I saw a simple amplifier but thought maybe I can do it better without to many components.
Here is the result. Its not very temperature stable but in class A it gets less hot the louder you play.
So it is just to measure the current in the output transistors = voltage over R8 or R9 and adjust it with P1 to
a little more than Feed voltage / 4 * R speaker. But take half an Hour for the heat to be stable after the last adjustment.
It is easily adapted to other voltages and speaker impedances. Distortion is about 0,1% which maybe some people don't hear.
Noise is extremely low under 5 uv 20 - 20k. Common mode rejection is determined by C2. Frequency response is good 25 Hz to 95kHz -3dB.
View attachment 1418335
But looking at the results it is possible to do it much better. Faster and much lower distortion but a little more noise.
The problem now is that the P1 is very sensitive in adjusting the current.
Now the anti thump + radio interference filter on the input is included. But still pretty simple.
I changed the R12 to 0,82 ohm because I believe the IRF 540 has about 5S at about 1A.
Here is the result. Its not very temperature stable but in class A it gets less hot the louder you play.
So it is just to measure the current in the output transistors = voltage over R8 or R9 and adjust it with P1 to
a little more than Feed voltage / 4 * R speaker. But take half an Hour for the heat to be stable after the last adjustment.
It is easily adapted to other voltages and speaker impedances. Distortion is about 0,1% which maybe some people don't hear.
Noise is extremely low under 5 uv 20 - 20k. Common mode rejection is determined by C2. Frequency response is good 25 Hz to 95kHz -3dB.
View attachment 1418335
But looking at the results it is possible to do it much better. Faster and much lower distortion but a little more noise.
The problem now is that the P1 is very sensitive in adjusting the current.
Now the anti thump + radio interference filter on the input is included. But still pretty simple.
I changed the R12 to 0,82 ohm because I believe the IRF 540 has about 5S at about 1A.
Hi,
I have been looking around for simple class A amps. Ofc you can't get around the Pass stuff, but what I like in your design is the fact that it doesn't use hard to get exotic parts like jfets of 8 euro per piece that need to be matched etc.
You did build it I suppose, remarking it takes half an hour to stabilise, how does it sound?
Thanks!
I have been looking around for simple class A amps. Ofc you can't get around the Pass stuff, but what I like in your design is the fact that it doesn't use hard to get exotic parts like jfets of 8 euro per piece that need to be matched etc.
You did build it I suppose, remarking it takes half an hour to stabilise, how does it sound?
Thanks!
The topology of the output stage here is called Shunt Regulated Push Pull.
Based on circuit from the OP, the output stage can and only work in Class A. It cannot transition to class B. I don't like it.
It is more like an improved version of single ended class A that with an active load, so that it forms a push pull and only requires half of the current comparing to single ended class A.
Based on circuit from the OP, the output stage can and only work in Class A. It cannot transition to class B. I don't like it.
It is more like an improved version of single ended class A that with an active load, so that it forms a push pull and only requires half of the current comparing to single ended class A.
I learned the output topology in the 1960s- At that time it was used with tubes and 800 ohm voice coil speaker elements.
It was called ironless amplifier as it had no output transformer.
I used the topology 1973 as i updated a sinus oscillator from the 1940;s to be better than 0,01% distortion with only three tubes.
I must confess i too dont like the topology although it is my baby.
An opamp at the input would give much better results and thermal stability. But then we will leave the simpliest possible.
It was called ironless amplifier as it had no output transformer.
I used the topology 1973 as i updated a sinus oscillator from the 1940;s to be better than 0,01% distortion with only three tubes.
I must confess i too dont like the topology although it is my baby.
An opamp at the input would give much better results and thermal stability. But then we will leave the simpliest possible.
Hi
Thanks for coming back on this stigigemla
I have basic knowledge about electronics, but wouldn't be able to design something like this myself. So, here to learn and watch. In the mean time I also found this one, which seems quite nice and also simple:
I made a simple headphone amp with an OP-AMP and a BJT push-pull output stage. Experimenting with various OPamps I noticed clear differences between them. I tried for example the classic NE5532, the OPA275 and finally settled for an AD823. Interesting stuff what we can hear but might be hard to measure!
Thanks for coming back on this stigigemla
I have basic knowledge about electronics, but wouldn't be able to design something like this myself. So, here to learn and watch. In the mean time I also found this one, which seems quite nice and also simple:
I made a simple headphone amp with an OP-AMP and a BJT push-pull output stage. Experimenting with various OPamps I noticed clear differences between them. I tried for example the classic NE5532, the OPA275 and finally settled for an AD823. Interesting stuff what we can hear but might be hard to measure!
Now you've got a differential amp and still kept it minimalist. That's better!
There is no reason for not having a differential amplifier and there are many reasons to have it.
CMRR is one of them, otherwise ripple from power supply ends up in the speakers.
You can simulate the ripple by adding an 120Hz AC source of about 2V, for example, in series with the DC source to check.
There is no reason for not having a differential amplifier and there are many reasons to have it.
CMRR is one of them, otherwise ripple from power supply ends up in the speakers.
You can simulate the ripple by adding an 120Hz AC source of about 2V, for example, in series with the DC source to check.
The CMRR is not very good because the diff has no current generator. But it is planned for an old laptop PSU.
They use mostly around 40kHz switchmode technic so the R13 + C9 and C6 takes most of the ripple.
They use mostly around 40kHz switchmode technic so the R13 + C9 and C6 takes most of the ripple.