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

[jsteiger]

.....I'm guessing I may have put the LED in backwards?

This is most likely the problem.

 

[rwrwrw]

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]

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]

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]

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]

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?

 

[jsteiger]

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]

Sweet, thanks for your help! Excited to try this out now

 

[rwrwrw]

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?

 

[jsteiger]

The 150k load R increases the load the mic sees from around 1k2 to 1k.

 

[the new frenchy]

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

 

[the new frenchy]

some picture

 

[the new frenchy]

some picture

 

[the new frenchy]

the last

 

[Potato Cakes]

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]

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?

 

[the new frenchy]

Could RV1 be broken?

 

[the new frenchy]

I mesure between "out Hi" and the blu green yellow & orange bourns of the out put transformer, the value is moving so RV1 is Ok but why the sound does not fall?

 

[Potato Cakes]

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

 

[the new frenchy]

Thanks again Paul!
I Pull RV1 and there is a very very little sound which pass again! Is it normal? or should it have no sound?