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

[Walrus]

You have got the 10kOhm resistor in series with the LED haven't you?

 

[Mrosso]

Kevin,
No, I do not. I thought that the Rev D boards didn't need resistor on the LED.
Thanks!

 

[Blondino]

Hi there...
For some reason today I decided to modify my Vp312. When I builded it I left out R3, 150K. And I decited to put it on it. Nothing major, I did the job, plugged into my lunchbox with no opamp and R5 smoked. Seems weird to me, since the pre was perfectly fine without that R3.
I just replace R5 but didn't plug it back, and I removed R3 since I lived without it till now.
Before i plug in it again, could be I burned other stuff other than R5?   
Thanks

 

[Isax1984]

Hi this is my first build and I m not getting signal with LDC mics. Phantom power led is lit when turned on but there is only 4.8v at XLR pin 2 and pin 3 and with no load it measures 12.6mA. All my dynamic mics are working so I assume there is nothing damaged in the input transformer. My shure sm94 SDC has signal but crackles a bit. My rack is a brand new midas L6.

 

[Vibrowhatzit]

Just finished my first build of a VP312 VPR-Litz, no problems, works great. I had to ignore the recommendation from Jeff to bring it up with a known good DOA, since I also built the CA-0252 kit, and that's all I had, but all the static checks of the VP312 were good, and it seemed to power up in the rack ok without a DOA (i.e. no smoke or fire). So I just plugged in the DOA, powered up the rack, and held my breath. All good...

Kudos to CAPI for clear documentation, and a well packed and labeled kit. I would maybe hesitate to recommend the CA-0252 kit for a first time DIY builder (I think Jeff has stated the same), but if you have decent solder skills and the right tools (REALLY important!), the VP312 is a straightforward build. The CA-0252 is really no harder, just things are a little tighter, and poor soldering skill is more likely to cook a transistor than a passive.

I've tested a bit with a couple of different mics, on different sources, and overall I'm very pleased with the sound. It's certainly got a desirable 'color' that I don't have with any of the other pres I own.

I've got a second one to build now, and I'm thinking of taking some photos and creating a more formal, VP312-specific (Rev B) build guide if anyone has any interest?

 

[Tinning-Tina]

When I'm testing resistance between the DOA sockets, it starts at ~500k Ω and then it slowly goes up until it rises over the range of my DMM (2MΩ).

Is that normal?

 

[jsteiger]

When I'm testing resistance between the DOA sockets, it starts at ~500k Ω and then it slowly goes up until it rises over the range of my DMM (2MΩ).

Is that normal?

If you are talking about the +/-V sockets then yes.

 

[Tinning-Tina]

If you are talking about the +/-V sockets then yes.

Awesome, many thanks, Jeff!

 

[Myhells]

Hello,

I just powered up my VP312 for the first time and smelled burning. I removed the unit and noticed the DOA was hot. I'm pretty sure I just cooked it. Can anyone point me in the right direction to why this happned?

Thanks

 

[jsteiger]

Hello,

I just powered up my VP312 for the first time and smelled burning. I removed the unit and noticed the DOA was hot. I'm pretty sure I just cooked it. Can anyone point me in the right direction to why this happned?

Thanks

Could be incorrect resistor placement, wrong facing diodes, incorrect transistor placement and/or turning them the wrong orientation. This is most likely all a problem with the opamp itself and not the preamp.

Rule of thumb, never test a fresh module build with a fresh opamp build.

 

[Myhells]

Could be incorrect resistor placement, wrong facing diodes, incorrect transistor placement and/or turning them the wrong orientation. This is most likely all a problem with the opamp itself and not the preamp.

Rule of thumb, never test a fresh module build with a fresh opamp build.

I have another VP312 with the same opamp. Should I try my questionable opamp in a known good preamp?

 

[jsteiger]

I have another VP312 with the same opamp. Should I try my questionable opamp in a known good preamp?

Yes.

 

[Hybridpi]

So I have a vp312 that doesn’t seem to be powering up. I’ve tried it with multiple op amps, and have retouched all the solder joints. I ordered a 500 series power extender so I can trace the circuit with power going through it, but one thing I noticed is, when I measure the components with my DMM (out of the rack) the output and com sockets for the DOA beep like an open circuit and only measure about 10 ohms when I use the probes from my DMM. I saw on an earlier post where Jeff said that there is an issue if the O and C sockets are only measuring a few ohms. They’re securely soldered in and I’d be really surprised if there’s a cold joint, but at this point I’m kind of at a loss as to what I did wrong. I went back over the BOM and made sure every part is correct, and that I put the litz transformer wires in the right holes, and all that is correct, but I’m still getting no signal and the LED doesn’t light up when I turn on the 48v switch. Any help would be appreciated. Thanks,
Dan

 

[surfgreentele]

Hello,

I just received my first CAPI VP312 kit.
The PCB I got is a CAPI VP312-VPR Rev C but I can't find any overlay or BOM for a Rev C on the CAPI website.
Is it just like the Rev B? Because it looks the same but I don't want to make any big build errors.

Thanks!

 

[jsteiger]

Hello,

I just received my first CAPI VP312 kit.
The PCB I got is a CAPI VP312-VPR Rev C but I can't find any overlay or BOM for a Rev C on the CAPI website.
Is it just like the Rev B? Because it looks the same but I don't want to make any big build errors.

Thanks!

Use Rev B docs for Rev C PCBs. The only difference was an updated square silkscreen footprint for the inout transformer.

 

[surfgreentele]

Use Rev B docs for Rev C PCBs. The only difference was an updated square silkscreen footprint for the inout transformer.

Thanks a lot!

 

[PaulSmith]

Hello there,

I've built many kits over the years and have recently built 4 VP26 / 4 VP312. All work as expected apart from one 312 which has a considerably lower output than the others. It doesn't sound thin, just a lot less volume, so I'm assuming (perhaps wrongly) that it's to do with the Bourns.

I have a good DMM but not much else - and I don't have much experience in diagnosing, so I don't know how or what to measure. I'm sure it's a bad solder join but any advice on how to narrow down the problem would be fantastic.

Thank you very much!

 

[jsteiger]

Hello there,

I've built many kits over the years and have recently built 4 VP26 / 4 VP312. All work as expected apart from one 312 which has a considerably lower output than the others. It doesn't sound thin, just a lot less volume, so I'm assuming (perhaps wrongly) that it's to do with the Bourns.

I have a good DMM but not much else - and I don't have much experience in diagnosing, so I don't know how or what to measure. I'm sure it's a bad solder join but any advice on how to narrow down the problem would be fantastic.

Thank you very much!

It could be misplaced resistors?

 

[PaulSmith]

It could be misplaced resistors?

thanks so much for your speedy reply Jeff. I’ve double checked and all resistors are good. I built 4 units at the same time so odd that only one doesn’t work properly. I’ve checked the soldering and it looks pretty good. I reflowed all the joints on the bourns and the input transformer which didn’t help. what else could I look out for/measure?

Many thanks indeed! I’m sure it’s something simple.

 

[jsteiger]

thanks so much for your speedy reply Jeff. I’ve double checked and all resistors are good. I built 4 units at the same time so odd that only one doesn’t work properly. I’ve checked the soldering and it looks pretty good. I reflowed all the joints on the bourns and the input transformer which didn’t help. what else could I look out for/measure?

Many thanks indeed! I’m sure it’s something simple.

I would check the level at either end of the 1R on a good unit and then check on the problem unit with all controls the same. This could narrow it down to the output transformer.