your ear, while it can detect noise and distortion at low signal levels, suffers from a masking effect at high signal levels. your ear cannot detect at high signal levels what a good oscope and spectrum analyzer can. your ear also can't detect oscillation unless it's within the audible spectrum (it can detect distortion from oscillation but can't tell you what the cause of that distortion is). another thing that was first proven to me at APT when i was working there was that the ear can't detect transient clipping in loud passages of music if the amp behaves well during clipping. the intro to the Eagles' "Victim of Love" is a good example of this. if you have a well behaved amp and it's turned up to where the loud parts of the passage barely clip (up to about 5%), your ears don't detect the clipping, but test equipment can. a badly behaving amp, however will turn that 5% into 10% almost instantly(usually from "overhang"), and you can hear it.
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As a newbie this is a fascinating thread because I'm on my first amp.
If it helps, I will contribute my experiences to date as to what has worked for me:
a) start off with a proven topology (as a newbie you don't want to start in the wilderness)
b) understand the topology. This is where simulations helped me a lot. I could play around quickly and inexpensively (spice is free) to see where currents flow, how sub-circuits interact and what amplifier performance trends you can expect from tweaks and changes. You also get good starting values for the components for first prototype.
c) consult others - I didn't see this as a step included above, but it has been the single most important part of my approach. Don't form ideas about things too quickly, or at least be willing to change them as you go.
d) I used a signal generator and a CRO for the first power-up, on a bench with current-limited power supply. Being able to see the output, see how it clips, compare phase with input, look for oscillations - invaluable in my view. Can it be done without a CRO - probably.
e) Since you now know there's nothing nasty happening you can power it up, check dc offset with DMM and connect speakers (cheap ones first)
f) Now I'm tuning by Ear. Trouble is, I only have the Bronze Ear, hope it will upgrade to Silver and maybe Gold one day. I change parts on the bench, then I only check dc offset and voltage between output device emitters and signal output, before adding speakers and listening. I feel the heatsink with my hand and touch the emitter output resistors for signs of oscillation. Listening tests are difficult, I use my Bryston as a benchmark and switch between L and R channels so I can AB comparisons. After awhile you heard ghosts, you can't really say what is changing. You have to tune for what you want, not what you think other people will admire.
This isn't so different from Lineup/Hugh, except that if you are selling amplifiers you would expect to do a lot more than this (as Hugh stated).
If it helps, I will contribute my experiences to date as to what has worked for me:
a) start off with a proven topology (as a newbie you don't want to start in the wilderness)
b) understand the topology. This is where simulations helped me a lot. I could play around quickly and inexpensively (spice is free) to see where currents flow, how sub-circuits interact and what amplifier performance trends you can expect from tweaks and changes. You also get good starting values for the components for first prototype.
c) consult others - I didn't see this as a step included above, but it has been the single most important part of my approach. Don't form ideas about things too quickly, or at least be willing to change them as you go.
d) I used a signal generator and a CRO for the first power-up, on a bench with current-limited power supply. Being able to see the output, see how it clips, compare phase with input, look for oscillations - invaluable in my view. Can it be done without a CRO - probably.
e) Since you now know there's nothing nasty happening you can power it up, check dc offset with DMM and connect speakers (cheap ones first)
f) Now I'm tuning by Ear. Trouble is, I only have the Bronze Ear, hope it will upgrade to Silver and maybe Gold one day. I change parts on the bench, then I only check dc offset and voltage between output device emitters and signal output, before adding speakers and listening. I feel the heatsink with my hand and touch the emitter output resistors for signs of oscillation. Listening tests are difficult, I use my Bryston as a benchmark and switch between L and R channels so I can AB comparisons. After awhile you heard ghosts, you can't really say what is changing. You have to tune for what you want, not what you think other people will admire.
This isn't so different from Lineup/Hugh, except that if you are selling amplifiers you would expect to do a lot more than this (as Hugh stated).
well thanks for your suggestion lineup, the reason why I chose to take this approach in the first place is because I find people opinion on what makes for great sound as well as taste is so diverse you cannot make an amp that would please everyone. Even when speaking about accurate reproduction.
But I must say building, lengthy listening and tweaking dozens of amplifiers over the years thought me things that I would not have learned without getting my hands dirty. This forum which is my favorite by the way does have a lot of conflicting views on what makes an amp sounds better which would have confused me if I had not experience for myself.
The statement about you cant trust your ears was always funny to me, should I listen to an amp that someone else says sounds good or measures perfect even if it sounds worse, no thanks wasted 9 years doing it that way even though I should have known better.
regards
But I must say building, lengthy listening and tweaking dozens of amplifiers over the years thought me things that I would not have learned without getting my hands dirty. This forum which is my favorite by the way does have a lot of conflicting views on what makes an amp sounds better which would have confused me if I had not experience for myself.
The statement about you cant trust your ears was always funny to me, should I listen to an amp that someone else says sounds good or measures perfect even if it sounds worse, no thanks wasted 9 years doing it that way even though I should have known better.
regards
another good test by ear of how well an amp behaves on transients is the intro to "green grass and high tides forever" by the outlaws, a real quiet guitar intro with very loud parts interspersed in it, or "i'd love to change the world" by ten years after (i think the outlaws intro is a better mix of quiet and loud passages).
it's always best to use music you are extremely familiar with for testing, you know what it "should" sound like. i use "too rollin stoned" by robin trower for speaker testing. a 3 piece band is very good for speaker testing, as you have well defined lows, mids and highs in the mix. something with a "fatter" sound is good for testing amps, like "hush" or "highway star" by deep purple (i guess my favorite music styles are evident by what i use for testing.......)
it's always best to use music you are extremely familiar with for testing, you know what it "should" sound like. i use "too rollin stoned" by robin trower for speaker testing. a 3 piece band is very good for speaker testing, as you have well defined lows, mids and highs in the mix. something with a "fatter" sound is good for testing amps, like "hush" or "highway star" by deep purple (i guess my favorite music styles are evident by what i use for testing.......)
I think there are still people using this method.
It is interesting to see if they would arrive to some amplifier built with standard method.
Nobody can ever argue against that listening to amplifier is what really counts.
Now, this wouldn't exclude measuring, too.
Yes lineup, I'm still using this method since i dont have scopes etc... i just need a multi tester for simple measurement and the rest is the loudspeakers. If i don't like the sound then i will start to tweak the primary components like the Cdom, feedback components etc....As of now i still have my amp working built 15 years ago during ny college days...still stable....
For me a good amp sound is enough.There are amp with good measurement but not as good as the sound itself.
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