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Advice on setup...blowing amp
- Thread starter Jonesy4fnk
- Start date
Is each 2x10 cabinet 4 ohms?
If so both ran in parallel would be 2 ohms.
This could very likely blow the amp in bridged mode.
When you say that one of the cones may have tapped the magnet, is there any damage/rubbing that might cause a short when the cones are extended to a certain point - like when produce deep lows.
You may want to have a tech double check the impedance with a meter just in in case. It it does not read close to 4ohms, it could be one speaker has a different impedance or the cabinet could be miswired.
A local kid here that opened for us a few weeks ago had a similar problem - he was blowing fuses on his amp after a few songs. He has had the problem for several months and keeps spare fuses as he knows he can't make it through a set.
He had purchased a used 2x15 cabinet that was marked as 4ohms. One could tell that the speakers were different models from the outside of the cabinet. We took the speakers out after the gig and one was a 4 ohm speaker and the other a 8 ohm speaker. His head was only rated for 4 ohms.
The short term fix was to wire the speakers in series - until he can purchase another 8ohm 15.
This cut his volume but at least he is not blowing fuses.
As for the question of frequencies/effects pushing an amp. Subharmonics can use up alot of power quickly in an amp and not sound very loud if the cabinet can not produce the frequencies. I've never seen an amp blown from subharmonic frequencies but I have blown speakers using a subharmonic synthesizer (trying to reproduce frequencies in the 20-30hz range). I have seen an amp light clip but almost no sound output from a speaker when a keyboardist was demonstrating detuning with a pipe organ sound (possibly 20hz range).
You have to monitor the output of the amp on an oscilliscope while the effects are being run through it.
By the way.....another issue with the SVT-4Pro, and also with some other brands of amps, is that they use Mosfets.
When the board is out being repaired, it is very static sensitive. it is fine in the unit, but when out, it is open to damage.
Mosfets, are very tough parts, but can be damaged or killed by static electricity from the tech's grubby little static-laden claws getting on the leads..... I learned this the hard way, and ended up owning a few sets of blown replacement Mosfets that I thought I had sold to the customer.....
It is easy to generate 20,000 volts rubbing your hind end on the typical plastic-covered repair bench stool, which will damage most anything except a tube (hah...another good reason.....but I digress)
Anyhow, if your guy didn't use a static strap when working on it, he probably just damaged the amp with static while trying to fix it. Been there, done it, couldn't afford the T-shirt afterwards.
Even if you put too low a load on it, the 4pro should stand it. Might shut off from overheat, but should not blow.
When the board is out being repaired, it is very static sensitive. it is fine in the unit, but when out, it is open to damage.
Mosfets, are very tough parts, but can be damaged or killed by static electricity from the tech's grubby little static-laden claws getting on the leads..... I learned this the hard way, and ended up owning a few sets of blown replacement Mosfets that I thought I had sold to the customer.....
It is easy to generate 20,000 volts rubbing your hind end on the typical plastic-covered repair bench stool, which will damage most anything except a tube (hah...another good reason.....but I digress)
Anyhow, if your guy didn't use a static strap when working on it, he probably just damaged the amp with static while trying to fix it. Been there, done it, couldn't afford the T-shirt afterwards.
Even if you put too low a load on it, the 4pro should stand it. Might shut off from overheat, but should not blow.
Thats a good point about the MOSFETs. I'll check with him and see what he thinks. I guess I'll find out when SLM gets to check the head out, I'm sending it back today.
The amp was never run at less than 4 ohms per side, and we checked the speakers/impedances too.
As for the input noise, I did notice that in my effect chain, the Lexicon input signal would clip for a second then stop, even with no signal going to it. I didn't hear anything in the speakers. But every few minutes it just flashed a clip then stopped. arrgggg....one more thing to check.
I'll figure it our eventually.
Thanks everyone.
The amp was never run at less than 4 ohms per side, and we checked the speakers/impedances too.
As for the input noise, I did notice that in my effect chain, the Lexicon input signal would clip for a second then stop, even with no signal going to it. I didn't hear anything in the speakers. But every few minutes it just flashed a clip then stopped. arrgggg....one more thing to check.
I'll figure it our eventually.
Thanks everyone.
so I sent the head back to SLM and they checked it out and replaced the entire PCB board. They didn't get into why it could have happened but they fixed it for no charge and so far its been working well. We'll find out on a gig Friday.
Their customer service was excellent I must say.
I'm still not positive what caused the problems but I've had no problems with my backup head running the same setup so I'm thinking it must have been the amp.
Their customer service was excellent I must say.
I'm still not positive what caused the problems but I've had no problems with my backup head running the same setup so I'm thinking it must have been the amp.
