Smoke from Line 6 HD150

[ninvertigo]

Hello,

I have a roughly two year old Line 6 Spider IV HD150 amp head. I was running it with stereo outs to a crate 4x12 and never had any problems. Today I purchased a Line 6 DT50 412 4x12 cabinet and hooked it up. The cabinet only has a single 8ohm input, so I left the other output of my amp head disconnected. I played for about 30 mins without any problems at about 15% volume. My wife left the house with our newborn so I decided to crank it up while I had the opportunity to do so. When the master volume was at about 50% I heard some clicking like you would hear from rapidly removing/inserting the instrument cable to the guitar followed by the amp completely shutting off and smoke just ROLLED out of the back. I was very close to the amp when this happened so I almost immediately cut power via the power conditioner give 120v to the head.

After I let the room air out and the head cool I took it apart. Looking at the power output board(that is mounted to the heat sync) the right tda7293 chip is cracked/melted, and pin 14 (PO) has completely melted from the IC. The other TDA7293 chip looks fine, and there are no other markings or burned areas on the PCB or adjacent tracers/components. I ordered two new tda7293 chips to replace both just in case, however I was a little worried. When I supply power to the unit with the entire power output board disconnected it will not power on. I am not an electric engineer(though I have dabbled building IC's and embedded programming etc over the years), but as far as I can tell this unit should still power on without the output board attached. It is possible that the mute circuit acts as a failsafe on the mainboard and prevents it from powering on?

I guess my question is, what are the chances that this severe overheating of that one component could have damaged other components like the mainboard or transformer? And if so, where should I start looking... or should I just wait until I receive the new chips, install them and cross my fingers when I power it back on?

Thanks,
nin

[Jazz P Bass]

As you must know the Line 6 (later models) amps rely very heavily on DSP & microcontroller IC's.
Most of (if not all) of the front panel functions are micro controlled.
So maybe the amp is powering on but a failed 5 volt source is not indicating power on.
You need to carefully go through the power supply.
The high voltage supplies can be checked right at the TDA ic pads.
I am assuming that you checked the main fuse?
http://circuits.datasheetdir.com/271/TDA7293-pinout.jpg

[ninvertigo]

Yes I replaced the fuse. Turns out a diode and a couple of those bigger resistors were bad. I swapped those out and she powers on now and the headphone jack works with audio out. Now I am just waiting on the TDA7293's to arrive. After removing that torched one from the board I am left with a mess though. Pin 14 on that chip spot welded itself and the leg next to it to the damned pcb, so I had to cut tracers and make a couple of jumpers on the bottom side of the board. I just used the leads I clipped off of the diode I replaced. Do you see an issue with this thickness of wire? The pin it goes to is the power output. I figured by the time I add some thermal compound to the back of the chip and mount the heat sink it should hold up to the current.

Does anyone here have experience with the HD150? Ive read a couple of places that you shouldnt leave one of the 8ohm speaker outs disconnected. Is it possible to bridge the two TDA7293's together to gain higher output? I mean the output from one at around 75watts is MORE than enough. I am just worried about it tolerating the load again and smoking more TDA7293's in the future.

Thanks!

[The Dude]

The repairs you did on the PCB traces should be fine and there should be no reason why you can't run one side of the amp unloaded. My question would be why don't you just wire the cabinet stereo so you get the full stereo effect of the head- stereo chorus, stereo reverb, leslie effect, etc.?

[ninvertigo]

I just picked up this cabinet:

Line 6 DT50 412 4x12 Guitar Speaker Cabinet | GuitarCenter

It only has one input on it at 8ohms. Which is why I am not running both outputs.

[Jazz P Bass]

Can you take back the cab & get an 8 ohm stereo cab.

[ninvertigo]

I suppose I could return it. However, I checked that amp head with every cabinet guitar center had on the floor, I just fell in love with this cab and its split use of vintage 30's and G12H90's. I use the spider iv for amp modeling and home studio recording, not so much for the built in effects. Would it be possible to wire that cabinet for stereo without much trouble? Im not entirely sure how the impedance changes of parallel/series would affect the sound if made for 2x8ohm.

[Jazz P Bass]

Making the cabinet into a stereo 8 ohm depends on what speaker impedance is currently in the cab.
If they are all 4 ohm or all 16 ohm you can pull it off.
If they are all 8 ohm you will have to settle for a stereo 16 ohm cabinet. (less total output power)

[The Dude]

Making the cabinet into a stereo 8 ohm depends on what speaker impedance is currently in the cab.
If they are all 4 ohm or all 16 ohm you can pull it off.
If they are all 8 ohm you will have to settle for a stereo 16 ohm cabinet. (less total output power)

Yes, but the OP is only using one side of a stereo amp at this point, so even at 16 ohms, you'd still be ahead of the game.

[The Dude]

I suppose I could return it. However, I checked that amp head with every cabinet guitar center had on the floor, I just fell in love with this cab and its split use of vintage 30's and G12H90's. I use the spider iv for amp modeling and home studio recording, not so much for the built in effects. Would it be possible to wire that cabinet for stereo without much trouble? Im not entirely sure how the impedance changes of parallel/series would affect the sound if made for 2x8ohm.

Some options (thinking "out loud"):

1) Continue to use the rig as you are loading only one side of the amp.
2) Drill the new cabinet, add a jack, and rewire it.
3) Pull the speakers that you like and swap them into the cabinet that is already set up for stereo. Sell the leftovers.

[Jazz P Bass]

Yup.

[ninvertigo]

Okay, so as far as I know all four speakers are 8ohm. Since it has one input at 8ohm impedance I would assume that it has two sets of (two speakers wired in parallel @ 4ohm) wired together in series for the 8ohm input.

So if I follow you, you are saying that I should wire both sets of speakers in series, and run independent inputs for each set of two at 16ohms, ergo I have two inputs on the cab at 16ohms.

Since the impedance is higher on the cab I dont worry about straining the amp head, got it. However, doesn't double in the impedance half the output?

Would this have any significant impact on the tone?

Finally, should I use a thinner gauge wire as well when rewiring?

[The Dude]

Yep, you are correct- 2 inputs on the cabinet each wired to 2 speakers in series. Each side of the amp will be driving a 16 ohm load. This does give you less output power than 8 ohm loads, but not a significant loss in volume (half power does not equal half volume). Also you'll be using the entire amp instead of just half of it, so it'll actually be louder. You don't need to use thinner wire. You can use what's already there. It should not have a significant impact on tone, but that's of course subjective and dependent on your definition of "significant".

[defaced]

What does the manual say about running with only one output connected?

[Jazz P Bass]

Good question.

The Spider IV is labeled as a stereo amp.
I am not too sure about that.

My Peavey Stereo Chorus 400 is a stereo amp.
The two outputs have a different signal on them, depending on the chorus.

The Line 6 manual states that the output jacks are in parallel, with a max rating of 4 ohms.
That is Not stereo, even though the rear panel is printed Left 8 ohms & Right 8 ohms.
So maybe it would be best if the OP simply plugs in the 8 ohm cab that he bought.