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Discussion in 'Shock Brother's DIY Amps' started by kleydejong, Jan 26, 2020.
These guys have been around a good while.
Agree with just about everything you said here. Your comment about bad quality boards and parts, and problems caused by parts mounted on-board that really shouldn't be, is exactly what the OP was asking about. I think PCB certainly can be done right (yours looks beautiful BTW), but when you're a manufacturer with an order of 100,000 and have a bottom line to chase, well, you know...
I etch my own PCBs at home for various pedals I've built, and using plain FeCl works very well and is negligible as an environmental hazard in pedal-sized one-off quantities (I even called up the local EPA years ago just to make sure). The only thing I regret is buying up a bargain stack of 8x12 copper-clad at a surplus shop and finding out that 35mil fiberglass board with bare-minimum copper foil is not really thick enough to condone reliability. It works, but don't try to repair the same part twice
One of these days I'm going to re-work my op-amp Big Muff clone...
Thank you very much for your input. I think this is some of what I'm looking for. I acknowledge a lot of the 'traditional' disadvantages. Amps made for cheap focused on cost saving, pain in the butt to work on, crappy quality, etc... But I feel like much of what you describe hits the nail on the head for me. I understand that PCB may not be best for everyone and every build. But I really feel like one can make design changes to overcome many of the traditional weaknesses.
First and foremost I appreciate you mentioning the process. I've been learning EAGLE and am aware of a few Chinese factories that accept the digital file EAGLE creates and will make and ship a PCB to me for a pretty reasonable price.
I have a few questions, if you don't mind.
1. Looks like you mount the tube sockets, filaments, and hardware off board just like a traditional eyelet/turret build. Have you experimented at all with mounting tube sockets and filaments on board? My thought is it may be easier for a pure beginner, but it would require extra design considerations. Tube sockets also pose a problem for mounting in 'typical' chassis. You'd probably need a custom chassis designed for that layout, no? What about supplementing your main component board with a tube socket converter board (think something like a pedal 3PDT switch board like: http://www.diyguitarpedals.com.au/shop/index.php?main_page=product_info&cPath=1&products_id=70. Like I said, I'm thinking about optimizing the experience for the pure beginner.
2. How do you think about grounding on your PCB? Most pedal PCB's I see establish the entire bottom as a ground plane with traces cut for signal flow as needed. In amp design I feel like ground requires a bit more thought and consideration. Even something like cutting some thick traces for a preamp ground and power amp ground. Preamp sends out to the input jack. Power amp sends out to the lock washer / nut on a PT leg.
3. Any thoughts on making PCB easier to maintain? What you pictured looks easy to maintain to me. Perhaps just as easy as a eyelet / turret board. Only thought is if you nuke a via / trace. Can you make the pads a little thicker?
I've not used onboard sockets, no. Initially, out of concern for durability. Having since spoken with builders who have been using PCB for years, I'm not at concerned. Seems as we might have guessed, a lot of the problems we see in the Blues Jr for example -- cracked solder joints at sockets and jacks -- have more to do with ultra low quality boards and soldering, less to do with the inherent nature of onboard components.
I agree it's easier in terms of paint-by-number, one thing you can't see in my pic are the offboard grid resistors, etc. I am still following traditional rules with respect to mounting grid resistors directly on the sockets (via terminal strips). So having 100% of the circuit onboard has its advantages...
I am still following traditional tube amp grounding practices on the PCB. It is not overly tedious to do so and I feel like it's the best way to guarantee the desired end results. I would love to just use ground planes (simpler) if I could be sure they wouldn't cause me problems. So I'm with you, go with what you know. Here's what my grounding looks like on that main board:
You can see there's a ground bus that runs down the middle of the board from the power board interconnect on the right, all the way to the left where there is a pad to connect to chassis. The little stray ground trace at the top-right is the only power amp grounding on this board. They ground the 1R test point resistors coming off the power tube cathodes.
Then the entire top layer of that 4-layer board is a copper pour, connected to the same chassis preamp grounding point. So the entire PCB is shielded between chassis and that top layer.
Well, I was surprised to find out that these boards we can get made in China (I use PCBWay) are much more durable than the mass-production stuff where traces lift up if you hit them with the iron too hot and/or too many times. On this small SMPS board I made, I put a 750F iron on the same trace dozens of times and there is no damage to pads or traces whatsoever. The most fragile part of the boards is the solder mask, it scratches off pretty easily. So, if that's what you were concerned with... you'll be relieved to see it's not such a problem. Also with thru-hole plating (standard on the boards we buy, non-standard on mass production!) you can solder to the top of the board if you like. This is a big damn deal! I have a Peavey Classic 30 on the bench right this moment, I can't replace the burned out resistor from the top of the board! Have to pull it.
Some maintenance-minded things I implemented:
- a separate power supply board that can be removed for service. While it can be argued that preamp power supply filter caps should be closer to the preamp, I chose to put all caps on one, separate board for future maintenance.
- axial electrolytics in cathode bypass positions, easily clipped out and replaced later
Some other ideas that I didn't implement:
- use axial caps on the main power supply board (they are being phased out by a lot of manufacturers, sans legacy purposes, so I'm resigned to designing for radial caps from now on)
- install turrets for axial electrolytics
- use molex connectors between main and power supply board / transformer leads
Other than that... so long as we can avoid ever having to pull that main board, I feel like we're good to go. Your thoughts?
I’ve broken copper leads on pedals. Building, repair, even big name brands (my Big Muff reissue used very cheap PCB, for example).
PCB still makes absolute sense in small pedals.
I don’t know, maybe there is a perception of a more rigorous life in the larger and heavier package of amps, rather than pedals. In car trunks, bounced around at gigs, borrowed by the next band, etc.
They’re furniture. Appliances.
For me, it’s about lifetime. I might mod a pedal once. Twice, and I know I might lose a PCB lead. But my amps I end up servicing (filter caps over the decades) or modding as my tastes evolve over the years. I want my amps to survive my awful soldering attempts (I have developed tremors and need to see a doc).
Just came across discussion regarding a super high quality PCB, a unifed Dumble board on .125" FR4. Dimensions are 450mm x 94mm (17.7" x 3.7").
It looks like this:
Your minimum order for a 2-layer board like this is 5pcs @ $225 shipped to USA, or $45 a board. At 10pcs you're at $30 a board. The per-board prices are not terrible compared to turret boards Hoffman can fabricate for you on same .125" thickness FR4. It's the MOQ that hurts. Not super practical for one-offs.
Again, this is just regarding fancy PCB orders. You can slow ship this same board on .0625" FR4 for 5pcs @ $87.
My 5e3 with a pcb is quieter than any other 5e3 I have ever heard-dont know why, nor care. Since I built it, I am pretty sure I can repair it. Worst to worst I can repopulate a new board in a evening- and enjoy the opportunity to have the task!