Rail voltage and Muses volume control
Folks,
I'm collecting the misc. parts to build my BA2018 linestage kit and am looking at the Mensus VCU volume control board. Application notes for that product suggest lowering the + and - voltages to a new "sweet spot" of 14 volts by changing R15 to 68k, and also changing the input resistor R18 to 470k to better match the vol control.
Is there a problem/negative impact on making these changes to the BA2018 linestage?
Thanks,
HappyJack
Folks,
I'm collecting the misc. parts to build my BA2018 linestage kit and am looking at the Mensus VCU volume control board. Application notes for that product suggest lowering the + and - voltages to a new "sweet spot" of 14 volts by changing R15 to 68k, and also changing the input resistor R18 to 470k to better match the vol control.
Is there a problem/negative impact on making these changes to the BA2018 linestage?
Thanks,
HappyJack
HappyJack: you mean the Muses VCU board from Academy Audio correct? The application notes’ changes were based on Wayne’s original schematic and not the updated one as far as I can see. I’m interested in the VCU as well so I’m interested in someone’s take on the changes they recommend.
Cheers
Cheers
Folks,
Yes, I am referring to the Muses VCU board from AcademyAudio.COM (~ $100US for the vol control board, remote and display)
As to the BA2018 Line stage, I purchased the board and parts kit from the DIY store back in May, 2021. It shipped out to me May 10,2021, so I assume this is the latest board and parts kit???
HappyJack
Yes, I am referring to the Muses VCU board from AcademyAudio.COM (~ $100US for the vol control board, remote and display)
As to the BA2018 Line stage, I purchased the board and parts kit from the DIY store back in May, 2021. It shipped out to me May 10,2021, so I assume this is the latest board and parts kit???
HappyJack
Attachments
Happyjack, I’m new to building but just thought I would throw in my 2 cents. I built the BA18 about 2 months ago using the Muses VCM along with the Helios PSU from Audiosy.net I questioned the modifications in the notes as well and contacted Lenny over at Academy about this. He had me send him the schematic from DIY Audio to confirm there were no changes. He recommended the changes because from what I understand the sweet spot of the BA18 is in the +/-18-20vdc where the VCM operate in the 10/16vdv range. Changing the resisters brings the sweet spot of the BA18 down to +/-13-15vdc. I ensured this info with the forum as well. After I got their blessing I preceded to build the BA18 as mentioned. To this point I love it. Have fun! Joe
Thanks Joe.
Glad you were able to confirm that making the changes to the resistor values and lowering the supply voltages to around 14 volts would not degrade the operation of the line stage.
Right now I’m using my ACP+ pre/headphone amp to drive my amp and am really liking that combination. I’m anxious to get the BA2018 finished and then compare the 2!!
Happyjack
Glad you were able to confirm that making the changes to the resistor values and lowering the supply voltages to around 14 volts would not degrade the operation of the line stage.
Right now I’m using my ACP+ pre/headphone amp to drive my amp and am really liking that combination. I’m anxious to get the BA2018 finished and then compare the 2!!
Happyjack
The two resistor changes are for two different reasons. As mentioned above, the 68k resistor is used to adjust the supposed ‘sweet spot’ of the power supply but the 470k input resistor is to match the logarithmic curves of the Muses volume chip. See page 2 of the BA2018 app note on the Academy Audio site.
I recently built a BA2018 using the VCU and used the 470k input resistor but not the 68k resistor as I did not use Lenny’s hybrid power supply. The VCU is a great-sounding volume control and the kit offered is, in my view, a great value for the price. Go for it.
I had a hard time getting my BA2018 working after assembling it. So I put it in a cardboard box when other things got in the way.
I finally got around to pulling the box of parts out. I traced each leg of all of the SMD's to the next component and checked for continuity. I found one that wasn't connected. It was the ground of Q2 leading to R17 (but the other channel). The lack of a connection was causing a 16v offset!
I put a new SMD in that spot out of the same batch and voila. Offset set to 0-3mv and I had sound!
The preamp sounds great with no star ground etc just sitting on top of my record player haphazardly connected to my F6 and a little Schiit Modi 3+ listening through my Bordeaux speakers (Jim and Curt design)
The sound is very full! Clear but not fatiguing on top. The more I listen, the more I become attuned to its awesome sound! I can see why Mr. Pass and Mr. Colburn make such a great team.
The sound is big. Very smooth and impactful if that makes sense. Exactly what I needed. Before the I was connected straight to the DAC which was very detailed but unrefined. I noticed more songs sound good vs before I found myself switching songs quite often. Before if I played songs that were both loud and complicated, I would switch. Now I can cruise through them no problem.
Okay I'll stop gabbing. Long story short, if you're getting a ridiculous voltage on your output to the amp, check SMD connections.
Also, thank you andynor for jumping in with your suggestions. One of them what what I did to resolve the problem.
I finally got around to pulling the box of parts out. I traced each leg of all of the SMD's to the next component and checked for continuity. I found one that wasn't connected. It was the ground of Q2 leading to R17 (but the other channel). The lack of a connection was causing a 16v offset!
I put a new SMD in that spot out of the same batch and voila. Offset set to 0-3mv and I had sound!
The preamp sounds great with no star ground etc just sitting on top of my record player haphazardly connected to my F6 and a little Schiit Modi 3+ listening through my Bordeaux speakers (Jim and Curt design)
The sound is very full! Clear but not fatiguing on top. The more I listen, the more I become attuned to its awesome sound! I can see why Mr. Pass and Mr. Colburn make such a great team.
The sound is big. Very smooth and impactful if that makes sense. Exactly what I needed. Before the I was connected straight to the DAC which was very detailed but unrefined. I noticed more songs sound good vs before I found myself switching songs quite often. Before if I played songs that were both loud and complicated, I would switch. Now I can cruise through them no problem.
Okay I'll stop gabbing. Long story short, if you're getting a ridiculous voltage on your output to the amp, check SMD connections.
Also, thank you andynor for jumping in with your suggestions. One of them what what I did to resolve the problem.
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Can someone point me in the right direction in terms of specifications for a 24v supply for this kit? There's a lot of pages and a lot of results in the topic here 
I'm building a temporary 24v linear supply with a couple TIP's and all, since the PSU we got for this was initially for the H2! Of course it's only 12v.
How many miliamps does a board pull on average on 24v, music included?
I'm building a temporary 24v linear supply with a couple TIP's and all, since the PSU we got for this was initially for the H2! Of course it's only 12v.
How many miliamps does a board pull on average on 24v, music included?
so, you have know how for power xformers ...... now's the time to improve skills of thread reading and circuit analysis
all I did is - go back to post #1, saw what major spender is (output pair), calculated what's current draw of these ....... and that's it
I did check first 100 posts to see can I paste link with VA specific info, but didn't found it, but you have enough info about rails .....
all I did is - go back to post #1, saw what major spender is (output pair), calculated what's current draw of these ....... and that's it
I did check first 100 posts to see can I paste link with VA specific info, but didn't found it, but you have enough info about rails .....