On my last build I mixed point to point with PCB layout. My preference is to build from schematics which can lead to, leads to a rather disorderly appearance at times. So for your viewing pleasure and debate as to the benefits and cons of Point to Point vs PCB and Layout Schemes, are the following examples.
I've used a Radio chassis AM/FM and an amp as examples. Both sounded just fine even though it looks like a veritable snakes nest. The Mcgohan amp was a PA of Old School design employing input transformers in front of the tubes. As a reminder keep in mind the RF in the multi-band radio would have a much easier time coupling to other components then audio signals.
Comments, jeers, observations?
silverfox.
Point to Point vs Layout PCB
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Point to Point vs Layout PCB
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Stevem
- Posts: 4614
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Re: Point to Point vs Layout PCB
The interactive capaccidences of circuit board traces laying next to each other, or even worse on top of each other on modern two sided boards wil always have some effect on a amps sound and or performance!
I have seen many a so called point to point rats nest of wires sound fantastic, and then as in vintage Hiwatt amps whose point to point wiring is near mind blowing neat suffer from the grounds being series strung and as such have 120 hz hum issues!
A cap meter testing out a circuit board for Ghost / fantom caps will quickly show you what I mean!
3 to 4 ghost cap readings in the PF range can make a otherwise great sounding amp have a nasal tone and a big drop in Sustane.
Others may tell Ya different, but the cap meter and your ears do not lie!
In short, give me the point to point rats nest any day over a circuit board and I will do some house keeping if need by to make it more pleasing to the eye!
I have seen many a so called point to point rats nest of wires sound fantastic, and then as in vintage Hiwatt amps whose point to point wiring is near mind blowing neat suffer from the grounds being series strung and as such have 120 hz hum issues!
A cap meter testing out a circuit board for Ghost / fantom caps will quickly show you what I mean!
3 to 4 ghost cap readings in the PF range can make a otherwise great sounding amp have a nasal tone and a big drop in Sustane.
Others may tell Ya different, but the cap meter and your ears do not lie!
In short, give me the point to point rats nest any day over a circuit board and I will do some house keeping if need by to make it more pleasing to the eye!
Last edited by Stevem on Sat Dec 27, 2014 1:07 pm, edited 2 times in total.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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JazzGuitarGimp
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Re: Point to Point vs Layout PCB
There are work arounds for the pcb approach. I have always been curious about alternate dielectrics. FR-4 is, of course, the most common, but Rogers is used for extremely high impedance circuits, though I don't know the specific numbers regarding stray capacitance. There may be other dielectrics available as well. It has been many, many years since a client has asked me to specify Rogers dielectric (the layout was for a gas chromatograph, as I recall) , but I am pretty sure it is still available.
Lou Rossi Designs
Printed Circuit Design & Layout,
and Schematic Capture
Printed Circuit Design & Layout,
and Schematic Capture
Re: Point to Point vs Layout PCB
SilverFox,
I also build from a schematic but I also do a lot of preplanning before I start to build. I do an actual size layout on a piece of paper with all the parts I will be using. My goal with this is not to create a 100% complete layout of every wire, but to see what will happen with the layout with transformers, tube sockets, pots, etc. located in X position and does this layout give me the cleanest, most direct route for the wires. There are always compromises to be made--if I move this part to make these wires shorter, then it makes those wires longer, etc. Based on experience (and common sense), I know that it's okay to have some wires longer but it would be better to keep some wires shorter (sensitive signal wires, for example).
If there was one overarching mindset to keep in mind when building an amp, it would be this: become totally "zen" with each wire and part you are installing. LOL, what da fork does that mean? It means there should never be a case where you just hook shit up with the idea that it will be okay to haphazardly run this wire willy-nilly and you will then make all the rest of the wires nice and neat and it will be okay. NOT! If you do this once, you will do it again, and again, and again. Rats nest.
Having said all that, I challenge anybody, in a blind listening/playing test, to hear the difference between a well-designed circuit board and a well-built point-to-point or turret board amp.
I also build from a schematic but I also do a lot of preplanning before I start to build. I do an actual size layout on a piece of paper with all the parts I will be using. My goal with this is not to create a 100% complete layout of every wire, but to see what will happen with the layout with transformers, tube sockets, pots, etc. located in X position and does this layout give me the cleanest, most direct route for the wires. There are always compromises to be made--if I move this part to make these wires shorter, then it makes those wires longer, etc. Based on experience (and common sense), I know that it's okay to have some wires longer but it would be better to keep some wires shorter (sensitive signal wires, for example).
If there was one overarching mindset to keep in mind when building an amp, it would be this: become totally "zen" with each wire and part you are installing. LOL, what da fork does that mean? It means there should never be a case where you just hook shit up with the idea that it will be okay to haphazardly run this wire willy-nilly and you will then make all the rest of the wires nice and neat and it will be okay. NOT! If you do this once, you will do it again, and again, and again. Rats nest.
Having said all that, I challenge anybody, in a blind listening/playing test, to hear the difference between a well-designed circuit board and a well-built point-to-point or turret board amp.
What?
Re: Point to Point vs Layout PCB
Here's some thoughts on this from about 14 years ago.
http://www.geofex.com/article_folders/p ... -to-pt.htm
A couple of salient points:
- PCBs have tiny parasitic capacitances. So do point to point layouts and tagboard layouts, and every other circuit technique. The devil is in the details of how much and what this does to the signal - if anything.
- The screaming advantage with PCBs is that you'll get nearly exactly the same parasitics every time. Not so with hand wired anything.
- PCBs are hard to mod well. Modders don't like them and consequently - being human - blame the problems on the PCB technology, not a lack of skill.
- Carelessly made PCB amps have been poorly done. That is not always the case, and not all hand-wired amps are well done, either. However, there are ways to do both of these well. But you have to know what you're doing.
http://www.geofex.com/article_folders/p ... -to-pt.htm
A couple of salient points:
- PCBs have tiny parasitic capacitances. So do point to point layouts and tagboard layouts, and every other circuit technique. The devil is in the details of how much and what this does to the signal - if anything.
- The screaming advantage with PCBs is that you'll get nearly exactly the same parasitics every time. Not so with hand wired anything.
- PCBs are hard to mod well. Modders don't like them and consequently - being human - blame the problems on the PCB technology, not a lack of skill.
- Carelessly made PCB amps have been poorly done. That is not always the case, and not all hand-wired amps are well done, either. However, there are ways to do both of these well. But you have to know what you're doing.
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schaublin65
- Posts: 88
- Joined: Sun Jul 08, 2012 11:59 am
- Location: Ireland
Re: Point to Point vs Layout PCB
Hi,
thanks for the link R.G. and thanks for writing your articles.
Your explanations were very helpful to me when I first found them.
take care..
John
thanks for the link R.G. and thanks for writing your articles.
Your explanations were very helpful to me when I first found them.
take care..
John
Re: Point to Point vs Layout PCB
Here's a pic that shows the difficulty in modding PCB circuits - this is a popular 18 watt PCB, with an FET source follower added.
I had to solder the wires on the legs of other components, and be very quick with the soldering iron.
If you build it and find a component is the wrong value, it's tough to remove and re-solder the component.
The best way (IMO) to handle this with PCBs is to use ribbon cables, molex strips, or other removeable wire harnesses, to allow the whole PCB to be flipped for servicing.
[img:684:523]http://i514.photobucket.com/albums/t346 ... attPCB.jpg[/img]
I had to solder the wires on the legs of other components, and be very quick with the soldering iron.
If you build it and find a component is the wrong value, it's tough to remove and re-solder the component.
The best way (IMO) to handle this with PCBs is to use ribbon cables, molex strips, or other removeable wire harnesses, to allow the whole PCB to be flipped for servicing.
[img:684:523]http://i514.photobucket.com/albums/t346 ... attPCB.jpg[/img]
Re: Point to Point vs Layout PCB
(deleted)
Last edited by matt h on Fri Mar 27, 2015 3:19 pm, edited 1 time in total.
Re: Point to Point vs Layout PCB
It seems like the red wire is the connection between the plate of the driving triode and the source follower, including a stopper.
The white wire is the B+ taken from the dropping resistor of the first two stages' node.
The blue wire is the signal going to the tonestack, but I can't understand why the ground wire goes to the gainpot grounding point.
The TO220 has a thermal resistance, junction to ambient, around 60 C/W.
Supposing 70 C inside the chassis, we have around 80 C before the maximum allowed temperature (even if I would stay way below).
Let's consider 100 C as a limit, we'll have half a watt as a limit.
With a B+ around 250 V and a source voltage around half that value, we'll have a limit of 4 mA before the need of an heat sink, that it's quite alot.
The white wire is the B+ taken from the dropping resistor of the first two stages' node.
The blue wire is the signal going to the tonestack, but I can't understand why the ground wire goes to the gainpot grounding point.
The TO220 has a thermal resistance, junction to ambient, around 60 C/W.
Supposing 70 C inside the chassis, we have around 80 C before the maximum allowed temperature (even if I would stay way below).
Let's consider 100 C as a limit, we'll have half a watt as a limit.
With a B+ around 250 V and a source voltage around half that value, we'll have a limit of 4 mA before the need of an heat sink, that it's quite alot.
Re: Point to Point vs Layout PCB
These very same issues would also apply to most PTP builds: You solder wires and components directly to wires, leads and rat's nests of other components. You have to be very quick with soldering iron, but in many cases there's so much thermal mass from the "blob" of components PTP'd together you can't. Components of wrong value are tough to remove and re-solder because they tend to adjoin 5 - 10 other components from the very same solder joint. In addition, the very same solder joint usually makes up half of the support for the said components. Etc.Ken Moon wrote:I had to solder the wires on the legs of other components, and be very quick with the soldering iron.
If you build it and find a component is the wrong value, it's tough to remove and re-solder the component.
It might be best practice for service / assembly. It might not be best practice considering overall performance or reliability. How much do you expect this thing to be on duty vs. on service desk anyway? If the thing gets 1000 hours of use, but the service is 1 hour more time consuming why is it such a big deal? How many amps actually do need fluent and quick repair on daily basis? Why?The best way (IMO) to handle this with PCBs is to use ribbon cables, molex strips, or other removeable wire harnesses, to allow the whole PCB to be flipped for servicing.
Re: Point to Point vs Layout PCB
If you have a pcb like this one, any mod or repairing is absolutely fast and easy.
[img:600:450]http://www.davideanastasia.com/blog/wp- ... 80_800.jpg[/img]
[img:600:450]http://www.davideanastasia.com/blog/wp- ... 80_800.jpg[/img]
Re: Point to Point vs Layout PCB
I like to use those little heatsinks as a way to mount any TO-220 device. It just holds it nicely in place. It doesn't get hot at all. (The gate stopper is 220R and the source-to-ground resistor is 100K.)matt h wrote:Out of curiosity, why did you bother heatsinking the source follower? Did you bias it extra crazy-hot or something?
I grounded the source follower to the pot because it was easy to solder it to the pot's solder lug, even though it made the ground wire a little long.
This PCB uses a signal ground, and a chassis ground which is connected at one point to the chassis, so I wanted to ground the SF to the signal ground, and not just to the nearest chassis ground.
Re: Point to Point vs Layout PCB
All good points, sir. Some of my own amps spend way too much time on the bench, and not nearly enough time rocking out. That's just the tinkerer in me...teemuk wrote:These very same issues would also apply to most PTP builds: You solder wires and components directly to wires, leads and rat's nests of other components. You have to be very quick with soldering iron, but in many cases there's so much thermal mass from the "blob" of components PTP'd together you can't. Components of wrong value are tough to remove and re-solder because they tend to adjoin 5 - 10 other components from the very same solder joint. In addition, the very same solder joint usually makes up half of the support for the said components. Etc.Ken Moon wrote:I had to solder the wires on the legs of other components, and be very quick with the soldering iron.
If you build it and find a component is the wrong value, it's tough to remove and re-solder the component.
It might be best practice for service / assembly. It might not be best practice considering overall performance or reliability. How much do you expect this thing to be on duty vs. on service desk anyway? If the thing gets 1000 hours of use, but the service is 1 hour more time consuming why is it such a big deal? How many amps actually do need fluent and quick repair on daily basis? Why?The best way (IMO) to handle this with PCBs is to use ribbon cables, molex strips, or other removeable wire harnesses, to allow the whole PCB to be flipped for servicing.