If it is not already abundantly clear from my post, I should provide the following disclaimer: I have zero experience working with electronic components. The CAPI builds are my first venture into the field. I have wanted to do this for years and finally found the opportunity to. Please be patient with me.I have a few questions for anyone that is kind enough to help out:1) Is some sort of pad or double sided sticky tape required for the underside of the EA2622 input transformer? What happens if it is not used?2) The circular gold ground plane of the +V socket of my preamp opamp slot has partially lifted from the PCB surface - Is a solder connection necessary between the pin and that gold ground plane or is it sufficient to have a soldered connection through the hole?3) Any general or specific advice with regard to building the opamps? I thought I had them perfectly soldered yet one caused the PR2 and PR4 resistors to fry. The Q7 and Q8 transisters (black blocks with the holes) overheat on another.I was so excited about building a pair of these vp28s and a pair of the vp312s.
1) no (it only makes it easier to solder in)2) Solder from the back and re-float the top.3) You have to be careful with heat around those transistors when soldering and they can get damaged.Despite my experience here in this topic I have successfully built many pieces. I got lazy and used solder that was to big and a tip that was to big. I have decent soldering skills and thought I could overcome the need for smaller solder etc. , I was wrong. I will only buy pre-made and tested DOAs as they took me and 1hr and a half a piece to build.
As to the tape thing with the input trans I can still see air under mine and have installed dozens of these style on PCBs without issue but I like to gently hold the piece against the PCB when soldering 2 of the leads and never clamp it hard as to do damage to the coatings on a PCB or have any stress on the leads. Chunger does some of the best tutorials ever and teaches good habits especially to people new to DIY so I should say that it's a good habit that would guarantee you don't dig in to the ground plain.Yes I removed the resistors and cleaned the board and no damage. No other damage that I can note or see. The odd thing is I measured the resistors and they were still close even after the meltdown.In respect to the opamps, the issue could be any of the issues you mentioned. Although you save money building them, if you destroy the board or other components you are about even or worse. I'm building 3 of these and will only buy pre-made for the remaining 2 and now for the one I have now. Enjoy the builds and remove any situation that will cause you grief ( such as as the opamp build) that's hard to test outside the pre. And don't get discouraged. There can be hiccups along the way but solving them makes it even sweeter when it's working and helps build confidence to attack the next project. This forum has some great advise and help when you ask for it. Hang in there!
The implication is that when installing it you scratch through to the metal underneath (which is the grounds Plate). Most likely not your issue. If you followed the instructions closely you should be ok. When my new opamps solve my issue you can feel a little better and maybe try the same. Mose issues you will experience are bad solder joints or bad grounds. I'll let you know tomorrow.
Allecstatic, I replaced the (4) 10 ohm resistors first . Note that after that amount of heat it is easy to lift one of the solder pads on the pcbs so dismantle to the point where you can access from the back and carefully remove the resistor with whatever desoldering tool you have and not forcing anything (be gentle). Once you are replacing the resistors solder and make sure that front and back pads are soldered and that goes for your opamp receiver as well. I would also note that the already assembled 1731 and 2520 had been soldered from underneath with a generous amount of solder with the solder bridges that are in the instructions but I hesitated to do when building. Long and short of it has fixed the issue and the pre is passing sound and well. Hope this helps.After seeing your pics I would recommend that if you have some extra wire from your transformer you strip it back and resolder and cover with heat shrink. Good luck!
How are you guys securing the opamps in their positions? Some of mine will stay on their own while others just slide out.
I don't mean to be rude but this has been cover a million times and I have a page at the site about it http://capi-gear.com/catalog/DOA_Install.php
The shop you took it to is mistaken regarding the pins. Brand new sockets require the initial break in, then after that, swapping out and seating new DOAs is easier, but it still requires a little bit of force. Once seated they should never come out on their own if the proper size pin and socket is used.Again: http://capi-gear.com/catalog/DOA_Install.phpAlso, Jeff, along with all the wonderful people here, who offer these amazing design so others can build world class studio gear at a fraction of the cost and get some electronics education in the process, have been and are extremely supportive with the products they offer, not supposedly. Thanks!Paul
I would double check the location of all R's specifically the 160R's and 4k99's just behind the mic/line switch. Next I would check all R's behind the preamp gain Grayhill. After that look for a solder bridge on the preamp gain Grayhill. Exactly 3dB is far too suspicious since all but the lowest 2 gain settings are 3dB.Are you 100% sure the preamp gain knob is orientated properly?