For those who don't understand the previous post.

Hello DSMNOISEM. What I see is with STK that are apparently made "on demand" for large eastern manufacturers, in quantities of 100K to 1M, depending on their specifications, which, obviously, are hi-fi, stereo, etc.. And what appears in the market must be an "excess production". The problem for an amateur builder like us, we must buy "what is", and this varies widely. In contrast, the LM3876 original, was later replaced by the LM3886, keeping the pinout (well, 1 pin was not used), allowing, if a chip design that is useful for many, for a long time. Look what happened with the TDA1514, used by Marshall and others: it costs a lot now it works with an STK that had happened many times. In contrast, abundant TDA20xx mono and all have the same pinout. The STK is typical of Sansui, Pioneer, etc. and I think someone used them as Yamaha, but if today you get a burn, you have to throw (or, ideally, fit). Saludos desde Buenos Aires.

You can over-voltage but it would be hard to over-current.

I'm using a 160VA 22 + 22 volt toroid to power two and it does fine but that's about as low as you can go for two. The 220 VA would give you all the power you'd need.

I've run a single LM3886 on a 18 + 18 volt 56 VA transformer and it was loud as hell!

RDV

That's about half what you need to get full power out of an LM3886. It will work, but will be woefully underpowered.

Sorry.

RDV

You need a big heatsink for those puppies. They do get hot but they also kick butt! I've got to finish the stereo paralleled version I've got going. I've got everything I need but time and energy.

RDV

Parallel was the choice I made for my LM4780 amps because they can go at 4 ohm loads and up. I think with bridge mode you're limited to an 8 ohm load? I willing to be wrong about this however.

RDV

A simple and flexable solution would be a stereo/dual mono thing where each chip runs a speaker(s) and you have the option of stereo or dual mono. Bridging and paralleling causes some issues like easier overheating that could be avoided by running stereo/dual mono.

HTH

RDV

Quote from: Stompin_Tom 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)?

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

For the PS you're working with:

You'll need either 2 transformers like the one you have, or a center tapped, or a dual secondary transformer. A single un-tapped secondary transformer will not give you two seperate AC voltages no matter how you wire it. You need to do a bit more research on power supplies before you proceed. I'd recommend ESP(Rod Elliott's website). http://sound.westhost.com/index.html

RDV

My newest amp will be in a really cool rack enclosure that a Peavey 2.6C amp was in. It belonged to the church and they donated it to me when it blew up.

RDV

I put the amps in old stereo enclosures that no longer work.

Like this one that I have my stereo LM3886 amp in.


I've got another old CD player that's going to house my stereo LM1875 amp.

I use an old guitar amp enclosure for my LM3886 guitar amp. Like this.


I also build simple cabinets. I think the best way though is to recycle old stuff.

RDV

All the diodes are facing the same direction with the metal sides towards the big caps?

RDV

B is in series though the capitance is added together in parallel.

RDV

Check the polarity of the big caps on the power supply. Something's not right there somewhere. You may be shorting out the chips also if the heatsink(s) is(are) charged and making contact with ground.

RDV

Quote from: trevize on July 17, 2006, 03:02:01 AM
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

...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