Nope. Don't even bother trying. I know in the guide I alluded to it being possible, (and in retrospect saying that was incorrect) -- after building and adjusting quite a few projects with P3, you must be able to see what you are doing if you are wanting channel to channel symmetry.
Having the ability to properly adjust and getting the amplification spectra balanced in both channels is nothing short of amazing sonically. You'll be very impressed.
Do you have a computer? ARTA software and a USB audio interface such as a Focusrite Scarlet or Tascam is a superior solution to any analog distortion meter. (And an impressive amount more inexpensive...)
ARTA Software
Focusrite Scarlett 2i2 | Sweetwater
TASCAM US-2X2 USB Audio Interface | Sweetwater
I decided to get a 2i2 and found a good price for it here …...I think…..in Europe:
Focusrite Scarlett 2i2 2nd Gen – Thomann Danmark
...if you don't need to load or save files the ARTA software seems to be free of use…….
I believe I will get this same unit. However, I have no idea what I am doing with it, or what ancillary tidbits are needed to use this device with ARTA in adjusting P3. Post your set up and so forth, I am going to start an "Adjusting P3" thread once I have this down. I have 3 different units with P3, and I am sure there are many others do too.
Russellc
I have not received the 2i2 yet and have never used the ARTA software before. I assume that the ARTA software is able to recognize the 2i2 when it has been installed on a PC. Then we will see what kind of cable adapters is needed to get the e.g. RCA out of a preamp into the 2i2 analog inputs. Then we will see what kind of measurements can be performed. Some kind of FFT analyze and maybe also a normal digital scope function. What could be nice is if the distortion waveform could be displayed like in 6L6's video...….we will see…...but fun to learn something new.
In messaging 6l6, it sounds like the basic procedure can be accomplished and it makes a big difference just getting the channels symmetrical....then there is the whole adjustment of various distortion levels to taste. Seems a lot is left on the table with these units with P3 if you can't set it properly. Just leaving them both mid position is no guarantee the two channels are symmetrical distortion wise.
Looking forward to figuring this out. Then anyone with this relatively inexpensive device can set it far better.
Russellc
I followed advice from xrk971 on this and made the following input protection/load circuit for my interface.
Sorry for the shoddy diagram, not my forte. In any case, R3/4 serve to limit the voltage going into the interface as a safety measure. I used 10-50W resistors for amp measurements, but for preamp i guess much less will do fine. I guess it's possible to do both channels simultaneously, in which case you'd need two of these, with one input on your 2i2 per channel.
Hope that's useful.
Sorry for the shoddy diagram, not my forte. In any case, R3/4 serve to limit the voltage going into the interface as a safety measure. I used 10-50W resistors for amp measurements, but for preamp i guess much less will do fine. I guess it's possible to do both channels simultaneously, in which case you'd need two of these, with one input on your 2i2 per channel.
Hope that's useful.
Attachments
In Jim's video for adjusting P3, watch as the the scope shows second harmonic go from being "in phase" to "out of phase" as he turns the pot. The spectrum analyzers were talking about here show the harmonics in relationship to the fundamental, but I don't really have handle on whether I'm adjusting the second harmonic in phase or out of phase with the others, or how much it really matters. This is something I would like to see cleared up in an "adjusting P3" thread.
I have a 2i2 also...when I get a chance I'll post pictures of the connections I've used in the past. Not saying they're correct, but I have had some results.
Maybe someone should start that new thread so we can post there.
I have a 2i2 also...when I get a chance I'll post pictures of the connections I've used in the past. Not saying they're correct, but I have had some results.
Maybe someone should start that new thread so we can post there.
I have 4 of these Pete Millett PCBs and components:
Regulated DC filament supply
I have component values suggested by Pete to upgrade it to a 24V supply. Do you think such supplies are noise free enough to be used as +-24V DC supplies for the BA-3 preamp or other preamps?
It was for a 300B project where I ended up using Rod Coleman regulators so I have 4 of these Pete Millett PCBs I want to use for something. I will probably put the regulator on an external heatsink and then maybe design it for 1A 24V which should be sufficient for most preamps?
Regulated DC filament supply
I have component values suggested by Pete to upgrade it to a 24V supply. Do you think such supplies are noise free enough to be used as +-24V DC supplies for the BA-3 preamp or other preamps?
It was for a 300B project where I ended up using Rod Coleman regulators so I have 4 of these Pete Millett PCBs I want to use for something. I will probably put the regulator on an external heatsink and then maybe design it for 1A 24V which should be sufficient for most preamps?
Ok.....if I design carefully so there is only 2V or so drop over the regulator not much heat will be dissipated so the PCB mounted heatsink can work. The regulator uses Schottky diodes which is nice. Also I have the common mode chokes which is nice too…..then I will probably built a couple of 2 x 24V external supplies that can be used for preamps.
Yes, there must be some tolerances......but 10% is a lot. 230 VAC …...goes down to 210 VAC. I think the mains is more stable where I live. So if I design with 3-4 volt over the regulator I hope to be safe. It can regulate at 1.25 V diff. Don't hope the mains can go 10% up. Have to look at the C/W of the heatsink...….