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

[kante1603]

Well, FOUR, but I'm taking my time. Wanna get it right. Funny, the 2520 didn't really seem that hard. I just went slowly and carefully.

Great to hear.Not too hard to do,but patience is the key,same as working clean and carefully,having steady hands and some soldering experience is helpful.Personally I don't understand this competition about who is the fastest.Seems somehow at least a few guys here in the forum are those who do them wrong after "quick assembly".
Have done around 60 of this type,no issues except one that had a cold joint,was an easy fix then.
Can't remember how long it took,quite a while I think.Doing more than one at a time speeds it up of course.

Best regards and happy soldering,

Udo.

 

[blackbird]

Hey udo..

So you feel the problem is more likely to be the power supply? Does the VP28 just directly route the 48 v from it's own power supply? I'll check the phantom power voltage on the heritage audio pre and see what's going on there. Silly I didn't check it before I left for the night. Will check tomorrow.

The power supply and rack is a 8 slot Radial workhorse.
I have the extender card, so can do all these tests asap.

Thanks for your help guys!

Cheers
Dave

Hi Dave,

I took a quick look at the Workhorse.So it has an external psu,right?
Don't know it o far,maybe it has a trim pot for phantom?
Seems like it is an smps....I don't trust them anyway due to bad experiences,I always build linear types.

When checking phantom on other preamps remember that without anything plugged to the input the measurement might be a tad higher because of the higher dmm input impedance.It should go down with a load,e.g. a condenser microphone.

Could happen that you must contact Radial Engineering.

Best,

Udo.

Hi udo.

I did check just one other pre before I went home, but not one in the 500 rack. It was my API 4312, and that read exactly 48v with nothing more than a mic cable and the multimeter. The same way I tested the vp28..

Hmmm. I think ya could be quite right about the rack being out on the phantom, as I have a feeling the phantom turn on with the heritage may be a scary one too. Looking forward to checking it out tomorrow..

Cheers
Dave

 

[kante1603]

Yep,do so.
What is "the heritage" btw.,the console (midas)?

Udo.

WAIT!!! DON'T TRY IT IF THE HERITAGE IS THE MICROPHONE FROM HEIL!!!
This is a dynamic mic!

 

[blackbird]

Yep,do so.
What is "the heritage" btw.,the console (midas)?

Udo.

WAIT!!! DON'T TRY IT IF THE HERITAGE IS THE MICROPHONE FROM HEIL!!!
This is a dynamic mic!

Heritage audio 1073.
http://www.heritageaudio.net/product-2-1073-500.php

Cheers
Dave

 

[kante1603]

O.k.,got it.

About your question how the phantom power works until it reaches the microphone:
The +48vdc is a single rail coming from the psu directly.
It is then "split" to your preamp input via the before mentioned 6,8kOhms resistors to each xlr pin 2(hot) and pin 3(cold) with refernce to audio/psu ground (that pin 1 carries).
Nothing else is in between.It then reaches your condenser mic or active d.i. and is normally taken via a resistor combo (voltage devider) to supply the inside active electronics and to polarize the capsule.

Best,

Udo.

 

[blackbird]

O.k.,got it.

About your question how the phantom power works until it reaches the microphone:
The +48vdc is a single rail coming from the psu directly.
It is then "split" to your preamp input via the before mentioned 6,8kOhms resistors to each xlr pin 2(hot) and pin 3(cold) with refernce to audio/psu ground (that pin 1 carries).
Nothing else is in between.It then reaches your condenser mic or active d.i. and is normally taken via a resistor combo (voltage devider) to supply the inside active electronics and to polarize the capsule.

Best,

Udo.

That makes perfect sense. Thanks for that udo.
So if the power supply reads fine on the multimeter, it can only be those 6.8k resistors.
I am feeling the power supply is the issue, as u mentioned, but tomorrow will tell.

Cheers
Dave

 

[kante1603]

You'll get a too high reading on your dmm,I'm 99,9% sure.

Udo

 

[blackbird]

You'll get a too high reading on your dmm,I'm 99,9% sure.

Udo

Hi udo..

You were spot on. The heritage is spitting out 55 v as well with phantom power. Radial rack off to tech.

So it seems I'm good to go then! One more VP28 alive and well in the world.

Thank you all who have commented and steered me right. You're a good lot.

Cheers
Dave

 

[kante1603]

Good to hear the VP28 is alive and healthy,sad for you the rack psu isn't.
May I suggest to build rack(s) and psu yourself in the future?
The stuff Jeff,Cemal and Volker have in their store are absolutely bullet-proof and easily top all industry stuff I've seen so far.And the biggest advantage is that you will learn a lot about how a psu works and then be able to service it.And the fun factor,it's a great feeling to see how fast it all grows,hahaha!Also the "51x-Advantage"(additional +/-24dc rails) will open up the possibility to build some of the more exotic or formerly non-500-series modules while it is always API/500-series-compatible.

Have fun,

Udo.

 

[blackbird]

Good to hear the VP28 is alive and healthy,sad for you the rack psu isn't.
May I suggest to build rack(s) and psu yourself in the future?
The stuff Jeff,Cemal and Volker have in their store are absolutely bullet-proof and easily top all industry stuff I've seen so far.And the biggest advantage is that you will learn a lot about how a psu works and then be able to service it.And the fun factor,it's a great feeling to see how fast it all grows,hahaha!Also the "51x-Advantage"(additional +/-24dc rails) will open up the possibility to build some of the more exotic or formerly non-500-series modules while it is always API/500-series-compatible.

Have fun,

Udo.

Hey udo.

Yeah, the racks been around for quite a while now. Before I was aware of the rack kits..
I've been eying them off, and will go that way once this power rack goes back home.

So is need to get a power supply kit, and the rack kit? Easy build?

Cheers
Dave

 

[kante1603]

So is need to get a power supply kit, and the rack kit? Easy build?

Cheers
Dave

Hi Dave,

yes,the rack is super easy to build.
For the external psu please read through this thread:

http://groupdiy.com/index.php?topic=48959.0

To keep this thread (about the VP28) clean please post and discus over there.
Take your time reading and ask if necessary,

best,

Udo.

 

[nicholasdover]

Hi Guys
I just made a pair of these with 1731/2520 combos in each and in use I'm realising one of the 2520's I built has a problem - as notes tail off there's a distorted sizzle. I've checked by swapping everything else around (glad I made a pair to make that job simpler!) and I'm pretty sure it comes down to the 2520. I just wondered if any of you had encountered this issue or could point me to which component can generate sizzly overtones (not just the nice drive they do when you ask them to)? I should re-wet each solder joint I guess. I did make the classic mistake of putting 139/140 power transistors in wrong way round so they've been overheated for sure during removal, just don't know if this is how that would fail. It's cheap to make a new one - I'm just in uk so bit of a wait for customs to decide if it's a DOA or an IED...
Any help v welcome
Cheers

 

[Commander Fluffypants]

Powered up my VP28's and listened to each for a second and both appear (so far) to be working perfectly! LED's, switches, all working (I think; cursory test, but had to come say "HOORAY!")

If I can do this, anybody can! Just take your time. My first one took 14 hours. The second one, ten. Op Amps about two hours each. Nothing was difficult, but I had to be diligent and careful the whole time. Before this I only soldered cables and one Group DIY reamp box.

Thank you Jeff, Chunger, Udo, Group DIY, the folks talking about this stuff on Gearslutz, etc. I don't know any of you, yet your generosity and skill have helped me a lot.

Six more slots in this rack and an empty wallet...

 

[kante1603]

Great to hear,you'll have a lot of fun working with them,promised!
Bazillions of sounds possible by just changing the ratio between input (gain) and output (fader) stages.My first choice for a lot of tracking jobs meanwhile.

Best regards,

Udo.

 

[Commander Fluffypants]

Got it all hooked up to my rig. Tested both a dynamic and a condenser mic. Everything works. TONS of gain.

 

[nicholasdover]

I just made a pair of these with 1731/2520 combos in each and in use I'm realising one of the 2520's I built has a problem - as notes tail off there's a distorted sizzle. I've checked by swapping everything else around (glad I made a pair to make that job simpler!) and I'm pretty sure it comes down to the 2520. I just wondered if any of you had encountered this issue or could point me to which component can generate sizzly overtones (not just the nice drive they do when you ask them to)? I should re-wet each solder joint I guess. I did make the classic mistake of putting 139/140 power transistors in wrong way round so they've been overheated for sure during removal, just don't know if this is how that would fail.

Just in case anyone else has had the same problem as I did, and is scanning through the thread for a fix, I thought I'd mention that re-wetting all the solder joints cured it and only took a few minutes. Couldn't see which one was bad but it's gone now. Thanks so much to Jeff and Chunger for the great kit and instructions respectively. Just finished first full track with everything going in through it and it's absolutely what I'd hoped for - I may never have to reach for the Decapitator again with drive like this available on the way in!

 

[martin bluenoise]

Hi all, I guess this is my first post even though I've lurking around for quite some time now.

I finally went ahead and ordered 2 vp28. upon getting them, i was amazed at the overall quality of all the parts.

anyhow, just by being patient and thorough, i managed to get them both working at the first try!!

before installing the opamps i measured something incorrectly, and jeff was there to answer my questions and get me sorted right away. trully amazing service.

chunger's step by step build guide was also a great source of information and confidence. and so was this whole thread.

thus, to sum it up, thank you all, and cheers to an amazing product!!

 

[Ultralag]

Hi,
I registered just to say thank you!
The building of this kit was fun and quite easy following the step by step photo guide and the whole thread.

I never soldered before building this kit and never cared about resitors or capacitors, didn't even know what they where!
I've been using my pres and stuff without real attention for what was going on inside the box and was looking for a new pre to add to my lunchbox and ended here...I bought this kit and in two weeks it was waiting for me on my new workbench, new Hakko 888D soldering station and 60/40 Multicore solder. Everything new to me.
It took many hours of work just because I triple checked everything and learned using a multimeter during the build.

I have no other experience but the kit is very very well built and everything is where it should be, perfectly organized and top quality and in the end I'm glad to say it worked on first try with dynamic and condenser mics. Plus, the HPF is a brilliant choice and I can see me using it often in the future.
I grabbed a 57, hooked it in my lunchbox and the sound coming out of the speakers was a pleasure to hear...well...twice the pleasure because it was DIY.
It takes attention and patience in the process but if I could do it so could anyone!
I'm really proud of it.

Someday I'll get another vp28. 

Ultralag
Happy Italian Capi customer

 

[nicholasdover]

I have built a pair of VP28's and while they both work and sound great, one is consistently 3dB louder than the other. I have 2520/1731 combos in each and have switched them around to check, but strangely it's not the opamps. I've checked resistor values all over each board. All that leaves are transformers really. Any ideas? It's workable, but not ideal...

 

[jsteiger]

There is most likely a resistor error in the gain switch or fader area. If you can't spot it that way, you need to be scientific. Inject signal and trace/measure it thru the pre to see where things are different. There is a pdf for test points earlier in this thread.