LM3886/Vox SS Amp Thread(w/ Samples!)

[RDV]

..Line-6 uses them extencivly....

I wonder how they're getting 75 watts out of a 68 watt chipamp? 

RDV

[R.G.]

I wonder how they're getting 75 watts out of a 68 watt chipamp?

Oh, that's simple. Advertising watts is smaller than real watts.

I wonder if any commercial versions of this exist?

Not in that variation. I did find a wall o' modules at one NAMM. They were a different variation, though, each with a preamp itself.

[RDV]

Yes I know, this thread is probably starting to get old now, but I had to post this.

I decided to drag my little 112 open-back cabinet with a Peavey 8 ohm Black Widow out and see how it sounds with the amp and it sounds real, real good. Huge in fact.

Better still, I turned off the amp and felt the heat sink and it was barely warm at all.
It had been BLAZING a few minutes earlier through one 10"at very low volume.
The little 10"s in the cab I've been using must be VERY inefficient, or even half-blown.

Jeez! All that worrying about the amp, and the problem was the damn speakers.

Guh.

RDV

Edit: I wonder if that's what happened to the amp part of the 210 cab(It was a Peavey Stereo Chorus 210)?

[petemoore]

  The 2x 10's were putting an 8ohm load on the amp?
  Half blown I would think could put some hefty 'spikes' as far as ac resistance on the output,  [especially if continuity is intermittently lost during cone movement] ,
which wouldn't show with DC testing, . Something like that might warm the heat sink  . 

[RDV]

  The 2x 10's were putting an 8ohm load on the amp?
  Half blown I would think could put some hefty 'spikes' as far as ac resistance on the output,  [especially if continuity is intermittently lost during cone movement] ,
which wouldn't show with DC testing, . Something like that might warm the heat sink  . 

In parallel they were 4 ohms, and seemed to check OK. But the amp would run just as hot with only one of em' at 8 ohms.

RDV

[petemoore]

  I finally got back to, and finished debugging and trying this thing out.
  The Vox Preamp with inductor...cool sound...
  Does a good job adding character to the sound.
  A little bit 'wah' tonish, the inductor can be heard, as can the transistors, of which I found I'm enjoying a lower gain Ge for Q1, and a lower gain Si for Q2.
  "Clear Bright' is the standout tone I'm hearing, this is with treble up some/some more.
  It certainly reminds me of the 'Vox Beatle' .. Thomas Organ SS amp I had for a time.
  I can see this as a way to get cleanish highly characterized tone that would effortlessly cut through a stage mix. Careful with the cutting edge though, as it can be quite sharp.
  Dialing back the guitar volume...Big Change in tone, rolls off highs, but not to dullness right away, between say 6 and 10, a pretty radical shift in frequency responses and amount of mid hump resonance can be 'mixed in'...ie higher GVolume levels and you really hear the inductor inducting, lower settings sound more...normal.
  I think it's the perfect place for my 'spare' inductor.
  Kind of turns the guitar, and amp into like a whole nuther horseteam...HB's sounded more like SC's, and tube amp sounded like a 'brightly colored SS...

[RDV]

Yeah Pete, ya have to watch the treble on it or the blood will pour from your ears!

I wanted to ask everyone in general their opinions on aluminum chassis versus steel. There's not a real big price difference. I'm thinking of putting together another amp together and mounting it in a chassis in my little Peavey 210 Chorus cabinet. I'll have a version of the Vox pre in there, but there'll be preamp out/poweramp in jacks also.

The amp I've built so far is in an old(like 20+ years) Dean Markley K-20 combo amp cabinet(w/8" speaker long gone), with the preamp and controls up in the little chassis, and the powersupplys/poweramp in the bottom. The K-20 had been long burned out, though I ordered the TIP-120 and Tip-125 that power the amp today and will be restoring it.

RDV

[didier]

boy,

i would be so happy if i made my own working amp...

good to hear this (simple looking) amp sounds so great!
i'll save the schematics maybe for later use...

keep on rocking 

[RDV]

I just bought these with which I'm going to build a dual mono version. I got a deal. I'll be able to incorporate these into the structure of a head of sorts(as sides with a chip per side). I'm gonna make this one be a slave in stereo or dual mono. It's gonna kick a$$!! It'll be a 'swiss army knife' of amps, being able to carry music or the noise I generate!

RDV

[RDV]

Hi again:

I finally worked out the last bit of hum in my TV/LM3886 amp. I had the mains ground hooked to the CT on the transformer(rather than to the star ground). Duh.

Was reading over at ESP and saw this which told the tale.

Going to start a Dual Mono LM3886 amp very soon(waiting on PCBs). I'm gonna have a loud computer!

RDV

[RDV]

I'm wondering(out loud of course) what values I might tweak in this preamp to reduce the extreme treble I'm getting with me strat. The Les Pauls sound peachy through it, but I'd sort of like to rig up a bright/mellow switch. Perhaps the .0047µF or .033µF caps before the volume pot? If anyone has suggestions I'm all ears!

Thanks

RDV

[RDV]

I just had a strange experience with the LM3886. In "Gainclone" mode(straight into the poweramp) I just played a good 30 minutes of blasting music from Mp3. It is incredible as a hifi stereo amp. It blew away my old Peavey Monitor head(which is supposed to be 130 watts... yeah right!). I know what those guys on the gainclone web-ring are talking about. These amps sound really good. An application for us here on this forum would certainly be as a studio monitor amp.

I'm building as stereo one as soon as a few more parts come in. I'm thinking of making a switchable input between a guitar preamp or line ins for the computer playback.

Uhh... I gotta find some speakers.

RDV

[RDV]

I forgot to say that with prerecorded music(bypassing the TV Preamp/Limiter) this amp doesn't even get hot, barely warm even. With the guitar amp thing going it heats up almost instantly. I wonder if I should cap couple the input of the poweramp section?

RDV

[R.G.]

with prerecorded music(bypassing the TV Preamp/Limiter) this amp doesn't even get hot, barely warm even. With the guitar amp thing going it heats up almost instantly. I wonder if I should cap couple the input of the poweramp section?

It's always a good idea to cap couple if you can to prevent rogue DC from getting in.

I'm not too surprised that it doesn't warm up on prerecorded music. There's a generally accepted rule that prerecorded music has a crest factor (peak power to average power) of about 20db. The peaks are 20db larger than the average level. So if you play it cleanly, the average level barely warms the heatsinks. Not so for guitar by itself, especially with a square wave fuzz going into it. The worst thing you can to to your amp is not to play full-bore sine waves or music through it. The worst thing you can do is to play half-maximum swing square waves. That means that each output device is alternately handling half the power supply voltage and half the full current. That's the peak power dissipation point in the output transistors. Playing louder square waves actually lets them cool off some from there.

... of course, you could have some DC leaking in too...

[RDV]

Big thing. Huge heatsink for guitar amp. Smaller for stereo amp. I'm not sure at this point that these chipamps are too great for guitar. They get so hot.

Still Working.

RDV

[RDV]

Changed to huge heatsink. Still gets hot and shuts down. At a stinking loss. Must've done something wrong somewhere but don't know what in the world it could be. I hope my PCB versions turn out better than this perf one, it just gets worse and worse. Don't get me wrong, it sounds good but heats up and shuts down in 5 to 15 minutes.

Arg.

RDV

[RDV]

DEAD CHIPAMP WALKING. BIG FLASH, LOUD CRACK.

AMP GO BOOM.

RDV

[B Tremblay]

Loud crack, flash! - it's a gas, gas, gas!

Seriously though, I'm sorry to hear that happened.  I've been following your adventures with great interest.

[RDV]

Oh man, just when I thought I had the overheating thing licked the little daughter-board with the mute resistor & cap made some solid contact with one of the rails and ccccrrraaaaaccckk!!!! with the accompanying requisite blue flash(at the chip). I tried another fuse before I figured out the deal. I think the chip's DOA but I'll have to wait till the stores open back up to find out. I sure as hell ain't sticking no tinfoil in there cause I'd have to take it out of my tinfoil hat!

RDV

[RDV]

The chip survived but still gets hot as nuts even with a huge heatsink. I don't get it because when I first built this thing it hardly got hot at all. I just don't know what went wrong. All I can figure at all is when I had lots of hum, it ran cool, but when I established a star ground it got quieter but started getting hot. Perhaps I grounded something that shouldn't have been.

RDV