[BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread

[jsteiger]

No problem. It's just beyond your DMM. Sounds like you are OK.

 

[Curran]

yeah I dropped in the one of the four gar2550's and it fired right up and sounds awesome. I got three built and all the gar2550 kits done in about 8 hours. right now they are all waiting to get used on the next session!!!! the layout PDF is awesome and the build is super easy!!! the opamps are tiny and a bitch but the layout PDF is wonderful for getting that tiny little thing populated and ready for your opamp needs!!! one more kit to build and then I am gonna enjoy the fruits of my labor with some heavy duty recording!!!

 

[jsteiger]

yeah I dropped in the one of the four gar2550's and it fired right up and sounds awesome. I got three built and all the gar2550 kits done in about 8 hours. right now they are all waiting to get used on the next session!!!! the layout PDF is awesome and the build is super easy!!!

Nice! 

the opamps are tiny and a bitch...

Yes, they are tiny... and a bitch is a good description too. Very rewarding though indeed.

I am curious to hear what you think after a good session, especially when compared to the OSA.

Best, Jeff

 

[Curran]

I will definitely let you know, I will also put them up against the Five Fish MK-II's I have with the cinemag input transformers.

 

[babyhead]

I have just finished QCing 4 of these and I want to finish the last 2. I have some original Melcor 1731 that are stickered +/- 15. The problem is that my 500 rack puts out +/- 18. Am I risking my opamps by putting them in circuit? Should I replace the protection diodes with drop down resistors?

So far these amps sound GREAT!

 

[letterbeacon]

I'm thinking about putting two AP26 pre amps horizontal in a 1U rack.  What do I need to supply the modules with power wise?  Is it +/-15v and +48v for the phantom power?

 

[babyhead]

I'm thinking about putting two AP26 pre amps horizontal in a 1U rack.  What do I need to supply the modules with power wise?  Is it +/-15v and +48v for the phantom power?

It depends on your opamps, but otherwise, yes.

 

[haima]

The problem is that my 500 rack puts out +/- 18.

+/- 18v? what 500 rack is it? i thought the 500 standard was +/- 16v.

the VP2X boards have series diodes on the power rails which should drop 0.6ish of a volt per rail, depending on your current draw. so if you rack is in fact bipolar 16v you could be close to 15v at the actual opamp pins anyway...

check the voltage at the opamp pin sockets while another, higher voltage opamp is installed - you might need to use an external card edge connector and bench power supply to get access to the pins though...

if you are really worried you could run the original Melcor 1731s off a bench power supply for a while and slowly edge up the voltages from 15v up to your final "measured at the pin sockets in the rack" voltage. look and listen for problems - too much heat, excessive current draw, strange noises, (EXPLoSIoNS and fire...haha ) etc

if you need to drop the voltage down a bit you could try replacing the series power supply diodes (near the finger edge) with 2 or more diodes connected in series (all facing the same direction!) that can drop the voltage a little more if you need to. you might have trouble if you want to go all the way from 18 to 15 using that method though... lots of diodes needed!

if you really need to drop some more serious volts you could kludge a little zener diode "regulator" onto the board or some veroboard - check out schems for the JLM baby animal for an example... you'll need to adjust the resistors and zener values to suit though.

 

[letterbeacon]

I'm thinking about putting two AP26 pre amps horizontal in a 1U rack.  What do I need to supply the modules with power wise?  Is it +/-15v and +48v for the phantom power?

It depends on your opamps, but otherwise, yes.

Great, thanks.  I've built +/-15v power supplies for my modular synth before, but are there any designs out there that can output +48v?  Has anyone else put these pre amps in a 1U rack before?  I had a search on the forums here but I can't see anything...

Cheers!

 

[[silent:arts]]

http://www.jlmaudio.com/JLM%20Power%20Supply.htm

 

[haima]

Has anyone else put these pre amps in a 1U rack before?

jeff also makes the VP312 boards that can be trimmed to squeeze 4 channels in a 1RU box.

also - being a synth guy, you might be interested in his upcoming VP312DI which is the same thing but with some great DI options built in. i think they will be available from his shop within the next few weeks.

volker, JLM ACDC? i second the emotion - i've used lots of those. handy and compact!

 

[jsteiger]

Don't forget about Owel's nice PSU kit from FiveFish. You can buy the full kit with toroid for only $75! That is a pretty good deal I think. 

I have also built a JLM Powerstation and you cannot go wrong there either. 

jeff also makes the VP312 boards that can be trimmed to squeeze 4 channels in a 1RU box.

      8)

 

[Tweekhead]

Can anyone tell me what components I would need to substitute if I was to build a VP25, or VP26 and use a Carnhill 9045 for the input?

 

[haima]

you'd need to adjust any input transformer "zobel" or loading resistors (C3 and R2 in this case AFAIK). these components that sit on the secondary of the input transformer and adjust the loading for best squarewave response.

as far as what to replace these components with, look at what's done with neve preamps and copy that for a start. i believe you might want to try a 180p cap and maybe a 5k resistor - in PARALLEL (not series like the VP2X) across the transformer secondary (pin 7 to 10?). check the "EZ1290 assembly.pdf" file for more info...

and you'd need to secure the transformer using cable ties - you may need to drill some holes in the PCB for this - be very careful not to hit any traces on the top or bottom of the board!

let us know how it goes, or if you need more help!

 

[Meathands]

jeff also makes the VP312 boards that can be trimmed to squeeze 4 channels in a 1RU box.

This sounds great!  How much current would a setup like this need?

 

[haima]

depends entirely on the opamps... some opamps use more than others - i can't find any specs around right now, but there should be some around on the forum.

i did a quick google search for the API 512 specs - "Power Consumption:     ±12/18 Volts/DC, @40 ma." so that gives you a rough guide...

 

[jsteiger]

Well, a VP preamp driving a 600ohm load draws around 51mA. So that X 4 plus some headroom and you are in business. If you want the PSU in the case, the case will have to be deep enough. Otherwise, outboard will eliminate and potential toroidal induced noise issues.

 

[jsteiger]

I should note, that 51mA was a single channel with a gar2520. Scott's SL2520 is nearly identical as far as current draw.

 

[haima]

oops- i should have shut my mouth - the real info, straight from the horses mouth! thanks jeff  ;D

 

[jsteiger]

oops- i should have shut my mouth - the real info, straight from the horses mouth! thanks jeff  ;D

No, no, no...the help is appreciated indeed! 

Interesting spec you found though. I bet that is idle or no load on the DOA. Ours are about 23mA idle. Maybe the extra juice is for the LM39xx and the IC meter buffer?