Without knowing exact speaker reactive behavior I would use 2x22VAC(max.)/250-300VA as a sensible choice.
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As far as I can see the schematic as given has nothing to do with a proper operation of an LM4780...it is just a decoy schematic for confuse others Chinese copycats.
The schematic appears to follow the PCB and the values don't seem far away from the application notes. A few are different such as 22k instead of 20k for the Rf and Rf2.
Are you able to elaborate a little? What is badly wrong with the schema?
I have realised that the silk screen on the board is labelled 28v-GND-28v at the AC input - but the schematic shows the rectified voltage as being +/-28VDC 😱
So using a modified version of Tom's calculator, as you both mentioned, a transformer of 22-0-22 250-300va will cover a 4 ohm load or 180-160va if restricted to 8 ohm loads (assuming Vcc=28, Cf=dB).
I'm guessing the output power from 16 ohms wouldn't be worth bothering with?
Are you able to elaborate a little? What is badly wrong with the schema?
I have realised that the silk screen on the board is labelled 28v-GND-28v at the AC input - but the schematic shows the rectified voltage as being +/-28VDC 😱
So using a modified version of Tom's calculator, as you both mentioned, a transformer of 22-0-22 250-300va will cover a 4 ohm load or 180-160va if restricted to 8 ohm loads (assuming Vcc=28, Cf=dB).
I'm guessing the output power from 16 ohms wouldn't be worth bothering with?
Thanks Mark. I've been staring at the schematic for ages trying to figure out how it works (it doesn't seem like it should) and that's because the schematic is a pretty bad inaccurate copy.
I managed to find the correct schematic on another thread from 5 years ago and it makes a whole lot more sense now.
Regarding the 10R resistors, I found the following quote that might be of interest:
I managed to find the correct schematic on another thread from 5 years ago and it makes a whole lot more sense now.
Regarding the 10R resistors, I found the following quote that might be of interest:
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R13 - 14 should be 2.7 ohms. And, if you use the stability parts in the feedback then Cc (220pF) is also missing.
Does anyone have a BOM for the board from the first post ? I have 2 boards from audiomodule.eu ,but no values for elements.I was searching net but no luck for this bords.
Regards
zoky2
Regards
zoky2
Thanks for the pointers Mark.
I'm getting myself confused with the calculations:
If I were to make this board parallel (connect the jumper between 'R OUT' and 'L OUT') for LH channel and then do the same again for a RH channel, what would the effect be in terms of power supply requirement?
For instance if I have 22VAC/~30VDC supply for a 4 ohm load expecting to be 250-300VA, what would the VA requirement be if I join the outputs on the board and add another board?
Sorry, I can't find any details of what's fitted to that particular board.
Don't do that without thinking!!!!
Say you have a 1% difference between amplifiers. At some moment, one is at 20V, the other at 20.2V. This is a 0.2V difference across the jumper. The amplifiers' output resistance may be less than 0.01 Ohms. Say the jumper is similar. 20V across the 8 Ohm load is 2.5 Amps to load, but 0.2V across 0.03 Ohms jumpering is 6.6 Amps of waste current and heat in the chip!
Thanks for the warning PRR.
The schematic says to 'short out the jumper' and the PCB is designed with a shorting link..
But looking at the datasheet, it suggests 2x 0.1 ohm 3W resistors in series with the output in the centre.
I take it that this would work as it would reduce the 6.6A/1.3W to 2A 400mW?
edit: the audio sector boards appear to use 0.15R 3w power resistors (output).
The schematic says to 'short out the jumper' and the PCB is designed with a shorting link..
But looking at the datasheet, it suggests 2x 0.1 ohm 3W resistors in series with the output in the centre.
I take it that this would work as it would reduce the 6.6A/1.3W to 2A 400mW?
edit: the audio sector boards appear to use 0.15R 3w power resistors (output).
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Are they not the large green resistors with R10 printed on them? R10 and R19 printed on the board.
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Hello everybody,
I just stumbled across this thread for the same reason as OP, as it turns out, audiomodule.eu is down and I never received the PCB schematic and BOM via email, but I did get them printed out with my purchase.
After a long search I managed to find them, hope this does the trick.
Best regards.
I just stumbled across this thread for the same reason as OP, as it turns out, audiomodule.eu is down and I never received the PCB schematic and BOM via email, but I did get them printed out with my purchase.
After a long search I managed to find them, hope this does the trick.
Best regards.
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LM4780 I am using in parallel output with one important thing, resistors which defines amplification should be 0,1% accuracy, after that amp is working without issues which PRR mentioned.
Killersupra,
thank you very much for the schematic and BOM,now I can put together the board .
Regards
zoky2
thank you very much for the schematic and BOM,now I can put together the board .
Regards
zoky2
Hi to all, thanks a lot indeed! It is also very nice that some basics were discussed again,
really appreciate it.
All the best,
Salar
really appreciate it.
All the best,
Salar
What volume pot to use with this board? Is it dependent on R11&R18? Sources are
strictly line level DACs. Is 10k the value to go?
strictly line level DACs. Is 10k the value to go?
One thing I still do not understand. The board has for each channel 3x2200µF caps on the voltage input.
Input is DC, not AC, no rectification on the bord, this has to be done externally.
So what capacitance value do I choose after rectification?
Input is DC, not AC, no rectification on the bord, this has to be done externally.
So what capacitance value do I choose after rectification?
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