noob question..How to connect ground of amplifier???

[spitso]

Hello all

Im working with an IC chip lm4780 which is stereo 60w (per channel). I've followed the schematic provided by the data sheet , just i still cannot make it work. I'm using a bench top power supply testing between 25v-30v and on connection theres a little spark and some oscilation coming from speakers then after 1second it stops and only draws 0.01A.

I beilieve it's my ground. then 2 pins labelled gnd, should i connect them to negative??

thankyou attached is schematic

 

[Nigel Goodwin]

That circuit requires a spilt supply, you can't feed it (as is) from a single rail.

 

[crutschow]

As Nigel stated, (and also the data sheet) you need another power supply. -VEE should be a negative voltage equal to the positive voltage applied to +VCC. The common point of the two power supplies are connected to all points with the GND symbol.

 

[kinarfi]

other than it may not be able to handle 60 watts per speaker, would this work for noob's circuit?
Kinarfi

 

[spitso]

ok i understand. on my bench top power supply theres 3 pins, negative, positive and it has gnd. can't i connect that to the ground of this circuit, theoritically is that what you mean? it still difnt do anything though

 

[Nigel Goodwin]

Is it a split supply? - it's VERY likely that it's just a floating earth point, and you connect it to either negative or positive as you wish, which means it's just a single supply.

 

[hdc090360]

It sounds like your power supply is a single rail isolated supply with the option of providing a ground reference. The ground reference is not what you need. If you had a second power supply you could connect its negative to Vee and its positive to the negative of the Vcc supply and also to the gnd on your amplifier.

 

[spitso]

ok damm.

any ideas on any way around this, using my benchtop power supply, i heard someonewere you can make a ground from a single power supply using some components? diagram would be appreciated.

 

[Nigel Goodwin]

Use two supplies - converting the amplifier to single supply is probably beyond you.

 

[kinarfi]

Using the cheat in this drawing burns lots of power and would be totally unsuitable to you needs. My previous post my work, but I haven't tried it yet, did something similar years ago. Hoping for a comment about it from someone out there.
Kinarfi.

 

[hdc090360]

Using the cheat in this drawing burns lots of power and would be totally unsuitable to you needs. My previous post my work, but I haven't tried it yet, did something similar years ago. Hoping for a comment about it from someone out there.
Kinarfi.

This cheat won't work for a high power amp. It is only useful for something which has equal loads on both the positive and negative rails. Otherwise the Ground will shift with respect to Vcc and Vee causing noise and other problems.

The best solution is to build a dual power supply. This only requires a centre tapped transformer, a bridge rectified and a couple of large filter caps.

 

[crutschow]

Figure 4 in the data sheet shows a single power supply hookup. But that's for the stereo (two amp) connection, not the bridged single speaker connection that the op showed.

 

[spitso]

open the below attachment. Would this do the trick?
what specs would the zeners need to be if running at 25-30v?

 

[Nigel Goodwin]

open the below attachment. Would this do the trick?
what specs would the zeners need to be if running at 25-30v?

No - you're not listening! - USE A REAL SPLIT SUPPLY.

Or rebuild the amplifier to use a single supply - but you may already have killed the chip anyway.

 

[spitso]

wooow chill man

i apreciate the help, its just like most electronic enthusiasts i can't wait to see my next project come to life, and this project ive been most excited by soo far (ive only worked with 6w stereo amps from TVs). So wanted to see if theres a tempoary alternative to test it.

Well...theres my life story. I should be getting a torodial soon. ill keep yous updated.

thanks everyone

 

[audioguru]

but you may already have killed the chip anyway.

And maybe also killed the speakers.

 

[spitso]

hey all

Ive gone andbought a 160va toroidal 2x25v secondaries (240v input). And am hanging to connect everything up.

Has anyone got any diagrams on how to wire one of them up? How will ground be made?

thanks

 

[spitso]

Ok i've wired everything up and connected everything as shown in the schematic.......and BANNNNGGGGGGGGGGGGG!!!!!!!!!!!!!!!! one of the 10uf caps blow up connecting negative to ground then the 1000uf cap opens from the top with THICK white smoke filling up my workroom/brothers bedroom, i disconect power open window close door and run.

Why in the schematic does it have caps running from -ve to ground the wrong polarity? Ground is the reference point and -vee is 30v below that so -vee is more negative then ground????

Anyways i installed another temporay capacitor (only 100uf elec) the right way around, and for a laugh id check if anything would happencif i re-applied power (seeing how much trouble/damage this circuit has caused me). And funny enough another BAANNNNNNNNGGG!!!, but this bang was a good bang...it was the bang of music playing. couldnt believe my eyes....eyes. After everything thats happened it was still working, and the music loudness and quality are excellent.
tough chip,

everyone thank-you for your advice/help it was greatly needed and helped me alot.

cheers Jordan
(anyone still know whats the deal with the capacitor polarity problem though?)

 

[Nigel Goodwin]

Why in the schematic does it have caps running from -ve to ground the wrong polarity?

It doesn't, assuming you're meaning Cs4 and Cs7?, they are clearly shown -ve to -ve, and +ve to chassis/ground.

Ground is the reference point and -vee is 30v below that so -vee is more negative then ground????

That's the whole point of a split supply.

 

[spitso]

i've connected it to the grounding of my toroidal, i though thats what i was mean't to do.

Below i've drawn a ROUGH schematic ive my setup of my toridal to rectifing to connecting it to the circuit.

Could you please look over it and suggest what you think?

thankyou