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A Ling ?

Chuck Berry - My Ding A Ling (1972)

The man refined and developed rhythm and blues for 70 years, and he is remembered for singing a dumb ditty about his wee-wee. (This was his only #1 hit, and next-to-last top 40.)

much much longer version

In the OP's schematic pin 2 of the NE555 should connect to pin 6 not to +V.  This error is not present in the Elektor schematic below.

wow. all that shaping of the square wave, you could just take the pin2/pin6 output and buffer it for a sawtooth-ish output.

I think the filter is intended to give a nicer sine output than just the exponential output across the cap.   The advantage of *starting* with the exponential output is the level is automatically set by the NE555 regardless of the frequency pot setting.

To me the circuit around C6 looks wrong.  I think there should be another 10k resistor between C4 and C6. Another options could also pull C6; which now seems more likely - see below.

The problem with making the frequency variable is the level of the sine output (and triangle and exponential outputs for that matter) will decrease with frequency.

Replaced R1 with a 1M pot and inlined the 10k resistor with that as without it would cut out if the frequency got too high, presumably outside the spec for the chip or something like that.

You would do better making R2 variable so the output remains more or less square when you adjust the frequency.   Making R1 variable means the shape of the waveform changes when the frequency is adjusted:  the output high time varies and the output low time is fixed.

For R1 variable, putting 10k in series with the pot is necessary to ensure the oscillator can oscillate.   For R2 variable you don't need the 10k but it is very desirable because without it the frequency will increase rapidly at the end in an impractical manner - 10k to 50k is a good choice.

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Looks like the original Elektor circuit has the sine filter error as well:
(Need a resistor between C7 and C4, could also just pull C4.
 But oddly enough the kit PCB seems to have C4 loaded, like the schematic.)

https://worldradiohistory.com/hd2/IDX-UK/Technology/Technology-Modern/Archive-Elektor-IDX/IDX/00s/Elektor-2000-12-OCR-Page-0097.pdf

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Seems like there's a few problems with that circuit.  Some tentative fixes.
The idea was to work out what the circuit was based on the sine output level in the Elektor (Dec 2000) article.



I'm seeing about 0.7V p-p on the square output, 2.5V p-p on the exponential output, 0.7Vp-p on the triangle output.

With the square output the buffer is being totally cut-off on the negative swing because the 1k on the divider is killing the bias on the output buffer.   The same thing isn't allowed to happen on the exponential and triangle waveforms as that would chop off the negative tips of the waveform.  Luckily as you progress down the 10ks it finds a new bias point which keeps the output buffer biased enough not to clip.

Ok, so I checked R12 and 13 - both are 47K and correct. I tested R12 and one lead is getting the full VA (8.61v) and the other side reads the same as the end of R13 that it’s tied to (4.25v), but the strange thing is that I read 0v on the + pad of C10. As a contrast, on the “B” side of the pedal I read the 4.25v on the + pad of C20.

I even tried installing another 100uf/25v cap I have here and same thing - no 4.25v on the + pad. When I install a small jumper from the C12/13 junction to + of C10… still nothing.

This has got me stumped. Considering starting over, though I’d really like to see this through.

Interesting they swapped the order of the Low and High EQ sections on the YH and the PP.  Presumably so the same PCB can be used to get treble boost on the PP and bass boost on the YH in the lone EQ setting.

Probably good idea to do a NPN version.  Seems like a good idea to keep the gains >= 200.
[FYI: The generic 2SA666 has a typical gain of 250.   However these devices come in
gain sorted -P, -Q, -R, -S, -T versions.  For those -R is hFE 180 to 360, and -S is hFE 260 to 520.
I don't know what the original used.  Need PCB pics.
I found a Red Ranger pic (Musitronics era) which had a 2SA666-R.]

Here's some more info:



Oh, it seems flat isn't flat.  I checked the sim and it seems to be the case.   It's the 470k resistors.  They are not large compared to the 2x82k =164k.   If you want flat in the flat position use a bypass switch or change the 470k's to something much larger.

I used phone's own case because I thought it was just neat.

Cool idea.