Casio VL-Tone Circuit Mystery (is this an error in the envelope detector schematic?)
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- Опубліковано 7 тра 2024
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They’ve also cut out any base resistors (there needs to be one for the lower mixer transistor if nothing else), I imagine they accidentally cut a few too many resistors in the name of legibility. Maybe you can find an image of its PCB and find out for certain.
Looks like nobody has taken a photo of both sides of the smaller board, but there are some good images of the component side so you can look near the three transistor section and maybe see if you can recreate the single-sided layout. Or just message some of the guys with photos to see if they can take a photo of the other side of the small board.
Oh, yeah, I was wondering how they weren't blowing up that transistor. ;)
@@Lantertronics
could also be an open collector comparator, but in that case it’s just the pull-up resistor they missed instead of the series resistor.
Whoa. I had a little black/dark grey Casio keyboard(edit: it was a PT-10 Mini Synth apparently) about that size back in the mid 80s. Got it when I was like 5-6 yrs old. I had it for a long time and it always worked. I just quit playing with it.
Apparently it has the same chip as the VL-1 👌
I wonder if the emitter should be connected to the other side of that diode. It seems to make more sense that way... dumping high freq to ground
2:21 would help to know what kind of transistor is being used nmos, pnmos, cmos
Is it open collector and not TTL
Transistors can be used in a analog/linear fashion too... Considering it being an audio output
And audio is technically an ac waveform
Typically with +3v and -3v rails is a sign that it may be some sort of push pull configuration, to generate a true ac waveform not a pulsed DC waveform with smoothing
6V drop across the transistor with no current limiting seems like a very bad idea. Does seem like a mistake.
If you think thats odd take a look at a picture of the insides of the VL-5 its pure insanity inside. 30+ bodge wires, through hole components mounted as surface mount, 3 separate NTC thermisters doing god knows what oh and 2 red leds on the inside doing ... something in the power supply section...
Reminds me of the Emerson Arcadia 2001 PCB. I had assumed that the unit my student I were looking at were subject to some repairs, but apparently they all look like that!
Okay, I just googled for pics of the inside of the VL-5, and... WHOA! You were not kidding!
@@Lantertronics and 0 documentation or service manual :'(
@@krishna34674 I often tasks my students with reverse engineering such things; I try to make sure it doesn't lead them into madness. ;)
My vl5’s display only works when powered by an external psu. BUT theres a constant very loud hum when doing so, much louder than using batteries. Any idea? Im scared to open it and just poke around in case i kill it
I guess, they simply forgot to draw the emitter resistor between the diodes anode and -3V
Why you are so fascinated with this ? I think this is what made you become the famous professor Lanterman. Whwn I close my eyes I see a12 year old Aaron Lanterman opening up his brand new, yet second hand, Casio VL-1 to find out how this thing works and I think you never stopped exploring since 😁
The envelope detector schematic must be faulty. Looking at the signals SP1 and the output of the envelope detector, both the higher audio frequency and the digital volume stepping are filtered out. The signal at SP1 is a frequency/pulse width variable signal with a (digital controlled) stepped volume (most likely using a very crude R-2R ladder DAC). The transistor is an emitter follower with the resistor between the emitter and -3V missing. The diode/capacitor is a peak detector to remove the audio from the signal and the resistor (both the resistor and capacitor are connected to -3V, not the emitter) results in the low pass filter stage for the envelope. There must also be an additional resistor between the collector and the +3V to create a low pass on the rising edge, otherwise you would still have the digital step on the rising edge of the envelope.
It wasn't this, but I recall having some sort of electronic keyboard toy when I was very young, where it came with all the parts exposed and bare metal contacts for the keys, as some sort of educational electronics thing. Maybe Heathkit? Maybe Radio Shack? I can't recall for sure. My first real synth was a Sequential Multi-Track my parents kindly got me when I was starting high school I think.
I can pretty much trace my current job to playing Akalabeth (Lord British's first game, before Ultima) on the Apple II+ and having it completely BLOW MY MIND.
I’d say it’s more likely a PGA after the timer PWM output, as opposed to an R2R ladder. If it were an R2R, having 11 steps would be strange.
Probably Re is missing there in Env detector.
It looks like an error to me as well ... unless there is something really strange going on with the impedance of the -3V source.
That's why it's simplified diagram. There must be a resistor there. It's only there to basically demonstrate the working.
I'm sure it's drawn incorrectly, I've seen a ton of similar errors on older schematics. Not sure what the correct component configuration is though, could be missing a component (?) or could just be configured the wrong way.
Probably not an "error" as much as their idea of a simplified schematic. Just look at the op amp section right below it. It's almost certainly not operating without negative feedback. I would guess there's a resistor in series with -3V though a more complete schematic would be interesting to see.
The op amp below is operating as a comparator, so it wouldn't necessarily have negative feedback, but it's certainly an incomplete diagram, so you've got about about it being their idea of a simplified schematic. And you are quite right, if you put a resistor between the emitter and the -3 V it would indeed make a lot more sense.
It really makes me wish there's a complete schematic out there somewhere...
Post the question to the sdiy list if you're not planning to do that already.
@@Gameboygenius Oh that's a good idea.
I think "Divider 1" is an meant to be an envelope follower circuit.
It's definitely *meant* to me an envelope follower. I'm just puzzled that what's drawn there isn't that... it's like whoever was assigned to draw the simplified circuit just randomly left stuff out. ;)
My impression is they told a person who had no understand to draw a circuit with the symbols for these parts @@Lantertronics
no resistor on the base, no resistor on the emitter to GND, the current would take the easy path.
I did a simulation the capacitor doesn't seam to have any effect, even removing the cap, resistor, alternating but with resistor on the emitter to GND, the diode conducts bi-polar signal. Even with a push button on the base i can't see an effect of the capacitor (no matter what size), accept the voltage drop from the diode.
Must be a "block" type of circuit just for demonstration purpose and not the real thing.
Yeah, it's definitely not the real circuit. I wonder whose idea it was to draw that though, simplified schematics should illuminate instead of confuse. ;)
@@Lantertronics "I wonder whose idea it was to draw that though"
hahaha, you made my day with that comment.
I made or are in the process of making a Push Pull amp, also making mosfet PSU PCB that handle like 5 amps to power that.
But I'm sure you like my Push Pull circuit.
Linea circuit is good.
I’ve had a VL-Tone for more than forty years, and all it’s ever done when switched to ADSR is produce an infinitesimal blip. I’ve always assumed that it supposed to be an envelope, but it’s never worked as such. What, if anything, have I been doing wrong since 1982?
You need to read the instruction manual, I had the same experience til I read the manual. You could also just search here for an instruction video, pretty sure there are a few.
Well, it's been about 40 years, but if I remember correctly, you store a number into the memory of the calculator when in calculator mode, and that value is used as the ADSR value in keyboard mode.
I believe you have to enter a program sequence via the calculator function. There’s tutorials here on UA-cam.
@@Lantertronics I did eventually find a video that described the process, not just showed a chap tapping in a string of random numbers…
I have a casio vl tone vl 1 and i'd be happy to share pcb pictures! let me know if you still need them and how i can reach ;)
I think I’m good, someone sent me a link to a real schematic (I’ll make a follow up video at some point)
Replicate it on a breadboard already please...