LM3886 Bass guitar amp

[docz]

Hello guys, been a while since my last post.

I have been toying around with the idea of building a bass guitar amp for band practice. The idea was to get 150ish watts into a 8 ohm 15".

I stumbled onto this thing: LM3886 3 x 159W Parallel Mono Channel Amplifier Board - eBay (item 270644493655 end time Nov-02-10 21:31:50 PDT)

Which looks promising, allthough I have no idea if these chips will work well for bass guitar.

I think I'm going to build a simple preamp, something like this: http://www.diyaudio.com/forums/attac...ar-para-eq.gif

What I'm wondering, will these chips handle the task of being a bass guitar amp?

Will I need more power, or will that 168W thing work?
I have a 8x12V Halogen light transformer, maybe I can use that thing? Never used it, I tried to hook it up once, but I couldn't get a voltage reading from it, I guess it needs a load to fire up... not sure quite how I do that

What kind of power supply do I need? and what VA rating? 168VA? or 612VA?

Will a heat sink suffice for cooling? Or do I need fans?

DocZ

[gruni]

Originally Posted by docz

Hello guys, been a while since my last post.

I have been toying around with the idea of building a bass guitar amp for band practice. The idea was to get 150ish watts into a 8 ohm 15".

I stumbled onto this thing: LM3886 3 x 159W Parallel Mono Channel Amplifier Board - eBay (item 270644493655 end time Nov-02-10 21:31:50 PDT)

Which looks promising, allthough I have no idea if these chips will work well for bass guitar.

I think I'm going to build a simple preamp, something like this: http://www.diyaudio.com/forums/attac...ar-para-eq.gif

What I'm wondering, will these chips handle the task of being a bass guitar amp?

Will I need more power, or will that 168W thing work?
I have a 8x12V Halogen light transformer, maybe I can use that thing? Never used it, I tried to hook it up once, but I couldn't get a voltage reading from it, I guess it needs a load to fire up... not sure quite how I do that

What kind of power supply do I need? and what VA rating? 168VA? or 612VA?

Will a heat sink suffice for cooling? Or do I need fans?

DocZ

they will easily handle the task of being a practise amp. for stage performances you would need more power, i think (when not playing through pa).
you can use the 8x12V transformer. wire 4 x 2 windings in parallel and use two of them in series for each rail, so you will get 24-0-24 V AC and about 34V DC, which should be fine.
you dont need fans as long as your heat sink is large enough. i would say just try it. if it gets too hot, the lm3886s will shut down. using them without any cooling will surely destroy them.

[docz]

Thank you for your reply, it will be used as a practice amp in my band practice space, with the band. I used to have a 60W amp, which worked "OK", but I needed to crank that sucker to the max to get it to a descent volume against my drummer and guitarist. Thought 150W would give me more headroom. But maybe I need to get up to 200 - 300w? can I bridge two of those boards perhaps?

I'm sitting here messing with that transformer. How do I "switch it on" ? just to test it...

DocZ

[tangmonster]

with +-35V dc and 8ohm load that 3 x lm3886 will give no more than 50W.

The reason for paralleling chip amps is to get more power into lower resistance loads.

To get 100W you need to bridge two lm3886 chips into 8ohm load.

That board will delivery 150W but only into 2.7ohms but then power supply must not be higher than +-28V dc

[abraxalito]

Originally Posted by docz

Thought 150W would give me more headroom. But maybe I need to get up to 200 - 300w? can I bridge two of those boards perhaps?

150W will give more headroom, but it will be barely noticeable. You'd need to go all the way up to 600W to get it to sound twice as loud as 60W. 600W is possible with multiple paralleled-bridged chip amps, but not into your 8R unit, you'd need a lower impedance. It would be cheaper to use some kind of soft clipping circuit to get the sound louder. LM3886s do not clip tidily - for this reason, if you don't use a soft clipper/compressor, I would recommend the TDA7293 as a more suitable part. They have the advantage of being able to be paralleled without sharing resistors.

[docz]

Ok, I've checked out that TDA7294, I viewed the suggested circuit in the datasheet and it looks kinda complex, the LM3886 has much simpler suggested circuit. Is it possible to make a simple circuit with two bridged TDA7294?

DocZ

[abraxalito]

Two bridged TDA7294 would probably only give a maximum of 120W into an 8R load. The application can be simplified if you don't need clickless power up/down. Also with a bridged circuit you'll only need one set of diodes/caps/resistors for the mute/shutdown function.

[docz]

Well if it is all down to the ohmage of the speaker cab, I guess I can wire them up for 4 ohm or 2 ohm for that matter... I thought I'd build a 4x10 cab, using four 10" greenbacks 100W 8 ohms.

DocZ

[abraxalito]

In that case, I'd suggest the easiest is one amp per unit. Paralleled amps are far more of a challenge to get working.

[docz]

How much will I get into a 2 ohm load? With just one chip? Either LM3886 or TDA7293?