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Newbie builds Classic Audio Product's VP26 and VP312DI
« on: November 08, 2010, 06:59:12 AM »

Newbie here.  I've been lurking around for a while, and recently decided to jump on the GroupDIY 51x bandwagon and give DIY a try.  In the search for beginner-friendly projects, I came across Jeff's API type preamp.

The step-by-step documentation for this project is so good, that I cannot add very much to what's already provided.  Maybe a clearer picture here or there, but otherwise, completely redundant.  This is more to get myself warmed up to DIY projects in general and to figuring out my documentation workflow.  Plus, I'm waiting for parts to come in for the rack and the PSU, so I was getting a bit restless and wanted to keep moving forward.

I don't know if it was foolish or not, but the first thing I tried was the gar 2520 op amp kit. . . uh. . . because the bag was smaller  ???  

I bought a spare because I read this is a difficult build, and I figured a spare would be wise to have on hand given the low cost of the unit.

While not readily available online, the documentation that comes with this kit is ridiculously good.  I have no idea what I'm doing, and probably would have been able to put this together based on the provided images alone, but I opened up a chart to identify resistor values, and pretty much that's all I needed to get through this op amp build.

The only real difficulty I had was getting the pins to line up straight.

I tried flipping it over and putting it on a flat surface. . . that didn't look to workable.

Then, I tried soldering a couple of pins on and then flipping it upside down and re-melting the solder to see if it wound naturally  even out in the slots. . . and that didn't work too good either.

So, finally, I just pulled out the VP26 PCB and the inserts for the op amp and that gave me a much better chance of aligning the pins reasonably straight.

The rest is pretty much paint by numbers.  As mentioned before, documentation photos, explanations, and diagrams leave nothing to the imagination.  As long as I was paying attention to details, and my soldering was decent, I felt fairly confident the whole way through.

IMPORTANT NOTE:  The 2 large transistors in these photos are REVERSED. . . BD139 should be on the right side and BD140 should be on the left side.  The op amp if built in the manner pictured will be bricked.

And. . . voila!

Does it work?  I dunno. . . guess I'll find out.

Next up. . . .

For this kind of work, I think it may be prudent for me to get a macro lens at some point.  A lot of cropping going on.  For web, you'd never know.  Macro would be nice though , but I do what I can with what I have.  Focus is also a bit touchy.  I should see if I can buy myself another f stop or 2 somehow.

« Last Edit: January 08, 2011, 02:32:01 AM by chunger »
DIY photo documentaries consolidated here:


Re: Newbie builds Classic Audio Product's VP26
« Reply #1 on: November 08, 2010, 10:37:06 AM »
Welcome Chunger!

Ive been following your bass thread in the TalkBass forum with great pleasure, nice to see you here as well.

Nice pictures as always!


Hmm... in which direction do the electrons actually go?


Re: Newbie builds Classic Audio Product's VP26
« Reply #2 on: November 08, 2010, 12:34:32 PM »
Hey. . . glad you're enjoying the bass guitar ramblings over at .  I guess the difference there is I actually know somewhat what I'm doing  :o .  But, same folding table  ;D.

Well, onward. . . resistors are installed per instructions, and I'm starting to find my way around resistor identification/color codes a bit better.

The switches gave me a big scare, and unfortunately, I was so involved in fixing it that I forgot to take photos.  I did not notice the plastic pads at the base of the 3 push switches and didn't seat them all the way initially.  Fortunately, I followed instructions and only soldered in 1 of the lugs on each switch. . . In trying to get them flush, I had to push REALLY hard on them.  I eventually ended up de-soldering the lugs and pulling the switches out and re-seating them.  However, as I pushed them all the way to flush, I ended up pushing a couple of the center lugs up and the lugs actually shifted inside of the housing (got pushed up).  I had to re-heat the solder pad on the 2 that got pushed and force them back down to level with the other lugs.  I thought I may have FUBAR'd the the parts, but testing with my meter, the switches all seemed to be functioning, so I'm hoping the internal mechanism is simple and set up so that the parts are still good.  In the end, I should have just left the parts where they were initially because they would have fit just fine.  There is a bit of wiggle room on the alignment of these push switches.

Caps are populated. . .

I did not have double stick tape on hand to stick the input transformer in as recommended in the instructions, so I rolled up some electrical tape instead, and it seems to have worked fine.

And, fully populated. . . the output attenuator pot is different from the one illustrated in the instructions manual, but the differences are very minimal.  I found it easier to use a bare stranded wire (20 gauge) instead of re-purposing on the cut-off capacitor leads to connect the middle terminals.

Knobs and op amp installed. . . the tests recommended without powering up the board checked out ok.

The hardest part of the build was the switch issue mentioned above, and dropping the little op amp sockets on the ground and searching for about 20 minutes all over the floor for it!  I was also short one PCB lock washer. . . but, the unit is built, and the whole thing took me an evening.  All-in-all, very smooth build, and I didn't feel lost at any point with the provided documentation.  I think I'll try the VP312DI later this week.  But for now:

DIY photo documentaries consolidated here:


Re: Newbie builds Classic Audio Product's VP26
« Reply #3 on: November 09, 2010, 02:23:42 AM »
Hey chunger

Hey man lookin GOOD.  Nice tip on the gar2520 pins.
Did a nice job soldering on the bottom of the PCB..

You will love the way this VP26/gar2520 combo sounds. !! :) :)

BTW.. your picts are very nice.

Best of luck



Re: Newbie builds Classic Audio Product's VP26
« Reply #4 on: November 09, 2010, 02:59:01 AM »
The Gar 2520 sounds great and is very reasonable price wise. I didn't have much trouble getting the pins straight. It's a little bit of a balancing act but no biggy. And they are excellent DOA's.

Nice pics on the Classic audio cards. I want six of them lol. But need another lunchbox...

Amateur experimenter


Re: Newbie builds Classic Audio Product's VP26
« Reply #5 on: November 12, 2010, 06:23:09 AM »
Built the "spare" gar2520.  If these vp26's sound as good as I gather on reviews, I will be wanting a bunch more, so the extra effort on more DOA's should not be wasted.  The build was easier the 2nd time through, and I noticed that many times, my photos on thread were a better reference than photos in the build manual (can see color bars and part numbers on components better).  But, I double checked everything with both references so I can triple check my 1st build as well as make sure the 2nd one was on track.  Hopefully, it all works.  VP312DI hopefully this weekend.

« Last Edit: November 12, 2010, 06:25:53 AM by chunger »
DIY photo documentaries consolidated here:


Re: Newbie builds Classic Audio Product's VP26
« Reply #6 on: November 12, 2010, 07:54:32 AM »
Wow, your photos look amazing! Puts my photos to shame  :(

Great build journey mate!

Tell us how it sounds when you finish building it.  :)
iva dunit formerly known as canidoit


Re: Newbie builds Classic Audio Product's VP26
« Reply #7 on: November 13, 2010, 03:06:04 AM »
Nice Job on #2 chunger.
Your pictures do look GREAT!! :)
Each one gets easer and easer.

Keep up the good work! :)

(but then I'm a bit biased ;D ;D)



Re: Newbie builds Classic Audio Product's VP26
« Reply #8 on: November 13, 2010, 05:41:36 AM »
OK. . . got to starting the VP312DI kit today.  There is no step-by-step assembly guide for this build, but a lot of critical build information is in the support thread here:

In conversations with Jeff, being new to electronics, he suggested I try the VP26 kit 1st before trying to tackle the VP312DI kit, so I did  ;D.  For this build, I'm hoping to catch and document all of the details required for an inexperienced builder like myself to get through it.

I purchased the VP312DI complete kit (51x version) from Jeff.  I also selected the APP2050E op amp option because I wanted to try running on the +-24V rails provided by the 51x rack.  I also purchased 3 of the modular DI kits to try out.  The IC kit, FET kit, and passive Pikatron transformer kit.  Due to cost, of the transformer, I opted out of the Jenson option for now.

After identifying generally how everything was organized in the baggies, I figured I should identify and sort parts first.  I grabbed my cheap multimeter and pulled up a capacitor ID chart as well as a resistor color code chart on my web browser and go busy sorting.  The bill of materials documents are organized by PCB, so I pulled up the PDF for the main board first.  The baggies that contained the DI kits seemed all self contained, so I set those aside for now.

I started with the diodes.  (note:I'm going to go ahead and apologize now for the size of some of the upcoming images.  I figure clarity trumps load time.  This forum does not seem to auto scale, so I will try to be cognizant of typical display resolutions.)  To organize, I used some 3x5 cards a pen, and some console tape.  I'm sure there are probably more efficient methods to be had, but this seemed like the thing to do at the time.

ok. . . I just realized I did not label CR7 (1N5243B) [top one in the above picture] on my card prior to shooting all my photos.  . . great.  Well, anyways, the markings on these things are absolutely minuscule and the clear body with contrasting internal colors does not help a bit.  What I wouldn't give for a macro lens right now. . .  >:( Here's what it looks like:


CR1 and CR2 (1N914) look like this:


CR3, CR4, CR5, and CR6 (1N4004) are much easier to identify

A few strips of console tape secure these diodes to the card for easy access later.

Next, I sorted my resistors checking both on multimeter and color code chart.  Hopefully I got these right.  Again, a piece of tape secures these to the card.

Next, I identified my electrolytic capacitors which was easy as they are all clearly marked in legible print.

And, a bit of tape to secure them.

And, same for the film and ceramic caps.  The markings on the blue caps are somewhat difficult to read, but not as hard as the diodes.  Hopefully I have posted with enough resolution to identify them in the pics.

C5 (.1uF) is marked like this:

And, I have  identified and sorted the parts for the main PCB.  A few components from teh baggies I opened are hanging out.  I think those will probably come into play on one or more of the smaller PCB's in the build.  But, for now:

« Last Edit: November 15, 2010, 02:51:41 AM by chunger »
DIY photo documentaries consolidated here:


Re: Newbie builds Classic Audio Product's VP26
« Reply #9 on: November 13, 2010, 09:39:28 AM »
I guess you will need to update your thread title!  :D

I can't say enough about the pics. It sounds like everyone agrees. Just killer.

The diodes pics I have thought about but don't think I could pull it off any where close to as well as you did. That is a great help for future people who build this DI preamp.

I must update my original help thread to point over hear.  8)

Fantastic Chunger!

Have fun, Jeff
For API style transformers and more cool DIY stuff:


Re: Newbie builds Classic Audio Product's VP26 and VP312DI
« Reply #10 on: November 14, 2010, 06:20:06 AM »
one more set of parts to sort before I can start sticking stuff together.  I figured out what those "extra" parts were.  I know it's one thing to have "extra parts" when you put your car back together, but I figured electronics is a different animal  ;D .  These are the parts for the "sub-DI" board:

CR1 and CR2 (1N5242B) look like this:


« Last Edit: November 14, 2010, 10:58:49 PM by chunger »
DIY photo documentaries consolidated here:


Re: Newbie builds Classic Audio Product's VP26 and VP312DI
« Reply #11 on: November 14, 2010, 06:38:21 AM »
Main board components are accounted for.  Following Jeff's pointers on the official support thread, I use 2 of the smaller PCB's as spacers for the output attenuator pot.

A bit of console tape helped me keep everything together so I could solder a couple of lugs.

I then found these standoffs, screws, and nuts to mount the main PCB onto the aluminum L bracket to test the fit before I solder more lugs.

I tighten down the rear standoffs to final torque.  They will not be coming back off if all goes according to plan.

The front ones go on loosely so the screws do not protrude above the standoff.  this is so you can slide the knobs through the front panel holes without interference.

the PCB should slide into the bracket and align with the standoffs like this:

The height of the pot in relation to the L bracket and the PCB looks good.

I then remove the PCB from the L bracket and solder all of the lugs on the output attenuator pot.  After this, I place the preamp gain pot but don't solder anything yet.

I re-assemble the PCB and L bracket again without soldering the preamp gain pot yet.

I assemble this time with the front panel to precisely align the preamp gain pot to the chassis prior to soldering.

Notice the spacing on the reveal between the L bracket and the front panel.  In all of these parts alignment procedures, I'm trying to make that small reveal at the top of the L bracket parallel with the front panel.

I am able to reach 3 lugs without much difficulty, so I solder those with the PCB/chassis assembled to lock in the position of the gain pot.

and, soldered in.

Then I take it apart again and solder the remaining lugs.

Voila!. . . are we done yet?

« Last Edit: November 15, 2010, 02:58:33 AM by chunger »
DIY photo documentaries consolidated here:


Re: Newbie builds Classic Audio Product's VP26 and VP312DI
« Reply #12 on: November 14, 2010, 06:54:43 AM »
Next, I install CR3, CR4, CR5, and CR6 because I need the cut-off legs from these diodes to mount the small DI sub-board to the main PCB.  Polarity matters when mounting the diodes.  Makes sure the end of the diode with the solid line corresponds with the little arrow mark on the PCB when mounting these.

The small DI sub-board goes here:

Per Jeff's notes in the support thread, I secure 3 corners first.  Except I did not populate the board prior to assembly.  I figured it would be easier to clamp without any components mounted, and a quick study of the board seemed to indicate I would not have any problems installing any necessary components after it is attached to the main PCB.

I used 2 clamps to ensure solid contact between the 2 boards prior to soldering.

. . . and corners are tacked in.

The rest of the appropriate holes are filled . . .

. . . and the 2 boards all soldered together.

After the boards are solidly attached, I set about populating the DI sub-board.

The 3 small toggle switches that control DI functions look like this:

They are a bit tricky to position for mounting.  I ended up securing them like this:

and then, I added a piece of tape to put some downward pressure on the main PCB so the switches pressed firmly against the PCB.

I then soldered only one of the main mount lugs on each of the switches so that fine adjustments could still be made to the final position.

Then, it was back to re-assembly to make sure everything was lining up still.

. . . and I decided I could reach all of the switch solder lugs with the chassis attached.  So that's how I soldered them in.

Jeff's notes said the pins for SW1 need to be trimmed to fit the small PCB that supports the 1/4" jack.

That small PCB goes here:

And the jack mounts like this. . .

Jeff's notes warned about the possibility of the PCB being longer than the jack housing, and mine was by a hair, so I used some 220 sandpaper on the table to grind down a little bit of the PCB's front edge.

. . . good to go.

I think I did the next set differently than described in the support thread, but it seemed to have worked out.  First, I placed the connector without soldering.

Then, I inserted the jack/PCB (also not yet soldered together) into the front panel hole at an angle. . . and then rotated the assembly into the connecting pins.

I then secured the nut for the DI jack to lock everything in place.

The way I saw it, I could reach all of the significant solder lugs from the outside with the PCB attached to the chassis and the jacks/pots attached to the faceplate.  I thought that would give me the best shot at perfect alignment of parts, so I soldered everything with the front panel attached.

Progress. . . all of the key front panel elements are now precisely aligned.  From building the VP26, I know the 3 push button switches have a lot of margin, so chances are, they will not be problematic if the rest of the pots and switches are aligned with the PCB, L bracket, and front panel reasonably well.

« Last Edit: November 30, 2010, 06:03:15 AM by chunger »
DIY photo documentaries consolidated here:


Re: Newbie builds Classic Audio Product's VP26 and VP312DI
« Reply #13 on: November 14, 2010, 08:21:29 PM »
Hi chunger

Please Please please take Newbie off the title of this thread...
You sir are a first class builder !! :) :)  All your work looks
Thanks for all the nice picts of your work as well.  I'm shure this will help lots
of guys and gals with their assembly.

Keep up the great work !!



Re: Newbie builds Classic Audio Product's VP26 and VP312DI
« Reply #14 on: November 14, 2010, 10:47:24 PM »
Up until my 2-312 D.I. builds, I had built 8 different Classicapi's pre's and 12 different op-amps all working first time without any problems. Jeff has great build instructions.
When I got the 312's, I figurered I knew how to build them and started with the diodes first, figuring they were all the same. Wrong. There are 3 different types and I must have tried reading them different 6 times. After figuring them out, all went well, and everything worked first time.
At that time there wasn't a lot of 312 D.I. build info. Your thread will help a lot of future 312 D.I. builders. Tip= when you finish soldering, take a tooth brush and some isopropyl alcohol (91-99%) and scrub those boards to remove any extra resin. Blot with a micro fine towel. It just makes them more pretty.


Re: Newbie builds Classic Audio Product's VP26 and VP312DI
« Reply #15 on: November 14, 2010, 11:22:06 PM »
Hi chunger

Please Please please take Newbie off the title of this thread...
You sir are a first class builder !! :) :)  

Hi Gary,  it would shock you how ignorant I am in the ways of electronics.  Sure, I can usually put something together (mechanically), but I can tell you right now that if something didn't go in right, or I burned a component on assembly, I wouldn't have the foggiest idea where to start tracing it down.  This is double incentive for me to get it right the 1st time  :o.  I'm hoping folks like you and Jeff are monitoring this thread for gross newbie errors like mis-reading the markings on a component, wrong polarity of a part that has been put in, or simply putting something in the wrong place.  The marking conventions are very foreign to me and even understanding the various broad categories of parts . . .. "electrolytic, ceramic, film, radial, etc."  All new to me.  I'd hate for someone to follow me off a cliff in their assembly because I did it wrong and have a beautiful picture of it being done totally wrong.

Well, on with the thread.  I actually finished the pre last night, but it was so late that I realized I would not be making much sense if I continued typing.  I'm weeding through ~250 images (many repeats to ensure sharp focus) to figure out which ones to post.  The documentation process is a drag the 1st time through, but I've needed to refer back to images plenty of times to trace down a mistake.  Plus, if this opens the door for other people (like me) to jump into DIY and the 51x platform.

Ok. . . where was I in the build? . .  . ah, I'm placing the mute, phantom power, and phase reverse buttons now.  These gave me grief on the VP26 because I didn't set them right the 1st time.  In hindsight, it would have been fine to just leave them as originally installed instead of re-heating and mechanically buggering the switches (pushing so hard the pins got pushed upwards in the housing. . . and then I had to re-heat and press them back down).  This time, I made sure the little plastic tabs were touching or darn close to touching the PCB before soldering anything.

And then, I only soldered in 1 pin on each connector at first. . .

. . . so I could re-assemble the PCB to the L bracket and faceplate to verify what I already knew would be the case. . . the buttons are sitting fine.  Well, the preamp looks all upside down, but besides that, everything is fine.   :P

« Last Edit: November 15, 2010, 03:08:31 AM by chunger »
DIY photo documentaries consolidated here:


Re: Newbie builds Classic Audio Product's VP26 and VP312DI
« Reply #16 on: November 14, 2010, 11:36:51 PM »
Next, I dis-assembled the preamp again and soldered up the push-button switch lugs.  Jeff recommended a soldering sequence in the VP26 manual, but I just made sure I jumped around like I was A.D.D. when soldering these in hopes of not overheating any single component.

At this point, I believe all of the mechanical components that can cause you grief in physical assembly if mis-aligned have been set.  So, I thought it would be a good time to start populating the main PCB.  I went with resistors first.  Since I had already pre-sorted my components, it was now a simple matter of locating the marked slot on the PCB and plucking he right part from my little 3x5 cards.  It's sometimes confusing when you don't have some sort of step-by-step instructions to figure out what to install first.  Everything on the PCB looks pretty accessible, but the reasoning behind my particular sequence was to start low on the PCB, and install those low components first. . . then, install higher and higher ones because the high components could potentially hinder me from reaching a lower component.

Then, my diodes. . . (Note:  polarity is important for diodes. . . each one will have a stripe on one side.  Make sure to align the stripe side of the diode with the little arrow marker on the PCB.)

Then, my ceramic capacitors.

For the ceramics, I ended up bending the leads outwards to secure the component and then soldered from the back side as opposed to from the front side for the resistors and diodes.

chop choppy.

I was trying to figure out how to keep the film capacitors from falling out of the PCB when I turned it over to solder, so this is what I ended up doing.

And, the film capacitors are in.

Then, the radial caps. . . each position on the PCB is marked + and - .  I made sure the vertical strip on the caps with the "-" sign in it aligned with the - terminal on the PCB for each of the Radial caps.  I hear this is important.

And again, like with the ceramic caps, I bend the leads to hold the radial caps in place to solder from the bottom.

« Last Edit: November 30, 2010, 06:07:43 AM by chunger »
DIY photo documentaries consolidated here:


Re: Newbie builds Classic Audio Product's VP26 and VP312DI
« Reply #17 on: November 14, 2010, 11:55:54 PM »
Next up... Poor Mans 670 (or other more intense build) hahah
A little bit of the sonic mayhem I bring to the table.....


Re: Newbie builds Classic Audio Product's VP26 and VP312DI
« Reply #18 on: November 14, 2010, 11:58:33 PM »
Next, I dumped out a pile of pretty little socket connectors for the op amp and DI plug-in modules.

Jeff's notes indicate that it's important to install all of these from the bottom side of the PCB.  Notice one of the holes does not require a socket.  This one does not have any markings next to it on the front side of the PCB because, well, I guess it doesn't have a function?

When soldering these little buggers, I turned up the heat on my soldering iron. . . (Note: I'm not sure this is a prudent thing to do, but those lugs looked hug and the pins have a lot of thermal mass).  I upped the juice to 380 degrees Celsius on my temp-regulated iron (that has stopped me from burning up a lot of bass guitar pots).  I head at the seam between the socket and the PCB lug and continue to apply heat until I see solder run down the PCB lug hole and feed quite a bit more solder through than I would a normal component.  I want to create a strong solder fillet on the front side and the back side of the PCB in one go so the sockets have no chance of slipping out as they will be mechanically stressed when inserting and removing modules.

And, this is how the front side looks keeping in mind this was 1 pass, meaning I didn't touch up any of the lugs from the front side because if I melt the solder, the socket would fall right out if soldering from the front side.  This ensures that there is solder within the full length of the PCB lug as well as on top and bottom.  Some are better than others because it's a blind process, but I made sure there was "something" on all of them.

Next, I installed the switches that toggle between 16V and 24V for the op amp and the DI module.  I'm so glad this design fully utilizes the 51x feature set!

And again, tape to the rescue to hold these on while I solder from the back side of the PCB.


« Last Edit: November 15, 2010, 03:12:10 AM by chunger »
DIY photo documentaries consolidated here:


Re: Newbie builds Classic Audio Product's VP26 and VP312DI
« Reply #19 on: November 14, 2010, 11:59:47 PM »
Next up... Poor Man   s 670 (or other more intense build) hahah

fixed it for you  ;D
DIY photo documentaries consolidated here:


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