Here is one example how to use GNFB with balanced inputs.
GNFB = 9 dB, THD = 1,4 % @ 12,6 W out. Input sensitivity ~ 1 Vrms
GNFB = 9 dB, THD = 1,4 % @ 12,6 W out. Input sensitivity ~ 1 Vrms
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That isn't balanced, as the two 330k at the input are not balanced. One goes to ground, the other to the output. Balanced means balanced impedances as well as +- inputs.
This is how balanced input is usually done if a transformer is not used.
Anyhow it has good CMRR so it works as it should.
With op-amps this is an usual method.
Anyhow it has good CMRR so it works as it should.
With op-amps this is an usual method.
Hi,
Ok i finally got round to doing the things you guys said.
Grid resistor to 1K
Reverse output secondaries
try various feedback values
It worked out nice with 100k for the feedback, gave just about 50% feedback. Got a nice sine and square wave out of it at 1k and 10k input signal. It goes way loud and sounds nice. will see in the next couple of weeks if i want to keep it to this feedback level or experiment a bit.
Thanks for the help!
Joris
Ok i finally got round to doing the things you guys said.
Grid resistor to 1K
Reverse output secondaries
try various feedback values
It worked out nice with 100k for the feedback, gave just about 50% feedback. Got a nice sine and square wave out of it at 1k and 10k input signal. It goes way loud and sounds nice. will see in the next couple of weeks if i want to keep it to this feedback level or experiment a bit.
Thanks for the help!
Joris
Hi,
Yes I will try it but not just now. My first goal was to try and get it working. Next step will be experimenting with different feedback values. Only after i've determined the amount of feedback i want and have an idea about the ratio of resistance values, i'll try balanced input.
Joris
Yes I will try it but not just now. My first goal was to try and get it working. Next step will be experimenting with different feedback values. Only after i've determined the amount of feedback i want and have an idea about the ratio of resistance values, i'll try balanced input.
Joris
OK.
Remember that the NFB-resistors do not determine the amount of GNFB alone.
The loop gain of the amplifier is also determining factor.
So if you change anything inside your amplifier but keep these 1k and 100k resistors as those are now, the GNFB will however change and can mislead your analysis.
If you modify your amplifier, check the GNFB too.
Remember that the NFB-resistors do not determine the amount of GNFB alone.
The loop gain of the amplifier is also determining factor.
So if you change anything inside your amplifier but keep these 1k and 100k resistors as those are now, the GNFB will however change and can mislead your analysis.
If you modify your amplifier, check the GNFB too.
Hi,
Yes i do realize that but thanks for reminding me. I'm actually not planning on making changes to the basic circuit. The input stage gives a gain of about 10x i think. Should be more then enough here.
The only change i might make is changing the grid resistors on the input to about 10 - 47k. Yes this is a heavier load on the pre amps but i think they can take it. value of the feedback resistor would then be 1 - 4,7M.
I'll report back.
Joris
Yes i do realize that but thanks for reminding me. I'm actually not planning on making changes to the basic circuit. The input stage gives a gain of about 10x i think. Should be more then enough here.
The only change i might make is changing the grid resistors on the input to about 10 - 47k. Yes this is a heavier load on the pre amps but i think they can take it. value of the feedback resistor would then be 1 - 4,7M.
I'll report back.
Joris
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