Search found 592 matches

by Synthiq
Mon Oct 19, 2020 11:09 pm
Forum: Music Tech DIY
Topic: Simple Voltage Generator (schematics feedback)
Replies: 3
Views: 83

Re: Simple Voltage Generator (schematics feedback)

+1 for the TL431. Besides being more accurate, it only needs <1mA to work correctly while the the zener diode is specified at a 20mA current. In the power section, the filter capacitors should be connected between the power and ground, not across the resistor. The filter resistor is listed as 1kohm,...
by Synthiq
Mon Oct 19, 2020 1:09 pm
Forum: Music Tech DIY
Topic: have you ever wondered what integrated circuits look like?
Replies: 7
Views: 246

Re: have you ever wondered what integrated circuits look like?

it's an N-type JFET, apparently. maybe somebody here can tell what these patterns are? BF862-zoom.jpg If this is a jfet, the symmetry would indicate that this an array of sources and drains connected to the round bond pads via the yellow metal lines. The darker spots on the yellow lines are the act...
by Synthiq
Mon Oct 19, 2020 12:19 pm
Forum: Modular Synth General Discussion
Topic: Is CMOS still analog? Best way to call out 'chip' logic vs uP logic?
Replies: 19
Views: 282

Re: Is CMOS still analog? Best way to call out 'chip' logic vs uP logic?

I would define a system that operates with discrete steps, either in time and/or amplitude, as digital to some degree. With that definition, CMOS or TTL logic is digital just as any microcontroller. "Analog" shift registers doesn't work with discrete output voltages but are sampled in time and suffe...
by Synthiq
Sat Sep 26, 2020 2:15 pm
Forum: Music Tech DIY
Topic: Any of these ICs worth keeping?
Replies: 19
Views: 782

Re: Any of these ICs worth keeping?

The oscillator in the video require an inverter with a Schmitt-trigger input. The 74LS04 doesn't have that so it will not work the same way.
by Synthiq
Thu Sep 24, 2020 12:54 pm
Forum: Music Tech DIY
Topic: Possible to tweak Tri to Sine converter for cem3340 direct tri output ?
Replies: 5
Views: 207

Re: Possible to tweak Tri to Sine converter for cem3340 direct tri output ?

When testing the circuit in LTspice, I got 11V peak-peak when adjusting the input level for lowest distortion. The input level was then 490mV so if you see a much lower output signal, I would check to see if the resistor values are correct. If the 50kohm pot or 18kohm resistor to -15V has higher val...
by Synthiq
Sun Sep 20, 2020 11:40 am
Forum: Music Tech DIY
Topic: Possible to tweak Tri to Sine converter for cem3340 direct tri output ?
Replies: 5
Views: 207

Re: Possible to tweak Tri to Sine converter for cem3340 direct tri output ?

Instead of ac couple the input, you can bias the base of Q2 at 2.5V to get a bipolar input signal. A 12.5kohm resistor from the base to +15V together with the 2.5kohm resistor to ground should give you the correct bias. [Edit] The resistor to ground is actually 2.2kohm so the resistor to +15V should...
by Synthiq
Thu Sep 17, 2020 12:16 am
Forum: Music Tech DIY
Topic: Adruino PWM and Sallen Key third order
Replies: 12
Views: 226

Re: Adruino PWM and Sallen Key third order

"It looks fine in an ac simulation but did you try a transient simulation? C9 adds positive feedback making the circuit unstable." ... But I don't realy understand what happening with a unstable circuit and why you would use or test for transient. Man I got a lot of reading to do ;) As an example w...
by Synthiq
Wed Sep 16, 2020 5:52 pm
Forum: Music Tech DIY
Topic: Ideas for small hard-to-accidentally-hit reset button?
Replies: 18
Views: 299

Re: Ideas for small hard-to-accidentally-hit reset button?

Have you considered using the watchdog timer to automatically reset the processor if the program locks up and you stop resetting the watchdog timer?
by Synthiq
Tue Sep 15, 2020 12:17 am
Forum: Music Tech DIY
Topic: Adruino PWM and Sallen Key third order
Replies: 12
Views: 226

Re: Adruino PWM and Sallen Key third order

I was just typing that you have the capacitors connected wrongly when I noticed the link from devinw1 above. Make sure you connect them properly or you won't get the response you are after. I simulated this circuit in Tina TI and it looked perfectly fine. It looks fine in an ac simulation but did y...
by Synthiq
Mon Sep 14, 2020 2:41 pm
Forum: Music Tech DIY
Topic: Adruino PWM and Sallen Key third order
Replies: 12
Views: 226

Re: Adruino PWM and Sallen Key third order

This site has some very nice calculators for active and passive filters. Here is exactly your case: http://sim.okawa-denshi.jp/en/Sallenkey3Lowkeisan.htm Plug-n-play! This simplifies things. Note, however, that these calculations assumes a gain of 1 in the amplifier. Higher gain will result in more...
by Synthiq
Mon Sep 14, 2020 1:10 pm
Forum: Music Tech DIY
Topic: Arduino AD help
Replies: 12
Views: 158

Re: Arduino AD help

by Synthiq
Sat Sep 12, 2020 6:54 pm
Forum: Music Tech DIY
Topic: Arduino AD help
Replies: 12
Views: 158

Re: Arduino AD help

The default PWM frequency for the Nano is just 490Hz so it would be a good idea to increase this frequency to reduce the ripple on the output signal. The PWM is normally also dubble-buffered so this is also the maximum frequency with which the output signal can be updated. There is a clock prescaler...
by Synthiq
Mon Sep 07, 2020 7:12 pm
Forum: Music Tech DIY
Topic: matching transistors - DIY
Replies: 493
Views: 80961

Re: matching transistors - DIY

If my calculations are correct, a 1% mismatch in current between the two transistors will result in a 0.26mV shift in the Vbe mismatch and with a 0.1% difference the error will be reduced to 0.026mV. What resistor tolerance you need depend on what accuracy you are aiming at.
by Synthiq
Thu Sep 03, 2020 1:27 pm
Forum: Music Tech DIY
Topic: Any of these ICs worth keeping?
Replies: 19
Views: 782

Re: Any of these ICs worth keeping?

The 74LSxx chips on your board are still manufactured today so they may be of less interest to remove and sell. Most of the interesting chips are MOS so they are sensitive to electrostatic discharge so they need to be handled with care if removed and sold.
by Synthiq
Thu Sep 03, 2020 12:29 pm
Forum: Music Tech DIY
Topic: Any of these ICs worth keeping?
Replies: 19
Views: 782

Re: Any of these ICs worth keeping?

HD6303 = 8-bit CPU, TMS2516 = 2kB EPROM, CDM6116 = 2kB SRAM, HD6350 = UART, MC1489 = RS-232 receiver for the UART, MC146818 = Real Time Clock. This is obsolete technology and you can get most of these functions in a single microcontroller today. It would be crazy to try to build something new with t...
by Synthiq
Thu Aug 27, 2020 1:29 pm
Forum: Music Tech DIY
Topic: Calling Power supply gurus
Replies: 26
Views: 934

Re: Calling Power supply gurus

I have used the same circuit and it works. The two capacitors driving the lower bridge rectifier must have their positive side connected to the jack, though.
by Synthiq
Wed Aug 26, 2020 2:11 pm
Forum: Music Tech DIY
Topic: Power Rails voltage drop
Replies: 31
Views: 528

Re: Power Rails voltage drop

An alternative to diodes are MOSFETs, which will have a lower voltage drop if you really need to squeeze the last few 100mV or so out of the rails. Neil Yes, you must of missed this mentioned above: I've seen some circuits with these mosfet diodes in place of the 1N5819. https://au.mouser.com/Produ...
by Synthiq
Wed Aug 26, 2020 12:08 am
Forum: Music Tech DIY
Topic: Power Rails voltage drop
Replies: 31
Views: 528

Re: Power Rails voltage drop

The processor uses at most 70mA at 72MHz so that doesn't explain the 200mA you see. Even with 70mA current consumption you should consider using a switching voltage regulator for improved efficiency and less current from the +12V supply. Do you need to run it at max frequency or can the application ...
by Synthiq
Sat Aug 22, 2020 3:40 pm
Forum: Music Tech DIY
Topic: Help me troubleshoot Fonitronic PS3100 LFO
Replies: 15
Views: 249

Re: Help me troubleshoot Fonitronic PS3100 LFO

Looking at the photos Q10 doesn't seem to be rotated 180 as it should be for the J111. Jay S. I agree. Now the gate is connected to the opamp output and the drain is connected to the R53 1Mohm resistor from the sync circuit. The 0.64V seen at the opamp output is simply the voltage drop over the for...
by Synthiq
Tue Aug 18, 2020 8:34 pm
Forum: Music Tech DIY
Topic: First DIY project - buffered multiple
Replies: 14
Views: 537

Re: First DIY project - buffered multiple

Did you actually simulate the noise in TINA with both the TL074 and OPA1604? While the OPA1602 has 7 times lower voltage noise than the TL074, the current noise is 180 times higher and will totally dominate the noise when you operate with a source resistance of 50-100kohm as is the case here. It mig...
by Synthiq
Mon Aug 17, 2020 3:24 pm
Forum: Music Tech DIY
Topic: Struggling with gate i/o buffers for arduino
Replies: 6
Views: 152

Re: Struggling with gate i/o buffers for arduino

looking at lots of datasheets, i see most of the 74HCxxx has maximum voltage of 7volts, what happens if there is a trigger around 10volts? Standard CMOS inputs have protection diodes from the inputs to both ground and positive supply. So if you in this case apply +10V to a gate input, there will be...
by Synthiq
Sun Aug 16, 2020 5:30 pm
Forum: Music Tech DIY
Topic: Struggling with gate i/o buffers for arduino
Replies: 6
Views: 152

Re: Struggling with gate i/o buffers for arduino

Since the output buffer is driven by 5V while the input is 3.3V maximum, I would suggest that you use a 74HCT451 instead. Even if a 74HC541 typically considers signals higher than half the supply voltage as a logic high, it is only guaranteed for signals higher than 70% of 5V, or 3.5V. A 74HCT541 on...
by Synthiq
Mon Aug 10, 2020 5:14 pm
Forum: Music Tech DIY
Topic: Robaux SWT16+ MIDI Expander
Replies: 2
Views: 113

Re: Robaux SWT16+ MIDI Expander

The MIDI adapter schematic looks wrong. Pin 5 of the connector is connected to the driver via 220 ohm. Pin 4 should be connected to +5V via a 220 ohm resistor and not to any MIDI input.
by Synthiq
Sat Jul 25, 2020 5:01 pm
Forum: Music Tech DIY
Topic: OPA1654 vs OPA1679
Replies: 36
Views: 1312

Re: OPA1654 vs OPA1679

To me I'm not all that worried about distortion in a synth circuit since most op-amps have ridiculously low distortion levels but more interested in keeping the noise down. Considering that a 100kohm resistor generates twice as much noise as a TL7X opamp, it will be difficult to reduce the noise le...
by Synthiq
Fri Jul 24, 2020 11:49 pm
Forum: Music Tech DIY
Topic: OPA1654 vs OPA1679
Replies: 36
Views: 1312

Re: OPA1654 vs OPA1679

To me I'm not all that worried about distortion in a synth circuit since most op-amps have ridiculously low distortion levels but more interested in keeping the noise down. Considering that a 100kohm resistor generates twice as much noise as a TL7X opamp, it will be difficult to reduce the noise le...

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