When I "play" with Arta software and Focusrite and do a loopback test using the internal generator (1 kHz sinus) the lowest distortion I can get (THD+N) is about 0.008%. 3rd harmonic is about 105 - 106 dB down compared to the fundamental. 2nd harmonic a bit lower. Is this "good enough" to be able to adjust BA3-pre distortion?
If test generator has more distortion than BA3-pre then I need to find an external generator which can do better?
What can be expected from BA3-pre if adjusted to lowest (3rd harmonic) distortion?
If test generator has more distortion than BA3-pre then I need to find an external generator which can do better?
What can be expected from BA3-pre if adjusted to lowest (3rd harmonic) distortion?
Ok.....it drives the MoFo's so I thought that set for minimum distortion with 3rd harmonic…...would be best for MoFo which is 2nd harmonic…..but we will see. Set to 2nd harmonic I have to know which way to turn the pot to get the "right" 2nd harmonic. I have installed the P3 with CW end as indicated in the schematic but it seems some have installed it reversed? For P1 and P2 I get more bias turning clockwise so here I also installed the pots according to schematic. Did you install the pots like this? …...think this is important if I watch the P3 YouTube video.....as I have no equipment to view the fase of the distortion.
It doesnt matter. Just turn P3 in the direction where you see H2 decreasing till it is at its lowest. This is what Mr. Pass refers to as the null point. The THD will also be lowest at this point.
From this null point H2 will increase whether you turn P3 CW or ACW. In one direction you will get positive phase of H2 and in the other the negative phase of H2. What matters is that in one direction the music staging seems to come a bit forward and in the other seems to go back a bit back. Set it the way you prefer. Also instrument timbre changes as you reintroduce some H2. Again, set it the way you prefer. Very easy to make out the difference in sound if you can play a classical violin and piano piece.
For a further understanding refer to post #146 in
H2
nash
I have made some measurement and I have played with P3 on one channel (using Focurite and Arta). I tried to adjust to minimum distorsion. The lowest I could get is shown at the picture. 2nd harmonic is still a bit higher than 3rd harmonic. So I am not able to get dominant 3rd harmonic using this measuring method. But as it is the lowest I can get then maybe a dedicated HP instrument with a 100% clean generator would show dominant 3rd?
I get THD = 0x0037% and THD+N = 0x0080%
Is that considered OK for the BA3-pre?
50 Hz hum is down with a bit more than 100 dB.....it is still visible....so not a 100% success with my external PSU. This is with top cover on (but not secured). When I take top cover off the 50 Hz noise goes up to -85 dB or so.....so very sensitive "stuff"...…..
I get THD = 0x0037% and THD+N = 0x0080%
Is that considered OK for the BA3-pre?
50 Hz hum is down with a bit more than 100 dB.....it is still visible....so not a 100% success with my external PSU. This is with top cover on (but not secured). When I take top cover off the 50 Hz noise goes up to -85 dB or so.....so very sensitive "stuff"...…..
Attachments
The other channel I was able to adjust just a fraction better.
THD = 0.0035%, THD+N = 0.0084%
Here 2nd and 3rd are almost equal. If I leave it there for now I don't hope the small channel difference will destroy the "imaging" or make it sound bad...….
Should it be possible to zero out the 2nd harmonic completely?
THD = 0.0035%, THD+N = 0.0084%
Here 2nd and 3rd are almost equal. If I leave it there for now I don't hope the small channel difference will destroy the "imaging" or make it sound bad...….
Should it be possible to zero out the 2nd harmonic completely?
Attachments
Yes, my setup looks like that on the picture. When you use Arta with internal generator the signal comes out at the back of FocusRite. From the back I connect to the input of the pre and the output from pre I connect to the input of the FocusRite. Then you have to find the right amount of internal damping of the test generator (I set to -3dB) combined with the right amount of monitor, input sensitivity of FocusRite and Volumen control of the pre 
Before that you have to find adapters that works so you can connect to RCA from FocusRite. I have spend some time with that and also playing with Arta and loopback test. First step is to be able to make a loop back test and play with Arta (spectrum analyzer) and learn how it works. I will say now after measuring that it is mandatory to adjust P3 as before that the distortion was 5-10 times higher than after the adjustment. Will see after a listening test if I can hear a difference. Then later I can adjust to more dominant 2nd harmonic…….if I want.
I did not recheck bias and offset.....maybe P3 could change these settings……?
Before that you have to find adapters that works so you can connect to RCA from FocusRite. I have spend some time with that and also playing with Arta and loopback test. First step is to be able to make a loop back test and play with Arta (spectrum analyzer) and learn how it works. I will say now after measuring that it is mandatory to adjust P3 as before that the distortion was 5-10 times higher than after the adjustment. Will see after a listening test if I can hear a difference. Then later I can adjust to more dominant 2nd harmonic…….if I want.
I did not recheck bias and offset.....maybe P3 could change these settings……?
Attachments
I use jack to RCA on both input and output of FocusRite. They comes in many variations. The one that worked for me is a "mono jack" to RCA. Something like this (but it was not actual that one…..but will probably work as I think these can be wired in only one way).
Monoprice 1/4in (6.35mm) TS Mono Plug to RCA Jack Adapter, Gold Plated (Yellow plastic center) - Monoprice.com
Monoprice 1/4in (6.35mm) TS Mono Plug to RCA Jack Adapter, Gold Plated (Yellow plastic center) - Monoprice.com