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

[samguaiana]

I would just replace the 120µF cap. Should be no biggie. Not sure why it failed.

Ok will do. I think two resistors are in the wrong spot. On the pre without the blown cap, two resistors are one way, on the other they're another way. I should probably swap those two right? I am so bad at this DIY business haha

 

[jsteiger]

I think two resistors are in the wrong spot. On the pre without the blown cap, two resistors are one way, on the other they're another way. I should probably swap those two right? I am so bad at this DIY business haha

No don't bother. Resistors are not directional so rotating them will make no difference.

 

[samguaiana]

I think two resistors are in the wrong spot. On the pre without the blown cap, two resistors are one way, on the other they're another way. I should probably swap those two right? I am so bad at this DIY business haha

No don't bother. Resistors are not directional so rotating them will make no difference.

Sorry, I think I worded it wrong. It's not that they're wired backwards, I think two are soldered in the wrong location. Would that cause the cap to blow? If you look at the pic, you can see that two of the resistors I think are in the wrong spots (R6 and R7). I'm not totally sure, as I said, I got them from someone in the shape they're in, so I don't have any frame of reference.
Thanks for the responses!

 

[jsteiger]

R6 and R7 both look to be 6k8's which is correct.

 

[samguaiana]

R6 and R7 both look to be 6k8's which is correct.

Holy crap you're totally right. I didn't notice both had the orange dot on them!

Thanks so much, stoked to get them back in my rack and party with some 312s

 

[jaminem]

Hi There, I have 2 of the original Rev A VP312's without the LED, pretty sure I saw a mod to include one - can someone help or point me in the right direction - Jeff?

 

[hydnwllms]

Hey all,

I've just built my first VP312 (new rev. with Litz transformer).
Have just done opamp socket testing and all the tests are coming up with resistance in the megaohms.
I thought C and O was meant to be lower on these than VP26, etc. - is having all reading so high OK (new revision or Litz xformer?)

Thanks so much guys!
Hayden

 

[jsteiger]

Hayden, for a VP312, C to O should be around 9Ω no matter the Litz or standard 2503. Make sure your DMM is set to that range, if its a manual type.

 

[plevine]

Hey Jeff,
    So stoked to have finally built my 312! Unfortunately, I'm having some issues and I'm wondering if you could shed some light on the problem.

I'm getting fairly strong level out of the pre, but along with some buzz, it looks as if there's distortion (or perhaps DC offset?) on the signal. Please see the attached picture. Do you know what could be causing this? I've done the pre-start checklist, checked my component values and direction, and checked the leads of the output transformer (litz) multiple times (and with multiple people ).

Attached is a picture of a waveform recorded through the pre. The phase flip in the the middle corresponds with me hitting the phase flip button.

Any help appreciated!
Thanks,
Phil

 

[jsteiger]

There should be no DC present after the 2503 since the transformer would block it.

What is the opamp and who built it?

 

[plevine]

I believe the opamp is an SL-2520 (Scott Leiberman). This one was borrowed for testing purposes, so I can't vouch for it's condition. Does this seem like a problem with the op amp itself?

 

[jsteiger]

I believe the opamp is an SL-2520 (Scott Leiberman). This one was borrowed for testing purposes, so I can't vouch for it's condition. Does this seem like a problem with the op amp itself?

Highly unlikely for a red dot. It is Liebers BTW  Is the amp fully seated? http://capi-gear.com/catalog/DOA_Install.php

If so I would next look for bad solder joint.

 

[plevine]

I reflowed the opamp connections and it works! Thanks Jeff. I had already done that at one point, but I suspect I seated the opamp when the pcb was already mounted on the metal frame (gingerly..), and that pressure probably lifted something. Anyway, it sounds wonderful - really appreciate you making yourself available to help!
All the best

 

[geardude]

I'm having an issue with my latest 312 build- the phase invert DRASTICALLY alters the sound when engaged. Sucks up all the bass when engaged.

Never encountered this with the 26,or 28 and I've built dozens of them however this is my first 312 so maybe this is normal? But I doubt it.

I've touched up all three button switches & tried a different xlr just to see if a cheap chord was the suspect and I'm still seeing this issue.

Any advice & happy holidays

 

[jsteiger]

Check the output transformer wiring as well as solder joints on the t-pad.

 

[geardude]

Check the output transformer wiring as well as solder joints on the t-pad.

Well hope the holidays are treating you well. Perhaps I really made a glaring and obvious mistake, I've attached a picture below. I just did the litz transformer in order down the line....so this is probably it?! facepalm I realize now after checking the hardware page for the litz it states the correct order now so I guess I'll whip out the desolder tools

 

[jsteiger]

I just did the litz transformer in order down the line....so this is probably it?! facepalm I realize now after checking the hardware page for the litz it states the correct order now so I guess I'll whip out the desolder tools

Yeah that is the situation for the smaller 2623-1 Litz option but due to the winding process, the colors for the 2503 need to be swapped around a bit. I try to keep it simple. You HAVE to follow the color code chart on the bottom left of the 2503-Litz datasheet here http://www.capi-gear.com/catalog/images/gallery/2503/2503-Litz-specs.pdf

 

[Santos76]

Hey there, I just built 2x 312's and the pre sounds fantastic. I love it! I feel like it has way more mojo somehow than my VP26's & VP28's to my ears although I love the like hell too. With my Lovechilds it's bliss. However, on one of the two 312's  I built the phantom isn't working. I examined both pres and they are identical and were built side by side simultaneously. When I engage the phantom on the unit in question there is a loud pop & then a powering up noise that leads to dead silence and no signal. I have been using the unit with the phantom disengaged and getting great sounds with dynamics but the phantom is a no go right now.

The leads on the phantom switch are in the correct position. The solders on the PCB connected to the switch look good. Before I start de-soldering and re-soldering the whole thing,  are there any dead giveaways/go to's I can try first?

Thanks,

C

 

[Potato Cakes]

Without seeing it, I don't know if there are any dead giveaways. You'll just have to meter where phantom power comes in the module and make sure it is evenly distributed across the In Lo and In Hi as shown on the schematic. There's only a handful of components to check, so you should see pretty quickly who the culprit is. No need to resolder the whole thing if it works properly with a dynamic microphone.

Thanks!

Paul

 

[rwrwrw]

Hi, I've successfully built 2 of the vp312 litz stepped gain modules and I really like the way they sound. However, the phantom power LED doesn't work for either of them - is this a big issue? I currently don't have any mics that need phantom power, but I want to make sure that I'm not going to somehow fry the board if one of the switches get flipped. The modules were built at different times. I'm guessing I may have put the LED in backwards?