[BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread

Do you mean the 2 pre's are off from each other by .3dB or the output level differs from the input by .3dB?

I mean .3 db from each other, but i did the test with the HPF engaged in one module...such an idiot. :double facepalm: Now the difference is just .1 db. I builded them slow to avoid mistakes...I was tired so...
Everything is ok!  8) Thanks for the reply Jeff! More will be coming

kante1603 said:

Hello and welcome to the forum.
A thin or lacking low frequency signal at a low level indicates a balancing issue most of times.
I'd check transformer wirings and functionality first,seems like a "hot" or "cold" signal part is missing.

Best,

Udo.

Click to expand...

Thanks Udo, I'll check tomorrow night and back to you.

Luc

kante1603 said:

Hello and welcome to the forum.
A thin or lacking low frequency signal at a low level indicates a balancing issue most of times.
I'd check transformer wirings and functionality first,seems like a "hot" or "cold" signal part is missing.

Best,

Udo.

Click to expand...

Quick check during lunch break! Good idea Udo, I have an open circuit between the Black and the Brown wire of the T3 Transfo = dead transformer I think.
I tried to swap with another Transfo that I have, but still the same issue.
I'll follow this idea as soon as I have time.

kante1603 said:

Hello and welcome to the forum.
A thin or lacking low frequency signal at a low level indicates a balancing issue most of times.
I'd check transformer wirings and functionality first,seems like a "hot" or "cold" signal part is missing.

Best,

Udo.

Click to expand...

Udo,

When I changed the TR yesterday, I only plugged the VP28 in my lunchbox, and saw that the green led didn't flashed.
Or, in addition of the TR issue, the A2 was dead.

Thanks for your help, the VP28 is working well now.

Thanks for helping me!

Luc

Hello Luc,

glad you got it sorted!
For the A2,I remember at least one person here had it inserted the wrong way around.
Doing this kills that ic,it doesn't "like" reversed supply voltage.

Have fun with your VP28,I really love mine (I have eight),

best regards and have a nice weekend,

Udo.

Hey! I just need some advice:

I have the 51x rack (extra 24V), and now I am not sure which version of the VP's to get.
For the time being, I won't be making use of the 24V capabilities of the 51x preamps version.

Is it possible to get the 51x version VP's, but just putting in gar2520's and plugging them into the 18pin sockets?
From the pictures here, I've seen that there is a spot on the PCB labelled 16V and 24V and you solder (jump?) in a certain way (see attachment - bottom right corner)
What would I have to do if don't need the 24V, but have the 18pin PCB and the 51x rack?

I like to give myself options, even though i might not use all of them at the moment, so if it is possible to use the 51x version preamps, with 16V DOA in a 51x rack out of the box, I'll get them, but if i have to 'mod' outside of Jeff's recommended boundaries, I'll just get the VPR version then, bc when it comes to electronics, I 've only soldered cables so far

Thanks for the help!

Yes it is possible. That is what the switch is for on the VP312 PCB. Just set it to 16V and you will be fine with a 2520 style opamp. If you ever decide to get a 24V capable opamp, install it and flip the switch to 24V. Pretty straight forward.

I recently ordered+built two kits and caught that the grayhill switches are now fixed 12 o'clock (nice!), but noticed there were no shaft adapters included for the knobs. I figured maybe they weren't necessary anymore either, but the knobs are definitely falling off...Is a shaft adapter still needed, or am I just not installing them well?

The shaft adapters are not needed as the knobs have an 1/8" hole for the GH's 1/8" shaft. Sounds like they need to be tightened more stoutly. 

I am just finished on my first Vp28 (ordered two).

However, on the finished one I just blew up the IC. Plugged it in and it blew instantly when i turned the electricity on.
This is what it looks like now, the top blew off.

http://cdn.imghack.se/images/ddbebde498ce582d4eb74fb7527d1145.jpg

Is there an obvious mistake i have made? If not, do you have any pointers for where to start troubleshooting?
And where can i get a new one?

I would guess it was installed backwards? Kinda hard to tell now. I have them in stock at the store. Just search for 4558 and you will find them.

It didn't even occur to me that it had a direction. I was already finished since yesterday, tried and remembered, "uh yeah, i got to add the IC thingey". Thats what you get for rushing. I do have the blown off top piece left, so i'll see which way it fits and check. Thanks!

jsteiger said:

The shaft adapters are not needed as the knobs have an 1/8" hole for the GH's 1/8" shaft. Sounds like they need to be tightened more stoutly. 

Click to expand...

That's what I figured/hoped...I'll tighten them up good this time! Thanks!

Built up a pair yesterday. Great design and really fun to build!
I have a problem with one of them. Distorting severely. From the waveform in the DAW, it looks like it is clipping on the negative swing of the waveform. Sounds fine with really low levels.
So I'm assuming there is a bias or supply voltage problem on one of the opamps.
Here's what I've done:
- All the features  (leds) work fine. No difference between good and bad units under careful visual inspection
- Swapped opamps between the good and bad unit.  Problem does not follow a opamp
- Checked V+/V- for DOAs, look good
- Checked voltages on Q1, same between good and bad unit.
- Removed IC - still have problem.

Any ideas?

I have managed to get one of my pair of vp28s built and working. Very pleasing build. However, I am having some difficulties with one of the gar2050 kits - as soon as I power on, the -16 volt power rail fuse blows. Can anyone direct me to the gar2050 support thread?

Regards,
rjuly

You'd have found it if you searched for 2520 instead of 2050     http://groupdiy.com/index.php?topic=33970.0

Unit7 said:

You'd have found it if you searched for 2520 instead of 2050     http://groupdiy.com/index.php?topic=33970.0

Click to expand...

Doh! Much obliged

I have a question regarding connecting the input on the vp28. While waiting for my vp28 kits to arrive I'm deciding how to patch them up in my setup later.

I would like to easily be able to patch the vp28's in my setup for use as:

- inserts
- mic amps for phantom powered mics
- mic amps for dynamic microphones
- line amps for balanced signal
- line amps for unbalanced signal

I'm new to using 500/51x hardware, as far as I can see the modules only have one input circuit each. If this is the case (please correct me if I'm wrong), I would like to connect each vp28's XLR input from a TRS patchbay. Plugging in one of the above (TRS for mic/balanced line or mono-jack for unbalanced signal from synths etc). What happens if 48V phantom power accidentally is engaged with line or unbalanced line plugged in? Can the vp28 or input hardware possibly recieve damage from this?

I traced the signal back to before the input transformer, seeing it clipped on the scope. If I engaged the line pad, the signal was fine on the outside of the 4.99k resistors, but distorted on the other side. I reflowed all the solder joints in the area and checked for any bridged connections.
The transformer measures similar DC as the other one.
At this point I thought I was really getting close to finding the problem, and my scope died.
This is a really strange problem.