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

[jsteiger]

actually to clarify, its the R14 spot on the GAR1731 op amp..

Ah ok.

Best thing is to have a look at that specific support thread. I would look at the larger BD transistors though. Most common error on the opamp builds is turning and/or swapping those with each other by accident. They are NOT interchangeable.

 

[Trench Studio]

Hello All. Not sure if this question has been asked prior or not. I was curious if a stock 2520 DOA from a 3124 would work properly in the vp26? I noticed the pins on the api op amp were a lot longer than the purchased red dot. I didn't check for clearing issues yet either. Thanks in advance.

 

[jsteiger]

Electronically, yes no problem. You will have to check the physical attributes though. You can trim those pins if need be.

 

[wirehair]

Hello,

Testing my first build (a Classic API vp26) and I think that I have a problem.  When testing the voltage with no DOA installed I  get +16v at the v+ but at the v- I get -22v.  Should I be concerned about this?

While setting up to test voltage with No DOA in using the test jig from Classic API I accidentally hooked up the header upside down and applied power.  I know….. totally newbie mistake I don't know how I missed it.  Would that cause a problem?  If so what might I have damaged?  I did test my API luchbox and it is putting out +16v and -16v. 

Thanks for the help

 

[[silent:arts]]

Are you sure your lunch box is putting out -16V?
If yes there would be magic involved having -22V in the VP26 module.

Sounds more like a blown -16V rail, which would be in the lunchbox, which for sure could have caused by powering the module upside down.

 

[wirehair]

Ok, so with fresh morning eyes I figured out my voltage problem but I have one more question for some peace of mind.

So having hooked up the header upside down if I look at the schematic I see that I sent the +48v to the chassis ground which I don't think I need to be worried about.  But I also see that the mistake sent the the +16v and -16v through RV1 the output potentiometer and in to the output transformer.  Do I need to worry about having damaged the output transformer, output potentiometer, or any of the components that follow? 

Thanks for the help.  This is not a mistake I will make again…..I guess that's how you learn.

 

[jsteiger]

If it was just for a short second or two I think you will be fine. I guess the true test will be once you get it up and running.

 

[okgb]

Profile 4804 A.P.I. type output transformer color code ?
any one have the diagram or know it ?

I'm building up a vp25 and using some profile output xmfrs ,
Does anyone have or can post the windings color code for the profile ?
I need to translate it to Jeff's vp25 board
I did get it working based on some info here, , but unsure it is correct

 

[ILR]

Hey everyone, I just recently finished my build on a pair of VP26 pre's. They fire up fine and pass audio, but am running into an odd problem that two different users also seemed to have happen. The issue is, all functions work fine, pad works as it should, phantom, etc. But, the phase invert switch, when pushed, sounds as if some comb filtering is happening. It changes a normal sounding source into a mid rangy mess. There is also a significant jump in gain (volume) when the button is pushed. I went through all my solder points on one module and made sure everything looks clean. I do not see and solder bridges or dry sockets. Any suggestions or solutions are very welcome. I am new to DIY kits, but am having a friend that builds amps and pedals guide me and fix and bad joints. I am running them off a brand new Fredenstien Bento 10. Heres a picture.

 

[jsteiger]

I did not check them but have you followed the wiring guide for the Litz 2623-1? The polarity switch is merely flipping the 2 wires of the 2623-1's primary so I would look for a solder issue with that switch or the mute switch or the 2623-1.

 

[ILR]

Yes, I followed the color to color swap and checked those solder joints as well. Everything on the main board looks good and have gone over it twice, could the problem be with in the DOA? I built the Gar2520 kit.

 

[jsteiger]

Yes, I followed the color to color swap and checked those solder joints as well. Everything on the main board looks good and have gone over it twice, could the problem be with in the DOA? I built the Gar2520 kit.

Yes I think that has been the case before. Is it fully seated? http://classicapi.com/catalog/DOA_Install.php I have mentioned it a million times, it is very hard to troubleshoot a fresh module build with a fresh opamp build.

 

[ILR]

Yes sir. I have seated the doa completely, clicked and locked into place. I have read through most of this forum and have gone through most of the suggestions that seem relevant. As I have the new rev B with the new transformers and myself being a new diyer, I was not expecting a flawless success. I am at a bit of a loss after trying to clean up all my solder joints and double checking values and assembly instructions. It seems like it should be a fairly simple fix, but am unsure where the most likely foul up would be.

 

[jsteiger]

Do you have another 2520 style amp around?

 

[ILR]

Not as of now, I left the preamps at my friends shop until Friday, when I'll be able hopefully sort out the issue and use them.  this is a pic from above.

 

[Trench Studio]

I'm curious in what position should the output attenuator be If I wanted it fully open? I'd assume full throttle? And If I chose to bypass the attenuation entirely how would I do that on the PCB? And does bypassing it sound much different? I'd assume it reduces a little of the load on the transformer allowing it to breathe a bit more?

I'm sure this has been explained in this post somewhere and I apologize if so... but I was hesitant to scan 38 pages for it. Thanks in advance.

 

[jsteiger]

Yes fully clockwise is wide open for the attenuator.

To bypass it, the best way is to remove the t-pad and then move the specific lead for the output trafo over to the pad near the edge connectors. It will be labeled [Opt no t-pad xxxxx] and then the color of lead to move.

 

[ninopelo29]

Hi All,

I've just completed building 2 VP26's and, wow, what a great build. The guide was great and the new site is super helpful. Such a good time to build!

My question is I am getting this crazy crackle when I engage phantom power on one of the units. The other is perfectly quiet.

I've changed the 200 ohm resistor, swapped out the switch, tried different cables and changed slots but still the crackle persists. 

I saw some posts by Brolik from back in 2011 in which he had the same problem but there were no posts about what he discovered the problem to be.  I sent him a message but he hasn't been active since 2014 so I'm not sure I'll get a response.

Has anyone had this same problem and, if so, how did you fix it?

Any help would be much appreciated!

 

[jsteiger]

Sounds like a bad solder joint somewhere. Check the PB switch as well as the 120µF cap.

 

[ninopelo29]

Hey Jeff, thanks for the quick response!

So now I've reseated and resoldered:
• the LED,
• the phantom power switch
• the pushbutton Pad
• all 3 resistors in the phantom power line and
• the 120µF cap. 

I've tried it with two different red dot DOA's (both working fine in other units), I've tried the phantom power without the LED and switch in the circuit (direct wire between the switch solder pads) and I've tried it in different slots with different (good) cables. I even put the unit on a soft pillow to try to eliminate any stray vibrations in case a component was shaking in there! 

I can't get the noise to stop.

I've tried wiggling components to see if I can make it sound better/worse, but it just seems to fluctuate on its own independent of what I do.

Is there a component that could be failing or a part you'd recommend I change out? Maybe the 120uF cap? It's perfectly quiet with the phantom power off.

Thank you for all your help!