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Chip Amps Amplifiers based on integrated circuits

Looking for the Circuit drawing of this LM4780 Board
Looking for the Circuit drawing of this LM4780 Board
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Old 17th April 2019, 02:34 PM   #21
aparatusonitus is offline aparatusonitus  Croatia
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Without knowing exact speaker reactive behavior I would use 2x22VAC(max.)/250-300VA as a sensible choice.
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Last edited by aparatusonitus; 17th April 2019 at 02:39 PM.
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Old 17th April 2019, 06:13 PM   #22
asuslover is online now asuslover  Romania
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Looking for the Circuit drawing of this LM4780 Board
Default Czech Lm4780

I knew I had it somewhere, but it has a very low resolution .
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Old 18th April 2019, 07:19 AM   #23
avtech23 is offline avtech23  Australia
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Looking for the Circuit drawing of this LM4780 Board
Thanks for all the suggestions (and apologies to the OP for threadjacking a little - hope it helps you too).

The schematic for mine is attached. Would I need to change any values for running at a lower voltage or would it be good to go?
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File Type: jpg s-l1600 (2).jpg (32.5 KB, 126 views)
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Old 18th April 2019, 09:52 AM   #24
aparatusonitus is offline aparatusonitus  Croatia
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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.
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Old 19th April 2019, 01:34 AM   #25
avtech23 is offline avtech23  Australia
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Looking for the Circuit drawing of this LM4780 Board
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.

Quote:
As far as I can see the schematic as given has nothing to do with a proper operation of an LM4780
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?
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Old 19th April 2019, 05:29 AM   #26
Mark Whitney is offline Mark Whitney  Netherlands
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Ground missing at C1 - C3 and C17 - C19?
R4 and R9 would normally not be 10 ohms.
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Last edited by Mark Whitney; 19th April 2019 at 05:32 AM.
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Old 19th April 2019, 06:54 AM   #27
avtech23 is offline avtech23  Australia
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Looking for the Circuit drawing of this LM4780 Board
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:
Quote:
REACTIVE LOADING
It is hard for most power amplifiers to drive highly capacitive loads very effectively and normally results in
oscillations or ringing on the square wave response. If the output of the LM4780 is connected directly to a
capacitor with no series resistance, the square wave response will exhibit ringing if the capacitance is greater
than about 0.2μF. If highly capacitive loads are expected due to long speaker cables, a method commonly
employed to protect amplifiers from low impedances at high frequencies is to couple to the load through a 10Ω
resistor in parallel with a 0.7μH inductor. The inductor-resistor combination as shown in the Figure 6 isolates the
feedback amplifier from the load by providing high output impedance at high frequencies thus allowing the 10Ω
resistor to decouple the capacitive load and reduce the Q of the series resonant circuit. The LR combination also
provides low output impedance at low frequencies thus shorting out the 10Ω resistor and allowing the amplifier to
drive the series RC load (large capacitive load due to long speaker cables) directly.
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Old 19th April 2019, 07:19 AM   #28
Mark Whitney is offline Mark Whitney  Netherlands
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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.
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Old 19th April 2019, 07:05 PM   #29
zoky2 is offline zoky2  Slovenia
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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.

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Old 22nd April 2019, 07:20 AM   #30
avtech23 is offline avtech23  Australia
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Looking for the Circuit drawing of this LM4780 Board
Quote:
Originally Posted by Mark Whitney View Post
R13 - 14 should be 2.7 ohms. And, if you use the stability parts in the feedback then Cc (220pF) is also missing.
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?

Quote:
Originally Posted by zoky2 View Post
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
Sorry, I can't find any details of what's fitted to that particular board.
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