[Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

rwrwrw

Member
Joined
Mar 16, 2017
Messages
11
jsteiger said:
This is most likely the problem.

Yep that was it. Phantom power works fine.

On another note, I'm finding that I like the tonal variations that the optional resistor adds. Would it be hard to wire a switch into the vp312 so the user can choose whether they want the optional resistor in or out on the fly? An air switch I guess?
 

jsteiger

Well-known member
White Market Member
Joined
Apr 11, 2008
Messages
3,400
Location
Nashville TN
rwrwrw said:
Yep that was it. Phantom power works fine.

On another note, I'm finding that I like the tonal variations that the optional resistor adds. Would it be hard to wire a switch into the vp312 so the user can choose whether they want the optional resistor in or out on the fly? An air switch I guess?
Yeah for sure. Super easy. And after all its DIY!
 

rwrwrw

Member
Joined
Mar 16, 2017
Messages
11
Cool. Unfortunately I'm a bit of a noob when it comes to figuring out how to mod something like this on my own... Whats the best way to go about adding a switch? Do I need a SPST switch?

Thanks for your help! Feel free to point me in the direction of any literature if that would be easier. Or if anyone else has any suggestions that would be greatly appreciated!

 

jsteiger

Well-known member
White Market Member
Joined
Apr 11, 2008
Messages
3,400
Location
Nashville TN
Yes a SPDT switch is all you need. Either the 150k R gets connected to ground or it floats. Its pretty east once you wrap your head around what is happening.
 

rwrwrw

Member
Joined
Mar 16, 2017
Messages
11
Hm alright I've got some spdt switches, lemme see if I've got this right - I've attached a photo of a possible diagram... It is the same wiring as the phantom power switch?
 

Attachments

  • unnamed.jpg
    unnamed.jpg
    868.2 KB · Views: 7

jsteiger

Well-known member
White Market Member
Joined
Apr 11, 2008
Messages
3,400
Location
Nashville TN
rwrwrw said:
Hm alright I've got some spdt switches, lemme see if I've got this right - I've attached a photo of a possible diagram... It is the same wiring as the phantom power switch?
Bingo! You got it!
 

rwrwrw

Member
Joined
Mar 16, 2017
Messages
11
Got em modded up now (the 312 on the left was the guinea pig...)! The difference is subtle, but its a nice option to have. I find that if I want something to cut more in the mix, then I don't want the resistor in there. But if I need a track to sit back in the mix, then that's when I want the resistor.  Thanks again for your help jsteiger! Now heres one of the things I can't wrap my head around yet... Why does this resistor effect the high frequencies?
 

Attachments

  • IMG_1762.JPG
    IMG_1762.JPG
    1.3 MB · Views: 22

the new frenchy

Active member
Joined
Jun 13, 2015
Messages
26
Location
Somewhere in the world :-)
Hi Jeff!
I finish soldering 2 VP312, now I believe I have about 25 of your preamps! Thanks for your Job!
One is OK an the other is OK to,  but the output pot doesn't work.... it let the signal pass but I can't push down the output level?
All your Quick Startup Testing Procedure is ok for me, I read all the posts on this blog and don't find why this output level doesn't work? Can you help me?
I change the amp op... I've the same problem...
Thanks
 

Potato Cakes

Well-known member
Joined
Jul 1, 2014
Messages
1,932
Location
Nashville, TN
The output pot is a connection between the output transformer and the Bourns T-pad. If you are getting full signal all of the time then there is a short or bad connection on the transformer leads PCB connection points or the T-pad solder points. You could pull the Bourns pad and measure resistance to see if changes when you turn it to verify it is good.

It has to be related to one of those things assuming it is passing full signal.

Thanks!

Paul
 

the new frenchy

Active member
Joined
Jun 13, 2015
Messages
26
Location
Somewhere in the world :-)
Thanks Paul,
I do all the point welding around the output transformateur, and the output pot RV1... I still have the same problem!
I try to make continuity test between the output transformateur and RV1, to try to understand but I don't really now which point is which bourn, (I don't know if it's clear...)
your believe you can help me or must I wait Jeff answer me?

 

Potato Cakes

Well-known member
Joined
Jul 1, 2014
Messages
1,932
Location
Nashville, TN
Go to CAPI's website and pull up the VP312 schematic:

http://www.capi-gear.com/catalog/images/gallery/VP312/VP312-VPR-Rev-B-Schematic.pdf

You should be able to trace where you should be getting continuity.

You can also just pull Bourns T-Pad and see if you are still getting signal to the output.

Either you have a bad T-Pad (possible, but unlikely) or there is a short between the Blue transformer solder pad and Out Hi (pin 2 on the edge connector).

Thanks!

Paul
 
Top