Ditto biasing. If you don't adjust the bias every once in a while on SWR heads, they run unnecessarily hot and lose a lot of oomph. Much cheaper than buying a whole new amp.
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SWR SM 900 Never Ending Problems... Please help me!
- Thread starter Gokhan91
- Start date
I had one of the original SM-900s about 12 years ago and had the same issues as the OP. I had the amp checked out and it actually put out more watts than spec, but it sure didn't sound like it. These amps put out a lot of lows which suck up a lot of the power and don't punch thru the band.
Be sure that you are not using the aural enhancer at all - turn it completely to the left.
I also made my own rack with a hole and fan on the side where the amp exhausts - if I recall correclty the amp sucks air in from the top and exhausts out the side. Don't put it in an SKB or similar rack because there is not sufficient space on the side to let the exhaust air flow out. With the rack I made the amp ran reasonably cool, but it is correct that these amps are made to run hot (the manual even said so).
After several months of frustration with the sound/volume I sold the SM900 and never looked back. Hope you can find a satisfactory solution with yours.
Be sure that you are not using the aural enhancer at all - turn it completely to the left.
I also made my own rack with a hole and fan on the side where the amp exhausts - if I recall correclty the amp sucks air in from the top and exhausts out the side. Don't put it in an SKB or similar rack because there is not sufficient space on the side to let the exhaust air flow out. With the rack I made the amp ran reasonably cool, but it is correct that these amps are made to run hot (the manual even said so).
After several months of frustration with the sound/volume I sold the SM900 and never looked back. Hope you can find a satisfactory solution with yours.
Take all the advice in this thread! Except the bit about selling the amp.
A few things to know about these amps:
-They need good ventilation
-They need to be properly re-biassed once in a while
-They don't like 4 Ohm operation in bridge mode (please check whether you're using bridge mode or true stereo) at all. Once biassed right, stereo should give you 240W ish per side on an older model into 8 ohms.
- The clip LED comes on at about 100W output or even less, way before actual clipping starts.
A few things to know about these amps:
-They need good ventilation
-They need to be properly re-biassed once in a while
-They don't like 4 Ohm operation in bridge mode (please check whether you're using bridge mode or true stereo) at all. Once biassed right, stereo should give you 240W ish per side on an older model into 8 ohms.
- The clip LED comes on at about 100W output or even less, way before actual clipping starts.
I'm not going to add anything new here- just reinforce what other SM-900 owners have said. I had a pre-fender unit in a 2-space rack for several years and loved it.
It gets hot.
I ran mine bridged into two Eden 15's.
EQ was set flat except bass and AE knobs at 1:00.
Awesome tone with my SR5.
Sold my whole rig to lighten up the load-in. I miss it.
It gets hot.
I ran mine bridged into two Eden 15's.
EQ was set flat except bass and AE knobs at 1:00.
Awesome tone with my SR5.
Sold my whole rig to lighten up the load-in. I miss it.
I'll disagree with this, and stick to my earlier statement.
Reason being is that from the first 50% of travel the AE does not get into the mid scoop at all. In fact, with the AE off, I believe the amp then does not really utilize the second triode of the 12AX7.
Keep the AE at mid point and you get both triodes of the tube, but do not yet start getting into mid-scoop land.
Because of the heat and little output I stand behind biasing. Also OP are you using banana plugs? Could one be flipped causing your cabs to be out of phase?
You can bias the amp yourself if you have the tools. It isn't that difficult and can save you a lot of headaches down the line.
I am attaching the biasing instructions that I received from SWR back in the day:
Power amp biasing instructions
if link doesn't work for you, PM me and I'll send you the PDF.
I am attaching the biasing instructions that I received from SWR back in the day:
Power amp biasing instructions
if link doesn't work for you, PM me and I'll send you the PDF.
- May 12, 2007
- 481
- 43
- Disclosures
- Endorsing Artist for Low End bass guitars, DNA Amplification
Here's a silly question -- are you using speaker cables? What gauge?
I know a silly goof in Nashville who tried using guitar cables in a pinch, and the load made the amp hot and a LOT of his signal went away.Had to ask.
