Hola

Excuse me my wrong English.

I am interested in experimenting with the microphone preamplifier schematic that appears in SSM 2220 datasheet, specifically the three SSM paralleled (see datasheet) but with the AOP habitual realimentation configuration (see image attach).

datasheet ssm2220 example:

http://mihalcz.ingyenweb.hu/riaa/MCasyElek.pdf

In Elektor 12/98 appears a version for MC cartridge preamplifier, that is my inspiration, (see link). I think it’s easy to convert a microphone preamplifier:

http://mihalcz.ingyenweb.hu/riaa/MCasyElek.pdf

As alternative I would change the OP27 with OPA 627 or another best known audio OPA.

In Pordigy search, don’t appears information for this circuit (or at least, I do not find).

I have some questions and doubts and do the following comments:

1.- Has someone experience with this circuit?

2.- The Elektor circuit give great importance to the R9 (realimentation resistance) thermal noise effect, (in that circuit shows only 5,62 Ohms…!).

5,62 Ohms = 4,51 * 10-8 Vrms thermal noise = -144,7dBu noise

3.- But with this little resistance appears the problem to obtain a correct AOP realimentation loop (at least 600 Ohms in total), see R11 trick in Elektor project.

4.- But in SSM2220 datasheet appears this resistance with large value (100 Ohms).

100 Ohms = 1,91 * 10-7 Vrms thermal noise = -132 dBu noise.

Obviously there isn’t a low value resistor loop AOP realimentation problem.

5.- In really, I think if you have a standard 200 Ohms microphone calculation noise (= -129dBu noise), is there no importance if you install a 5,6 Ohms or 100 Ohms R9 resistance, and then, datasheets circuit are OK.

6.- MAT03 isn’t in the usual market in Spain (Farnell, RS, etc.) (neither the venerable and ubiquitous LM394 not applicable because is NPN)

7.- Farnell (the best shop in Spain) has the SSM2220, but at the moment I think with a little stock, and expensive (It is like to eliminate it…?). But there are another PNP modern matching transistors SMD as:

BCM 856

BCM 857

DMMT 3906

And… Very very cheap (less than 50 cents…)

8.- Has someone experience with this semiconductors to substitute SSM 2220?.

9.- Why in that semiconductors datasheets appears only the (strange for my) NF (Noise Figure) in dB, and not the habitual Noise Voltage Density (NVD) in nV/sqroot Hz.

10.- How can I convert the NF in NVD (if that is possible).

Can sombebody help my?...

Very thanks from Spain

Very thanks

Miquel

Excuse me my wrong English.

I am interested in experimenting with the microphone preamplifier schematic that appears in SSM 2220 datasheet, specifically the three SSM paralleled (see datasheet) but with the AOP habitual realimentation configuration (see image attach).

datasheet ssm2220 example:

http://mihalcz.ingyenweb.hu/riaa/MCasyElek.pdf

In Elektor 12/98 appears a version for MC cartridge preamplifier, that is my inspiration, (see link). I think it’s easy to convert a microphone preamplifier:

http://mihalcz.ingyenweb.hu/riaa/MCasyElek.pdf

As alternative I would change the OP27 with OPA 627 or another best known audio OPA.

In Pordigy search, don’t appears information for this circuit (or at least, I do not find).

I have some questions and doubts and do the following comments:

1.- Has someone experience with this circuit?

2.- The Elektor circuit give great importance to the R9 (realimentation resistance) thermal noise effect, (in that circuit shows only 5,62 Ohms…!).

5,62 Ohms = 4,51 * 10-8 Vrms thermal noise = -144,7dBu noise

3.- But with this little resistance appears the problem to obtain a correct AOP realimentation loop (at least 600 Ohms in total), see R11 trick in Elektor project.

4.- But in SSM2220 datasheet appears this resistance with large value (100 Ohms).

100 Ohms = 1,91 * 10-7 Vrms thermal noise = -132 dBu noise.

Obviously there isn’t a low value resistor loop AOP realimentation problem.

5.- In really, I think if you have a standard 200 Ohms microphone calculation noise (= -129dBu noise), is there no importance if you install a 5,6 Ohms or 100 Ohms R9 resistance, and then, datasheets circuit are OK.

6.- MAT03 isn’t in the usual market in Spain (Farnell, RS, etc.) (neither the venerable and ubiquitous LM394 not applicable because is NPN)

7.- Farnell (the best shop in Spain) has the SSM2220, but at the moment I think with a little stock, and expensive (It is like to eliminate it…?). But there are another PNP modern matching transistors SMD as:

BCM 856

BCM 857

DMMT 3906

And… Very very cheap (less than 50 cents…)

8.- Has someone experience with this semiconductors to substitute SSM 2220?.

9.- Why in that semiconductors datasheets appears only the (strange for my) NF (Noise Figure) in dB, and not the habitual Noise Voltage Density (NVD) in nV/sqroot Hz.

10.- How can I convert the NF in NVD (if that is possible).

Can sombebody help my?...

Very thanks from Spain

Very thanks

Miquel