HELP ON MY AMP!

jps · Post by **jps** » Sat Nov 06, 2004 12:21 pm

Just don't run the two power amps into the same speaker!

aceonbass · Post by **aceonbass** » Sat Nov 06, 2004 12:38 pm

I had a friend who's GK bass amp would do this at gigs but never practice. I walked over to his amp one time and put my hand on it and it was quite warm while at gigs it turned out it was quite HOT. Then it hit me...I pulled the speaker cord out and looked at it. It was a GUITAR cord! He didn't realize that there was a difference, and using the proper unshielded speaker cord solved the problem. Barring something as simple as that, you should get it to a repair shop. Running the pre-amp into another power amp or putting a fan on it would be crutching the situation.

timenbacker · Post by **timenbacker** » Sun Nov 07, 2004 4:46 am

I don't see any pre-amp inputs. Only the speakers, effects loop...there's an input that says "To Tuner"...not sure that's it

jps · Post by **jps** » Sun Nov 07, 2004 7:14 am

The effects loop send can be used as a preamp out. It is post EQ so it will affect the tone to the slave amp.

timenbacker · Post by **timenbacker** » Sun Nov 07, 2004 1:20 pm

ah..I see..so you recommend I get another amp and hook them together? do you think this will help?

timenbacker · Post by **timenbacker** » Sun Nov 07, 2004 1:28 pm

but if I did that, where would I hook up my compressor? I currently have that hooked up to my effects loop on my amplifier.

Would it take the pressure off one amp if I got, say I got a 300W amp and hooked them together (current one is 400W). If so, how could I hook up my compressor? (a dbx166)

Again, opinions here on what I should would be helpful.

aceonbass · Post by **aceonbass** » Sun Nov 07, 2004 1:36 pm

Run the "Effect Out" from your SWR 400 into your compressor and then into another power amp. Again, this is only a quick bypass of the SWR's power amp section until it's fixed.

timenbacker · Post by **timenbacker** » Mon Nov 08, 2004 3:57 am

stupid question, Dane...if let's say I added another 400W amp...would I be able to run my current 400W amp at half the power and get the same result? Thereby, putting less pressure on my original amp?

atomic_punk · Post by **atomic_punk** » Mon Nov 08, 2004 7:24 am

Your current amp would be used to shape the tone only, bypassing the amplifier section. The new amp you add will give you all the volume. You could even just use a power amp instead of a bass amp, since the SWR will now be like a pre-amp.

aceonbass · Post by **aceonbass** » Mon Nov 08, 2004 7:32 am

Well..yes. If your problem only occurs at high volume. However, this solution is only a temporary fix. If your SWR 400 actually blows anyway, even at a lower volume, the resulting pure square wave sent to your speakers will blow them out.

jnbass · Post by **jnbass** » Mon Nov 08, 2004 10:30 am

only if the preamp section were clipping.

check to see if the limiter led lights up. if it does the preamp section would be 'clipping' the waveform, thus sending the dreaded squarewave (not good) to the power section.

I echo Dane's observation in that this may be a band-aid approach to an existing pattern. find out what's wrong-then fix it.

there is no such thang as a free lunch...

timenbacker · Post by **timenbacker** » Mon Nov 08, 2004 1:28 pm

well, I just won another amp - a G-K - on Ebay. So I'm gonna have the SWR looked at in the meantime. Can someone email me off-line and give me some very specific instructions for hooking my G-K amp, SWR amp, and compressor together? [email protected]

thanks in advance.

Tim

philco · Post by **philco** » Tue Nov 09, 2004 4:50 pm

Things to consider: 1) A switch or relay that goes intermittent when it heats up. I had this happen on a power amp once. It only happened at moderate to loud levels, that is at high enough current to heat the switch. Appy Caig DeOxit to all switches and contacts and operate them repeatedly with power off. Other cleaners work, but DeOxit is better. I have drilled small holes in sealed power switches and sprayed them full of DeoXit. It almost always gets them working again, unless mechanical breakage or excessive wear is the cause of failure. 2) Power amps get hottest at 1/3 of maximum power output level. That's usually very loud with some clipping. Compressors allow higher average power levels without clipping. At some point, you may have thermal runaway with some solid state output devices, causing thermal protection to kick in, then cooldown to turn-on, then thermal runaway to cut-off again in a repeating cycle. Install more cooling, play at a lower level, or get another amp. A higher end Crown power amp usually guarantees reliability, and you could use your bass amp to drive it at big gigs. While some amps are rated 2 ohm load capable, it's smart to stay 4 ohms or above if you can. Low load impedances heat up output transistors fast. 3) Thermal devices only kick in when they get hot. For sudden failures not heat related, you should have fast blow fuses in your power supply rails or speaker outputs. Speakers can short and take out amps; it's not always amps that take out speakers. Shorting speaker windings can heat up amps, as well as shorting components in the cpeaker cab. Ohm out your speakers WHILE STILL WARM to verify they are the proper impedance and not the cause of current overload on the amp.

Count those output transistors! Don't buy any amp with undersized output sections. A high output power amp should have at least 1 pair for every 100 watts of power output if it's fan cooled. High end power amps run about 1 pair for every 50 watts at the 8 ohms power rating to prevent noisy fans from being necessary. A lot of guitar amp manufacturers will cheap out and use less. I'm talking big transistors here with about 15-20 amps of max current capability before blowing. Your best bet for reliability are top grade power amps by Crown and other quality manufacturers. You can literally arc weld with a properly designed solid state power amp with good protection circuits, and Audio magazine actually did it with a Mark Levinson amp a long time ago. Beware, cheap amps exist in the PA power amp world as well.

rictified · Post by **rictified** » Tue Nov 09, 2004 7:17 pm

I was going to ask you what impedance your speakers were, are you running one 8 ohm cab, two? 4 ohms? etc. I too don't think heads those will work well under 4 ohms and the tip about using good speaker cable is a good one too. Heat kills amps quicker than anything else besides spilled beers and cokes.

atomic_punk · Post by **atomic_punk** » Tue Nov 09, 2004 7:23 pm

Tim, which GK model did you win?
And Bob and Philip make some VERY good points.