lm3886 guitar amp?

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
that is just the standard datasheet implementation for the LM3886....

i built an awesome guitar amp useing a LM3886 that was pretty much the same as what you posted accept i put a preamp with tone controlls before the LM3886 stage and put a couple of overdrive pedal curcuits with bypass switches before the preamp....

so a LM3886 with a good overdrive curcuit in front of it and a good speaker will make a very good sounding amp, mine sounds awsome and is really loud......

Cheers
 
Hey Guys, i am quite happy to find this post and also while its still active.
As i am a few days in Singapore and decided to build something similar for my bass guitar.

Any ideas on a simple pre-amp? i have seen someone mention the jFet fetzer valve from ROG in this link: http://runoffgroove.com/fetzervalve.html
but i am not sure if they meant it as a pre-amp.
- i am a big fan of ROG!!!! and its damn simple looking like the amp is which is great for me because of time and noob constraints.

I know bass amps should rightfully be louder, but i am not going to try to compete with any drummer, maybe only with my neighbors' peace of mind. (and if i do find some friends to jam with i will make sure the drummer plays the congos until i get something better :) .

what i want to know basically is
a: would the above be sufficient as my pre-amp
b: would i need to make any mods for bass
c: anyone know a good place to buy the lm3886 in Singapore
d: what is an 18v bipolar power supply?

Much thanks, Gideon
 
First, it doesn't have input decoupling capacitor, and there's nothing to protect the amp against nasty oscilations coming trought the cables.

Althought it have the inductor + resistor protection, it don't have much protection as it is missing the RC output filter. It use to be 4R7 + 100nF.

input Impedance is determined by the POT, and this is not good, as if the pot start to make noise, the amp can blow.

That's why its a bad implementation.

I've drawn quickly a little schematic, it's missing the power supply bypass caps, and mute function, but you can see what I'm talking about.

An oscilating amp gets hot, sounds fool, and is likely to blow. This is MUCH more safe.

Check out:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=108488

It also works for you, and the board is far better, also the amp is more powerful, as it can handle +/- 40V rails on 8 Ohms.
 

Attachments

  • 3886.png
    3886.png
    19.5 KB · Views: 1,573
thank you nando :) . i will do your mods. i wasn't planing to use a pot for the volume but to solve it somehow from the preamp.

can i ask you about the decoupling cap in the input, would it effect the bass freqs? and also i understand it should be in series with the resistor and not connected to the ground?

i dont know too much about the tda7293 chip, i chose the lm3886 because there seems to be alot of info about it on the web.

one last question, what kind of power supply should i be useing?

thank you very much for your help :)
 
I have a working prototype of an LM3886 based guitar power amp. I did the impedance trick mentioned in this thread to raise it up to about 5 ohms. It is playing through an eminence GB128 12" guitar speaker. With 35V rails, it gets VERY loud... loud enough to rattle the floor and walls upstairs. These things rock for guitar amps!
 
Gideon,
I am using a 30V/30V transformer (I think it's a 300VA, but can't remember right off hand) but I have some things going on in the power supply that aren't typical. DO NOT use a 35/35 or you will have way too much voltage and will either blow the chip up, or it will go into limiting (SPIKE protection).
I would use a 24 or 25V transformer if I were you. It will have plenty of power but will be safer on the chip.
I only have 1 channel running right now with a single LM3886TF chip (isolated plastic case) on a BIG heat sink (think pass labs, haha) for the prototype. It will be a stereo amp when I'm done.
The impedance raising trick works really well... you should try it. I will warn you that I ran into excessive DC offset at the output and had to try a few tricks to get it to settle down.
Also, stay fairly low on the power supply filter capacitor values for the best sound.
 
In My LM3886 guitar amp i used 10,000uF per rail running off of +/-26v rails and +/-15 regulated for the Preamp...i tried it with 4700uF Per rail but I noticed that I didn"t have a very good low end responce.....

I have mine running into a 12in 8 Ohm Fender Gold label speaker and it really kicks *** , i have never gotten the pre past 7 and the amp hasn"t been past 5 and it is plenty loud enough to drown out the drums even at half Volume....It even sounds great as a bass amp.....

In my preamp i have 4 different Gain stages that can be bypassed or added up for a really Insane Overdrive/distortion and it has an active Treble,Bass & Mid EQ section and is actually one of the best SS Guitar amps that I have ever played and I made most of it out of scavenged parts so it was pretty cheap to make if you don"t count the countless hours I spent tweaking the preamp section to get the sound I wanted.....

If done properly these can make great guitar amps, but the secret is to get a really great speaker to get a great sound....


:D
 
nobody special said:
Minion,
I hope you understand that, unless there is photographic evidence, said amp does not really exist. We want pictures! :D
As far as the power supply is concerned, I think it depends on what you are looking for. I was going for a more vintage sound.


Well i do have pics but they are of the amp in it"s beginning stages....this is before I added the Overdrive stages and the wireing was really messy and before I added the fender speaker and I removed the crossover I had in these pics.....

An externally hosted image should be here but it was not working when we last tested it.


The amp looks pretty much the same from the outside accept I put better knobs on it and added a speaker cover...The insides are still pretty messy but there is also a lot more going on in this amp now than in these pics, so the pics really don"t do it justice....

:D
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.