Search found 4702 matches

by guest
Tue Oct 27, 2020 8:41 pm
Forum: Music Tech DIY
Topic: Can't get LM13700 Sample and Hold Circuit to work
Replies: 9
Views: 50

Re: Can't get LM13700 Sample and Hold Circuit to work

no worries. whats happening is that current is leaking off the capacitor into the darlington buffer. this leakage is around a 1uA or so with the 1k in place, which discharges teh cap really quickly. even if you go to 1M resistor, you still have 1nA of leakage, which is a fair bit. a FET or FET input...
by guest
Tue Oct 27, 2020 8:34 pm
Forum: Music Tech DIY
Topic: Can't get LM13700 Sample and Hold Circuit to work
Replies: 9
Views: 50

Re: Can't get LM13700 Sample and Hold Circuit to work

i dont think that circuit can hold a voltage for more than 10ms. either increase the capacitor, increase the 1k (to like 100k or 1M), or use an opamp in place of the darlington buffer.
by guest
Tue Oct 27, 2020 8:31 pm
Forum: Music Tech DIY
Topic: Can't get LM13700 Sample and Hold Circuit to work
Replies: 9
Views: 50

Re: Can't get LM13700 Sample and Hold Circuit to work

what happens if you put in a bigger sample capacitor? like 1uF?
by guest
Tue Oct 27, 2020 8:29 pm
Forum: Music Tech DIY
Topic: Can't get LM13700 Sample and Hold Circuit to work
Replies: 9
Views: 50

Re: Can't get LM13700 Sample and Hold Circuit to work

what are the voltages on all pins of the 13700 in "hold" mode?
by guest
Tue Oct 27, 2020 8:23 pm
Forum: Music Tech DIY
Topic: Can't get LM13700 Sample and Hold Circuit to work
Replies: 9
Views: 50

Re: Can't get LM13700 Sample and Hold Circuit to work

is your negative rail to the 13700 -5V?
by guest
Tue Oct 27, 2020 6:05 pm
Forum: Music Tech DIY
Topic: Understanding suitable transistor and opamp substitutions
Replies: 2
Views: 35

Re: Understanding suitable transistor and opamp substitutions

unfortunately there isnt a single answer here, as it really depends upon what the part is being used for. lets take your BC558B as an example. first off, they do have them at digikey, so you can get the part if you want it, but maybe its not strictly necessary? in the CGS64 that transistor is used a...
by guest
Tue Oct 27, 2020 4:17 pm
Forum: Music Tech DIY
Topic: Yusynth Trigger Delay - Latch up
Replies: 5
Views: 60

Re: Yusynth Trigger Delay - Latch up

i suspect that the CD4538 is bad. if you turn the pulse width knob to minimum, what is the voltage on pin14? turn the power off and measure the resistance of R6, is it 10k (set pulse width to max for this measurement)? is there anything else accidently connecting to pin14 or R6?
by guest
Mon Oct 26, 2020 8:59 pm
Forum: Music Tech DIY
Topic: Yusynth Trigger Delay - Latch up
Replies: 5
Views: 60

Re: Yusynth Trigger Delay - Latch up

im still a bit confused, is it this project: http://yusynth.net/Modular/Commun/PULSEDELAY/pulsedelay-sch.gif is the pulse time you are referring to the output pulse width, or the pulse delay? did you build a dual, and if so are both exhibiting the issue? what are the voltages on all pins of the CD45...
by guest
Mon Oct 26, 2020 8:23 pm
Forum: Music Tech DIY
Topic: Yusynth Trigger Delay - Latch up
Replies: 5
Views: 60

Re: Yusynth Trigger Delay - Latch up

is this for short delay times, or output pulse width, or both? how long are the pulse widths when it latches up?
by guest
Sun Oct 25, 2020 10:12 pm
Forum: Music Tech DIY
Topic: CV Theremin and A-178 reverse engineering
Replies: 21
Views: 301

Re: CV Theremin and A-178 reverse engineering

thanks KSS! i think i find other peoples circuit issues more interesting than my own, and it always forces me to learn new things. gives me new ideas. the muse is a crazy synth, down to almost every detail; like how its assembled - sort of a jigsaw puzzle. and the huge pcb slider switches. i had som...
by guest
Sun Oct 25, 2020 9:54 pm
Forum: Music Tech DIY
Topic: rhythm wolf teardown: any questions?
Replies: 219
Views: 10129

Re: rhythm wolf teardown: any questions?

unfortunately i buttoned mine back up. but, if i recall correctly, U36 is on the backside of the board, a little SOIC-8 device. i think i ran the resistor on the backside of the board as well. C104 is an electrolytic cap, so you can solder to the pin that pokes through the board to the backside. loo...
by guest
Sun Oct 25, 2020 11:41 am
Forum: Music Tech DIY
Topic: CV Theremin and A-178 reverse engineering
Replies: 21
Views: 301

Re: CV Theremin and A-178 reverse engineering

thats a good point. also, if you have access to one, you can just look at the circuit and see what they did.
by guest
Sun Oct 25, 2020 12:46 am
Forum: Music Tech DIY
Topic: CV Theremin and A-178 reverse engineering
Replies: 21
Views: 301

Re: CV Theremin and A-178 reverse engineering

yes, the simple circuit can work well if things dont change. but, its hard to predict these things in a gallery setting. i was hoping to get the schematics drawn up today, but didnt have time. ill do my best to just describe the method of integrating pulses: 1. take output of 555 to a capacitor that...
by guest
Sat Oct 24, 2020 10:11 pm
Forum: Music Tech DIY
Topic: CV Theremin and A-178 reverse engineering
Replies: 21
Views: 301

Re: CV Theremin and A-178 reverse engineering

the main thing an external circuit does for you is get rid of the offset and add some gain. a hand near an antenna varies capacitance by 0.1pF at a foot, and then goes up to 1pF as you get within an inch, and then 10pF as you get within a millimeter. so the variation is really small depending upon t...
by guest
Sat Oct 24, 2020 9:47 pm
Forum: Music Tech DIY
Topic: CV Theremin and A-178 reverse engineering
Replies: 21
Views: 301

Re: CV Theremin and A-178 reverse engineering

depending upon the level of sensitivity you need, you can also just do a microcontroller based capacitive sensing circuit. its essentially the same thing as using a 555, you set up a bit of code to make an oscillator around a capacitor and resistor. might be worth hacking up and seeing what it can d...
by guest
Sat Oct 24, 2020 8:49 pm
Forum: Music Tech DIY
Topic: CV Theremin and A-178 reverse engineering
Replies: 21
Views: 301

Re: CV Theremin and A-178 reverse engineering

ok, if you want something stable that doesnt require recalibration, i have another circuit for you (ive used this sort of thing for art installs as well). the issue with capacitive sensing is that it can easily drift. temperature effects it, as does the placement of furniture or other objects in the...
by guest
Sat Oct 24, 2020 12:42 pm
Forum: Music Tech DIY
Topic: EURO x0x-heart - Complete "Kit"
Replies: 164
Views: 13399

Re: EURO x0x-heart - Complete "Kit"

looks good!
by guest
Sat Oct 24, 2020 12:26 pm
Forum: Music Tech DIY
Topic: Getting power from MIDI socket?
Replies: 5
Views: 131

Re: Getting power from MIDI socket?

you might be able to open up the faderfox and modify the circuit so the phantom power works. or just put a battery on the bluetooth dongle you have.
by guest
Sat Oct 24, 2020 9:22 am
Forum: Music Tech DIY
Topic: CV Theremin and A-178 reverse engineering
Replies: 21
Views: 301

Re: CV Theremin and A-178 reverse engineering

yes, that would work for V/F conversion, although you can also make one out of an opamp. it pretty much will do the same thing as the chip: convert incoming frequency to pulses and then integrate those pulses to make a voltage. i can post a schematic later today.
by guest
Fri Oct 23, 2020 8:02 pm
Forum: Music Tech DIY
Topic: CV Theremin and A-178 reverse engineering
Replies: 21
Views: 301

Re: CV Theremin and A-178 reverse engineering

do you have a TLC555? if so, build up the "astable operation" circuit from the datasheet. if not, use a TL072 to make an oscillator: https://www.learningaboutelectronics.com/images/RC-op-amp-oscillator.png for either of these, use a small capacitor (10pF) and connect the antenna to the capacitor. fo...
by guest
Fri Oct 23, 2020 6:03 pm
Forum: Music Tech DIY
Topic: midiphy wirescanner cable tester
Replies: 5
Views: 143

Re: midiphy wirescanner cable tester

thats really cool!
by guest
Fri Oct 23, 2020 4:40 pm
Forum: Music Tech DIY
Topic: CV Theremin and A-178 reverse engineering
Replies: 21
Views: 301

Re: CV Theremin and A-178 reverse engineering

theirs uses the TLC555 to do the relaxation oscillator thing. the TLC is important because it has a higher input impedance.
by guest
Fri Oct 23, 2020 4:37 pm
Forum: Music Tech DIY
Topic: CV Theremin and A-178 reverse engineering
Replies: 21
Views: 301

Re: CV Theremin and A-178 reverse engineering

i dont know what circuit that is, but you can build a pretty quick/easy theremin by making a relaxation oscillator from an opamp, but instead of using a capacitor, just run a wire to your antenna. use a large feedback resistor, like 1M or so. to get CV there are a few options, but an easy one is to ...
by guest
Fri Oct 23, 2020 4:26 pm
Forum: Music Tech DIY
Topic: AS3397
Replies: 4
Views: 173

Re: AS3397

70x is pretty crazy, if its just OTA gain stages. im guessing its for two reasons: reduce noise and increase amplitude. you can make an OTA with fewer transistors that only has +/-200mV swing, but thats not so great for an output signal, so they might take the final stage and make the standard OTA t...
by guest
Fri Oct 23, 2020 11:14 am
Forum: Music Tech DIY
Topic: Dannysound EN129 failed build help!
Replies: 10
Views: 211

Re: Dannysound EN129 failed build help!

thats the 78L09, i think he needs the 79L09, which is looking quite hard to get these days. never thought id see that day.

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