Smoke from Line 6 HD150

[defaced]

The datasheet for the TDA7293 seems to support the parallel configuration stated in the manual:

Modularity (several devices can easily be
connected in parallel
to drive very low
impedances)

A little work with a volt meter would verify if the chips are paralleled or stereo. Since the amp should be able to drive that load properly, my hunch is that the speaker change and the chip blowing are not related. The old correlation does not imply causation axiom.

[ninvertigo]

The rest of the amp is at home so I cant plug in to verify. However I do have the TDA7293 pcb here at work(utilized the engineering lab . It looks like they are wired together, so based on this and the data sheet I would guess that each IC outputs ~75watts and will send 150 out if bridged?

Here is a pic of PCB.
http://i.imgur.com/n3vJwKw.jpg

So I am better off just connecting one input into the cab then correct? I swore I saw somewhere that you should not leave that second output disconnected, but that would only make sense in a tube amp, or atleast not in this setup.

[oc disorder]

From the picture 75 watts per side 8 ohms.


from the patent :-

"It is a still further object of this invention to provide features not typically offered by guitar amplifiers. These features include a "stereo spread" effect which gives the illusion that the speakers are spaced farther apart. The present invention also includes a built-in guitar tuner, and an auxiliary input channel to amplify any audio input (e.g. an accompaniment instrument). Preferably, auxiliary channel has independent equalization and reverberation controls."

http://www.google.co.uk/patents/US5789689

[defaced]

Hmm.... Dumb question. Have you identified which chip blew? Was is the one connected to the output you were using or the one connected to the output you were not using?

I'm at work so I can't troll through the datasheet in depth, but for others who may be interested: http://www.st.com/st-web-ui/static/a...CD00001887.pdf

Looks like pin 14 is the output pin.

[Jazz P Bass]

This sucks not having the schematic.

Pin 14 is the output pin of the TDA ic.
Looking at the front of the chip it is the right most pin on the rear row.
If the amp is mono bridged, the two pin 14's should be connected.
Use a meter to find out.

From the looks of it, it is a stereo amp.
Each TDA has it's own zobel network.

I looked at the Spider 212 (advertised as a stereo amp) & the output ic's (LM3886) each go to there own output jack.

A meter reading will end the suspense.

[The Dude]

Unless advertised wrongly, the literature clearly says it's a stereo amp.

[g1]

I swore I saw somewhere that you should not leave that second output disconnected, but that would only make sense in a tube amp, or atleast not in this setup.

There was a Line6 Spider stereo cab that was stereo 8 ohm when using both inputs, but 4 ohm mono when using only one input. They warned about connecting to the HD150 with only one cable as it would put a 4 ohm load on one side of the amp and possibly damage it. Is that what you were thinking of?
"Be aware that the Spider cabinet jacks will produce an impedance of 4 ohms (either left or right jacks) when a single cable is connected, which will damage the Spider 150 HD."

[mozwell]

I don't have the HD150, but the HD75 may be the same, just with stereo power amps, if not then these are here for psoterity

[ninvertigo]

So I hooked that power pcb up to a volt meter and checked the resistance across the two ICs... It looks like they are bridged. Not only is pin 14(Output) connected between the ICS's there are a number of other pins that are aswell.

G-one yes that I was I was thinking about, but I cant confirm that with any documentation that I can find.

So where does that put us? Not a stereo amp as advertised, two by 75 watts bridged, and a mono 8ohm input cabinet. I am more confused now than when I started.

[ninvertigo]

Okay now I am getting even more confused. Assuming the guy posting in the reply is actually part of line 6 support.

Line 6 - Support

He states that it is indeed stereo and and yes you have to run it in stereo mode or risk damaging the transformer... well wtf on a lot of accounts. My resistance checks on that board shows that the IC's are indeed wired together, and I dont know about the transformer, but leaving one disconnected *could* have been the cause of my amp going up in smoke, or it could have just been happenstance.

I also found this little tid-bit deep in a forum post. http://line6.com/support/page/kb/_/a...st=0#comment_0

Why in the holy hell is it so hard for line 6 to provide schematics and proper documentation???

Ultimately I *love* the sound that this amp modeling head gives with that cabinet and its speaker combo, far more so than the default cabinet that line6 makes specifically for that head. To me its so versatile, and sounds decent, even compared to my Mesa dual rec combo. AND I got that cabinet for 300 dollars, a total steal, cheaper than the speakers by themselves. I want to keep the cabinet.

So is the "Safe" thing to do, simply to wire up my cabinet into 2 x 16ohm input and deal with the reduction in output?

[defaced]

So I hooked that power pcb up to a volt meter and checked the resistance across the two ICs... It looks like they are bridged. Not only is pin 14(Output) connected between the ICS's there are a number of other pins that are aswell.

Careful with resistance measurements on damaged boards. Parts could have failed short giving you an incorrect indication of what is connected on the board.

Instead of resistance checking the chips, you could try following the traces (if you can see them without removing the SMD IC). You also might get an idea of if they're bridged or stereo by following the output header wires to the output jack PCB. If each chip is wired to only one jack, that would indicate they're stereo.

This will also help to tell us which chip failed, the one connected to the jack you were using or the one that was open. Answering that question will tell you how to proceed with the cab.

This makes me wonder. Are the output jacks shorting jacks? If so, the unused chip may have been driving a dead short.

[ninvertigo]

Okay, allow me to correct myself. Output pins are NOT connected. The solder pad that was damaged was repaired by me connecting the tracer next to it to a resistor. That cut tracer had a small flake on it that was shorting. So, I went through with a magnifying glass and verified all of the burnt/melted debris have been removed and that my own soldering fixes were not shorting. All looks well, stereo output 2 x 75 watts.

defaced, the IC that blew was the one that was connected.

[Jazz P Bass]

It very well appears to be a stereo output.
Line 6 specifically states that you Not run either side at 4 ohms.
That setup right there, at 3/4 power output, will kill the TDA ic.

The TDA ic's do go bad, that is a fact.
They can also be severely abused & fail.

So rewire your 16 ohm cab speakers for 2 parallel pairs.

[defaced]

Okay, allow me to correct myself. Output pins are NOT connected. The solder pad that was damaged was repaired by me connecting the tracer next to it to a resistor. That cut tracer had a small flake on it that was shorting. So, I went through with a magnifying glass and verified all of the burnt/melted debris have been removed and that my own soldering fixes were not shorting. All looks well, stereo output 2 x 75 watts.

defaced, the IC that blew was the one that was connected.

Good work.

Seems to me the chip over dissipated and died. I'm surprised it didn't thermal on you and shut down as described in the data sheet. I'd add good thermal compound and careful seating of the chips to the heat sink to the reassembly list.

Since you really like that cab, I think re-wiring it is a reasonable approach. If you fab up a jack plate that fits in the same spot as the original plate, you can make the modifications completely reversible in the event you want to change or sell it.

[g1]

Okay now I am getting even more confused. Assuming the guy posting in the reply is actually part of line 6 support.

Line 6 - Support

He states that it is indeed stereo and and yes you have to run it in stereo mode or risk damaging the transformer...

That page is a disaster. Don't know why the actual company would not straighten that out as it is a "support" forum.
Transformer?
Oddly, it is very similar to an issue from a couple years ago relating to a Fender stereo solid state 75W per side amp (Mustang V). Same issue where someone in tech support claimed if both sides were not loaded, damage could be caused to the "transformer".
After some back and forth with tech support, the long and short of it was that there were no output transformers, no damage could occur, the worst that could happen was it might not sound right. That is all. You won't get both sides of stereo effects. So it may be like listening to a stereo recording, but only hearing the left side, or only the right.
http://music-electronics-forum.com/t23380/