Mouser's mark in going from US to UK pricing is quite good for profit margin !
1cent to 1.6p is +164%
1.5cent to 2.4p is +164%
We pay 2.64times what our US Members pay!
Assumed 1.65US dollars to 1UK pounds
If you want to find base resistance values relevant for noise calculations, you will have to measure the noise level at a very low source impedance (0 ohm, for example) and a fairly high bias current (say 10 mA). What equipment have you got?
If you manage to design a phono preamplifier such that it works with different input transistors, you could of course use the preamplifier itself for relative measurements. Just try different options, record the output noise and listen.
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Well, I have the usual stuff, voltmeters. Power supplies. Sig gens, a pico scope digital O-scope. What would I need extra? It seems from what Ive seen that I could measure rb with this. I may try the idea of just seeing what works best. But, I'd like to get a MC cartridge to make the measurements truly valid.
If your oscilloscope has a spectrum analyser function, all you may need extra is a preamplifier if its sensitivity is not enough. If it hasn't got a spectrum analyser function, you need a filter as well to get a defined measurement bandwidth. A couple of resistors of different values also come in handy; by measuring total noise at different source resistances, you can apply some mathematics and derive what part is voltage noise, what part current noise and what part the predictable noise of the resistors.
Here's a lab method for bipolar transistor noise measurement -- while they use an HP analyzer, you could use a bandpass filter and a decent true RMS meter:
http://users.ece.gatech.edu/mleach/ece6416/Labs/exp04.pdf
http://users.ece.gatech.edu/mleach/ece6416/Labs/exp04.pdf
Mr. Vogel has a circuit for measuring Rbb on page 55.
http://www.pearl-hifi.com/06_Lit_Ar...apers/Vogel_Burkhard/The Sound of Silence.pdf
http://www.pearl-hifi.com/06_Lit_Ar...apers/Vogel_Burkhard/The Sound of Silence.pdf
My choices in the past were the National supermatch pair or ROHM 2SB786
Since these are no longer made an excellent choice for MC preamp would be the Linear Systems LSK389 dual fet which is a remake of a device originally made by Toshiba
Since these are no longer made an excellent choice for MC preamp would be the Linear Systems LSK389 dual fet which is a remake of a device originally made by Toshiba
Toshiba semiconductor produced the 2SA1316 and 2SC3329 with an advertised Rbb of 2 ohms. They are not listed in the Toshiba semiconductor products now. Toshiba produced some semiconductors with amazing specifications but they all seem discontinued.
Looking at the schematic on pg75, shouldn't R8 be 2k421? That way the gain will be 3.01dB. I understand the difference is only a few mili dB, but if your making a measurement, do it right.
More Toshiba low-noise PNP transistors
Speaking of single PNP transistors, you could consider Toshiba's 2SA1163 and 2SA1312. These are 150mW devices rather than 100mW, so may offer more design flexibility than the 2SA1587.
Among dual PNPs, Toshiba makes the HN4A51J (300mW 5-pin package with shared base), HN4A06J (300mW 5-pin package with shared emitter), HN3A51F (300mW 6-pin package).
Toshiba even offers the HN4B06J, but as it is a PNP + NPN in a 300mW 5 pin package with a shared emitter, it won't be the easiest transistor to design with.
I believe that Toshiba continues to manufacture a selection of low-noise NPN transistors also.
hth, jonathan carr
Speaking of single PNP transistors, you could consider Toshiba's 2SA1163 and 2SA1312. These are 150mW devices rather than 100mW, so may offer more design flexibility than the 2SA1587.
Among dual PNPs, Toshiba makes the HN4A51J (300mW 5-pin package with shared base), HN4A06J (300mW 5-pin package with shared emitter), HN3A51F (300mW 6-pin package).
Toshiba even offers the HN4B06J, but as it is a PNP + NPN in a 300mW 5 pin package with a shared emitter, it won't be the easiest transistor to design with.
I believe that Toshiba continues to manufacture a selection of low-noise NPN transistors also.
hth, jonathan carr
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