No global feedback preamplifier

[smithomo]

Hi,
I'm currently designing my new pre amplifier.
The aim to have below features.
-No global negative feedback.
-Direct coupling.
-Class A.
-Simple design.
My designed as here. but unfortunately I can't acceptable with it's voltage gain.
I would like to have 5-10 times gain, but it is actually 100 times voltage gain.
So can anyone give me an advise, or the a suggest schematic.

[Elvee]

Load it

[smithomo]

[QUOTE=Elvee;2825348]Load it[/QUOTE

Thanks that a nice one but it is a global feedback one with easy to specify the voltage gain.

[CBS240]

Ohms law. Reduce VR1 and VR9 by reducing the resistor value. This will reduce the change in voltage of the emitter resistors of Q5 & 8, reducing the output current change vs input voltage. But because your output is from the dependent current source of the transistors, that being the collectors, there must be a specific load impedance in order to control voltage gain. If the load Z is not constant, then you may need some form of FB be it current or voltage FB, to achieve constant voltage gain.

[Elvee]

Originally Posted by smithomo

Thanks that a nice one but it is a global feedback one with easy to specify the voltage gain.

Do you call a resistor between output and node 0V a global feedback?

[DF96]

As Elvee said, all you have to do is load it. You have built a transconductance amplifier - it outputs a current so you need to convert it to a voltage. A rough calculation suggests a bit below 1mA/V, so perhaps a 1k2 load would give unity voltage gain.

You will need input and output DC blocking capacitors, unless you can guarantee that the adjacent equipment already has these and can cope with a potentially large DC offset. Note that the DC offset might not show up in simulation if the complementary pairs of BJTs are regarded as true complements - in real life they won't be.

[knutn]

Like Elvee says, connect a resistor between the output and ground. A value of 8.2k will give you a gain of 20 db (10 times). However, with your design you will have serious offset problems...