[BUILD] CAPI VP312DI~500/51x Series~Preamp + Direct Inject~Official Support Thread

[bartbusch]

I eventually stumbled upon this picture on the product page for the VPR jumpers and here's what that looks like.

 

[bartbusch]

Here's what the final build of the Rev D version with stepped gain looks like.

 

[bartbusch]

Here's another view

 

[TheLavaBed]

Hey Mike

With no HiZ Plug-In installed, the VP312DI will work fine in mic mode. It will only work for DI when in "Post 2622" mode. The most common error with these builds are wrong locations/orientation for the diodes on the relay PCB.

Hi Jeff (and everyone smarter than me)...

So, I built two VP312DI's - one is (mostly) working, and the other is not working at all.  I built them at the exact same time (put components on one board, and then the other).  I've inspected visually, and can not see anything wrong.  I'm more than happy to take measurements, but I have no idea where to measure in a way that would be helpful.  I saw this on a previous post, but I don't know where to take these measurements (I'm assuming on the card end pins):

-V and +V = xxxx
-V and C = xxxx
C and +V  = xxxx
C and O = xxxx
V+ and O = xxxx
-V and O = xxxx

My rack is a 16V rack.  Opamp is a GAR that I purchased assembled from CAPI.

Anyway, here are the issues:

Preamp 1:  Microphone side seems to be working completely.  Input pot, Output Attenuation, Phantom, etc.  However, when I plug in a bass into the DI section, it works for a minute.  All switches seem to do something.  Then, after about 15-30 seconds, it gets distorted sounding, and begins to fizzle out, eventually making no sound at all.

Preamp 2:  Totally dead, no audio passes.  Phantom power light turns on.  When plugging and unplugging patch cables on the front side of the preamp, nothing shows up in Pro Tools.  When unplugging cables on the output side (after the pre) pops are seen on Pro Tools.

Any help would be appreciated.  I love CAPI Pres (thanks Jeff!!).  These are the 7th and 8th CAPI's I have built, but the ones I'm having the most difficulty with... I'm losing it as I get older.  I had to buy magnifying glasses this time to read the diodes... Never had to do that before 

Thanks,
Mike

 

[jsteiger]

Mike, it sounds potentially like bad solder joint(s). The biggest error folks make on these builds is misplace diodes on the small relay boards.

 

[TheLavaBed]

Mike, it sounds potentially like bad solder joint(s). The biggest error folks make on these builds is misplace diodes on the small relay boards.

Thanks Jeff - I'll look into it and let you know what I find.  I've read your posts about the relay boards, and tried to take a close look at those.  I'll go through the main board of each first and see if it helps.  If not, I'll remove the relay boards, and see if touching up those solder joints helps.

Thanks for the support of your products Jeff!!

-Mike

 

[Hynek]

Here's what the final build of the Rev D version with stepped gain looks like.

bartbusch - your photos were a lot of help, sped up my build quite a bit, thank you!

 

[DrywOwens]

Hi all,
I just finished a VP312DI Rev D build using vintage API components. As I perform the test, I seem to be getting 10.1 ohms resistance between V+ and C on the DOA sockets. I currently do not have a DI board installed. Is this normal?? All other tests result in a reading well above 200K.
Thanks in advance!

 

[jsteiger]

Hi all,
I just finished a VP312DI Rev D build using vintage API components. As I perform the test, I seem to be getting 10.1 ohms resistance between V+ and C on the DOA sockets. I currently do not have a DI board installed. Is this normal?? All other tests result in a reading well above 200K.
Thanks in advance!

This is totally normal and expected for a VP312DI or VP312.

 

[Kevinkmny]

I'm getting 4.0K ohms on that same measurement....is that ok too?

 

[jsteiger]

I'm getting 4.0K ohms on that same measurement....is that ok too?

It is dependent on where the shunt jumper for the DC cap coupled output is at. It should be fine though.

 

[Kevinkmny]

Hmmm,

In apply power with the op amp not installed I'm getting 16 volts (or -16V?) between -V and C but nothing between +V and C...

 

[jsteiger]

Hmmm,

In apply power with the op amp not installed I'm getting 16 volts (or -16V?) between -V and C but nothing between +V and C...

Did you jumper over the voltage select switch as shown on the VPR mod?

 

[mdmitch2]

I built one of these recently, and everything is working fine except I'm not sure about the IC1 hi-z plug in. It's insanely hot. The only way I can use it with a bass is to use the 20db pad, and input gain at zero or one. I also have a pikatron, and it works fine, and the level is actually lower than when using post 2622 mode. 

So is it normal to need the pad when using the IC1? I verified that it's assembled correctly... it would be pretty hard to screw up.

 

[jsteiger]

I built one of these recently, and everything is working fine except I'm not sure about the IC1 hi-z plug in. It's insanely hot. The only way I can use it with a bass is to use the 20db pad, and input gain at zero or one. I also have a pikatron, and it works fine, and the level is actually lower than when using post 2622 mode. 

So is it normal to need the pad when using the IC1? I verified that it's assembled correctly... it would be pretty hard to screw up.

Well, it goes like this. The Hi-Z Plug-In output is coupled to the 2622 input transformer so there is gain from that as well as the rest of the preamp. The IC1 is a balanced output and runs about 6.5dB hotter than the FET1 which is about 15dB louder than the Post 2622 mode. The FET1 is basically a unity gain impedance convertor. Technically speaking, the Post 2622 mode is down about 17dB since there is no gain from the 2622.

You can try adding a u-pad to the output of the IC1 board. Replace the two 100Ω series output R's with 820Ω R's and then solder a 160Ω shunt across them at the output side. This will drop the output to pretty well the same level as the Post 2622 setting. Of course simply engaging the mic pre pad will do almost the same thing.

 

[mdmitch2]

Thanks Jeff -- I'll just use it with the mic pad -- no biggie.

 

[rwrwrw]

Hi,

I'm currently building a couple of these vp312DI preamps and I wanted to know how leaving the optional capacitors C10 470 uf 6V3 & C11 .01uf 100V out effects this preamp?

I know that leaving the R2 150k resistor out gives a more open sound. Curious if these capacitors do something similar.

 

[jsteiger]

Hi,

I'm currently building a couple of these vp312DI preamps and I wanted to know how leaving the optional capacitors C10 470 uf 6V3 & C11 .01uf 100V out effects this preamp?

I know that leaving the R2 150k resistor out gives a more open sound. Curious if these capacitors do something similar.

They are there to block DC from possibly damaging the output transformer when the DI is used in Post 2622 mode. If you ever plan to use the DI in Post 2622 mode then make sure the caps are installed and the shunt jumper is set to leave them in the circuit.

 

[rwrwrw]

Ok good to know!

I'm guessing that means the shunt jumper should be on "DC Block/Cap Coupled Output" ?

 

[jsteiger]

I'm guessing that means the shunt jumper should be on "DC Block/Cap Coupled Output" ?

Yes, exactly