 pre amp uses FET inputs along with 2SC2240 (IIRC) transistors for the phono amp section. The noise floor is very low. Not bad for an almost 30 year old design. And that's with JBL 2425 drivers! You'll be quite happy with FET inputs.
Ron

[claudio]

Hi All,
the schematic is pretty simple and alike already seen phono pre. As Hugh thought it is a 2 stage ampli, with a passive RIAA in the middle of the two; at the end there is a follower for a low output impedance. For the PSU I was thinking at Jung SR II; a doubt I have is that the same PSU will power the phono and the line preamplifier: is it wise to use a RC filter on the phono power line?
The schematic below is still at simulation stage, so any input is welcome; I will use the LSK389, even if in the schematic there are 2 2SK170; I am using a source resistor since it lowers both THD and input capacitance, while increasing the noise a bit, but since I am using 2 parallel Jfet I suppose it is not to worry about.

peranders wrote:
... mmm ... but his design was for MC cartridge.

Does it change something about the upper cascode BJT noise discussion?

Regards,
Claudio


http://paginas.terra.com.br/educacao...test/phono.png

[nuvistor]

Your schematic is similar to L'Pacific Optime.

Your webpage does not allow links from other websites, I had to cut and paste into the address bar to see it

[claudio]

Yes Nuvistor it's similar: as I said before mine it's alike already seen before phono pre. However, the Pacific Optime uses 2 different voltage supply; I think the schematic I show is more similar to Pearl Phono.

I am aware of the link problem and I am sorry; this should work better: phono schematic

Regards,
Claudio

[claudio]

a doubt I have is that the same PSU will power the phono and the line preamplifier: is it wise to use a RC filter on the phono power line?

Any point of view?

And about the rbb value for the transistor 2SC2240 and MPSA18, does anyone knows their value? I am curious to know for future reference, since in the above schematic the rbb doesn't interact with noise.

Regards,
Claudio