Cursitor Doom wrote:> On Tue, 04 Jul 2017 14:58:42 -0700, pcdhobbs wrote: > >> <http://www.LearnByDestroying.com/jeffl/crud/HP-Catalogs.jpg> >> >> I'm pretty sure CD and I were both talking about having an HP200C, not >> just the catalogue. Mine is actually the slightly newer 200CD, which was >> the last tube model they made. > > I think I'm right in saying the only HP sig gen I have is an old analogue > one (probably Wien Bridge internals) that only covers 10hz to 512Mhz IIRC. > It's a joy to use because it's so simple, unlike some of the others which > require considerable re-familiarisation with every time I break one of > them out in anger. This wonderful simplicity is why it gets used more > than any other sig gen I own unless its limited range makes it unsuitable > for the task. > Sorry, Phil, but that list will probably never get written; I just don't > have enough time to itemise everything.In the RF spectrum, do the HPs stand on the extreme left, or are they simply (politically) blase?
The HP Original for sale
Started by ●July 2, 2017
Reply by ●July 4, 20172017-07-04
Reply by ●July 4, 20172017-07-04
On Tue, 4 Jul 2017 14:58:42 -0700 (PDT), pcdhobbs@gmail.com wrote:><http://www.LearnByDestroying.com/jeffl/crud/HP-Catalogs.jpg> > >I'm pretty sure CD and I were both talking about having an HP200C, >not just the catalogue. Mine is actually the slightly newer >200CD, which was the last tube model they made. >Cheers >Phil HobbsWith all due respect, the ambiguity is primarily your fault. You stated: "The 200C isn't the original 1939 model. It was the last tube instrument HP sold (CRTs and PMTs apart) and was in their 1985 catalogue. (Yes, I have one.) ;)" The "Yes, I have one" comment seems to suggest that you have a 1985 catalog to which CD appended that he also has one, which by implication would be a 1985 catalog. Since neither of his replies clarified the matter, and I didn't have anything interesting to say about the HP200C, I proceeded on the assumption that you both have 1985 catalogs, not HP200C generators. My only experience with an HP200CD was using one to build a mechanical sweep generator. The HP200CD dial is logarithmic, so I reasoned that I could use a log taper potentiometer mechanically coupled to the dial to produce a voltage suitable for the horizontal on an X-Y scope. This was done with a flat turntable drive belt coupled between the big frequency knob on the 200CD, and a similar size plywood wheel on the potentiometer. The gear ratio calibration was set by adjusting the layers of electrical tape around the rim of the wooden wheel. It worked well and provided a useful audio frequency response display, until a proper function generator with a sweep output was purchased several years later. To HP's credit, the 200CD was one piece of equipment that I didn't (or couldn't) break. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Reply by ●July 5, 20172017-07-05
On 05/07/17 05:57, pcdhobbs@gmail.com wrote:>> Engineers probably worked for years to design clever "DCOs" which >> frequency-locked analog oscillators to a temperature stable reference >> clock, divided down under microprocessor control. > > Way before microprocessors, there were "top octave generators", strings of dividers running off a strategically-chosen crystal. > > They were too accurate, so they sounded thin.More precisely, they were accurate to a rational (fractional) scale, not to a well-tempered scale. So you lost all the single-digit Hz variations. Also, the lower octaves were again all divided exactly by two, so there was no "stretch tuning" the pianos are tuned. Pianists differ in the amount of stretch tuning they prefer, but a full semitone distributed between the 87 steps is usual, and some prefer up to two full semitones, meaning that the top octave is numerically 12% high (a full tone sharp) in frequency compared to the bottom octave. There is a physical justification for this. The Mersenne equation does not account for string inharmonicity, usually attributed to "end effects" - the the fixed ends of the string acting as bending columns with Bessel behaviour. This results in increasing harmonics of a string being increasingly sharp. A well-tempered tuning can tune the fundamentals only (which is numerically double) or it can bend towards harmonising the second or third harmonic - which results in stretch tuning. Needless to say, simplistic digital dividers like the top octave generators do not produce any of these effects! Clifford Heath.
Reply by ●July 5, 20172017-07-05
On Tue, 04 Jul 2017 17:51:14 -0800, Robert Baer wrote:> In the RF spectrum, do the HPs stand on the extreme left, or are they > simply (politically) blase?This one's on the extreme left, yes.
Reply by ●July 5, 20172017-07-05
On 07/04/2017 11:41 PM, Clifford Heath wrote:> On 05/07/17 05:57, pcdhobbs@gmail.com wrote: >>> Engineers probably worked for years to design clever "DCOs" which >>> frequency-locked analog oscillators to a temperature stable reference >>> clock, divided down under microprocessor control. >> >> Way before microprocessors, there were "top octave generators", >> strings of dividers running off a strategically-chosen crystal. >> >> They were too accurate, so they sounded thin. > > More precisely, they were accurate to a rational (fractional) scale, > not to a well-tempered scale. So you lost all the single-digit Hz > variations. Also, the lower octaves were again all divided exactly > by two, so there was no "stretch tuning" the pianos are tuned.The top octave was likely tuned to 12th-root-of-two equal temperament, same as most modern non-piano polyphonic instruments (and synthesizers)> Needless to say, simplistic digital dividers like the top octave > generators do not produce any of these effects! > > Clifford Heath.Yeah, but I don't think that's the reason they sounded "thin", it was mainly because linearly mixing simple square waves of different frequencies but the same phase relationships just sounds bad.
Reply by ●July 5, 20172017-07-05
On 07/04/2017 03:57 PM, pcdhobbs@gmail.com wrote:>> Engineers probably worked for years to design clever "DCOs" which >> frequency-locked analog oscillators to a temperature stable reference >> clock, divided down under microprocessor control. > > Way before microprocessors, there were "top octave generators", strings of dividers running off a strategically-chosen crystal. > > They were too accurate, so they sounded thin. > > Cheers > > Phil Hobbs >Tonewheel organs just generated top ocatave sine waves too, but sounded great because you could mix in different harmonics from wheels of various sizes to do basic additive synthesis. Then push the result through an overdriven tube amplifier and a rotating speaker. Still popular in all styles of music: <https://www.youtube.com/watch?v=cYC5cUQMU8I> Yes. Yesss....
Reply by ●July 5, 20172017-07-05
On 05/07/17 21:32, bitrex wrote:> On 07/04/2017 11:41 PM, Clifford Heath wrote: >> On 05/07/17 05:57, pcdhobbs@gmail.com wrote: >>>> Engineers probably worked for years to design clever "DCOs" which >>>> frequency-locked analog oscillators to a temperature stable reference >>>> clock, divided down under microprocessor control. >>> >>> Way before microprocessors, there were "top octave generators", >>> strings of dividers running off a strategically-chosen crystal. >>> >>> They were too accurate, so they sounded thin. >> >> More precisely, they were accurate to a rational (fractional) scale, >> not to a well-tempered scale. So you lost all the single-digit Hz >> variations. Also, the lower octaves were again all divided exactly >> by two, so there was no "stretch tuning" the pianos are tuned. > > The top octave was likely tuned to 12th-root-of-two equal temperament,No - they were integer approximations of the required dividers. The most widely used chips audibly diverged from equal temperament. You can do the sums yourself: <http://synthdiy.com/files/2001/mk50240.pdf> <http://www.armory.com/~rstevew/Public/SoundSynth/TopOctave/topdividers.html>>> Needless to say, simplistic digital dividers like the top octave >> generators do not produce any of these effects! > > Yeah, but I don't think that's the reason they sounded "thin", it was > mainly because linearly mixing simple square waves of different > frequencies but the same phase relationships just sounds bad.It does. But all the ratios in stretch tuning and equal temperament that are not rational numbers generate a lot of low frequency beats that create a kind of vibrancy that you just don't get with simple fractions.
Reply by ●July 5, 20172017-07-05
On Tuesday, July 4, 2017 at 1:03:10 PM UTC-4, bitrex wrote:> On 07/03/2017 09:54 PM, Phil Allison wrote: > > bitrex wrote: > > > > ------------------ > > > >> > >> Tangentially related - the audio sine wave oscillator I've been using > >> for several years is a solid state box labeled "LofTech"; manufactured > >> by "Phoenix Audio Labs, Manchester, CT". > >> > >> It's mostly full of LM13600s and TL074s with date codes from the middle > >> of 1986. I don't have a THD analyzer so I can't say what its specs are > >> now in that regard; visually at least the sines it puts out look math > >> textbook perfect on a scope. The brochure claims a maximum THD of 0.5% > >> > >> Unfortunately frequency stability isn't good - it's very drifty with > >> time and temperature; sometimes 3-5 Hz up and down over time just > >> sitting in a shop at room temperature, which is annoying. The brochure > >> scan online doesn't say anything about drift specs so I don't know if > >> that's normal for the product's design or if it should be serviced. > >> > > > > ** See link: > > > > http://www.barryrudolph.com/recall/manuals/loftts1.pdf > > > > The unit has a single pot that sweeps the audio band, assuming it is a carbon track type, frequency stability WILL be poor. > > > > Firstly, the track has a large tempco plus the wiper will have some drift after setting. So it is not faulty. > > > > My bench oscillator use a dual gang WW pot with hundreds of turns plus it only covers a decade range. A rotary switch choses which one of five starting at 2Hz. Drift is very small. > > > > The all valve one I mentioned also has low drift, once it fully warms up, as the frequency determining bits are an air capacitor and MF resistors. > > > > > > > > .... Phil > > > > Got it, thanks. Probably time to invest in something a little better.I love my rigol DG1022, ~1 milli-Hz to 20 MHz. (Sine). It has two channels with synchronous phase control for each. (Well there's an align phase button you have to press.) George H.
Reply by ●July 5, 20172017-07-05
On 07/05/2017 08:47 AM, Clifford Heath wrote:> On 05/07/17 21:32, bitrex wrote: >> On 07/04/2017 11:41 PM, Clifford Heath wrote: >>> On 05/07/17 05:57, pcdhobbs@gmail.com wrote: >>>>> Engineers probably worked for years to design clever "DCOs" which >>>>> frequency-locked analog oscillators to a temperature stable reference >>>>> clock, divided down under microprocessor control. >>>> >>>> Way before microprocessors, there were "top octave generators", >>>> strings of dividers running off a strategically-chosen crystal. >>>> >>>> They were too accurate, so they sounded thin. >>> >>> More precisely, they were accurate to a rational (fractional) scale, >>> not to a well-tempered scale. So you lost all the single-digit Hz >>> variations. Also, the lower octaves were again all divided exactly >>> by two, so there was no "stretch tuning" the pianos are tuned. >> >> The top octave was likely tuned to 12th-root-of-two equal temperament, > > No - they were integer approximations of the required dividers. > The most widely used chips audibly diverged from equal temperament. > You can do the sums yourself: > <http://synthdiy.com/files/2001/mk50240.pdf> > <http://www.armory.com/~rstevew/Public/SoundSynth/TopOctave/topdividers.html>Yeah, as the 12th root of 2 is irrational you would have to truncate the real number somewhere into a rational approximation, and apply something like a Stern-Brocot tree to find the best approximation with the granularity you have available. <https://en.wikipedia.org/wiki/Stern%E2%80%93Brocot_tree> I guess the top-octave chips of the time were using counters that didn't have many "bits", so it sounded off. "DCOs" in synthesizers from the 1980s had counters with more resolution; my Roland Juno (circa 1986) uses Intel 8253 16 bit PITs under uP control to divide an 8 MHz crystal clock and sync the analog sawtooth generators to that.>>> Needless to say, simplistic digital dividers like the top octave >>> generators do not produce any of these effects! >> >> Yeah, but I don't think that's the reason they sounded "thin", it was >> mainly because linearly mixing simple square waves of different >> frequencies but the same phase relationships just sounds bad. > > It does. But all the ratios in stretch tuning and equal temperament that > are not rational numbers generate a lot of low frequency beats > that create a kind of vibrancy that you just don't get with simple > fractions.The Farfisa organ sounded OK in moderation: <https://www.youtube.com/watch?v=deB_u-to-IE>
Reply by ●July 5, 20172017-07-05
On 06/07/17 03:32, bitrex wrote:> On 07/05/2017 08:47 AM, Clifford Heath wrote: >> On 05/07/17 21:32, bitrex wrote: >>> On 07/04/2017 11:41 PM, Clifford Heath wrote: >>>> On 05/07/17 05:57, pcdhobbs@gmail.com wrote: >>>>>> Engineers probably worked for years to design clever "DCOs" which >>>>>> frequency-locked analog oscillators to a temperature stable reference >>>>>> clock, divided down under microprocessor control. >>>>> >>>>> Way before microprocessors, there were "top octave generators", >>>>> strings of dividers running off a strategically-chosen crystal. >>>>> >>>>> They were too accurate, so they sounded thin. >>>> >>>> More precisely, they were accurate to a rational (fractional) scale, >>>> not to a well-tempered scale. So you lost all the single-digit Hz >>>> variations. Also, the lower octaves were again all divided exactly >>>> by two, so there was no "stretch tuning" the pianos are tuned. >>> >>> The top octave was likely tuned to 12th-root-of-two equal temperament, >> >> No - they were integer approximations of the required dividers. >> The most widely used chips audibly diverged from equal temperament. >> You can do the sums yourself: >> <http://synthdiy.com/files/2001/mk50240.pdf> >> <http://www.armory.com/~rstevew/Public/SoundSynth/TopOctave/topdividers.html> > > Yeah, as the 12th root of 2 is irrational you would have to truncate the > real number somewhere into a rational approximation, and apply something > like a Stern-Brocot tree to find the best approximation with the > granularity you have available. > <https://en.wikipedia.org/wiki/Stern%E2%80%93Brocot_tree>It's trivial to find rational approximations using continued fractions. Here's the output of my program, given the twelfth root of 2: $ ~/bin/continued_fraction 1.059463095 Usage: ratvalue [number [maxnumerator]] number defaults to PI, maxnumerator to 500 Rational approximation to 1.059463095000000 1 / 1 = 1.000000000000000 with error 0.059463095000000 10 / 9 = 1.111111111111111 with error 0.051648016111111 11 / 10 = 1.100000000000000 with error 0.040536905000000 12 / 11 = 1.090909090909091 with error 0.031445995909091 13 / 12 = 1.083333333333333 with error 0.023870238333333 14 / 13 = 1.076923076923077 with error 0.017459981923077 15 / 14 = 1.071428571428571 with error 0.011965476428571 16 / 15 = 1.066666666666667 with error 0.007203571666667 17 / 16 = 1.062500000000000 with error 0.003036905000000 18 / 17 = 1.058823529411765 with error 0.000639565588235 53 / 50 = 1.060000000000000 with error 0.000536905000000 71 / 67 = 1.059701492537313 with error 0.000238397537313 89 / 84 = 1.059523809523810 with error 0.000060714523810 107 / 101 = 1.059405940594059 with error 0.000057154405940 196 / 185 = 1.059459459459460 with error 0.000003635540540> I guess the top-octave chips of the time were using counters that didn't > have many "bits", so it sounded off.The dividers on the MK50240 produced a scale in which three of the notes are more than one cents flat (compared to the mean line - compared to the tonic it was even worse). But though that's easily audible to folk with ear training, it's the LF beats that are notably missing; hence the extensive use of tremolo in a weak attempt to make up for it. You can clearly hear that in "Light My Fire". It's a classic sound, so we like it; but doesn't resemble the sound of physical resonators. Clifford Heath.
