LM3886 By General Guitar Gadget

[ciscothehellspawn]

I would like to build the famous general guitar gadgets schematic (http://www.generalguitargadgets.com/pdf/ggg_lm3886_amp.pdf)

The short guide indicates a power supply of + - 18v. I know that might be more to pull out more watts... I would go on +-30V at least

Is it possible?

I would like to get about 60w (MONO) into 8ohm

thank you in advance

 

[JMFahey]

Downoad the LM3886 datasheet and follow what it says.
I think max into 8 ohms was 50W, close enough.

 

[counter culture]

You can get 50W into 8 ohms with +/-35v, but you will need to pay particular attention to heatsinking, use thermal compound at the junction. It'll be that little bit less problematic if you just settle for a bit less output.

 

[wazzy]

I have built two of these using the boards but a slightly different schematic, also using a 22-0-22v 300va transformer, dead silent at full volume decent design i found will attach photos as soon as i know how.

 

[ciscothehellspawn]

thanks! how many watts you have got with this transormer?

 

[JMFahey]

Probably around 60W into 4 ohms and 40W into 8 ohms.

 

[Enzo]

Going to a lot of trouble to get a few extra watts may niot be as productive as you think. If you went from 25 wats to 50 watts, the result would only be 3 decibels louder.

 

[AndrewT]

and 63W gives a further +1db.
But the really important part of going from 25W to 63W is not the extra SPL, but the extra overhead that reduces the incidences of clipped output by raising the clipping threshold by that 4dB.

 

[ciscothehellspawn]

I would like to get 60w into 8ohm at least, probably a bridge connection of a pair of circuits is needed... I think I'll search for something powerfull... like the tda7294

 

[JMFahey]

50W and 60W is practically the same, so if you have an easy solution for 50 and a complex one for 60, choose the easier one.
Now if you need 100W or more, then you'll need to go discrete.
The beauty of chipamps is simplicity.
Once you need bridging or (ugh !!!), parallelling, they become as complex as discrete and are not worth it.

Edit: TDA7294 is only slightly more powerful than LM3886, which are far more popular, which means lots of PCB and transformer options, lots of Forum experience to relie on, etc.

But of course, it's your choice.

 

[ciscothehellspawn]

you are right...

this is the 7294's project I was thinking: LINK

 

[wazzy]

Generalguitargadget board.

Two boards both with basic components for proof of concept, made them with the toner transfer off photo paper method. I have since changed the components to 'better' ones still using the same pcbs and I'm happy with the sound. I am using 4ohm speakers as well.

 

[JMFahey]

Cool. Congratulations.

 

[ciscothehellspawn]

hi to all, thanks for all replies!

ok, I think I can start with the GGG project!

Concerning the PSU, I've found this schematic from chipamp: http://chipamp.com/images/ps-rev3-sch.gif

Question 1: the +pgnd & -pgnd need to go to the chassis togheter? If you know some simplest schematic (but good too) please let me know...

Question 2: As reported here HERE, to have a +-35Vdc (in order to get 50w into 8ohm), I need a transformer with 25 Vac at secondary.Is it right? How much VA are recommended?