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Author Topic: LM3886 Guitar Amp Build Report...  (Read 9049 times)

RDV

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LM3886 Guitar Amp Build Report...
« on: July 16, 2006, 08:10:06 PM »
...again.

About a year or so ago I ordered a chip from National Semiconductor and built my 1st chipamp to use as a practice guitar amp. I followed the schem from the datasheet and guessed at a PS from reading at Rod Elliott's website. I built all this on perf but made a bunch of rookie mistakes cause I was too cheap to buy one of Brian's kit's or boards. A series of calamities culminated in the utter destruction of this 1st amp when the charged heatsink made contact with ground resulting in a very firey smokey end to that 1st chip. I had made the mistake of buying the uninsulated version and then didn't follow good advice to insulate it myself.

So now, I acquired a PCB set from Joe and set about doing this right. I even used the recommended polypropylene caps this time. It sounds really good and doesn't even get warm so far whereas the old one stayed hot due to oscillation caused by my horrible perf layout. I'll try to get some pictures up within the next few days.

The preamp I used was already there and is well documented. It may not be for everyone but I like it a lot.


RDV

joecool85

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Re: LM3886 Guitar Amp Build Report...
« Reply #1 on: July 16, 2006, 08:13:59 PM »
Thats great you are getting this thing going RDV!  I can't wait to see some pics of it all together.
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trevize

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Re: LM3886 Guitar Amp Build Report...
« Reply #2 on: July 17, 2006, 03:02:01 AM »
do you have samples of this amp with clean settings? I saw the diodes in the end, probably ther limit pot makes an emulation of tube compression, so you can have crunch sounds too, right?

How does this preamp takes pedals?

I'm really interested in how this preamp work altough i would probably change the tone stack (never been familiar with the vox one i always end with bass and treble on 10, i suppose i need mid controls).


RDV

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Re: LM3886 Guitar Amp Build Report...
« Reply #3 on: July 18, 2006, 12:02:43 PM »
do you have samples of this amp with clean settings?

Yes. http://fatboy.ssguitar.com/index.php?dir=Samples/Chipamp_Samples/&file=Bminor.mp3

 I saw the diodes in the end, probably ther limit pot makes an emulation of tube compression, so you can have crunch sounds too, right?

It gets a little crunchy but mostly it just keeps the signal limited so as to not overload the chip.

How does this preamp takes pedals?

Very well IMO. Here's some samples:
Uglyface> http://fatboy.ssguitar.com/Samples/Chipamp_Samples/Uglyvox.mp3

Transistor Obsidian> http://fatboy.ssguitar.com/Samples/Chipamp_Samples/MRB%20Obsidian.mp3

PT-80 Delay & BMP> http://fatboy.ssguitar.com/Samples/pt80-3.mp3

I'm really interested in how this preamp work altough i would probably change the tone stack (never been familiar with the vox one i always end with bass and treble on 10, i suppose i need mid controls).

If you don't use the tonestack, you won't get the MRB which is at the heart of the tone. It stands for MidRange Booster. It requires a wah-wah inductor.

HTH

RDV

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Re: LM3886 Guitar Amp Build Report...
« Reply #4 on: July 19, 2006, 11:07:13 AM »
very nice clips! The clean sound is good and it works great with pedals, i do like the Obsidian clip!

Thank you RDV!

Stompin_Tom

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Re: LM3886 Guitar Amp Build Report...
« Reply #5 on: August 17, 2006, 02:42:07 PM »
So, here's a noob question... RDV's preamp requires 15v... How do you power that from your poweramp transformer?... or do you need to have another transformer for that (or a custom job with more secondaries)?
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RDV

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Re: LM3886 Guitar Amp Build Report...
« Reply #6 on: August 17, 2006, 03:01:44 PM »
So, here's a noob question... RDV's preamp requires 15v... How do you power that from your poweramp transformer?... or do you need to have another transformer for that (or a custom job with more secondaries)?
I used a transformer that had multiple secondaries that R.G. Keen found for me on eBay. There are a # of ways to do it though. A good place to look is Rod Elliott's website. He shows a way to do it using Zener diodes and resistors. Regulators are another way. I used a seperate transformer at one point when I was trying 9volt circuits.

http://sound.westhost.com/project27.htm
The project above shows how Rod used the zeners to bring 35v +/- to 15v +/-

HTH

RDV

Stompin_Tom

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Re: LM3886 Guitar Amp Build Report...
« Reply #7 on: August 17, 2006, 04:50:41 PM »
ah... so think of it as a wall wart. I mean regulate or whatever you have to do to get the voltage where you need it. Thanks!
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