Looking for the Circuit drawing of this LM4780 Board

[Salar]

Hello to all,
I bought this LM4780 Board from a czech seller on ebay two years ago.
Unfortunately I do not have a circuit drawing or any naming on the board.
Maybe someone recognizes it and can send me the circuit drawing or tell
the brand?
Thanks a lot, all the best,
Salar

 

[aparatusonitus]

PCB comes from audiomodule.eu, but their site has been shut down for some time now.
Try to get something out from the waybackmachine search engine. See here for reference https://www.diyaudio.com/forums/swap-meet/334989-lm4780-pcbs-soldered-chips.html#post5722172

 

[asuslover]

Ebay seller: https://www.ebay.com/usr/amplifi_07

 

[Salar]

Hello,
many thanks to you both!
But I have already contacted the seller amplifi_07 before starting this thread
as he did not respond. So the board is from audiomodule.eu, many thanks for that.
On the wayback machine I only find the statistics of the site, no schematics.
Maybe someone here in the forium can still provide schematics and documentation.

Anothr question: What would be a sensible VA Power for this board? Space is limited,
would be a 150VA toroid sufficient, or even less?
All the best,
Salar

 

[aparatusonitus]

2x18VAC/150VA trx should be sufficient for EACH board...after rectification and filtering you will get about +/-24DC.

 

[peranders]

Is the board populated or do you need help with this? You can rather easily do a reverse engineering together with the data sheet for LM4780.

 

[Salar]

It is populated. But being a new on chipamps, I would like to get the documentation
of this board. It must be floating around as it was offered with the sale.
I got it via ebay messenger in 2016 but it was erased by ebay at some point.
Aparatusonitus, with 2x18VAC/150VA you mean a total of 300VA?
Shouldn´t be 2x18VAC/125VA / 250VA more than sufficient?
I love big toroids and a bit of overengeneering but this time, there is not so much space available...

 

[asuslover]

250va for 2 channels is perfect.

 

[aparatusonitus]

Shouldn´t be 2x18VAC/125VA / 250VA more than sufficient?

It seems it has to be (if we consider space constraints, that is)...but do not be cheap on PSU capacitors, buy the best you can afford, fresh ones from reputable sources because they ARE in signal path.

 

[Salar]

Noone with the schematics of this board? The ebay seller amplifi_07 never responded, contacted him twice and via mail...

 

[avtech]

I managed to get a couple of pages up on Wayback machine:

2x60W Amplifier with LM4780 | Audiomodule.eu

https://web.archive.org/web/2016110...nt/uploads/2015/04/lme4780_3.1_sm-268x268.jpg

Finally, you will need a dual unregulated DC power supply 2x35V driven by an 120-150VA transformer.

Haven't managed to find a schematic though.

2x18VAC/150VA trx should be sufficient for EACH board...after rectification and filtering you will get about +/-24DC.

I bought some boards recently that are marked as requiring 28VAC centre tapped which puts me in the region of +/-38VDC. Would that be too much for a LM4780? Seems to be on the upper end of the datasheet.

 

[Salar]

Thanks for the effort.
I hope some user of diyaudio will be able to provide the schematics.
In the moment I have no ckule where and how the volume´s variable resistor is connected and which value is needed.
As far as I know abouit the transformer, 2x18V / 24V after rectification will be sufficcient for 8Ω speakers...

 

[aparatusonitus]

I bought some boards recently that are marked as requiring 28VAC centre tapped which puts me in the region of +/-38VDC. Would that be too much for a LM4780? Seems to be on the upper end of the datasheet.

Yes, it would...sell these and buy proper one(s).
For reference LM3886 chip power amplifier power supply design.

 

[avtech]

Yes, it would...sell these and buy proper one(s).

Which would you deem to be 'proper' ones?

 

[aparatusonitus]

What is your speaker impedance and efficiency (measured if possible, if not just read the specs)?

 

[avtech]

Still designing the system but looking likely to be 8 ohm and around 88-89db.

Other boards I have looked at so far have specified 24-28VAC supply for dual rails between 32-38VDC.

 

[Mark Whitney]

There is information about rail voltage in relation to the output impedance in the LM3886 datasheet.

 

[avtech]

I must not be able to read the datasheet properly because as far as I can see, +-35v into 8 ohm is acceptible for the LM3886 and isn't the LM4780 just 2 LM3886 in one package?

So I don't get why I should "sell these and buy proper one(s)" based on the input voltage on the PCB being 28-0-28VAC Maybe the extra couple of volts is too much, even though it is below the supply limits? Instead of selling the boards can I not just dial the voltage down to ~35VDC?

I was thinking 24/25VAC (~32/34VDC) might be more appropriate for moving away from the +/-42VDC rail limits but I also don't see why the voltage would need to be as low as 18-0-18VAC (~24VDC).

 

[asuslover]

Lm4780 is a very fine chip . But your transformer is not the greatest for this situation. I would buy an 2X 20-22V(200-250VA) transformer and that would be good for 4, 6 or 8 ohms.

 

[Mark Whitney]

Figure 35 and 36 shows you the dissipation at different voltages and load impedance. You want to run these amps as cool as possible. I use 2x24V which normally produces +/- 33 V DC with transformer regulation.