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Topic: [SPAM] The Circuit Based On TL062ACD about Audio Clipping Indicator (Read 4061 times) previous topic - next topic
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[SPAM] The Circuit Based On TL062ACD about Audio Clipping Indicator

Recently I have see a circuit based on TL062ACD about audio clipping indicator inteded to detect clipping in preamp stages,mixers and amplifiers and so on. It also can be used as a seperate,portable unit,to singal by means of a LED when the output wave form of a particular audio stage is “clipping” i.e.is reaching the onset of its maximum permitted peak to peak voltage value before an overload is occurring. This will help the operator in preventing severe, audible distortion to be generated through the audio equipment chain.
The datasheet of TL062ACD
The heart of the audio clipping circuit is a window comparator formed by two op-amps packaged into IC1. This technique allows to detect precisely and symmetrically either the positive or negative peak value reached by the monitored signal. The op-amps outputs are mixed by D1 and D2, smoothed by C4, R7 and R8, and feed the LED driver Q1 with a positive pulse. C5 adds a small output delay in order to allow detection of very short peaks.
I saw this circuit and very much liked the idea of a clipping detection circuit so i know when the gain of my mixing desk is too high. I’ve have tried to build this circuit multiple times now though and i can not see to get it work at all. I’ve tried chaining the transistor and op-amp and to no avail. I’m using a 9V power supply too. I have attached a picture of the circuit and would very much appreciate it if you could see what i have done wrong ? Any help would be massively appreciated!!

Many thanks,

Spam site
http:// www . ky n i x . com/uploadfiles/pdf9675/TL062ACD.pdf

Re: The Circuit Based On TL062ACD about Audio Clipping Indicator

Reply #1 –
I think you'll get a better answer in an electronics forum like DIYAudio or EEVBlog.
Also include the schematic of the circuit, so it can be compared with what you built. 
Regards,
   Don Hills
"People hear what they see." - Doris Day

Re: The Circuit Based On TL062ACD about Audio Clipping Indicator

Reply #2 –
Yeah...  I'm not going to try converting that to a schematic in my head or on paper...     You also haven't identified any power/ground/signal/reference connections, but those should be on the schematic if you can produce one.

From your description (and from my understanding of how such a thing should work) there should be a full-wave peak detector (or "envelope follower") followed by a comparator.   There may be additional circuitry to hold the LED or, or they may rely on the decay of the peak detector circuit (the discharge of a capacitor through a resistor).

Do you have a multimeter?   With a multimeter, you can measure the voltage out of the peak detector as well as the reference voltage.    When/if the signal exceeds the reference, the state of the comparator will "flip".

Quote
I’m using a 9V power supply too.
What was specified?  Most op-amp circuits require dual (positive & negative) supplies, but this circuit could be an exception.

Quote
I’ve have tried to build this circuit multiple times now though and i can not see to get it work at all. I’ve tried chaining the transistor and op-amp and to no avail.
Assuming the circuit is designed correctly, and assuming you built it correctly, the most likely problem is your voltage reference, which should be derived from the audio circuit's power supply.    Lower the reference to the point where it's below the audio signal, and "bing"...   the LED comes on...    If the signal clips below the level set by the reference, the LED never comes on.


Because the reference voltage comes from the unit's existing power supply, which is often not "accessible", the clipping detector is normally built-into (or added inside) the existing enclosure.

So the first question is...      Is the power supply from the audio circuit connected to the clipping detector?

The audio circuit's power supply limits the amount of signal (voltage) you can get-out before clipping...  Raise the power supply voltage and you can get more signal before clipping.  Lower the voltage and you'll clip at a lower voltage.

Now, here's the big unknown...   A preamp with +/-12V power supplies will NOT give you the full 24V peak-to-peak output swing.   There is some unknown "voltage" loss in the circuitry.     So if you use 12V as a reference you'll never detect clipping.   You have to use something less (maybe 9 or 10V?).    There should be a pot to adjust the sensitivity, or a resistor may need to be selected to work with your audio circuit.

Also depending on the audio circuit, it may be possible to clip an input-stage without clipping the output-stage.  This is especially true if there's a volume control somewhere in the circuit.    If the clipping is happening somewhere other than the output stage, you'll never detect it at the output.

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inteded to detect clipping in preamp stages,mixers and amplifiers
Practically speaking, a preamp or mixer should have meters and a ship-load of analog headroom and (if set-up properly) should not the 1st thing to clip.  

An analog-to-digital converter should have a clipping indicator (if not already built-into it's peak-indicating meter) and it can be useful on a power amplifier.

The clipping reference for an ADC would be the ADC's reference voltage (not the power supply voltage), or it could simply be detection/recognition of 0dBFS on the digital-side.   (There's no logical reason to have an analog voltage  detector on an ADC.)

If you wanted to use that circuit with a power amp, you'd have to "be careful" and you'd possibly need to modify the circuit to prevent from over-voltageing it, which could potentially short it out, and then short-out your amp, and fry everything!

Re: The Circuit Based On TL062ACD about Audio Clipping Indicator

Reply #3 –
Quote from: DVDdoug on
Quote
I’m using a 9V power supply too.
What was specified?  Most op-amp circuits require dual (positive & negative) supplies, but this circuit could be an exception.
Most modern op-amps will work quite nicely on a single supply, often as little as 5 volts or less. This is especially not a problem when working with AC signals.

Re: The Circuit Based On TL062ACD about Audio Clipping Indicator

Reply #4 –
You haven't put the schematics but if you are using the one that I attach as I think, then you are using two 22nf capacitors instaed of 220nf capacitors (the light blue ones), the value on the little brown can not be seen and I can't verify its value, this three capacitors are critical for the detection.

Re: The Circuit Based On TL062ACD about Audio Clipping Indicator

Reply #5 –
That particular circuit has no external reference.   R5 should be adjusted to so LED comes on at (or near) the clipping point.     So, you need an oscilloscope to calibrate to the clipping point.   Or, maybe you just drive the audio circuit into hard-obvious clipping and adjust R5 until the LED "just comes on", and cross your fingers and hope that "slight clipping" is also detected.

If the circuit can't be adjusted for your particular audio circuit, you may need to change resistor values or add another pot to reduce the audio signal level, etc.

It's not that reliable because as the battery discharges the reference changes.   And if the audio circuit doesn't have a tightly regulated power supply (or if it runs on batteries) the actual clipping point will change when the power supply voltage changes and the clipping detector won't know that...    It's not really detecting clipping, it's detecting the point at which clipping is expected.

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Most modern op-amps will work quite nicely on a single supply, often as little as 5 volts or less. This is especially not a problem when working with AC signals.
Of course the op-amp itself doesn't require dual power supplies.  The op-amp doesn't even "know" if there are dual supplies.   Voltages are all relative, and there's no "ground pin" on an op-amp chip.    But, I'll stand by my statement that most op-amp circuits  use dual power supplies.

In the above posted schematic, the input signal is biased at 4.5V with the R2/R3 voltage divider, and that bias is isolated from the source by C2.   That bias is required because of the AC audio signal swings negative, but there is no negative power supply.   If this were a audio amplifier, you'd need another capacitor at the output to block/filter the DC bias.   Or, you'd need a virtual ground circuit, or some other way of getting-around the lack of a negative supply.

Re: The Circuit Based On TL062ACD about Audio Clipping Indicator

Reply #6 –
A problem with your clipping detector is that it does not actually detect clipping. It simply lights an LED when a threshold is reached which may or may not be clipping. If the power line Voltage is low, the amp will clip at a lower level which may not even trigger the LED. Conversely if the line Voltage is high the amp will deliver more power and have a faulty display of clipping.The TL062 is an opamp, not a comparator and while you can use an opamp as a comparator, it's the wrong device.  Basically it's a lousy circuit.

Most solid state amps are based a differential input amplifier - basically a jumbo operational amplifier (opamp). Under normal operating conditions opamps will have nearly identical values on both inputs but when clipping is reached, one input will continue to increase but the other input will clip. Building logic to monitor both inputs of the amp would be far more accurate in detecting actual clipping.

If I still ran amps loud enough to clip, I might design a clip detector but it's easier to buy a bigger amp or simply turn it down.

G²
 

Re: The Circuit Based On TL062ACD about Audio Clipping Indicator

Reply #7 –
Quote from: Glenn Gundlach on
A problem with your clipping detector is that it does not actually detect clipping. It simply lights an LED when a threshold is reached which may or may not be clipping. If the power line Voltage is low, the amp will clip at a lower level which may not even trigger the LED. Conversely if the line Voltage is high the amp will deliver more power and have a faulty display of clipping.The TL062 is an opamp, not a comparator and while you can use an opamp as a comparator, it's the wrong device.  Basically it's a lousy circuit.

Excellent point!  A real clipping indicator has to monitor both the input and output of the equipment being monitored. If one is not a near-perfectly scaled version of the other, the amp is not behaving ideally. 

This has been done many times in real world gear, sometimes with as few as  6 parts, 4 of which are diodes, such as used by QSC in their power amps.