Walrus
Well-known member
You have got the 10kOhm resistor in series with the LED haven't you?
[Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
- Thread starter jsteiger
- Start date
Help Support GroupDIY Audio Forum:
Mrosso
Well-known member
Kevin,
No, I do not. I thought that the Rev D boards didn't need resistor on the LED.
Thanks!
No, I do not. I thought that the Rev D boards didn't need resistor on the LED.
Thanks!
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
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
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
New member
- Joined
- Nov 27, 2020
- Messages
- 1
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?
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
Member
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?
Is that normal?
If you are talking about the +/-V sockets then yes.
Tinning-Tina
Member
Awesome, many thanks, Jeff!
Myhells
Member
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
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
Member
I have another VP312 with the same opamp. Should I try my questionable opamp in a known good preamp?
Yes.
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
Dan
surfgreentele
New member
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!
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
New member
Thanks a lot!
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!
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?
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.
