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-   -   LM1876 Mute by Voltage divider. (http://www.diyaudio.com/forums/chip-amps/224566-lm1876-mute-voltage-divider.html)

pra3718 29th November 2012 05:38 AM

LM1876 Mute by Voltage divider.
 
1 Attachment(s)
Recently I build LM1876 sounding good. Mute not used. I think I am near to simple solution.

If I supply below +2.5VDC at mute pins. Amp in play-mode. And supply > 2.5VDC Amp in Mute-mode. (Please correct me if I wrong)

Yesterday, I test voltage divider.

Test 1 : (Figure A ) 20VDC Supplies output is 10VDC (Approx)

Test 2 : (Figure A ) Adding 2200uf Capacitor, I test with Digital Multi Meter (DMM) I hold DMM's pins at output & ground and told my son to turn power ON, I found, DMM shows 20VDC and dropping slowly and settled to 10VDC approx.

I want my circuit should draw 20VDC when I power ON and should drop slowly and settle to below 2.5VDC (which is mute pins requirement for play-mode)

One solution : If I raise R1=22k the output voltage should dropped.

Or Another solution : (Figure C) My supply voltage is 5VDC then output must be 2.5VDC

Summary : (Figure C) Input 5VDC output 2.5VDC with capacitor delay.

I have already build complete Amp which is sounding good. But I did not attach this circuit to mute pins. I fear, I don't what to spoil my amp. I am not electronics man so can you advice me, this (voltage divider) circuit would work for me ? Or Should try this circuit with mute pins ? just for try without damage.

bobodioulasso 29th November 2012 07:18 AM

Assuming you use a symetrical supply.
As per datasheet, the mute pin doesn't want to see more than 5 volts.
Only fig 3 is acceptable.(10v output must be a mistake?)
Making R1=R2 stabilise at 2.5v which is too near from muting treshold. Better to go lower using R1 larger than R2.
You can use a smaller cap if using a larger R2 value. IT's the time constant R*C that counts.(the time it takes for unmuting)

Minion 30th November 2012 10:52 PM

try a 2.5v zenner diode ...

pra3718 1st December 2012 06:56 AM

@ bobodioulasso : Thank you for boosting my confidence.. Audio-Electronics is my hobby. I get few time to do this. Today I am going to try this.

@Minion : LM1876's mute pin works like if V+>2.5V, amp is silent, V+<2.5V Amp is play mode. When I power switch ON, I need V+ should be >2.5V and should drop slowly and stabilize below 2.5V. (which is too near from muting treshold.) And I think 2.5v zenner, would supply constant 2.5V ( please correct me if I am wrong )

Or, Please post in detail what you have to advice ?

KSTR 1st December 2012 09:15 AM

Just hook up a time-constant to (without dividing action) the MUTE pin, with a 100k protection resistor in series, see datasheet Fig.7 for the basic idea. The time-constant is a C from Vcc and and R from Vss (NOT GND!) so that initially after power-up, while the C is charging the MUTE pin is being pulled up putting the chip into MUTE state. You won't need more than a second of delay, so something like 220uF+47k should do.

AndrewT 1st December 2012 11:07 AM

Quote:

Originally Posted by pra3718 (Post 3262067)
Recently I build LM1876 sounding good. Mute not used. I think I am near to simple solution.

If I supply below +2.5VDC at mute pins. Amp in play-mode. And supply > 2.5VDC Amp in Mute-mode. (Please correct me if I wrong)

Yesterday, I test voltage divider.

Test 1 : (Figure A ) 20VDC Supplies output is 10VDC (Approx)

Test 2 : (Figure A ) Adding 2200uf Capacitor, I test with Digital Multi Meter (DMM) I hold DMM's pins at output & ground and told my son to turn power ON, I found, DMM shows 20VDC and dropping slowly and settled to 10VDC approx.

I want my circuit should draw 20VDC when I power ON and should drop slowly and settle to below 2.5VDC (which is mute pins requirement for play-mode)

One solution : If I raise R1=22k the output voltage should dropped.

Or Another solution : (Figure C) My supply voltage is 5VDC then output must be 2.5VDC

Summary : (Figure C) Input 5VDC output 2.5VDC with capacitor delay.

I have already build complete Amp which is sounding good. But I did not attach this circuit to mute pins. I fear, I don't what to spoil my amp. I am not electronics man so can you advice me, this (voltage divider) circuit would work for me ? Or Should try this circuit with mute pins ? just for try without damage.

Figure C must have an AC input for the voltage doubler action to happen.

You cannot get that doubled output voltage from figC if the input really is 5Vdc.

pra3718 2nd December 2012 11:56 AM

Today's Job, SUCCESS
 
1 Attachment(s)
As per fig.D, Regulated supply 5V supplied. After various values of resister, finally selected R1=100K and R2=2.7K. Mute is working. 2200uf cap delaying good time. Several times Power ON and OFF. I found NO pop or click at power on.

I kept circuit as it is for half an hour. And power on again. This time amp was mute and could not play. Power switch OFF and ON immediately, Amp started playing after 2-3 Seconds. I could not understand, why amp could not played first time ?

One more thing, this circuit could not work on power OFF. There is little POP/CLICK on power OFF. I think some expert's experiment needs here.

I am not going to surrender and accept as it is. Some experiment will do in next day..

sofaspud 2nd December 2012 12:22 PM

I have no explanation at this time for the half-hour problem. For the power OFF problem... on power-up, the mute needs to start high and switch low. This has obvious inherent drawbacks. At power OFF it has to quickly switch high again, and again there are the same inherent drawbacks.
An inverter, discrete or integrated, may provide a solution, but I agree experimentation is necessary.

AndrewT 2nd December 2012 12:26 PM

the 2200uF cap is discharged before first start up.
That applies 5V to the mute pin when you start up from cold.
Then the resistors take over and slowly charges the 2200uF to final voltage. This reduces the mute pin voltage to ~2k7/100k*5V. This charging follows the usual RC time constant law. ~ 95% charged in 60ms.

Will the mute pin survive that 5V pulse? and after the onehundredandtwentythird time?

Is this another unhelpful post?

pra3718 2nd December 2012 12:45 PM

One more thing, for play mode Amp needs below than 2.5V means 2.4V should be acceptable. (as per data-sheet) But not, for play mode it needs below than 0.5V or not connected.


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