PCB Vs. PTP

[DetroitBlues]

Great article by Proguitarshop's Session guitarist Andy, can be found here:

 

http://proguitarshop.com/andyscorner/2011/04/04/pcb-vs-handwired/

 

PCB vs. HANDWIRED

Ah, the great debate. Which is superior, point-to-point hand wiring or PCB construction in guitar amplifiers. Welcome back to the Corner folks. This week we will address this subject and try to paint a picture of the pros and cons of each type of build to enable you to make a decision based on your specific needs. There are a few factors we will explore in this article, durability, noise, serviceability, and two of the most important factors tone and price.

 

What are PTP and PCB?

 

First, there may be some people that don’t know what PTP (point-to-point) wiring or PCB (printed circuit board) construction are so let’s dive in. PTP wiring is exactly what it sounds like; the point of contact for every component is wired directly to the point of contact for the following component on the shortest possible path. This can be accomplished a couple of ways, some amplifiers and effects have the components directly soldered to the next component in line via terminal strips with no sort of mounting for the components themselves, this is known as “true” point-to-point wiring and since the component usually spans most of the gap between connections, it is a very sturdy design. Another way to achieve PTP wiring is through the use of a turret or eyelet board. A turret board provides an inline plane for wiring circuits. Basically it’s not much different than the direct method but provides a more organized setup for the components and easier access to changing them out. In both cases, chassis mounted components (transformers, pots, tube sockets, jacks) are wired via flying leads (wires) directly to the component they interact with.

 

 

 

The PCB, though patented first around 1903, came into use, as we know them after WWII. The idea was to replace bulky tube radio wiring with a more compact solution. A PCB is a mounting board for electrical components that not only offers the electrical connection (solder pad) but also contains traces. Traces are copper pathways running throughout the board that actually make the electrical connections as opposed to having every component soldered directly to the next one in line. The PCB allows for any sort of component layout since the pathways are etched into it. Then whatever chassis mounted components are wired into the circuit. This design allows for more complex circuitry to be organized and utilized with less space than a PTP design. The first PCB’s were single sided, this means the traces were etched into only one side and the soldering took place on that side alone. With the introduction off more complex circuits, multi-layer PCB’s came about. These, commonly called through-hole, have multiple layers of traces completing even more complex paths in less space. This design also runs the solder all the way through the board to a solder pad on the top as well providing a more stable mount for components that is less prone to vibration damage or cracked solder.

 

 

 

Point-to-Point

 

First let’s look at the positive aspects of a PTP circuit. They are tough. The direct contact between components or the component and turret board are fairly large and in the case of “true” PTP the component leads are usually hooked around each other to form a solid connection, pre-solder. Once solder is applied, this is a sturdy connection that is resistant to vibration and ends up being very durable. Take apart an old Ampeg or Fender PTP amp and have a look. Guaranteed that in most cases, 90% or more of the solder joints are original. This means that joint has lasted 40+ years!

 

A PTP circuit also allows for the shortest possible paths between electrical connections. If a PTP circuit is designed correctly with the components and wiring properly placed, there will be a minimum of crosstalk and parasitic coupling that will affect the overall tone of the amp. If it is not designed correctly, there can be crosstalk, poor frequency response, and noise. PTP circuits more often than not resemble artwork, with carefully laid out wiring at precise right angles and perfect parallels with the shortest possible lengths of wire. This is not due to the fact that amp manufacturers take pride in their work (most of them do but this is beside the point). Yes, it is pretty but it also serves a purpose. Any two electrical conductors that run at different voltages produce some capacitance between them. This is the parasitic coupling mentioned above. Avoiding or minimizing this is paramount in amplifier design to keep the tone clean and responsive. Too much of this will result in loss at certain frequencies, most often noticed in the highs. The precise layout of the wiring in most amplifiers is specific to that amp to reduce this unwanted interference.

 

 

 

 

A PTP amp design is also more repair/mod friendly. Components can be de-soldered and swapped out with a minimum of effort without removing the turret board or terminal strip. Techs love PTP amps for this reason. If they are laid out well, it’s very easy to troubleshoot and repair as well as mod. Also, components can be removed and replaced multiple times without any degradation to the terminal strip or turret board. This is an important consideration for the avid amp modder or technician.

 

As with anything, there are some down sides to PTP design. A well-built PTP amp circuit is expensive in more ways than one. First they are expensive and time consuming to design well. A poorly designed PTP circuit can contain crisscrossing wires and parts that can lead to a ton of electronic anomalies. Next, they are more labor intensive, requiring highly skilled human hands to assemble instead of a machine. If the labor force is not skilled or properly trained an expensive design can turn into a nightmare of cold solder and improperly placed wiring, effectively nullifying the cost of the design in the first place. Both of these factors result in an increase in production cost and time. This illustrates our next point; this cost is passed to the consumer meaning PTP amps are expensive. A hand-wired version of an amp will probably cost 2-3 times more than a PCB version. A last strike against the PTP amps is weight. There are not many point-to-point tube amplifiers out there that are lightweight. This is a problem for some and not for others.

 

 

 

PCB

 

So this brings us to PCB designs. A good lot of guitar amp enthusiasts, hobbyists, aficionados, players, and all sorts will run from a PCB amp like it was the devil himself. There are a lot of theories out there like PCB amp sound sterile, PTP will always sound better, PCB traces cause capacitance between components, etc. Truth? Let’s take a look at the ups and downs of this design.

 

Let’s start with an important pro of PCB amps; they are less expensive to the consumer. A lot of builders will move to a PCB design in order to produce a model or two that is more affordable to the end user. They can be produced en masse and are populated and soldered by machines as opposed to people (mostly). This allows the builder to produce more amps with less overhead resulting in an overall price drop for the consumer.

 

A PCB amplifier normally will have a more uniform tone from amp to amp than will a PTP. A PTP design is built by hand and the wires tend to “float” some. This can cause changes in the ghost capacitance between conductors resulting in slight tonal variations from amp to amp (not always a bad thing but definitely a consideration). Another consideration is uniformity of solder joints. A PCB is soldered in production using a technique called wave soldering. This is a method of soldering all components at once and results in mechanically and electrically uniform couplings.

 

Now there are two different types of PCB layout, good and bad. Bad PCB layout is not as uncommon as we all wish and is the reason behind some of the “myths” between PCB and PTP. However, a PCB that is properly designed and built can sound every bit as good as a PTP layout and offer the uniformity from amp to amp. A solid PCB construction will usually have through-hole design with thicker than normal boards and traces. This results in a solid construction that is very reliable and hard to shake loose. Also, a well-designed PCB will normally be thicker (usually 1/8” thick is considered to be enough) and contain solidly etched traces that are beefy enough to handle the more current than is to be expected in the circuit. If the PCB is laid out well, the traces will be etched in such a way as to avoid parasitic coupling or ghost capacitance.

 

Now let’s address some of the downside of PCB designs. One important factor between good and bad PCB design is the chassis mounted components. In order to cut costs many companies have taken to mounting the jacks, tube sockets, and switches directly to the PCB itself instead of running wires to the PCB. This is a problem. Tube sockets mounted directly to the PCB will heat up and cool down the PCB with operation. Over time this causes the PCB to form small cracks that can lead to major issues down the road. Cheaper plastic jacks are usually used to mount directly to the PCB instead of the tougher metal ones found in most PTP amps. Due to the nature of amplifier input jacks and the abuse we as guitarists put them through, the plastic jacks often break sometimes taking part of the PCB with them.

 

In order for a PCB to be trouble and noise free, it requires a proper design layout. This involves laying out the components in some sort of order that makes sense but more importantly it involves laying out the traces to avoid the parasitic coupling we mentioned above. This is not as easy as it first may seem and requires a designer that is familiar with analog circuits. A lot of mass produced amplifiers will have an automated program that will layout the design of the board. Unfortunately, a lot of these programs are designed for digital circuits and don’t take into account the problems faced by an all-analog audio circuit. If the initial design is not done properly, the amp is doomed.

 

Lastly, PCB’s are normally made of glass-epoxy materials. As mentioned above, a nice thick board is desired but a lot of more affordable PCB based amplifiers will contain a board that is 1/16” thick and fairly large due to the trace layout. If the board is not mounted properly to the chassis with enough stress relief, vibration and movement can cause the board to develop cracks over time or even break in some extreme cases. Obviously this is not desirable. Once a board is broken, it’s done for. Sure there are technicians out there who will repair traces and get the amp working again, but once a PCB is damaged in this way, it needs to be replaced in order to have some sort of reliability again.

 

 

 

 

In conclusion, there are good and bad points to both designs. If a PCB based amplifier is properly designed, it can be every bit as sweet sounding as that vintage hand-wired job you have in the closet. With a thick PCB that has plenty of stress relief and plated through solder pads for the components, it is every bit as durable as a PTP build. In some ways a PTP build is superior and if you’re willing or able to pay the higher price for one then go for it. The lower cost of a circuit board build is attractive to most working musicians but a little research can go a long way when buying one in order to make sure the build quality isn’t shoddy and the amp isn’t noisy or dead sounding. As with higher priced item, talk to your friends and technicians about the amp you’re interested in. Try some out in your local store or at your buddy’s house and see what you really enjoy the sound of. Your friends and fellow players can give you a good sense of the quality of tone and a technician can be invaluable in determining build quality. No one wants an amp that lives in the shop. Thanks for reading and we’ll see you next time, in the Corner

[pegleg32]

Nice article DB, helps an ampidiot like myself understand some of the differences, and arguments, in construction methods.

[GuitArtMan]

"perfect parallels" - sorry but this is WHAT causes cross talk and interference NOT what avoids it. I laugh when I see those amps with everything bundled in parallel and those neat little "right angle" bends. Looks neat and pretty and every body goes "ooh... ahh..." but this is what causes cross talk, interference, and stray capacitance problems NOT what prevents it.

[GuitArtMan]

 

[kbp810]

 

I always get a kick out of seeing that!

[DetroitBlues]

That's funny! I didn't even catch that at first...

[JeffB]

But at the end of it all.........what does it sound like?

[kbp810]

But at the end of it all.........what does it sound like?

Exactly, thats the thing that matters the most in the end.

[DetroitBlues]

Exactly, thats the thing that matters the most in the end.

 

Its also why I got rid of my Peavey Valveking. While its a great sounding amp today, that doesn't mean it will remain sounding great in the future as the PCB might break down...

[jjkrause84]

I prefer PTP because it's pretty.....

 

 

To be honest, I REALLY like the idea tha tall my amps can and will last on this Earth MUCH longer than I will.

[ingeneri]

 

 

 

Duh, it just took me all afternoon to get this

[kbp810]

Thing is... a great well built amp is going to be a great well built amp, PCB or PTP... when it comes to readily replicating production amps (I'm trying to avoid saying mass producing, but that's what I'm leaning towards here), PCB can either be faster, or it can be faster and cheaper. If a builder is going PCB to be faster and cheaper, well then they are probably skimping elsewhere as well. Poor traces/layout, cheap components, wimpy solder joints, etc... it can all add up to a big sack of crap.

 

Conversely, PTP ain't always going to be so great either. Cold solder joints, poor layout and dress, inconsistency, etc... can also add up to a big sack of crap.

 

The only major advantage I see that PTP has over PCB, is perhaps a little more flexibility in modding and/or substituting/replacing components - as an example, say you want to swap some caps and the original PCB board is spaced for a small watt rated ceramic capacitor... you wanted to swap it with an orange drop (or similar), but it's just not going to fit in that pre-fabricated space. Of course, that's not to say a PTP builder will have always left you enough space in that same scenario, but seems like in most cases there's going to be a better chance of making it fit.

 

Just my 1 and 3/4 cents

[Steiner]

I have both kinds. Akin to KBP810's sentiment; I'm just looking for a happy ending and they give it to me.

[schundog]

I have both kinds. Akin to KBP810's sentiment; I'm just looking for a happy ending and they give it to me.

 

 

Agreed. Now, it's time-a to make-a da pizza....

 

[JeffB]

It really isnt even a consideration for me, though I guess hand soldered point to point wiring implies something special and unique if I stop to think about it. Like some one labored and toiled lovingly on the amp.

Chances are though, they are like me and do what ever crap they have to do to get through the day.

Heres an inside shot of my next amp, or rather the amp that is taking center point of my gaseous state.(its quite bad. Im thinking of selling stuff. Already have buyers lined up)

I have, and have had hand wired PTP amps. They were made that way because that was the technology of the day. They were good amps, so are my PCB amps. Wouldnt have bought any of them if they werent.

[Hfan]

Cool thread will read when I can, will say I have modded and refurbed pwa and point to point amps and the point to point are more fun to work on as an amateur. No traces melting on circuit boards no ribbon cable solder joints breaking. Tone wise not sure.

[Hfan]

Agreed. Now, it's time-a to make-a da pizza....

 

 

This gives me a headache..that looks like one of the machines that used to torture me ..I mean that I used to service

[mars_hall]

It really isnt even a consideration for me, though I guess hand soldered point to point wiring implies something special and unique if I stop to think about it. Like some one labored and toiled lovingly on the amp.

Chances are though, they are like me and do what ever crap they have to do to get through the day.

Heres an inside shot of my next amp, or rather the amp that is taking center point of my gaseous state.(its quite bad. Im thinking of selling stuff. Already have buyers lined up)

I have, and have had hand wired PTP amps. They were made that way because that was the technology of the day. They were good amps, so are my PCB amps. Wouldnt have bought any of them if they werent.

 

Looks like something straight out of Petaluma...

[DetroitBlues]

It really isnt even a consideration for me, though I guess hand soldered point to point wiring implies something special and unique if I stop to think about it. Like some one labored and toiled lovingly on the amp.

Chances are though, they are like me and do what ever crap they have to do to get through the day.

Heres an inside shot of my next amp, or rather the amp that is taking center point of my gaseous state.(its quite bad. Im thinking of selling stuff. Already have buyers lined up)

I have, and have had hand wired PTP amps. They were made that way because that was the technology of the day. They were good amps, so are my PCB amps. Wouldnt have bought any of them if they werent.

 

That's why I really like my KBP810 RD amp. Brian took the time to do everything right and check it along the way. He put the whole thing together and tested it to get any bugs out of it before delivering it to me. Its that kind of quality assurance I needed to make the choice to get an amp from him.

[nuke]

I always get a kick out of seeing that!

 

 

Yeah, it's good for a chuckle while I'm in there resoldering the tube-socket pins.....

[big bob]

Yeah, it's good for a chuckle while I'm in there resoldering the tube-socket pins.....

nothing like old school..

sound city 120

[DetroitBlues]

I'm always amazed at how complex the insides of amps are...

[Mr535]

Personally, I like PTP better. I think they simply SOUND better than their PCB counterparts. Not that PCBs sound bad or anything, but every PCB I've played, or even HEARD I don't COMEPLETELY LOVE the sound of. Even amps that I didn't know were PCB until reading it online on a forum, or whatever. There is always something they lack, that their vintage counterparts have.

 

Really, though, if your were to compare EXACTLY the same amp, with EXACTLY the same circuit PTP and PCB, I think MOST people probably would BARELY hear the difference. I'm, somply a tone freak, I think, hehe. I listen to different amps, guitars, pedals, etc. for hours, putting them through rigorous, carefully formulated tests to find THE BEST sound possible. Most people don't have the level of OTD (Obsessive Tone Disorder) that I have (probably) .

 

As for reliability, if it's WELL MADE PCB (like the VHT listed above), then I think it won't have any reliability problems. Maybe it won't last quite as long as PTP, but it should still last pretty long.