an important Zener configration for audio

[neil.johnson]

not every one thinks about and still sell commercially, although they pretty fail miserably when doing YouTube "tutorials", at least some.
But it's the nature of the Human when the presentation is good, it must be good.
Like: having a CD4017 connected to 12V and receiving input from a 10V.p.p. signal trough a diode, is like 4.3V left, it barely makes the CD4017 move.
Or inventing a new type of Voltage controlled filter as a non engineer.
But yet they have some 30k followers and sell their stuff (as diy packages).

It's called "cargo cult", and it probably says more about the followers than the doers.

Most schematics i have seen use 100K on the input.
so do i.

Do you know why?

Doing Math aint the problem, knowing the formulas is the problem, Ohm's law, calculating power is easy.
Also sometimes decoding the format/notation of formulas is a thing.

however i forgot how to calculate the voltage drop through a resistor, not connected to anything.
: )

View attachment 93300

hope to find help.

Looks like that question is simply asking for the resistance between the A and B terminals. That one can be done in the head, no need for calculators (the values have been carefully chosen).

Neil

 

[JohnRoberts]

don't break my head.
Have added test points on the PCB, a common practice and on some parts i use custom footprints for easy removal.

when in doubt listen to what Abbey said....

JR

 

[Analog_Fan]

Do you know why?.

Neil

Thank you for reply.

most "synthesizer" modules schematics i have seen, many or most start/end with a opamp.

using 100K. at least for most accept for a few that use 10K.

on the OTA's it's usually a voltage divider 100K to 1K or 100K to 560R.

Most signals are also sourced from a opamp.
the opamp's input is at "high impedance", so it doesn't really pull (consume) from the source opamp.

What makes the 100K so special (i got close to 1000 of them), compared to a 10K or 49K9.
Would the power consume increase if you use a 10K setup, the feedback resistor?
Would it benefit the audio using 10K?

 

[abbey road d enfer]

What makes the 100K so special (i got close to 1000 of them), compared to a 10K or 49K9.

Typically, an opamp is capable of driving a 2k load without limitation. Actually a 741 is more comfortable with 10k.
So in order to avoid loading problems, the Ancients opted for a much higher typical input impedance, which allows patching a single output to several inputs.

Would the power consume increase if you use a 10K setup, the feedback resistor?

It's not a matter of current draw, but rather a measure of conservation of signals.
However, one could opt for 5532's for the outputs, which is capable of driving 300 ohms, but te current draw may be excessive.

Would it benefit the audio using 10K?

Not very much in the control voltages. BJT opamps used with 100k can be noisy, and that would translate as artefacts in the sound. The almost ubiquitous use of FET opamps has solved this issue.
Regarding audio, until recently, very low noise opamps were only bipolar (BJT): noise optimization required low impedance around them. That's why the 10k resistor is so common.
With the recent arrival of super LN FET opamps (AD743/745), it may be replaced by the 100k (or more), the limit being the sensitivity to parasitic capacitance.

 

[Analog_Fan]

the Ancients

You made my day.

It's not a matter of current draw, but rather a measure of conservation of signals.
However, one could opt for 5532's for the outputs, which is capable of driving 300 ohms, but te current draw may be excessive.

Not very much in the control voltages. BJT opamps used with 100k can be noisy, and that would translate as artefacts in the sound. The almost ubiquitous use of FET opamps has solved this issue.
Regarding audio, until recently, very low noise opamps were only bipolar (BJT): noise optimization required low impedance around them. That's why the 10k resistor is so common.
With the recent arrival of super LN FET opamps (AD743/745), it may be replaced by the 100k (or more), the limit being the sensitivity to parasitic capacitance.

this is my control voltage circuit.
there is a simple mixer circuit in front of IC1A.


do i need to take in account the miller effect and change C12 to 560pF?

Currently i also have a trimmer on top of the long tail for balance, but using a ALD1105 matched pair current mirror, i probably can skip that, not?


that AD743 is a expensive beast @ almost 18€
the Would set the price to around 125€ for a single VCA, no one pays that.
I'm not capable of doing extensive test on that and provide a detailed brochure/test report.

 

[abbey road d enfer]

do i need to take in account the miller effect and change C12 to 560pF?

I don't see how a supposed Miller effect would be compensated by increasing this cap.
Where do you think this Miller effect happens?

Currently i also have a trimmer on top of the long tail for balance, but using a ALD1105 matched pair current mirror, i probably can skip that, not?

I don't see wher it would be on your schemo.

that AD743 is a expensive beast @ almost 18€

Check this:
https://fr.aliexpress.com/item/1005...016516680138938935ea3be|12000020681250315|seaI can't guarantee they are not fake, but there are several good suppliers on Ali Express.
Anyway a 743 in this application is overkill. A basic TL07x is perfectly adequate.

 

[Analog_Fan]

I don't see how a supposed Miller effect would be compensated by increasing this cap.
Where do you think this Miller effect happens?

well, in a schematic like Mutable Instruments Ripples there is a 560pF in the feedback of an opamp working on a pnp.
but that's a slightly different circuit.

I don't see wher it would be on your schemo.

It's situated on top of the long tail.
But in documents where people use matched parts, they don't use it.
i can't place a 25 turn trimmer, no room left, so i placed to a 1K Bourns 3362P.
but using matched pair might make it overkill and not precise or to hard to adjust.
But it the only resistor i have above the P type current mirror.

Check this:
https://fr.aliexpress.com/item/1005...016516680138938935ea3be|12000020681250315|seaI can't guarantee they are not fake, but there are several good suppliers on Ali Express.
Anyway a 743 in this application is overkill. A basic TL07x is perfectly adequate.

By the time it arrived here, it's almost the price that mouser is asking, need to pay 7€ import fee or more if it's over 20€ in value, than it's 21% vat.
it has become a hassle now, importing stuff, first you get a letter with a code, you gotta pay online and after a few days.
I was lucky sourcing real CA3080 and 2SK30A from the Chinese in Shenzhen, but rather prevent that.

 

[ccaudle]

do i need to take in account the miller effect and change C12 to 560pF?

Miller effect is primarily a concern at the transistor level. When you see a capacitor from output to inverting input of an op-amp it is to reduce the gain at high frequency to improve stability.

 

[JohnRoberts]

+1 not to over simplify but "miller effect" is generally discussed in the context of discrete gain stages where some physical internal capacitance between input and output gets effectively multiplied by the voltage gain of that discrete gain stage.

Op amps are different animals with different issues. There may be miller capacitance effects within internal circuit blocks but global negative feedback is used to address stability and transfer function.

JR

 

[abbey road d enfer]

By the time it arrived here, it's almost the price that mouser is asking, need to pay 7€ import fee or more if it's over 20€ in value, than it's 21% vat.
it has become a hassle now, importing stuff, first you get a letter with a code, you gotta pay online and after a few days.

I would think your "Universe" is somewhere in western Europe, right?
I place low-value orders and they put the stuff in a simple envelope, and I haven't yet had to pay taxes or whatever ransom.

 

[Analog_Fan]

ransom.

lol

that's something they introduced this year.
i had to pay 7€ for something valued 10us$.
They have "mailman" function as tax collectors, the gov must have run out of money that they can't pay their employees or something or used them for something else. the world is weird today.

 

[user 37518]

If it is really the case, this simulator is bad. Ditch it.

I have already told him this before, but he insists on using that simulator, which TBH, its only for educational purposes.

 

[Analog_Fan]

I have already told him this before, but he insists on using that simulator, which TBH, its only for educational purposes.

now, i got both, although not an expert on LTSPICE, seams you need to set a timelimit for simulation, still need to catch up on that.
While the Falstaff is continuously producing a graph.

Also the Falstad simulator allows you to rotate/mirror components.

 

[abbey road d enfer]

now, i got both, although not an expert on LTSPICE, seams you need to set a timelimit for simulation, still need to catch up on that.
While the Falstaff is continuously producing a graph.

LTspice is not a real time simulator. In particular it does operating point, frequency sweep and noise simulations, which cannot be real time.
Actually no version of Spice is real-time.

Also the Falstad simulator allows you to rotate/mirror components.

LTspice too. Just grab the component (F8 or F7) and the rotate and mirror symbols appear in the upper tool bar.
Neglecting reading the Help is not advised.

 

[Analog_Fan]

LTspice too. Just grab the component (F8 or F7) and the rotate and mirror symbols appear in the upper tool bar.
Neglecting reading the Help is not advised.

thanks, i saw the menu and the F. keyed commands.
but didn't saw that one, to rotate.

the next day, i returned to fine tuning/routing my schematics.

 

[user 37518]

now, i got both, although not an expert on LTSPICE, seams you need to set a timelimit for simulation, still need to catch up on that.
While the Falstaff is continuously producing a graph.

Also the Falstad simulator allows you to rotate/mirror components.

No professional simulator will do real-time, the closest to the Falstad simulator that I know of is Multisim, which allows an "interactive" mode, but is still not real time, even the Falstad is also not real time. Interactive simulators such as the Falstad are nice for preliminary simulations, but for accurate results you should really use an off-line simulation.

With the exception of Multisim, no Spice based simulator will continuously provide a graph. If you want a graph in the time domain, such as the one that you would see in an oscilloscope, use the transient simulator, if you want frequency and phase response, use AC Sweep.

One of the big disadvantages of a simulator like the Falstad, is that it doesn't allow you to simulate transient events properly, which is why you need off-line simulation. No professional would use the Falstad simulator for a serious circuit. Again, the Falstad is a Java app design to teach about electronics, not to perform critical simulations.

 

[abbey road d enfer]

thanks, i saw the menu and the F. keyed commands.
but didn't saw that one, to rotate.

 

[abbey road d enfer]

now, i got both, although not an expert on LTSPICE, seams you need to set a timelimit for simulation, still need to catch up on that.

A transient sim is done over a period of time, that you have to choose according to your needs. For example, if you want to see a sinewave, the simulation time should be at least one entire cycle, like 1ms for a 1kHz signal. Now if you want to see the response to a square wave at the edge, you may want to use a smaller time that will give you finer details.
Conversely, if you want to analyze the behaviour of a compressor, you may want to extend the measurement over a length of several 100's of ms.
A real time simulator cannot be accurate at both very short and very long times.

 

[Analog_Fan]

A transient sim is done over a period of time, that you have to choose according to your needs. For example, if you want to see a sinewave, the simulation time should be at least one entire cycle, like 1ms for a 1kHz signal. Now if you want to see the response to a square wave at the edge, you may want to use a smaller time that will give you finer details.
Conversely, if you want to analyze the behaviour of a compressor, you may want to extend the measurement over a length of several 100's of ms.
A real time simulator cannot be accurate at both very short and very long times.

thank you.