Yes, I'm still playing around with these to try to find a combination that suits me best. Waiting for some more caps and resistors at the moment.
Nice summary of your build!
Really great write up detailing your build Anand! I’m sure this will help potential builders of Alpha Nirvana.
Now, get to enjoy some music 😊!!
Now, get to enjoy some music 😊!!
Thanks Hugh (as well as everyone involved) for designing it and sharing it with all of us! It is definitely a very fun/enjoyable amplifier! I'm still going through my library and having a great time!
I plan lending it to a couple friends for some listening sessions. You might know one of them, Thomas and Stereo on Youtube? When possible, I'll have Fab over to my place as well, should be quite fun day! 🙂
All the best!
Do
I plan lending it to a couple friends for some listening sessions. You might know one of them, Thomas and Stereo on Youtube? When possible, I'll have Fab over to my place as well, should be quite fun day! 🙂
All the best!
Do
I know Fab from his work; I will be very interested in his review!!
The single ingredient with my amps is always 'engagement'. I like my music to be involving......
I continue developing the AN in fact. Maybe I will do one for commercial; but a Class A is always very challenging because of the high dissipation and low power; a combination which makes it expensive to build, as you know well.
Hugh
The single ingredient with my amps is always 'engagement'. I like my music to be involving......
I continue developing the AN in fact. Maybe I will do one for commercial; but a Class A is always very challenging because of the high dissipation and low power; a combination which makes it expensive to build, as you know well.
Hugh
That sounds like a fun day at your place Do. What are the main speakers you listen to with these amps?
I am looking forward for this fun day…..😉
As you have probably noticed Do is a very prolific amplifiers builder and he also gives me the chance to listen to his second to none realizations🙂
Fab
As you have probably noticed Do is a very prolific amplifiers builder and he also gives me the chance to listen to his second to none realizations🙂
Fab
No, Mr. DIY is actually another DIY person, I never met him. I see the videos and Thomas makes many references about him but I don't know him.
Best!
Do
Best!
Do
Actually, Hugh, post #1 has (in your original blue schematic) ... R4 = 220R and R5 = 33R.
This became (in the v2 white schematic a bit lower down in post #1) ... R5 = 330R and R6 = 47R.
This then became (in the white schematic further down in post #1, with X's "As Built" values - and using the new component numbering matching the PCBs) ... R114 = 330R and R115 = 47R.
This was for the 8R version ... the 4R schematic (that I think you gave me) which I used for:
- the 8R-to-4R numbering translation table that I developed
- and my 4R build
... had R6 / R114 = 330R and R7 / R115 = 33R.
Anyway, I've just measured one of my AN 4Rs (and the other one should be the same, as I bought lots of the KSA992FTAs and carefully matched them). The LTP current (through R113 on the PCB - which in my case was 100R) was 2.4ma ... with output offsets of -3mV and -5mV.
So it seems I lucked out with the LTP current, when chasing zero DC offset! 👍
Andy
I thought I would share some findings from my experiments with the AN.
Playing around with the sim, I tried moving the bootstrap caps a bit, and found that moving the upper bootstrap cap (C131) to the source instead of the output (other side of the source resistor) just about halves the output impedance of the amp. I could not believe it would make such an impact, but that seems to be the case. I also ran a sim with the tian probe and distortion sims, and nothing seems to change there. So, a couple of days ago I did the modification. It was pretty easy, I only had to drill a new hole, turn the cap 90deg and solder in one leg in the new hole. The source resistor limits the diameter of the cap, so I had to take what I had, and that ended up to be 1000uF that were smaller in diameter, but higher. The value should not matter much, I went from 470u that I built the amp with.
After the mod I did some quick distortion measurements just to check, and they seemed to be the same as before.
The first listening impression was that bass had more 'transient attack' and more control, and that impression has lasted while I have been listening to the amp. More of the so called PRAT I would say, more foot-tapping when I listen now than before..
I think there is less of the smoothness and (single ended?)character the amp had in the original configuration. So I think in summary, if you are keen on experimenting, and listen to music with dynamic bass (drums, bass etc) I would recommend trying this out, but if you only listen to classical and acoustic music and like it sweet and smooth, I think the original setup is probably better.
I attach a schematic and picture of the moved bootstrap, here you can also see the values I used in the nested feedback, and I'm pretty happy with that. I still plan to try 1n on the cap instead of 2.2n.
Don't mind the cut traces and cables on the picture, those are for my separate front end supply.
Playing around with the sim, I tried moving the bootstrap caps a bit, and found that moving the upper bootstrap cap (C131) to the source instead of the output (other side of the source resistor) just about halves the output impedance of the amp. I could not believe it would make such an impact, but that seems to be the case. I also ran a sim with the tian probe and distortion sims, and nothing seems to change there. So, a couple of days ago I did the modification. It was pretty easy, I only had to drill a new hole, turn the cap 90deg and solder in one leg in the new hole. The source resistor limits the diameter of the cap, so I had to take what I had, and that ended up to be 1000uF that were smaller in diameter, but higher. The value should not matter much, I went from 470u that I built the amp with.
After the mod I did some quick distortion measurements just to check, and they seemed to be the same as before.
The first listening impression was that bass had more 'transient attack' and more control, and that impression has lasted while I have been listening to the amp. More of the so called PRAT I would say, more foot-tapping when I listen now than before..
I think there is less of the smoothness and (single ended?)character the amp had in the original configuration. So I think in summary, if you are keen on experimenting, and listen to music with dynamic bass (drums, bass etc) I would recommend trying this out, but if you only listen to classical and acoustic music and like it sweet and smooth, I think the original setup is probably better.
I attach a schematic and picture of the moved bootstrap, here you can also see the values I used in the nested feedback, and I'm pretty happy with that. I still plan to try 1n on the cap instead of 2.2n.
Don't mind the cut traces and cables on the picture, those are for my separate front end supply.
Rf
Thanks for the report back! If you have the ability to measure the output impedance at say a test frequency of less than 500Hz (perhaps 100Hz), that would be useful info as well.
I believe the original design has a damping factor of 160 into 8 ohms, or about 0.05 ohms. Did you get an output impedance of 0.025 ohms, i.e. a damping factor of 320 into 8 ohms? Either number imho opinion is very adequate.
Best,
Anand.
Thanks for the report back! If you have the ability to measure the output impedance at say a test frequency of less than 500Hz (perhaps 100Hz), that would be useful info as well.
I believe the original design has a damping factor of 160 into 8 ohms, or about 0.05 ohms. Did you get an output impedance of 0.025 ohms, i.e. a damping factor of 320 into 8 ohms? Either number imho opinion is very adequate.
Best,
Anand.
Depending on the nested feedback config, the output impedance will vary with frequency, so I only used the theoretical minimum which was just under 15mOhm in standard config, and just under 8mOhm with the bootstrap moved. I have not measured it, and I think I would mostly be measuring wiring resistance etc if I attempted to measure, and I would also have to move the capacitor back to the original position to compare the measurements.
I'm happy with the sim results, and the subjective test.
I post the sim bode plots with and without nested feedback (using my values, not the original ones), comparing the bootstrap cap position. Keep in mind that the impedance minimum will be at even lower frequency using the 4.7n in the nested feedback. Simulation is done with 1VAC fed though 1Ohm resistor to the output of the amp, and voltage on the amp output is plotted.
I'm happy with the sim results, and the subjective test.
I post the sim bode plots with and without nested feedback (using my values, not the original ones), comparing the bootstrap cap position. Keep in mind that the impedance minimum will be at even lower frequency using the 4.7n in the nested feedback. Simulation is done with 1VAC fed though 1Ohm resistor to the output of the amp, and voltage on the amp output is plotted.
I just found another thing in simulation. My turn on thump got worse (really only a temporary offset though, because it's slow and inaudible) when I put in the 1000u for C131 in the mod above, so I simulated different cap values. I have now ordered 1500u that I will use for C132 keeping C131 1000u as is. According to sim that will give me a slow 2V negative thump. That will do, because that is what I could get locally.
The best combination I have found in simulation is C131=470u and C132=820, this is almost flat in simulation, only a slow 0.2V variation on the output at startup. Should be totally inaudible and not visible on the woofers when no output relays are used. Well, maybe I'm the only one running without output relays? Bigger caps also delay the time before current starts flowing through the output stage, in this case abt 120ms from power on. This would give the PS some time to settle before current starts flowing. See graph below.
I could not come up with a smooth startup using smaller caps.
The best combination I have found in simulation is C131=470u and C132=820, this is almost flat in simulation, only a slow 0.2V variation on the output at startup. Should be totally inaudible and not visible on the woofers when no output relays are used. Well, maybe I'm the only one running without output relays? Bigger caps also delay the time before current starts flowing through the output stage, in this case abt 120ms from power on. This would give the PS some time to settle before current starts flowing. See graph below.
I could not come up with a smooth startup using smaller caps.
Output relays also prevent damage from a bad output stage that puts out full rail DC offset. It’s a wise thing to have if you value your speakers. The SSR cost $60/channel ready to run and can protect a much more expensive (or hard to find) woofer. Plus, no more turn on or off thumps.
Yes, it's just that I prefer to do it this way. My woofers are nothing special, standard 8" and it would be a good reason to upgrade them if they blew. Why pay the same for the insurance on the old car as you would pay for a new car 😉
So, instead I try to minimize the thumps, and share the info in case it would be useful to somebody else.
So, instead I try to minimize the thumps, and share the info in case it would be useful to somebody else.