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

[jsteiger]

Thanks for the reply

Readings:
1-3 62.0
2-4 68.9
5-6 1.567
1 to can OL
2 to can OL
3 to can OL
4 to can OL
5 to can OL
6 to can OL
7 to can 0.6
8 to can OL

Jeff says this fully checks out. Transformer orientation was correct. I can’t explain it other than to say it didn’t work in two different preamps but the one I swapped from a working preamp did. I’m an engineer and I don’t believe in coincidences, and for me to solder it bad twice I wouldn't have thought likely, but I can't exclude it.

Jeff was nice enough to get a replacement off to me. I'll send him this one and see how he makes out with it.

Wait a second. I guess I read your email too fast. The secondary winding and DCR should be between pins 5 and 8 not 5 and 6. Pin 6 is the internal screen and gets grounded. If pin 5 has continuity to pin 6 then that is indeed the issue.

 

[mkerlin]

Wait a second. I guess I read your email too fast. The secondary winding and DCR should be between pins 5 and 8 not 5 and 6. Pin 6 is the internal screen and gets grounded. If pin 5 has continuity to pin 6 then that is indeed the issue.

Sorry Jeff, my typo. The 6 should have been 8. 5-8 was 1.567. Pin 6 to can is OL.

 

[Volume11]

Does anyone know the wire color coordination for the transformers on the most recent kits? I have pink, purple, and grey, instead of blue, brown, and green.

Thanks

 

[jsteiger]

Does anyone know the wire color coordination for the transformers on the most recent kits? I have pink, purple, and grey, instead of blue, brown, and green.

Thanks

The links you'll need are in the first few lines of info here https://capi-gear.com/catalog/product_info.php?cPath=22_117_55_169&products_id=478

 

[Volume11]

The links you'll need are in the first few lines of info here https://capi-gear.com/catalog/product_info.php?cPath=22_117_55_169&products_id=478

Thanks Jeff, I guess I looked everywhere but the most obvious place, my bad.

 

[woofy]

I built two vp28s, no issues for a week or so, however now the yellow polarity LED is getting stuck always lit. Sometimes when i power down for a while and back on, the issue resolves until the unit is heated up a little bit. Any advice appreciated

 

[jsteiger]

I built two vp28s, no issues for a week or so, however now the yellow polarity LED is getting stuck always lit. Sometimes when i power down for a while and back on, the issue resolves until the unit is heated up a little bit. Any advice appreciated

Try exercising the switch a bunch. Might be a faulty pushbutton switch or needs some deoxit. Also make sure the LED's leads do not extend past the solder pads.

 

[ctrombley]

Hi, I just finished 2 VP28 builds. I found some issues validating voltages at the test points:

Module 1: TP1: .221, TP2: 1.388, TP3: 2.469, TP4: .611, TP5: .610, TP6: .610, TP7: 1.284, TP8: 1.896

Module 1: TP1: .221, TP2: 1.388, TP3: 2.469, TP4: LOW, TP5: LOW, TP6: LOW

These measurements were taken with the gain at unity. As you can see, I'm measuring double the expected voltages at the test points for both modules.
For module 2, voltages drop out at TP4.

 

[jsteiger]

Hi, I just finished 2 VP28 builds. I found some issues validating voltages at the test points:

Module 1: TP1: .221, TP2: 1.388, TP3: 2.469, TP4: .611, TP5: .610, TP6: .610, TP7: 1.284, TP8: 1.896

Module 1: TP1: .221, TP2: 1.388, TP3: 2.469, TP4: LOW, TP5: LOW, TP6: LOW

These measurements were taken with the gain at unity. As you can see, I'm measuring double the expected voltages at the test points for both modules.
For module 2, voltages drop out at TP4.

TP4 is immediately post the Grayhill fader switch and resistor network. TP3 is immediately before that business.

 

[all-over-again]

Hello

I finished soldering the vp 28, before i posted this, i went over everything again, but i have no power i rechecked everything all over again with the resistor calculator, and now I'm stuck, i did notice a resistor pull up as i was soldering but i put it back in place and soldered it again, can not remember where it was, really thinking that was where i am going wrong maybe..
some help would be appreciated as i am guessing i should at least get a green light, i have a xt 500 xtender which i tested to see if it works with another preamp....
am i just bad at soldering or something?
or have bad luck today...

still a lot of fluff on the board from me trying to clean it

 

[thelivingroom]

Hello

I finished soldering the vp 28, before i posted this, i went over everything again, but i have no power i rechecked everything all over again with the resistor calculator, and now I'm stuck, i did notice a resistor pull up as i was soldering but i put it back in place and soldered it again, can not remember where it was, really thinking that was where i am going wrong maybe..
some help would be appreciated as i am guessing i should at least get a green light, i have a xt 500 xtender which i tested to see if it works with another preamp....
am i just bad at soldering or something?
or have bad luck today...

still a lot of fluff on the board from me trying to clean it

I could be wrong, but the green light is for signal presence and typically wouldn’t be lit unless the opamps are installed and there’s signal going to the unit. Did you check the power pins with a meter set to measure DC, with black probe to power 0v and red probe to the V+ and V- of the opamp pins? If you press the switches, do their corresponding LED’s light up?

Also, make sure you remove every solder remnant from the board. You never know where those may end up down the line. You can use your fingernail to pop the stubborn ones off. When I zoomed in I could see some between pins on both of the Grayhill switches. I’m not trying to be rude, but the soldering isn’t the best. I’d recommend viewing some tutorials on proper soldering techniques, and the OCD in me would spend more time with cleaner/more square component placement in some spots, specifically the LED’s.

Is this your first kit build? If so, it’s one of the more difficult of the CAPI modules for a beginner. The VP25 and VP26 are much easier; I can build a pair of those and the kit opamps in less than 8 hours, from unbox to testing.

 

[Rob Flinn]

There are lots of blobs of solder between some of the rotary switch pins & there are 2 solder connections that are in the centre of the board where the solder doesn't appear to have taken to the legs of the component.