i'm making an opa549 based amp when the amps gain is -6 and the buffers gain is -5 , that way u get gain = 30
UrSv said:
😱
I have a pre (OPA627+BUF634) with a gain at around 3.5x.
My power amp has a gain of 22x.
Can you make me those maths?😱
My audio buffer was already finished on yesterday night. 😀 Oh! I heard very nice sound from mine. Anyway, after I turned off CD player but did not turn off my amp, I heard humming. 
How will I do?
How will I do?
theres nothing wrong with that 😀
anyways
try to use a resistor between input and ground to reduce input impedance , maybe that will help
anyways
try to use a resistor between input and ground to reduce input impedance , maybe that will help
Yes, there are nothing wrong 🙂 Ummm! I have to check it again on this night.
The buffer brings more details of sound out. I think it like the crystal sound. 😀
The buffer brings more details of sound out. I think it like the crystal sound. 😀
I used simple power supply circuit for mine and didn't use any regulator. I think I should apply the regulator for my preamp.
Lee
here it is, my psu, including the tube part:
Actually, I did not use regulators for the opamp, but maybe it is better? I will try it.
I simplified the schematic of my hybrid amp:
I removed the cathode bypass capacitor. This way, there is local current feedback in the tube stage, this way reducing the gain and distortion.
It should be possible, to build a push pull amp with two EL84, what give 10-15 watt.
Just an idea... 😎
Franz
here it is, my psu, including the tube part:
An externally hosted image should be here but it was not working when we last tested it.
Actually, I did not use regulators for the opamp, but maybe it is better? I will try it.
I simplified the schematic of my hybrid amp:
An externally hosted image should be here but it was not working when we last tested it.
I removed the cathode bypass capacitor. This way, there is local current feedback in the tube stage, this way reducing the gain and distortion.
It should be possible, to build a push pull amp with two EL84, what give 10-15 watt.
An externally hosted image should be here but it was not working when we last tested it.
Just an idea... 😎
Franz
For my PSU, I used R 1K to step down voltage from +/-34V to be +/-15V. 😀 It's not so good solution but I don't want transformer 2 Pcs, just one piece O.K. for me 😉
So, why not use regulators, to provide the +-15V (just some mA)?
But: some german engineers told me, 7815/7915 are not the best choice, (too much noise?).
But don't ask me, what could be the better choice.
Franz
But: some german engineers told me, 7815/7915 are not the best choice, (too much noise?).
But don't ask me, what could be the better choice.
Franz
Hi Franz,
A simple LM317/337 PSU will do.
Make it like on the amp, that is, with the same component values for Cadj. (33~47uf cap) and the small film cap on the output (47~100nf).
It works very well on the LM338, and also on the LM317/337.😎
Oh, you should have good regulation if you want to bias the op-amp into class-A, don't do it with an unregulated PSU.
I see you have now the OPA637😉 , with a gain of 21.😱
A simple LM317/337 PSU will do.
Make it like on the amp, that is, with the same component values for Cadj. (33~47uf cap) and the small film cap on the output (47~100nf).
It works very well on the LM338, and also on the LM317/337.😎
Oh, you should have good regulation if you want to bias the op-amp into class-A, don't do it with an unregulated PSU.
I see you have now the OPA637😉 , with a gain of 21.😱
No, Carlos
I still use the 627, as I have just this type. But I wrote 637 in the scratch drawing, because it uses gain.
BTW: whats wrong with a gain of 21?
You're confusing me more and more with your so called "class-A". Class A-amps normally really don't benefit from regulated supplies!
Franz
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