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

[kante1603]

I just went back through it to find the PDF. Came up empty.

It opens up in my case,

Udo.

 

[kante1603]

Here it is as a jpeg (hope that´s o.k. for you Jeff?),

Udo.

 

[blackbird]

Here it is as a jpeg (hope that´s o.k. for you Jeff?),

Udo.

Thanks Udo.

Downloaded and stored...

Ive ordered the extention jig from capi, as the design seems cool. Not having to pull out other units to get it in seems great. Worth the extra week or so wait compared to jlm.

Is it worth while me posting photos of the pcb whilst i wait for the jig? If so, what part of the build would you like to see?

Cheers
Dave

 

[blackbird]

Here it is as a jpeg (hope that´s o.k. for you Jeff?),

Udo.

Is there a page which has the corrosponding voltages for each test point?

Cheers
Dave

 

[kante1603]

Is there a page which has the corrosponding voltages for each test point?

Cheers
Dave

I can't remember to have seen such a page,but at least with a  signal on input you can trace it and see where it stops or misbehaves.I'm sure Jeff then can tell you where to look at.

Udo.

 

[kante1603]

Ive ordered the extention jig from capi, as the design seems cool. Not having to pull out other units to get it in seems great. Worth the extra week or so wait compared to jlm.

Yes,I have got one too and assembeled a few days ago,cool stuff and very handy with the cmrr measuring  extras on board.

 

[blackbird]

Ive ordered the extention jig from capi, as the design seems cool. Not having to pull out other units to get it in seems great. Worth the extra week or so wait compared to jlm.

Yes,I have got one too and assembeled a few days ago,cool stuff and very handy with the cmrr measuring  extras on board.

Must do some reading on the measuring part of the jig...

 

[kante1603]

Dave,

the measuring part is just about cmrr,not more.The guide is printed even on the pcb itself,not joking.Pretty cool.But that's a part you can do later.First wait for the jig to get the module attached outside the rack.Way easier then.Once you have it trace through to the test points and see where the sognal stops.
Do you know how to do it?If not we will guide you through it,I'm sure you will make this baby work,it's really worth it (I know what I'm talking about because I have eight!).

Be patient and have a nice weekend,

best regards,

Udo.

 

[blackbird]

Dave,

the measuring part is just about cmrr,not more.The guide is printed even on the pcb itself,not joking.Pretty cool.But that's a part you can do later.First wait for the jig to get the module attached outside the rack.Way easier then.Once you have it trace through to the test points and see where the sognal stops.
Do you know how to do it?If not we will guide you through it,I'm sure you will make this baby work,it's really worth it (I know what I'm talking about because I have eight!).

Be patient and have a nice weekend,

best regards,

Udo.

Hi udo.

I don't even know what cmrr is at this point. Will work it out now!

I know we can get my vp going! I built a hairball blue stripe before, and had a few teething problems, so I have no fear it will be up and running soon. Been here before.. Ha..

I completely agree on the sound of the vp's.. As soon as I get four of them done, my API 3124 will be going. The vp totally destroyed my api's for me. Loved the vp so much more. It changed my view on what the API sound is. It now makes sense to me how API should sound. Should be rich, creamy, cool. The api3124 is not any of that. It is good, but very different. 3124 is bitey, forward, excited kid on Christmas morning.. VP wears a leather jacket, smokes out the corner of his mouth, and peers over the top of a pair of wayfarers..

I also got to use a VP 26 along side the 28. They sat perfectly together. I had a 28 on kick, and 26 on snare that session.. Also tried some hairball Lola's on same session. They were surprising things! Nice..

Waffle over..

Cheers
Dave

 

[kante1603]

Very well put Dave!
I have temoraily set up two monsterstrips in one "to-go-51x-Rack":
VP28---F76(with APP992 & Lundahl)---LA500---My beloved Lovechild(LC53)---Pultec EQP1S5.
A dual D.I. from Bo in the middle slot.
Totally killer!

Best,

Udo

 

[blackbird]

Very well put Dave!
I have temoraily set up two monsterstrips in one "to-go-51x-Rack":
VP28---F76(with APP992 & Lundahl)---LA500---My beloved Lovechild(LC53)---Pultec EQP1S5.
A dual D.I. from Bo in the middle slot.
Totally killer!

Best,

Udo

That looks like a chain I'd enjoy!
I think after getting 2x28, and 2x 26, I'll fill some other slots with the jlm opto comp x2. perhaps it's a budget way of doing what the shadow hills comp does on the opto side.  That's one sweet sound to my ears.. Heard great reviews too.
Love child has interested me too, but I gotta get some Lola's I reckon. I think I want to get 4 Lola's, and get rid of my vintech 473. The 473 has become my 'run outta pres' unit now.. The Lola's were like a cooler version of what the vintechs are to me.

That fills a 10 slot PS right there.. Sweet.

VPs first though!

Cheers
Dave

 

[kante1603]

O.K.,let's stop this here because it is the VP28 help & support thread.
Otherwise Jeff might kill me...... ;D

Tell us when you have results from the testpoints.
Btw.,best to have nothing attached to the module (e.g. a patchbay,other modules,A/D converters etc.).
Just a signal source on input and a dmm or scope or whatever you have to work with.
What you can do while waiting for the extension jig is to check back your dmm manual up to which frequency you can do ac readings.This is a very important point,otherwise you'll get wrong readings.

Best,

Udo.

 

[blackbird]

O.K.,let's stop this here because it is the VP28 help & support thread.
Otherwise Jeff might kill me...... ;D

Tell us when you have results from the testpoints.
Btw.,best to have nothing attached to the module (e.g. a patchbay,other modules,A/D converters etc.).
Just a signal source on input and a dmm or scope or whatever you have to work with.
What you can do while waiting for the extension jig is to check back your dmm manual up to which frequency you can do ac readings.This is a very important point,otherwise you'll get wrong readings.

Best,

Udo.

Ok cool.. Back on track!.

So when checking the points outlined in the pdf, nothing but power it up, and put something like a 1KHZ tone through at 0DbU or so??

Cheers
Dave

 

[guerrilladigital]

Hi everyone. This is my first post on the forum.

I recently attempted to "fix" a vp28 build I did a few months back. When I used it for recording, I noticed it was tracking an audible, but distorted signal. I built a second vp28 simultaneously, and it worked correctly from the get go. Both have homemade gar2520 op amps in them. (Man, were those hard to build!)

When I plugged in my "fixed" vp28 last night, smoke started coming out of the top vents of my lunchbox. I immediately turned off the lunchbox and removed the unit. One of the two op amps smells really awful. As a noob (I've successfully built four vp26 and one vp28), I don't know where to start troubleshooting.

How can I test the resistance of the main PCB to rule that out? Jeff pointed me to this forum, but honestly, there's so much going on here, and I'm not exactly sure what search terms to put in. He said to "check the VP28 support thread at groupdiy.com for the DCR measurements". Does anyone have a link to the page where this info is listed?

If I put the op amps into a "known" working mic pre, will I risk destroying a properly working mic pre?

I'm really not looking forward to building two more gar2520s, but to match the other vp28 so I have a pair, it's gotta be done. If I can determine one to be good, and the other to be fried, at least I'll only have to build one more.

 

[Commander Fluffypants]

I just built my first VP28. No Op Amps built yet. I think I got it right so far, though. This being my first build of this magnitude, is there some testing that I can do to confirm that it was built correctly? Like before I plug it in and have something melt?

Also, thanks so much to Mr. Chunger for that amazing detailed build pictorial!! And thanks to Jeff Steiger and the rest of you guys too!

 

[Commander Fluffypants]

And another question....

The 1/16th hex key works for the bigger knob. Maybe I missed it somewhere, but what do you use to tighten the smaller knob? Not 1/16th hex, that's for sure...

 

[kante1603]

And another question....

The 1/16th hex key works for the bigger knob. Maybe I missed it somewhere, but what do you use to tighten the smaller knob? Not 1/16th hex, that's for sure...

0.050

Udo.

 

[Commander Fluffypants]

Thanks, Udo. I read this thread a bunch of times prior to the build. Rereading today (the whole thing) I discovered the answer had been stated several times in the thread. I also noticed a lot of references to my initial question about testing, but I actually don't understand them. I wanted to know if there are tests I can do BEFORE I power these up (almost done with the second one. Two LED's and knobs to go...!)

I took my time building them. Fourteen hours for the first. Ten for the second. I don't understand you guys who build three in an evening! I was very careful, and I'm as positive as I can be that all solder joints are good and everything is oriented correctly. Do I just put them in the rack and see if something melts, or can I test without power first? And then how? I'm going to be searching for that PDF soon...

 

[kante1603]

Hello,

without powering up there is not too much you can do.
Just look over the solder joints for cold or shorted ones,especially at the grayhill switches because of the quite small pin pitch.Best done with a magnifying light,view from different angles.

The led driver must be inserted the right way,it will die immediately if reversed.

After that you might  measure the in- and output dcr with your dmm set to ohms,you should get readings there,no short or open condition.Same on psu gnd to positive and negative supply rail,under no circumstance should there be a zero (or short) reading.

The most tricky part is the DOAs when you build them for yourself.Especially the output transistors (the two big black ones) are either swapped or mounted reversed,nearly 90% of non-working DOAs have this issue.

After that it's time to power up,best with an extender cable (Jeff has a nice one in his shop).It's easier to reach the trim pot for cmrr setting anyway.

Hope to have helped,

Udo.

 

[Commander Fluffypants]

Thanks again Udo!

I did see some tips in section 12 of the Vpx build guide. I don't understand what a lot of that means, but I'm starting to figure it out. Is it safe to assume that it applies to the VP28 as well? Anything additional or different for the VP28?

Thank you so much for being so generous with your time and knowledge. Your patience with the initiated is awesome. I'm going to check out that extender cable now...