I wouldn't.
The DC drifts as it gets up to temp, and a bit with signal, and the cap is there to keep everything working properly.
The DC drifts as it gets up to temp, and a bit with signal, and the cap is there to keep everything working properly.
Definitely not OK in my experience.
It's possible to adjust to 20mv offset or so but the offset swings wildly with temp. Just a finger on the mosfet heatsink can cause 100mv swings on mine. I have umbilical extensions to test bias and DC offset off the board on mine. In my opinion it's impossible to get a steady offset during normal operation. It moves a lot.
There is a cap for a reason.
It's possible to adjust to 20mv offset or so but the offset swings wildly with temp. Just a finger on the mosfet heatsink can cause 100mv swings on mine. I have umbilical extensions to test bias and DC offset off the board on mine. In my opinion it's impossible to get a steady offset during normal operation. It moves a lot.
There is a cap for a reason.
I am using F4 board without the input buffer which is pretty similar to the BA3 but has 2 capacitors instead of one on the input. It works somewhat differently and they block the DC offset.
Hi All
I finished my BA-3 preamp successfully !. It is powered with SSLV1.1 of Salas. The sound is spacious, good setting, good detail and very serious but the middle and upper area is now a little rough and wheezy. The female "s" are too metal. This is compared to a B1 I had before.
I've got a good balance of volume with the Ba-3 and my F5turbo, better than B1. To do this I simply lowered resistance r13 to half its value, placing another same in parallel. I have not touched the rest of resistance. Is this ok ?.
Associated volume control potentiometer resistance is a step by step with a fixed value of 10K
I have placed as a coupling capacitor one clarity cap SA 10uf + 1uf Mundorf supreme . Total 11uf.
Also, in my DAC output buffalo II I have a tubeizator with 2,2uf condenser. The creator say that this capacitor can not remove it.
Given 2,2uf capacitor. Is it correct value 11uf for the BA-3?
The sound too bright may be due to the sum of capacitors or something to adjust P3 ?.
P3 I adjusted it to half its resistance measured with the multimeter before welding.
The above configuration with the B1 sounded warmer and brighter BA-3. The other components such as potentiometer and others has not changed. Even 10uf capacitors and 1uf are those who were before in the B1.
I wonder WHAT CAN be causing that sound somewhat harder and metallic.
Thanks for spreading the knowledge 🙂!
I finished my BA-3 preamp successfully !. It is powered with SSLV1.1 of Salas. The sound is spacious, good setting, good detail and very serious but the middle and upper area is now a little rough and wheezy. The female "s" are too metal. This is compared to a B1 I had before.
I've got a good balance of volume with the Ba-3 and my F5turbo, better than B1. To do this I simply lowered resistance r13 to half its value, placing another same in parallel. I have not touched the rest of resistance. Is this ok ?.
Associated volume control potentiometer resistance is a step by step with a fixed value of 10K
I have placed as a coupling capacitor one clarity cap SA 10uf + 1uf Mundorf supreme . Total 11uf.
Also, in my DAC output buffalo II I have a tubeizator with 2,2uf condenser. The creator say that this capacitor can not remove it.
Given 2,2uf capacitor. Is it correct value 11uf for the BA-3?
The sound too bright may be due to the sum of capacitors or something to adjust P3 ?.
P3 I adjusted it to half its resistance measured with the multimeter before welding.
The above configuration with the B1 sounded warmer and brighter BA-3. The other components such as potentiometer and others has not changed. Even 10uf capacitors and 1uf are those who were before in the B1.
I wonder WHAT CAN be causing that sound somewhat harder and metallic.
Thanks for spreading the knowledge 🙂!
Is your bias set properly? 1V across R10 and R11?
The value of output capacitor is fine. I would suggest not paralleling caps, remove the Mundorf and see if that helps?
Metallic and sibilant are the last words I'd ever use to describe the BA-3 preamp, something is not right...
The value of output capacitor is fine. I would suggest not paralleling caps, remove the Mundorf and see if that helps?
Metallic and sibilant are the last words I'd ever use to describe the BA-3 preamp, something is not right...
I have a recently build F5 with the same feeling in the upper area. The mid's and high frequencies seem a little harsh. Maybe too metalic. I asked if this has something to do with the fine tuning of the P3 pot. I don't have the right gear to measure THD.
don't know if my tannoy sensis are the "problem". Whatever is the case, the sound is really impressive. Just this thing with the upper frequencies that cause fatigue to my ears.
any help with the P3 pot?
I used audioTester and my soundcard to adjust my F6 for minimum 2 tone dist,or maybe you want maximum 2 tone dist..? 🙂
Can you tell me how did you make the connection to your computer? i only have a laptop with built-in soundcard (realtek). i think this is not apropriate to do the measure...or maybe it is enough. through headphone out to F5 amp (to feed the 1khz tone) and then left or right channel out to the mic input of the soundcard? is that simple? i think i am oversimplifying this
Do you have a "line in" you can use?
I used a 100Kohm potentiometer between the amp and the soundcard,set it to max resistance and then gradualy lower it so you don´t "overload" the line input.
I used a 100Kohm potentiometer between the amp and the soundcard,set it to max resistance and then gradualy lower it so you don´t "overload" the line input.
I use the same setup, BA-3FE->F5, and the sound is pretty relaxed. I use a conventional speaker (Focal 826W), a Pearl II and Shelter 501. Harsh is the opposite of what I would call the sound.
I think the answer is simple. Adjust P3 using your ears until it sounds better. I just built the J-fet pre and had the same sound somewhat. I took out some resistors and added some pots to bring in some 2nd harmonic and the sound is much more to my liking. Using equipment to adjust P3 is probably best but your ears are your best judge of what sounds right to you. More time and effort involved but Cheap diy'ers have plenty of that. With some playing around you should start telling a difference adjusting P3.
If you do that (and it's a perfectly good suggestion), count turns and TAKE NOTES. You'll want to find neutral again because you might like it better the other way (as it has to do with absolute phase)
😀
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anything happens to bias when adjusting P3? do we have to observe voltages and adjust P1 and P2?
P3 will adjust the phase of the second harmonic as well. Keep that in mind if adjusting by ear.
Read the "Adjusting P3 - a video" thread and this will make more sense.
http://www.diyaudio.com/forums/pass-labs/259234-adjusting-p3-video.html
Read the "Adjusting P3 - a video" thread and this will make more sense.
http://www.diyaudio.com/forums/pass-labs/259234-adjusting-p3-video.html
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Great video. It will explain what is happening when you turn P3. I am going to bet you will find a spot that sounds better to your ears.
Does the sound really change that much when paying around with p3? As in: it is really easy to hear the differences?
When I was playing around this week adjusting the j-fet pre is was very obvious to me which way I turned sound best, I am assuming with more 2nd harmonic from the descriptions I have read. One way turning made the sound sound more quick but dry sounding and the other more to my liking, I am guessing introducing what Jim called soul in the video with more 2nd harmonic. It has been a couple of years since I built my BA3 and I do not remember how much a difference P3 made with it at that time I set it up. You should be able to hear some difference or the adjustment would not be there. This of course depends on ones hearing.
It's a very obvious change in soundstage and attack when adjusting p3.
A cheap USB audio interface (less than $30) and some FFT analyzer freeware will help a lot and figuring out what you like. In my experience turns of the pot don't mean much and are not consistent channel to channel. Measuring resistors with a meter in parallel with the pot is a better way although variations in jfets/mosfets cause the harmonics to not be consistent channel to channel at the same setttings. With software/scope you can actually get the channels consistent which is part of the goal.
Everyone raves about dominant 2nd harmonic....which results in a wide and diffuse soundstage that is not as tall. I actually preferred slightly 3rd dominant which has more attack, not quite as wide but is taller with cleaner bass and better, more stable location of instruments. If you listen to simple music (vocals, small scale jazz, etc.) you might prefer 2nd harmonic. For complex stuff, maybe more 3rd.
A cheap USB audio interface (less than $30) and some FFT analyzer freeware will help a lot and figuring out what you like. In my experience turns of the pot don't mean much and are not consistent channel to channel. Measuring resistors with a meter in parallel with the pot is a better way although variations in jfets/mosfets cause the harmonics to not be consistent channel to channel at the same setttings. With software/scope you can actually get the channels consistent which is part of the goal.
Everyone raves about dominant 2nd harmonic....which results in a wide and diffuse soundstage that is not as tall. I actually preferred slightly 3rd dominant which has more attack, not quite as wide but is taller with cleaner bass and better, more stable location of instruments. If you listen to simple music (vocals, small scale jazz, etc.) you might prefer 2nd harmonic. For complex stuff, maybe more 3rd.