I want pre-amp schematic with A s/n ratio 92 db or more

jinkuchi · 1st June 2004, 04:07 AM

I want pre-amp schematic, please.

with a s/n ratio 92 db or more.

I'm new in pre-amp. never have one.

tiger.

Nelson Pass · 1st June 2004, 04:01 PM

A weighted? No weighting?

Noise Floor? Wide band?

What voltage did you want that 92 dB referenced to?

jinkuchi · 2nd June 2004, 03:25 AM

the signal to noie ratio

I mean approximately.

Just want high quality preamp that has low noise.

thank you

tschrama · 2nd June 2004, 08:37 AM

If you want your preamp to be able to accept 2Vrms at it's input, then if the input noise must be lower than 92dB, this will equal:

2 x 10^-4.6 / sqrt(20KHz (bandwidth)) = 349nV/sqrt(Hz)

It's hard to design something so noisy. Every opamp known to me has an input noise lower than 40nV/sqrt(Hz), take you pick, NE5534, or opa227 (both about 3.5 nV/sqrt(Hz)), opa134 (about 8nV/sqrt(Hz) ? ).

Edit..: oops allmost forgot: Nelsons MOSFET preamps will meet this criterium too. BTW what is the EIN of a IRF610? something like 20nV/sqrt(Hz) ?

But if you want 92dB S/N for a 2mVrms (max input) preamp, you'll have a challange... you'll have to build a discrete BJT preamp, eg. a 6 transistor symmetrical input stage with Vbc = 0Volt and 300uA Iq each transistor, or a handfull 2SK170's in parrallel...

Goodluck,
Thijs

Nelson Pass · 2nd June 2004, 09:37 PM

Quote:

Originally posted by tschrama
2 x 10^-4.6 / sqrt(20KHz (bandwidth)) = 349nV/sqrt(Hz)

That's what I get, too.

You will be amused to know that the output noise of the First
Watt amp is about 20 uV, for an output floor of about 140 nV,
and an input floor of about 28 nV using an IRFP240 pair.

MuuuHahahahaha

wrenchone · 3rd June 2004, 02:22 AM

Nelson, do you twirl your moustache when you do that scary laugh?

grataku · 3rd June 2004, 03:30 AM

What does it matter what the thermal noise of the preamp is if what you are getting from the trafo and poor grounding and ripple is going to be 40 db above that?

jinkuchi · 3rd June 2004, 11:11 AM

how about transistor 2sc458?

tschrama · 3rd June 2004, 12:17 PM

I found this datasheet, but I cann't find any info on the noise specs. But generally, a discrete BJT preamp design can be made to have excellent noise performance, especially with low Z sources, pretty much with all comman transistor types.

http://s89326750.onlinehome.us/maran...ecs/2sc458.pdf

peranders · 3rd June 2004, 12:23 PM

Quote:

Originally posted by jinkuchi
I want pre-amp schematic, please.

with a s/n ratio 92 db or more.

I'm new in pre-amp. never have one.

tiger.

Are you after a preamp of "Nelson" style or any style?

Do you mean 92 dB at fulll, output?

A plain transistor has 1-3 uV noise max => 100-120 dB

1st June 2004, 04:07 AM	#1
jinkuchi diyAudio Member Join Date: May 2004 Location: shinjuku	I want pre-amp schematic with A s/n ratio 92 db or more I want pre-amp schematic, please. with a s/n ratio 92 db or more. I'm new in pre-amp. never have one. tiger. __________________ jinkuchi

2nd June 2004, 03:25 AM	#3
jinkuchi diyAudio Member Join Date: May 2004 Location: shinjuku	the signal to noie ratio I mean approximately. Just want high quality preamp that has low noise. thank you __________________ jinkuchi

3rd June 2004, 11:11 AM	#8
jinkuchi diyAudio Member Join Date: May 2004 Location: shinjuku	how about transistor 2sc458? __________________ jinkuchi

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1st June 2004, 04:01 PM	#2
Nelson Pass The one and only Join Date: Mar 2001	A weighted? No weighting? Noise Floor? Wide band? What voltage did you want that 92 dB referenced to?

2nd June 2004, 08:37 AM	#4
tschrama diyAudio Member Join Date: Jul 2001 Location: The Netherlands	If you want your preamp to be able to accept 2Vrms at it's input, then if the input noise must be lower than 92dB, this will equal: 2 x 10^-4.6 / sqrt(20KHz (bandwidth)) = 349nV/sqrt(Hz) It's hard to design something so noisy. Every opamp known to me has an input noise lower than 40nV/sqrt(Hz), take you pick, NE5534, or opa227 (both about 3.5 nV/sqrt(Hz)), opa134 (about 8nV/sqrt(Hz) ? ). Edit..: oops allmost forgot: Nelsons MOSFET preamps will meet this criterium too. BTW what is the EIN of a IRF610? something like 20nV/sqrt(Hz) ? But if you want 92dB S/N for a 2mVrms (max input) preamp, you'll have a challange... you'll have to build a discrete BJT preamp, eg. a 6 transistor symmetrical input stage with Vbc = 0Volt and 300uA Iq each transistor, or a handfull 2SK170's in parrallel... Goodluck, Thijs

3rd June 2004, 02:22 AM	#6
wrenchone diyAudio Member Join Date: Feb 2004 Location: Silicon Valley	Nelson, do you twirl your moustache when you do that scary laugh?

3rd June 2004, 03:30 AM	#7
grataku diyAudio Member Join Date: Dec 2000 Location: -	What does it matter what the thermal noise of the preamp is if what you are getting from the trafo and poor grounding and ripple is going to be 40 db above that?

3rd June 2004, 12:17 PM	#9
tschrama diyAudio Member Join Date: Jul 2001 Location: The Netherlands	I found this datasheet, but I cann't find any info on the noise specs. But generally, a discrete BJT preamp design can be made to have excellent noise performance, especially with low Z sources, pretty much with all comman transistor types. http://s89326750.onlinehome.us/maran...ecs/2sc458.pdf

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