My tech and I are stumped. Why am I frying completely different cabs?

bovine mind · #1 04-30-2010, 10:46 PM

Rig: Sunn 1200s rack amp, 1200w @ 2ohms, solid state 40hz slider all th way down, slight bump @ 60 and 120hz, compression on, limiter at the front of my effects chain. Sunn 215BH with Eminence Kappa 15LFAs, 600w RMS x2 = 1200w, two 8 ohm speakers @ 4ohm load. Ampeg 810E, 800w rms. Bass is tuned to CGCF.

I managed to fry two EV DL15w's I installed in the cabinet before, and a Yamaha SW118. I just installed the Kappa 15LFAs, and within three minutes I smelled smoke and turned off the amp. I tried a JBL 215 PA cabinet and smelled the same smoke. What's really strange is the 810 doesn't suffer any problems when run either solo or with any of the other cabs.

I tested both cabs with a multimeter and got readings of around 3.5, so each is pulling 4 ohms. My tech doesn't know what's up and neither do I. Why would the head fry any cabinet except for the 810E? I've tried different speakers cables and different outputs on the head. ???

therh · #2 04-30-2010, 10:49 PM

Silly question, are you using a speaker cable or instrument cable between the amp and cab?

OxJohnson · #3 04-30-2010, 10:51 PM

DC leak? Does the 810 have a crossover that has a cap on the input?

Ox.

Dark Horse · #4 04-30-2010, 10:53 PM

Have you checked to make sure that the head isn't putting out DC voltage through the speaker jack ?

EDIT: someone else had the same idea

JimmyM · #5 04-30-2010, 10:53 PM

couldn't be your insane, puke-inducing levels of volume, could it?

bovine mind · #6 04-30-2010, 10:54 PM

Quote:

Originally Posted by Dark Horse

Have you checked to make sure that the head isn't putting out DC voltage through the speaker jack ?

EDIT: someone else had the same idea

No. How do I test this?

bovine mind · #7 04-30-2010, 10:55 PM

Quote:

Originally Posted by JimmyM

couldn't be your insane, puke-inducing levels of volume, could it?

Aw, Jimmy. The amp was turned up to 3. Last two times I smelled smoke I wasn't even using effects or playing particularly rough with the gear. The speakers should be able to handle it.

bovine mind · #8 04-30-2010, 10:55 PM

Quote:

Originally Posted by therh

Silly question, are you using a speaker cable or instrument cable between the amp and cab?

Speaker cables, tried different cables.

Dark Horse · #9 04-30-2010, 10:57 PM

Quote:

Originally Posted by bovine mind

No. How do I test this?

Your tech should have a multimeter / voltmeter and can check - check AC voltage in idle as well.

OxJohnson · #10 04-30-2010, 11:02 PM

Quote:

Originally Posted by Dark Horse

Have you checked to make sure that the head isn't putting out DC voltage through the speaker jack ?

EDIT: someone else had the same idea

Woot! Now I can tell my wife that I, am in fact, not a total moron (or at least there is another one too)!

BTW, you can EASILY tell with an O-scope. Personally, I would see if there is a crossover in the 810, or if there is a cap on the input. This would give me the info I needed. Then I would take it to my brother who is indeed a custom amp builder (and has MY Oscope... that SOB).

Ox.

**B-string** · #11 04-30-2010, 11:02 PM

Get your "tech" to hook up a dummy load (not your 810) and measure DC volts on the dummy load. Sure sounds like excessive DC from the amp head. The 810 due to more drivers can handle dissipating higher level of DC, but it is not good for them either!! You should only see millivolts of DC on the output of the amp.

Sorry late to the party

OxJohnson · #12 04-30-2010, 11:05 PM

Quote:

Originally Posted by JimmyM

couldn't be your insane, puke-inducing levels of volume, could it?

Just because some of use need more that 50W does NOT mean that it is "puke inducing".... you old fart! And yes... I will get off your lawn now.

Ox.

P.S. Jimmy, I love you man.

**B-string** · #13 04-30-2010, 11:08 PM

Quote:

Originally Posted by OxJohnson

Just because some of use need more that 50W does NOT mean that it is "puke inducing".... you old fart! And yes... I will get off your lawn now.

Ox.

P.S. Jimmy, I love you man.

{Your still not getting Jimmy's Bud Light.}

JimmyM · #14 04-30-2010, 11:12 PM

Quote:

Originally Posted by OxJohnson

Just because some of use need more that 50W does NOT mean that it is "puke inducing".... you old fart! And yes... I will get off your lawn now.

Ox.

P.S. Jimmy, I love you man.

i always dreamed my love would come along, and his name would be "ox."

OxJohnson · #15 04-30-2010, 11:18 PM

Quote:

Originally Posted by B-string

{Your still not getting Jimmy's Bud Light.}

1 more off topic post... That cheap-o probably drinks PBR anyways.

(but this did make me laugh like JT seeing Metallica nekked).

Ox.

billfitzmaurice · #16 05-01-2010, 07:25 AM

Quote:

Originally Posted by B-string

Get your "tech" to hook up a dummy load (not your 810) and measure DC volts on the dummy load.

A dummy load is not required with a SS amp. If the 810 has 32 ohm drivers it would be less susceptable to damage from DC.

**B-string** · #17 05-01-2010, 10:34 AM

Quote:

Originally Posted by billfitzmaurice

A dummy load is not required with a SS amp. If the 810 has 32 ohm drivers it would be less susceptable to damage from DC.

Sorry BFM it is necessary to load the output devices if the failure is junction breakdown, unloaded they may be fine!

Need more coffie Bro?

bovine mind · #18 05-01-2010, 12:51 PM

Quote:

Originally Posted by B-string

Get your "tech" to hook up a dummy load (not your 810) and measure DC volts on the dummy load. Sure sounds like excessive DC from the amp head. The 810 due to more drivers can handle dissipating higher level of DC, but it is not good for them either!! You should only see millivolts of DC on the output of the amp.

Sorry late to the party

I actually haven't taken the amp to the tech yet. We diagnosed what we could over the phone, guess he didn't think to ask that. I'll call him today and suggest I bring the amp in for him to try this.

bovine mind · #19 05-01-2010, 01:03 PM

Quote:

Originally Posted by B-string

Get your "tech" to hook up a dummy load (not your 810) and measure DC volts on the dummy load. Sure sounds like excessive DC from the amp head. The 810 due to more drivers can handle dissipating higher level of DC, but it is not good for them either!! You should only see millivolts of DC on the output of the amp.

Sorry late to the party

If it is putting out excessive DC, how would the tech fix that?

seamonkey · #20 05-01-2010, 01:37 PM

Quote:

Originally Posted by B-string

Sorry BFM it is necessary to load the output devices if the failure is junction breakdown, unloaded they may be fine!

Need more coffie Bro?

Yep - I think you need more coffe

I read Bill's response to mean hook it up to the 8x10 and check for DC voltage. (use the 8x10 as a load)