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

[bugbrand]

Hmm - well, the unit is working nicely apart from the HIz Plugin (IC version) which is currently confusing me somewhat - though I do wonder if I'm doing anything dumb (not very up on preamps etc yet)

Running into the HiZ input, with PRE 2622 mode - if I turn up the Preamp Gain too much I start getting a nasty 10Hz oscillation - with the Pad switch in, this is up near the top of the preamp gain setting, and much lower on the dial with the pad out.

Working fine in POST 2622 mode. [which I believe bypasses the HiZ plugin card?]

Hooking up the scope (and running the module on one of your test jigs) - firstly, I see roughly 1VDC offset on both output pins (no offset on the input pin).
At high gain, out+ wobbles at 300mV PtoP, while out- is more like 2V PtoP! [10Hz jaggedy waveform]

Interestingly, with the stock OPA2604, once it has gone into this oscillation, I bring the gain back down but there's then a MHz oscillation still on the Out- pin [not present on the out+ pin] - the audio output is fine again, though that oscillation can't be all that good..
I chucked in a TL072 and that doesn't suffer the MHz oscillation, but behaves the same with the preamp gain 10Hz oscillations.

Any thoughts?!
Thanks! Tom

 

[ENS Audio]

Just finished my 312DI and started measuring resistance between DOA sockets as instructed by the assembly guide.  Everything measured out @ 200k + Ohms between the DOA sockets EXCEPT between V+ and C sockets where I get less than 10k Ohms. 

Went ahead and resoldered a few cold solder joints and I still get the same problem with resistance below 200k Ohms between V+ and C  DOA sockets.


Thanks.

 

[ENS Audio]

Also I tested voltages between the DOA sockets and everything is around 16 vdc.

 

[jsteiger]

.....between V+ and C sockets where I get less than 10k Ohms. 

This is correct on the VP312DI. The measurements shown in the VP2x Assembly Guide are specific to the VP25 and VP26.

 

[ENS Audio]

.....between V+ and C sockets where I get less than 10k Ohms. 

This is correct on the VP312DI. The measurements shown in the VP2x Assembly Guide are specific to the VP25 and VP26.

Ok then now I need to find out why the 2520 transistors are overheating (DOA voltage selection switch is selected at 16v btw)  even though all the measurements on the DOA sockets are correct. 

Also there is no output sound except for some low noise which cancels out when I hit the mute switch.  I've resoldered the few cold solder joints that were found as well.

Other than the DOA socket resistances I've checked, everything on the gain switch reads the correct measurements of 25k ohms.

Not sure which part of the circuit to start investigating next, this is driving me nuts lol.


By the way, I must commend you on the quality of these boards and everything I've purchased over at CAPI.  Especially the floor box PSU, love how the sides of the chasis are two great big heatsinks, great stuff.

 

[ENS Audio]

After looking around at the PCB I've noticed that I soldered one of the relay boards backwards like a total *******!  :-[  So I had to snip away all the header pins and desolder the relay board in order to remove it from the main PCB.

I'm going to solder some diode leads as a substitute and put the relay board in the correct orientation.  We'll see what happens after that.

Other than that everything else looks good, can't believe I soldered that thing backwards, must be dyslexic. 

 

[ENS Audio]

Went ahead and soldered the relay board in the correct orientation, now I get sound only through 48v phantom power with a condenser plugged in.  No sound when I plug one of my guitars into the DI input and the DOA transistors gradually start heating up after 10 mins or so with the unit running.  Guess it's safe to say I'll need a new relay board with components.

Is there anything else I should measure/test in the meantime til I replace that particular relay board?


Thanks,

 

[jsteiger]

Is the opamp a fresh build? Maybe there is trouble on that board?

 

[ENS Audio]

The DOA was already assembled when I received it, it's the version with the smd resistors.  I see something written on the board with the date 05 15 if that helps any.

 

[jsteiger]

The DOA was already assembled when I received it, it's the version with the smd resistors.  I see something written on the board with the date 05 15 if that helps any.

That's a red dot so it won't be that then. Just wanted to make sure the opamp wasn't a kit build. The output transistors to get nice and warm.

 

[ENS Audio]

The DOA was already assembled when I received it, it's the version with the smd resistors.  I see something written on the board with the date 05 15 if that helps any.

That's a red dot so it won't be that then. Just wanted to make sure the opamp wasn't a kit build. The output transistors to get nice and warm.

Until I get another relay board is there any other parts of the preamp I should check to see that I have proper measurements {volts/amps/resistance/ on such as the input and output transformers ?  Or am I going to have to go through checking values through each and every component?

Thanks,

 

[jsteiger]

Which relay board was the problem? You can view the schematic to see if it was the one that switches to DI mode. Sounds like you are OK in mic mode?

 

[ENS Audio]

IT'S FINALLY WORKING!  ;D  Looks like the 9v for my fretless bass needed to be changed, wow this sounds incredible and I don't even have it running through my bass amp yet.  I can only imagine how much better it will sound going through an LA2A and API Eq 

The only problem I've noticed very little hiss once it's turned all the way up and when the phase button is engaged it's a little crackly.

Would you happen to have a link to where I can get the calibration test results as far as noise levels, etc (if that makes any sense, still a noob at this)

Thanks for all your help and providing such awesome kits of the real deal,  all you guys at the white market have made it possible to finally own the stuff of legends few of us could ever afford.  8)



Now time to order some other Hi-Z plugins and other DOAs to try!

 

[jsteiger]

The only problem I've noticed very little hiss once it's turned all the way up and when the phase button is engaged it's a little crackly.

Is this 2 separate concerns?

 

[ENS Audio]

The only problem I've noticed very little hiss once it's turned all the way up and when the phase button is engaged it's a little crackly.

Is this 2 separate concerns?

There's some distortion when I have the gain 3/4th's or the output attn 3/4th's up.  I'm running the 312 through my focusrite saffire pro 14 and the gain is only turned up 1/4th of the way on the audio interface.

Do you want me to post a screen shot of the levels in visual analyzer?


Thanks.

 

[jsteiger]

Do you have the opamp fully seated? http://capi-gear.com/catalog/DOA_Install.php
If its correct, these other issues indicate you have something placed wrong or possible bad solder joints on the build.

 

[ENS Audio]

Do you have the opamp fully seated? http://capi-gear.com/catalog/DOA_Install.php
If its correct, these other issues indicate you have something placed wrong or possible bad solder joints on the build.

I'll check that as well, I suspect maybe some of the components were damaged on the relay board when I was desoldering it in order to resolder the board in the correct orientation.

Also, I tried looking for some information on calibrating the 312DI, wanted to know at what Hz should I set my signal generator when tracing out the board.  I am using visual analyzer and using the Focusrite Saffire Pro14 as my audio interface, unless you recommend I fire up my old tektronix 2225 50 Mhz scope.

Thanks.

 

[ENS Audio]

UPDATE:  Well it looks like I've made some progress here, turns out the tantalum cap on the Hi Z plugin was soldered backwards ('+' mark on the cap inserted to the '+' on the PCB layout DOH!)  Plus one of the wires I used to jumper the relay I desoldered wasn't soldered in the main board.

It sounds so awesome when I'm directly monitoring the output when my bass guitar is plugged in, I can turn the gain up full blast and can set the output atten to '0' BUT when I run the output from the preamp to the input of my focusrite saffire it appears the audio interface cannot handle all that gain and it clips terribly causing me to set the output atten more than halfway.

Is this because my audio interface only has so much headroom or do I need to further troubleshoot the mic pre for more problems?


Thanks.

 

[jsteiger]

I am no DAW guy so I can't say about interfaces and such. You can easily measure the preamp for max gain though. With the output full up at 0 and the preamp gain cranked, the pre will amplify the input signal by appx 60dB.

 

[the19thbear]

Hi. I just took over another guys project here. He couldnt get it working.

He had turned C6 and C5 diodes the wrong way around (the ones that are right after the +/-16 volt inputs) and a wire to the transformer had broken off. And the LED was turned the wrong way. He had it powered up this way, and im surpriced it didnt blow anything up.. (well maybe not).
After i fixed these very visible error i actually got the unit kind of working. Phantom power is on(led is on) and everything seems to work except that all the low freq from the mic input/di input are cut off. Its like a constant low cut at around 400hz or so (just listened through cheap headphones).
The mute/pad button work. I havent been able to test the phase button yet.

I can read i schematic and follow very basic signal flow, but is there something obvious that could have been damaged by the earlier person powering it on with C5/C6 turned the wrong way around?
Or is there a built in low cut filter where he might have put in a wrong resistor value?
I know this is a shot in the dark since you guys and gals dont have the actual unit in front of you, but any help would be appreciated! Maybe a way i can test each area on the PCB by tracing the sound?

Thanks