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

[jsteiger]

Michael, either one will work fine. You don't really need to have a socket.

If you have misplaced those, you have also misplaced the 5-pin 90 degree header for the HPF board to main PCB connection. Those 3 items are all together on a small piece of pink foam. With the way we pack/sort the kits, it is impossible that we missed them. They are counted in 50pc lots by 2 different people.

 

[kante1603]

Long-haired carpet? ;D
That's the place a lot of little things go to.


Best,


Udo.

 

[michaelwinston]

I just got to the hpf so I haven't missed the 5 pin header until now...

My guess is they got thrown out or they possibly got mixed up in packing material of something sent off earlier this week...  :-[

Is it possibly for me to order that single piece?  Or add it to a future order?

 

[jsteiger]

Yes no problem just remind me. They are always packing inside the pink bag with the resistors and diodes for the main PCB.

 

[markphilpot]

All,
  I just got in 4 red dot DOA's from Scott so I could test the pre….holy crap - it works perfectly. I'm stunned. Turns out I just can't build the 2520's very well!


Thanks Jeff and Chunger, etc!

  I think the pins I have on the 2520's got bent a bit or something and maybe that's where the connection was shorting…

Anyway, I'm thrilled and excited to start on VP28 #2. I may be hooked.

 

[Unit7]

Jeff,

On one of my VP28 builds, with the HPF disengaged, the -6/-12 switch cuts the output when in the -12 position but not for -6. When the HPF is turned on, everything works fine. I didn't see a schematic for the preamp to aid in chasing down the culprit. I resoldered any suspect connections, but to no avail. Any thoughts?

Thanks!

I have this problem too on one of my recent builds (that I emailed about, but decided to bring it here instead). But only occasionally and the -6/-12 switch is 'scratchy'. I've reflowed the switch, all pads on the HPF and the 5 pin header and replaced op amps (just in case..) but still no change. HPF works fine btw.

I'm about to order some Marconi knobs so I wonder if it's possible add a new -6/-12 switch and a new 5-pin header to that order? If you think that's a good idea.

 

[jsteiger]

Just remind me when you order and I'll include a new switch for you.

 

[michaelwinston]

Jeff, after you mentioned the IC, Socket, and header were packed in a bag with some of the main components I knew it couldn't have gotten thrown out so I searched everywhere only to find the parts sitting on my work table.. (you know, the place I had looked about 10 times...).  So, that being said, I finished up the pre, a 2520 and a 1731 and fired it up.  It sounds great! Now I just have to figure out what I'm going to build next...

 

[kante1603]

Now I just have to figure out what I'm going to build next...

Easy one:As many of them as you can,life is short! ;D


Welcome to the forum and congrats to your build!


Best,


Udo.

 

[drumski]

Hello.

I just finished my first VP28. I did two! Great kits, a pleasure to do. Thank you Jeff!

Now I started to make four gar2520 opamps. But very soon I was made mistake: I pulled out to my table all pins AND ALL the Q1-Q2 matched pair transistors from four bags/kits!  :'(

Now I have all of the eight matched transistors in front of me now. Whether they are matched in pairs, or are they all matched each other?

What I can do now?

 

[kante1603]

Hello.

I just finished my first VP28. I did two! Great kits, a pleasure to do. Thank you Jeff!

Now I started to make four gar2520 opamps. But very soon I was made mistake: I pulled out to my table all pins AND ALL the Q1-Q2 matched pair transistors from four bags/kits!  :'(

Now I have all of the eight matched transistors in front of me now. Whether they are matched in pairs, or are they all matched each other?

What I can do now?

Can you measure hfe?
If so then use the best matching as pairs.


Cheers,


Udo.

 

[drumski]

Can you measure hfe?
If so then use the best matching as pairs.

No. My multimeter hasn't HFE measurement feature.
Situation is now this that I have all calibrated transistors together on the table. Do you know are they all matched each other or only per couple?

 

[weiss]

No. My multimeter hasn't HFE measurement feature.
Situation is now this that I have all calibrated transistors together on the table. Do you know are they all matched each other or only per couple?

They are matched as a couple! that's the reason why you should get a multimeter with hfe measurement.

 

[drumski]

My two first VP28 are soon ready for testing.  I would like to test these prior to use. I have read through this thread, and I do not find clear instructions. Also instructions from classicapi.com do not contain any information about the testing procedure.  :-[

I'm going to buy from classicapi.com "500 Series Jig Extension Bundle", but in addition, I would like to know that when I connected the VP28 to rack with this extension jig so what do I need to measure? What values must be found and where from pins?

It would be great if someone would make a step-by-step instructions how to test the VP28 after the assembly. I would really appreciate if such instructions will be available. The plan is to make a few more VP28 and maybe a couple of classic LC53A (Love Child) equalizers. I'm really interested in learning more, and to make more these fine products from classisapi.com.

 

[kante1603]

@drumski


Hello and welcome,


there's no "complete guide" existing,we all have to read through this thread.
Getting the jig from Jeff is a good idea,it also has a provision for cmrr adjustment.You don't need this for the vp28,but you want it for the lc53.Good to have it then.


First check the voltages on the doa sockets with the doas removed.
If all is good you can insert them and do some basic tests.If something is wrong stop doing anything else but solving problems first!


One of the most often happening thing are the doas themselves,try to have a pair known as working for testing and/or using.Make sure they are seated properly.


Then check if all leds work when switching the corresponding knobs.


Next will be audio tests,e.g. unity gain test in line mode,do the gain and fader switches work,does the hpf work etc.


Hope to have helped and a happy new year,


Udo.

 

[drumski]

First check the voltages on the doa sockets with the doas removed.

Thank you. This is just what I was thinking… but what voltage values from what pins? This is what I need to know…

 

[kante1603]

First check the voltages on the doa sockets with the doas removed.

Thank you. This is just what I was thinking… but what voltage values from what pins? This is what I need to know…

Set your dmm to dc voltage reading.
Black probe to ground ("C"or "common").
Red probe on V+ should give around +16vdc,probe on -V should be -16vdc.
You might have a little drop on both rails due to the protection diodes (roughly -0,7v),this is o.k. then.
Test both doa locations.


Hope that's clearer now.


Will you have working (pre-built) doas then?


Udo.

 

[drumski]

Set your dmm to dc voltage reading.
Black probe to ground ("C"or "common").
Red probe on V+ should give around +16vdc,probe on -V should be -16vdc.
You might have a little drop on both rails due to the protection diodes (roughly -0,7v),this is o.k. then.
Test both doa locations.

Hope that's clearer now.

Will you have working (pre-built) doas then?

Happy new year 2015 and thank you for your advice.  Now I know what I need measuring and from where.
My four gar2520 DOA Full Kit Bundles are now under construction. But first I need to go local electronic shop and buy multimeter with HFE-feature because…  :-[  :'(  (read my first post above).

 

[weiss]

take your time with the 2520's! they are beasts

 

[kante1603]

Member weiss is right.
That's why I asked if you will have a known-as-working pair when you start testing.
Patience is the key!
They are a very dense build.Try to follow the build instructions exactly.
Non-working doas make about 90% of something going wrong here.
If you have any questions regarding them please ask over in the gar2520-thread:
http://groupdiy.com/index.php?topic=33970.0
Gary is a very helpful guy,same as Jeff here.
Have you ever built any doas?Or do you have a pair from another build for testing?
And about the hfe tests and matching,maybe you can borrow a tester from a friend or so.But in case you need a good or better dmm anyway then it's a good feature to have it of course.
Personally I bought a simple transistor tester in kit form for about 25 Euros or so,you'll find many of them on the internet.They are not precision instruments but do a good job for this purpose.
I always check all parts before assembly.A bit time consuming but keeps you away from running into serious trouble.


And now up to happy soldering,keep us posted,


Udo.