Bridged Mono help. Someone save me!!!

[gitfiddl]

Paid just north of a grand for mine. I was about five years into my corporate career in finance at that point. Maybe making $28K and feeling like I was on top of the world. Those were fun years despite the out of control inflation and skyrocketing housing prices.

Bought my SM-400 (ser # 122 ****) a month and a half ago for $245/shipped after dreaming of one for 30 years. It's a monster bridged into a 4x10.

 

[Jscriv]

Actually, this is what came in the box with an SM-400. I’m the original
owner of mine along with the Goliath Junior II cab I got with it. I just pulled it off the back of the amp and took a picture for the OP to reference.

View attachment 2963420

I have this cable along with the banana to phone with a 1/4 to speakon connected to it. I'm considering taking the cable pictures here and just connecting the speakon to it. Unless I just plug that into one of the 1/4 parallel inputs.

The amp went to a tete last year and was brought up to snuff. My old carvin can had the input fried letting another band use the right at a show. I think they maxed the limiter out and ran full tilt...4ohms into a 400w cabinet. That's 550w. But it never worked after that and I wanted to move to a 410. I haven't used the head since getting it back and figuring that out but I heard it work on my techs cab in his basement. At this point I'm hoping it's a stupid overlook on my part.

 

[gitfiddl]

I have this cable along with the banana to phone with a 1/4 to speakon connected to it. I'm considering taking the cable pictures here and just connecting the speakon to it. Unless I just plug that into one of the 1/4 parallel inputs.

I'd try your existing 1/4"-speakon cable into the L/R 1/4" outputs and make sure that the amp is functioning properly. Make sure the Stereo/Bridge switch is in the Stereo position. MAKE SURE THE AMP IS OFF before connecting/disconnecting any speaker cables and changing the switch. If both sides work, then I would change the cable to banana-speakon and try the amp in bridged mode.

 

[ihixulu]

Be sure your speaker is 8 ohms (I don't think they made a 4 ohm version) because the amp can not drive 4 ohms in bridge mode (and will likely fail, they weren't so robust in this way).

The SM-400 is, in fact, capable of safely driving a 4 ohm load in bridge mode. I've done it many times for hours over the years with various speaker configurations.

From the manual: The power amplifiers in the SM-400 can be used individually to provide full bi-amp capabilities when used with the built-in adjustable electronic crossover or can function as stereo, 200 watt power units. If you need more power, the amps can be bridged for 400 Watts @ 8 ohms or 420 watts @ 4 ohms.

 

[Jscriv]

So I finally got home from work and went up, ran the old banana to 1/4 that came with the amp some 25 years ago to one of the parallel 1/4 inputs. I'm bridged mono. And the cabinet absolutely thumps. I have no idea why the banana/phono to 1/4/speakon gave me no sound. Maybe I'll give it a.try again tonight before I go give it back to GC (that whole contraption was 50 damn dollars)

With that said Is there any reason I need to keep pushing to use these speakon connectors? Or are they just the latest craze? Cuz after this I don't think I wanna see one again

 

[ihixulu]

They are better for higher wattage amps because the surface area of the contacts is greater. And they can't yank out accidentally. I try to use speakons whenever I have the option to. However, I didn't for many years (as well as most if not all people) and it worked fine.

 

[gitfiddl]

So I finally got home from work and went up, ran the old banana to 1/4 that came with the amp some 25 years ago to one of the parallel 1/4 inputs. I'm bridged mono. And the cabinet absolutely thumps. I have no idea why the banana/phono to 1/4/speakon gave me no sound. Maybe I'll give it a.try again tonight before I go give it back to GC (that whole contraption was 50 damn dollars)

With that said Is there any reason I need to keep pushing to use these speakon connectors? Or are they just the latest craze? Cuz after this I don't think I wanna see one again

It's a more secure and safer, both physically and electrically, connection. I've seen more than one amp get smoked because a 1/4" cable got yanked out of an amp or speaker because of the "short" caused by the design of the typical 1/4" jack/plug. I've never been shocked grabbing a speakon connector, but that's always a possibility with a 1/4" plug because the conductors/contacts are exposed.

All of my speakers are now speakon-equipped and I'm working on outfitting my racked amps (including my SWR SM-400) with speakon patchbays in their respective racks.

 

[agedhorse]

So I finally got home from work and went up, ran the old banana to 1/4 that came with the amp some 25 years ago to one of the parallel 1/4 inputs. I'm bridged mono. And the cabinet absolutely thumps. I have no idea why the banana/phono to 1/4/speakon gave me no sound. Maybe I'll give it a.try again tonight before I go give it back to GC (that whole contraption was 50 damn dollars)

With that said Is there any reason I need to keep pushing to use these speakon connectors? Or are they just the latest craze? Cuz after this I don't think I wanna see one again

I'll bet the SpeakOn cable you received is wired 1+/2+ which is a bridge cable ONLY for amps that are SpeakOn out and follow the 1+/2+ convention (some rack mount stereo power amps).

 

[gitfiddl]

I'll bet the SpeakOn cable you received is wired 1+/2+ which is a bridge cable ONLY for amps that are SpeakOn out and follow the 1+/2+ convention (some rack mount stereo power amps).

Would that have given the OP any signal? He said at one point in the thread that he was getting some sound, but very low volume.

 

[S-Bigbottom]

Maybe I'll give it a.try again tonight before I go give it back to GC (that whole contraption was 50 damn dollars)

With that said Is there any reason I need to keep pushing to use these speakon connectors? Or are they just the latest craze? Cuz after this I don't think I wanna see one again

Take that one back and get your $50.00 refunded, then go to the connectors wall in the Live Sound area and get a four pole Neutrik Speakon connector for $6.00. Make sure it is the connector and not the to phone plug adapter, that can be a source of problems later.
Cut the phone plug off the banana cable, strip the wire back and screw it into the Speakon +1 -1 and done. Six dollars.

 

[agedhorse]

The SM-400 is, in fact, capable of safely driving a 4 ohm load in bridge mode. I've done it many times for hours over the years with various speaker configurations.

From the manual: The power amplifiers in the SM-400 can be used individually to provide full bi-amp capabilities when used with the built-in adjustable electronic crossover or can function as stereo, 200 watt power units. If you need more power, the amps can be bridged for 400 Watts @ 8 ohms or 420 watts @ 4 ohms.

Actually, this is kind of, sort of half true... there are several versions of the SM-400, the earlier ones were totally unsuited for 4 ohm bridged operation and were replaced by the "S" version, (some of these had fans, but some did not) which was a little better but still not very suitable, then there was 1993 version that included an on-board cooling fan and this was better still, and the SM-500 (another revision to the 400) was even better suited, and included SpeakOn outputs.

The earlier SM-400 would shut down and suffer a higher than acceptable failure rate when bridged into 4 ohms (or used at 2 ohms per channel), the later ones were better but still not all that reliable under those conditions.

Hindsight makes it pretty clear that some of the design choices made in the earlier versions were not very suitable for 4 ohm bridged operation. They also suffered from frequent output fuse failure (because of the inherent unsuitability at BTL 4 ohms) and if you were to run the calculations, 8 amp fuses (both are in series in BTL mode) = 8**2 x 4 = 250 watts (RMS) which would tend to open when hit hard for more than a couple of seconds, but without these fuses the failure rate would be even higher. These were times when the industry was on a huge learning curve, SWR was no exception.

This might help: Vintage SWR Products

 

[BadExample]

Take that one back and get your $50.00 refunded, then go to the connectors wall in the Live Sound area and get a four pole Neutrik Speakon connector for $6.00. Make sure it is the connector and not the to phone plug adapter, that can be a source of problems later.
Cut the phone plug off the banana cable, strip the wire back and screw it into the Speakon +1 -1 and done. Six dollars.

Get a PZ1 screwdriver or a 1/4" hex PZ1 tip for that screwing.

 

[ihixulu]

Actually, this is kind of, sort of half true... there are several versions of the SM-400, ...

This is kind of, sort of half right...

I've been using an early serial number SM-400 for over a decade now and have used it to drive 4 ohm loads on many occasions, including as a backline for all day rock festivals to drive a fridge. I've seen old SM-400 as reggae backlines in Jamaica driving all sorts of cabs. It was/is a solid head that serves those who like its tone well.

However, it is true that there are issues with the cooling method Rabe chose for the early SWR heads - strictly convection, no forced cooling - but those were usually the result of people sticking them in racks with insufficient airflow. It gets hot as hell, sometimes uncomfortably so, especially at 4 ohms bridged. But that's what it was designed to do.

The 400s added a fan to allow the output to be bumped to 250 per side at 2 ohm stereo, 500 watts at 4 ohm bridged, among other features which had been available as factory mods. It could be considered a transitional/separate model as it was renamed the SM-500 relatively quickly.

 

[agedhorse]

This is kind of, sort of half right...

I've been using an early serial number SM-400 for over a decade now and have used it to drive 4 ohm loads on many occasions, including as a backline for all day rock festivals to drive a fridge. I've seen old SM-400 as reggae backlines in Jamaica driving all sorts of cabs. It was/is a solid head that serves those who like its tone well.

However, it is true that there are issues with the cooling method Rabe chose for the early SWR heads - strictly convection, no forced cooling - but those were usually the result of people sticking them in racks with insufficient airflow. It gets hot as hell, sometimes uncomfortably so, especially at 4 ohms bridged. But that's what it was designed to do.

The 400s added a fan to allow the output to be bumped to 250 per side at 2 ohm stereo, 500 watts at 4 ohm bridged, among other features which had been available as factory mods. It could be considered a transitional/separate model as it was renamed the SM-500 relatively quickly.

The primary reason for the reliability issues was that by the time the SOA was derated for temperature, there was nothing left to spare. At 85 degrees C, the 200 watt power dissipation capability of the output devices falls by 50%, which places each rail pair dangerously close to the 2 ohm (stereo) load line. In theory, everything looks "ok", until it gets hot. The latest revision of the SM-500 (after 2005) added an additional pair of output transistors (1 per rail) to account for this, and also became fully complementary output stage. This amp version is no problem bridged into 4 ohms.

The SM-900, which uses the same or similar (depending on the version) module as the SM-400 can not be bridged into 4 ohms until the 2005 revision which doubled the number of output devices.

The 2005 revisions were all done by Fender to address the legacy issues, the owner's manuals for these products that say "Corona" on them represent different products than those that say Sun Valley. They represented a major improvement in reliability.

Just wanted to be clear, so that folks who own these amps don't unintentionally damage them due to bad, or inaccurate information.

 

[Reedt2000]

So I finally got home from work and went up, ran the old banana to 1/4 that came with the amp some 25 years ago to one of the parallel 1/4 inputs. I'm bridged mono. And the cabinet absolutely thumps. I have no idea why the banana/phono to 1/4/speakon gave me no sound. Maybe I'll give it a.try again tonight before I go give it back to GC (that whole contraption was 50 damn dollars)

With that said Is there any reason I need to keep pushing to use these speakon connectors? Or are they just the latest craze? Cuz after this I don't think I wanna see one again

As others mention the speakons lock in and make good contact, with the 4 conductor wires they can bi-amp a cabinet with a single cable (and the proper amp), and the exterior of the plug is not the ground. All that being said I've run a GK 700rb which is 380 watts and a hartke ha5500 which is 500 watts on 1/4" speaker cables for years with no problems. The only reason I'm not still running those amps is my uber-light markbass combo (I don't miss lugging that heavy gear AT ALL). You can make a cable pretty inexpensively, you can probably open the speakon jack on what you have and move conductors around so it works. In my opinion I don't think it's worth it.

 

[BassmanPaul]

In my mind SpeakOns are not a craze but the answer to a need that’s been obvious for years. That is the poor performance and lack of safety offered by the 1/4” Phone plug.

These were originally designed for telephone switchboards. Their design working conditions were essentially 48V DC at a current of a couple of hundred milliamps. That’s nothing near that that exists in a speaker cable. Add the fact that when the plug is inserted or disconnected the tip and sleeve are momentarily shorted. The end result is a very poor speaker cable connector.

I switched to SpeakOns exclusively for my cables years ago.

 

[BassmanPaul]

I’ll try this again now that my blood sugar is where it should be!

28.28V equates to 100W into an 8Ω load. When we consider the power available from our high power amplifiers, especially when in Bridge, a shock hazard exists from holding the plug in a hand. By the time we get to 1500W the connector has close to the US power grid voltage. IIRC Europe mandated that SpeakOn connectors be installed on the equipment being imported into the area.

 

[gitfiddl]

In my mind SpeakOns are not a craze but the answer to a need that’s been obvious for years. That is the poor performance and lack of safety offered by the 1/4” Phone plug.

These were originally designed for telephone switchboards. Their design working conditions were essentially 48V DC at a current of a couple of hundred milliamps. That’s nothing near that that a exists in a speaker cable. Add the fact that when the plug is inserted or disconnected the tip and sleeve are momentarily shorted. The end result is a very poor speaker cable connector.

I switched to SpeakOns exclusively for my cables years ago.

To clarify, you meant the 1/4" was developed for switchboard use. I can attest to that. In the early 1980's, I ran sound at Terry Parker Baptist here in Jacksonville. The church had been in existence since the late 1950's. The PA had been cobbled together over the years by gentlemen who worked for ATT/BellSouth. Miles of cloth-wrapped two-conductor cables. The 1/4" plugs had the old rounded ball-ends instead of the pointy tips we're used to now. Real Bakelite insulators. Patchbays that were made up of switchboard panels. Somewhere I've still got an operator's headset, complete with microphone.

 

[BassmanPaul]

To clarify, you meant the 1/4" was developed for switchboard use.

I thought that was what I said. LOL

 

[BadExample]

I thought that was what I said. LOL

It’s the accent, Sir Paul, the misunderstood