A simple discrete one-watt amplifier

[lineup]

I found this intresting dead simple headphone amp schematic, i also simulated it and it can do up to 2V rms.
View attachment 1425162

It is a simple follower without any voltage gain.
Most cases it can do well without the gain.
It is only headphones with higher impedance that needs voltage gain.

 

[HJH]

Gain is like R1/R2+1
Most cases there is not any need for an input capacitor.
R5 does not need to be 1M. It could even be 100k.

This one can be good and simple preamp too, must try it, because I have all parts available. Any suggestions about J113's Idss value or it doesn't matter?

 

[No ideas]

It is a simple follower without any voltage gain.
Most cases it can do well without the gain.
It is only headphones with higher impedance that needs voltage gain.

Thats why i wanted to use your preamp with it.

 

[No ideas]

It is a simple follower without any voltage gain.
Most cases it can do well without the gain.
It is only headphones with higher impedance that needs voltage gain.

if i run it at low enough voltage i could get a great iem/inear amplifier i think 5V is enough to get all of the voltage swing from any portable headphone dongle

 

[No ideas]

It is a simple follower without any voltage gain.
Most cases it can do well without the gain.
It is only headphones with higher impedance that needs voltage gain.

also what if i could replace the input bjt with a jfet to get rid of the input capacitor?

 

[HJH]

Some measured J113 for 'lineup' preamp. Message #210. They specify in datasheet only min Idss=2.0mA. Seems to be four fet's near 12mA.

 

[HJH]

'lineup' preamp proto, seems to work. Only DC voltages measured using HP3435A DMM.

 

[HJH]

When using only sinewave everything works well, but 10kHz squrarewave shows some ringing and 100kHz is even worse. This amp needs some compensation cap inside feedback loop, maybe over pnp transistors C-B junction.

Edit: one 20pF comp cap is enough to correct this , last picture shows 10kHz sq wave with comp cap. Simulations are fancy, but in most cases they don't show all.

 

[HJH]

Schema update. This one gives almost symmetrical clipping and no ringing.

 

[lineup]

Nice @HJH
My amp in real testing.
The capacitor is a good idea - 20pF
I might test this in my SPICE.
Unfortunately I can not build anything for real - I just simulate.

What is good is that no input capacitor is needed for this preamp.

 

[No ideas]

Why you cant build anything for real?

 

[lineup]

@No ideas
I have only a small room and a kitchen.
In my rooom I have no space left for electronics.
It is sad - I used to do audio work where I lived before.

 

[lineup]

its this one:
View attachment 1423157

I now will add this amplifier into my SPICE.
And do some run - let's see if there can be any improvements.

 

[No ideas]

@No ideas
I have only a small room and a kitchen.
In my rooom I have no space left for electronics.
It is sad - I used to do audio work where I lived before.

understandable

 

[Bigun]

I like this project, reminds me of my own, because of the kinda Sziklai feel about the circuit.

Thread 'Grasshopper'

2015-06-01 7:41 pm

Grasshopper - headphone amp for Grado

Headphone amplifier for Grado.

I just took delivery of some headphones. They have a low impedance of 32R which doesn't vary too wildly with frequency. It seems that they don't use a lot of voltage, line-level is enough. They will sit in their box until I have made something with my own hands to drive them.

I've never heard, designed or made a headphone amplifier before; time for Grasshopper to learn....

• Bigun
• Replies: 41
• Forum: Headphone Systems

There's something v satisfying in building simple topologies although there are plenty of details that need attention to make it an interesting project. I haven't used my amp for a few years, your thread has brought back some good memories of it.

 

[lineup]

I did feed the one watt into my SPICE.
At 1W into 8 Ohm it shows THD 0.053%
The circuit is very accurate regarding output DC-volt 5.9V
and output bias 0.3A

Here is my circuit in simulation:

 

[No ideas]

could you try to swap the constant current source with a bootstrap circuit?

 

[Bigun]

@No ideas
I have only a small room and a kitchen.
In my rooom I have no space left for electronics.
It is sad - I used to do audio work where I lived before.

Maybe something like this?

 

[lineup]

could you try to swap the constant current source with a bootstrap circuit?

I will try this.
Wait some hour

It look like the CCS is like 1.2mA. This is very little ...

 

[No ideas]

Maybe something like this?

View attachment 1426351

That looks cool