Many sins are committed in an attempt to make measurements look good. I had a cassette deck that handled tape beautifully --- it was a drawer-loading machine. But trying to transfer vinyl, even rather decent pressings with little visible vertical motion of the cartridge/tonearm, the machine overloaded and intermodulated hideously, I presume from someone's attempt to make the low-frequency response look better by including an inordinate amount of boost or low-frequency extension.
Possibly a cumulative effect of repairing things with poor and often way off components?
For example, an oscillator dies on them, and instead or repairing it with 1% or 0.5% quality metal film resistors, low quality carbon resistors, nominaly 10% tolerance but sometimes a lot more, are used?
A couple of such off components in the same ciruit can do wonders for special effects ...
My Sony TC-K 880 ES cassette deck doesn't od nasties like that, and I vouch for that, let's say that after owning various open reel decks from 1965 to 1995, I have learnt a few tricks myself, but surely what to look for as possible trouble.
Hard to think that organ notes are nearly pure sine waves ( or so I was taught ) . Nice to have 5Hz if possible , 16 Hz will do ( - 3 dB ) . The organist has to make the time delay work if to have true dynamics . Sub-woofer armchair !
https://www.youtube.com/watch?v=KU4IgHa21x0&feature=related
MAKE | Massive Subwoofer Chair
https://www.youtube.com/watch?v=KU4IgHa21x0&feature=related
MAKE | Massive Subwoofer Chair
Electric Hammond (tonewheel) organs use about 80 sine wave generators.
That's why they are so hideously heavy.
Any odd harmonics are produced by the 'percussion' circuit giving the note a more percussive attack (it's not a kind of drum machine. I think it's a kind of distortion circuit) or dirty contacts which in this case are actually a good thing.
In fact so important are dirty contacts to Hammonds that they had to be emulated before digital representations of tonewheel organs became truly popular.
The time delay is the question . I was given a demonstration of an organ with a 26 foot bottom pipe . How it was timed into the music was key to the sound . The organ was old and unpredictable . The Jesuit priest who was rebuilding it was in his own words just a technician , Xavier the organist could make it sing . The old priest was very found of Messiaen ( me too ) . I went to Mass as he promised to play The birds and the springs ( water ) , it suited his technician ability he said . I am 6 foot plus and was 29 years old . The people mostly 4 foot 8 inches , women and 90 years old . Firstly they screwed up their faces at the music ( most do ) . Secondly they were shocked at my obvious happiness . It was a weird day of magic and learning . Like Fahrenheit 451 a bit .
https://www.youtube.com/watch?v=UII6s-Xwikg
https://www.youtube.com/watch?v=UII6s-Xwikg
Once upon a time I've been on a school outing to have look at the workings of a large pipe organ. It was made possible by our music teacher who was an accomplished concert pianist and the father of one of the girls in my class who built and repaired pipe organs for living (he must have been good as he was constantly jetting around the world doing it).
Very interesting, it had about 2000 pipes altogether, the largest you could stand in to the smallest which were about 3 inches tall. The small ones were made from lead and tuned with which was basically like that little key you used to get to open tins of corned beef with. They had two little vertical slots cut and you just rolled it down until tuned.
Obviously one could only adjust the pitch upwards.
Very interesting, it had about 2000 pipes altogether, the largest you could stand in to the smallest which were about 3 inches tall. The small ones were made from lead and tuned with which was basically like that little key you used to get to open tins of corned beef with. They had two little vertical slots cut and you just rolled it down until tuned.
Obviously one could only adjust the pitch upwards.
We were looking at feedback mechanisms the other day and it was said all is predicable . Also that echos around a loop are unlikely . My thought for the day was has anyone measured short duration pulses both in and out of an amplifier ( simulate back EMF ). I know they are used , I do not remember inside the loop being looked at ? I assume the maths of feedback systems must be alike , is this paper saying anything ?
Transient feedback and global instability in non-homogeneous systems
Transient feedback and global instability in non-homogeneous systems
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Nigel, Here is where playing bridge and drinking beer instead of studying calc cones back to haunt me. The link lost me.
I do remember many years ago something on amp stability and back EMF. It was probably 30 years ago and I don't think it was talking audio. EDN maybe?
Servo systems come as either inherently stable, or inherently unstable. Transients that exceed their dynamic range upset them in different ways. That much I think I remember from school.
I do remember many years ago something on amp stability and back EMF. It was probably 30 years ago and I don't think it was talking audio. EDN maybe?
Servo systems come as either inherently stable, or inherently unstable. Transients that exceed their dynamic range upset them in different ways. That much I think I remember from school.
Servo feedback loops, as executed with op amps, can sometimes "breathe" or "pump". The bass lines somehow seem to be rolling, on the move, not static (as in unmoving - can you picture a drummer running around with his drum kit?).
I couldn't swear to it, but I think this sometimes happens when what they have to correct starts to very closely approach their maximum effect; if so, then this is more of a testimony that the amp has been poorly designed rather than the servo has problems all by itself. As far as I know, most are made to correct for +/- 100...120 mV offsets, but as I see it, that is already a very bad offset - more is criminal.
So, in effect, I agree with DF96.
Never happened to me, but I have witnessed two cases of this effect. Very odd.
I couldn't swear to it, but I think this sometimes happens when what they have to correct starts to very closely approach their maximum effect; if so, then this is more of a testimony that the amp has been poorly designed rather than the servo has problems all by itself. As far as I know, most are made to correct for +/- 100...120 mV offsets, but as I see it, that is already a very bad offset - more is criminal.
So, in effect, I agree with DF96.
Never happened to me, but I have witnessed two cases of this effect. Very odd.
But that can sometimes "work the other way" as well. Some months ago, a friend in Croatia put together a fully complementary amp based on my design. I had previously driven home the point that this type of circuit heavily relied on transistor matching, from beginning to end.
It seems I drove the point home, because when he clicked it on, the natural offset (without the servo) was less than 10 mV, which I see as an excellent result, given that he used no dual transistors, and had to pair them manually throughout.
I still advised him to use the servo anyway, mostly because of possible strong transients, which might increase this to less impressive levels.
It seems I drove the point home, because when he clicked it on, the natural offset (without the servo) was less than 10 mV, which I see as an excellent result, given that he used no dual transistors, and had to pair them manually throughout.
I still advised him to use the servo anyway, mostly because of possible strong transients, which might increase this to less impressive levels.
Some DC servos might have 'HF' peaks due to phase shifts, like any other feedback system, but a DC servo 'HF' peak could sit right in the audio low bass region. If, in addition, the servo is near one of its limits then heavy bass could send it banging into the limit so the servo then temporarily loses control and at the very least you get a transient bias shift.
I did find the maths very hard going ( if I need my neighbour 3 doors down will know , trouble is we always drink to much wine when maths is needed ) . The word pictures in the text were not difficult . It is the old question of loops closing .
Ever since I read a book on Chaos theory I wondered if the minor mysteries of sound quality might have a Chaotic quality ? I saw in my picture the music as a gathering storm .
Any wave I ever put through a sensible amplifier seemed to work . Some say if we re-digitize a signal and then compare with the original we might if very careful spot problems . We would be using music and not generated waveforms . Fraught with problems , not stupid I feel .
In part of this research someone said gravity is perhaps not a force as it has no known opposite ( thought anti gravity was spoken of ? ) . No idea if true and hope no one wants to pick that ball up ( I suppose relativity deals with that ) . I was just very surprised it came up .
Ever since I read a book on Chaos theory I wondered if the minor mysteries of sound quality might have a Chaotic quality ? I saw in my picture the music as a gathering storm .
Any wave I ever put through a sensible amplifier seemed to work . Some say if we re-digitize a signal and then compare with the original we might if very careful spot problems . We would be using music and not generated waveforms . Fraught with problems , not stupid I feel .
In part of this research someone said gravity is perhaps not a force as it has no known opposite ( thought anti gravity was spoken of ? ) . No idea if true and hope no one wants to pick that ball up ( I suppose relativity deals with that ) . I was just very surprised it came up .
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