I think he's referring to the fact that in some amps, the effects loop uses a switching jack that cuts the signal to the power amp if something is plugged into it. The jacks can get dirty and casue a signal loss with nothing plugged in.
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SWR Help
- Thread starter maconbass
- Start date
I used to have a SWR 400s and it was not a loud head at all. I was actually shocked at the lack of volume when I bought it. I've had other SWR heads too. SWR doesn't rate their products very accurately. My 400s certainly sounded more like 220 watts than 500 watts to me.
Mike
Mike
phishaholik said:
There's something wrong with the one you had too then, I've had 2 and they are really loud. Compared to SS Ampeg, SWR is alot closer on Wattage claims.
I agree that it's a loud amp if you set it up right. I usually have the input gain set close to noon with a Jazz, for example, and even then, the clip light rarely comes on.
BTW, the power is RMS and I'd bet that the other factor...the total harmonic distortion...where it's rated is much more realistic than Ampeg's. I had an Ampeg once that gave its rating at 10% THD, which is quite a bit, and is an easy way to raise the reported power.
It could be that a power transistor isn't working right, but an easy check would be to try each side separately in the stereo mode first.
BTW, the power is RMS and I'd bet that the other factor...the total harmonic distortion...where it's rated is much more realistic than Ampeg's. I had an Ampeg once that gave its rating at 10% THD, which is quite a bit, and is an easy way to raise the reported power.
It could be that a power transistor isn't working right, but an easy check would be to try each side separately in the stereo mode first.
SWR's power claims are somewhat accurate. Overall, still not the loudest amp. You shouldn't have those problems running the amp mono unless one of the power amps is not working. Have you checked both amps separately? I would start there and then find another shop
From what I was taught (or learned the hard way on my own) is that in order to get the fullest output from your amp, you need to find its specs and what its output is at a certain ohmage (example 4 ohms). Get 2 cabinets that ate 8 ohms, and hook them up in series or parallel (i forgot, i think serial) to get your 4 ohms and thus maximum out of your bass amp.
I never knew that and wondered why my 400 watt amp wasn't loud enough for practice with Marshall half stacks. I found out that since i only was using a 4x10 cabinet that i was only using about 220 max out of the 400 and in order to max my amp, i would have to hook up another cabinet to it (with the proper specs in mind)
I would say that something happened like it got dropped or something got adjusted when you didnt know. Bad tubes often make the sound all quiet and stuff liek that too...
I use an SWR and would love to know what the deal is with their stuff in case it happens to my workingpro 700
I never knew that and wondered why my 400 watt amp wasn't loud enough for practice with Marshall half stacks. I found out that since i only was using a 4x10 cabinet that i was only using about 220 max out of the 400 and in order to max my amp, i would have to hook up another cabinet to it (with the proper specs in mind)
I would say that something happened like it got dropped or something got adjusted when you didnt know. Bad tubes often make the sound all quiet and stuff liek that too...
I use an SWR and would love to know what the deal is with their stuff in case it happens to my workingpro 700
when this is all said and done, i would also write a letter to fender/swr telling them about this whole bad experience since they recommended these knuckleheads for service 
Hey guys. I called SWR today and asked if the SM-400S was 500 watts PEAK or RMS bridged at 4 ohms. The guy said that it was PEAK and if you constantly ran at 500 watts it would blow your speakers! I refused to believe that so I called again and got a different person. I asked the same question except I referred to the SM-500 to avoid confusing him. He also said that it is a PEAK rating. I still refuse to believe that. All these other amps are rated at RMS but not SWR?!?! When I bought this amp it was incredibly loud.
I'm looking through some old Bass Player issues. So far I have found a review of a 750X and SM-900. Also an old advertisement for a Super Redhead. They all state watts RMS. I guess I'll take those with me when I go to pick my amp up.
Are you sure the switch for bridged or stereo is in the correct position? When doing a"Tombolous" abcd test of cabs I didn't find the 400 to be as righteous (not as detailed and seeming to be slow and less efficient through the ags as through goliath jrs IIs and IIIs. But if this was a sudden occurrence then it's a malfunction.
Read that manual as many folks don't get the big sound out of these because they don't get the preamp power amp procedure right. Or they plug an SVT cab on one side and it's not loud enough. of course.
You are using a banana plug when you are bridging then daisy chaining your cabs or stacking the banana plugs coming out of the amp and a cable to each cab? This is the only way to develop your 500 watts at 8/4 ohms.
Read that manual as many folks don't get the big sound out of these because they don't get the preamp power amp procedure right. Or they plug an SVT cab on one side and it's not loud enough. of course.
You are using a banana plug when you are bridging then daisy chaining your cabs or stacking the banana plugs coming out of the amp and a cable to each cab? This is the only way to develop your 500 watts at 8/4 ohms.
vision
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tornadobass said:
+1
the guys from fender aren't the best source of information about the swr gear...
OK. I finally got an e-mail reply from SWR today and it says their power ratings are RMS. Now I have ammunition for these repair guys. Thanks for all of your opinions and suggestions.
ihixulu said:
Yep, that's what I meant.
As for the effects blend control, having it on less than full dry when nothing is plugged in the loop will attenuate the signal going to the power amp and would give the appearance of low power output.
I repair SWR amps and there is one clue as to what is going on that everyone has overlooked!
You said it has blown 2 tweeters! and has low output. if your blowing tweeters for no apparant reason. to me that say's its oscillating at a very high frequency. this is common with SWR amps and i have a modification that fixes a power supply problem. plus several other known problems.
To make a long story short, they way SWR mounted, or i should say, didnt provide a stable mount for a part in the power supply, causes one side of the pre-amp power supply to drop in voltage in relation to the other. this causes the pre-amp to oscillate driving the power amp to full power! and if the amp is oscillating out of the audio band, there is little room left for anything in band, meaning your bass signal, hence the low output.
SWR designed the amp sections to be very hi-fi, they will actually amplify signals twice as high as the human hear can hear, about 40khz!
I repaired a SM-900 with the same problem. and almost all SWR amps use the same power supply filter and regulator board. and in fact, most use the same amp modules, the only differences are the size and voltage of the transformers.
and a word about power ratings. for any amp to be able to deliver its rated power, it needs to have a stable line voltage. for example. lets say we have an amp that is rated for 200 watts at 8 ohms with a line voltage of 120 volts ac. to develop 200 watts at 8 ohms we need power supply voltage of about +/-70 volts dc 140 volts total. if we drop 10 volts at the AC line, then we drop 20 volts total on the DC side. that means we can only develop about 150 watts at 8 ohms!
The bigger the amp you have, the more current it will draw from the AC line, which will most likley cause the AC line voltage to drop, or sag. this is a form of compression if you play loud!
Most of the SWR amps i test, i test at 110volts AC and most wont develop full power unless the line voltage it kept right at 120v.
I would bet your repair shop isnt looking for the amp to oscillate, some will only do it randomly, or when the amp has been running for a while. tell them to check the resistor stack in the pre-amp voltage regulator stage of the power supply board.
If they look at you funny, grab your amp and run.
Zc
You said it has blown 2 tweeters! and has low output. if your blowing tweeters for no apparant reason. to me that say's its oscillating at a very high frequency. this is common with SWR amps and i have a modification that fixes a power supply problem. plus several other known problems.
To make a long story short, they way SWR mounted, or i should say, didnt provide a stable mount for a part in the power supply, causes one side of the pre-amp power supply to drop in voltage in relation to the other. this causes the pre-amp to oscillate driving the power amp to full power! and if the amp is oscillating out of the audio band, there is little room left for anything in band, meaning your bass signal, hence the low output.
SWR designed the amp sections to be very hi-fi, they will actually amplify signals twice as high as the human hear can hear, about 40khz!
I repaired a SM-900 with the same problem. and almost all SWR amps use the same power supply filter and regulator board. and in fact, most use the same amp modules, the only differences are the size and voltage of the transformers.
and a word about power ratings. for any amp to be able to deliver its rated power, it needs to have a stable line voltage. for example. lets say we have an amp that is rated for 200 watts at 8 ohms with a line voltage of 120 volts ac. to develop 200 watts at 8 ohms we need power supply voltage of about +/-70 volts dc 140 volts total. if we drop 10 volts at the AC line, then we drop 20 volts total on the DC side. that means we can only develop about 150 watts at 8 ohms!
The bigger the amp you have, the more current it will draw from the AC line, which will most likley cause the AC line voltage to drop, or sag. this is a form of compression if you play loud!
Most of the SWR amps i test, i test at 110volts AC and most wont develop full power unless the line voltage it kept right at 120v.
I would bet your repair shop isnt looking for the amp to oscillate, some will only do it randomly, or when the amp has been running for a while. tell them to check the resistor stack in the pre-amp voltage regulator stage of the power supply board.
If they look at you funny, grab your amp and run.
Zc
