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Can my cabinet fry my head?

McSalterson

McSalterson

Mar 11, 2023
74
124
#1
Could a wiring issue on a cabinet cause an amp to fry?

I bought a new 8 ohm Markbass 2x10 cab and an Ampeg Venture V3 head at the end of last year. Within a couple of weeks, I started getting a crackling noise. Ampeg replaced the head. The new one worked for about 5 months until it started crackling. When they replaced the 2nd unit, and I bought the specific Speak On cable they recommended (Pro Co S12NN3). It's been less than 2 months and I just started hearing the crackling noise on the 3rd unit in about 10 months. This can't be a coincidence, right?

The V3 is plugged into a Furman power strip and is connected to the 400w 8 ohm MarkBass cab using the recommended cable. I have my bass going through a pedal board before the amp, but even when I've used a different cable going directly to the amp with a different cable, it was having the same issue.

It's making me wonder if there could be defective wiring in the cab itself that is causing the amp to draw too much (or too little?) power from the head, causing the head to fry. Is that a thing? I like my rig, but I'm almost frustrated to the point of selling it all and getting something completely different.
 
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#2
Tested with another cabinet to see if the issue persists? Have you checked the cab (or had it checked) to make sure it's reading 8 ohms at the input jack? More ohms is less of a problem for SS heads than tube ones, and that head goes down to 4 ohms, so it'd need to be a pretty big dip from 8 ohms.

I'm sure the actual amp experts will drop in soon, but that would be where I start checking first. That's about all I can think of since the cab is on the receiving end, and incorrect impedance is all I can think of (other than intermittent connection) that could give you issues on that front. A Markbass cab doing that isn't something I hear often though...
 
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#3
If you have a multi-meter, the first thing you could do is plug a cable into the cab and check the resistance between hot and ground. It won't read exactly 8 ohms, but it'll tell you if it's way out (like if one of the speakers is shorting out). Or might be even easier to just put your ear up to the cab and listen to see if you're getting sound from both speakers, or watch and see if they're both moving in tandem when you hit a note.

I also have had poorly designed cabs damage amps through vibration before. I was getting a tonne of broken solder joints on my SVT 3PRO after buying a now-defunct company's 2x15. Turns out the cab wasn't much more than a pretty box with speakers mounted to it, with no internal bracing whatsoever. The cab was practically shaking the amp to pieces while sitting on top of it and playing at volume. Though i wouldn't expect that from a 2x10 made by a very reputable company.
 
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#5
ahbass2500 said:
Have seen a few failed Ampeg Venture heads on Reddit and there is also a Youtube video about one. Issue could be a defective design for the head.
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I’ve read about defective V3s and RB combos before. It does seem somewhat widespread, but since I’ve gone through 3 of them I was thinking it could be something else. You may be right, though.
 
#6
NKBassman said:
If you have a multi-meter, the first thing you could do is plug a cable into the cab and check the resistance between hot and ground. It won't read exactly 8 ohms, but it'll tell you if it's way out.

I have had poorly designed cabs damage amps through vibration before. I was getting a tonne of broken solder joints on my SVT 3PRO after buying a now-defunct company's 2x15. Turns out the cab wasn't much more than a pretty box with speakers mounted to it, with no internal bracing whatsoever. The cab was practically shaking the amp to pieces while sitting on top of it and playing at volume.
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I’m going to see if I can find my multimeter and I’ll look up exactly how to check it.

The cab is one of those ridiculously light ones (23lbs) and it seems like the V3 is more prone to soldering issues, so maybe they’re not the best match for each other? It’s pretty much a bedroom setup that I mainly play while the family is sleeping, so it is by no means cranked, but the vibration could be the issue.
 
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#11
Your speaker cable is definitely "the good stuff" and my sense is that the problem IME would not likely be that although a bad connector on the head or cab could cause issues. Usually a cab will show a DC resistance (what you measured) a bit lower than than the impedance rating...your reading looks a touch high to me, but measurement instrument accuracy comes into play as well, but to me it seems a little unusual.

As for the head, does it have the crackling problem without anything plugged into the inputs, just powered up, with the volume up while it is plugged into your cab? If so does it vary with the volume? Then disconnect the speaker cable and see if you hear the same noise with headphones plugged in and the cab unplugged. Then try the same things with just an instrument cable plugged in, and then again the cable and your bass. Each step here will will tell you something about where the problem might be.

A couple of quick things to check right away are: where do you have your cell phone when this is happening, are you close to a wireless router/MODEM/or similar transmitting device, and finally, are there any other things on the same outlet and /or circuit (especially nearby) that could be causing ether power line and/or EMI/RFI effects (like an LED light bulb)?

I'm not suggesting it is or isn't the head, but three in a row seems unusual for company like Ampeg and especially with a parent company like Yamaha.
 
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#12
Ok, there are some things that need to get set straight here...

1. The DC resistance of the speaker does not guarantee health, it only quantifies that the low frequency drivers are nominal 16 ohm and wired in parallel.

2. The DCR seems high, but since we don't know what the correct value is, there's not much value... though if it's varying by that much the meter is also reading acoustic noise that's impressed upon the DCR by sound in the environment. Some meters are filtered for this and some aren't. I would expect the DCR to be around 6.5-7 ohms.

3. There are certainly defects in the speaker than can cause such noises, such as an intermittent connection (Knockoff SpeakOns are the prime example), but also tweeter level controls, driver connectors, etc.

4. An open tweeter can also cause intermittent action of the amp's protection circuit. The protection circuit in the V3 is different than in the larger models, on the larger models the power amp will shut down, on this module it may make chirping or squeeking noises.

5. The comments about inherent defects in the amp may be misleading because the internet tends to amplify problems without any follow-up on root cause analysis. The power module that's being used in that model is the industry gold standard for class D modules of that size, and has a long verified history of extremely high reliability. I'm sure that's why Yamaha chose it.

6. Have you ruled out outside influences, things like WiFi over power line devices, LED bulbs with forged EMC certifications, etc?

7. I think more systematic troubleshooting is in order, I really doubt t hat it's the amp (though still a possibility)

[edit for bad typo in #1]
 
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#13
agedhorse said:
I think more systematic troubleshooting is in order, I really doubt t hat it's the amp (though still a possibility)
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Is it possible that the cable might be defective and short or open the circuit under certain conditions? Do you have another cable to try or the ability to borrow another one? The same possibility could exist for the jack on the cab. Also cabling and solder joints in the cab... Lots of variables.
 
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#15
gln1955 said:
OP said he brought it back to the store and it did the same thing there. Should we assume a different cab, cable and bass? If so, that kind of narrows it down to the head, no?
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IF he used a different cabinet, cable and bass, then yes.
 
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#16
dalahorse said:
Is it possible that the cable might be defective and short or open the circuit under certain conditions? Do you have another cable to try or the ability to borrow another one? The same possibility could exist for the jack on the cab. Also cabling and solder joints in the cab... Lots of variables.
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I had a similar problem years ago and to my surprise it was a faulty solder connection in a very high end, top quality manufacturer instrument cable. I actually had totally (and erroneously as it turns out) discounted the fairly new lifetime warranty cable and thought it was an intermittent/faulty bass or amplifier 1/4" jack.

I had the same symptoms the OP is experiencing. In my case it was a classic "assuming" mistake in troubleshooting where I didn't rule simple things out first. There is a reason most all electronic troubleshooting starts with, "Is the unit plugged in and turned on?". The simple and obvious is often too easy to overlook and we jump right onto imagining complicated issues.

I'm not suggesting that the OP made the same mistake I did (that one time only...for the record), but it's always useful to remind ourselves to start with the simple stuff and work from there.
 
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#18
Yes as above, have you eliminated the possibility of an instrument cable causing the issue? I had a new cable that was fine in the amps I tested in the shop in which I purchased it from, but always crackled when using my own amp, and so I thought it was my amp or speaker. Eventually I replaced the cable and never had the issue again.
 
#19
Pep said:
I’m confused with “drivers are nominal 16 ohms and wired in series.” Does resistance reading 7.7 to 9.0 ohms indicate a 16 ohm cab?
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Sorry, there was a bad typo, I meant to type parallel.

2 x 16 ohm drivers wired in parallel will be a nominal 8 ohms, the DCR will typically fall between 6.5 to 7 ohms, maybe as low as 6 ohms.

I think 7.7 to 9 ohms (that's a very wide variation) is not accurate. If it's correct, I would still consider it an 8 ohm nominal cabinet. A 16 ohm cabinet will fall between about 12 and 15 ohms.
 
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