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

ccstudios said:

I bought two pre built vp26s from a local engineer. He said that one or both had some problems and he thought it might have been the gar2520 opamps. I went ahead and purchased some ml2520 from whistle rock audio. When I tested the vp26s with either opamps, I would get clipping at low levels. And it's not clipping at all times..I know it's not clipping going into my converter. I read up on this thread and found out I should reflow the solder. I did that and put it all back together again, triple checking each component and solder joint...I still have clipping. Don't know what I should do now...any suggestions?

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having the same problems, distortion on lower levels (sounds grainy and stuttered). when input is increased to almost 12 o clock it goes away and "normal" coloration begins..

how did you solve the issue?
tested with gar 2520 and red-25 opamps

is it normal that the input gain knob is very noisy when turned?

Just finished my VP26 last night! It sounds great! I really dig the layout and simplicity of this kit.  My only confusion is with the Grayhill pot. When I put the knob on where it made sense to me (pointing at the first marker on the faceplate) in the fully attenuated position, the set screw isn't lined up with the flat detented side of the pot. So after adjusting the gain for a little while, the knob will slip until it catches that part. Is there a way to adjust the stops of the Grayhill so that the knob lines up with the flat side of the pot and matches. I feel like I'm missing something obvious, but this is my first experience with  a Grayhill knob so maybe this is a just a quirk I have to live with? Or maybe I just need to really crank down harder on the set screws?

Sadly, neither of the setscrews line up with the flat on the shaft. Its a bit of a bummer but par for the course with the Grayhills. I did check into full round shafts and the increase in cost was absurd. I line them up so that fully CW (wide open) is pointing down or 6:00. It may take a little fiddling your first time but very doable.

That seems to have done the trick! Thanks ! Great kit, cant wait to pick up some more in the future!

Hi Folks, just completed my first build of the Rev B VP26.  All is well other than no LED for 48v.  I have 48v, just no LED. 

Is the LED in backwards then?  Is there any documentation for the LED install?  I couldn't find it.

Huge thanks to CHUNG for his pics, can't wait for the updated detailed instructions from Jeff.

Thanks for any help on the LED.

Neil 

OK happy to answer my own question on the correct LED install.  The LED is indeed polarised (long leg positive, short leg negative), meaning the long leg goes at the 'base' of the arrow on the PCB.

Best to all.

NT

Hello all,

I am almost through my first vp26 build. I noticed that in the new guide (on this forum), resistor R1 doesn't appear to have been installed. Should it be? I'm not totally clear on that. Thanks in advance for the help!

P.S., having a blast putting this thing together. Can't wait to hear it

R1 must be installed for the LED to work.

Thanks for the quick reply Jeff. So, if I am not using the LED (which I think requires drilling a new hole for it), it should not be installed, or does it still need to be in the circuit?

All kits come with the LED. It has been that way for some years now, so yes install that 10k R.

Jonesey, check your faceplate. If you received a recent kit from Jeff you will have a hole already pre-drilled next to the hole for the 48v switch. 

Note my posts regarding correct install of the LED above.

Get to it!

Gotcha! Thanks

Hello, I got another two of the VP26's and managed to put them together rather quickly.  Was more sure of what I was doing this time.

I turned on one of the previous VP26's I have and it was making a horrible noise https://dl.dropboxusercontent.com/u/3526809/noise.mp3 (you might need to turn it up for the first bit, but it's very obvious towards the end)

I decided I'd try some trouble shooting. I tried the pre in a different slot to rule out the cabling/slot and the pre carried the noise to the other slot. I thought I'd swap the opamps over before looking for bad solder joints and the noise carried over to the other pre, so I'm narrowing it down to the opamp (self built Gar2520's). When I turn my lunchbox on, there's a very prominent pop from that one pre, but not the others.

Upon closer inspection, there's solder running down one of the millmax pins on the opamp. Trying to remove it has been tricky. I've managed to get the pin off but I can't get the solder off of the pin as it's wrapped right round it.

Is there a part number for the pins so I can order some from Mouser? I'd get them from Jeff, but I live in the UK so figure it would be quicker this way.

Failing that, I anticipate I'll be ordering another couple of pres, so I could just get a new Gar2520 kit then. I'll likely get a new socket for it to sit in, just in case any of the solder has scraped off.

jeid, it sucks you are having the trouble but I am happy you are sorting it out. Sounds like you are close!

The part for the opamp pin is Mill-Max #3103200210000080

Looks like Mouser are out of stock and it'll be another two weeks before they have any. I'm not in a huge rush, so I'll just get some when I order a couple of new pres.

Hmmm, after carrying out a further test, I swapped the opamp around and the original card made noise. Typically, after I just made an order for another opamp kit. Going to reflow the solder joints and test again.

Are the opamps fully and properly seated? http://classicapi.com/catalog/DOA_Install.php

Yup, looks good and I can't push it in any further. I'm confident it's not the opamp now as the same card was causing an issue with a different opamp. I've just reflowed the solder over everything and will test again. Cheers.

I retract my previous statement. Opamp to blame. I ordered one this afternoon so I'll get it built when it arrives in a couple of weeks

Hello,
I just put together my first vp26 but eveytime I try to plug it in to my lunchbox R6 starts to smoke and melt. Everything looks good and seemed to test as normal. Any idea what could be causing this?
Thanks for your time!