Installing The Resistors (and other axial components)

Resistors

The DIY500 utilizes many resistors, and a few other axial components (e.g. diodes, ceramic capacitors) of similar size and shape. Since these are the smallest, shortest, and most plentiful components used, we will make assembly easier by installing our resistors first.

Fig. 4 A pile of resistors, ceramic capacitor, and PCB on our slip mat.

These so-called axial components come to us with their leads (wire ends) sticking out of each side like the axle of a motor vehicle. On the DIY500 PCB, installation locations are indicated by a small printed rectangle with a metal plated hole at either side, and a component designation (e.g. “R8″) printed adjacent to it. The closely spaced vertical holes, which the component leads are inserted into to, indicate that we must bend the axial leads at a right angle such that they are pointing down and align with these two holes.

All holes are uniformly spaced 0.4″ apart, and we can bend the resistor leads roughly to length using our fingers (Fig. 5), or precisely to length using a graded component bending tool (Fig. 6).

Fig. 5 Bend resistor leads by gently pushing with your finger.

 or…

Fig. 6 Form leads to precisely 0.4" at 90˚ using a bending tool.

Once we have all of our resistors bent and separated by value (Fig. 7) it will be simple to insert them into the appropriate PCB locations. If you have a vice grip, you can use it to hold your PCB. If not, just hold the PCB in one hand and insert the resistors with your other hand.

Fig. 7 Bent axial components, ready to be installed.

We insert our axial components into the top layer of the PCB, which is screen printed  with the component designations in white (Fig. 8), but we (usually) want to solder them in place from the opposite (bottom) layer. Also, due to the effects of gravity and the long wire leads now poking out the bottom of each resistor mounting hole, sitting components may become easily displaced when setting down or turning over our PCB. To overcome these obstacles, we shall slightly bend outwards each components leads on the bottom layer while holding it flush against the PCB surface on the top layer, as shown in figures 9 and 10 below.

Fig. 8 Zero ohm (0 Ω) jumper resistors (shorts) installed in place of the optional protection diodes; D1, D2, and D3.

Fig. 9 Resistors installed from the top layer can fall out unless...

Figure 10. Exposed leads on the bottom PCB layer are bent outwards to hold components in place.

 

Once we have installed all of our tiny axial components in this fashion, we can lay the PCB face down on our work surface (or in a vice grip) and get ready to solder.

Fig. 11 With all axial components installed and held in place, place the PCB face down on your work surface.

Recalling proper soldering technique, proceed to carefully solder each joint in place (Fig. 12).

Fig. 12 Heat each joint (where the lead exits the hole) and flow solder onto it. Two hands are required.

Good solder joints flow from the lead into the hole and onto the surrounding plated area, forming a smooth reflective slope as shown in figure 13.

Fig. 13 Properly completed solder joints.

When you’re done with this stage of soldering, your PCB will look like figure 14.

Fig. 14 All axial components have been soldered in place.

Now it’s time to clip (shear) off all of the excess component leads. Beware these sharp little pieces of rigid wire being launched into the air once clipped! Eisen Audio does not want you to injure yourself, and recommends the following safety practices:

1. Wear safety goggles, and perhaps even safety gloves.
2. Point the bottom of the PCB (solder side) away from your face while clipping leads.
3. Gently place your finger over the lead(s) to be clipped, as this will block it from being launched into the air, but beware skin penetration! (Figures 15, 16)

Fig. 15 Clip leads close to the PCB, while (gently) guarding the excess portion with a finger tip.

Fig. 16 Clip all excess leads while holding the PCB away from your face.

 

Now your PCB will look like this (Fig. 17). Verify that you’ve installed all of the axial components in their appropriate locations, correlating with the list of values for your particular preamp configuration. If everything is okay, then it’s time to move on to the next step.

 

Fig. 17 All leads have been clipped just above the solder joint.

Fig. 18 All resistors and similar axial components have now been installed.

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