seva
Well-known member
I can´t find IC4A supply rail in the soundcraft manualI- forget the 100r- have tried 10R and 100R- I am still over 16Vcc+-, but I don´t think that could makes the dc on the outputs.
LED peak meter with fastest transient detection (clipping indication meter)
- Thread starter seva
- Start date
Help Support GroupDIY Audio Forum:
It looks like there's some current drawn or injected in the rectifier by the circuitry that follows - I guess it's the comparators, although TLO's should have negligible input bias current. Do these voltages exist when disconnected from the LED drivers?seva said:
seva
Well-known member
Thank you for your time Abbey!
If the comparator stage is not connected, all leds light up and I measure 0.6v at the input of this stage.
The rectifier level then shows -0.001mV at the output of the stage, but -220mv at the OP output.
I have some understanding problems with Grounding and minus poling. Therefore, I had to expriment until the comparator stage has worked.
the first time I had put each first LED of the four 8 LED arrays to minus 17v. I had not noticed that the Soundcraft circuit differs from that of you. In addition, I have found other circuits in which synonymous with negative voltage is worked. Unfortunately, it did not work with me and it is all first LEDs burned. The LEDs then responded individually in seven blocks.
After measurements and the loss of a LED's, I have GND instead of minus17v. After that, it has worked until the lowest LEDs light up when no signal is present.
I try again to make an entire circuit diagram. ICh have here only one eagle lite version and had therefore the comparator stage split to the maximum PCB measure not exceed. Now everything has become quite complicated to do that quickly. I hope you understood me correctly. I do not know yet exactly what I do here. I still have to learn a lot
If the comparator stage is not connected, all leds light up and I measure 0.6v at the input of this stage.
The rectifier level then shows -0.001mV at the output of the stage, but -220mv at the OP output.
I have some understanding problems with Grounding and minus poling. Therefore, I had to expriment until the comparator stage has worked.
the first time I had put each first LED of the four 8 LED arrays to minus 17v. I had not noticed that the Soundcraft circuit differs from that of you. In addition, I have found other circuits in which synonymous with negative voltage is worked. Unfortunately, it did not work with me and it is all first LEDs burned. The LEDs then responded individually in seven blocks.
After measurements and the loss of a LED's, I have GND instead of minus17v. After that, it has worked until the lowest LEDs light up when no signal is present.
I try again to make an entire circuit diagram. ICh have here only one eagle lite version and had therefore the comparator stage split to the maximum PCB measure not exceed. Now everything has become quite complicated to do that quickly. I hope you understood me correctly. I do not know yet exactly what I do here. I still have to learn a lot
You need to measure the current there; it looks like the comparators eat significant input current. One thing is that it should be preceded by a buffer (or the detector followed by a buffer).seva said:
That is utterly normal; that's what it takes to compensate the voltage drop across the diode (it is commonly accepted that this voltage drop is 0.6V, but at extremely low currents, the voltage is lower).
seva
Well-known member
Yes.seva said:
[/quote] If so, is a tl07x a good choise for buffering or should i go for ne553x?
I understood that tl07x´s are very slow, so i don´t wanna place many of them in series.
[/quote] They are plenty fast, compared to the rectifier signals, that are quite slower than audio signals. You need to put high value resistors (1Meg) across the switch contacts; if you don't, the non-invering input floats during switching.
seva
Well-known member
Ok, I understand. rectified DC voltage is slower than the audio AC voltage.
that is a good tip with the resistance at the switch. I've updated the circuit attached.
You said something about current measurements at the input of the comparator stage ... that I will do next. This will give me information about the total consumption of the LEDs, right? Depending on the LED's and their consumption at current?
This way I have to do again later to calculate the total current of the hole circuit to avoid destroying the transformer of the power supply. right?
should I measure the current from each parallel connected stage at the input and then admit values, give 5% headroom and then calculate VA of power supply?
that is a good tip with the resistance at the switch. I've updated the circuit attached.
You said something about current measurements at the input of the comparator stage ... that I will do next. This will give me information about the total consumption of the LEDs, right? Depending on the LED's and their consumption at current?
This way I have to do again later to calculate the total current of the hole circuit to avoid destroying the transformer of the power supply. right?
should I measure the current from each parallel connected stage at the input and then admit values, give 5% headroom and then calculate VA of power supply?
Attachments
seva
Well-known member
It could be useful to boost the input signal by 6dB. so I changed the balanced input stage. I have modified an appealing circuit to choose between + 4dBu and + 10dBu. 6dB is a factor of 2. For that I have calculated 300Ohm.
I have no idea if this is a good idea is to connect the output signal over a relatively long distance in the housing to a switch mounted on the front panel.
I would like to have a indication LED for the mode of the meter. 0dB and + 6dB mode, with two separate LED´s on the front panel.
I have planned a 3pdt for the correct switch. I will upload the hole connection plan of the meter.
here is the schematic of input stage with the boost option and leds
I have no idea if this is a good idea is to connect the output signal over a relatively long distance in the housing to a switch mounted on the front panel.
I would like to have a indication LED for the mode of the meter. 0dB and + 6dB mode, with two separate LED´s on the front panel.
I have planned a 3pdt for the correct switch. I will upload the hole connection plan of the meter.
here is the schematic of input stage with the boost option and leds
Attachments
seva
Well-known member
seva
Well-known member
seva
Well-known member
found a nice adapter for the clip detector stage IC to adapt the smd opa
http://www.digitale-elektronik.de/shopsystem/product_info.php?products_id=651
http://www.digitale-elektronik.de/shopsystem/product_info.php?products_id=651
seva
Well-known member
You need two resistors, both to the common and one to the NO, teh other to the NC.seva said:
No, that would just inform how much current the inputs draw, which is an imortant info if you intend to drive them from a resistive source.
seva
Well-known member
No, because all these signals are correctly referenced to zero Volt.seva said:updated
should I do the same at the switch of the new input stage for +6dB and 0dB boost?
seva
Well-known member
I have another question about calibrating the detector stage.
Is it enough to measure a sine wave to get from the RMS value on the exact peak value?
I have the calculation attached
Or, better to create DIRAC's in the DAW, then normalize them to -3dB at the output of the DAC at + 1dBu. On the analog domain, I can boost this signal in half dB steps to + 7.5dBU to calibrate detector stage accordingly.
Is it enough to measure a sine wave to get from the RMS value on the exact peak value?
I have the calculation attached
Or, better to create DIRAC's in the DAW, then normalize them to -3dB at the output of the DAC at + 1dBu. On the analog domain, I can boost this signal in half dB steps to + 7.5dBU to calibrate detector stage accordingly.
Attachments
Yes. The 1.414 factor is long-proven.seva said:
Not better IMO, since you're adding calculation/measurement steps that are sources of errors (mistakes, actually).
seva
Well-known member
I am a little bit confused about an exact calibration of the trimmers (variable resistors) in the detector stage.
Can somebody tell me what trimmer types are used for stable values in audio circuits?
I had read some datasheets but I have no experience with stability of trimmers.
For my understanding its not important to have a 1%tolerance of the trimmer instead of 30%, because I can adjust it to an exact value. right?
It´s clear that more turns will give me a more precise adjustment of a value.
my prototype meter uses “Piher 6,4mm 1turn Trimmer“ the size is very usefull for my project, but i am concerned about the exact adjustment with access to only 1turn.
I am searching for an alternative trimmer in a flat size, adjustable from side.
Prices can get very high for these trimmer types. I am not sure what´s the best compromise for my project.
I don´t wanna readjust trimmers for any reason. I wanna have stable values over a long time.
How much changes trimmer values effecting by temperature changes or other things?
What would you use for this application?
thanks!
Can somebody tell me what trimmer types are used for stable values in audio circuits?
I had read some datasheets but I have no experience with stability of trimmers.
For my understanding its not important to have a 1%tolerance of the trimmer instead of 30%, because I can adjust it to an exact value. right?
It´s clear that more turns will give me a more precise adjustment of a value.
my prototype meter uses “Piher 6,4mm 1turn Trimmer“ the size is very usefull for my project, but i am concerned about the exact adjustment with access to only 1turn.
I am searching for an alternative trimmer in a flat size, adjustable from side.
Prices can get very high for these trimmer types. I am not sure what´s the best compromise for my project.
I don´t wanna readjust trimmers for any reason. I wanna have stable values over a long time.
How much changes trimmer values effecting by temperature changes or other things?
What would you use for this application?
thanks!
seva
Well-known member
need nuggets - real nuggets!
you need to relax...seva said:need nuggets - real nuggets!
Different trimmers are engineered for different purposes... for a fairly non-critical application (like a few dB before actual clipping) a cheap trimmer should suffice. In fact I probably wouldn't use a trimmer at all..
JR
