EC8010:
>Even better, switch the auto-router off and take the time to work out a layout that doesn't need more than one layer. One layer per power supply (and 0V) is nice, but shouldn't really be necessary for an analogue power amplifier.<
Although I agree that in many cases it is better to avoid the auto-router like the plague, designing for one layer only isn't a worthwhile priority, IMO. Although my circuits tend to be fairly complex affairs as far as audio designs go, usually there will be circuit nodes that benefit from the impedance control to be gained by intimate proximity to a ground or power plane. If parasitic capacitances are detrimental to a given circuit node, open the ground or power plane in that locale only.
Compared to designing 2-dimensionally with a single-layer PCB, designing quasi 3dimensionally with a multi-layer PCB is far more likely to get you a compact circuit that has smaller antenna area and therefore less sensitivity to RF pickup. Besides, 4 or more-layer PCBs allow you to do various tricks that would be impossible with a double-sided or single-sided PCB, unless you don't mind _lots_ of jumpers (been there, done that).
That circuit may not _need_ more than one layer, but it will probably measure and sound better with a more sophisticated board design.
SY:
>What do you think the tradeoffs are between ground planes and putting some bandwidth limiting at the input to keep the RF out in the first place?<
I do both.
hth, jonathan carr
>Even better, switch the auto-router off and take the time to work out a layout that doesn't need more than one layer. One layer per power supply (and 0V) is nice, but shouldn't really be necessary for an analogue power amplifier.<
Although I agree that in many cases it is better to avoid the auto-router like the plague, designing for one layer only isn't a worthwhile priority, IMO. Although my circuits tend to be fairly complex affairs as far as audio designs go, usually there will be circuit nodes that benefit from the impedance control to be gained by intimate proximity to a ground or power plane. If parasitic capacitances are detrimental to a given circuit node, open the ground or power plane in that locale only.
Compared to designing 2-dimensionally with a single-layer PCB, designing quasi 3dimensionally with a multi-layer PCB is far more likely to get you a compact circuit that has smaller antenna area and therefore less sensitivity to RF pickup. Besides, 4 or more-layer PCBs allow you to do various tricks that would be impossible with a double-sided or single-sided PCB, unless you don't mind _lots_ of jumpers (been there, done that).
That circuit may not _need_ more than one layer, but it will probably measure and sound better with a more sophisticated board design.
SY:
>What do you think the tradeoffs are between ground planes and putting some bandwidth limiting at the input to keep the RF out in the first place?<
I do both.
hth, jonathan carr
I have had a chance to review a lot of designs at the PCB level. There are many many cases where a GROUND PLANE IS NOT a good idea, especially for audio circuity. When you have a ground plane, you have very little control over where the current flows, hence you can get current flow from your high current outputs into your low level inputs. In almost all cases for analog design, a very careful layout of traces (of appropriate widths), will result in a better layout than just pouring a plane.
Digital of course is a whole nother matter where the primary goal is power supply stability at the IC pins, controlling impedances, etc.
Of note, improper use of power and ground planes can even contribute to radiated noise.
Alvaius
Digital of course is a whole nother matter where the primary goal is power supply stability at the IC pins, controlling impedances, etc.
Of note, improper use of power and ground planes can even contribute to radiated noise.
Alvaius
One thing I have noticed in a lot of commercial designs is poor power supply design. They can almost always use improvements. All too often, the supply caps are too small, the bridges can't handle enough current, and mosfets aren't able to dissapate enough power. 90% of the amplifier and electronic repairs I do are power supply related. I have seen more power supply caps that have exploded than I can count.
One thing we can learn from this is to try and engineer everything to handle any power load we may throw at it. I like to over-engineer my power supplies if I can. For example......Use caps that can handle higher voltages than the circuit needs. This will help if you have any power surges or unusually high current draws from your supply. This goes for the rectifiers as well. Go ahead and use rectifiers that are over rated for your aplication.
These are just my thoughts on the subject. I hope this helps.
Cheers,
Zach
One thing we can learn from this is to try and engineer everything to handle any power load we may throw at it. I like to over-engineer my power supplies if I can. For example......Use caps that can handle higher voltages than the circuit needs. This will help if you have any power surges or unusually high current draws from your supply. This goes for the rectifiers as well. Go ahead and use rectifiers that are over rated for your aplication.
These are just my thoughts on the subject. I hope this helps.
Cheers,
Zach
The thing to note here is that there are two grounds: signal ground and power ground. Don't mix them up, and you'll avoid this problem. Inevitably they need to get connected electrically, but this should be done at a single point on the board, away from heavy current paths. It is still possible to have a star point with copper floods on the board (and you aren't limited to just one).
On another point, one of the constraints (money) often makes it impossible to have multiple development iterations of boards, so we try to do it best first time around. An inexperienced builder, could be forced into overcomplicating the design because of trying to get all the best goodies in at once. Rule here is to keep it simple, and grow slowly, steadily gaining confidence (OK, I know I'm just repeating here what someone said above...)
Jonathan,
thanks for the links. I had already read nr. 2, that's a good one.
I just has a brief look at the first one, and it seems quite
useful too.
I am afraid your japanese texts wouldn't be of much help to me.
Although I did take a short course in Japanese a few years ago,
just out of curiosity about the language, I didn't get very far
and I don't remember more than a few useful phrases like
"watashi no atarashi jidoosha akai"
(which I probably
don't remember correctly anyway and besides, my jidoosha
is shiro not akai). It's an interesting language,
though, which I wouldn't mind learning more about if I only
had the time.
thanks for the links. I had already read nr. 2, that's a good one.
I just has a brief look at the first one, and it seems quite
useful too.
I am afraid your japanese texts wouldn't be of much help to me.
Although I did take a short course in Japanese a few years ago,
just out of curiosity about the language, I didn't get very far
and I don't remember more than a few useful phrases like
"watashi no atarashi jidoosha akai"
(which I probablydon't remember correctly anyway and besides, my jidoosha
is shiro not akai). It's an interesting language,
though, which I wouldn't mind learning more about if I only
had the time.
Alvaius:
>When you have a ground plane, you have very little control over where the current flows<
On the contrary, it is feasible to analyze the grounding and locate the circuit nodes that tie into the grounds in a manner that allows for rather well-controlled ground currents.
>hence you can get current flow from your high current outputs into your low level inputs.<
The most basic precaution that you can take is to keep the power and signal grounds separate and tie them together only at one point. With multilayer circuit boards, it is just as easy to star planes as it is traces.
>In almost all cases for analog design, a very careful layout of traces (of appropriate widths), will result in a better layout than just pouring a plane.<
Naturally, the designer should study, measure and think carefully before he does anything. "Just do it" isn't good enough. For low frequency applications, starring traces is usually sufficient, but for wider bandwidth designs, I would recommend starred planes, or combining starred traces and planes.
My designs also incorporate active grounding (discrete circuits which accomplish similar functions as the TLE2426), which allows me to take care of many grounding requirements while simplifying the currents flowing in the grounds.
>Of note, improper use of power and ground planes can even contribute to radiated noise.<
No doubt. Incompetent use of anything can cause problems, but more often than not, the problem lies with the designer, not his tools.
hth, jonathan carr
>When you have a ground plane, you have very little control over where the current flows<
On the contrary, it is feasible to analyze the grounding and locate the circuit nodes that tie into the grounds in a manner that allows for rather well-controlled ground currents.
>hence you can get current flow from your high current outputs into your low level inputs.<
The most basic precaution that you can take is to keep the power and signal grounds separate and tie them together only at one point. With multilayer circuit boards, it is just as easy to star planes as it is traces.
>In almost all cases for analog design, a very careful layout of traces (of appropriate widths), will result in a better layout than just pouring a plane.<
Naturally, the designer should study, measure and think carefully before he does anything. "Just do it" isn't good enough. For low frequency applications, starring traces is usually sufficient, but for wider bandwidth designs, I would recommend starred planes, or combining starred traces and planes.
My designs also incorporate active grounding (discrete circuits which accomplish similar functions as the TLE2426), which allows me to take care of many grounding requirements while simplifying the currents flowing in the grounds.
>Of note, improper use of power and ground planes can even contribute to radiated noise.<
No doubt. Incompetent use of anything can cause problems, but more often than not, the problem lies with the designer, not his tools.
hth, jonathan carr
Sy:
>Would you say that there are advantages, other than consistency unit-to-unit, to using a PC board as opposed to point-to-point?<
Oh yes. Planes and striplines in P2P are an iffy proposition at best. And multilayer PCBs allow you to deal with relatively complex circuitry that would drive you batty if you ever attempted them in P2P.
But PCBs also have drawbacks, including problems with high-impedance nodes and leakage currents, and only two surfaces for installing parts. This is why in my own designs, multilayer PCB layouts with comprehensive ground and power planing serve as the foundations, but these are then augmented with component and board stacking, localized P2P, guard rings, floating isolater pads, teflon-insulated standoffs, clover-leaf terminals, and various other structural go-faster tricks.
regards, jonathan carr
>Would you say that there are advantages, other than consistency unit-to-unit, to using a PC board as opposed to point-to-point?<
Oh yes. Planes and striplines in P2P are an iffy proposition at best
. And multilayer PCBs allow you to deal with relatively complex circuitry that would drive you batty if you ever attempted them in P2P.But PCBs also have drawbacks, including problems with high-impedance nodes and leakage currents, and only two surfaces for installing parts. This is why in my own designs, multilayer PCB layouts with comprehensive ground and power planing serve as the foundations, but these are then augmented with component and board stacking, localized P2P, guard rings, floating isolater pads, teflon-insulated standoffs, clover-leaf terminals, and various other structural go-faster tricks.
regards, jonathan carr
Most DIY'ers (and Pro's) mostly SS I think fall short in the PSU department. Using SS diodes with huge caps right behind them.
http://www.nutshellhifi.com/library/Tube_Fest_Talk2.html (bottom part)
I am assuming that Lynn Olson is right here. And my gut says he is.
Cheers,
Bas
http://www.nutshellhifi.com/library/Tube_Fest_Talk2.html (bottom part)
I am assuming that Lynn Olson is right here. And my gut says he is.
Cheers,
Bas
PCBs
jcarr, what I was getting at, in espousing single-layer boards, is that many PCBs have longer, more convoluted tracks, and links than necessary, but single-layer design forces you to think hard. Of course, from a point of view of design efficiency, the time required to achieve an ideal design is not worthwhile - there's a parallel here with computer code.
SY, aren't input filtering and ground planes two different issues? Ground planes help us to avoid local noise, and input filtering assumes that we picked up noise on the incoming cable.
In case anyone here thinks I'm in the business of teaching grandparents to suck eggs, I only stuck my oar in because I've had disappointments caused by "professional" PCB designers. The best example was when I allowed my boss to persuade me to let a PCB designer take my circuit and implement it. The (digital) circuit compared the timing of two video signals in three stages of severity. It worked on breadboard (even the 4.43MHz phase comparator), and it worked on wirewrap. The first PCB couldn't even manage the middle stage test. (The electrical connections were fine, and it matched the circuit diagram, but the poor layout stopped it.)
Everyone else has now said all I want to say about PCBs. Good layout is an art, and is driven by many (and conflicting) rules.
jcarr, what I was getting at, in espousing single-layer boards, is that many PCBs have longer, more convoluted tracks, and links than necessary, but single-layer design forces you to think hard. Of course, from a point of view of design efficiency, the time required to achieve an ideal design is not worthwhile - there's a parallel here with computer code.
SY, aren't input filtering and ground planes two different issues? Ground planes help us to avoid local noise, and input filtering assumes that we picked up noise on the incoming cable.
In case anyone here thinks I'm in the business of teaching grandparents to suck eggs, I only stuck my oar in because I've had disappointments caused by "professional" PCB designers. The best example was when I allowed my boss to persuade me to let a PCB designer take my circuit and implement it. The (digital) circuit compared the timing of two video signals in three stages of severity. It worked on breadboard (even the 4.43MHz phase comparator), and it worked on wirewrap. The first PCB couldn't even manage the middle stage test. (The electrical connections were fine, and it matched the circuit diagram, but the poor layout stopped it.)
Everyone else has now said all I want to say about PCBs. Good layout is an art, and is driven by many (and conflicting) rules.
Ground is ground, right???
A ground plane can turn out to be good antenna, both for transmitting and receiving.
Biggest problem that we ever had, was filter caps. They all sound different, different enough to really screw up an amp if you pick the wrong ones. Too big, or too small, can mess things up. Even picking the wrong style can be a mess.
We never had enough time, or money, to source every possible type available. Sometimes the best ones were not availble unless we bought more than we could use.
Wish I could give a definite answer on how to do that, but that was one problem we never had a handle on. Each amp also sounded different depending on topology and transformer, so what we learned on a previous product didn't necessarily hold true for the next.
Jocko
A ground plane can turn out to be good antenna, both for transmitting and receiving.
Biggest problem that we ever had, was filter caps. They all sound different, different enough to really screw up an amp if you pick the wrong ones. Too big, or too small, can mess things up. Even picking the wrong style can be a mess.
We never had enough time, or money, to source every possible type available. Sometimes the best ones were not availble unless we bought more than we could use.
Wish I could give a definite answer on how to do that, but that was one problem we never had a handle on. Each amp also sounded different depending on topology and transformer, so what we learned on a previous product didn't necessarily hold true for the next.
Jocko
The Weakest Link
Any design is only ever going to be as good as it's weakest link, and it's therefore impossible to make generalisations.
I agree though with everything Jonathan has said. In audio details matter, a lot.
So many problems are simply a matter of assuming that it doesn't matter, when in fact were you to perform an error budget and work it out, it often does. Bear in mind errors occur in many domains too.
Tiny errors, in the order of uV make differences, much of audio is simply about reducing errors, so reading about precision design (which is often of a DC nature) then applying it to AC design makes for big differences.
No magic PCB or universal panacea applies, but to really be sure of the improvements you make stick with a design and find it's limits / limitations.
So many here build a multitude of different circuits / topologies but never optimise any. Build a design, listen, measure then build another.
Now you can iteratively improve the design, always with reference to the last. It's time consuming, but really worth the input in my experience, and you always have a reference to refer to - none of those 'I think it's better' changes.
You will be astonished with the magnitude of improvements you can get from this approach, but choose the initial design carefully, some are VERY hard to get working properly.
Final tip - ignore most of the published audio reference work, it will tell you far less than a good detailed scout through the semi-manufacturers online (and free) libraries. There's a few exceptions to the above, but not many.
Above all have fun, when you get it right, there's no better feeling in the world (and it will also give you far greater insight into the price tags charged by comercial companies too - there's a lot of labour involved in good audio design).
Andy.
P.S. the current flows in a ground plane are highly predictable - remember current flows in loops - analysing those loops is a crucial bit to getting it right.
Any design is only ever going to be as good as it's weakest link, and it's therefore impossible to make generalisations.
I agree though with everything Jonathan has said. In audio details matter, a lot.
So many problems are simply a matter of assuming that it doesn't matter, when in fact were you to perform an error budget and work it out, it often does. Bear in mind errors occur in many domains too.
Tiny errors, in the order of uV make differences, much of audio is simply about reducing errors, so reading about precision design (which is often of a DC nature) then applying it to AC design makes for big differences.
No magic PCB or universal panacea applies, but to really be sure of the improvements you make stick with a design and find it's limits / limitations.
So many here build a multitude of different circuits / topologies but never optimise any. Build a design, listen, measure then build another.
Now you can iteratively improve the design, always with reference to the last. It's time consuming, but really worth the input in my experience, and you always have a reference to refer to - none of those 'I think it's better' changes.
You will be astonished with the magnitude of improvements you can get from this approach, but choose the initial design carefully, some are VERY hard to get working properly.
Final tip - ignore most of the published audio reference work, it will tell you far less than a good detailed scout through the semi-manufacturers online (and free) libraries. There's a few exceptions to the above, but not many.
Above all have fun, when you get it right, there's no better feeling in the world (and it will also give you far greater insight into the price tags charged by comercial companies too - there's a lot of labour involved in good audio design).
Andy.
P.S. the current flows in a ground plane are highly predictable - remember current flows in loops - analysing those loops is a crucial bit to getting it right.
The bits between the bits
In addition to the above, the circuit elements you can't see on the schematic often dominate the ultimate performance of a circuit (as alluded to by Jonathan's post).
To get a real handle on this, redraw your schematic showing all junction capacitances, non-ideal component characteristics, trace inductance, C etc.
For a first iteration, just the semi's junction C's and maybe cap's non-ideal parameters will tell you a lot.
Now analyse the effect of every one. Dealing with these, through component choice, topology etc. often brings REALLY BIG rewards, definitely bigger than fiddling with audio-grade components in non-optimal designs will, and it's cheap - a big benefit for skinflint DIY'ers like me
Once those bits are sorted, then you get to the minutaie of components, where the audio-grade bits have a part to play.
Andy
In addition to the above, the circuit elements you can't see on the schematic often dominate the ultimate performance of a circuit (as alluded to by Jonathan's post).
To get a real handle on this, redraw your schematic showing all junction capacitances, non-ideal component characteristics, trace inductance, C etc.
For a first iteration, just the semi's junction C's and maybe cap's non-ideal parameters will tell you a lot.
Now analyse the effect of every one. Dealing with these, through component choice, topology etc. often brings REALLY BIG rewards, definitely bigger than fiddling with audio-grade components in non-optimal designs will, and it's cheap - a big benefit for skinflint DIY'ers like me
Once those bits are sorted, then you get to the minutaie of components, where the audio-grade bits have a part to play.
Andy
jcarr said:Sy:
>Would you say that there are advantages, other than consistency unit-to-unit, to using a PC board as opposed to point-to-point?<
Oh yes. Planes and striplines in P2P are an iffy proposition at best
But PCBs also have drawbacks, including problems with high-impedance nodes and leakage currents, and only two surfaces for installing parts. This is why in my own designs, multilayer PCB layouts with comprehensive ground and power planing serve as the foundations, but these are then augmented with component and board stacking, localized P2P, guard rings, floating isolater pads, teflon-insulated standoffs, clover-leaf terminals, and various other structural go-faster tricks.
regards, jonathan carr
Jonathan (and ALW), thanks for all the inside tips from your posts. They all seem so logical, but it always does in hindsight. In the exitement of the moment, it is good to lean back and go through the mental checklist of all the important issues. It seems that this is necessary to get a real good design out. Like Andy says, you need to dig in deep to really understand your design, only then can you progress.
One advantage of a double sided PCB I haven't seen noted is the fact that it makes it easier to keep a design compact without long looping traces (compared to a single side design). That for me makes it worth while, even without the ground plane options.
In the initial design of a PCB I often use the auto router to verify optimum placing of components. It's a bit easier than using the ratsnests, at least for me. But then I delete all routes and do it manually, starting with sensitive and/or input lines to keep those compact, then the PS decoupling caps, keep them close to where they are required, then the rest. Then leave it for a few days, then look at it again. Often I need many iterations, including some major repositioning of components, before I get it to my liking.
Jan Didden
Jocko:
>A ground plane can turn out to be good antenna, both for transmitting and receiving.<
Absolutely. And in general, ground in an amplifier is one of those fictional abstractions that is only as real and reliable as the designer makes it.
>Biggest problem that we ever had, was filter caps.<
I try to design so that any capacitor will operate in either constant voltage conditions or constant current conditions, but not both at the same time. I find that doing this won't altogether eliminate the sonic fingerprint of a capacitor type on a circuit, but will reduce it considerably.
>Sometimes the best ones were not availble unless we bought more than we could use.<
IME, this is a more common occurance than "sometimes". The minimum-order policies for special or custom capacitors varies according to the manufacturer, but the sums and quantities are never piddling.
>Each amp also sounded different depending on topology and transformer, so what we learned on a previous product didn't necessarily hold true for the next.<
Different board layouts and physical constructions can also affect the sound to a surprising extent. Keith Herron mentioned to me that for some of his products he spent over a year iteratively designing board layouts and measuring and listening to them before he was satisfied.
regards, jonathan carr
>A ground plane can turn out to be good antenna, both for transmitting and receiving.<
Absolutely. And in general, ground in an amplifier is one of those fictional abstractions that is only as real and reliable as the designer makes it.
>Biggest problem that we ever had, was filter caps.<
I try to design so that any capacitor will operate in either constant voltage conditions or constant current conditions, but not both at the same time. I find that doing this won't altogether eliminate the sonic fingerprint of a capacitor type on a circuit, but will reduce it considerably.
>Sometimes the best ones were not availble unless we bought more than we could use.<
IME, this is a more common occurance than "sometimes". The minimum-order policies for special or custom capacitors varies according to the manufacturer, but the sums and quantities are never piddling.
>Each amp also sounded different depending on topology and transformer, so what we learned on a previous product didn't necessarily hold true for the next.<
Different board layouts and physical constructions can also affect the sound to a surprising extent. Keith Herron mentioned to me that for some of his products he spent over a year iteratively designing board layouts and measuring and listening to them before he was satisfied.
regards, jonathan carr
EC8010 said:
Weeeelllll... perhaps not. Letting the ground plane get too close to the inverting input of a differential amplifier (discrete or op-amp) is not such a good idea, for one example - the capacitance introduces a destabilizing phase shift.
Also, ground planes really only shine at audio frequencies when the node impedances they surround are low! High node impedance = high signal rolloff due to the shunt capacitance.
In my experience, ground planes are really best suited for high speed digital and RF circuits, where all node impedances are either low or tightly controlled.
'Course, a well-designed ground planed board will likely beat the pants off of a poorly designed plain board any day of the week, which is why I qualified this whole reply with "perhaps" right there in the beginning!
EC, I was responding to your statement, "Treating audio as RF is a very good move, especially if you're having to deal with the output of a dodgy digital source that produces lots of ultrasonic noise." That kind of issue, I think, is amenable to input filtering.
jonathan, I'm fairly familiar with the techniques you've outlined (I've even used them in my non-audio products), but I've seen people in this forum claim that p-t-p is much superior sonically. Now, in my audio gear, I normally use p-t-p, but that's because I build one-offs, you know, DIY, and have to watch the dollars. With no cost constraints, I'd use PC. The claims of p-t-p superiority don't make much sense to me, but as I haven't tested this myself, I thought I'd take the opportunity to ask someone who has. Domo domo.
SY:
>I'm fairly familiar with the techniques you've outlined (I've even used them in my non-audio products)<
Very interesting! So you have made commercial products that incorporate localized P2P, teflon standoffs, clover-leaf terminals and what-not? May I ask what type of products these were? I know of companies that utilize these techniques for prototypes and really small-scale runs (and I have seen the guts of some missile onboard radar systems that were built similarly on stepped teflon-over-machined metal "pcbs"), but I don't recall seeing any modern commercial products that used such techniques (perhaps some of the older Tektronics test gear would be somewhat similar).
>The claims of p-t-p superiority don't make much sense to me, but as I haven't tested this myself, I thought I'd take the opportunity to ask someone who has.<
For certain things, P2P can be decidedly superior. If you consider a high-impedance gain node, the impedance that you can get on a pcb is usually limited by the board material and construction (Japan and much of East Asia has a very humid climate, which makes matters worse). If you make that same node as a dead-bug P2P structure, the limitation is more likely to be the Early voltages of the active devices.
OTOH, design is all about goals and priorities. While I reckon that P2P can be superior for certain tasks, right now I am mostly interested in developing topologies to obtain superior performance and sonics. And many of those topologies are complicated enough that you wouldn't want to execute them as P2P. In the future, if I become interested in simpler topologies once again, at that time I may want to consider using P2P more extensively.
regards, jonathan carr
>I'm fairly familiar with the techniques you've outlined (I've even used them in my non-audio products)<
Very interesting! So you have made commercial products that incorporate localized P2P, teflon standoffs, clover-leaf terminals and what-not? May I ask what type of products these were? I know of companies that utilize these techniques for prototypes and really small-scale runs (and I have seen the guts of some missile onboard radar systems that were built similarly on stepped teflon-over-machined metal "pcbs"), but I don't recall seeing any modern commercial products that used such techniques (perhaps some of the older Tektronics test gear would be somewhat similar).
>The claims of p-t-p superiority don't make much sense to me, but as I haven't tested this myself, I thought I'd take the opportunity to ask someone who has.<
For certain things, P2P can be decidedly superior. If you consider a high-impedance gain node, the impedance that you can get on a pcb is usually limited by the board material and construction (Japan and much of East Asia has a very humid climate, which makes matters worse). If you make that same node as a dead-bug P2P structure, the limitation is more likely to be the Early voltages of the active devices.
OTOH, design is all about goals and priorities. While I reckon that P2P can be superior for certain tasks, right now I am mostly interested in developing topologies to obtain superior performance and sonics. And many of those topologies are complicated enough that you wouldn't want to execute them as P2P. In the future, if I become interested in simpler topologies once again, at that time I may want to consider using P2P more extensively.
regards, jonathan carr
jonathan, my more exotic work was in aerospace and instrumentation (electrochemical, spectroscopic, data acquisition, FT methods). More prosaic work in computer peripherals, where I became VERY familiar with environmental demands in Southeast Asia. Now I do wine corks. Sic transit gloria SY.
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