Audio buffer amplifier

[cumesoftware]

Well, I discovered that if I use a zener and a resistor network to stabilize the base, I might be able to kill the hum almost completely. The higher the resistor in series with the zener, the better. At this point, a JFET might be the best solution.

Of course, I tried to use 10K resistors at the base, but only attenuated the hum. And with 330K resistors it ran into distortion.

 

[cumesoftware]

Well. The discrete amplifier was a dissapointment, With FETs or no FETs, with zenner or no zenner. The thing still has supply humming with a filtering with 5% ripple.

I guess I will try the OPA2134 idea. I will try it with the resistor inside and outside the loop, and without the resistor.

I wonder it the TL071 is good too.

 

[lineup]

Well. The discrete amplifier was a dissapointment, With FETs or no FETs, with zenner or no zenner. The thing still has supply humming with a filtering with 5% ripple.

I guess I will try the OPA2134 idea. I will try it with the resistor inside and outside the loop, and without the resistor.

I wonder it the TL071 is good too.

for a discrete (JFET or Biploar), to reduce hum,
I suggest a dual supply.
This way you can bias the input from 0V.
Instead of bias with 2 resistors from supply.

You can arrange for output dc-offset adjust ( to 0.00 V )
without output cap.

Or you can let there be some DC-offset and use one output cap.

 

[lineup]

Here is nice & easy Buffer, using 2 N-JFETs.

By using dual supply, +-12 Volt, for example,
we get the ampifier less sensitive to hum or supply noise.
Because ......
there are no resistors from supply to the input GATE (G).


As you can see, 1.006 Volt AC input, gives 1.000 Volt out.
( Which gives a gain very close to 1.0. Any follower will have some little drop ).

The distortion ( 0.002 % ) is so low no man alive will hear it.
This I can promise. (even if some other fools will tell you the opposite )


You can find similar Buffers at the the web, using 2 JFETs.
One upper and one lower of same sort, for Current Source.
Also in our forum, you can find such circuits.
After some searching


Lineup Happy discrete Buffering

 

[cumesoftware]

The thing is that my last experiment had the hum reduced drastically. With music it wouldn't be noticed, but with silence it would produce a bzzzzzzt. I guess I used the wrong FETs too. Is there any JFET suitable for audio?

I don't notice much difference between bipolar and JFET.

Here is nice & easy Buffer, using 2 N-JFETs.

By using dual supply, +-12 Volt, for example,
we get the ampifier less sensitive to hum or supply noise.
Because ......
there are no resistors from supply to the input GATE (G).
...
Lineup Happy discrete Buffering

Unfortunately, the project I'm doing is fed by a single external supply. However, I might use the current mirror idea to stabilize the amp further.

By the way, what software are you using?

 

[peranders]

If you use such kinds of circuits you must have a stabilized power supply and notice, better than with opamps.

 

[lineup]

The thing is that my last experiment had the hum reduced drastically.

With music it wouldn't be noticed, but with silence it would produce a bzzzzzzt.

Unfortunately, the project I'm doing is fed by a single external supply.

By the way, what software are you using?

2 methods, using only capacitors to filter input divider resistors.
( zener diodes are not best method, they are 'noisy' )

Color markings:
Blue = clean & normal.
Orange = Hum + Ripple.
Green = Good clean GROUND.

Left circuit.
You should not take input ground, from the return rail from Filter caps.
C5 is wrong. C6 input is correct.

Anything a capacitor filters away, is injected into ground.
Better use a separate line for input GND. Coming directly from 0 Volt central grounding point.

Right circuit.
Uses 2 capacitors to filter the divider.
22 uF and 10 uF. Will make even more effective reduction of any hum.

 

[lineup]

Originally posted by cumesoftware:

The thing is that my last experiment had the hum reduced drastically.

With music it wouldn't be noticed,
but with silence it would produce a bzzzzzzt.
-------------------------------------

JFETs are very good to pickup Radio Signals.
And other very high bzzzzt noise.
This is at several MHz, high above audio signals,
and should be STOPPED from entering your JFET input.

R2 + C2 is such filter added. ( 2k2 and 220pF )
C2 will filter away anything above 400.000 Hertz,
and put it away back to ground point.
So it will not go into JFET.

All amplifier needs such a little filter at input.
You see it in most every good amplifier.

People use other things to Listen to Radio and HF, high frequency noise
than audio amplifiers.

 

[cumesoftware]

So, the first two circuits are good for any kind of transistor while the third one is the one I should use for a FET right? (Well, I don't like the sound of the bipolar, since it had that lack of presence).

I assume that C3 filters 100Hz frequencies coming from the supply. Am I right?