That sounds typical of the DC offset protection cutting in (relay clicking)
and on the J11 it show 0v 0v 0v for the ground left and right but its 7.8v! not 0v
What is J11 ?
Can we go back to the pot and the readings you initially took.
Referring to your diagram in post #6 can you re-measure the voltages you see on 1,2 and 3. Have no audio playing.
Put your meter on DC volts and connect the black meter lead to ground for this. If you really do have around 7.8 volts on both pins 1 and 3 then it sounds like the control is configured unconventionally... and I wouldn't like to guess without seeing a circuit although there are configurations that would give that result.
The fact it plays audio well and the control works means that it can't be anything totally drastic like a missing supply or floating earth.
Thank you guys for your help. You will never believe this but the dac i was using has output dc of 8v!!!!!!!!!!!!!! wasnt even my Dac! I am so mad thanks again guys I was going crazy! Mooly thanks for sayin non existent, some times the answer is between the lines! I cant thank you guys enough!
Great to hear you have found the reason. So this amp must either be DC coupled at the inputs (or possibly using an electrolytic that leaked current if reverse biased).
Interesting, and a good lesson to all those diy'ers that insist on having 100% DC coupling throughout. The coupling cap to the power amp input (C1 in your image) saved both the amp and your speakers.
Nice one
Interesting, and a good lesson to all those diy'ers that insist on having 100% DC coupling throughout. The coupling cap to the power amp input (C1 in your image) saved both the amp and your speakers.
Nice one
Thanks for your help but this has taught me what to look for if it was a problem with the amp itself!! I have learnt a lot and very thankful!
just last question does this make any sense? I have adjusted channel bias before but voltage not current. I found this online doesnt make any sense to me!
important bias info:
1. connect the AC- ampmeter to the AC powercord, connect 8Ohm loads to the LS outs
2. set the bias values to min. : "RV22 (fully ClockWise) & RV122 (fully anti ClockWise)"
- take care on writen words: my bias pots have other number (RV 1 & 2) in EVO2 - unsure if given direction to minimum is correct for every pcb Revision...
4. with bias on minimal, and no Signal, idle current should be:
24mA for 220/240Vac
48mA for 110VAC
50mA for 100VAC
5. Now open the bias trimmer:
+48mA/ch for 240VAC
+50mA/ch for 220VAC
+100mA/ch for 110VAC
+110mA/ch for 100VAC
6. do the same for channel 2
just last question does this make any sense? I have adjusted channel bias before but voltage not current. I found this online doesnt make any sense to me!
important bias info:
1. connect the AC- ampmeter to the AC powercord, connect 8Ohm loads to the LS outs
2. set the bias values to min. : "RV22 (fully ClockWise) & RV122 (fully anti ClockWise)"
- take care on writen words: my bias pots have other number (RV 1 & 2) in EVO2 - unsure if given direction to minimum is correct for every pcb Revision...
4. with bias on minimal, and no Signal, idle current should be:
24mA for 220/240Vac
48mA for 110VAC
50mA for 100VAC
5. Now open the bias trimmer:
+48mA/ch for 240VAC
+50mA/ch for 220VAC
+100mA/ch for 110VAC
+110mA/ch for 100VAC
6. do the same for channel 2
You can't do what you would normally do with this amplifier, as it has no emitter resistors.
Normally you would connect a multimeter across an emitter resistor, and adjust the bias pot until the meter reads so many millivolts across the resistor. Using ohms law you can work out what the value of millivolts corresponds to in terms of current.
This amp seems to be saying you should connect an AC ammeter in line with the amplifier's mains cord, and adjust until 48mA is being drawn from the mains. That's an incredibly stupid way to do it. I'd leave it alone in this case.
Normally you would connect a multimeter across an emitter resistor, and adjust the bias pot until the meter reads so many millivolts across the resistor. Using ohms law you can work out what the value of millivolts corresponds to in terms of current.
This amp seems to be saying you should connect an AC ammeter in line with the amplifier's mains cord, and adjust until 48mA is being drawn from the mains. That's an incredibly stupid way to do it. I'd leave it alone in this case.
Here is my take on it...
1/ AC current meter in the mains lead 'aint the way to do this on any amp. As long as the DC offset is zero speakers can be attached, if there is any offset then that offset skews the result.
Standard advice is bias is always performed with no load attached.
2/ Vague vague vague. CW or CCW depends which side of the board you are looking. Max and min resistance settings may or may not correspond to max and min bias.
Standard advice is to understand the circuit and make your own decision which way to turn the preset.
(if the amp conforms to the basic architecture of post #16 then setting for minimum resistance will give minimum bias current).
3/ We don't seem to have.
4/ Rig up a way to measure the bias properly. Adding a 1 ohm 1 watt resistor in series with the Drain of either FET is the way to do this. Measure the voltage across the 1 ohm and set the bias current by calculating the required voltage needed. A pair of lateral FET's are optimally biased at around 100 milliamps as this is where the positive and negative temperature coefficients effectively cancel. So that would be 0.1 volts across the 1 ohm.
1/ AC current meter in the mains lead 'aint the way to do this on any amp. As long as the DC offset is zero speakers can be attached, if there is any offset then that offset skews the result.
Standard advice is bias is always performed with no load attached.
2/ Vague vague vague. CW or CCW depends which side of the board you are looking. Max and min resistance settings may or may not correspond to max and min bias.
Standard advice is to understand the circuit and make your own decision which way to turn the preset.
(if the amp conforms to the basic architecture of post #16 then setting for minimum resistance will give minimum bias current).
3/ We don't seem to have.
4/ Rig up a way to measure the bias properly. Adding a 1 ohm 1 watt resistor in series with the Drain of either FET is the way to do this. Measure the voltage across the 1 ohm and set the bias current by calculating the required voltage needed. A pair of lateral FET's are optimally biased at around 100 milliamps as this is where the positive and negative temperature coefficients effectively cancel. So that would be 0.1 volts across the 1 ohm.
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