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

[OOF!]

thanks for the reply Jeff,
yes i've switched rack slots and the problem followed the unit.  switched op amps and the problem stayed with the unit.  i will use it tonight and if it still distorts i'll try bypassing the pot as you say.
btw- love the pre and will be ordering more and perhaps some of your new 28s too.
thanks,
David

 

[Seditionary]

hey!  re-checked the color codes on every resistor.  i tested every single resistor before putting them into the preamp.  i tested them with the dmm and then separated them on paper.  the only mistake i could have made… is that i followed the numbers he had (and the ones jeff listed) and matched them to the resistor numbers… i.e. R1, R2, etc.  did those change at all from the original BOM? 

i'm sure that isn't the problem… but just a trouble shooting thought. 

thanks!

 

[Seditionary]

also -- is there a way someone could post a photo of the empty LED part on the board going to the output attenuator?  i just soldered that jumper cable between them (which chunger didn't do in his build).  do you think that this could be the problem?

 

[jsteiger]

....the only mistake i could have made… is that i followed the numbers he had (and the ones jeff listed) and matched them to the resistor numbers… i.e. R1, R2, etc.  did those change at all from the original BOM?...

I just verified the new Rev B PCB that 'Chung built and the R's are indeed correct. I will have to look at his pic of the R's on the sheet but I will assume if they made it to the correct position on the board, they are correct in his pic.

Below is a copy of the email text I have been sending out with the new Rev B boards.
Since we are now shipping the Rev B version of these boards, the support docs have change. It is crucially imperative that the first step you make is to read the "1_VP25-26 Rev B Addendum.pdf" file that is in the attached zip file. Read it completely start to finish before doing anything else. This way, things will go very smooth!

Did you check out the Addendum PDF before you started? Below is tip #1 from the Addendum.
1. Use only the proper Rev B BOM when stuffing your boards. Following the BOM shown in the
Assembly Guide or an older Rev A BOM will cause many issues.

 

[jsteiger]

also -- is there a way someone could post a photo of the empty LED part on the board going to the output attenuator?  i just soldered that jumper cable between them (which chunger didn't do in his build).  do you think that this could be the problem?

This will most likely cause other issues. The drain wire jumper will go from the typically unused lug on the phantom toggle to the LED hole that the little arrow points to. Post a pic of yours and I will verify if it's correct.

 

[Seditionary]

"I just verified the new Rev B PCB that 'Chung built and the R's are indeed correct. I will have to look at his pic of the R's on the sheet but I will assume if they made it to the correct position on the board, they are correct in his pic."

>> Cool, thanks man!  I mostly followed his markings on the paper and cross-referenced many of them with the rev b bom as well.  Will double check to see if the components on my board match up.

"Below is a copy of the email text I have been sending out with the new Rev B boards.
'Since we are now shipping the Rev B version of these boards, the support docs have change. It is crucially imperative that the first step you make is to read the "1_VP25-26 Rev B Addendum.pdf" file that is in the attached zip file. Read it completely start to finish before doing anything else. This way, things will go very smooth!'"

>> The first thing i did was read the addendum (lots of times)  

 

[Seditionary]

photo 1

 

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photo 2

 

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photo 3

 

[Seditionary]

photo 4

 

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photo 5

 

[Seditionary]

the only thing that i notice that is different from chunger's… is that i have the panasonic cap in the opposite way.  there is no polarity on that cap though, right?  also, took a photo of how i soldered the green cable to the other lug of the 48 volt switch, etc.

thanks!

 

[jsteiger]

Well, the drain wire for the 48V switch is correct. Your other components appear to be correct as well.

The WIMA cap is not polarized so no worry there.

I think the easiest thing to check next is the output transformer. This is posted somewhere above but to simplify, you need to desolder all the leads for the 2623-1 and make sure they are in mid air and not touching each other. Using your DMM set to measure resistance, measure the DCR from red to orange, green to blue and then brown to black. Those will all be around 30 ohms or under but not less than 15 ohms.

Next, make sure that no windings are shorted. Start at one end of the colors as they come out from the bobbin. Check for resistance between that lead and all the others. Then go to the next color, rinse and repeat. Here you are looking for a direct short or resistance of say 1 ohm or less.

I just went thru a similar situation via email with a guy. His problem was a cold solder joint on one of the components that the signal directly passes thru (the 1K R, 470uF Cap). It doesn't hurt to add a tiny bit of solder while reheating the pads. I see none coming up onto the top which is not a problem but there is typically a few pads that have the solder flow thru when all is heated good and solder is applied well.

FWIW, on future builds, the circle in the silk for the vertical resistors indicates where the body should go. When done like this, there is enough room as the bodies alternate position when the R's are directly in a row.

 

[Seditionary]

thanks for the quick response, jeff.  will desolder and unscrew the output transformer and test for resistance on the color cables as you've described. 

if it reads correctly, will re-solder all the connections on the board and then will return with results.  thanks sir.

ps -- i tried placing the vertical resistors in their markings where the gain stage is... i think they might have just moved a tiny bit when soldering &c.  moved them a tiny bit to ensure that none of their leads were touching

 

[mulletchuck]

none of your thru-hole stuff has solder running all the way from one side of the board to the other.

 

[Seditionary]

cool -- i'll try and get more solder in there

 

[jsteiger]

none of your thru-hole stuff has solder running all the way from one side of the board to the other.

Well, as long as you have a good solid joint on the bottom, it is not really necessary to solder from the top. I use to recommend that before I changed the ground plane location. Some inexperienced guys had trouble soldering the pads that connected to the ground plane. It is much easier on the new Rev B boards. It will not hurt anything though.

I would still check the trafo first.

 

[Seditionary]

Unsoldering the cables on the transformer as we speak. When only putting a bit of heat on one of the wires, I noticed something on the board flaking off -- when inspecting closer, noticed it was one of the circular gold traces flaking off!  I remember a similar thing happening/flaking off when soldering in another component. Without the gold trace in the hole on the bottom that easily flaked off, would it still be making a connection? Should I solder from the top too just in case?

 

[jsteiger]

Can you post a close pic of this? It is pretty rare to loose a pad on these boards. The majority of the traces are on the bottom of the PCB so you would be best to gently scrape a little solder mask off the trace immediately adjacent to the hole and solder there. If the complete pad is gone from the bottom and the trace is on the bottom, chances are, the pad on the top will not be connected to the trace.

 

[Seditionary]

Red-orange about 16.8. Green to Blue about 33. Brown to black about 31.