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39 votes

Why does music synthesizer built from chain of astable multivibrator circuits get "out-of-tune" after a few hours?

You have clearly built a circuit that is fully analog in nature and produces a frequency in each oscillator that is dependent upon various factors such as: Changes to the voltage level of the power ...
Michael Karas's user avatar
34 votes
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Why does music synthesizer built from chain of astable multivibrator circuits get "out-of-tune" after a few hours?

What I can't figure out is why the circuit appears to get spontaneously detuned, i.e. one or more of the individual circuits end up with frequencies that are different from what they were tuned to (...
Todd Wilcox's user avatar
26 votes
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Stability of input filter in SMPS - Theoretical explanation

It is an extremely complicated subject. I have taught an APEC seminar in 2017 and tried to explain the interaction between a filter and a switching converter. First, you need to understand that a ...
Verbal Kint's user avatar
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19 votes

What frequency stability crystal do we need?

Too long to read all that stuff so, here's the short story From comments under the question, Trevor says this: - we think the caps are correct. We have 2x 15pf to ground. The crystal we're using is ...
Andy aka's user avatar
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16 votes
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What is noise gain, really? And how is it determined in the general case?

Okay, after a lot more research, I think I've gotten to the bottom of this. Actually I'm certain it's only approaching the bottom, as I've found this topic area quite deep, but I think I've gotten ...
scanny's user avatar
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16 votes
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Reasons for implementing op-amps which are not unity-gain stable

A tale of two op amps.... The OP37 and OP27 are very similar internally, but their high-frequency compensation differs, making OP27 unity-gain stable, while OP37 is not. Simply by modifying an ...
glen_geek's user avatar
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15 votes
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Where do the oscillations on the output voltage of my buck converter come from?

Repeat your measurements but this time connect your probe tip to the same point as your earth clip. What do you see? If your probe is picking up a signal directly due to the inductive loop it forms ...
Andy aka's user avatar
  • 460k
15 votes

What frequency stability crystal do we need?

If you have a suitable means of measuring the frequency, you can adjust one of the load caps with a trimcap to get closer to the ideal. However you will need some means of measuring without altering ...
Spehro Pefhany's user avatar
12 votes
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What is actually meant by stability of a control system in practice?

Imagine you're driving down the road, and trying to stay in a lane. Neither your car nor the lane is perfect, so you occasionally have to nudge the steering wheel to keep between the lines. As long as ...
Matt S's user avatar
  • 3,532
12 votes

Would a solderless breadboard be able to handle 20V without short circuiting?

I've put 2000V on breadboards before, though with careful monitoring, current limiting, and avoiding nearby positions. Possible they might even handle as much between adjacent positions... at least ...
Tim Williams's user avatar
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11 votes

Feedback loop-gain(beta) derivation for the inverting amplifier?

Definition: The feedback factor beta is defined as the portion of the output voltage that is fed back to the differential opamp input (input source grounded). Therefore, regarding beta there is no ...
LvW's user avatar
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11 votes

Meaning of long term stability unit (µV/mo)

month μV/mo means microvolts per month.
Neil_UK's user avatar
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11 votes

Reasons for implementing op-amps which are not unity-gain stable

It's one of a handful of things you can sacrifice to get increased bandwidth. Decompensated op amps like this can have significantly higher gain-bandwidth product than unity-gain-stable ones. Not even ...
Hearth's user avatar
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10 votes
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Are film capacitors affected by DC bias?

Film capacitors have a very stable capacitance over DC bias. Look at this: But it comes to happen that film capacitors are not the only ones immune to DC bias: So, the actual question is why do ...
Enric Blanco's user avatar
  • 5,791
10 votes

Why does music synthesizer built from chain of astable multivibrator circuits get "out-of-tune" after a few hours?

Yet another factor which has not been mentioned is the fact that the circuit is battery-powered. Since you are driving a speaker, power consumption will be significant (as evidenced by your use of an ...
WhatRoughBeast's user avatar
10 votes
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Low LDO output capacitance (stability)

LDOs are feedback systems, so their stability depends on open loop gain: output voltage -> error voltage on FB pin -> internal error amp -> pass device -> output voltage. The classic ...
bobflux's user avatar
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10 votes
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Poles of system seem counter intuitive

You have a pair of poles on the Y-axis. That is the abstract representation of an oscillator without damping. If your input is of finite duration, once the input goes to zero the oscillation will be ...
John Doty's user avatar
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10 votes
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Filter non-inverting input of operation amplifiers or directly to GND?

in general why should I use this filter on the non-inverting input? what would be the benefit? The OPA838 doesn't need the RC to work but, if you don't have the 100 kΩ, the input bias currents can ...
Andy aka's user avatar
  • 460k
9 votes
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Understanding in-loop compensation for capacitive-loaded OpAmp

I believe the authors used fast analytical circuits techniques or FACTs but I am not sure about their results. The principle is based on the generalized Extra-Element Theorem or EET from Dr. ...
Verbal Kint's user avatar
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9 votes

How to calculate aging tolerance of Resistor?

According to the datasheet, the test is done in compliance with MIL-STD-202, method 108 (pp 37-38), condition D (1,000h). This is an accelerated aging test at (probably) 100% rated power (while "ON")...
Enric Blanco's user avatar
  • 5,791
9 votes
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Capacitor of choice for low noise applications

HighK ceramics like X7R, Z5U etc have huge variation of capacitance versus voltage. Using them in filters or any kind of coupling application guarantees humongous distortion. They are piezoelectric: ...
bobflux's user avatar
  • 78.4k
9 votes
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Capacitor after Voltage Reference "for stability"

The reference has a low dropout, so as you can see on the internal schematic (datasheet page 10) it is implemented as a bandgap reference followed by a rail to rail buffer opamp. Notice the polarity ...
bobflux's user avatar
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9 votes
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Non-inverting op-amp configuration with capacitor

A lot of times I hear that it's useful for stability but I don't get why and how to calculate it's value. Consider that the non-inverting pin might have a parasitic capacitance of maybe 4 pF. That'...
Andy aka's user avatar
  • 460k
9 votes
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How to evaluate the stability of a full wave precision rectifier

When an AC steady-state analysis is done, a DC .op (operating point) analysis is done first. This determines which bias levels, feedback paths, etc. are active in the circuit. In short, diodes are ...
Tim Williams's user avatar
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9 votes
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Why is a peak in the gain a sign of instability in a closed loop op-amp circuit?

1.) A peak in the frequency response for a closed-loop gain is NOT an indication for instability. It rather indicates that the phase margin is smaller than app. 65 deg (for a 2nd order system). This ...
LvW's user avatar
  • 27k
9 votes

Reasons for implementing op-amps which are not unity-gain stable

An op-amp is a multi-stage amplifier, to which the user applies negative feedback to get the desired gain with high linearity. Due to parasitic resistance and capacitance an amplifier inevitably ends ...
Peter Green's user avatar
  • 22.5k
8 votes

Diode Clamp failing with LDO Circuit

Alternative design concept: simulate this circuit – Schematic created using CircuitLab You may be able to eliminate R2 if the minimum draw from other circuitry is similar (a few hundred uA). ...
Spehro Pefhany's user avatar
8 votes

Capacitor after Voltage Reference "for stability"

This has to do with loop stability. I won't go into the details of the Barkhausen stability criterion as I think it would go to far for this, but perhaps an analogy can explain what is going on. This ...
Joren Vaes's user avatar
  • 12.6k
8 votes

What's the impact of a crystal's frequency stability, ESR and load capacitance on micro-controllers?

It would probably be better for you to choose a crystal oscillator rather than a crystal. You just buy it and it works, and is guaranteed to start and conform to stated specifications. If you are ...
Spehro Pefhany's user avatar
8 votes
Accepted

Why is phase margin considered more important than gain margin in dc-dc converters?

For many DC-DC converters there is a "fairly" resonant low pass filter involved at the output and, it changes its phase angle "fairly" rapidly from 0 degrees to 180 degrees over a short part of the ...
Andy aka's user avatar
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