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

[pittsburgh]

Jeff, removing that T-Pad is realistically going to destroy it, or remove traces from the board from my end. Without a desoldering iron I'm faced with the reality of reheating 13 joints and getting lucky with a pump, or cutting off leads from the top of the board and getting rid of the remaining leads. If that is absolutely the way to go I'm ok with this, but that T-Pad will never work again if that does indeed turn out to not be the case.

I'm not understanding why what seems like a failed transformer test by not getting signal when placing ground at the black lead of the OT and the probe at the blue wire seems to not make a difference here. If the writing made earlier by Haima is correct than I should be getting signal at this point, but I am not. 



G) probe the "blue" lead of the output transformer - got signal? if so,

I get no signal at this point.

 

[jsteiger]

Well, its because the DCR measurements reported earlier tell us that the 2623-1 is fine.

 

[jsteiger]

Just humor me and move the blue 2623-1 lead over to the opt-blue pad near the gold fingers. I forgot that on this Rev of PCB that will bypass the t-pad.

 

[jsteiger]

Also, not sure what device you are using for a signal generator but you should have the opamp installed and inject signal into the pre's input, not the opamp sockets. The output transformer in an API mic pre circuit is a pretty heavy load that should be driven by a 2520 or similar. In your test scenario, it is most likely too much of a load since you are essentially connecting whatever you are using as a signal generator directly to the 2623-1's primary winding.

 

[pittsburgh]

I'm having the same issue with the transformer blue lead going to the optional no tpad point. The problem must be related to the output transformer. My tests with an auto sensing DMM must be the weak link here, as I have no way to put my tester into a setting into the >50 ohm band.

I say this while testing with my pre assembled GAR 2520 in place and running signal through a powered lunchbox.

 

[jsteiger]

Send me an email thru the store and I'll get a new 2623-1 out to you. Please include your full name.

 

[Anacondaq]

Hi jeff, i have had 2 kits of VP26 for quite some time now with gar2520 op amps. I built the first one and although it passes audio it seems its not quite right, there seems to be no low end and it sounds overly bright and buttons do not work correctly. Ie. the phase button changes the gain applied. I have gone over the whole board and preamp for dry solder joints and checked polarities. I'm pretty sure that theres nothing on the 2520 that is short circuiting, this is quite a fine circuit and i did my best! i do need an iron with a smaller tip though.

Unfortunately this is where my trouble shooting knowledge ends and sifting through this long forum, although it probably already has the answers im looking for, begs the question of what to check next and how to test it?

Thanks in advance

Ben 

 

[Reverend]

Hello to all. Does anyone have any idea when Jeff is going to have more VP26 kits available? Floor PSU for the 51x too?

 

[mhuss]

I have a pair of stepped VP26s I built a while ago, but just started using them as a pair, and noticed their gain is mismatched a lot, perhaps 20-30db! I carefully checked that all the resistor color codes match on both units and I'm pretty sure I measured them all when I built the preamps as a safety check.

I swapped 2520s but it made no difference. Can you suggest anything else I can check? Is there any way a transformer could be bad?

 

[jsteiger]

It could be a cold solder joint. It will not hurt to reflow the solder joints real quick. The next step will be injecting a sine wave and seeing where the levels change from pre tp pre. There are some steps earlier on in the is thread on how to do this.

 

[mhuss]

Arrgh. I need a couple of those 500 'extender' boards, troubleshooting these 500 modules in the rack is a pita...

--mark

 

[gabygab]

Hello! I just wanted to take a second to thank Chunger and Mr.Steiger for the great support and great products!

To all the lurkers around here that might be afraid to jump on the DIY bandwagon, take it from me. DO IT! These builds are fun and straightforward. I feel great now that I've finished them and I only want MORE! Also, they sound amazing!

 

[midnitestudios]

Where can I get the bom for the new vp25?
thanks!

 

[jsteiger]

Where can I get the bom for the new vp25?
thanks!

Support doc emails have been sent out for all open orders. They often end up in spam/junk folders for some reason.

 

[burglar]

Hi folks,

I have a strange problem.  I've recently built x2 sound skulptor MP 12 api clones with EA2622's, EA2503's & GAR2520's.  Upon firing them up I had EXACTLY the same distortion as is in the soundcloud link below.  The problem was identical.  Fizzy distortion that reacts to input (is only audible with signal) and increases when I turn the output pad up.  If I bring the output pad down and increase the gain, things begin to clean up (example in clip). This distortion does not always start with power up, it can take 10-20 seconds to creep in.

After the opamp in the sound skulptor builds there is a Servo / DC offset option including jmp3, P3, U1 & JMP4 as per this schematic http://www.soundskulptor.com/pdf/mp12-schematic.pdf I omitted this option under the advice of Jean Pierre, set the GAR's to +/- 15.5v & rubbed down the underside of the GAR's with isopropyl.  Since then the preamps have been working fine so I thought all was cured.

Just last night I built a VP26, stole a gar from one of my sound skulptor modules, installed it in the vp26, installed the vp26 in a lindell 510 and powered up.  I was surprised to hear exactly the same distortion as I had mith the Mp12's !!

The only conclusions I have been able to draw are that the lindell rails are +\- 16v ass opposed to 15.5 which should no difference really?

The problem is opamp based even though they appeared to work fine in the other pre's.

I used the same kettle lead from the same socket as the sound skulptor pre's so if there is some AC problem it could have been that?

I have built a new computer recently but this doesn't sound like interference?

Any help is much appreciated.  I am a newb and am vexed at this stage : /

https://soundcloud.com/overtoneuk/vp26-distortion/s-ysRkP

Ed

 

[clearkutz]

Hello i am in the middle of my first build i am a newb but i have have took on this with having researched for quite a while and i have to other people to rely on that have some experience with building electronics as well as standard equipment for compiling these preamps together. after carefully going over the instructions provided for the build both of the preamps are together and when powered up everything is ok (nothing is blowing up or burning out but there is no audio when pushing in the mute and polarity buttons there is a spike in the channel metering ..this does get louder when the gain is increased but there is still no audio being passed .. the pots do nothing as far as audio is concerned I'm also not sure if i am getting power to the led as it doesn't work either for phantom  i have used two mic to test phantom (one that requires and one that doesn't ) and still nothing … i have place pics below am i missing something ?? what should i do to trace where there is a problem ?? thanks in advance for any advice …

this is my first build but i feel if i can get one to work i will know how to ensemble them from here on out

 

[jsteiger]

The phantom LED is most likely in backwards. Is the opamp a kit or prebuilt? If a kit, I would suspect it is not working properly.

 

[clearkutz]

i thought that maybe the led is in backwards and the op amp is a kit that i built  and i am willing to by a prebuilt one to test .. i built the opamps first before buying the kit just to see if i could get it down and honestly they went pretty smooth how do you test to make sure it is operating correctly ??  i have a multi meter  also the problem sounds like it stems for the opamp and not anywhere else ?? here is a pic of the op amp

 

[midnitestudios]

Just finished building my vp25 but i am not getting any sound. The led turns on when i flip the 48 switch.

 

[midnitestudios]

I switch the red dot opamp with gar2520 and it started working. Any ideas?
Thanks!