Bas Horneman said:
Hi Bas,
I totally agree to the observation about lack of regulated output stages.
I also know the reason for this as, with SS amps, powerfull output stages require currents and voltages which are beyond limits of commercial available voltage regulators.
The alternative: building a regulated powersupply from discrete components is not a complex task. The result however would
a: increase the part count dramatically (for each 1 - 2 ouput devices there should be an regulating device roughly)
b: increase the amount of heat which needs to be dissipated.
For my simple JLH-amps I stick to fully regulated powersupplies.
I design the single sides PCB's from my basic set of rules just using Corel-Paint and my gut-rules:
-layout should reflect the circuit diagram;
-avoid long traces;
-keep high-current traces short and wide;
-use the physical dimension of the components to cross other lines. (I personally use resistors for this, and make sure that the resistor is not mounted flat to the board where there is a crossing),.
and NO SQUARE's on edges as this seems to be more vulnerable.
jos
Regulate And Rule.
Hi,
Hats off to you, Jos.
Bas already knows I am a big fan of regulated supplies and I would point to the PSU as the main part were most manufacturers try to save bucks.
It certainly is my experience that almost any commercial amp can be improved by either beefing up the PSU or adding regulation.
The latter is 9/10 almost out of the question on commercial designs due to lack of voltage headroom unless you make on outboard supply.
Thing is, not many people are knowledgeable about regulators though, neither with valves nor transistors.
In the age of digital hash pollution they deserve a huge welcome.
More later perhaps,
Hi,
Hats off to you, Jos.
Bas already knows I am a big fan of regulated supplies and I would point to the PSU as the main part were most manufacturers try to save bucks.
It certainly is my experience that almost any commercial amp can be improved by either beefing up the PSU or adding regulation.
The latter is 9/10 almost out of the question on commercial designs due to lack of voltage headroom unless you make on outboard supply.
Thing is, not many people are knowledgeable about regulators though, neither with valves nor transistors.
In the age of digital hash pollution they deserve a huge welcome.
More later perhaps,
Protection racket.
Hello Frank,
trouble is, regulators aren't terribly good at dealing with RF hash. Jolly good otherwise, though. If they can be protected from the RF racket, then they're good. But, as you point out, they cost almost as much as the audio amplifier, and (being single-ended) they're harder to design for low distortion under varying current.
Hello Frank,
trouble is, regulators aren't terribly good at dealing with RF hash. Jolly good otherwise, though. If they can be protected from the RF racket, then they're good. But, as you point out, they cost almost as much as the audio amplifier, and (being single-ended) they're harder to design for low distortion under varying current.
Re: Protection racket.
RF hash, ground planes and a lot of other interesting stuff is discussed in the folloing excellent paper
http://focus.ti.com/lit/misc/sloa089/sloa089.pdf
that Jonathan recommended earlier in the thread. I'd say this
is highly recommended readin on PCB layout for those, like
me, who do not alraeady know how to get things right (got
the time to read it today).
EC8010 said:
RF hash, ground planes and a lot of other interesting stuff is discussed in the folloing excellent paper
http://focus.ti.com/lit/misc/sloa089/sloa089.pdf
that Jonathan recommended earlier in the thread. I'd say this
is highly recommended readin on PCB layout for those, like
me, who do not alraeady know how to get things right (got
the time to read it today).
Hello Christer,
that's a cracking chapter (he uses the get-out "beyond the scope of this book"), and I've saved it ready to print later for more considered digestion. I'll be looking for the book next.
What I was actually getting at was a much simpler limitation. All regulators are fundamentally an op-amp, a voltage reference, an output sampling element, and a power regulating element. Because of this, they suffer from the fundamental limitation of any op-amp. They have a finite gain-bandwidth product, which is further compromised by the power regulating element. As a consequence, their noise rejection falls with frequency, and it's usually pretty poor by 10kHz, let alone RF. This applies whether the op-amp in question glows in the dark, or is this month's wonder op-amp, just a matter of degree. So they all need protection. But you knew that..
that's a cracking chapter (he uses the get-out "beyond the scope of this book"), and I've saved it ready to print later for more considered digestion. I'll be looking for the book next.
What I was actually getting at was a much simpler limitation. All regulators are fundamentally an op-amp, a voltage reference, an output sampling element, and a power regulating element. Because of this, they suffer from the fundamental limitation of any op-amp. They have a finite gain-bandwidth product, which is further compromised by the power regulating element. As a consequence, their noise rejection falls with frequency, and it's usually pretty poor by 10kHz, let alone RF. This applies whether the op-amp in question glows in the dark, or is this month's wonder op-amp, just a matter of degree. So they all need protection. But you knew that..
Dear Christer:
I tend to re-read certain papers before starting any new schematic or board design, and SLOA-089 is one of them. Nearly all of the concepts mentioned therein are things that are simple, obvious and should be committed to heart, yet being exposed to the occasional reminder is never a bad idea.
I think that you will also find it useful to have some knowledge of guard ring concepts. Audio amplifiers are essentially analog calculators, and methods that can reduce measurement and calculation errors are invariably worth implementing.
http://www.ce-mag.com/ce-mag.com/archive/01/03/0103CE_028.html
http://www.quadtechinc.com/resources/library/articles/testfixtures.asp
hth, jonathan carr
I tend to re-read certain papers before starting any new schematic or board design, and SLOA-089 is one of them. Nearly all of the concepts mentioned therein are things that are simple, obvious and should be committed to heart, yet being exposed to the occasional reminder is never a bad idea.
I think that you will also find it useful to have some knowledge of guard ring concepts. Audio amplifiers are essentially analog calculators, and methods that can reduce measurement and calculation errors are invariably worth implementing.
http://www.ce-mag.com/ce-mag.com/archive/01/03/0103CE_028.html
http://www.quadtechinc.com/resources/library/articles/testfixtures.asp
hth, jonathan carr
on guard against rings
The reference:
http://www.ce-mag.com/ce-mag.com/archive/01/03/0103CE_028.html really refers to digital design and may be contrary to the best strategies for analog circuits. It was really too brief and general for much insight into EMI and signal integrity. I would dig around at the links section of www.sigcon.com for resources on the subject of board design for EMI reduction. I have several reservations about guard rings. Most of the real applications or guard rings that I have seen were to keep DC leakage currents for introducing DC error terms into high impedance DC coupled circuits. The introduction of increased capacitance at the inverting input can cause problems. The capacitance at this node is usually best made very small for high bandwidth devices an circuits. The usual mistake I see is excessive lead lenth between this node and the junction of the feedback resistors that connect to this node. Keep this connection as short and small as possible is one of the highest priorities in layout of an analog amplifier/preamp circuit. Try and design guard rings for a surface mount op amp so typical these days and you will see what I am going on about. I have had very fast op amps work better with the inverting input pin bent up off the PCB and the resistors soldered to it with minimum lead length. This made a big sonic improvement on a diffential op amp buffered S/PDIF digital input and was a pain to buld in prduction but worth the sonic benefits.
One of the best resources on grounding and layout for analog is
http://www.analog.com/UploadedFiles/Application_Notes/135208865AN-202.pdf
which we have both posted the link to before but is worth doing again.
This one, High Speed Amplifier Techniques by Jim Williams at Linear Technology, will change your life and is one of my favorite ap notes ever:
http://www.linear-tech.com/pdf/an47fa.pdf
The reference:
http://www.ce-mag.com/ce-mag.com/archive/01/03/0103CE_028.html really refers to digital design and may be contrary to the best strategies for analog circuits. It was really too brief and general for much insight into EMI and signal integrity. I would dig around at the links section of www.sigcon.com for resources on the subject of board design for EMI reduction. I have several reservations about guard rings. Most of the real applications or guard rings that I have seen were to keep DC leakage currents for introducing DC error terms into high impedance DC coupled circuits. The introduction of increased capacitance at the inverting input can cause problems. The capacitance at this node is usually best made very small for high bandwidth devices an circuits. The usual mistake I see is excessive lead lenth between this node and the junction of the feedback resistors that connect to this node. Keep this connection as short and small as possible is one of the highest priorities in layout of an analog amplifier/preamp circuit. Try and design guard rings for a surface mount op amp so typical these days and you will see what I am going on about. I have had very fast op amps work better with the inverting input pin bent up off the PCB and the resistors soldered to it with minimum lead length. This made a big sonic improvement on a diffential op amp buffered S/PDIF digital input and was a pain to buld in prduction but worth the sonic benefits.
One of the best resources on grounding and layout for analog is
http://www.analog.com/UploadedFiles/Application_Notes/135208865AN-202.pdf
which we have both posted the link to before but is worth doing again.
This one, High Speed Amplifier Techniques by Jim Williams at Linear Technology, will change your life and is one of my favorite ap notes ever:
http://www.linear-tech.com/pdf/an47fa.pdf
Re: on guard against rings
Amen to that. Guard rings are for things like pH meter amplifiers - zero ac bandwidth needed and input imedances that won't load down a 100+ megohm electrode.
Amen to that, too! This is by far one of the most comprehensive references on op-amp application ever written. I've printed it out 3 times because it keeps falling apart from use! What a gem!
Fred Dieckmann said:
Amen to that. Guard rings are for things like pH meter amplifiers - zero ac bandwidth needed and input imedances that won't load down a 100+ megohm electrode.
Amen to that, too! This is by far one of the most comprehensive references on op-amp application ever written. I've printed it out 3 times because it keeps falling apart from use! What a gem!
Good question. Lots of good stuff written already. Some of my favourite pitfalls are:
1) Assuming wire/pcb traces have zero impedance
2) Assuming semiconductors behave like the "typical" figures in datasheets
3) Ignoring parastics (datasheets don't tell the whole story)
4) Forgetting that currents flow in loops (at audio frequencies)
5) Inadequate consideration of non-linearities and their effects
6) Thinking you can hear above 20kHz
7) Inadequate performance measures/unreliable test methods
Item 1 leads to many problems, especially in high feedback designs, and has been highlighted in the discussions on ground planes vs point to point. Item 2 is a really easy trap to fall in to, many people don't realise the parametric spread in semiconductors even between two devices with identical part numbers. ALW mentioned item 3. Item 4 has been mentioned and should be considered at the same time as item 1. In my experience item 5 is woefully neglected in most press and "expert" websites and is often swept under the carpet and almost never measured intelligently. Item 6 is a common misunderstanding - it is my way of combating the wide-bandwidth is ALWAYS better club. Honestly, you cannot hear above 20kHz. Item 7 is the very most neglected area and is one way I use to judge waht "experts" expound upon. If they say "x" is better because it is made of gold leaf from the mines of Solomon I ask "why?" and "how did you measure the improvement?". The why is usually not explained convincingly and the measurement process is often ill-conceived.
A few amateurs do manage to bridge these pitfalls and make really great sounding amps.
This one is worth highlighting again and sits nicely alongside 'the components you can't see on the schematic' theme.
Not only do they vary between devices, but vary in the same device, in a non-linear fashion, dependant upon operating characteristics.
Also, understand the limitations of the components - those data sheet specs for that op-amp for example look marvellous, but try driving a capacitive / low-impedance load with them and many fall apart, primarily because their output stages are mostly crap. You won't get this info from your spice modelling either, because the output stages aren't modelled (in most cases).
Deal with this though, in terms of the load the op-amp sees and often things are often transformed!
Some simple pre-testing of components such as these can reveal loads of useful data.
Andy.
P.S. I really like no.1 above - most engineers I meet seem to think room temperature superconductors exist, in the form of PCB copper traces
I would just like to thank for the references supplied by
Jonathan and others. I have only had time to read the sloa-89
so far, and I had already read the an-202. I find them both
excellent reading and highly recommendable, also from my
non-expert point of view. To anybody who hasn't yet read them,
do so! YOu won't regret it.
It is intereting, BTW, that while there seems to be frequent
controversies on this forum, and similar ones, about whether
RFI is a big problem or not for audio gear, sload-89 which is
not in any way focussing on audio in particular seems to state
clearly that RFI is important to consider also at audio frequencies.
Jonathan and others. I have only had time to read the sloa-89
so far, and I had already read the an-202. I find them both
excellent reading and highly recommendable, also from my
non-expert point of view. To anybody who hasn't yet read them,
do so! YOu won't regret it.
It is intereting, BTW, that while there seems to be frequent
controversies on this forum, and similar ones, about whether
RFI is a big problem or not for audio gear, sload-89 which is
not in any way focussing on audio in particular seems to state
clearly that RFI is important to consider also at audio frequencies.
Many shortcomings are very basic
I think many shortcomings in DIY design are even more basic. I see three main problem areas, at least for myself:
1 - lack of breadth in theory and in experience. What I mean is this: a professional designer had to learn all the theory at least once, even the parts he didn't like, and design a lot of stuff that probably wasn't his pet project aither. Result? A lot of related nackground that is there as a diffuse library of knowledge to solve problems.
The average DIY'er has a good to very good (read: deep) knowledge of some isolated issues. Some are into capacitors, some into cables... and some have extremely good understanding of the spotlights in their interest. Still they often seem to lack a good comprehensive view of the whole, of what's most important and what is not, etc. Plus, most DIY'ers including myself naturally pick the areas they like most and ignore the rest. Then they fall short when they encounter a problem that needs a broader insight.
It can be as simple as finding a formula for a filter or recalculationg a modified design. I have done complex math in high school but didn't particularly like it. Now I am too weak in math to catch up with the application notes: the author usually assumes you know all the basics! Most DIY'ers don't. I don't. Not to mention the routine of buying a product and replacing selected parts of a carefully designed circuit with "better" parts of radically different specs (op apms with 10x speed...). Ugh.
2 - Secondly, as said before, measurement and calibration are often rudimentary. Example: I don't have a scope, a frequency generator, or a frequenzy analyzer. Not even a variable bench supply. Just a DMM and a fast peak meter, which can be a good enough crutch sometimes. That's good enogh for the initial simple copies of published designs. Once you want to create something a bit more complex however, you need more or it leaves you guessing in the dark even where you suspect problems for a good reason. But I don't have the instrument to verify my problem theory in a minute. All I can do is resolder the circuit and see if "it's still there". Sigh. Again it's a dollar problem for once, but you must also know what to measure and how! Not trivial.
Iam a scientist in a non electronic field ... and I know for sure that the hardest problem is often just what to measure and how to do it.
3 - Finally, layout problems. Even a finished, published design can vary a lot depending on how you build it. This has been covered before in this thread and I second that.
One anecdote on that. I built chip power amps a few years ago and use them til today. Ah nowadays they are called Gainclones, nevermind. The past weeks I became quite unhappy with the performance that had seemed good so far. Well, I just knew it sounded bad, not why, and it was insiduous: zero self noise, zero hum, zero nothing, but clearly distorted on certain musical passages. Just the thing to drive you nuts. So I checked the whole DIY eqipment, everything, connections, solder joints, grounding, installed RFI filters (Christer, they still seem to work OK! - but that wasn't the problem after all), uncovered and corrected a few errors I had made , and all this improved the sound somehow. But it did not really fix it for good, or not well enough. Finally I check the main PSU I hadn't touched in 2 years. What do i see? I had connected the ground lead the wrong side of the filter caps, plus on a terminal strip rather than soldered between the main caps.
Well, fixingt this did more for the sound than anything else. This really was the main problem. There still is room for improvement and now I know where - it's all in the PSU department - but these 2 excess inches along a string of 14 ga wire made the difference between annoying transient ringing and a quite natural sound. So natural that after the 20 min resoldering job I spent 3 h listening to some of my less-frequently-listened-to-CD's. I had not done this in weeks because it sounded so annoying. !!!! .
Or in short: many circuits are fine. But the physical layout will make or break them, even in a PSU with, what, 6 (six) components all in all, transformer, rectifier, 4 caps. And here you need experience or a good teacher that looks over your shoulder.
I think many shortcomings in DIY design are even more basic. I see three main problem areas, at least for myself:
1 - lack of breadth in theory and in experience. What I mean is this: a professional designer had to learn all the theory at least once, even the parts he didn't like, and design a lot of stuff that probably wasn't his pet project aither. Result? A lot of related nackground that is there as a diffuse library of knowledge to solve problems.
The average DIY'er has a good to very good (read: deep) knowledge of some isolated issues. Some are into capacitors, some into cables... and some have extremely good understanding of the spotlights in their interest. Still they often seem to lack a good comprehensive view of the whole, of what's most important and what is not, etc. Plus, most DIY'ers including myself naturally pick the areas they like most and ignore the rest. Then they fall short when they encounter a problem that needs a broader insight.
It can be as simple as finding a formula for a filter or recalculationg a modified design. I have done complex math in high school but didn't particularly like it. Now I am too weak in math to catch up with the application notes: the author usually assumes you know all the basics! Most DIY'ers don't. I don't. Not to mention the routine of buying a product and replacing selected parts of a carefully designed circuit with "better" parts of radically different specs (op apms with 10x speed...). Ugh.
2 - Secondly, as said before, measurement and calibration are often rudimentary. Example: I don't have a scope, a frequency generator, or a frequenzy analyzer. Not even a variable bench supply. Just a DMM and a fast peak meter, which can be a good enough crutch sometimes. That's good enogh for the initial simple copies of published designs. Once you want to create something a bit more complex however, you need more or it leaves you guessing in the dark even where you suspect problems for a good reason. But I don't have the instrument to verify my problem theory in a minute. All I can do is resolder the circuit and see if "it's still there". Sigh. Again it's a dollar problem for once, but you must also know what to measure and how! Not trivial.
Iam a scientist in a non electronic field
... and I know for sure that the hardest problem is often just what to measure and how to do it.3 - Finally, layout problems. Even a finished, published design can vary a lot depending on how you build it. This has been covered before in this thread and I second that.
One anecdote on that. I built chip power amps a few years ago and use them til today. Ah nowadays they are called Gainclones, nevermind. The past weeks I became quite unhappy with the performance that had seemed good so far. Well, I just knew it sounded bad, not why, and it was insiduous: zero self noise, zero hum, zero nothing, but clearly distorted on certain musical passages. Just the thing to drive you nuts. So I checked the whole DIY eqipment, everything, connections, solder joints, grounding, installed RFI filters (Christer, they still seem to work OK! - but that wasn't the problem after all), uncovered and corrected a few errors I had made , and all this improved the sound somehow. But it did not really fix it for good, or not well enough. Finally I check the main PSU I hadn't touched in 2 years. What do i see? I had connected the ground lead the wrong side of the filter caps, plus on a terminal strip rather than soldered between the main caps.
Well, fixingt this did more for the sound than anything else. This really was the main problem. There still is room for improvement and now I know where - it's all in the PSU department - but these 2 excess inches along a string of 14 ga wire made the difference between annoying transient ringing and a quite natural sound. So natural that after the 20 min resoldering job I spent 3 h listening to some of my less-frequently-listened-to-CD's. I had not done this in weeks because it sounded so annoying. !!!! .
Or in short: many circuits are fine. But the physical layout will make or break them, even in a PSU with, what, 6 (six) components all in all, transformer, rectifier, 4 caps. And here you need experience or a good teacher that looks over your shoulder.
As for layout, I used to start with the circuit and then run into problems with the seemingly trivial "rest".
Now my priorities are reversed. I would even go so far as to say the first thing to consider in a project is the enclosure. Next, the connectors and switches/pots, then the PSU. All the above are so expensive and individually different / hard to compare / assess, that experiments are almost out of the question for the average DIY'er. Also, their quality and effects on end result are usually ignored in application notes or textbooks.
Next in priority are grounding, and then the other connections from and to pcb - read, the interfaces. Here the parts are cheaper, and can be experimented with, but the subject is tricky. Interface design is an art I guess. Literature exists but is sometimes conflicting (grounding philosophies anyone?).
The circuit itself compared to the above is almost a piece of cake ;-). At least with the circuit the parts are cheap, can be easily experimented with on a breadboard, and many different types and solutions exist. The circuit can also be calculated and modelled. Try that with enclosures....
Now my priorities are reversed. I would even go so far as to say the first thing to consider in a project is the enclosure. Next, the connectors and switches/pots, then the PSU. All the above are so expensive and individually different / hard to compare / assess, that experiments are almost out of the question for the average DIY'er. Also, their quality and effects on end result are usually ignored in application notes or textbooks.
Next in priority are grounding, and then the other connections from and to pcb - read, the interfaces. Here the parts are cheaper, and can be experimented with, but the subject is tricky. Interface design is an art I guess. Literature exists but is sometimes conflicting (grounding philosophies anyone?).
The circuit itself compared to the above is almost a piece of cake ;-). At least with the circuit the parts are cheap, can be easily experimented with on a breadboard, and many different types and solutions exist. The circuit can also be calculated and modelled. Try that with enclosures....
I second MBK's three points and ALW's remarks.
In all my years of designing and listening and modifying and listening and making measurements using extremely expensive test gear courtesy of my last employer and then listening, one of the biggest lessons I've learned is that the cause of problems is usually simpler than you think. Being able to see the wood for the trees is the trick. And there are so many trees - all sorts of people are planting veritable forests all the time, often of complicated, ill-considered theories of relatively low importance.
Sometimes I think it is even more of a challenge for engineering graduates because many of the sweeping assumptions that work well in general electronics do not in audio and the graduate must discard years of learned assumptions and apply much more care and attention to unexpectedly important details.
The amateur is a easy victim of the profusion of academic papers and pseudo-amateur websites, which invariably are either too focussed on obscure and low priority items or contain much that is speculation disguised as fact. Which idea is most important? Who's opinion do you trust?
The good news in my experience is that audio design is a great leveller. You don't need a degree or a PhD to be the best. You just need to be able to think very clearly, believe that everything can be understood and always let your ears drive your theories.
In all my years of designing and listening and modifying and listening and making measurements using extremely expensive test gear courtesy of my last employer and then listening, one of the biggest lessons I've learned is that the cause of problems is usually simpler than you think. Being able to see the wood for the trees is the trick. And there are so many trees - all sorts of people are planting veritable forests all the time, often of complicated, ill-considered theories of relatively low importance.
Sometimes I think it is even more of a challenge for engineering graduates because many of the sweeping assumptions that work well in general electronics do not in audio and the graduate must discard years of learned assumptions and apply much more care and attention to unexpectedly important details.
The amateur is a easy victim of the profusion of academic papers and pseudo-amateur websites, which invariably are either too focussed on obscure and low priority items or contain much that is speculation disguised as fact. Which idea is most important? Who's opinion do you trust?
The good news in my experience is that audio design is a great leveller. You don't need a degree or a PhD to be the best. You just need to be able to think very clearly, believe that everything can be understood and always let your ears drive your theories.
Test gear?
Talking about test gear, what do the panel consider essential bits of kit? I'd reckon instability problems are pretty impossible to track down without at least a scope, but what about more specialist bits of kit (distortion analysers and the like)?
Has anybody used PC-based audio analyser software (e.g. Sample Champion & the like)? Obviously, I assume a lot depends on the quality of your A-D/D-A.
Cheers
IH
traderbam said:
Talking about test gear, what do the panel consider essential bits of kit? I'd reckon instability problems are pretty impossible to track down without at least a scope, but what about more specialist bits of kit (distortion analysers and the like)?
Has anybody used PC-based audio analyser software (e.g. Sample Champion & the like)? Obviously, I assume a lot depends on the quality of your A-D/D-A.
Cheers
IH
Ian, you've poked a stick at my bete noir. When someone says that they want to design a speaker or an amp, but they haven't got a scope or FFT system, I just shudder. It's like saying, "I want to build a house, but I don't have a saw or a hammer."
Bare bones minimum:
Amps/preamps:
Analog voltmeter (having analog has saved my skin more than once!)
Digital voltmeter with high input Z
Scope, at least 2 channel, at least 20 MHz
Signal generator
Instrumentation amps
Bench power supplies
Speakers:
Calibrated test mike
FFT/MLS tester
Test amp and precision resistor (for Z measurements)
Pink noise source
Signal generator
1/3 octave spectrum analyzer
More equipment can be better (though best of all is the right equipment AND the know-how to use it properly). A willingness and ability to jury rig tests is essential. But this is the bare bones, the hammer and saw.
Bare bones minimum:
Amps/preamps:
Analog voltmeter (having analog has saved my skin more than once!)
Digital voltmeter with high input Z
Scope, at least 2 channel, at least 20 MHz
Signal generator
Instrumentation amps
Bench power supplies
Speakers:
Calibrated test mike
FFT/MLS tester
Test amp and precision resistor (for Z measurements)
Pink noise source
Signal generator
1/3 octave spectrum analyzer
More equipment can be better (though best of all is the right equipment AND the know-how to use it properly). A willingness and ability to jury rig tests is essential. But this is the bare bones, the hammer and saw.
More tools make life easier, now to say what's truly essential... I guess a DVM, a Test CD, and a fast peak meter.
Actually a good Test CD probably comes before the scope, with a variety of signals that are for some reason hard to handle or where distortion is easy to hear.
Then in order of "making it easier":
a good and non-DIY reference system with AB or ABX switching functionality - to check what you're up against, to check "industry standard" (the competition). In my house now almost everything is DIY or tweaked (or so cheap and nasty that it's useless as a reference). That makes it hard to say anything because I can only talk about "before and after tweak".
scope
function generator
frequency analyzer
distortion analyzer
... yet often it's not the gross distortions that need analyzing - those can be heard, or guessed at (IC's getting hot...). What is most troublesome to measure is those intermittent problems, such as random pops and clicks, or transient distortions. How to measure that I don't even know.
The Elliot website has a couple of nice DIY test gear at http://sound.westhost.com/index.html .
Actually a good Test CD probably comes before the scope, with a variety of signals that are for some reason hard to handle or where distortion is easy to hear.
Then in order of "making it easier":
a good and non-DIY reference system with AB or ABX switching functionality - to check what you're up against, to check "industry standard" (the competition). In my house now almost everything is DIY or tweaked (or so cheap and nasty that it's useless as a reference). That makes it hard to say anything because I can only talk about "before and after tweak".
scope
function generator
frequency analyzer
distortion analyzer
... yet often it's not the gross distortions that need analyzing - those can be heard, or guessed at (IC's getting hot...). What is most troublesome to measure is those intermittent problems, such as random pops and clicks, or transient distortions. How to measure that I don't even know.
The Elliot website has a couple of nice DIY test gear at http://sound.westhost.com/index.html .
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