Amp seems to work, but doesn't like 'regular' input

[petemoore]

  but after all that I can't connect an input.
  It's a lm3886 amp.
  I decided to DC decouple the output with the Biggest FCap's I could find [I made two electrolytics into a bipolar], and that seems to preserve the coils in the speakers for testing, and BLAAAAPPPPS the speaker when I touch the input wire.
  However, connecting a guitar to the input is the problem, the tip wire is not grounded, the pot works fine, it's just the signal going through the volume pot to the input jack tip, no shorts to ground on the signal, but signal won't go in the amp...I kinda wanted a volume control and a jack and a DC blocking cap for the input, Imma scared to connect my guitar pickup straight into the 1k input resistor of the amp chip.
  It's like the input is pulled to ground, or the output for that matter [I guess the amp's super quiet, messing with the input stops all noise].
  I have the jack and input volume connected to ground [sleeve, outside lug] other outside lug to input jack tip, wiper to input...hanging there not touching anything else..
  Sorry for the stupid post, I've been working on this thing like it's my first fuzz box yesterday and today.
  Good news was the chips were ordered friday, here first thing this morning [mon].
  Doesn't really make sense, the only thing I can figure is changing is the 100k 'pulldown' [through the potwafer] at the input when I attach the pot and jack.

[petemoore]

  Edit...found some wierd voltage, I'll check that out....
1 18.5
2 
3  17
4  -18.6
5 -18.6
6
7
8 -16.1
9 16.1
10 .1 I can see 3 and 9 arent right...for good starters...
Looks like it should bias like an opamp...
Provides powerful thumbuzz sound when my thumb is connected as source.
  Plug any kinda cabling or anything, boost the input...nothing.
  Even just the input, alone, through a cable makes only a strong clicking sound as though it is biasing and shutting off only. 2 known working monster cables and a couple others tried.
  Everything is connected properly, I eliminated the jack and input volume, touching the ground and tip while strumming the guitar.
  I can't seem to get input to this amp!
  I tried a DC blocking cap
  I tried the volume control as an 'input bias'.
  I also added an input ground, as it seems necessary ?
  Twiddles the little speaker real good and hard, the basic thumbuzz sound amplified.
  Any way that measureing voltage on this chip would help ? I measured the ones I figure like V+ and V_, gnd...etc.
   Just got back.
  I added the DC jack again, and can get signal from my thumb real good, buzzes the speaker pretty loud. as soon as I plug any cables in, just clicks.
  Click when I touch, click when I let go.
  Tried all the other cables and the guitar too, just nothing or clicks.

[petemoore]

  DC blocking cap on the input?
  Buzzes just fine with a 6'' monster cable, same as open input, sleeve to ground tip to input thumb across the other end.
  12' cable reduces that to just a click.
  Guitar just reduces output to nothing, except I got some light gating 'spits' when whammin' on it.
 

[petemoore]

  For some reasons I assumed pin 8 needed to stay open.
  Lazy.
  It is shown as open.
  It isn't muting when open, or only sorta.
  Now I'm gettting a nice tone and guitar through the amp, it sounds to be about 1 watt.
  I was thinking more like 40w, but maybe this needs a preamp, it's not near as loud with Pin 8 [mute] connected to V_, but it sounds guitar.
  How loud does this amp [when wired right] get with a guitar input?
  I'll take some more voltages and see what I can figure out. Could be it's working right, guitar comes through real clear, just not loud at all.
  I think I'll hook up a respectable speaker to the output and a Rocket to the input, see whappens then...

[petemoore]

and then it just shuts off after a bit. Like gate fades to grit 'n nothin'.
  works again later.
  Fingers burnt real good 'n stuff, nice tight stretch going down the R index, thumbs more used to that kinda pinch burn, er didn't get it as bad.
all feewarrikking day long for five now.
  K louder with the Rocket al the way up, I feel like an opamp might be fried, at one point I think pin 3 [output] got 18.V+...
  Anyway, gets loud and really alotta noisy, course the Rockets' all the way up too.
  Bigger freakin' board, healed up fingers and stuff might help.

[petemoore]

  Ok..I think I got this one about 1/2 figured out.
  Sounds jest fine and crankin' a 12''er w/the Rocket, not really noisy anymore, pin 3 decided to do 0vdc on the output, that's better than sitting next to the V+.
  I think connecting the mute resistor to V_ is what did it...
  Sounds pretty nice w/Rocket [9v] "pre-amp", I'll see what it does when I hit it with a hotter input signal.

[Minion]

Well....First I would check that your Heatsink is big enough because if it stuts off after a while then it could be because the Thermal protection (SPIKE) is kicking in.....These chips are Class A so they need a LOT of Heatsinking...

With the LM3886 the Mute pin has to be conected to Ground through a 100uF Capacitor as per the Datasheet example.....

also you will not get full output Plugging your guitar amp directly into the LM3886 Chip because for one thing the output from a Guitar isn"t enough to Drive the LM3886 (check the Input sencitivity specs in the Datasheet) also the ouput impedance of a Guitar in somewere in the 1m ohms to 10m ohms range which is FAR too high for the LM3886 so you will get decreased output and increased noise if you plug directly into the LM3886, It needs a Low impedance input (say under 50k).....

I also use a LM3886 Guitar amp that I designed and Built.... It has 3 different types of Overdrive (Distortion) and Treb/Mid/Bass Tone controlls and Pre and Master Volume and Mute controlls and I am thinking of adding a compressor.....I am useing a 12in Fender Princeton Speaker and it goes very Loud and had a great Clean and Overdriven sound and it is constantly evolveing as I am constantly adding and changeing things.....

I am also in the process of building a LM3886 Bass amp useing Two LM3886 in Bridged/Paralell Config and should put out about 100w to 120w into 8 ohms.....I have over 40,000uF of filtering in the PSU and it is regulated for the Preamp stages (+/-15v).....The preamp for the Bass amp just needs to be built, I have it designed allready and just need to etch and assemble the PCB...This preamp first has a Buffer (Gain x3) and then it has a Low pass Salen/Key filter (Gain 0db filtered at 20hz)and then it goes into a INA217 Mic preamp chip(Gain 60db) and then into a Bandaxal Tone stack (Bass/Mid/Trebble) and then into an Optional Overdrive stage and then an output buffer and then out to the LM3886 Power amp stage..... It should sound good but with most of my projects and designs it will probably need some tweaking.....

Good luck with yer amp.....


Cheers

[petemoore]

Well....First I would check that your Heatsink is big enough because if it stuts off after a while then it could be because the Thermal protection (SPIKE) is kicking in.....These chips are Class A so they need a LOT of Heatsinking...
  12'' x 3'' x 3'', HUGE sink, transistor gets warm.

With the LM3886 the Mute pin has to be conected to Ground through a 100uF Capacitor as per the Datasheet example..... Maybe my capacitor is bad, amp don't work at all without the 39k between 8 and V-...

also you will not get full output Plugging your guitar amp directly into the LM3886 Chip because for one thing the output from a Guitar isn"t enough to Drive the LM3886 (check the Input sencitivity specs in the Datasheet) also the ouput impedance of a Guitar in somewere in the 1m ohms to 10m ohms range which is FAR too high for the LM3886 so you will get decreased output and increased noise if you plug directly into the LM3886, It needs a Low impedance input (say under 50k).....
  Gets louder and pretty good with the Rocket driving it, what I have here to use right now.

I also use a LM3886 Guitar amp that I designed and Built.... It has 3 different types of Overdrive (Distortion) and Treb/Mid/Bass Tone controlls and Pre and Master Volume and Mute controlls and I am thinking of adding a compressor.....I am useing a 12in Fender Princeton Speaker and it goes very Loud and had a great Clean and Overdriven sound and it is constantly evolveing as I am constantly adding and changeing things.....
  Have you tried running a boost or whatever off the power supply between Gnd. and V+ ? My boosters should/wont work as far as I can tell.
  I am also in the process of building a LM3886 Bass amp useing Two LM3886 in Bridged/Paralell Config and should put out about 100w to 120w into 8 ohms.....I have over 40,000uF of filtering in the PSU and it is regulated for the Preamp stages (+/-15v).....The preamp for the Bass amp just needs to be built, I have it designed allready and just need to etch and assemble the PCB...This preamp first has a Buffer (Gain x3) and then it has a Low pass Salen/Key filter (Gain 0db filtered at 20hz)and then it goes into a INA217 Mic preamp chip(Gain 60db) and then into a Bandaxal Tone stack (Bass/Mid/Trebble) and then into an Optional Overdrive stage and then an output buffer and then out to the LM3886 Power amp stage..... It should sound good but with most of my projects and designs it will probably need some tweaking.....
  Separate power supply ?
  Thanks for info minion !

[Minion]

Hi, It is working good with the "Rocket" Probably because it acts as a Buffer so it has a Low output impedance....

Yes, I am useing a Booster in my guitar amp that uses a single supply (+V and G) ....It is basicly a Non-Inverting opamp (OPA134) with a Gain of 34 and a couple clipping Diodes in the Feedback Loop.....If you are haveing problems with useing a single supply curcuits try useing a Virtual Ground (Voltage referance) to create a split supply and connect the -V power pin to Ground and use the Voltage referance for all other grounds (audio ground)...... You create a Voltage Referance by useing a simple Voltage divider with the Ground set to Half Supply Voltage.....also an Output cap should be used with single supply curcuits because of DC Offset.....

The PSU I am useing for my Amps supplies a regulated +/-15v for the Preamp Pluss a Unregulated +/-26v for the LM3886 Chips all from the Same Power supply....It works very well and supplies all the Voltages I need in my amp....I have a PCB designs for it if you want to use it....?


Cheers

[petemoore]

1 24
2
3 17
4 -18.4
5 18.5
6
7
8 1.3
9 2.9
10 .01
  POS...too easy, I don't think the arcing [real easy to touch the pins across the back of the chip together] doesn't help. ! Maybe I'll pass out on the soldering orin or patch another chip in there...OUCH.