while we all are waiting someone really smart to chime in , I can tell that 1500uF can be freely used instead of 1000uF for C1,C2 positions , ref to attached schm
R1 and R2 are having their own function , helping that usually disoriented (when laying in drawer) small Jfet certainly knows it's own orientation in Universe and broader ...... so not having particular connection with attenuator issues
I've been running my BA-3FE without R2 (47K).
Last night I installed some 47K resistors in the R2 slot and guess what? Bias was more stable (DC offset used to wander a lot) and now my stepped potentiometer doesn't make pops and clicks when adjusting volume. I can't tell any difference in SQ otherwise.
Mr. Pass mentions that you can vary the bias of Q1 and Q2 by reading the voltage across R3 & R4.
What do you actually do in order to change the voltage across R3 & R4?
Aren't P1 & P2 for biasing Q3 and Q4 and adjusting the DC offset?
What do you actually do in order to change the voltage across R3 & R4?
Aren't P1 & P2 for biasing Q3 and Q4 and adjusting the DC offset?
Mr. Pass messed up parts nomenclature in article , either inserting wrong picture or looking at wrong one while writing that part of text
you have one of my posts in article comments , where you can find Papa's explanation of circuit , with edited parts nomenclature
you have one of my posts in article comments , where you can find Papa's explanation of circuit , with edited parts nomenclature
So the bias of Q1 & Q2 are not adjustable and can only be changed if R3 and R4 are changed to different values?
having them in BL range is prerequisite
though , even "higher" ones (being Violet ones ) are adequate , with correction of source resistance , to keep them in normal dissipation range
anyway - explanation in article is covering everything , to decide what to change and keep/achieve desired gain and oomph
though , even "higher" ones (being Violet ones ) are adequate , with correction of source resistance , to keep them in normal dissipation range
anyway - explanation in article is covering everything , to decide what to change and keep/achieve desired gain and oomph
Essentially yes. The Jfets self-bias, as based on their Idss, and the Mosfets bias via the pots.
You an change the bias of the Jfet by changing the source resistance, but it's easier to just use them in the proper Idss range - anyting from 7.0-11.0 will work witn no issues, outside of that you might be needing to adjust the Jfet source resistors.
Just adjust the front-end bias until you have 1V across R10 and R11. The bias of the output stage is different than the front-end.
Thank you 6L6 & Zen.
I just got my BA-3 up and going. I don't know if anyone here has stated this before, but I just learned that P1 sets the voltage across R10(I used R10 instead of R11) and P2 adjusts the DC offset BEFORE the capacitor of course.
Also, it takes quite some time for the readings to stabilize.
Readings across R3 & R4 are slightly different on one channel at 57mV and 59mV.
I'm still not sure what to do with the P3 trimmers since I don't have any fancy equipment to look at distortion and such.
All I had for output caps were a pair of 9.1uF Erse Pulse X MKP's.
I'm using a 10K volume pot in front of mine.
I think it sounds really good.
Certainly well worth the time, money and effort I've put into it.
I just got my BA-3 up and going. I don't know if anyone here has stated this before, but I just learned that P1 sets the voltage across R10(I used R10 instead of R11) and P2 adjusts the DC offset BEFORE the capacitor of course.
Also, it takes quite some time for the readings to stabilize.
Readings across R3 & R4 are slightly different on one channel at 57mV and 59mV.
I'm still not sure what to do with the P3 trimmers since I don't have any fancy equipment to look at distortion and such.
All I had for output caps were a pair of 9.1uF Erse Pulse X MKP's.
I'm using a 10K volume pot in front of mine.
I think it sounds really good.
Certainly well worth the time, money and effort I've put into it.
Yes, it can feel like that. Everything is interconnected, but once it gets going one pot will seem more direct to bias and the other pot feels more tied to the offset. But just for clarification, it's not always going to be "P1 = Bias"
Close enough to not matter. 🙂
You can always ignore it. Or, and you must be careful about taking notes, turn it a few (5) turns in one direction or the other and see what it sounds like.
No worries at all. Nice caps, the value is fine.
Yep, it sure does!
Hi guys, |I finished last night BA 3 but I have a weird problem, any thoughts or suggestions appreciated. voltage at r10 is at 1 volt both sides and biased at 5 to 10 mv slightly drifting, and all seems in order except volume control. When I test with amp and CD player I get huge volume at lowest setting and fear speaker meltdown... I tried for five seconds but i get this wierd problem with volume.
Without Preamp, I can run amp via B1 through Fetzilla amp lat full throttle and have good but not super loud volume levels. With preamp between old sony cd player and Fetzilla at
lowest setting I get volume, turn a fraction, and much too loud. I am using PEC 25k carbon pots.
I connected the pots between the in RCA and the In on the board. Should I have put the pots between output of the board and the out RCAs?
Trying to measure resistance with the pot connected to the board with the BA3 off gives me weird figures, it goes from zero to 25k disconnected, but when the pot is connected to the board, meauring resistance from input rca to connected in terminal on the board I get something like 4.7k when pot turned all the way down, jumping almost immediately to 12k or so on turning, then between 12k and 6k as it turns to higher volume. I have r2 installed on the board, and the pot connected directly between input rca and input on board.
Afraid to hook up to my f5 as is, do not want to burn anything up or blow up my speakers.
Should I connect pot to board between board output and output rca instead. Do I simply have too much gain giving me this wierd volume control problem and should I change R13 to lower value, i have 330r I believe as this is was in standard bom.
any thoughts or ideas appreciated. Will try to upload photos if I can figure out how to do this.
John
Without Preamp, I can run amp via B1 through Fetzilla amp lat full throttle and have good but not super loud volume levels. With preamp between old sony cd player and Fetzilla at
lowest setting I get volume, turn a fraction, and much too loud. I am using PEC 25k carbon pots.
I connected the pots between the in RCA and the In on the board. Should I have put the pots between output of the board and the out RCAs?
Trying to measure resistance with the pot connected to the board with the BA3 off gives me weird figures, it goes from zero to 25k disconnected, but when the pot is connected to the board, meauring resistance from input rca to connected in terminal on the board I get something like 4.7k when pot turned all the way down, jumping almost immediately to 12k or so on turning, then between 12k and 6k as it turns to higher volume. I have r2 installed on the board, and the pot connected directly between input rca and input on board.
Afraid to hook up to my f5 as is, do not want to burn anything up or blow up my speakers.
Should I connect pot to board between board output and output rca instead. Do I simply have too much gain giving me this wierd volume control problem and should I change R13 to lower value, i have 330r I believe as this is was in standard bom.
any thoughts or ideas appreciated. Will try to upload photos if I can figure out how to do this.
John
it's easier to figure that out , then figure it out what's wrong , without pictures
same problem with both sections of pot ?
check trice how you connected it
input to one side lug
mid lug-wiper- output from pot
other side lug - to gnd
when you observe pot from shaft , lugs down , left side lug goes to gnd
edit , rephrased :
when you observe pot from shaft , lugs down :
- left side lug , goes to gnd
-mid lug signal , hot goes to next stage (outgoing signal)
-right side lug , signal hot from preceding stage (incoming signal)
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Perfect ZM, your solution works great/. I still have the knobs just 1/8 of a turn and this is enough volume, a quarter of turn the windows shake, and more I am afraid for my speakers.
This gives a lot more gain or volume than my akido lv preamp. It sounds good very nice. Great soundstage, instruments sound like real instruments.
would a 100K pot give me less volume or should I change r12 to cut gain. What would you suggest?
Wow, I actually built something without major problems. Thanks to all for the help. Nelson was very kind to support our hobbies like this, appreciate it.
Cheers, John
This gives a lot more gain or volume than my akido lv preamp. It sounds good very nice. Great soundstage, instruments sound like real instruments.
would a 100K pot give me less volume or should I change r12 to cut gain. What would you suggest?
Wow, I actually built something without major problems. Thanks to all for the help. Nelson was very kind to support our hobbies like this, appreciate it.
Cheers, John
value of attenuator is having everything with everything else , but attenuation amount 😉
change that I/V resistor to cut gain
now , you owe Nelson to invest time in some reading , to not build blindly next time
change that I/V resistor to cut gain
now , you owe Nelson to invest time in some reading , to not build blindly next time
Sorry it is R 13 to cut gain, not r12. I am using 330r 3watt, What are other people using and what is current suggestion? Does changing this alter the sound or just the gain?
How important is it to have good caps 10 uf output? I have some Russian square metal caps which I believe are oil filled from ebay on it now, Will different caps alter the sound significantly?
Wow, listening for just 30 minutes now and music sounds so alive.
How important is it to have good caps 10 uf output? I have some Russian square metal caps which I believe are oil filled from ebay on it now, Will different caps alter the sound significantly?
Wow, listening for just 30 minutes now and music sounds so alive.
I am trying on my fetzilla amp, I was disappointed in this amp before, but sounds really really nice with this Ba3 infront. Will try it on the F5 next.
designation of part (R13 or not) is pretty irrelevant to me , being lazy to remember all these schematics in details , and also to search for them ( when poster who's asking didn't posted link to ref. schmtc 
) ....... but that's resistor from output node to gnd , acting as I/V part
regarding caps , I'm finding that nice polycarbonate bypass ( ranging from 10n-1uF) is always good to have , whichever biggie cap is in question
Papa isn't naive at all , placing Elna Silmic in many places ; that one plus MKC is hard to beat , speaking of greenies/sound ratio
) ....... but that's resistor from output node to gnd , acting as I/V partregarding caps , I'm finding that nice polycarbonate bypass ( ranging from 10n-1uF) is always good to have , whichever biggie cap is in question
Papa isn't naive at all , placing Elna Silmic in many places ; that one plus MKC is hard to beat , speaking of greenies/sound ratio
I just finished my BA-3. I'm using 220 ohms for R13 and still have almost too much gain. You may want to try 180 ohms.