power problems

[harps]

hello there.

i have a power problem that is proving difficult to solve with my limited electronics knowledge , i have a single rail psu for my project box and need to power three ICs , one IC needs dual rail and the other two can run from single rail.

i have an electret mic connected to an op amp (TL071), then to a line balancing IC(DRV134) for sending to a mixer. there is also a VU meter (lm3915)attached to the op amp output.

each of the IC circuits work well, i've tested them seperatley and in pairs, but when i try to connect the single rail to a floating ground dual rail ,they are not happy at all.

i am trying to figure out how to power all these things so they can connect together without strange ground loop issues.

here is a schematic to aid explaination, ive taken out the power wires so its not so cluttered, and i've highlighted the power and ground connections with red and green dots.
hope you can help : )
View attachment 63494

 

[audioguru]

You have pin 3 of the preamp opamp connected to +2.5V instead of to half the supply voltage (+6V). Then the first opamp might be simply a very poor rectifier.

The balanced line driver says it has dual rail power which is not shown on your schematic.

 

[harps]

h : )

instead of wiring up the power on the schematic , i placed red and green dots , just to show where power needs to go. because i cant figure out how to make a them connect without ground problems

i can make the op amp work. the line driver work, and the VU work . they all work.

but when i put them together, the dual rail power does not want to work with the single rail ( the regulators)

i have a 12v and a 5v regulator in the project box. the line driver needs dual rail , so i create a flaoting ground type of circuit, but the grounds of the flaoting ground and the regulators cause problems together.

I have also tried powering the op amp and the line driver with a dual rail floating ground, that worked o.k , but when i added the VU circuit there were problems a soon as i connected the ground.

pheww. not sure what to do? maybe create another flaoting ground circuit for the VU IC.? so that all the IC's have a floating ground?

 

[alec_t]

Shouldn't pins 3, 5 and 6 of the line driver connect respectively to the floating ground, actual ground and +12V?
Perhaps a coupling cap drive for the VU meter?

 

[harps]

a coupling cap sounds interesting! i tried an opto coupler, betweeen the op amp out and the VU in. that worked ,all three ics worked together, but the dynamic range of the vu meter was very heavly reduced.

i have now connected both the op amp and the line driver to the dual rail power, so they are both dual rail with a floating ground. they work great together, but the VU meter being single rail, fowls the circuit up and i get a big 'Pop' and all the VU leds light up soild. unless i use an oppto coupler.

a way to couple them seems the only way to make this work?
can you tell me a little more about this coupling idea?

thanks for help : )

 

[alec_t]

can you tell me a little more about this coupling idea?

With no guarantee that this will work, try connecting ~1uF (non-polarised) in the line leading to pin 5 of IC2. At the moment you have this pin 5 directly connected to pin 4 of the line driver: that may be causing a problem.

Edit: With the cap in place you might also find you need a resistor (say ~100k) from IC2 pin 5 to actual ground to prevent pin 5 floating.

 

[audioguru]

The input pin 5 of the LM3915 MUST have a resistor to ground to provide a reference of 0VDC.
Pin 3 of your DRV134 balanced line driver also MUST have a reference voltage of of 0VDC (yours is floating). It should be connected to 0V.

 

[harps]

thanks guys!

well spotted , i missed the ground from my breadboard when i created the schematic. I added a resistor to give refrence to the LM3915 as you mentioned. i also added a coupling cap , between the LM3915 and the op amp out and ....it works!!! i can hardly beleive it , Ive been messing with this for a long time. for some reason only the + positive from the opamp is needed for the VU to work, if i add ground it becomes unstable.

here is an updated schematic so you can see what i mean. : )


View attachment 63503

 

[audioguru]

You do not understand.
The LM3915 and the DRV134 both need a resistor to 0V at their inputs. It can be the SAME resistor. Then you do not need an extra coupling capacitor because only one is needed (C14) to block the DC from the output of the opamp.

Pin 4 of the LM3915 MUST connect to 0V. Yours is floating so the LM3915 does not know which LED to light.

 

[harps]

darn : .( , but your right, i do not fully understand.

you say:

"The LM3915 and the DRV134 both need a resistor to 0V at their inputs"

does "0V " mean: the ground of the 12v regulator?

Pin 4 of the LM3915 was not happy when i connected it to ground. maybe because i have the other bits wrong.

There is resistor (R1) which is going from pin 5 of the Lm3915 to ground, is that wrong?
and (R2 ) is going to the dual rail floating ground , maybe if I change that to the regulators ground?

: /

: )

 

[audioguru]

Sorry, I did not understand your schematic and it was very pastel so I could barely see it.
I added some contrast to your schematic.

You DO NOT have a dual rail power supply (I thought you did). Instead you have +12V and ground. The DRV134 must have its "GND" pin 3 connected to your +6V reference voltage (just like pin 3 on the TL071).
You also do not have and do not need GND2.

I fixed your schematic so it will work properly.

 

[harps]

wow, thank you Audioguru, i shall try this out. : )

 

[harps]

Thank you audioguru, i managed to make the audio circuit work, how you managed to figure out changing those parts, and using a refrence 6v:? You must have been working with electronics for many years to do what you do, as you do for so many people, with what seems such ease. im still quite baffled, and i have wires all over the place, yet the earth/ground ..they finally all connect together : )

cheers audioguru. : P