My BA3 preamp is almost complete. I am waiting for transformer.
https://www.dropbox.com/sc/wqoj60jr46z4vk2/RemAtNSPI9
https://www.dropbox.com/sc/wqoj60jr46z4vk2/RemAtNSPI9
Power supply is with C-R-C, regulator stage is with zener diode 4x6,2V and series transistor, or cap multiplier or LM317/337 reg. (PS with or without feedback)
Input selector is with 5 inputs, mute relay and 7 relays for attenuator. You can use pot like on picture. Relay attenuator and pot can be connected as classic or as shunt type.
Preamp section can use for BA3 unbalanced or balanced (two boards needed), for Uskok unbalanced or balanced, with one par 2sj74/2sk170 or two, with 2sj79/2sk216 or 2sj313/2sk2013 (different side of heatsink) or IRF610/9610.
This board dont have DC servo like Uskok. It was hard to make on one layer pcb.
https://www.dropbox.com/sc/szifw4k3lqwbzym/hq56Od4w3b
Input selector is with 5 inputs, mute relay and 7 relays for attenuator. You can use pot like on picture. Relay attenuator and pot can be connected as classic or as shunt type.
Preamp section can use for BA3 unbalanced or balanced (two boards needed), for Uskok unbalanced or balanced, with one par 2sj74/2sk170 or two, with 2sj79/2sk216 or 2sj313/2sk2013 (different side of heatsink) or IRF610/9610.
This board dont have DC servo like Uskok. It was hard to make on one layer pcb.
https://www.dropbox.com/sc/szifw4k3lqwbzym/hq56Od4w3b
I haven't finished the B3-pre yet, but I did get a chance to upgrade the MOX II active crossover from one power supply to dual. The change was significant. Better channel separation, solid imaging instrument placement, bit more depth and more bass. Not sure how dual power supplies improves bass response, but I assume the XO drives the amps with more ease.
Still using 1 transformer, but might eventually add another.
Preamps seem to respond well to power supply upgrades.
I recommend dual power supplies (one for each channel) for the B3-pre as well. I think it's worth the extra effort.
Vince
Still using 1 transformer, but might eventually add another.
Preamps seem to respond well to power supply upgrades.
I recommend dual power supplies (one for each channel) for the B3-pre as well. I think it's worth the extra effort.
Vince
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I tried yesterday my BA3. Bias through the output transistors was 45mA and the sound was too slow and bass dominating. Could not get a kick from the bass.
I reduced current to 30mA and I got a neutral medium and high, lower bass area, but the sound is a bit slow. I will reduce more current to try to get a more realistic tone but while to keep smooth sound.
Gain is 3x, current through jfet-s 9mA. Drain resistor for jfet-a is 200 ohm, sors resistor for output fet-s is 65ohm (2x130) and load is 170ohm (3x510 parallel).
At this settings current through load resistor at maximal signal, 3V, is 18mA and output fets stay in A klass.
What the currents optimal for BA3 as a preamp?
I reduced current to 30mA and I got a neutral medium and high, lower bass area, but the sound is a bit slow. I will reduce more current to try to get a more realistic tone but while to keep smooth sound.
Gain is 3x, current through jfet-s 9mA. Drain resistor for jfet-a is 200 ohm, sors resistor for output fet-s is 65ohm (2x130) and load is 170ohm (3x510 parallel).
At this settings current through load resistor at maximal signal, 3V, is 18mA and output fets stay in A klass.
What the currents optimal for BA3 as a preamp?
I think it could be less a problem of the current, more of the THD spectra, sounds like You have k2 around 20dB over k3, use the distortion trim pots!
You can get out any sound of these circuits....if you do not use trimming or matching in a adequate way.
I hope my words do not sound too rigid....
I`ll get back in a few days with sound impressions
forgot when you turn the distortion pot you mistune offset and bias a bit…
to much offset will not come through the cap, but increase distortion,
so you have to correct offset after finding your daily distortion value….
I need some advice.
Now that the BA-3 FE is done I've taken more notice of the acoustics in my room. The room has a sloped ceiling from the left to right. Probably drops from 20feet to 10 feet.
This is causing the center "image" on vocals to appear a foot or two to the right of the center of the speakers. Its also causing bass to appear "uncentered". It's not the amp or preamp, I've swapped cables and speakers and the effect is constant. I have also used a SPL meter right up on each speaker and it appears pretty well matched. It is the room. I've always noticed it, it's just the BA-3 FE is really imaging stronger and making this problem more pronounced.
Other than adding a balance control what can I do? I've adjusted speaker positioning but bringing one speaker closer looks strange (it's my living room) and brings about some other weird acoustics.
Can I add a resistor to the input or output on the B-3 to pad one channel a decibel or two? Anyone have any ideas for that? I'd rather not use a pot if possible.
Now that the BA-3 FE is done I've taken more notice of the acoustics in my room. The room has a sloped ceiling from the left to right. Probably drops from 20feet to 10 feet.
This is causing the center "image" on vocals to appear a foot or two to the right of the center of the speakers. Its also causing bass to appear "uncentered". It's not the amp or preamp, I've swapped cables and speakers and the effect is constant. I have also used a SPL meter right up on each speaker and it appears pretty well matched. It is the room. I've always noticed it, it's just the BA-3 FE is really imaging stronger and making this problem more pronounced.
Other than adding a balance control what can I do? I've adjusted speaker positioning but bringing one speaker closer looks strange (it's my living room) and brings about some other weird acoustics.
Can I add a resistor to the input or output on the B-3 to pad one channel a decibel or two? Anyone have any ideas for that? I'd rather not use a pot if possible.
