Last night I completed the my BA3 preamp. I am using a simple CRC PSU (50VA 2 x 18V sec., 10000uF, 10R, 10000uF) and an old enclosure for this first test phase. If it turns out as good as everyone has been saying I may try the balanced version. Either way, it will get a decent enclosure with a well regulated PSU some time in the future.
It is currently driving my Aleph J in my study. Sounded a bit harsh when I switched it on but it is getting better as it and the AJ warm up.
1. Does anyone have any idea how long a burn in I should allow for before the sound stabilizes?
2. Has anyone else used Vishay MKP 1839 10uF in this (or other) amps?
And now a real noob question: To test in my main setup I require dual outputs (I bi-amp my old Magnepan MG3A's).
3. Can I simply parallel connect two RCA connectors to the D and G pads?
Thanks,
Albert
Build info:
I used the store board and I followed the BOM and Pass standards (Dale RN55D/CMF55 and Panasonic 3W resistors, matched Toshiba 2SJ74/2SK170, matched Toshiba 2SJ313/2SK2013, 1000uF Silmic II) but used Vishay 1839 10uF for C3 as I had some in my drawer.
Volume control is through a home built 50k 24 step shunt attenuator using Takman resistors (was the volume control in my B1 until recently).
I left P3 in the middle for now and biased the fets to a 1V drop across R10/R11 with minimal DC offset .
It is currently driving my Aleph J in my study. Sounded a bit harsh when I switched it on but it is getting better as it and the AJ warm up.
1. Does anyone have any idea how long a burn in I should allow for before the sound stabilizes?
2. Has anyone else used Vishay MKP 1839 10uF in this (or other) amps?
And now a real noob question: To test in my main setup I require dual outputs (I bi-amp my old Magnepan MG3A's).
3. Can I simply parallel connect two RCA connectors to the D and G pads?
Thanks,
Albert
Build info:
I used the store board and I followed the BOM and Pass standards (Dale RN55D/CMF55 and Panasonic 3W resistors, matched Toshiba 2SJ74/2SK170, matched Toshiba 2SJ313/2SK2013, 1000uF Silmic II) but used Vishay 1839 10uF for C3 as I had some in my drawer.
Volume control is through a home built 50k 24 step shunt attenuator using Takman resistors (was the volume control in my B1 until recently).
I left P3 in the middle for now and biased the fets to a 1V drop across R10/R11 with minimal DC offset .
Thanks for the tip. I think I have read this before, but have not really looked into it or tested different cap sizes myself. The current PSU is one I had lying around for another project, so worth using to test the BA3. A good regulated supply (the store super regulator?) should be next. Would the current CRC PSU (with higher voltage secondaries) make a nice first stage? The reason I suggest it is that in the Pearl 2 paper Wayne describes 10000uF per rail in the first stage of the PSU.
I do think 10,000f might be a bit much for use with a super reg (according to Jan) but with a 78XX or lm317 or other reg it might be preferred. I am not sure and it might be variable depending on the circuit and type of regulator...honestly I don't know. I am guessing a shunt reg would prefer a lot more capacitance than a series reg.
I am using a CRC supply with 2x2,200f in front of a jung super regulator on mine. But I've got 10K UF in front of a shunt reg in my phono stage.
I would just use what you have and not worry too much about it.
I am using a CRC supply with 2x2,200f in front of a jung super regulator on mine. But I've got 10K UF in front of a shunt reg in my phono stage.
I would just use what you have and not worry too much about it.
Extra smoothing capacitance cannot do any harm.
It costs more, it weighs more, it takes up more space, so what, none of these make the filtering effect any worse than when using a small values of smoothing capacitance.
Pass B1 is just such an example, no fancy power supply, just a cheap wall wort plug in, followed by a single large capacitor.
6L6, You know the Peter Daniels power supply I used on my first BA-3 preamp, as you helped with its assembly greatly!
But on my second build I am using a power supply from Tubecad.com:
GlassWare PS-19 Bipolar Power Supply Kit
It is very similar, at least as far as my question goes, to the Tubecad.com power supply you used on your build thread BA-3 preamp. I am using the same transformer I used on the first one: (it is available, and I already have it)
AS-0522 - 50VA 22V Transformer - AnTek Products Corp
Like the power supply you have, instead of having 4 pads connecting to the portion of the power supply with the rectifier/diodes, it has 2, and a third pad marked CT. I noted in your build thread you said you used a "configured as centertap" connection to power supply for your transformer, which was a 20 + 20 volt unit very similar to mine.
Is this an example of how it should be hooked up to this tubecad.com power supply? Looking at your build pics this appears to be correct, but thought I would double check: (top illustration for 120 volt mains) I can not tell for sure where the secondaries are going on your pics, but I think this appears right.
https://www.google.com/search?q=cen...hqsvbEjJM:&usg=__fTRWI4Ew66Cv-SFRFJU7m1bd9eI=
Thanks,
Russellc
But on my second build I am using a power supply from Tubecad.com:
GlassWare PS-19 Bipolar Power Supply Kit
It is very similar, at least as far as my question goes, to the Tubecad.com power supply you used on your build thread BA-3 preamp. I am using the same transformer I used on the first one: (it is available, and I already have it)
AS-0522 - 50VA 22V Transformer - AnTek Products Corp
Like the power supply you have, instead of having 4 pads connecting to the portion of the power supply with the rectifier/diodes, it has 2, and a third pad marked CT. I noted in your build thread you said you used a "configured as centertap" connection to power supply for your transformer, which was a 20 + 20 volt unit very similar to mine.
Is this an example of how it should be hooked up to this tubecad.com power supply? Looking at your build pics this appears to be correct, but thought I would double check: (top illustration for 120 volt mains) I can not tell for sure where the secondaries are going on your pics, but I think this appears right.
https://www.google.com/search?q=cen...hqsvbEjJM:&usg=__fTRWI4Ew66Cv-SFRFJU7m1bd9eI=
Thanks,
Russellc
Last edited:
I'm stuck/stumped by bias process.
OK, so I passed the smoke test. Mains/primary/secondary/d.c power supply voltages all seem good. The problem that I have is that I measure very low voltages across R10 and R11 with zero volts offset, I get a maximum 1.1mv / 2.1mv on one channel and .8mv / .8mv on the other channel.
The 500 ohm pots P1 and P2 on either channel are at maximum. I hear them "click". I don't know what I need to troubleshoot next. BTW, I have repeated these steps numerous time now but now I'm stumped.
I'm hoping for some guidance.
TIA,
John
OK, so I passed the smoke test. Mains/primary/secondary/d.c power supply voltages all seem good. The problem that I have is that I measure very low voltages across R10 and R11 with zero volts offset, I get a maximum 1.1mv / 2.1mv on one channel and .8mv / .8mv on the other channel.
The 500 ohm pots P1 and P2 on either channel are at maximum. I hear them "click". I don't know what I need to troubleshoot next. BTW, I have repeated these steps numerous time now but now I'm stumped.
I'm hoping for some guidance.
TIA,
John
According to 6L6, yes. See post #196.
http://www.diyaudio.com/forums/pass-labs/258022-ba-3-preamp-build-guide-4.html#post4306674
Russellc
6L6 said there was no difference in sound quality (See post # 192 here ). I have only tried the Toshiba devices myself. They sure are cheaper! Mouser has the Fairchild parts very cheap....I just paid 6-7 bucks a piece for the Toshiba parts, which are discontinued....I still have 4 pairs I am saving for BBA-3 mono blocks, but wanted another set for my latest BA-3 pre build. I have the standard value parts on hand is all, and I understand the Fairchild pieces require other values.
Russellc
Last edited: