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[audioguru]

Which transformer did you buy?
Voltage regulators do not work when they are in parallel.

 

[MrDEB]

building a duel polarity supply

found all sorts of circuits with the 78xx and the 79xx in parell.
I need to order a different transformer-I mistakenly ordered a 24v but need at least 30 as I need a 12v+ and a 12v- plus a ground.
Need to calculate current as I am no longer going to multiplex. going with 10 LM3916's
**broken link removed**

 

[audioguru]

found all sorts of circuits with the 78xx and the 79xx in parell.

Voltage regulators do not work properly when they are in parallel. The one with the highest voltage will hog the load until it overheats or begins to limit the current which reduces the output voltage. Then the regulator with the next highest voltage begins to work. So one regulator is hot and the other is cold.
You don't need much current now so you don't need to connect regulators in parallel.

I need to order a different transformer-I mistakenly ordered a 24v but need at least 30 as I need a 12v+ and a 12v- plus a ground.

A 30V center-tapped transformer is 15V-0V-15V and will produce an unregulated supply of +20.4V and -20.4V which is much too high and the regulators will be extremely hot.
A 24V center-tapped transformer is 12V-0V-12V and will produce an unregulated supply of
+16.2V and -16.2V which is fine for feeding 12V regulators.

 

[MrDEB]

Going with 9v instead of 12V

Have a 24v transformer(need to see if it's CT) but either way it should work if running 9v duel supply instead of 12v duel supply.
Still need the ground as well.

 

[MrDEB]

Have CT transformer

transformer is a 12-0-12 1 amp transformer
need to order 9v regeulators.
Question on input caps for audio - electrolic or non polarized caps?
In the AND8177/D schematic it has a bypass (flat) circuit so one can compare EQ results (on/off). Muy plan is to incorporate using a 4066 bi lateral switch so both channels switch together.
Also adding a mode switch so the dot/bar on the 10-LM3916's can be switched on/off. planning either a transistor or relay?Only need to wire all the mode pins together?

 

[Hero999]

That will work but why are you using a regulated supply for an audio circuit?

Generally audio amplifiers have lots of negative feedback which helps them reject power supply fluctuations.

 

[audioguru]

I design audio circuits to have a DC voltage across an audio coupling capacitor to use a polarized electrolytic capacitor.
Other circuits that have an unknown polarity like yours are designed with a high enough input impedance to use 330nF or 470nF poly capacitors for coupling audio.

Some products use many non-polarized electrolytic capacitors for audio coupling.

With a supply as high as 9V then the LM3916 ICs might overheat and be damaged if they are in the BAR mode and the input is at maximum for more than a few seconds if the LEDs are bright (high current). In my sound Level Indicator project I used a 10 ohm/1W resistor in series with the 4V LEDs to prevent the LM3915 from overheating with a 7.2V supply.

 

[MrDEB]

I contemplated a resistor

In the 9v supply feeding the leds.
In my circuit I have the schematic from the data sheet for the led intensity control and the voltage reference,
! 10 ohm 1 watt resistor--yes I just may do it.
I was wondering how big of a resistor (wattage) for 10 smd leds.
Off to working on the Bi-Lateral switching for by-pass (flat ) mode

 

[audioguru]

With a 9V supply and 2.0V LEDs at 25ma each, the total current is 250mA when all 10 LEDs are turned on and the power dissipated in the LM3916 is 1.75W. Its max allowed dissipation is 1.365W so it will fail.
A 15 ohm/2W resistor in series with all the LEDs would dissipate nearly 1W so the LM3916 will dissipate 0.81W which is fine. Then a 10uF electrolytic capacitor should be used to ground from the LEDs anodes as a bypass.

 

[MrDEB]

Will make changes

after dumping the multiplexing circuit things were going good until I found I wired my op amp buffers wrong on half circuit.
found I used several resistor numbers more than once.
Still in a quandry about using a non polarized capacitor (10uf, 1uf and 3.3uf capacitor) in series with op amp inputs see pic, C4 as example.
It indicates an electrolic but they I understand are noisy.

 

[audioguru]

Your circuit has the log amp that doesn't work. It might have been used with the LM3914 ICs that you are not using. The LM3916 IC doesn't need a log amp.
Your circuit still has many of the parts that were used for multiplexing that are not needed now.
R13 is in the wrong location.

You have a huge 3.3uF coupling capacitor for C4 that will have a low frequency cutoff at nearly DC.
A 220nF poly capacitor will have a cutoff frequency of 7Hz which is low enough.

 

[MrDEB]

Sorry I posted wrong circuit

That WAS the old version
Here is updated one
Sorry

 

[audioguru]

The new circuit is much better BUT:
1) If R1 and R4 are 100k then C1 can be a 220nF poly type and will have a low frequency cutoff of 7Hz which is low enough. C4 should also be a 220nF poly type.
2) R17, U5 and U6 are not needed.
3) C7 and C8 should be 100nF.

 

[MrDEB]

changing caps and resistors BUT

U5,U6 are buffers to prevent any noise (yes no maybe? from entering listening audio (what else to call it?)
the R17 and associated circuit is from data sheet.
be nice to drop the U5 etc op amps.
Will look at in TINA
finishing up a 7805 current regulator circuit for panel led back lights and EQ/FLAT indicator led.

 

[MrDEB]

THANKS check is in the mail

I removed the buffers and changed R1, R4, C1, C4
Looks the same as without the changes. Just less PCB landscape
7805 current regulator in lower left corner-going to power several panel back light leds (blue) and one EQ indicator led (RED)
may go with larger resistor for 20ma instead of 30ma as pictured 100-150 ohm 2watt resistor?.
Will have total of 9 knobs x 2 leds per = 18-20 leds.
TINA dosn't have a 7805 so the TLE2425 is all I have to simulate.

 

[audioguru]

U5,U6 are buffers to prevent any noise (yes no maybe? from entering listening audio (what else to call it?)

Multiplexing caused noise but it is gone so the opamp buffers are not needed.

the R17 and associated circuit is from data sheet.

The datasheet doesn't know that the new peak detector transistor circuit is driven from the very low output impedance of an opamp so the resistor does nothing.

be nice to drop the U5 etc op amps.

Good riddance.

finishing up a 7805 current regulator circuit for panel led back lights and EQ/FLAT indicator led.

A 7805 is a voltage regulator, not a current regulator. LEDs do not need regulation, they just need a series resistor to limit the current.

 

[MrDEB]

OUPS I was wrong

I reexamined the sweeps with and without U5 and U6
the sweep loses its peaks.

 

[audioguru]

LEDs are diodes, not lightbulbs, so they don't work in parallel. Connect a few in series and in series with a current-limiting resistor instead of using a regulator.

 

[audioguru]

I reexamined the sweeps with and without U5 and U6
the sweep loses its peaks.

Something is wrong with TINA for the low frequency peak. Maybe the pot is not adjusted the same as before. The high frequency peak is fine.

 

[MrDEB]

will double check TINA

I found the current regulator circuit online and in a Forrest Mims project book.
Kinda figured it would work??
I started adding leds to reg circuit and it stays at 30ma.