Samuel Gromer low noise opamp

[robmil]

Hi all

I was looking at the low noise designs of Samuel Gromer. He uses a 2SC3329 and compliment on one of them. What do people do now for low noise transistors as the 2SC3329, 2SC2547 etc are either obsolete or impossible to get?

Rob

[Ian Finch]

Little Diode of New Malden, Surrey claim to have them in stock so, like all our dwindling through-hole parts, get a quantity while you can. Tomorrow may be too late.
Depending on the voltages and location , 2SC1815/2SA1805 or the the old faithful 2SC2240/2SA970 are good and can can still be selected for lowest noise if that is your aim.

[lineup]

Should be 2SC1815/2SA1015

[robmil]

Thank you for your responses and just a quick correction...it is Samuel Groner.
Sorry Sam

Rob

[lineup]

I use often 2N5551/5401.
Not the lowest noise perhaps. But robust and good quality and takes high voltage and current.

Besides I use 2SC2240/SA970. Takes high voltage. Low noise and precision.

Also BC550C/560C I use.
BC550C/560C are handicapped of take max 45 Volt = 2x22.5V

2SC1815/2SA1015 are good gain, low noise and think can take some voltage.

Samuel Groner:
SG-Acoustics · Samuel Groner · Discrete OpAmps

[lineup]

Here I have used BC550C
in a transistor line preamp with gain x10 and no global feedback.
Is fed by a discrete lowdrop regulator at 24.0 Volt.

Shows that we can get low THD (0.003% at 1Volt) using no global feedback.
The x10 is acheived by use of two gain stages.
The output is buffered into a load of 10k

[CBS240]

Hi

THAT 300 series matched arrays have en=0.8nV/SQRT(Hz) @ 10Vce, 1mA, 1KHz. Ft at that quiescence is 350MHz. I like to cascode these devices with J-fets when supply voltage allows. They're great for IPS.

[willy]

I get lots of 2SC1815s & 2SA1015s from old junk radios & stereos from the trash at a local repair shop. I have found a goldmine of parts from this heap of junk. Couldn't live without it. heh!

[Samuel Groner]

Unfortunately there are (as far as I know) no easily sourced complementary parts which show, at the same time:

* low rbb' (gives low voltage noise)
* high hFE (gives low current noise)
* low excess noise (gives low low-frequency current and voltage noise)
* matching hFE for complementary pairs (gives low input bias current)

To give a specific recommendation you'll need to elaborate on your specific application. What's the source impedance, what input bias current is acceptable, is low-frequency noise a major concern?

Samuel

[robmil]

thanks for your input.

I am finding it extremely hard to get low noise complementary trannies. What are we to do in the future with many of our great LN transistors being discontinued?

Sam I like you zero feedback line preamp Have you tried it yet?

regards

Rob