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

[jsteiger]

The 12V shunt supply for the relays is always connected to the +16V rail. It is before the switch for DOA voltage, not after. The assumption is that this module will be in a 51x rack where there will be +/-16V as well as +/-24V all day, all the time.

Maybe elaborate on what is working and what is not, and on what voltages and so on.

 

[qmp audio]

2 modules... 2 different issues im trying to resolve:

1:  Had a vpr modded vp312 di  working great for almost 2 years now.  now the relay on the DI doesn't seem to be switching off.  no mic signal only DI.  everything looks good, and its been working,  so im assuming its a failed part somewhere.  was going to start w/ the neutrik, but curious if anyone has an idea of where to look first,  or if there's been anything similar.

2:  just finished a 51x version.  threw a 990c in there as its the only 24v opamp i have around.  everything works great except noticed 2 things.
•  the post xfr switch results in a loud pop.  but works otherwise.
•  the 10db pad on the di gets very noisy,  but the noise goes away when the low pass is engaged.
Could these issues be related to the 990c opamp?  or could the be some other issue?  The 990c is new and functional.
Thanks much for any insight.

 

[jsteiger]

1. Could be a solder joint as well. Very hard to say. If you have a good desoldering tool, you could try a different relay PCB to see of the trouble follows the relay PCB or not.

2. I would try with a 2520 and see if the issues go away. You can also measure for DC offset not only after but before the opamp. My guess is the 990 is not a happy camper in this circuit. Typically, the 990 is not a good match for a 2622.

 

[qmp audio]

1. Could be a solder joint as well. Very hard to say. If you have a good desoldering tool, you could try a different relay PCB to see of the trouble follows the relay PCB or not.

2. I would try with a 2520 and see if the issues go away. You can also measure for DC offset not only after but before the opamp. My guess is the 990 is not a happy camper in this circuit. Typically, the 990 is not a good match for a 2622.

Thanks much.  DI was in fact a solder joint on the neutrik.  a reflow solved that issue.

Will report back on the other module when i finally swap the amps out and test DC offset.

 

[mhuss]

I just finished up my 51x VP312 DI build, and it worked the first time.  ;D However, I noticed one problem -- when I'm in Post2622 mode, and I engage the -10db switch, it attenuates the signal as expected, but there's a *very* noticeable hiss added as well. The preamp is dead quiet in all other configurations, Hi-Z and normal.  (God forbid I should have to disassemble that Sub-DI section...  :-\) Is it possibly just Johnson noise from the series 2M2 resistor?

I'm using the discrete FET1 Plug-In, 51X +/-24v, and a 24v 990 DOA from Hairball .

--mark

 

[qmp audio]

I'm using the discrete FET1 Plug-In, 51X +/-24v, and a 24v 990 DOA from Hairball .
--mark

Try switching to 16V and throw a 2520 in there.  see if the issue persists.  I have the same issues when i put a 990c in the circuit.  I understand that the 990c really wants a different impedance than the 2622 provides.

I do have a 312 setup in 24V w/ a 990c in the circuit.  I primarily use that module as a bass DI with the post xfmr in.  However... the pad does introduce noise w/ my JH 990c for me.  I also get some popping artifacts w/ the 990c when flippin switches ( i always mute when changing things) .    i think it sounds great as a DI w/ only the post xfmr switch engaged.  That's my primary use for that module w/ the 990c.  I've been using it as my tom mic pre w/ the 990c and really like the sound w/ my 421s.

do some searches for 312 and 990c and theres some good info ( some from john hardy ) about how the 990c interacts w/ the 312 circuit.
Jeff also has commented about 990c interactions in the 312 circuit... earlier in the thread i believe
 

If you want to use 24v w/ the 312,  look into the jlm 2520s.  there are others but that one seems to work really well in the vp312.

 

[entresolmusic]

Hello!

I am a happy Vp312 Di kit owner. I have the stepped version and i have a question. I am in the middle of soldering the first resistors for the gainswitch.

It says that i am suppose to get 25 k. Well i do get 25k from : left of R11 and at the bottom left of R1?.

It says that it is suppose to be from the wiper pad. Is that to the left of between R2-R3? when i probe from there nothing happens. but i do get 25 k the other way.

Any help would be appreciated.

Thanks!


Edi

 

[jsteiger]

I need to correct those directions. It should be from one end of the switch pins to the other, not the wiper.

 

[mhuss]

If you want to use 24v w/ the 312,  look into the jlm 2520s.  there are others but that one seems to work really well in the vp312.

I do -- I'm filling up my 51X rack with 16v modules. 

I got a 2520 from JLM, and I like it a lot. Thanks for the pointer.

--mark

 

[tgs]

Two VP312DI 51x modules built; one working perfectly, the other needs some love and care!

I tried the DOA in a different module and it's working; also tried the module in a different slot. So I've ruled out those things. Relays are "clicking" as they should, too.

The problem: I'm getting very weak signal and it's only treble. Same thing with DI, or I can't even hear the signal. Strangely, when I switched the DOA, I was getting no signal, until I really pushed the input and the signal jumped out, now with full frequency range. But after some silence it's dead again. Changed back to the first DOA, weak, treble-y signal again. I can turn the input gain all the way up and I can hear the signal distorting. So, something wrong with the output?

Where should I start looking?

 

[jsteiger]

Are the the opamps fully seated? http://classicapi.com/catalog/DOA_Install.php

I think you will have to inject signal and follow the signal thru the circuit using a probe to see where things go south.

 

[tgs]

Are the the opamps fully seated? http://classicapi.com/catalog/DOA_Install.php

I think you will have to inject signal and follow the signal thru the circuit using a probe to see where things go south.

I think so but I will have a closer look tomorrow. Bit odd that I get the same problem with both the DI and mic input though.

I can send a test tone through the pre when I'm back in the studio tomorrow. But will I need an oscilloscope? I don't have one yet. Even if I did, I would feel a bit lost on where to measure too.  :-[

 

[jsteiger]

There are many posts here about signal tracing probes. I don't do it this way myself but you can use a powered speaker so you can actually listen for extreme changes. You can also use a DMM set to ACV.

Doe the problem happen with DI set to both post and pre 2622?

 

[tgs]

I'm ALMOST certain it does but I'll have to double check. I'll report back tomorrow.

EDIT: I should probably also mention that this is the board where I managed to run a gar2520 with the NPN and PNP mixed up AND ran 24V through it... So maybe I damaged something else in the process as well?

 

[tgs]

I checked now and I get the same behavior with Post 2622 activated. The behavior is the same as the other one, i.e. the level drops when I activate Post 2622, but the output is still VERY weak and only top-end. I am quite sure that the DOAs are properly seated as well, they seem to go all the way down like on my other modules and they sit flush with the board.

See edit in my previous post for some additional cause for concern though.

 

[jsteiger]

Well, I would assume from the pre/post 2622 when in DI mode symptoms that the 2622 is not the cause. It's time to inject and trace signal. There is no magic bullet cure except figuring out where things go bad.

 

[kante1603]

Hi,

if you have a working module lay them side by side and compare them,try signal tracing as Jeff suggested.
Despite of that when you say the signal lacking of bass and being weak  often indicates something like "one leg lifted" on the output or swapped or badly connected transformer wires.
Might be a godd idea to check them and also look for cold solder joints.

Just an idea,

Udo.

 

[tgs]

Took the board out, cleaned it a bit, went over some solder points. Gray cable from the transformer looked a bit funny so I fixed that (does that actually go anywhere though? Trying to learn how to read schematics properly.). Red and brown looked like they may have been bridged so I cleaned off the solder and applied new.

Long story short: it's working!! Thanks for the help, guys!

 

[kante1603]

Congrats

Udo.

 

[entresolmusic]

Hello,

I have an  issue on my VP312Di that I didn't had before, it used to run very good.

When I run sound through it (mic or a DI) it sounds very thin, low, like a crackling low pass filter. The switches for post 2622 seems to work, the -10 too, and I don't know about the JLPF. The PAD doesn't work, the MUTE does. Phantom too and both gain and fader works too.

I really don't know where to start since it was fine before. maybe something came loose or moved.


Let me know if there is any test I can start with or if you guys need more info.



thanks!



Eddie