Bipolars for low noise input - Alternatives to 2SC2240

[Blackjack8635]

Originally Posted by 5th element

There's always the KSC1845/KSA992 from fairchild. These come in both through hole and SMD packages and are inexpensive too.

I just searched on these little fellas and can find nothing other than the Fairchild data sheet with very brief info and certainly nothing relating to rbb or noise.. Do you have a link to info?.

[hifidaddy]

This stage is 12 components, just 5 components more than the well known Hiraga LePrepre.

Of course, because of both floating inputs being on the same voltage level, one could dispense the trimmer. But I feel safer, when both inputs are really on 0.000V level, in case of the cartridge leads getting contact to ground.

This is my first sketch, and I will try to build it later in the evening. I consider replacing the output cap with a simple servo later.

HartmutIMG_7903_MCstage1.jpg

[5th element]

Originally Posted by Blackjack8635

I just searched on these little fellas and can find nothing other than the Fairchild data sheet with very brief info and certainly nothing relating to rbb or noise.. Do you have a link to info?.

The noise specification is quoted on the first page of the data sheet. Only it's expressed as a voltage so would have to be evaluated with regards to a specific design, as the Toshiba figures are.

[Workhorse]

Hi Hifidaddy,

My take is BC860/850C low noise pairs, they work best in my dynamic mic preamps.





Kanwar

[Blackjack8635]

Originally Posted by 5th element

The noise specification is quoted on the first page of the data sheet. Only it's expressed as a voltage so would have to be evaluated with regards to a specific design, as the Toshiba figures are.

Thank you found it! I wasn't looking for mV's!


That will take a little while to calculate back, A bandwidth of 1KHz incorporating all the low frequency flicker. A source impedance of 100K and referenced to an 80dB gain. That won't be much of a guide to a MC phono amp with an Rg of 3 ohm.

On one sheet the operating parameters were missing!

NV Noise Voltage V

CE = -5.0V, IC = -1.0mA,
RG =100KW, GV = 80dB,
f = 10Hz to 1.0KHz

25 mV typ. 40 mV max

[rayfutrell]

Could somebody explain the meaning of this noise specification? I don't understand it. Probably Rg is a source resistance of 100k, not 100kw. Is gv the voltage gain so you have to divide the specified noise level by the gain to reference it to the transistor input?
http://www.fairchildsemi.com/ds/KS/KSA992.pdf

[Blackjack8635]

Originally Posted by rayfutrell

Could somebody explain the meaning of this noise specification? I don't understand it. Probably Rg is a source resistance of 100k, not 100kw. Is gv the voltage gain so you have to divide the specified noise level by the gain to reference it to the transistor input?
http://www.fairchildsemi.com/ds/KS/KSA992.pdf

My own interpretation is the same as your own, the datasheets are actually incompetently written. On the other one, the 1845, the test conditions are not mentioned.
It is very bad practice to use the data of a specific test in a data sheet. Data sheet info should be referred back to inputs and generalised into a useable format. But... Hey transistor manufacturers never ever bothered to do that.

[MRupp]

Hello Hartmut,

could you possibly elaborate on what exactly you dislike about the sound of these transistors? I have a bunch of 2SC2545E/2SA1085E that I have not tried yet but that I wanted to use in the future, so I am really curious.

From what I have seen in circuits so far they were usually biased at ca. 3-4mA, which is supposedly optimal from a noise perspective, so maybe if you parallel to fit your current needs? Also, did you play with load and voltage across the transistors? NP has an interesting article "The Sweet Spot" where he shows how much optimising the operating point effects distortion. Re. BJTs: "The reduction in distortion is less dramatic, but it's still about 7 or 8 dB better ...". So maybe a different operating point would help?

Btw. Sanyo 2SC3504/2SA1433 and 2SC3601/2SA1407 should have a similarly low Rbb. Syn08 posted some measurements some time ago (should still be in his WEB site).

[P.Lacombe]

Originally Posted by rayfutrell

Could somebody explain the meaning of this noise specification? I don't understand it. Probably Rg is a source resistance of 100k, not 100kw. Is gv the voltage gain so you have to divide the specified noise level by the gain to reference it to the transistor input?
http://www.fairchildsemi.com/ds/KS/KSA992.pdf

Yes, 100kohm. W is very frequent mistake for (omega) see :

http://www.datasheetcatalog.org/data...nec/2SA992.pdf

[hifidaddy]

Originally Posted by MRupp

Hello Hartmut,

could you possibly elaborate on what exactly you dislike about the sound of these transistors? I have a bunch of 2SC2545E/2SA1085E that I have not tried yet but that I wanted to use in the future, so I am really curious.

...

Martin,

I had tried them in discrete opamps, Mark Levinson style and the like, biased at 50uA to 125uA, but this was about 20 years ago. So my experiences don't apply to this case, where they are to be used at 3..6mA in a non-feedback configurtion.

BTW, the Swiss producer DNM uses exactly these transistors in their preamps.

Hartmut