[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.

 

[all-over-again]

Thanks for the reply's, the problem is, i didn't put the op amps in from the beginning before i tested as to why no green light , that is the main reason why it looks messy, as i franticly resoldered, only resistors though, as im sure about diodes and i know transistors don't let heat, not to sure about caps.
i got some flux, so i will clean up the board before i continue,
btw that photo wasn't the photo i was meant to send as i do clean up the board with ipa, was the before i cleaned the board photo....

After i solder and install op amps i will know my luck,
thanks this forum for being here, if it wasn't the board would look like glue and solder, after the enormous amounts of using the soldering iron as a magic wand ....

I feel lucky today

It took around 6 hours, considering the amount of time using the soldering iron and testing with resistor calculator, i didn't get good results with the multimeter after everything is soldered plus ever time no green light i sat down deflated , im like a hobbyist as I've only soldered a few things in the last two years, but i have made audio kit before which work fine first attempt, this would of been the same but i lacked a little knowledge...

i will add the op amps a little later, to see if my soldering improved...

I also changed the photo, looks better than the unclean version, had lots of hair on it, as i ran out of cotton buds and was using something else, i don't see any errors, but a few scratches ... also leds are fine, just the angle of photo
Thanks you

 

[Rob Flinn]

Thanks for the reply's, the problem is, i didn't put the op amps in from the beginning before i tested as to why no green light , that is the main reason why it looks messy, as i franticly resoldered, only resistors though, as im sure about diodes and i know transistors don't let heat, not to sure about caps.
i got some flux, so i will clean up the board before i continue,
btw that photo wasn't the photo i was meant to send as i do clean up the board with ipa, was the before i cleaned the board photo....

After i solder and install op amps i will know my luck,
thanks this forum for being here, if it wasn't the board would look like glue and solder, after the enormous amounts of using the soldering iron as a magic wand ....

I feel lucky today

It took around 6 hours, considering the amount of time using the soldering iron and testing with resistor calculator, i didn't get good results with the multimeter after everything is soldered plus ever time no green light i sat down deflated , im like a hobbyist as I've only soldered a few things in the last two years, but i have made audio kit before which work fine first attempt, this would of been the same but i lacked a little knowledge...

i will add the op amps a little later, to see if my soldering improved...

I also changed the photo, looks better than the unclean version, had lots of hair on it, as i ran out of cotton buds and was using something else, i don't see any errors, but a few scratches ... also leds are fine, just the angle of photo
Thanks you

It's a while since I built one of these but I don't think you get a green led come on. That is a signal present light but I think that will only come on with a signal present AND the op amps installed. You should however get the other leds come on when you depress the relative switches. If you have a meter you could check to see that you have the right volts come up on the power pins for the 2 op amps. Then after that really you need to plug the op amps in to test any further.

 

[all-over-again]

It's a while since I built one of these but I don't think you get a green led come on. That is a signal present light but I think that will only come on with a signal present AND the op amps installed. You should however get the other leds come on when you depress the relative switches. If you have a meter you could check to see that you have the right volts come up on the power pins for the 2 op amps. Then after that really you need to plug the op amps in to test any further.

i made a big mistake again,,.. took me one hour to fix it , i put the bc 161 in the place of the bc141 , lucky i only soldered one... took me so long as i didn't want to heat up the pins for to long , then to get the solder out of the holes, what a nightmare, hopefully it still works,
also put the legs the wrong way round, it was the last thing and i was excited lol, when i should of been paying attention ....

i have a multimeter but I'm not adept with it, i can measure some things, putting the meter on a live current seems worrying, there is nothing wrong on the board as i checked it many many times, hence to why i posted here, i added a picture of the op amp, just finished it and it took over two hours, mainly because of the transistor mix up...

i didn't notice the other lights coming on the pre amp when i was trying to power it up, i hope that's not a thing..


(i finished but its dark now, last transistor were hard to place, testing and cleaning tomorrow, need better natural light)

 

[Rob Flinn]

i made a big mistake again,,.. took me one hour to fix it , i put the bc 161 in the place of the bc141 , lucky i only soldered one... took me so long as i didn't want to heat up the pins for to long , then to get the solder out of the holes, what a nightmare, hopefully it still works,
also put the legs the wrong way round, it was the last thing and i was excited lol, when i should of been paying attention ....

i have a multimeter but I'm not adept with it, i can measure some things, putting the meter on a live current seems worrying, there is nothing wrong on the board as i checked it many many times, hence to why i posted here, i added a picture of the op amp, just finished it and it took over two hours, mainly because of the transistor mix up...

i didn't notice the other lights coming on the pre amp when i was trying to power it up, i hope that's not a thing..

I would suggest that you work out how to use the multimeter. When you say there is nothing wrong with the board because you have checked it many times is not a good check. Visual inspections are not safe for verifying electrical connections, you need to verify through the connections with a meter on continuity. Wehn I say through the connections I mean the meter probes on components so you are actually testing through the connection.

You normally take the voltage readings witrh respect to 0v/ground. So you put the black probe on 0v/ground & probe around the points you want to take a reading with the red probe. On the VP28 there is nothing to get a shock much to get a shock from so there is no need to worry. The only very slight possibly of a shcok is fromthe 48v for Phantom power but unless you have really wet or sweaty hands the most you will get is a very slight tingle & there is not much 48v on the board anyway. WHat I would do is see if you get volts on the respective power pins where you are plugging the op amps in. You could also see if you get any volts on the legs of the led's when you depress their respective switches.

 

[jsteiger]

Testing a fresh module build with 2 fresh opamp builds is a giant no no. If things aren't working its very hard to know where the problem(s) are at.