A simple discrete one-watt amplifier

[njswede]

Let’s design a preamp! I need a preamp.

 

[No ideas]

well what do you want in an preamp?

 

[HJH]

Let’s design a preamp! I need a preamp.

Yes, this design needs also a simple preamp, best if it works with 12V supply.

 

[No ideas]

the 12V is pointless you could try using it at 19V with bigger emitter resistors to decrease the distortion even further

 

[HJH]

Could it be something like this ?

 

[No ideas]

the thing is that do you need an preamp? the amplifier has a lot of gain on its own and by changing the input resistor you change its gain

 

[HJH]

Yes, I need. And there is one more who needs.

More gain means more distortion and smaller input impedance for this amp. Have used this with diy riaa amp and little bit more gain is better.

Also a discrete preamp can be a good learning project for all and can help someone who can build a preamp but not design one.

 

[No ideas]

how much more gain? EU headphone out to US headphone out? or EU headphone out to 2V rms?

 

[HJH]

Maybe, 6dB or 8dB gain, must check this later, but wait until we see what others need. This could be a good project.

 

[No ideas]

should we include things like input selectors and tone controls?

 

[lineup]

There is not much happening here.
Most of us don't even know what amplifier you are talking about 😀

 

[No ideas]

a very fancy version of this:

the fancy version of this being the amplifier from post #92

 

[No ideas]

There is not much happening here.
Most of us don't even know what amplifier you are talking about 😀

its this one:

 

[HJH]

There is not much happening here.
Most of us don't even know what amplifier you are talking about 😀

@lineup

We started to talk about preamp which could be used with this or someone other amp.
---
Have something under construction, not ready and no tonecontrols. Just a simple try.

 

[lineup]

its this one:
View attachment 1423157

Thanks @No ideas 🙂

What are the diodes D2 D3 ??

 

[HJH]

D1,D2,D3 = 1N4001 ,if this was the question.

 

[HJH]

Preamp try :

First schema for preamp, no tonecontrols added and volume pot can be used after preamp, can be used almost any supply voltage changing Re, or split supply if Q2's base is grounded (drop away R4, R5, R6 and C2). Use R6 to set output voltage at V+/2.

Seems to be stable at low gain with two compensation caps, but needs maybe LTspice simulation to check gain- and phase margin at HF.

 

[No ideas]

That is a differential pair, if we were to make it a part of the overall amplifier feedback loop we would get way better distortion and higher input impedance.

Or its a simple buffer block that we/you are gonna scale same way people do with op amps.

 

[No ideas]

Preamp try :

First schema for preamp, no tonecontrols added and volume pot can be used after preamp, can be used almost any supply voltage changing Re, or split supply if Q2's base is grounded (drop away R4, R5, R6 and C2). Use R6 to set output voltage at V+/2.

Seems to be stable at low gain with two compensation caps, but needs maybe LTspice simulation to check gain- and phase margin at HF.

one more issue i see here is that the feedback loop isnt properly closed

 

[HJH]

Actually this one works and sounds good, maybe picture is someway wrong, feedback is closed.

But for preamp, tonecontrol could be an option, with added complexity. Volume and balance is minimum and two or three inputs.