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

[kante1603]

I cannot hear any noticeable hum at all on any of mine

Same here......

@unit7:

Hello,

picking up hum can appears in quite a few ways,e.g. from strong magnetic fields,unbalanced wiring,
bad shielding,wrong wiring on patchbays,mixing up different groundings etc......and all combinations of that.Even a mic capsule can do that.

So for sorting the VP28s out from that just disconnect that 500 type rack which contains the preamps and monitor them directly with a phonesamp or mixer or..........
Don't use those Y-cables (most of times no good idea,could work but mustn't).
You can do some experiments concerning grounding in your 500 rack,don't know which one you have,but e.g. in a 51x-rack one has a lot of options:
The 0 volts from the circuit can be connected to the mains ground(earth) or the 0volts from the psu or even left open.This is done by jumpers inside the rack.All this for every in-and output!
Let the inputs of the preamps connected to one of the grounds since you will need it for running the phantom power correctly.
Try to change the output ground or leave it open,it's o.k. to do so,you'll have an "earth-free" balanced out on linelevel then.

Just a thought,

Best regards from germany,

Udo.

 

[Unit7]

@unit7:

Hello,

picking up hum can appears in quite a few ways,e.g. from strong magnetic fields,unbalanced wiring,
bad shielding,wrong wiring on patchbays,mixing up different groundings etc......and all combinations of that.Even a mic capsule can do that.

So for sorting the VP28s out from that just disconnect that 500 type rack which contains the preamps and monitor them directly with a phonesamp or mixer or..........
Don't use those Y-cables (most of times no good idea,could work but mustn't).
You can do some experiments concerning grounding in your 500 rack,don't know which one you have,but e.g. in a 51x-rack one has a lot of options:
The 0 volts from the circuit can be connected to the mains ground(earth) or the 0volts from the psu or even left open.This is done by jumpers inside the rack.All this for every in-and output!
Let the inputs of the preamps connected to one of the grounds since you will need it for running the phantom power correctly.
Try to change the output ground or leave it open,it's o.k. to do so,you'll have an "earth-free" balanced out on linelevel then.

Just a thought,

Best regards from germany,

Udo.
[/quote]


Thanks for the tips Udo!

Re Y-cable, no worries, I almost never use it, just did it yesterday for a quick A/B w the AMS/Neve. And the very quiet hum I got was there when using straight cable too. I'm fairly sure it's a magnetic field or perhaps from another unit in my rack. I always have problems w el guitars using single coil, and also with certain old RCA ribbon mics. Not much to do because it's a very old building. Besides that I believe my cabling, patchbays etc is ok becuase I have a LOT of outboard and never have issues with hum, and I don't think this case with the VP28 even could be called an issue, but thanks anyway for your concern!

All the best from Stockholm
Paul

 

[tylerromo]

Built 2 of these with no problems this weekend after getting the package saturday. Thanks for the walkthrough chunger! Amazing pack job as always, Jeff! One thing I'll add about the opamp kits, PUT THE MATCHED PAIR OF TRANSISTORS BACK IN THE BAG after you dump the pins out. I panicked thinking I mixxed them up towards the end of my first shot at a 2520, and then noticed the hfe matched transistors' pins are spread from the gain matching. I lucked out because Q1 and Q2 were both still in the parts box.

 

[emfrank72]

Just finished my first VP28.  It works and sounds great.  Only problem is that the 4 LEDs on the left don't work.  The signal LED works fine.  I am guessing that there must be a + and - on them.  How can you tell which way they go in?  Is there something else that could be wrong?

Thanks,
Eric

 

[Unit7]

Just finished my first VP28.  It works and sounds great.  Only problem is that the 4 LEDs on the left don't work.  The signal LED works fine.  I am guessing that there must be a + and - on them.  How can you tell which way they go in?  Is there something else that could be wrong?

Thanks,
Eric

The way they came, one leg was longer. Chunger's manual suggests keeping the longer leg longer when cutting, and the shorter leg soldered to the side where the arrow on the pcb is pointing. I'm sure Jeff will chime in! I'm just a noob!

 

[jsteiger]

The signal present LED is by itself and in no way associated with the 4 status LED's.

The 4 status LED's are in a constant current series string together. The signal enters the string at the phantom LED and ends at the top LED. To test them, first make sure all 4 pushbuttons are in the out position. Try them one at a time. Make sure you leave the switch in the outward position before trying the next one. Which ever ones do not illuminate are in backwards.

 

[kante1603]

Hello Jeff,

hope you're fine.
Just wanted to know when the preamps will be available again.I know you're lacking of transformers,but can you tell us roughly estimated timeframe please?

Thank you in advance,

best regards,

Udo

 

[jsteiger]

Hi Udo

We are waiting for the 2622's to come in. They were suppose to ship last week but we have not gotten a UPS update yet. They should come literally any day now.

 

[kante1603]

Hi Udo

We are waiting for the 2622's to come in. They were suppose to ship last week but we have not gotten a UPS update yet. They should come literally any day now.

Another six of those beasts ordered and paid-hurrrrrrraaaayyy! ;D

Cheers,

Udo.

 

[rtroast]

Greetings all... just finished 3 VP28s, all of which appear to work great (checked voltages, passed signal). The only exception is that on one of them, the green signal LED is lit at all times. Any suggestions? I checked and they appear to be installed identically on each of the three builds.

Thanks in advance!

 

[jsteiger]

I would check orientation on all the 1N914 diodes and also the 4558 chip. Maybe the LED is backwards?

 

[rtroast]

I just thought of the diode orientation as well, so will go check. Ditto on the 4558 chip but I'll double check. The LEDs appear to all have been installed the same way. Thanks for the response.

 

[Thanatopsis]

What size allen wrench does the top knob use?  I have a ton of allen wrenches here but none small enough.  Stopped by WalMart after work tonight (only place open at 1AM) and they did't have anything smaller than what I have.

I had one of those allen wrench Swiss Army knife type things that fit both perfectly so that might work for people that have a hard time finding the right fit.

 

[qmp audio]

What size allen wrench does the top knob use?  I have a ton of allen wrenches here but none small enough.  Stopped by WalMart after work tonight (only place open at 1AM) and they did't have anything smaller than what I have.

I had one of those allen wrench Swiss Army knife type things that fit both perfectly so that might work for people that have a hard time finding the right fit.

0.050"

 

[sharpeleven]

Greetings all... just finished 3 VP28s, all of which appear to work great (checked voltages, passed signal). The only exception is that on one of them, the green signal LED is lit at all times. Any suggestions? I checked and they appear to be installed identically on each of the three builds.

Thanks in advance!

I had a similar problem with the LED staying lit about 30 minutes into operation. Turned out to be an opamp issue in my case. Try switching opamps around and hopefully it might be just that.

 

[kante1603]

Oooooops (I did it again!)

Another 6 PreAmps:Ordered,paid,built,tested,ROCKS! (You like,Jeff? ;D)
GAR 2520s on all of them.





Greez,

Udo.

 

[Trench Recordings]

Udo, stop hogging all the transformers 

Other people want to build some too ! lol

 

[kante1603]

No.

;D

 

[jsteiger]

Oooooops (I did it again!)

Another 6 PreAmps:Ordered,paid,built,tested,ROCKS! (You like,Jeff? ;D)
GAR 2520s on all of them.

Wow Udo...awesome rack you've got there!!  ;D



Greez,

Udo.

 

[tonycamp]

Oooooops (I did it again!)

Another 6 PreAmps:Ordered,paid,built,tested,ROCKS! (You like,Jeff? ;D)
GAR 2520s on all of them.





Greez,

Udo.

you know the only thing that would make that rack look better?? Another rack full of vp's and Lc's right next to it!!! It's a sickness!! ;D