initially when I got the amp from the same vendor in the above post there was crackling sound in the beginning for about 10 mins and after that it disappeared and everything started to work fine but when I made the board things were different now as I get the sound only after turning off as its using the charge in the caps to give out the sound...
I have noticed that by mistake i have used 10k instead of 1.2k at the zener diode now fixed to 1.2k. But now when i power up I get negative displacement on speaker cone with some louder pop and settles down to its normal position and my 180 ohm resistor gets bloody hot even though i have used 5 x 1k resistors in parallel just to cope up the heat ... I see a bias of 25ma across the source resistor .22ohm ( voltage being 5mv) now reduced the pot to 930 ohms but strangely I see 14V ! across the 180 ohm resistor fearing that it might catch fire im turning the amp off and in any of the case the sound doesnt come...
what could be wrong?
I checked and rechecked the circuit with the pcb again and again everything seems working fine and the transistors are from Mouser that too genuine.
I just get music with some noise in it once the power is off as Schmidt trigger fashion and finally attenuates...
Im unable to find where is the problem is coming from..
what could be wrong?
I checked and rechecked the circuit with the pcb again and again everything seems working fine and the transistors are from Mouser that too genuine.
I just get music with some noise in it once the power is off as Schmidt trigger fashion and finally attenuates...
Im unable to find where is the problem is coming from..
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Firstly, you need something to limit the power supply current to the output stage so that you do not kill the transistors all the time.
A 15ohm hi-power resistor to each rail for example...
Then;
measure the voltage between the chips sink and source (or base voltages of the driver stage)...
And report back to here.
A 15ohm hi-power resistor to each rail for example...
Then;
measure the voltage between the chips sink and source (or base voltages of the driver stage)...
And report back to here.
unfortunately I dont have a dimmerstat but I did re assemble everything this time and figured out one issue that is I see a solid 10.9V of DC offset in the amplifier with some small buzz and noise coming up. When I turn off the power switch I get nice sound from the speaker. Bias stable at 50ma and none of the 180ohm resistor is getting heated.
The voltage at the power supply pins are are also symmetrical +/- values for both driver and output stages.
When I turn on the amplifier the speaker cone displaces to its maximum and ill get a sound at low volume and when I turn off the power supply the cone gets to its rest state with nice sound coming but with little noise.
what would be the issue here?
The voltage at the power supply pins are are also symmetrical +/- values for both driver and output stages.
When I turn on the amplifier the speaker cone displaces to its maximum and ill get a sound at low volume and when I turn off the power supply the cone gets to its rest state with nice sound coming but with little noise.
what would be the issue here?
I have checked the older version of the board by double checking everything what has been done there are few things observed...
1. The voltage across the 5200 transistor source resistor was around 21.3V which is shocking... which in general has to be in the order of few mV and this is without any input signal.
2. The difference between the source and sink is still the same.. 2.3v
1. The voltage across the 5200 transistor source resistor was around 21.3V which is shocking... which in general has to be in the order of few mV and this is without any input signal.
2. The difference between the source and sink is still the same.. 2.3v
Is D1 still OK?
Is R1 10k?
Are you sure all the GNDs are OK, connected properly?
What are the source/sink voltages relative to GND when the amp is not amping and when it is playing the sweet sounds of heaven (after you have pulled the plug)?
Voltage across R7 = 21.3V?
Voltage across R12?
Is R1 10k?
Are you sure all the GNDs are OK, connected properly?
What are the source/sink voltages relative to GND when the amp is not amping and when it is playing the sweet sounds of heaven (after you have pulled the plug)?
Voltage across R7 = 21.3V?
Voltage across R12?
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Voltage across R37.4V
voltage across R12 = 6.4mV
all the grounds are ok..
Voltage across D1 is 5.12 V constant...
The voltage between the source to GND 6.1V and
sink to GND 8.3V..
Its not like heaven but the sound is having some noise when i turn off the switch...
well there is one thing that is observed that with a DMM ive checked the psu capacitors as I found a constant DC both positive and negative symmetric in values but when I checked it by selecting AC voltage measurement in DMM I found
for DRV the voltage AC is 123.2 from ground to +ve and same for negative..
for Output stage the PSU AC is 112 from ground to +ve and same for negative is this normal?
Looks like the LM4702 is trying to do its best to compensate for the burned output stage...
LM4702 seems to be OK, which should be a good news at least...(?)
Can not figure out why it burns the output stage though, if not because of the over bias. Hope someone else can reason (with the given information), why???
You (usually) can easily burn the output stage if you have one loose ground connection there (outpuit stage)(for example).
Check also the driver stage transistors. But if you have 37V across a base resistor, it should mean the output transistor is now a good super conductor (or would be here at the north pole at least)...
LM4702 seems to be OK, which should be a good news at least...(?)
Can not figure out why it burns the output stage though, if not because of the over bias. Hope someone else can reason (with the given information), why???
You (usually) can easily burn the output stage if you have one loose ground connection there (outpuit stage)(for example).
Check also the driver stage transistors. But if you have 37V across a base resistor, it should mean the output transistor is now a good super conductor (or would be here at the north pole at least)...
found the problem... while routing the pcb i didnt connect the signal ground to the star ground now the signal ground is connected to the ground of the psu filter caps and now im getting all good everything is stable and no cone excursion to max at the output already run the amp for 3 hours its working like charm... bias stable at 25ma and one thing that bothers me is the DC offset at the output which is -18.5ma...how to reduce this?
Why bother? The only pressing need is your sense of aesthetics. Technically, 18mV at the output is of no consequence if its relatively stable.
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