Low output impedance preamp needed.

[Dxvideo]

Hi all,

I need a low output impedance (about 1K) preamp stage with no gain. I prefer JFETs to use and if possible with one transistor on each channel.

Does anyone know that kind of preamp schematic?

Thanks a lot in advance.

 

[Ayne]

JFET input .
No gain.
Low output impedence..

I think it's all u needed.

 

[AndrewT]

Hi,
a source follower will give you what your after. Well nearly, the Rs <<1k0 and gain may be <1.0
It will perform better if a CCS loads the tail.
Have a look at the various schematics here and in diyhifi.org

 

[Dxvideo]

Thank you Ayne.
But I am a bit confused about op-amps. Because I have tried TL072, NE5532, LM833 and LM4562 also.They all for specially audio applications. But I afraid I need a warmer sound. Because my amplifier is a lateral MOSFET Class A-AB one.
I like its sound too much but when I connect it a high output impedance device then I can hear some noise and I want to reduce that noise. This preamp is needed for that. And naturally I dont want to change its sound.

 

[Dxvideo]

And for Andrew;

An externally hosted image should be here but it was not working when we last tested it.

Do you mean a circuit like that?

 

[AndrewT]

No.
that's a dual complementary LTP with cascode and then a complementary follower (or is it a VAS?). =8fets, expensive in real estate and dollars.
You asked for single jFET transistor.
I suggested a follower (on it's own).

I think NUUK's site shows exactly what you are after. His update right at the end after the opamp options.

 

[juma]

No, Andrew meant a circuit like one of these :

 

[juma]

Sorry Andrew, you were quicker !

 

[Dxvideo]

Ok I see. I saw a lot of circuit like that. But somebody says
"that kind single ended circuits very prone to noise"
What do you say about that?
And also what do you say about that circuit;

An externally hosted image should be here but it was not working when we last tested it.

Is that the same kind circuit?

 

[juma]

Yes it is. The lower JFET acts as a constant current source (the source resistor should be of smaller value - something like 22 Ohms). But you said that you want a circuit with one JFET.
Source follovers are not noisy, but they perform better with good power supply.

 

[Dxvideo]

Ok then.
So if you compare that circuit with a 1 gain non-inverted op-amp stage, which do you prefer for a MOSAMP?
And a second question (as usual); Should I use big snubbers (4700u) plus regulators for power supply of that circuit?
Thanks again.