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Wiring and PCBs
#1
Hi Guys

I just posted the text below in a different thread but thought it should be here for more general viewing.

In the modern age of computerised PCB layout and overall design, it is very easy to eliminate all the wiring or very nearly so, but this means the whole amp or product is on one board. The chassis must have one panel that can be removed if one is to install or remove the card. It all looks good on the monitor and the assembly is quick, plus the board is complete so it can be tested prior to mounting in the chassis. Even though I am aware of the trap and know better, I have done this myself.

Wiring is the repair person's salvation provided it is done carefully.PCBs on the front panel, PCBs on the rear panel, maybe other PCBs for the PSU etc, wired to each other with generous lead lengths - service loops as they are historically known - allow smaller portions of circuitry to be dealt with more easily. It may end up that to replace a panel pot, say, one has to free all the front panel pots, but if this means you do not also have to free up the rear panel items or other things, then it is one step closer to being a breeze to service. Breaking the control and jack boards into yet smaller pieces makes it quicker still.

The other thing having some wiring does for you is to improve the reliability with regard to mechanical strain due to flexure of the chassis. Typically the pots, jacks and switches secure the PCB to the panel and there can be strain on the solder connections depending on how much overall support there is for the card. A further benefit to having some wiring and smaller PCBs is that each is mechanically only related to a small part of the chassis and therefore measurement and placement is less critical and tolerances of the chassis bends and dimensions is less critical. The reality is that everything is designed at once in the same software, so mechanical alignment will be as good as the chassis fabrication allows.

In the case of the PA66, the PCB is supported by metal standoffs, four around each power tube and three on the front-end. The tube socket leads are bent over for mechanical integrity prior to soldering. The preamp PCBs are similar with enough mounting positions over the length of the board. This is actually quite robust provided one takes the normal amount of care during tube insertion and extraction.
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#2
You've made some really insightful points about the practical advantages of incorporating some wiring in PCB design for easier servicing and overall reliability.

While the trend is certainly towards integrating everything on a single PCB to simplify assembly and reduce costs, there are definite trade-offs when it comes to repairability and durability. Your example of using "service loops" to create manageable sections for troubleshooting and replacement is a great one. It not only makes servicing easier but also allows for some mechanical flexibility that can prevent stress-related damage, especially in more dynamic environments or situations where physical access is a challenge.

The PA66 design you've described, with well-supported PCB standoffs and mechanically secured tube socket leads, sounds like a balanced approach between modern PCB design and practical serviceability. It's interesting to see how some traditional design principles, like the use of standoffs and careful soldering practices, still hold strong even in the face of more streamlined, integrated approaches.

Do you see these design considerations playing a bigger role as more products move toward miniaturization and integrated design?



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#3
Hello everyone

I believe your question is answered already?

The design trend towards the least costly solution favours elimination of wiring as that typically involves Human hands and Human effort and presumably too many Humans involved. The use of surface mounted components makes the overall PCB smaller and can make the overall size of equipment smaller, but not universally so.

For example, look at guitar pedals. Simple distortion or tone shaping pedals could always be made in the standard "single pedal width". Modern forms may use SM chips, resistors and caps but the overall size of the pedal remains much the same. A complicated digital reverb might have been built in a double-width chassis but now is single width using SM. The presence of surface mounted components practically shouts at one that "This unit is disposable". It is certainly an aggregious thing to attempt to repair!

A pedal is easy to manufacture without wiring but only if a specific chassis is used that allows the jacks to slide in and out vertically with the main PCB, or if multiple PCBs are used which snap together using board-to-board connectors. Given that connectors are on the spendy side and every piece of equipment is trying to eliminate them - look at computing devices and handhelds - the latter approach is unlikely in a guitar pedal.

Generally, wiring is only used where it is uneconomical NOT to have wiring. I believe the first post made that amply clear.

Cheerio
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