This conversation brings up a question I have had for a while. More related to volume controls than selector switches. Why aren't rotary optical encoders used for volume control. They aren't that expensive and it's my understanding that they can be operated outside the main Circuit and are absolutely noise free. Sounds like everything high end audio wants and needs. I say this with very little knowledge of circuits. They are used for this exact same thing on aircraft avionics.
Don
Don
Thanks everyone! This unit sure does sound fabulous. I was listening to the Doors on vinyl and the soundstage was about a foot and a half outside the speaker positions....just marvelous!
Seen on my shelf is a Dynaco PAS 2 with original tubes but a new power supply, all new caps, an alps volume control and tone controls disabled. It was a work in progress, but between this preamp and the Korg B1, I don't know for what reason I should keep the PAS 2 lol.
Seen on my shelf is a Dynaco PAS 2 with original tubes but a new power supply, all new caps, an alps volume control and tone controls disabled. It was a work in progress, but between this preamp and the Korg B1, I don't know for what reason I should keep the PAS 2 lol.
I have a pas 3 with a VA build inside. It collects dust now as the BA3 is my main pre.
I ordered this muses volume control kit. Is there a way to source +-15VDC from the power supply in my BA-3 that is feeding +-24VDC to the BA-3 board? Or is a separate supply the way to go? I happen to have an extra that I would feed with the same transformer.
Sure, there are a couple ways. You could use two zener diodes (Figure 1 below) and two resistors. 6L6 was probably posting in a hurry and accidentally omitted the resistors from his description. Or you could use a couple of voltage regulator ICs, one to produce +15V and another to produce -15V (Figure 2 below).
Either will work but I prefer Figure 2 myself.
(BTW Mouser has many many 1N5929B zener diodes in stock. 15V and 3 Watts: link )
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Attachments
Thanks, how about these regulators:
https://www.mouser.com/ProductDetail/ON-Semiconductor/MC79M15CTG?qs=sGAEpiMZZMuLLNXTG1MZak6HpgO6pjZJx4khxPKvBKg%3D
https://www.mouser.com/ProductDetail/ON-Semiconductor/MC7815ACTG?qs=sGAEpiMZZMutXGli8Ay4kCBGNN2haXZXl%2FF7GTwr8so%3D
And what would the electrolytic cap values be?
Hello everyone
I finally finished my BA-3 preamp but have some problems biasing each channel. I am using Toshiba 2SJ313 in Q3 and Toshiba 2SK2013 in Q4
500-ohm pots in P1 and P2. I get 0vdc across R10 and R11. I am getting 23vdc at R12 also at R13 to ground where the DC offset is supposed to be 0vdc. The rotation of P1 and P2 seem to have very little effect on the DC offset. My power supply is rock solid +/- 24vdc. Is it possible the MOSFET's are bad? There was no smoke or smell of burring parts at power-up I slowly dial up Variac and there I could see the meter measuring DC offset going up.
Any help would be appreciated
Thanks
Dave
I finally finished my BA-3 preamp but have some problems biasing each channel. I am using Toshiba 2SJ313 in Q3 and Toshiba 2SK2013 in Q4
500-ohm pots in P1 and P2. I get 0vdc across R10 and R11. I am getting 23vdc at R12 also at R13 to ground where the DC offset is supposed to be 0vdc. The rotation of P1 and P2 seem to have very little effect on the DC offset. My power supply is rock solid +/- 24vdc. Is it possible the MOSFET's are bad? There was no smoke or smell of burring parts at power-up I slowly dial up Variac and there I could see the meter measuring DC offset going up.
Any help would be appreciated
Thanks
Dave
I will get some taken I work all weekend now so late Sunday I can post some
Q1 23vdc Q2 -22vdc
Assuming everything is functioning and installed correctly; it sounds like Q3 has started conducting (+V across R13), therefore you must have a small amount of voltage across R10.
Adjust P1 until Q4 starts conducting, the output offset will start to fall, adjust to 0V while monitoring the voltage across R10 & R11; then slowly adjust P1 & P2 by small amounts, balancing the output offset against the required voltage across R10 & R11.
Adjust P1 until Q4 starts conducting, the output offset will start to fall, adjust to 0V while monitoring the voltage across R10 & R11; then slowly adjust P1 & P2 by small amounts, balancing the output offset against the required voltage across R10 & R11.
