substitutes for BC413C/414C/415C/416C

[John Doe]

What would be good substitutes for the BC413C
414C, 415C and 416C in the US? They should
have very low noise with a reasonably high beta.
Circuit is a RIAA preamp with an input impedance
of about 10k - 50k (cartridge) and *NO* global
feedback.

There may not be any local feedback either, but the
circuit is the weirdest amplifier I've even seen with
some intricately interconnected current mirrors,
so I don't fully understand how the circuit works.

 

[Dave Platt]

What would be good substitutes for the BC413C
414C, 415C and 416C in the US?

#snip#

Consider the 2N4401 and 2N4403. According to an article by Marshall
Leach I read a few years ago, these have been sort of a "secret
weapon" for some analog-circuit designers.

Hah - found it.

http://users.ece.gatech.edu/~mleach/headamp/

This describes the use of these transistors in Leach's phono head-amp
design.

There may not be any local feedback either, but the
circuit is the weirdest amplifier I've even seen with
some intricately interconnected current mirrors,
so I don't fully understand how the circuit works.

Anything like the current-mirror common-base version of his head-amp
circuit, as shown in the URL above?

--
Dave Platt <dplatt@radagast.org> AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

 

[Watson A.Name - \"Watt Su]

"John Doe" <spam@sucks.com> wrote in message
news:TSQOd.15037$uc.477@trnddc05...

What would be good substitutes for the BC413C
414C, 415C and 416C in the US? They should
have very low noise with a reasonably high beta.
Circuit is a RIAA preamp with an input impedance
of about 10k - 50k (cartridge) and *NO* global
feedback.

There may not be any local feedback either, but the
circuit is the weirdest amplifier I've even seen with
some intricately interconnected current mirrors,
so I don't fully understand how the circuit works.

Some commonly used low noise, high gain transistors for
preamps are the 2N5088 and 2N5089. Also the 2N5232 and
2N3565. There are numerous others.

 

[Dave Platt]

In article <TSQOd.15037$uc.477@trnddc05>, John Doe <spam@sucks.com> wrote:

What would be good substitutes for the BC413C
414C, 415C and 416C in the US? They should
have very low noise with a reasonably high beta.
Circuit is a RIAA preamp with an input impedance
of about 10k - 50k (cartridge) and *NO* global
feedback.

Consider the 2N4401 and 2N4403. According to an article by Marshall
Leach I read a few years ago, these have been sort of a "secret
weapon" for some analog-circuit designers. They have a very low base
spreading resistance, and this leads to low noise (even though they
aren't specified as a low-noise transistor). Leach originally used
2N5210 and 2N5087 transistors (spec'ed by Motorola as being low-noise)
in one of his audio amp or preamp circuits. He later replaced these
by the 2N4401/2N4403, and the circuit's SNR was improved by 4 dB.

A couple of years ago I opened up my old PS Audio moving-coil phono
pre-preamplifier (which I find to be a very quiet device), and found
that its active devices are all 2N4401/2N4403.

There may not be any local feedback either, but the
circuit is the weirdest amplifier I've even seen with
some intricately interconnected current mirrors,
so I don't fully understand how the circuit works.

There certainly has to be *some* local feedback (presumably via those
current mirrors?) or the distortion levels would be sky-high.

--
Dave Platt <dplatt@radagast.org> AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

 

[John Doe]

"Dave Platt" <dplatt@radagast.org> wrote in message
news:110nold3kr79a17@corp.supernews.com...

Consider the 2N4401 and 2N4403. According to an article by Marshall
Leach I read a few years ago, these have been sort of a "secret
weapon" for some analog-circuit designers. They have a very low base
spreading resistance, and this leads to low noise (even though they
aren't specified as a low-noise transistor).

I think a low Rb is especially useful when the input impedance is
low. This amplifier is for an MM cartridge, and their impedance is
usually significantly higher compared to MC cartridges. I'll more
than likely try several transistors to see which combination performs
the best.

Leach originally used
2N5210 and 2N5087 transistors (spec'ed by Motorola as being low-noise)
in one of his audio amp or preamp circuits. He later replaced these
by the 2N4401/2N4403, and the circuit's SNR was improved by 4 dB.

Interesting. The 2N5087 has an NF max of 2, which is a fairly low
number.

There certainly has to be *some* local feedback (presumably via those
current mirrors?) or the distortion levels would be sky-high.

I guess you're right on this. I think I need to study the circuit
a bit more.