[HN Gopher] Reverse-engineering the waveform generator in a 1969... ___________________________________________________________________ Reverse-engineering the waveform generator in a 1969 breadboard Author : picture Score : 55 points Date : 2022-03-09 18:04 UTC (4 hours ago) (HTM) web link (www.righto.com) (TXT) w3m dump (www.righto.com) | kens wrote: | Author here for all your questions about obsolete oscillator | circuitry :-) | adrian_b wrote: | Even if I do not have any question, because I happen to be | familiar with this kind of circuits, I just want to thank you | for your work resulting in one more interesting article. | | I suppose that there must be many like me, who normally would | not feel the need to comment your articles, but who nonetheless | enjoy very much reading them. | | A long time ago, when I was young, I have worked with many | devices and circuits similar to those reverse-engineered by you | in this series of articles. Unfortunately at that time it was | tedious and expensive to make photographic records of such | technologies and such work, so now I am sad that I do not have | records and the memories fade away. | | Your articles fill this void and I am grateful for them. | tgflynn wrote: | I'm curious how you were able to source the parts to replace | the burned out transistors and other components. | AdamH12113 wrote: | Nice write-up! Question about the (excellent) schematic PDF -- | in the pulse trigger section, the emitter of Q3 seems to be | tied to the top of R14, but I don't think that can be right? Is | it supposed to be connected to ground? | kens wrote: | You should expect about 90% accuracy from the schematic :-) I | didn't check the transistor part numbers, so I kind of | guessed at NPN vs PNP. Most likely it's a PNP transistor. But | the pinout could also be wrong. | parksy wrote: | There's a group in my city who meet every month to generate wacky | noises from all sorts of things. With this thing's built-in | generator and layout I feel like you could build a primitive step | sequencer with those switches and dials and deliver a godlike | performance of audio and engineering prowess. | | Even better if you can voltage control the frequency. Then if you | can introduce a delay in the oscillator output, filter it, then | feed back into the variable resistor(?) that controls its | frequency, you have the basis of a mini-FM synth - if you can get | it to stay stable in the normal human hearing range of course... | | Nothing really to add on the engineering side, just seeing how it | looks, I want to hear it making some noise, although it's not its | intended purpose. | | Nice work on figuring out how to get it going again! | earthscienceman wrote: | Which city and how do I join something near me? Denver?! | scarecrowbob wrote: | You might take a peek at the Colorado Modular Synth Society: | | https://www.facebook.com/groups/1216704935132398 | parksy wrote: | Our local one is https://www.noizemaschin.com/ - they're | based in London and Perth Australia, it's kind of a hybrid | maker space / underground scene. Good folk from all walks of | life. | | Not sure about Denver but I did some searches for | experimental music, perhaps jump on the local subreddit as it | seems there's a small noise music scene but I wasn't able to | pinpoint anything specific. | bragr wrote: | I love the hand hewn charm of these old boards. Now even homemade | boards are designed in software so everything is very straight | and regular, but with old boards you can tell everything was done | by hand from the design to the layout to the assembly. Don't get | me wrong, it's great that you can cad something up, send the | files off, and get perfect boards in 2 days, but these old boards | are the electronic equivalent to a charming, rustic, cabin in the | woods. | thecloud wrote: | If you buy a guitar pedal from a small-ish boutique company, | you might just get a little box with a lot of charm that you | can open up and peek at some beautiful hand assembled/soldered | circuits :) | gzalo wrote: | Am I the only one that thinks that $1300 is absurdly high? | acording to radioshack catalogs, in 1968 you could get an rf | signal generator for just 30 bucks, and an oscilloscope for 130 | bucks, so why whould you spend that much in this breadboard? it | doesnt seem like it would cost that much! | kens wrote: | I think that the signal generator is closer to HP test | equipment quality than Radio Shack quality, which may explain | the price. I was expected a simple circuit, but when I looked | inside it turned out to be very complex. | | Here's the brochure for the breadboard with specs and the | price: | https://archive.org/details/TNM_Elite_1_2_3_dynamic_breadboa... | amelius wrote: | You can't get very high signal integrity on a breadboard. | bragr wrote: | Zooming in on the unit, the range knob on the function | generator goes from 1hz to 1Mhz and the pulse generator 100ms | to 100ns. I looked in a 1968 catalog a didn't see anything with | close to those capabilities. | https://radioshackcatalogs.com/flipbook/1968_radioshack_cata... | ChuckMcM wrote: | Lovely. And I really like the design aesthetic of the knobs and | switches (similar to analog computers which I also find pretty | fascinating). I've seen the variable voltage regular to change | output amplitude trick in circuits where that signal is low | impedance and designed to have a lot of drive current. One was a | pulse generator that provided the signal for an animatronic | robot, and the pulses were basically used directly to fire the | solenoids on the pneumatics. Saved having a transistor on every | solenoid. | formerly_proven wrote: | > The sine-wave shaper appears to be inspired by the similar | circuit in the HP 3300A Function Generator, introduced in 1965. | The schematic below shows the HP 3300A's sine-wave shaper; the | breadboard's network is similar. The resistances are carefully | chosen to achieve the sine wave. | | In some Philips FGs they had sine shaping ASICs (presumably with | a ton of taps and good matching) and managed to get distortion | down to 0.1 % iirc (which for the 70s or early 80s would have | meant that you don't really need a proper RC oscillator any more | for testing audio amplifiers). ___________________________________________________________________ (page generated 2022-03-09 23:00 UTC)