diagnosing an unhappy amp

[LopezEG]

Hello - So I got this used / hacked up 4x10 cabinet super cheap (it's an Aguilar S410). It had been converted into a sub for a nightclub by wiring some speaker cable directly into the crossover after cutting out all the input jacks. I removed the speaker wire, replaced the missing SpeakOn connector and wired that into the crossover inputs. I now get continuity through the circuit right at 6 Ohms measuring from a SpeakOn cable plugged into the back of the cabinet. The crossover looks untouched, and the tweeter volume pot on it measures like it is working just fine.

So - I also have this amp laying around unused. it's a 'pro audio' style monster of a rack unit, supposedly good to drive as low as a 2 ohm load, rated for 540 watts at 8 Ohms. Specs are here:

Epicenter5202 - 2 Channel Power Amplifier | 2 Ohm Stable

Seismic Audio offers the highest quality PA Power Amplifiers at the lowest cost with the best selection on the web. Get a 2 Channel Power Amplifier and consolidate your amplifier needs. Run your subs, mains, and monitors from one amplifier! Our Epicenter Power Amplifier is a Beast and has plenty...

www.seismicaudiospeakers.com

I figured this amp should be able to run this cabinet without any issues. I've got it hooked up to a Tech21 VTBass DI via the XLR output which according to the instructions is the correct line-level output to directly drive a power amp, and I should adjust the volume with the level knob on the pedal. This is connected to a passive P-bass. On the VTBass Phantom & Ground connect was disabled, XLR -20bB was OFF. Cabinet is wired to the amp via the above-mentioned speakon cable.

This produced output from the cabinet VERY QUIETLY for about 30 seconds, even with the amp channel turned up to around 50-75%, sweeping the VTBass level from 0 up to basically 100%. Guitar was turned up all the way. And then the amp's PROTECT light came on, and wouldn't go off no matter what I did. So I stopped, double checked everything, and couldn't find anything obvious I was doing wrong.

This should work, right? Or is this amp just not suitable for this?

What am I doing wrong here (or if nothing, what should I check to try and diagnose what is up?)

 

[MIMike]

IDK, but did you try the 1/4” out on the VT instead of the XLR?

 

[LopezEG]

I should mention:

This worked fine BEFORE I hooked up the cabinet, in a sense. I did not realize I had the speakon connector tabs inside the cabinet incorrect - the speaker cable I am using has only two of the four connectors hooked up internally and I had the cabinet jack wired to the wrong pair - which meant effectively running this whole thing with the cabinet disconnected from the amp.

In this configuration I was able to get a signal into the amp from the VTBass which registered on the amp's meter like it was playing something loud - just like you would expect - just with silence and I figured I might have a broken cabinet wire or something. Digging into that I realized I just had to connect the crossover to the other set of tabs on the back of the speakon jack.

Then - poof...

And no, I don't have the cabling on hand to connect the 1/4" output on the VT to the amplifier.

 

[agedhorse]

Sounds like you damaged the amp via an incorrect load. At this point, it appears that your bargain mess of a cabinet, incorrectly “fixed”, damaged your bargain basement power amp with ineffective protection.

The connection details are not just important, but critical to prevent damage.

Your options are now pretty limited, the cost of repair of the amp will likely exceed the value of the amp, and there is probably more going on with your cabinet than you realize.

This would be a good time to consult a qualified service tech.

 

[ardgedee]

Hello - So I got this used / hacked up 4x10 cabinet super cheap (it's an Aguilar S410). It had been converted into a sub for a nightclub by wiring some speaker cable directly into the crossover after cutting out all the input jacks. I

I would be surprised if that was the only change. Are the drivers original, and is the wiring between the crossover and drivers original?

 

[eniac]

I'll assume you were using Channel A.

Is it possible you had the Operation Mode switch set to Bridge but the SpeakOn connector was wired for Stereo?

Or (conversely) the Operation Mode switch set to Stereo but the Speakon connector wired for Bridge?

Do you know from personal use that the power amp is in working condition? Was it ever loaned out since the time you last used it?

 

[eniac]

Rear panel:

 

[LopezEG]

I double checked all the settings - it was in stereo (that's what my first mistake was - the cabinet was hooked up internally to +2-2 not +1-1).

I think I need to pull the whole thing apart (the cabinet) and check all the drivers and wiring for shorts next.

And the amp is fine - it reset without issue on a power cycle. And I do know it works. We used it for only a few hours previously - it's practically brand new. It runs a regular audio signal input just fine.

 

[agedhorse]

You MAY have gotten lucky.

Start with the amp in stereo mode, input the signal to the channel A input and take the speaker output from the channel A output. That's NOT a mistake.

Be sure that the wiring is correct inside the speaker, because you created a fault in the wiring. Amps often do not completely protect from faults like this, consider this your "free pass".

Bridge mono wiring requires special wiring at the amp end, but there's more power than the speaker can safely handle in that mode. Also, the amp canNOT drive 2 ohms in bridge mono mode, 4 ohms is the minimum.

 

[1958Bassman]

When a multimeter is used to test resistance, it's going to read lower than you expect- it's reading DC resistance, not impedance. You can only measure impedance with an impedance meter or my measuring the voltage drop across the terminals, then doing some calculations. If you don't like doind calculations or don't know what calc are needed, take comfort in the fact that DC resistance of 6-6.4 Ohms (the latter is a bit more typical) is fine for 8 Ohm speaker(s). If it was much lower, THEN worry.

 

[MVE]

Sounds like you have an unhappy cab.

I wouldn’t plug any amp into it until you are sure its wired correctly.

 

[Mike Caldwell]

Sound like something is shorted in the cabinet, connectors, speaker cable.....all of the above.

Take a Speakon connector off of the cable and see what the speakers do touching a 9 volt battery to leads, they
should all move in the same direction. if they don't move at all or you barely get a slight click something is shorted.

As mentioned check the resistance across the speaker line.
How are the speakers wired?
Post a picture of the crossover connections, the jack plate connections and the Speakon connections.

Cafe beating on your amp, those are not the most heavy duty amps!