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

[jsteiger]

Bruce,

This is basically the circuit I use on the relay board.

Is it possible that you swapped the 4V3 zener and one of the 914's? Probably not but thought I would ask.

I can send you a few parts if you need them.

I won't be able to check my build until later today.

Cheers, Jeff

 

[bruce0]

When testing V+ to C after the build, I got 40K resistance, and the appropriate resistance is higher according to the VP2x Docs.  It turns out that if I set the DMM on the 20M range or the 2M range, it showed high resistance.  On 200K however it showed 40k.

This only happens when the OP-AMP switch is turned to 16V.  On 24 V it is fine.  This is because the relay card is in the 16V circuit only.  And Notice that the same is true of the relay card itself.  There should be high resistance between V+ and VC (which is normally grounded on the board when there is no DI plugged in). I was getting 40K ish there too.

This whole problem can be attributed to a strange Meter, or interaction between the meter and the capacitors in the circuit.  

I went and bought a new meter, and everything reads fine (high resistance).

Just in case someone else had the problem.

bb

 

[bruce0]

Now that I got the problem sorted out (turned out there was no problem), I got a chance to try it out today.  Tried various guitar and bass through it.  Really liked some of the bass sounds, the attenuator gives a lot of control, which is fun.


One problem.  When the Post2622 switch is flipped left, I get no audio signal from the DI.  TO the right it works fine.  The same is true with 2 different HiZ cards.



So maybe I do have some problem.

 

[jsteiger]

Switching the "Post 2622" right will give you the "straight into the 2520" Bo circuit.

Switching that left will run your signal thru the HiZ Plug-In module. Did you get a passive version of the plug-in? If so, checking with that could eliminate your HiZ Plug-In as the cause.

Make sure you have voltage on the +V socket of the HiZ Plug-In.

Can you power the module with it flat on your bench? You will need to. With no HiZ Plug-In, voltage applied to the module, insert a mono 1/4" jack into the socket. Keep the "Post 2622" switch to the left. Probe with your DMM to make sure you have continuity between the 1/4" jack tip and the HiZ In socket of the HiZ Plug-In.

If you do not have continuity...the issue will probably be on the relay card just behind the 1/4" jack socket.

If you do have continuity...the issue is with the HiZ Plug-In.

Let us know.
Best, Jeff

 

[bruce0]

Jeff:

Thanks so much.

Yes I can power the unit open on the bench.

I presume from your description that the relay card behind the 1/4" socket is the one that is activated by the Post 2622 switch, and the one in the center of the board is activated by insertion of the 1/4 Jack. Is that correct?  So the one that goes to Bo Mode, is the one near the jack?

I have tried the unit with a Passive (DIY - Old Altec Mic Pre Transformer reversed), and with an active.  I do have 2 different actives, and after I make your tests I can try that ( I was reluctant to Fry 2 if there was some problem).

I will make the tests, but based upon the fact that the Passive didn't work either, it sounds like it is the relay card near the Jack.  Is that consistent?

(Luckily... and thanks to your suggestion, I have a Hakko 808...  And as you said, it does just want to make me de-solder something... it works so well (I have been harvesting old mic-pre transformers)).

I will return with more data.

 

[jsteiger]

...I presume from your description that the relay card behind the 1/4" socket is the one that is activated by the Post 2622 switch, and the one in the center of the board is activated by insertion of the 1/4 Jack. Is that correct?  So the one that goes to Bo Mode, is the one near the jack?

Yes, correct Bruce.

I will make the tests, but based upon the fact that the Passive didn't work either, it sounds like it is the relay card near the Jack.  Is that consistent?

Yes I would agree. With a 1/4" jack inserted, you should hear that relay clicking/activating when you flip the "Post 2622" switch back and forth. Without a 1/4" jack inserted, the "Post 2622" switch does nothing since it needs the ring-sleeve-ground connection made by the jack body itself.

Which reminds me, DO NOT USE A STEREO PLUG FOR A GUITAR CABLE HERE!!!

(Luckily... and thanks to your suggestion, I have a Hakko 808...  And as you said, it does just want to make me de-solder something... it works so well (I have been harvesting old mic-pre transformers)).

;D ;D 8) 8) They are not super cheap but well worth the money.

Keep us posted.
Jeff

 

[bruce0]

I pulled the relay cards out, which is possible with the hakko desolderer amazingly, and traced one. 


I figured out that the Zener was in the wrong place all the time (switched with one of the 914b's exactly the same on both cards).  Ooops.
I had checked it against the BOM but somehow missed it.  I think you may have asked this first... and I did check.

In any case, thanks for your help.  Pre is tested and working fine.


(... the way I found this was I traced the card, wrote up a schematic, looked at it, and realized it wouldn't work. )

 

[jsteiger]

Hey all,

I have published a long-over-due pic with some notes on how to complete a proper & permanent VPR 500 series mod to the VP312DI PCB.

Here is a thumb:


I have also updated the first post of this thread with this info.

Happy Saturday! 

Cheers, Jeff

 

[rob61]

I'm interested in adding a pair of these to my new 51X rack.

1. What difference in sound is there between the FET and the IC version of the active DI circuits?

2. Has anyone tried the new 24V APP2050E DOA? I've been using the gar2520 and Red Dots in my other +16 CAPI pres. How would this compare in sound?

 

[chunger]

I'm interested in adding a pair of these to my new 51X rack.

1. What difference in sound is there between the FET and the IC version of the active DI circuits?

2. Has anyone tried the new 24V APP2050E DOA? I've been using the gar2520 and Red Dots in my other +16 CAPI pres. How would this compare in sound?

I find the FET IC to be bity and aggressive perhaps in the upper mids?  Very forward to my ear. . . the IC version runs very hot gainwise.  Bass response is very smooth on that one in fact, I find it pretty neutral and smooth. .. perhaps due to the larger cap?  This is primarily playing with it on bass guitar and primarily on the APP2050E.

 

[rob61]

Thanks Chunger... have you also used gar2520 or Red Dots? If so, how does the APP2050E compare? I'm finishing up wiring my 51X...

Anyone else compare these? Any input appreciated.

 

[chunger]

don't have red dots, but have the 2 gar2520 and the gar melcor clones.  Haven't played with them in the VP312DI though.  Only on the VP26's.

 

[NoBass]

Help !!

My VP312DI killed one of my DOA  :'(

It worked very well for a few weeks, with AWESOME results on both kick and drum ambience, but all of a sudden, between two takes, it stopped making sound. At first I thought it was my old API2520 that had gone wrong, but I put a red dot inside and it didn't make a sound. The DI however, is still working. I switched it off, and afetr only 2 minutes of testing, I could feel the red dot burning hot.

What's wrong ?

(BTW I tried my old API2520 in a VP26, it just doesn't work anymore  :'( )

NoBass

 

[jsteiger]

Believe it or not, this is a first, IIRC. What rack are you using? Is the VP312DI built VPR style or 51x style? My first thought is to check the voltages at the DOA sockets. Are you 100% sure that CR1 and CR2 are 1N914'a and not the zener's from the Sub-DI board? Also, if you are using the DI circuit set to post 2622 a lot, the shunt jumper should be set to DC Block/Cap Coupled Output. I have heard of guys smoking there PPA amps this way because of the higher DC offset. The DC offset from API2520 is typically pretty low, unless the opamp was on it's way down anyhow.

 

[NoBass]

I'm using a 51x rack ; the VP312 is 51x-style. The voltages are the first thing I checked after the DOA died, and they're just about right (+- 0,5V). I ran the DOA at 16V (of course). I never used the DI, I just checked it, and yes the jumper is set at "coupled output"...
I can't really check CR1 & CR2 because their name is toward the pcb but I remember checking them...

About the opamp, I know nothing about its history, so I may have been "on its way down".

But as I said, even with another op-amp, it does not produce any sound and I'm not comfortable letting the opamp get this hot...

 

[jsteiger]

If it's not passing a mic signal and the DOA is known to be good, I would first check the PK2 relay to make sure that with no 1/4" jack inserted, pins 8 and 10 get coupled to the input transformers primaries. With a ground signal present at PK2's VC pin, the rear mic in will be couple to the 2622. When a 1/4' jack is inserted, the normal of the sleeve's contact is broken/opened which disconnects the ground from PK2's VC pin and switches the relay to the HiZ Plug-In as the source for the 2622's input.

If all of that is good, you will have to look at the output section. That is very short and sweet really but I would make sure it is not a solder joint on either the Mute or Polarity C&K switches.

Did you get the skiz I sent out a few weeks ago?

Cheers, Jeff

 

[jsteiger]

Hey guys

To help keep things simple and easy, I put a link to the most current version of the VP312DI schematic near the beginning of the first post of this thread.

The most current one has today's date of 7-12-2011. I found a small error and corrected it. The VC labels for the PK relay's were flipped the wrong way around.

Cheers, Jeff

 

[jsteiger]

Hi all

Since the Rev C.1 version of this project has been officially released and started shipping, I had to update a number of the support docs and details.

--The new schematic can be found near the top of the first post of this thread. The older Rev B.1 is still there for history sake.

--I also added the VP-Gainswitch install guide PDF to the first post. Both the Bourns and Grayhill 71 gain options are now found on the PCB.

--I added a few pics to aid in installation of the new Bourns t-pad, since the footprint is on the main PCB.

--I added a pic of the new LED layout as that has changed slightly.

I think that's it. Ask away if anyone has any questions.

Cheers, Jeff

 

[mulletchuck]

finished my build!  Fired up perfect first time!  couple q's, tho:

Should I hear the relay's switching on/off when i flip some of the toggle switches in the front?  cuz I only hear them switch when i turn on the 51x power supply or turn the power supply off.

Everything worked, tho.  DI was nice and clean, Mic sounded just like the VP26.

 

[jsteiger]

Chuck, when you insert a 1/4" plug, it will open the normalled contacts on the Neutrik 1/4" jack, which will activate the relay that's behind the input transformer. Once a plug is inserted (and only with plug inserted) flipping "Post 2622" will activate the relay just behind the Neutrik jack.

This pre will sound a little different than a VP26 once you start comparing them side by side.