This is an offshoot from the Alpha Nirvana amp thread here:
https://www.diyaudio.com/community/...8ohm-class-a-amp.344540/page-110#post-6949783
@minek123 adapted @AKSA ’s 39W Class A amp to use a JFET input opamp as the input stage.
This has several advantages as explained by Minek including lower distortion, etc usual things opamps offer.
I wanted to move the discussion to a new thread as it really is a different and new amp. This will keep discussion of the original Alpha Nirvana amp less confusing for those looking for info on the base amp.
Thank you to Hugh Dean for the original Alpha Nirvana and to Minek for the new modern opamp variant.
https://www.diyaudio.com/community/...8ohm-class-a-amp.344540/page-110#post-6949783
@minek123 adapted @AKSA ’s 39W Class A amp to use a JFET input opamp as the input stage.
This has several advantages as explained by Minek including lower distortion, etc usual things opamps offer.
I wanted to move the discussion to a new thread as it really is a different and new amp. This will keep discussion of the original Alpha Nirvana amp less confusing for those looking for info on the base amp.
Thank you to Hugh Dean for the original Alpha Nirvana and to Minek for the new modern opamp variant.
Ok, thread is moved, so I'll post my next question here.
Could you post some loop gain plots? I'm guessing it's pretty high? See any issues stabilizing it? I'm guessing it could differ a lot depending on the op-amp, so swapping op-amps could be tricky?
Could you post some loop gain plots? I'm guessing it's pretty high? See any issues stabilizing it? I'm guessing it could differ a lot depending on the op-amp, so swapping op-amps could be tricky?
My favorite opamp is the OPA1656, and recently a single version came out called OPA1655. Vunce and I both have some on hand ordered direct from TI. The specs are amazing and sound is quite special. Capable of 100mA drive too.
https://www.ti.com/lit/ds/symlink/opa1655.pdf
https://www.ti.com/lit/ds/symlink/opa1655.pdf
Hi Minek
I will spice up a Bode plot.
I have been keen to use the OPA1656 as front end as I've tried them and I think this IC family has finally come of age.
As Minek and X mentioned the combo of matched jet input stage, control of offset without a shunt electro and low cost makes it irresistible.
By setting the output driver base at ground you fix the opamp output at +1.6V and this skews its offset which avoids crossover discontinuities, giving quasi Class A operation. Very good design, and while independent IC supplies are not convenient on the pcb layout the decoupling from the output stage gives very high PSRR and very low hum/noise. This is a mark of a superior design.
Minek, I agree with your resistor values although I need to do more analysis....
Rallyfinnen makes a good point on the take up point of the bootstrap cap. He found much better bass with the cap taken to the source of the nmos.
Thank you for adding excellent value to the AN!
Hugh
I will spice up a Bode plot.
I have been keen to use the OPA1656 as front end as I've tried them and I think this IC family has finally come of age.
As Minek and X mentioned the combo of matched jet input stage, control of offset without a shunt electro and low cost makes it irresistible.
By setting the output driver base at ground you fix the opamp output at +1.6V and this skews its offset which avoids crossover discontinuities, giving quasi Class A operation. Very good design, and while independent IC supplies are not convenient on the pcb layout the decoupling from the output stage gives very high PSRR and very low hum/noise. This is a mark of a superior design.
Minek, I agree with your resistor values although I need to do more analysis....
Rallyfinnen makes a good point on the take up point of the bootstrap cap. He found much better bass with the cap taken to the source of the nmos.
Thank you for adding excellent value to the AN!
Hugh
The feedback network is connected to the non-inverting input of U1, why is that?This is an offshoot from the Alpha Nirvana amp thread here:
https://www.diyaudio.com/community/...8ohm-class-a-amp.344540/page-110#post-6949783
@minek123 adapted @AKSA ’s 39W Class A amp to use a JFET input opamp as the input stage.
This has several advantages as explained by Minek including lower distortion, etc usual things opamps offer.
I wanted to move the discussion to a new thread as it really is a different and new amp. This will keep discussion of the original Alpha Nirvana amp less confusing for those looking for info on the base amp.
Thank you to Hugh Dean for the original Alpha Nirvana and to Minek for the new modern opamp variant.
I was talking to the admins to change the ownership of this thread, but it doesn't look like it's going to happen.
So I created new thread Beta Nirvana Class A New Amp where I'm going to be posting new stuff.
Sorry for the confusion, it wouldn't happen if Xrk simply asked me to create new thread, instead of doing it for me.
So I created new thread Beta Nirvana Class A New Amp where I'm going to be posting new stuff.
Sorry for the confusion, it wouldn't happen if Xrk simply asked me to create new thread, instead of doing it for me.
Sorry about that Minek - was just trying to help. We can simply close this one out if that’s the case. Not much has happened here yet.
very interesting, especially if it can be a drop in replacement of the existing PCB so we don't have to tinker too much with the chassis!
Do
Do
Hi. At +/-20v its safe to use ne5534. Im betting that getting rid of d1 and d2 might be worth whatever the trade off there is downgrading from lt1056. There is also opa551 thats jfet and works up to 35v differential.
This is an amazing design and i will be building it in the near future. I bet it measures and sounds incredible.
Edit: oops just realized theres a bigger thread for this. Ill repost my comment there
This is an amazing design and i will be building it in the near future. I bet it measures and sounds incredible.
Edit: oops just realized theres a bigger thread for this. Ill repost my comment there