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

[resilient]

Thank you for the reply, Jeff.

R1, C1, R5-R8 all look correct to me.  Some of them were soldered from the front and then again from the back (I used the wrong tip on the front during assembly, went back with a "chisel" tip to reflow the solder joints from the back after assembly), so they look not so great on top. 

I also went through RG1-RG11 and all of those are correct, too.  Which leaves me with the gain knob.  Is it possible to put the gain switch in backwards somehow? 

Here are pics of the mentioned sections:

https://www.dropbox.com/s/njob03rt28953hp/20190401_115508.jpg?dl=0

https://www.dropbox.com/s/wa2h9nj5r21vkym/20190401_115502.jpg?dl=0

https://www.dropbox.com/s/inxz6r1wfud2a9i/20190401_115458.jpg?dl=0

https://www.dropbox.com/s/az898f7ppdld69f/20190401_115454.jpg?dl=0

I'm at a bit of a loss. 

Brandon

 

[jsteiger]

Thank you for the reply, Jeff.

R1, C1, R5-R8 all look correct to me.  Some of them were soldered from the front and then again from the back (I used the wrong tip on the front during assembly, went back with a "chisel" tip to reflow the solder joints from the back after assembly), so they look not so great on top. 

I also went through RG1-RG11 and all of those are correct, too.  Which leaves me with the gain knob.  Is it possible to put the gain switch in backwards somehow? 

Here are pics of the mentioned sections:

https://www.dropbox.com/s/njob03rt28953hp/20190401_115508.jpg?dl=0

https://www.dropbox.com/s/wa2h9nj5r21vkym/20190401_115502.jpg?dl=0

https://www.dropbox.com/s/inxz6r1wfud2a9i/20190401_115458.jpg?dl=0

https://www.dropbox.com/s/az898f7ppdld69f/20190401_115454.jpg?dl=0

I'm at a bit of a loss. 

Brandon

I have no idea how the bottom of the board looks but there are for sure some questionable solder joints on the top. All of those giant solder blobs must be cleaned up. I see at least 2 that look like they could be shorting to the top ground plane. Also, I would suggest cleaning up the residual flux. It can sometimes be conductive.

 

[resilient]

Thanks, Jeff.  I'll go through them, clean them up, and try again. 

Brandon

 

[resilient]

I have gone through and cleaned up all of the solder joints in the areas you pointed out are before TP2 and I am still getting 109mv at TP2.  I am at a bit of a loss here.  Any other ideas on things I can try?

https://www.dropbox.com/s/rfbauorn1grlqsw/20190407_151525.jpg?dl=0

https://www.dropbox.com/s/p12vewssq5hpqpj/20190407_151510.jpg?dl=0

Thank you for your assistance, Jeff.

Brandon

 

[jsteiger]

I have gone through and cleaned up all of the solder joints in the areas you pointed out are before TP2 and I am still getting 109mv at TP2.  I am at a bit of a loss here.  Any other ideas on things I can try?

https://www.dropbox.com/s/rfbauorn1grlqsw/20190407_151525.jpg?dl=0

https://www.dropbox.com/s/p12vewssq5hpqpj/20190407_151510.jpg?dl=0

Thank you for your assistance, Jeff.

Brandon

I can see in the pic that the R next to C5 is 200Ω and it should be 20k. That is your problem but also you need to find the missing 20k which I am guessing is in the spot of a 200Ω somewhere...

 

[resilient]

#facepalm  Thank you so much for taking a closer look.  I'll go back through everything again and see what I can find.

Brandon

 

[jsteiger]

#facepalm  Thank you so much for taking a closer look.  I'll go back through everything again and see what I can find.

Brandon

I did give you those part #'s to check previously. 

 

[resilient]

I did give you those part #'s to check previously. 

:-[ :-[ :-[ Indeed you did.  I really did check them, but clearly I didn't check that one close enough.  Fortunately I had transposed it with R1, so it was super quick finding where the 20k went.  I switched the resistors, put the transformer leads back in, and all is well!  Thank you so much for your help and for a great kit, Jeff.  If I still lived in Nashville, I'd buy you a beverage of your choice. 

Brandon

 

[Leon]

The question probably has been asked before. Is the double-stick foam tap required for installing the input transformer? I don't see it in the kits. What is its purpose? I guess it helps holding the transform in place.

I have to say Chunger's tutorials are super helpful, without which I would never have the gut to take on the project. Thanks Chunger!

Here is what my progress so far after one evening's work (2-3 hours):

 

[jsteiger]

The question probably has been asked before. Is the double-stick foam tap required for installing the input transformer? I don't see it in the kits. What is its purpose? I guess it helps holding the transform in place....

The double sided foam tape is not nor has it ever been included. Its only a suggestion to elevate the bottom of the mu-metal can to keep if from shorting to the PCB. There is some more info here. http://capi-gear.com/catalog/Build_VP26-S_Rev_C.php#Sec5

 

[Leon]

Wow! Appreciate the fast response. I see the purpose now, and I am glad I asked. I will look at the VP26's build guild to assist finishing my 1st kit.

 

[Leon]

One last question, is C3 33uF 60v or 25v? In the BOM it says 25v. The only 33uF capacity in my kit is 60v. Since 60v is greater than 25v so I think it should work. Not the other way round, right?

Thanks again,
Leon

 

[Fuzz Face]

One last question, is C3 33uF 60v or 25v? In the BOM it says 25v. The only 33uF capacity in my kit is 60v. Since 60v is greater than 25v so I think it should work. Not the other way round, right?

Thanks again,
Leon

No problem using a higher rated cap

 

[jsteiger]

One last question, is C3 33uF 60v or 25v? In the BOM it says 25v. The only 33uF capacity in my kit is 60v. Since 60v is greater than 25v so I think it should work. Not the other way round, right?

That is also covered in the VP25/VP26 Pictorial Build Guides. The old tan 25V parts were discontinued a few years ago by BC/Vishay.

 

[Leon]

Thanks again for the help. I just finished the build yesterday evening and I gave it a test this morning. It worked and sounded amazing! This is almost too good to be true . The only mistake I made is applying one sticker to the wrong end of the knob. I had to peel it off and ended up with a not so nice looking sticker for the bigger knob.

Now it is time to build the second one.

 

[Leon]

Just finished my second kit, also worked on first try. This time I made another silly small mistake near the end, I put the red button on the phase flip rather than phantom power. Is there an easy way to correct this? I deliberately used the grey buttons for HOF because I think it looks better that way.

Here is a picture of the newly built pair (next to a pair of BT50s someone else just built for me):

 

[Potato Cakes]

The caps can be removed unless they are super glued in place. You can use a tiny flat head screw driver to gently pry it off the switch. That's how I have done it in the past.

Thanks!

Paul

 

[Leon]

Thanks Paul! Looks like I am not the only one making this mistake . I tried your tips, but I am afraid that I was going to break it so I stopped. I installed the caps with the two openings slots facing other buttons which makes them hard to pry off. I guess I have to live with it now, until I can order some replacements.

Best,
Leon

 

[Potato Cakes]

You would probably have to remove faceplate to do this. But if you don't have OCD then it won't matter.

Thanks!

Paul

 

[recarcar]

Hello All,

I have been combing through the thread to see if anyone had similar issues but I can't seem to find anything.  My VP28 build does not seem to be passing any signal. The green LED does not light up and there seems to be nothing passing through. The other LEDs are working and everything seems to look fine but not sure where to start. Does anyone have any suggestions on where to look first? Thanks!