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VP26 Stepped Rev C Pictorial Build Guide
MAKE SURE the build guide you follow matches the Revision of the PCB you are building!

Table of Contents
1. Information, Documents & Downloads
2. Parts Identification
    A. Resistors and Diodes
    B. Capacitors
    C. Hardware

3. The Crux Of The PCB Build
4. PCB & L-Bracket ~ Temporary Assembly
5. Transformer Install
6. Final Assembly
7. Preflight Testing
8. Discrete Opamp Install Tips
9. Copyright Notice and Disclaimer
 
1. Information, Documents & Downloads Back to Top
Preface
    The VP26 Stepped Rev C Pictorial Build Guide is written with the beginner to intermediate builder in mind. If you have some basic skills this is a fine kit to start with however I do recommend a pre-built opamp if this is your first complete module build attempt.

The VP25 and VP26 are extremely similar. In fact, the only difference is the output transformer. That said you can use either build guide to help you out since the VP25 is shown with Variable gain and the VP26 is shown with Stepped gain. Both build guides show the standard EA version and the optional Litz output transformer installed.

FYI, the VP312 is also extremely similar. It has a few less components so its a little easier than a VP25 or VP26!

BOM (Bill Of Materials)
  VP25-VP26 Rev C PCB BOM  [Last upload 3/17/2024]

PCB Overlay
  VP26 Rev C Overlay  [Last upload 1/24/2019]

Schematic
  VP26 Rev C Schematic  [Last upload 1/24/2019]

Support Thread
  VP26 Stepped Rev C [Build] support thread at groupdiy.com
 
2.A Parts Identification - Resistors and Diodes Back to Top
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2.A.0 The following resistors and diodes can be found in a pink antistatic bag inside the Main PCB bag.
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2.A.1 Use this Resistor Sorting Chart to help keep your parts straight.
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2.A.2 Properly identifying and sorting the resistors is very important. This task can be done many ways. If you wanna roll old school, click the pic to the left to download my Resistor Color Code Chart.
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2.A.3 The best way is to use a high quality DMM (digital multimeter) that has an Auto Range function.
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2.A.4 If your DMM has a Manual Range, make sure you have it set properly or you will get no reading or even a false reading.
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2.A.5 Note the different range settings used to identify the high value resistor.
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2.A.6 Once properly identified, all of the smaller resisters (and 1N4004 diodes) can be bent to .4" centers. The 1/2W 10R is .5" centers. A handy dandy Lead Forming Tool can really make this easy and make your project look neat and tidy!
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2.A.7 Fairchild 1N4004 diode, label is "1N4004"
 
2.B Parts Identification - Capacitors Back to Top
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2.B.0 The following capacitors can be found inside the Main PCB bag.
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2.B.1 Use this Capacitor Sorting Chart to help keep your parts straight.
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2.B.2 BC 27pF ceramic capacitor, label is "BC 27J"
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2.B.3 BC 82pF ceramic capacitor, label is "BC 82J"
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2.B.4 BC 220pF ceramic capacitor, label is "BC 221"
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2.B.5 BC 1000pF ceramic capacitor, label is "BC 102"
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2.B.6 WIMA 100pF ceramic capacitor, label is "WIMA 100/100-"
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2.B.7 Nichicon 47µF 25V radial electrolytic capacitor
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2.B.8 Nichicon 120µF 50V radial electrolytic capacitor
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2.B.9 Nichicon 330µF 16V radial electrolytic capacitor
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2.B.10 BC/Vishay 33µF 63V axial electrolytic capacitor
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2.B.11 BC/Vishay 470µF 10V axial electrolytic capacitor
 
2.C Parts Identification - Hardware Back to Top
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2.C.0 The small hardware bag can be found inside the Main PCB bag.
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2.C.1 Hardware bag contents.
 
3. The Crux Of The PCB Build Back to Top
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3.0 And we begin with a blank canvas.
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3.1a Identify and install the resistors for the stepped gain section of the PCB. The eleven RG resistors can be found in their own pink antistatic bag labelled "VP-Gainswitch Resistor Set". Bend the leads slightly over and solder only from the bottom of the PCB.
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3.1b Identify and install the 0.1% and 1% resistors for the main section of the PCB. Bend the leads slightly over and solder only from the bottom of the PCB.
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3.3 Install the protection diodes and the .5W resistor. Solder only from the bottom of the PCB.
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3.4 Install the small ceramic capacitors.
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3.5 Install the 100pF film capacitor.
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3.6 Prepare to install the two axial capacitors by familiarizing yourself with their positive and negative ends.
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3.6a Install both axial electrolytic capacitors.
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3.7a Install all radial electrolytic capacitors observing polarity.
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3.7b Double check to make sure they are all orientated with the correct polarity.
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3.7c DO NOT bridge the pads of C5 or C6!!
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3.8a Insert one of the six Mill-Max opamp sockets from the bottom of the PCB.
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3.8b Solder the socket. Rinse and repeat.
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3.8c Make sure there are no solder bridges between any of the sockets.
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3.8d No need to solder from the top. If the sockets are properly heated, a decent amount of solder will flow thru the plated thru holes.
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3.9a Start the installation of the three Toneluck pushbutton switches by soldering only two pins on each switch.
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3.9b Check the front of the switches to make sure they are sitting tight and flat to the PCB. Adjust as necessary.
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3.9c Check the back of the switches to make sure they are sitting tight and flat to the PCB. Adjust as necessary.
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3.9d Look across the plungers of the three switches making sure they are in a straight line with each other. Adjust as necessary.
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3.9e Solder the remaining pins in the order suggested. This should eliminate overheating of the switch innards.
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3.9f Install the pushbutton switch caps, black-white-black by using the rubber handle of a pliers or similar. Fingers will work but the tool is much easier.
 
4. PCB & L-Bracket ~ Temporary Assembly Back to Top
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4.0a This is the game plan for final fixing of the PCB to L-bracket although the lockwashers won't be utilized until final assembly.
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4.0b Install the four standoffs to the L-bracket with 3/16" undercut flat head screws. I use a nut driver on the standoffs which typically works so well that a screwdriver is not needed.
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4.1a Locate the Grayhill 1x12 rotary switch. Discard the lockwasher and put the nut to the side. Solder the wiper pin and the two outside switch deck pins.
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4.1b Check that the tan shroud is tight to the PCB on both sides. Heat the respective pin and adjust as necessary.
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4.1c Check that the body is parallel to the PCB. Heat the respective pin and adjust as necessary.
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4.1d Solder the remaining switch pins. When finished, double check with a magnifier to make sure you have no solder bridges.
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4.2a Locate the 3mm red LED and take note of the small spurs just below the body.
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4.2b Using needle nose pliers, take hold of both LED leads just below both of the spurs. Make sure the jaws of your pliers are parallel with the bottom of the LED's body.
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4.2c Make sure you have the anode/cathode orientation as shown here. By pushing on the LED's body, bend it over just below the spurs to a 90° angle.
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4.2d Trim the leads to no less than 3/8" from below the spurs.
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4.2e Insert the LED into the PCB holes.
DO NOT solder at this time!!
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4.3 Locate the Bourns attenuator potentiometer. Discard the lockwasher and put the nut to the side. Insert the Bourns t-pad attenuator into it's PCB position.
DO NOT solder at this time!!
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4.4a Slip the entire PCB assembly into position in the L-Bracket guiding the projecting components into their respective holes as needed.
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4.4b While slightly pushing the PCB assembly forward towards the L-bracket, mildly tighten the four 3/16" pan head screws to the standoffs. This is temporary so do not use lockwashers at this time.
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4.4c Adjust the t-pad to be centered in it's L-bracket hole and aligned flat against the L-bracket.
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4.5a Prepare a 1/4" and 3/8" socket for assembly use. I use console tape on the edges to not mar the faceplate finish. A deep well socket works the best.
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4.5b Slide the faceplate into position and hold in place with a rubber faced clamp. Align so pushbutton caps are centered in their holes.
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4.5c Make sure the edge of the faceplate is parallel to the edge of the L-bracket.
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4.5d Adjust the t-pad potentiometer fully tight to the L-bracket and finger snug the nut to the front panel.
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4.5e Be sure the t-pad's body from side to side is parallel to the PCB.
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4.5f Be sure the t-pad's body from front to back is parallel to the PCB. Lightly tighten the front panel nut with the taped up 3/8" socket. FYI, it is only temporary at this time.
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4.5g Adjust the Grayhill switch fully tight to the L-bracket and finger snug the nut to the front panel. Lightly tighten the front panel nut with the taped up 1/4" socket. FYI, it is only temporary at this time.
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4.6a Solder one of the LED leads at the top of the PCB. I use a small screwdriver to keep the LED fully seated into the faceplate hole until the solder sets. Next solder the 2nd LED lead.
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4.6b Solder all four of the Bourns t-pad mounting bracket pins at the top of the PCB. Be careful not to hit the pot body or other components while preforming this step.
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4.7a Remove the faceplate. Carefully remove the PCB assembly from the L-bracket. Solder and trim the LED leads.
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4.7b Solder all leads of the Bourns t-pad. Use an alternating pattern to not heat up the innards.
 
5. Transformer Install Back to Top
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5.1a Prep for install of the CA2622 transformer. This step can be improvised. I use a small piece of foam tape that is only stuck to the PCB not the transformer. The goal is to slightly elevate the bottom of the can so it does not short with any of the pads. Foam tape is not included with the kit.
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5.1b Insert the CA2622 into the PCB holes. The red dot on the label indicates pin #1 so match it up the the white dot on the PCB and the square #1 pad. Carefully adjust the pins if necessary.
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5.1c Install the CA2622. You can trim the pins after soldering if you want but its not required.
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5.1d Try and maintain an approximate 0.03" space between the bottom of the can and the PCB.
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5.2a Take note of the hardware layout for the output transformer installation.
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5.2b Insert the 3/4" screws thru the top of the transformer. While holding the screw heads with your fingers, turn the transformer over and slip a lockwasher over each screw.
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5.2c Lower the PCB over the transformer and place the 4-40 nuts onto the screws. Due to the nut size and proximity to the transformer bobbin, you will not be able to thread the nuts onto the screws.
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5.2d While securing the nuts with a pair of your fingers, carefully flip the entire assembly over. Use a small screwdriver to snug the screws while holding the nuts in place with your fingertips.

5.2d Fully tighten the transformer screws holding the nuts with a needle nose pliers or small wrench.

5.2e Cut, strip, tin and install the transformer leads. Save two of the cutoffs for the 48V toggle switch installation.
**Pro Tip: Measure twice, cut once.
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5.2f If you are building with the 2623-1-Litz output, use this pic as a color code cross reference.
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5.2g If you are building with the EA2623-1 output, its pretty straight forward. Red to RED, Orange to ORA etc.
 
6. Final Assembly Back to Top
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6.1a Cut two of the salvaged transformer leads into 1 5/8" long pieces. Strip approximately 3/16" from each end and tin with solder.
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6.1b Solder these wires to the #1 and 2 PCB pads for the 48V toggle switch.
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6.1c Secure PCB assembly to the L-bracket as done before. This time is permanent though so put a 4-40 lockwasher on each 3/16" pan head screw.
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6.1d Slip the faceplate into position and install the Grayhill switch nut using a 1/4" socket.
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6.1e Double check alignment over the pushbutton switch caps. Make sure the faceplate is parallel to the L-bracket. Install the t-pad's panel nut. Fully tighten both panel nuts.
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6.1f Prepare the 48V toggle switch by threading one of its panel nuts almost all the way down the bushing. Drop the lockwasher onto the bushing.
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6.1g Insert the 48V toggle into position and thread the remaining panel nut onto the bushing so it stops approximately flush with the top of the bushing leaving little to no thread exposed.
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6.1h Use the supplied toggle switch wrench to tighten the lower panel nut towards the panel. By using this method you will never need a tool against the front panel.
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6.1i Hold the body of the toggle with an appropriate wrench so the panel nut can be fully tightened.
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6.1j Insert the tinned wires into the solder lugs of the toggle. The wire from pad #1 goes to the lowest switch lug. The wire from pad #2 goes to the middle switch lug. Solder theses joints.
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6.2a Install the colored knob inserts.
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6.2b Use a pliers to turn the Grayhill switch five clicks in the CW direction. If you have not previously messed with it, this will put the switch in the 12:00 position. Use pliers to turn the t-pad shaft fully CCW.
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6.2c Install the CAPI control knobs. The attenuator knob pointer will be every so slightly past the 7:00 position as the total pot rotation is slightly under 270°. Semi tighten one of the set screws using a 1/16" hex wrench then rotate the knob fully CW to make sure it is even at both ends of the rotation. Once aligned, fully tighten both set screws.

For knob installation, the Grayhill gain knob will be pointing exactly to the 12:00 indication dot. Since the switch has twelve positions, min gain will be 7:00 and max gain will be pointing down to the "hidden" 6:00 position.
 
7. Preflight Testing Back to Top

7.0 Preflight tests will be preformed with the preamp not connected to a power source. Also, no discrete opamp should be installed. Use of a DMM set to measure resistance is required. If you are using a manual range DMM and not measuring any resistance during these section 7.0 tests, make sure you try all range settings. Anything well below a 200k Ω reading will require finding the source of the problem. A direct short is a real problem!

FYI, the below resistance measurements are specific to a VP25 or VP26 only! All other CAPI modules will yield different results.

7.0a Probe between the "-V" and "+V" sockets for the DOA.

Your reading should be a high resistance, over 200k Ω.

7.0b Probe between the "-V" and "C" sockets for the DOA.

Your reading should be a high resistance, over 200k Ω.

7.0c Probe between the "+V" and "C" sockets for the DOA.

Your reading should be a high resistance, over 200k Ω.

7.0d Probe between the "C" and "O"(Output) sockets for the DOA.

Your reading should be a high resistance, over 200k Ω.

7.0e Probe between the "+V" and "O"(Output) sockets for the DOA.

Your reading should be a high resistance, over 200k Ω.

7.0f Probe between the "-V" and "O"(Output) sockets for the DOA.

Your reading should be a high resistance, over 200k Ω.

7.1 The tests for section 7.1 will be preformed with the preamp connected to a power source. A 16V bipolar supply is recommended for 2520 style opamps. Still, no discrete opamp should be installed. Use of a DMM set to measure DC < 400V is required.

7.1a Probe between the "+V" and "C" sockets for the DOA.

Your reading should be approximately +15.3V DC. (This should be 0.7V less than your supply voltage due to the voltage drop over the 1N4004 protection diode.)

7.1b Probe between the "-V" and "C" sockets for the DOA.

Your reading should be approximately -15.3V DC. (This should be 0.7V less than your supply voltage due to the voltage drop over the 1N4004 protection diode.)
 
8. Discrete Opamp Install Tips Back to Top

8.0 The Mill-Max sockets are very stiff when they are virgin. So stiff that you may get the feeling you will break something if you keep pushing on your open or unpotted DOA. A properly seated DOA is very solid and will typically never come out even when the module is moved/turned around quite a bit.

A simple way to prep your virgin Mill-Max sockets can be accomplished with a small paperclip and a few minutes of time.
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8.1 Lets start by locating a small paperclip. The wire of a small paperclip will measure about .034" (.86mm) in diameter. The typical DOA pin is .04" (1mm) in diameter. You definitely want to make sure that the paperclip is a little smaller in diameter than the DOA pin. The tape is not necessary. It only demonstrates the depth the paperclip will travel in the socket. That's about .2" (5mm).
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8.2 Position your module flat in front of you on a desk or table. DO NOT HAVE A DC POWER SOURCE CONNECTED AT THIS TIME!! Insert the paperclip into each of the six Mill-Max sockets.
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8.3 You will insert the paperclip until it bottoms out inside the Mill-Max socket. Some significant force may be required. Don't worry. You will not hurt anything. Don't twist or turn the paperclip. Just insert it straight and then pull it out. Again, the paperclip will travel down about .2" (5mm).
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8.4 Once all of the sockets have been loosened up, it is time to install the discrete opamp. It is important to try your best to push down evenly to prevent bending over the Mill-Max pins on the DOA. Use your fingertips to push on the PCB, NOT ON THE COMPONENTS!!
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8.5 Continue putting even downward pressure on the DOA unit it will absolutely not go any further.
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8.6 When the DOA is properly fully seated, you will have approximately 3/16" (4.8mm) between the top of the main PCB and the bottom of the DOA PCB.
 
9. Copyright Notice and Disclaimer Back to Top
The contents of this assembly guide page, including but not limited to all text, photographs and diagrams, is the intellectual property of Classic Audio Products, Inc. Reproduction or re-publication by any means whatsoever, whether electronic, mechanical or electro-mechanical, is strictly prohibited under International Copyright laws. The sole purpose for this document is to aid in the assembly of the VP26 Stepped Rev C kit offered by Classic Audio Products, Inc. Commercial use is prohibited.
Classic Audio Products, Inc. is a DIY parts / kit retailer and provides no direct support for any of the products available on this site. Support for the kits can be found at the respective [Build] thread at groupdiy.com. Any support Classic Audio Products, Inc. chooses to provide, is provided "as is" without warranty of any kind. We cannot offer any guarantee as to the consequences of the support provided. Should the support cause damage or loss of any kind, Classic Audio Products, Inc. shall not be held liable to you or any other person for indirect, special, punitive, incidental, or consequential damages or losses. While the successful build rate is extremely high, there is no guaranteed favorable outcome. Always research and plan any project you undertake thoroughly. Sometimes, a project is over your head, and it just makes more sense to hire a qualified professional.
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Classic Audio Products, Inc. is not affiliated with API. Customers and fans should not refer to Classic Audio Products, Inc. as "Classic API." API is a registered trademark of Automated Processes Incorporated. Classic Audio Products, Inc. has no affiliation with Automated Processes Incorporated.
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