PCB vs matrix vs strip board for phono pre-amp

[ptheskil]

Ha ha. I never got a definitive answer from a bunch of engineers in my life! I'm gathering information here and then I'll make up my mind. Consult then decide rather than trying to reach consensus if you'll forgive a platitude. That's why I would like to try and understand the advice in the context of the physics that's going on. Physics or data will persuade me - hearsay or superstition won't.

Please, nobody take offense at the engineer comment as I would describe myself as one. There, I said it.

Looks like I'm gonna enjoy this forum.

[DF96]

Yes, lots of VHF/UHF mush around these days. I suspect it is partly responsible for the different sound of amps which according to pure audio measurements ought to sound similar.

[Speedskater]

Originally Posted by DF96

Yes, lots of VHF/UHF mush around these days. I suspect it is partly responsible for the different sound of amps which according to pure audio measurements ought to sound similar.

I think that you are exactly correct!

And has soon as you start hooking up test equipment or doing a A/B blind test the setup sitution changes and the interference changes.

[davidsrsb]

Think about supporting the board. One of the advantages of a real pcb is that it can be more compact and be properly mounted. A phono preamp can be a bit microphonic and will pick up vibration from loud music.

[marce]

Rather late, sorry, but other things are taking over my sanity at this time...
Here is a link to some Keith Armstron notes that are worth having a look at. There is a whole series of them (8 now I believe) that I have downloaded as PDF's so dont have all the links handy, this is probably the most pertinant :
EMC Compliance Club – Advanced PCB design and layout for EMC. Part 3 – PCB-to-chassis bonding
Using the follwoing search (changing the number at the end should lead to all the articles) that cover in detail screening, noise etc in both analogue and digital designs.
"Design Techniques for EMC – Part 1"
eg
EMC Compliance Club – Design Techniques for EMC Part 0 Introduction & Part 1 - Circuit Design and Choice of Components (SECOND PART)

[ptheskil]

Thanks marce. I found the paper on star vs multi-point grounding particularly interesting. I might try some experiments with that when I get round to the build. I am leaning towards a PCB with a decent ground plane; partly so I can experiment with single- vs multi-piont grounding and partly to minimise the problems of coupling VHF+ "mush".

DF96 and Speedskater, thanks for making that point. It makes sense to me to avoid stressing the circuit with any signals outside of the range of interest even if the products of the interaction themselves are inadudible or filtered from the output. That point alone justifies to me a carefully designed PCB. I still reckon that for immunity from audio frequency noise sources a careful layout on matrix/strip board and assembly within the enclosure would be sufficient.

If anybody else is following this here's a link to a top level page with index and access to the papers: EMC Information Centre (you will need to register)

[marce]

At the risk of being lynched, I am not a fan of star grounds or over complex grounding where too much thought has gone into trying to control return currents and grounds, every time I have seen a system where it has been 'optimised' for ground control, you get problems. Where systems are designed with a scheme more biased to a mesh ground (and where ground currents/returns) can make their own way home, you have less (if any) problems. To solve the problems with the former, you often see nice thick bits of wire tying two ground points together to alleviate the problem (creating a mesh ground). Star grounds can work on simple set ups, but as a system gets more complex, they have limitations and can make fault finding a nightmare. One of my favorite quotes referring to star grounds is:
"Ground leads and shields can cause plenty of trouble, and there is a lot of misunderstanding on this subject. The problem, in a nutshell, is that the currents you forgot about flowing through a ground line can generate a signal seen by another part of the circuit sharing the same ground. The technique of a ground "mecca" (a common point in the circuit to which all ground connections are tied) is often seen, but it's a crutch; with a little understanding of the problem you can handle most situations intelligently."

[indianajo]

Originally Posted by marce

At the risk of being lynched, I am not a fan of star grounds or over complex grounding where too much thought has gone into trying to control return currents and grounds, every time I have seen a system where it has been 'optimised' for ground control, you get problems.

I disagree with the above. I fought a hum & hiss war with my $15 op amp disco mixer and won a few battles. My system consists of steel case disco mixer as safety grounded hub, with power amp (floating) record player (floating) FM radio (floating) and CD player (floating). The record player tone arm is grounded to the disco mixer through the green wire. This star arrangement minimizes hum. I removed the RCA jacks from the steel case of the disco mixer and isolated them with rubber o-rings.
I also removed the AC power transformer from the disco mixer and moved it to the power strip as a wall transformer. This cut a lot of hum. The power switch was right next to the op amps. A separate box in the mixer for AC items might have helped, a la dynakit PAS2 preamp, but the wall transformer solution was cheaper and easier.
Against RF hash the disco mixer had 22 pf ceramic caps from RCA jack center to outside, but was still picking up CB'ers driving by and hash from the lamp dimmer in the next room. I used some chokes salvaged from PCAT power supplies on the power inputs to stop that. The whole hum hiss war is detailed here:www.diyaudio.com/forums/analog-line-level/164102-improving-disco-mixer-mid-fi-performance.html
The disco mixer had its own non-optimum ground plane PC board, but my next op amp project will use these: In the USA Circuit Boards within Project Accessories - MCM Electronics Category
In Europe Prototyping Boards
I do TO92 and leaded component prototyping on undrilled paper 1/16" electronic board I got at a yard sale, also for sale in sheets from mcmaster.com. I drill them myself with a hand crank drill. The glass reinforced stuff is a ***** to drill with steel drills, they really need carbide. I use turret board for tube stuff but they are really too big for transistor projects.
If you build up a prototype and then rebuild it using a custom PC board from a shop, let us know how you fair on the noise front. Most of the people contributing here seem to be rich enough to go right to custom manufactured board and pay for the several revisions. I'm experimenting on a complete shoestring, using garbage mostly, a few key active components and a lot of new electrolytic caps.

[marce]

Star grounds can work on simple set ups, but as a system gets more complex, they have limitations and can make fault finding a nightmare

Indianajo, i did also state the above. And most of our home systems are going to be quite simple, with only a few components joined together. Both my comments and the Tony Waldren links are to just inject a alternate view to what can be a pain, grounding a system. Every system is different, and every solution different. I was playing devils advocate a bit, but do think the differing views are worth looking at even if they are not
During the day I do PCB's for a variety of systems, most recently communications. We always use ground planes and max copper pours on the top and bottom layers, though where power outputs are involved, copper pours are used to get the current handling, but not full planes. The noise immunity of multilayer boards with planes is better than breadboarded, and due to the complexity we often go straight to PCB. How much difference this will make, to the final result is hard to quantify, our main concern is EMC and signal integrity, so the test the designs are subjected to are way over what we would be able to do at home, and the kit used way beyond most budgets.
What does happen though when a ground loop apears is the wire comes out and some strategicly placed wires help ease the symptoms, if not find a cure.
The big problem is when hooking up kit that we havn't made, such as headphones or similar, where w you have no controll over the connectivity.
Like you I have to do things on a budget, and try and get things when I have the funds.
As I said there will be hundreds that dont agree with me on star grounding as a universal panacea, but it does prompt some interesting debate.

[ptheskil]

OK, so this is where I have got to...

o Low frequency noise/hum will be dealt with by careful topology and screening.
o Final stage of PSU (regulators) will be on pre-amp boards - one board per channel.
o Individual regulators for each board fed from common PSU (capacitor smoothing and first order LPF filtered plus resistor damping for diode switching).
o I have decided to make all reasonable efforts to minimise effects of RFI for reasons stated above:
- capacitor filtering at enclosure boundaries
- unbroken copper ground plane with distributed grounding for each board
- electrically sealed enclosure as much as possible.

In terms of the original question (PCB vs matrix vs...) I have come across something called "dead bug construction". It seems to be referred to by a number of different names but I will be using the variant which builds off a continuous copper-clad board. I can pick up a ground point wherever I happen to be on the ground plane; I can keep path lengths really short; very compact construction; robust; gives me a decent ground plane without having to go through painful (and let's face it quite boring) PCB layout and prototyping; I can test parts of the circuit as I progress through the build...

What's not to like? Anyone got an argument against using "dead bug" construction for a phono pre-amp?