Hi!
I have this circuit in my new project. I’s plays nice but I need some ideas to keep the dc offset at 0V. The problem is biggest when I start it up, DC power on and then the dc offset is about -2V. After a wile when the circuit is warm then it’s down to 0,2V.
Please give me some god ideas.
See picture...
Ola A.
I have this circuit in my new project. I’s plays nice but I need some ideas to keep the dc offset at 0V. The problem is biggest when I start it up, DC power on and then the dc offset is about -2V. After a wile when the circuit is warm then it’s down to 0,2V.
Please give me some god ideas.
See picture...
Ola A.
Attachments
For differential input amps without a servo the feedback input is often:
1) tied into a variable resistor between +V and -V to sum in a warm-mode output null-offset voltage. This compensates for the imperfect matching between components
2) a large cap is placed in series with the feeback resistor to ground... typically 470uF paralled with 100pF for high freq rejection. this allows only AC feedback
Take a look at the Krell KSA100 or SysSym amp threads for examples.
1) tied into a variable resistor between +V and -V to sum in a warm-mode output null-offset voltage. This compensates for the imperfect matching between components
2) a large cap is placed in series with the feeback resistor to ground... typically 470uF paralled with 100pF for high freq rejection. this allows only AC feedback
Take a look at the Krell KSA100 or SysSym amp threads for examples.
Hi
If you add all the current sources to your per amp then your circuit is not all that different from the one that I normally use.
The main difference is that I use LM394, a dual transistor, for the input diffrential pair.
I agree with the replies you have received to date. However I have been able to avoid using a capacitor in the feedback by adjusting the values of the resistors. It does take some time however.
I also found that the current source of the diferential pair was critical. Possibly this is your problem area. It helps if that supplies a constant current as the temperature varies.
I also found that fastening all the transistors to a common heatsink helped. Heatsinking the input pair and the current supply to the differential pair on one heatsink made the bigest difference. ( Most of my circuits use p to p wiring so I simply aligne the transistors that I want to heatsink.)
Just my findings but I hope this helps.
Don
If you add all the current sources to your per amp then your circuit is not all that different from the one that I normally use.
The main difference is that I use LM394, a dual transistor, for the input diffrential pair.
I agree with the replies you have received to date. However I have been able to avoid using a capacitor in the feedback by adjusting the values of the resistors. It does take some time however.
I also found that the current source of the diferential pair was critical. Possibly this is your problem area. It helps if that supplies a constant current as the temperature varies.
I also found that fastening all the transistors to a common heatsink helped. Heatsinking the input pair and the current supply to the differential pair on one heatsink made the bigest difference. ( Most of my circuits use p to p wiring so I simply aligne the transistors that I want to heatsink.)
Just my findings but I hope this helps.
Don
sources that every one today uses
If I was using resistors then I had used that in the schematic.
I have really god ones with led as voltage fix. And npn transistors for the high output impedance… sources that every one today uses
Thanks AMV8 I almost expected that solution. However the input N-fet are in the same substrate. Even if you put everything on a common heat sink how long time takes it to you get to the correct dc-offset? or do you play from the beginning with a high DC-offset. The speakers don’t have any problem with a couple V as long you playing music…
If I was using resistors then I had used that in the schematic.
I have really god ones with led as voltage fix. And npn transistors for the high output impedance… sources that every one today uses
Thanks AMV8 I almost expected that solution. However the input N-fet are in the same substrate. Even if you put everything on a common heat sink how long time takes it to you get to the correct dc-offset? or do you play from the beginning with a high DC-offset. The speakers don’t have any problem with a couple V as long you playing music…
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