[BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread

[3nity]

looks like a lots of cold solder joints...
At least from my pov.

Talking about 500 rack options im thinking to get a Chameleon Labs CPS-500.
it holds 1 x 500 unit and price is 169$

Thanks.

 

[mjenki14]

mulletchuck, i accidentally got some solder on the finger, got off as much of as i could.  I checked its continuity when hooked up to the power supply and seemed to be fine.

I tried both op amps I have in the board with no difference.

3nity, I have re soldered multiply times, but will again.  I will try removing all I can to try and start from scratch on the solders. 

Still working on getting a signal probe and understanding schematics better.  I can follow the schematic to the layout, but I'm having trouble understanding the T and H pad calculations.

Again, thanks for all the help.  I'm sure i've made some mistake I keep overlooking.

Michael

 

[jsteiger]

...Still working on getting a signal probe and understanding schematics better.  I can follow the schematic to the layout, but I'm having trouble understanding the T and H pad calculations...

You can use a DMM for this just measuring ACV.

I think I will add a resister kit to the store that is prefect for a line in on one of my preamps (or any other preamp). That will take all the guess work out of things for guys with the H-pad config. It will just be 5 resistors but the like pairs are .1% precision 15ppm.

 

[bigevil]

and I was so proud of myself for getting through this build with no major hiccups (took my time and did it right [i thought]).... unfortunately after returning from holiday I threw it into a lunchbox to test it and it actually causes the whole lunchbox to not function right (the power seems to drop and all of my other modules no longer light up fully, the API power indicator on the lunchbox glows weakly but not at full). When I remove the VP25 everything goes back to normal. Also, it seemed like I smelled that electronic component burning smell but for the life of me I can't locate any damaged components.

Any help is greatly appreciated, not sure what I must have missed here....

attached are pics(as great as I could) that cover the most recent build. if anything sticks out, by all means, please!

 

[jsteiger]

bigevil, is the opamp a known good one that has been tested in another preamp? I would try removing the DOA and then inserting the module to see if you still get the same issues with the rack. My first guess is something opamp related. If the rack seems fine then insert a known good working opamp from another build in this preamp to test out.

 

[bigevil]

Jeff.
good idea. Swapped it out with a known good one and it doesn't have the power issues anymore and infact seems to work great. The audio is lower compared to the other pre's in the rack but when I get the chance I'll A/B it with my other VP25 and see if its consistent with it.  I'll head over to the GAR2520 to troubleshoot that.

Thanks much, keep you posted!

 

[chunger]

World's best newbie preamp kit just got easier!  I've started a build to hopefully help jsteiger put together a revised assembly manual as complete as the original.

Let's see what's in the box?

And here we go.  Pretty new Rev. B PCB:

And contents (note: front faceplate missing from photo)

I decided to follow the general format of the VP26 assembly manual and start with the resistors. . .

well, actually, I decided to just go ahead and sort the components according to the new REV. B BOM.

Careful with the little capacitors.  The markings are small.

Resitors placed.

The recommended assembly method now is to bend the leads and solder from the back side. . . the ground plane on the new PCB has shifted to the other side.

Next, I hit the 2 diodes in the same manner making sure to place them in the correct polarity.

Next, I do the small ceramic capacitors

The WIMA film capacitor. . .

And then the axial capacitors.  Polarity is important on these.  Please double check and make sure they are facing the right way.  Solid line indicates "-" side of the capacitor.

Then the radial capacitors. . . again, these have polarity.  Make sure you insert the longer of the legs into the "+" marked hole.

Next, sort the hardware. . .

Locate the Milmax sockets and place them from the back side of the PCB.

And solder. ..

 

[chunger]

Next, install the screws and standoffs on the back side of the L-bracket competely.

And the front side of the L-bracket, we install the screws half way so we can slide the PCB and attached switches/pots over the standoff.

Next, we attach the gain pot, but remember NOT to solder yet!  (Note: I am building the standard configuration here with a Bourns pot. . . there is an option for a stepped grayhill switch on the PCB).

And, place the T-pad. . . again, DO NOT solder yet.  You may need to bend some of the legs to straighten them.

Next, assemble the main PCB to the L-bracket with the pot and T-pad loosely placed.

Align the pots to center on the L-bracket holes to the best of your ability.

Install the nuts to lock the pots into final position. . .

And solder everything you can reach from the front side.

Next, disassemble the PCB and solder the remaining lugs from the back side.

 

[chunger]

Next, place the 3 push-button switches pressing firmly to the PCB surface

I solder only 1 center lug on each switch.

Then, I re-assemble the PCB to the L-bracket and the front panel to check for optimal alignment of the 3 push-button switches.  I slightly tweak the angle to optimize if necessary.  Keep in mind there is still a little bit of adjustment possible on the front panel positioning, so I try to get this as close as possible, but still have some room to maneuver if necessary.

And, solder in the rest of the lugs.  I jump around a lot to keep from overheating the switches during this operation.

 

[Ben]

Hi guys!

just completed a VP26 build. Instructions were very clear and easy to follow.
the good news is the pre amp is passing sound, the bad news is that it doesn't sound like it should.

these are some problems I've encountered:

-The preamp passes sound, but I have to completely crank it to get some kind of level and the sound is rather thin
-output knob does nothing
-Mute and pad both work, phase changes my sound (and I'm only recording with 1 mic so this shouldn't happen right?)
-phantom power works

any idea's what might be wrong?

thanks!

 

[jsteiger]

Ben

Unsolder all the leads for the output transformer and measure the DCR between the following:

Red to orange
Brown to black
Green to blue

The resistance measurements should all be between 16 ohms and 31 ohms, or so.

Report back with your findings.

Cheers, Jeff

 

[canidoit]

Chunger, you should start a new thread on your build. Your build threads are really inspiring and also educational and I think it would be more useful as a thread on its own like your 51x rack thread.

 

[mjenki14]

For any interested, it turns out my output transformer was bad.  When replaced with a different one, everything seems to work.  Hopefully all will go well with the next unit.  I appreciate all the help!

Michael

 

[chunger]

OK. . . time to finish out the VP26 build. . . since the ground plane was moved to the front side, it's a little bit more critical in the rev. B to use some sort of insulating tape on the input transformer. 

Here, I purchased some double sided tape.

Note the position of pin 1 which is marked with a dot on the transformer's label sticker and clearly labeled on the PCB.

I cut a piece of double sided mounting tape

And apply to the bottom of the transformer

Next, place the transformer making sure to align pin 1.

And solder from the back side.

 

[chunger]

output transformer next. . . find screws and washers and put in this configuration.

Next, insert into output transformer.

Put 2 more washers on under the transformer.

Position carefully on the PCB and place 2 lock washers.

Then, the nuts go on. . . I found it easier to tighten from the screw side while holding the nuts in place.

Carefully trim the output transformer wires to the correct length. . . it's easier to leave them longer than necessary and trim several times to get to the correct length than to trim them all at once and too short. . . if that happens, hilarity would ensue.

Once length is determined, strip back about 1/8" and tin the tips before inserting into the color-marked hole and soldering from the back side.

I used a couple short pieces of shrink tubing to clean things up a bit.

Repeat for all the other output transformer leads.  Lengths will vary.

Next, grab the excess red and orange leads from the output transformer.

Strip back about 1/8" on the ends and tin them.

. . . and solder these leads into the holes labeled "1" and "2".

now, re-mount the PCB to the L-bracket hopefully for the final time.

Use lock nuts this time to secure the PCB on the standoffs.

. . .and snug them down.

voila!

 

[chunger]

to protect the finish on the front panel, I used console tape on the sockets to tighten the nuts onto the knobs.

reference the top edge of the L-bracket and front panel to make things straight when tightening the nuts.

Next, locate the phantom power switch.

Thread one of the included nuts onto the switch. . .

Then, add the lock washer.

Position the switch onto the front panel.

And secure the remaining nut from the front side being careful not to mar the front panel

Next, cut the red and yellow leads to length and solder to the phantom power switch.

The preamp is now complete as far as the electronics go.

Next attach the knobs with the allen key set screws.

Locate the push-button caps

And press them on. . . a little force might be required here.  I use the rubber, padded end of my wire strippers.

Next, apply the colored decals to finish up the cosmetics.

And the VP26 rev. B kit is complete.

Follow the test procedures outlined in the original build manual, and install the opamp of your choice.  Here I'm using one of Gary's fine GAR2520's.  A great fit for this pre and righteously priced.

And, fully assembled.

Humans win!

 

[jsteiger]

Absolutely beautiful work as usual 'Chung! Your attention to detail is impeccable!!

 

[minor_glitch]

Quick question for Jeff.  I have the original green board version of the VP26 and I was planning to get a second so I could have a relatively matched stereo pair.  Is the rev b too different to make a stereo pair with the original version?

 

[jsteiger]

Quick question for Jeff.  I have the original green board version of the VP26 and I was planning to get a second so I could have a relatively matched stereo pair.  Is the rev b too different to make a stereo pair with the original version?

Good question. No worries, the audio signal path is identical. You will indeed end up with a stereo pair. That holds true for all the updated Rev's of my mic preamp boards.

Cheers, Jeff

 

[minor_glitch]

Excellent, thanks!