Pink Noise using tl072...can't get it to work..

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pablobolche

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Using the scematic for pink noise in ESP site..it is for Dual power supply
from here http://sound.whsites.net/project11.htm
 

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working with single supply...
the following is the schematic adaptation I have been working on...

I get white noise after the 1rst opamp....
thing is that after the basic filter on the second opamp I get the same white noise...
I have checked and double checked connections as well as played around with it but just doesn`t fliter the white noise to pink..
I have very rudimentary opamp skills...please can some one point me in the right direction...
thanks

 

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> second opamp I get the same white noise...

Not much to go wrong except wrong values.

Just as a test, you could lift the left end of the 10uFd and feed ordinary audio through. It should come out very bass heavy and treble light.
 
-3dB/octave filter has gain of 20dB at low frequencies so most likely this filter is overloaded (it depends of PS voltage also) with the source.  Also, C8 is reverse connected for sure, C4 probably also.
 
Ok...
This is part of a slightly bigger project...a  DI-Pink Noise-Mic Box..
I have attached the complete schematic...

I have been messing around with the circuit and I can get a Pinkish noise while conecting a 10n capacitor from pin 7 to gnd..
Box  works with phantom power....internally with 9V...Using TL074 with  - V to GND
I am suspecting I have some gnd issue between the pink noise and the DI...maybe they are not compatible as is....

I appreciate all your comments
 

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Few things...

  The White point will have no signal as it's a virtual earth point. Also, you are ASSuming the reverse biased BE junction gives white noise, the 1/f frequency of that noise is quite high so it will be pink noise to start with for some part of the spectrum.

  Second, if you have something connected at the instrument input and activate the noise you would feed the noise to the instrument (or whatever you connected to it) You could call it a feature but I'm concerned if you connect a line driver with low output z it might bring some problems.

  Third, C5 would blow with phantom power, it should be reversed. Also you are missing 150Ω in series with C6 which is a huge unbalance for a mic level, I'd rather go with 100R for R5 and R6 and 50Ω (can be 47Ω) in series with C6.

  For the phantom PS you should check another design, I don't think that's right. 100Ω resistors doesn't seem right, LEDs doesn't seem right, more like few k resistors and no diodes I think, maybe a zenner if you want to have "always" the same voltage.

  I don't know the electret amplifier, for sure there are better 3 transistors circuit but I have no real experience with them.

JS
 
What average voltage are you getting at pin-10 of the pink noise opamp? Reason I ask is that the reverse voltage of the PN junction is not guaranteed, so it might be outside the common-mode range of the opamp? In which case you'll need to feed it through a coupling cap and bias resistor to the opamp.
 
I have attached a picture of what happens...

joaquins said:
  Second, if you have something connected at the instrument input and activate the noise you would feed the noise to the instrument (or whatever you connected to it) You could call it a feature but I'm concerned if you connect a line driver with low output z it might bring some problems.

This is for stage use....I would call it a feature as you say...to troubleshoot stuff on stage....same goes for the leds in the PSU....
100R resistors are to be changed to the highest value that triggers the PSeudo White Noise.....

merlin said:
What average voltage are you getting at pin-10 of the pink noise opamp? Reason I ask is that the reverse voltage of the PN junction is not guaranteed, so it might be outside the common-mode range of the opamp? In which case you'll need to feed it through a coupling cap and bias resistor to the opamp.

These are some DC volts of the circuit...
+V                  10V
PIN 10          9V
PIN 5            0V

In normal operation I get

PIN 6            when I conect the Multimeter it Measures 9V and goes fairlyfast to 8.5V     
PIN 7            9.5V
PIN 8            9V

If I disconect conections to pin6 I get 0.5V


Still working on some values that need changing....and not sure it is doing what it should...




 

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and if I conect a 2700p wima cap I have from pin7 to GND I get the attached response curve....


 

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finally... pink noise from audio program through the DI gets back in pretty flat so the DI seems to work ok,


 

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pablobolche said:
I have attached a picture of what happens...


This is for stage use....I would call it a feature as you say...to troubleshoot stuff on stage....same goes for the leds in the PSU....
100R resistors are to be changed to the highest value that triggers the PSeudo White Noise.....

These are some DC volts of the circuit...
+V                  10V
PIN 10          9V
PIN 5            0V

In normal operation I get

PIN 6            when I conect the Multimeter it Measures 9V and goes fairlyfast to 8.5V     
PIN 7            9.5V
PIN 8            9V

If I disconect conections to pin6 I get 0.5V


Still working on some values that need changing....and not sure it is doing what it should...
If you are only using a single supply and connecting pin 11 to 0V , you can not also connect op amp inputs like pin 5 to 0V . Connect pin 5 to v/2 at + end of C2.

JR
 
pablobolche said:
These are some DC volts of the circuit...
+V                  10V
PIN 10          9V
PIN 5            0V

In normal operation I get
PIN 6            when I conect the Multimeter it Measures 9V and goes fairlyfast to 8.5V     
PIN 7            9.5V
PIN 8            9V
Well there's your problem -the opamp is saturated.

If you are only using a single supply and connecting pin 11 to 0V , you can not also connect op amp inputs like pin 5 to 0V . Connect pin 5 to v/2 at + end of C2.
This. And couple the PN junction to the opamp using a cap and bias resistor/s. Also you appear to be missing an input resistor to pin-6 (pink filter opamp). Basically, your current circuit does not match what you originally posted.
 
JohnRoberts said:
If you are only using a single supply and connecting pin 11 to 0V , you can not also connect op amp inputs like pin 5 to 0V . Connect pin 5 to v/2 at + end of C2.

JR
Great...I will


merlin said:
Well there's your problem -the opamp is saturated.
This. And couple the PN junction to the opamp using a cap and bias resistor/s. Also you appear to be missing an input resistor to pin-6 (pink filter opamp). Basically, your current circuit does not match what you originally posted.

I will redraw the circuit with all things considered....

Thank you for your replies
 
Hello...
I re-did the pcb and after strugling a bit got it working....great..
My selection of blocking caps made the whole thing make no sound/then oscilate....and finally
it's working as expected...will post a schematic once I finish...JA!

Now I want to check the Electret Mic part of this box..

joaquins said:
  I don't know the electret amplifier, for sure there are better 3 transistors circuit but I have no real experience with them.

JS

Any better options for the electret mic schematics are more than welcome...what I have in mind is that the electret connects ok to any mic pre...I tried the schematic posted and worked pretty nice...don`t really know if its good or bad yet...I would apreciate recomendations of mic capsule options...some are probably better for a test/flat mike?? and other better for instruments or vocals...
The electret  capsule I found in my local  electronics dealer specs.....
response 20hz to 20khz 
Sensibility -42db
signal to noise ratio 58db

Other stuff in my mind is...The limit for phantom power is 8mA @48v?!!correcto??....If I work internally at 12v I can use 32ma??
What would be the real-life limit for power consumption of Phantom Power??? Are there any specific recomendations to follow??

Thanks again for passing by this thread and yer comments..
Gracias








 

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pablobolche said:
This is for stage use....I would call it a feature as you say...to troubleshoot stuff on stage....same goes for the leds in the PSU....
100R resistors are to be changed to the highest value that triggers the PSeudo White Noise.....
...

  I'd rather use a periodic signal for that application, much easier to spot (with less level required) on a noisy environment, and much less prone to be confused with other noise on the chain. I'd just use an oscillator, square wave, maybe a bit filtered so bandwidth doesn't go up to the sky, but square waves are easier to leak inside the gig to the other signals, when not in use, you could turn off your oscillator when not in use. I'd add a series resistor on it's output, as it's meant to work on instrument level, higher output impedance is not a problem and can be less problematic when miswired.

JS
 
pablobolche said:
Other stuff in my mind is...The limit for phantom power is 8mA @48v?!!correcto??....If I work internally at 12v I can use 32ma??

Only if you use a DC to DC buck converter. They can be 90% or so efficient. something like this:
http://www.ebay.com/itm/DC-DC-3V-5V-12V-24V-48V-Buck-Adjustable-Step-Down-Voltage-Converter-Module-Car-/192076520025?hash=item2cb8a71a59:g:j48AAOSw241Yd0SO

But just using regular linear regulators or a zener to go from 48v to 12V would use up all that current in heat.
Be warned those DC to DC converters are noisy around audio circuits.
 
pablobolche said:
Other stuff in my mind is...The limit for phantom power is 8mA @48v?!!correcto??....If I work internally at 12v I can use 32ma??

Short answer, no.

Think of phantom as "soft power", where as soon as you put any load on it, the voltage drops, a lot.

From memory, in order to pull the most power in watts from phantom, I believe it needs to be loaded down to near 28 volts

Gene


 
> loaded down to near 28 volts

"Near"?

This is one time when Matching Theorem applies. P48 is 48V from 3.4K. Max load power is 24V, and at that point you can have 24V/3.4K= 7mA. (Yeah, 28V won't be a lot different.)

If you had a perfect 24V-12V converter, this could be 12V 14mA.

Maybe I missed something. I had a "noise" source on a chip. Ate 9V at a couple mA. A 9V battery lasted for years. Pink-filter was passive; actually it was the E-V Speaker Test curve with less power below 100Hz or above 5KHz. The particular "feature" was that a short digital "noise" source repeats; this repeated every 1.7 seconds. The repeat caused a mild "thump". So even if there was another hiss in the system, this source was easy to identify.
 
Gene Pink said:
Short answer, no.

Think of phantom as "soft power", where as soon as you put any load on it, the voltage drops, a lot.

From memory, in order to pull the most power in watts from phantom, I believe it needs to be loaded down to near 28 volts

Gene
Longer answer, with Phantom Power each of the signal leads is connected to 48V [this could be a lot lower voltage on some cheap pres/mixers, but ignoring that], in series with a 6.8k resistor. Thus if you short these to ground, you get 7mA each or a total of 14 mA. Of course, at zero volts you won't get any power out.

To get the most power out (this is called "maximum power transfer" in EE terms), the load resistance must equal the source resistance, and when this happens you get 1/2 the source voltage at the terminals, or 24V.

But this isn't necessarily what you want. You just want enough voltage and current to run the circuit.  Lighting a LED to a reasonable brightness takes a large proportion of the available current, so depending on how much current the rest of the circuit takes, you may want to drop the idea of using a LED.
 

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