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Amplifier basics - point-to-point vs PCB vs surface-mount PCB. Plus Kit building

Xulonn

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#1
My 60-year interest in audio as a hobby is not based on seeking audio nirvana or the perfect sound, but rather a fascination with the incredibly wide range of electronics technologies and speaker designs that can reproduce music in a satisfying and often quite realistic manner. Although the proponents of various approaches and methods can often get into serious "food-fights," I have enjoyed the results of several approaches to high-fidelity audio.

While writing another post in an amplifiers evolution thread, I drifted off into a discussion of amplifier wiring methods and DIY projects of various levels. So I transferred that portion here and started this thread to discuss some of the myriad aspects of amplifier design, not from the aspect of differences in the electronic circuits, but related to the physical and mechanical aspects of assembly and interconnection of the internal electronic components that make up circuits. I will likely return here occasionally with a new andlg on the subject.

Disclaimer: I am not an electronics engineer, or even an electronics technician. However, I can solder, use a multimeter and oscilloscope, do a bit of crude metalwork, and have a very basic understanding of electronic circuits.

1960 to 1990 was a fascinating period of rapid audio amplifier design evolution that went from from point-to-point wired tube amps to "through-hole" printed circuit boards to surface-mount technology. Most consumer electronics amplifiers now use surface-mount designs, but in the audio enthusiast community, there are still many vacuum tube amplifiers being made that use - and often swear by - point-to-point wiring. Through-hole PCB designs are also still used for both tube and SS amplifiers.

In that other thread, I suggested that people check out a website - Vintage Audio Addict. It is dedicated to repairing and restoring 1960's-1980's vintage audio gear. The extensive collection of projects at Vintage Audio Addict includes the restoration of a Pioneer SX-1980, and the website shows what is inside this and other classic components. One fascinating aspect of his presentation style is the opportunity to observe the evolution of audio circuits from the first one - point-to-point wiring - to including one or more simple printed circuit boards, and then moving on to more modern-style complex, high component density PCBs. If you look at some of his projects, you can also see some of the different circuit implementation "styles" used by various manufacturers. The website is not a step-by-step how-to, but rather is shows a few interesting points for each project.

If you not an audiophile or audio hobbyist when you first arrive at ASR, and if you end up liking this place and hang around for a while, you are more than a typical consumer electronics customer and user. And if you don't know much about electronics and would like to learn a bit, you can hang out at ASR and follow some of the links that are posted in many threads. There are some great opportunities here to begin to learn a bit about what is on the inside of audio components.

If you decide to try a DIY audio project, I see three levels of amplifier-assembly:
  • From scratch or "barebone" kits (requires substantial skill and knowledge)
  • Component and/or module kits with anywhere from a little to a lot of soldering. Soldering point-to-point circuits can be complex and difficult unless you have the desire and patience to learn the skills. Positioning and soldering components on "through-hole" printed circuit boards can be easier than P-to-P wiring.
  • Easiest of all are the modern, ultra simple "screw together and snap together" kits such as like the Ghent/ICEPower or Hypex amplifier kits, or RaspberryPi+HiFiBerry computer/DAC kits.

I will be assembling a Ghent/ICEpower kit, the version with a bit of soldering, and also a "snap-Together" RaspberryPi/HifiBerry or similar kit in a couple of months. Expert DIY'ers make fun of those kits, and I agree that they do not contstitute "building" an amplifier or computer/DAC - but they can certainly save you a lot of money.

And don't hesitate to ask the experts here (not me) about what you are looking at in the interior of amplifiers and other audio components, because learning comes from asking questions - not coming from a perspective of cluelessness and then telling the experts what they should do.

Let's start this with three basic circuit styles. Point-to-point, which is still popular in modern vacuum tube amplifiers
Point-to-point.jpg

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Below is what appears to me to be a (1980's) single-layer "through-hole PCB - soldering on the bottom

Pioneer SX1980 Restoration.jpg

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And here is a modern surface-mount PCB - complex layout, likely multi-layer construction, tiny solder connections, and very difficult to hand-solder chip/component replacements. This particular board is the main board of a Teac A-H01 - a DAC/25wpcAmp. I bought one of these in 2012, and brought it with me when I moved to Panama, and it died six years later - it simply stopped working. My local electronics tech said that it needed a new main board, and Teac did not respond to my email inquiry - so I threw it in the trash. Experts, please correct me if I am wrong, but many modern amplifiers/DACs use complex boards like this that are not typically repairable in the field. I assume that "good" amplifier manufacturers replace boards for warranty repairs, and possibly return their more expensive boards to the PCB manufacturer/assembly people for repair when possible. I also assume that repair of older complex amplifier PCB's is often prohibitively expensive - if not impossible.
Teac A-H01 DAC-Amp.jpg

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Last, here is a variation of the "through-hole" PCB - what looks to me to be a double layer PCB. This is from a USB DAC + tube/SS hybrid amplifier ([email protected]Ω) that is available from Canada's Musical Paradise for $188 - a real bargain if it's as good as its owners report.

MP303 DAC-Amp.jpg
 

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Blumlein 88

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#2
I had an early VTL 75/75. It managed to connect everything with component leads. No wire, no PCB, some solder of course. Everything was point to point component leads except for about 4 inches leading from the rear RCA's to the middle of the amp. I've seen other tube amps that could have managed it, but used wiring looms instead.
 

March Audio

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#3
I had an early VTL 75/75. It managed to connect everything with component leads. No wire, no PCB, some solder of course. Everything was point to point component leads except for about 4 inches leading from the rear RCA's to the middle of the amp. I've seen other tube amps that could have managed it, but used wiring looms instead.
and now everything is practically invisible surface mount. Tweezers and magnifying glasses/microscope. Doesnt bode well for DIY, but I do have an inexpensive reflow oven (read toaster oven) for prototyping so it can be done.
 

Blumlein 88

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#4
and now everything is practically invisible surface mount. Tweezers and magnifying glasses/microscope. Doesnt bode well for DIY, but I do have a reflow oven for prototyping so it can be done.
It does bode well for DIY reflow oven's however. :)

 

somebodyelse

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#7
Experts, please correct me if I am wrong, but many modern amplifiers/DACs use complex boards like this that are not typically repairable in the field. I assume that "good" amplifier manufacturers replace boards for warranty repairs, and possibly return their more expensive boards to the PCB manufacturer/assembly people for repair when possible. I also assume that repair of older complex amplifier PCB's is often prohibitively expensive - if not impossible.
I'm not an expert, but I've done a few repairs over the years as a hobby, including a relatively recent class d guitar amp. The issue is often more economic than technical - for all but the most trivial faults or expensive boards it is more cost effective to find and replace the board containing the fault, or the entire unit, than it is to find and replace the faulty component if you're doing it on a commercial basis. If you're doing it as entertainment many things in the scrap bin are repairable. It's a lot easier if you can track down the service manual, assuming it exists. Having said that there are limits with components that can't be reliably reworked, anything that needs programming, bits that can't be bought and so on.
 

Wombat

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#8
When I was building tube guitar amps I used eyelet boards.

imagesGY9USHXN.jpg


Alternative to eyelets are turrets:

imagesGRJUC3ZD.jpg


I only built one simple tube amp using point-to-point(rats-nest arrangement) connections and moved on to the above method.

Once PCBs moved beyond single-sided I lost interest in working on SS ccts. SMDs fill me with horror. o_O
 
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sergeauckland

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#9
For DIY I prefer to use turrets/pins in matrix board, and hard-wire between the pins. That leaves reasonably long leads on the components I can attach scope probes to for testing. As most of my DIY builds are one-off, I don't need to make a PCB after the prototype, the prototype is the finished unit.

Most of what I repair is from the 70s and 80s, and so is single or double-sided PCBs, and so manageable. The few valve circuits I play with are mostly point-to point and they're a bit more difficult, as in those days it was standard practice to make a sound mechanical joint first, then solder over that. Unsoldering components wrapped round tag strips can be a pig, especially when there might be three resistors onto one tag, and they're all wrapped round. several components onto one tag of a valve base can also be 'interesting'. I've seldom come across valve circuits on PCBs, although the few I have tend to be thick paxolin single sided, so easy to deal with.

I too share a horror of SMD, especially chips with more pins than I can count, or those tiny little chip resistors. Fortunately, SMD equipment not tends to be pretty reliable, so don;t often have to get inside it, but when it does fail, it's either a throw-away item, or has to go back to the manufacturer for rework. Of greater concern in the long-term is the lack of service information as few manufacturers make circuit diagrams available, even on request, requiring stuff to go back to their service department. OK until the manufacturer goes bust or decides something's out of support and they both won't repair it themselves and won't make service information available.

S
 

sergeauckland

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#11
The wiring of these old circuits, with proper right-angle bends in the wires, and in some case cableformed using twine is a real pleasure to behold.

Back in the early 1970s, I worked for a company that employed two brothers as wiremen, wiring up the chassies for our audio routing switchers. They competed against each other to do the neatest wiring, and each one was a work of art. Every wire had to turn exactly at 90°, every tag had a bit of sleeving over it. All cableforms had the individual wires running parallel with no overlaps. Just lovely to look at.

S.
 

Xulonn

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#12
The wiring of these old circuits, with proper right-angle bends in the wires, and in some case cableformed using twine is a real pleasure to behold.
The first picture I posted - point-to-point wiring - represents my memories of they typical eagle's nest wiring of 1940s and 1950s radios and hi-fi gear. Below is a photo of a fairly recent Australian-made Melody 2A3 amplifier (one of the most beautiful tube amps I have ever seen). It is just as beautiful on the inside. Below that is an unknown guitar amp with precision wiring layout.
Melody 2a3 Wiring.jpg


Guitar Amp.jpg
 

mansr

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#13
I too share a horror of SMD, especially chips with more pins than I can count, or those tiny little chip resistors.
I'm the opposite. So many wonderful parts available as SMD. 0.5 mm pitch QFN allows for compact layout and is still a breeze to solder. I do think twice before using BGA, though.
 

restorer-john

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#14
----------------------------
Below is what appears to me to be a (1980's) single-layer "through-hole PCB - soldering on the bottom

That's actually a closeup of AWR-154, the regulated power supply and protection board for a Pioneer SX-1980 from 1978. Due to the placement of the power supply and the lack of air circulation, the series regulator transistors get very hot. Hot enough to char the board and de solder themselves.

Incidentally, it is the most powerful receiver Pioneer ever built at the end of the receiver wars of the 1970s. 270W+270W (tested [email protected]) per channel. Huge and heavy- 34kg. They regularly sell (restored) for US$3-6K and are a joy to own and operate.

Here's one I restored a little while back. This particular one was bought in the US, shipped to Australia in a crate, driven up from Melbourne to me and then collected a year later after restoration and driven back home. It's happily driving some monstrous JBLs to this day.

Waiting on a dolly for its turn on my bench:
DSC_0270 - Copy (Medium).jpeg


The same power supply board you pictured above:
DSC_0269 - Copy (Medium).jpeg

Partial dismantling:
DSC_0248 - Copy (Medium).jpeg

Output stage for one channel only:
DSC_0235 - Copy (Medium).jpeg


Without numerous PCBS and point to point wiring looms, this gigantic receiver could have never been built in the first place. Certain parts are no fun to work on, but he sheer substance and care of construction means that it can be repaired, rebuilt and continue to perform to spec 40+ years later.
 

LTig

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#15
[..]While writing another post in an amplifiers evolution thread, I drifted off into a discussion of amplifier wiring methods and DIY projects of various levels. [..]
Great post - just my 2 cents:
  • Point-to-point: only suited to very simple circuits or high voltage circuits (bigger distance)
  • Single or dual layer PCB: suited for complex circuits below ... say 500 Mhz (thumb rule just invented by me;))
  • Multi Layer PCB: required for circuits running at high speeds (up to several GHz) or high precision analog circuits. Both profit from being able to implement several different grounds or ground planes to reduce unwanted ground currents.
For DIY I use premanufactured double sided PCBs with through holes in 2.54 mm raster, see here an old photograph of the PCB (160 x 100 mm) of the MC phono preamp:

pre1-phono.jpg


You have to use wire to make the connections between the components. The advantage is that the resistance of wire is much lower than a similar wide track on a PCB, even when they are thicker.
 

JohnYang1997

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#18
I prefer pcb + 0805 (0402 to 1206) size resistor/ capacitor + soic spacing ics and through hole for power related. I won't use smd 220uF capacitor or diodes or i/o sockets for example. 1206 47uf smd cap is one of my favorite thing to use on a board.

I'm still afraid qfns, but anything with pins shouldn't be too bad. VSSOP is fine because it's easy to check for the connection. Bga tho that's a different level. I wouldn't trust myself using bga.
 

Soniclife

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#19
Of greater concern in the long-term is the lack of service information as few manufacturers make circuit diagrams available, even on request, requiring stuff to go back to their service department. OK until the manufacturer goes bust or decides something's out of support and they both won't repair it themselves and won't make service information available.
Is this going to be addressed in any of the right to repair legislation that get's talked about?
 

somebodyelse

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#20
Is this going to be addressed in any of the right to repair legislation that get's talked about?
Unlikely from what I've seen - it's more aimed at those actively obstructing 3rd party repair like Apple and John Deere.

I'd also worry about anything containing software and a network connection of any sort - how long will they provide security updates, and how long will the advertised feature set continue working?
 

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