SWR SM-400 amp issue. Need expert input. FIXED

[BadExample]

Good point, they are getting smaller and smaller while at the same time getting bigger and bigger!

I liked the comment on another thread where someone claimed we pay so much more for class D and get so much less (and he said to just look inside how little is there or he said he did). Of course he forgot to count the SMT components and didn't consider inflation.

 

[Omega Monkey]

I mean, that just means the amp lasted even longer before having issues (which you seem to have fixed on your own for free or cheap). If you want to get really nitpicky, the SVT has design flaws (like weighing 90 pounds, only being 300w, etc...), but people still love them. All the ACC stuff was heavy as sin and you basically got nothing about 2k Hz or so, yet people loved them and many still use them and/or lust after them. $900 over 33 years works out to about $2.25 a month for that amp, less if you consider you could probably sell it tomorrow for $150 (which means you would have paid less than 2 bucks a month for it). That's not bad considering people buy brand new PF-500s for $400 bucks or so and might get a dud which has to go back after 6 months (at least when they were having lots of problems).

A less aggressive hpf is not necessarily a "design flaw" it just means it may work better for some people than others. It's not a flaw, it's just a different choice than many others make. Those kinds of choices are usually what make for the most interesting gear. Gibson went with set necks and Fender went with bolt ons. Gibson went with humbuckers and Fender went with single coil (even though "technically" humbuckers are "better"). At the time those earlier SWR amps were being designed and built, bassists were using rigs with wider and wider ranges (due in part to SWRs own work, Trace, etc...). So you could debate that they took the quest for massive low end too far, but they were offering something that hadn't really been done before much if at all. Honestly, it just sounds like you're looking for something different. But it doesn't mean the amp is bad, it just means it might not be right for you. But somehow whenever the general public (ie not SWR fans) here discuss SWR, they may as well be discussing the groin rash they caught on their tropical vacation. No other brand really seems to get that level of undeserved trash talking. It hasn't been super aggressive in this thread in particular, but that undertone is definitely there.

 

[beans-on-toast]

Unrealistic expectations, combined with increasing amplifier power and lack of good common sense

You design a product to meet the application plus a good engineering safety factor. You exhaustively test it. But you can count on someone using or abusing it in a way which you never could have imagined.

I once had a speaker cabinet with a horn tweeter on public display. It had a small pointy cone deep in the horn. Naw, it didn’t need protecting we all thought. Along comes someone with a little kid. He put his tiny hand in there faster than anyone could anticipate and smashed the thing.

There’s always a way to screw things up.

 

[agedhorse]

How well does -6 db roll off respond to + 6 db of eq?

Nowadays a lot of us have a lot more eq at hand, which of course results in a lot more overextended speakers

Correct, that would require 4X the power at those frequencies, which is the root of the reliability challenge when the power is available and the speaker capacity is not.

 

[Deleted member 165050]

I liked the comment on another thread where someone claimed we pay so much more for class D and get so much less (and he said to just look inside how little is there or he said he did). Of course he forgot to count the SMT components and didn't consider inflation.

That's quite amusing in this age of miniaturisation I just bought a voltage regulator PCB that is actually smaller than my thumbnail...

 

[Al Kraft]

And FWIW I can get more useful tonal adjustments using a 2-band Bandaxall design preamp stage than I can with the dashboard on my SM-400. More doodads and controls don't automatically translate out to more useful settings.

As an SM400S owner I will simply add that truer words were never spoken IME. It was a great head for its time (still own and love mine), but it did tend to work better for people who were engineers and knew how to use all those controls. Other than the the SM400S and TH500 there are very few heads that I've run across that have as steep a learning curve to get them to sound really good - and are as easy to get really poor sound out of.

Depending on the intent, anything from a 2 pole to 4 pole filter, typically with a Butterworth of Chebychev type alignment.

IIRC the Chebychev filters have a steeper roll-off, but inculde a ripple type artifact in the pass band, whereas the Butterworth implementation typically tends to be quite flat in the pass band with a more gradual slope in the roll-off. Are your preferred HPF designs a kind of hybrid of these two or are you able to minimize the ripple impact with some design magic when using the Chebychev? Also, does working in the class D realm offer you some options in this area that you might not have in class AB? Thanks for whatever you can share.

 

[agedhorse]

As an SM400S owner I will simply add that truer words were never spoken IME. It was a great head for its time (still own and love mine), but it did tend to work better for people who were engineers and knew how to use all those controls. Other than the the SM400S and TH500 there are very few heads that I've run across that have as steep a learning curve to get them to sound really good - and are as easy to get really poor sound out of.

IIRC the Chebychev filters have a steeper roll-off, but inculde a ripple type artifact in the pass band, whereas the Butterworth implementation typically tends to be quite flat in the pass band with a more gradual slope in the roll-off. Are your preferred HPF designs a kind of hybrid of these two or are you able to minimize the ripple impact with some design magic when using the Chebychev? Also, does working in the class D realm offer you some options in this area that you might not have in class AB? Thanks for whatever you can share.

I tend to range between the two alignments, which are basically the same filter with slightly different equation coefficients, but usually closer to Butterworth than Chebychev unless I need to get really aggressive.

 

[beans-on-toast]

That's quite amusing in this age of miniaturisation I just bought a voltage regulator PCB that is actually smaller than my thumbnail...

Ya but how big are your thumbs.

 

[beans-on-toast]

Filters are a hot topic in the synth and effect music world. There are many interesting virtual synth plugins that heavily rely on filters to sculpt the sound.

This is an example where ripple in a filter can be good. Sometimes a filter like the Chebychev that has more ripple can add life to a sound, making a signal sound less stale. You have to listen and see what works best for any application.

An interesting side note, Chebychev attributed his music teacher for instilling in him exactness and analysis. The complexity of music has a lot in common with mathematics.

 

[40Hz]

So you could debate that they took the quest for massive low end too far, but they were offering something that hadn't really been done before much if at all. Honestly, it just sounds like you're looking for something different. But it doesn't mean the amp is bad, it just means it might not be right for you.

At the end of the end of the day a design flaw is a design flaw. Good intentions don't have any bearing on the correctness (in the engineering sense) of a design. And with the SM-400 their design produced an amp that ran very hot and produced a junked up sound. I don't know anybody who would find that the ideal amp for them. And in the case of this amp, adding a HPF - or designing it for less low frequency response to begin with - is what was needed. Saying SWR was trying to do something different and push the envelope doesn't change that. Some of the worst engineering disasters in history are the result of nothing more than legitimate mistakes that were made with the best of intentions. But that didn't change the outcome. Or eliminate the body count.

Nobody here is making any sort of personal attack on the company or its founders. (Just for the record, the industry reputations of the founders was a major factor in my decision to buy an SWR amp in the first place.) This discussion and its tangents has focused on the technical merits of this particular SWR model. I really think the only person here who is taking any of this as some sort of personal attack on SWR (in this thread at least) might be you right now.

 

[Al Kraft]

You engineers; no sense of humor
OK so you can't run a flashlight with it but it's a trouble maker

While the SM400 output isn't quite DC enough to run a flashlight, it's thermal management approach is such that it will keep a cup of coffee placed on top of it warm.

 

[Omega Monkey]

And with the SM-400 their design produced an amp that ran very hot and produced a junked up sound.

So "junked up" you've only been using it for 33 years. Ok, so you added a $150 or so outboard hpf at some point, and you happen to prefer a different preamp (and no you don't have to be an "engineer" to understand a semi-para EQ, you have frequency, and you have gain, x4, it's not exactly rocket surgery), but for many people, that tube preamp with extensive EQ is great. Honestly, I've never had any issues with my Bass 350 OTHER than that an extra band or 2 of semi-parametric mids would be nice so I don't have to choose "either/or" (although the aural enhancer also helps with that). I haven't used it lately because it suffered some physical trauma and needs a minor repair (ie nothing to do with the design), and I've been missing it, even in the presence of KILLER amps from Genz and (recent) Trace (and a Hartke I had for a bit as well). A nice passive bass with the gain cranked up a bit through an old school 15 is magical with that amp. Very good for early Yes/Rush kind of stuff (my aluminum neck Kramer is also medium scale so has a bit of Ric vibe to it). But then you run it through a Goliath and it can sound very clean and "studio" sounding a la Steely Dan type stuff. I mean, you know you don't have twirl ALL the knobs and sliders, right? You could pick 1 or 2 and leave the others "flat". And if you get lost, just zero everything out and start again from scratch. The biggest difference between the SWR and the Genz and Trace is the para/graphic distinction. The Genz 750 is 5 bands of tone knobs at set frequencies. And that's pretty flexible, but sometimes you want to just nudge one of those bands up or down a bit to work with a particular bass or cab or effect, and you can't. The Trace is a 12 band graphic, but it's "optimized" for bass, rather than being evenly spaced, and sometimes that can leave gaps where it can be tricky to cut or boost in just the right place. Both of those amps are capable of amazing sounds, and I'll probably never get rid of either, but they do tend to require more finessing to get what I want. The SWR is much more "set it and forget it", because you just sweep that frequency knob until you find exactly what you want, and the Q of the control (which is fixed) seems to be very musical.

I don't know, maybe the 4 semi-para plus h/l shelving is not something some people take to naturally, but it seems to be to be a damn near perfect combination of flexibility and simplicity. Not too different than what's on my Genz, except one extra band and you get to choose the 4 middle ones. If you use your ears, I don't understand how that could be that hard. If you go through them systematically, you'll figure out what sounds good or doesn't relatively quickly. With controls like that, I just set the cut all the way down and then sweep the frequency until it sounds best, and then bring the level to where that sounds best (ie isn't too extreme). With 6 controls, you may have to do 2 or 3 passes through (like tuning a guitar with a floating bridge, by the time you get to your high E, the low E is flat because you've put more tension on the bridge and pulled it slightly closer to the nut). But again, you have the control to do what you need, or not.

And to get back to the minimal onboard hpf for a second, ok, maybe that's a design that's somewhat more suited to someone that's pretty aware of what's going on with their sound, and knows how to keep things under control. But those people are out there and I'm one of them. I was using my Bass 350 with just a single 400w EV 15 in a vintage ported cab for a long time with nary a problem. That cab is still like brand new (the driver was NOS in around 2010 or so, probably manufactured 15-25 years before that) and sounds awesome. I'm looking forward to eventually trying the SWR head with my Genz 410 XB (acquired when the SWR was non-functioning), which is a much deeper voiced cab, especially now that I basically play 5 and 6 string almost exclusively. The less restricted low end of the SWR, at the roughly 250w it will put out at 8 ohms, with the lower tuned/bigger Genz cab (rated at 500w), with a stout 5 or 6 string bass should be pretty awesome, knowing what I know about that amp and that cab.

But saying the more laissez faire hpf is a "design flaw" is kind of like saying a Fender Twin has a "design flaw" because it doesn't sound like a cranked up Mesa Triple Rec (or vice versa). It just has different goals. It comes from a different time when things were moving in a different direction than they are now. And yet, a Twin is still a thing of absolute beauty to behold, even if most guitar players crank them way too much. BUT, if they're on stage with Eric Clapton or something, it's like "yeah, there you go". Bottom line is the SWRs are excellent amps. Whether or not they're for a particular bass player is another matter, which has more to do with the bass player than the amp. I mean, perversely, people talk more glowingly here about peavey than swr, which makes no sense. I've never played an inspiring peavey bass amp, and most of their stuff sounds horrible. And I'm not sure they ever made anything remotely innovative in the bass world. Their stuff has tended to be well built and cheap, but the swr was always well built, and at least for the last 10 years or so has also been pretty cheap (on the used market at least). It's just weird that that double standard exists. Or people RAVE about Phil Jones cabs that cost 2500 bucks and weigh 80 pounds and do about as much as my $175 50 pound single 15. And SWR gets dumped on constantly, it's just really bizarre. Maybe people just need to justify to themselves jumping on the latest bandwagon dujour. I was never a "joiner" so that stuff doesn't really affect me.

 

[40Hz]

So "junked up" you've only been using it for 33 years. Ok, so you added a $150 or so outboard hpf at some point, and you happen to prefer a different preamp (and no you don't have to be an "engineer" to understand a semi-para EQ, you have frequency, and you have gain, x4, it's not exactly rocket surgery), but for many people, that tube preamp with extensive EQ is great. Honestly, I've never had any issues with my Bass 350 OTHER than that an extra band or 2 of semi-parametric mids would be nice so I don't have to choose "either/or" (although the aural enhancer also helps with that). I haven't used it lately because it suffered some physical trauma and needs a minor repair (ie nothing to do with the design), and I've been missing it, even in the presence of KILLER amps from Genz and (recent) Trace (and a Hartke I had for a bit as well). A nice passive bass with the gain cranked up a bit through an old school 15 is magical with that amp. Very good for early Yes/Rush kind of stuff (my aluminum neck Kramer is also medium scale so has a bit of Ric vibe to it). But then you run it through a Goliath and it can sound very clean and "studio" sounding a la Steely Dan type stuff. I mean, you know you don't have twirl ALL the knobs and sliders, right? You could pick 1 or 2 and leave the others "flat". And if you get lost, just zero everything out and start again from scratch. The biggest difference between the SWR and the Genz and Trace is the para/graphic distinction. The Genz 750 is 5 bands of tone knobs at set frequencies. And that's pretty flexible, but sometimes you want to just nudge one of those bands up or down a bit to work with a particular bass or cab or effect, and you can't. The Trace is a 12 band graphic, but it's "optimized" for bass, rather than being evenly spaced, and sometimes that can leave gaps where it can be tricky to cut or boost in just the right place. Both of those amps are capable of amazing sounds, and I'll probably never get rid of either, but they do tend to require more finessing to get what I want. The SWR is much more "set it and forget it", because you just sweep that frequency knob until you find exactly what you want, and the Q of the control (which is fixed) seems to be very musical.

I don't know, maybe the 4 semi-para plus h/l shelving is not something some people take to naturally, but it seems to be to be a damn near perfect combination of flexibility and simplicity. Not too different than what's on my Genz, except one extra band and you get to choose the 4 middle ones. If you use your ears, I don't understand how that could be that hard. If you go through them systematically, you'll figure out what sounds good or doesn't relatively quickly. With controls like that, I just set the cut all the way down and then sweep the frequency until it sounds best, and then bring the level to where that sounds best (ie isn't too extreme). With 6 controls, you may have to do 2 or 3 passes through (like tuning a guitar with a floating bridge, by the time you get to your high E, the low E is flat because you've put more tension on the bridge and pulled it slightly closer to the nut). But again, you have the control to do what you need, or not.

And to get back to the minimal onboard hpf for a second, ok, maybe that's a design that's somewhat more suited to someone that's pretty aware of what's going on with their sound, and knows how to keep things under control. But those people are out there and I'm one of them. I was using my Bass 350 with just a single 400w EV 15 in a vintage ported cab for a long time with nary a problem. That cab is still like brand new (the driver was NOS in around 2010 or so, probably manufactured 15-25 years before that) and sounds awesome. I'm looking forward to eventually trying the SWR head with my Genz 410 XB (acquired when the SWR was non-functioning), which is a much deeper voiced cab, especially now that I basically play 5 and 6 string almost exclusively. The less restricted low end of the SWR, at the roughly 250w it will put out at 8 ohms, with the lower tuned/bigger Genz cab (rated at 500w), with a stout 5 or 6 string bass should be pretty awesome, knowing what I know about that amp and that cab.

But saying the more laissez faire hpf is a "design flaw" is kind of like saying a Fender Twin has a "design flaw" because it doesn't sound like a cranked up Mesa Triple Rec (or vice versa). It just has different goals. It comes from a different time when things were moving in a different direction than they are now. And yet, a Twin is still a thing of absolute beauty to behold, even if most guitar players crank them way too much. BUT, if they're on stage with Eric Clapton or something, it's like "yeah, there you go". Bottom line is the SWRs are excellent amps. Whether or not they're for a particular bass player is another matter, which has more to do with the bass player than the amp. I mean, perversely, people talk more glowingly here about peavey than swr, which makes no sense. I've never played an inspiring peavey bass amp, and most of their stuff sounds horrible. And I'm not sure they ever made anything remotely innovative in the bass world. Their stuff has tended to be well built and cheap, but the swr was always well built, and at least for the last 10 years or so has also been pretty cheap (on the used market at least). It's just weird that that double standard exists. Or people RAVE about Phil Jones cabs that cost 2500 bucks and weigh 80 pounds and do about as much as my $175 50 pound single 15. And SWR gets dumped on constantly, it's just really bizarre. Maybe people just need to justify to themselves jumping on the latest bandwagon dujour. I was never a "joiner" so that stuff doesn't really affect me.

We’re going in circles here. I get you love your SWR gear. That has nothing to do with the inherent problems (well documented and acknowledged by numerous owners btw) of the SM-400 amp. The mechanical issue with the switch in mine had nothing to do with the larger issues surrounding this particular SWR amp. Which is it puts out frequencies that virtually no bass cab in existence that’s designed for live stage use as an instrument cab can reproduce. So you get speaker distortion (sometimes leading to catastrophic failure), and the amp runs extremely hot trying to push a cab to do something it’s incapable of delivering. That’s not just someone’s opinion. That’s the physics of this particular equation. You’re entitled to your own opinion. But you’re not entitled to your own facts.

That’s bad design. The fact it can be made to work with some degree of acceptable performance - but only with a bunch of workarounds - is just making excuses for it. Sorry if that bothers you for some reason I will freely admit I don’t understand. The only time I take the time to criticize something is if I care about it. I’m a big advocate for Gibson basses. But there’s also nobody more critical of Gibson than I am. Sure, a lot of times I think Gibson gets an underserved bad rap. But by the same token, there’s a lot of things Gibson takes heat for that are fully deserved. And much as I like Gibson basses, I flat out refuse to make excuses for them when the criticisms are justified and supported by reality. Therein lies the key difference that separates an admirer (or connoisseur if you prefer) and a fan. I am an SWR owner and user, and a would-be admirer. But I am not SWR’s nor any other brand’s fan. My brain just doesn’t work that way.

I can’t comment anout Phil Jones gear since I never owned or played any. But even so, what Phil Jones users may think (or the company us doing) is irrelevant to this discussion - which is about the SWR SM-400. I notice the other SM-400 owners who chimed in here support my earlier contentions about the product. So I get the distinct feeling I’m not completely delusional about an amp I’ve owned and played longer than some people at TB have even been alive.

So I guess we’re going to have to agree to disagree on some things you’re saying. I have no deep issues with SWR as a company, or anything to say about any other player’s experiences with any other SWR product. My comments apply to my SWR amp, which is the “A” or first version of the SM-400 ca.1985. If you talk to other owners of that particular amp model I think you’ll find we all have much the same opinion.


(Note: the reason I never really cared for my SM-400 that much is because it was designed to be a full range amp - which is something I discovered , but only after I bought it, that I don’t much care for the sound of. I don’t like the sound of most boutique hifi type basses either. I prefer an old-school warm and more organic tone. I just assumed with that extensive equalization section I could dial in anything I wanted. But I was mistaken. And while that hifi baked-in SWR sound worked well for the heavy synth band I was working with at the time - and for which I specifically bought that amp for - it never really fit in that well with most other things I’ve done since. These days I’m mostly just using its power stage with several outboard preamps - and I now like it much more because of that. So it’s not going anywhere anytime soon.)

 

[agedhorse]

Design philosophies evolve. What was once popular can, if done to excess" become more like a fad.

As an example, the aural exciter in the SM-400 was a novel(ish) idea but it was too much of a good thing for many players so it slowly fell out of favor. Had it been about 1/2 as "effective" it might have lived on as a more popular option for a larger number of players. I understand what Steve Rabe was trying to achieve, but the fact that it became the signature SWR sound made it vulnerable to standing out too much in a crowd.

I have designs that I feel were maybe a bit too much as well. For example, the roundness of the low end in the Streamliner is maybe a bit overdone for some players (especially those with large ported cabinets with plenty of low end extension) but at least a little roll down of the bass eq control can easily tame it. Into a sealed or tightly damped 810 though, it's a better match (as intended). If I had the chance to do it over, I might have chosen a couple dB less low end roll-up in the voicing tone stack arrangement. Hindsight is 20-20, so take things for what they are to you.

 

[Omega Monkey]

Oh, it can definitely dial in warm old school tones, you must just not be doing it right, and/or using the wrong bass/cab combo.

Anyway, you pretty much confirmed my point while arguing against it. The amp's design goals and your usage goals differ, which is not the fault of the amp. And plenty of people are using these amps with no problems damaging their cabs, so again, not a "flaw" just a different design goal. You could say it's something for users to watch out for. A high end sports car also has things for users to watch out for. Doesn't mean it's poorly designed, just means it's designed with a specific application in mind that isn't yours. If you just want a car to go down to the store with, MAYBE a Ferrari 575 is not for you. Etc... You would prefer your Ferrari with a couple hundred pounds of cinder blocks in it to tame the performance, but others like and can handle the raw performance as is. Or maybe they like something in between. But if the cinder blocks were glued into the car from the factory, you would only have the one choice.

There's also a big factor of people "hearing with their eyes" around here, so if it's "common knowledge" that "xyz", then people will say "oh yeah, I totally hear *xyz* with this amp" whether or not they actually do or if it's to the point of being a tangible issue. I mean, we still get underpowering threads here like at least once a week. No one ever underpowered a cab in the history of history, yet since it's a "concept" that exists, tons of people are worried about it.

How long did you run your SM400 before you started using a hpf with it? And how many cabs did you damage with it in that time specifically from the lack of a more aggressive hpf? If the first answer is 25-30 years and the 2nd answer is 0 like I'm guessing, you're talking about a theoretical problem and calling it a "design flaw" when in fact the amp has performed it's duties just fine for decades.

 

[Al Kraft]

How long did you run your SM400 before you started using a hpf with it? And how many cabs did you damage with it in that time specifically from the lack of a more aggressive hpf? If the first answer is 25-30 years and the 2nd answer is 0 like I'm guessing, you're talking about a theoretical problem and calling it a "design flaw" when in fact the amp has performed it's duties just fine for decades.

First off, I like and still own my SM400S, so call me a Steve Rabe admirer (slightly short of fan) at least to some extent. That said, I noticed excessive cone movement right away with that head and also felt it seemed to work too hard when I needed higher gig volumes.

I'm an engineer and tend to pay attention to things very closely. As soon as I added the HPF to the equation the speaker cone movement (dead fish flopping imitation) was gone and I could get high volume with reasonable headroom and the fan didn't come on nearly as often.

Could I have used the head without the HPF? Sure! Was it better for me with it? Absolutely! Does that make it a design flaw? No. Would that have been a design choice I would have made? No.

As for the Aural Enhancer, I like the additional gain in the first half of the control, but was never a fan of the effect in the second half. That's simply a matter of taste as agedhorse said and not necessarily a good or bad design decision. Many heads have a bit (or a lot) of a signature tone/voicing/sound, SWR simply tended to be a tad more extreme and I might argue unusual/unique than some.

All that said, I still like my slightly quirky SWR SM400S even though I would have preferred a few things to be different in the design. Truth be told, I'm guessing Steve Rabe might have even done it bit differently if he was designing bass heads today...HPF's would more than likely been in the equation today.

 

[Omega Monkey]

Fair enough, Al.

On my Bass 350, I tended to use the AE at about noon to 1 or 2 o clock. It does seem to fatten things up but after a certain point is probably less effective/desirable. It doesn't seem TOO much different in results than the contour knob on the GK RB series. I prefer both to be turned up at least a little, otherwise the sound can get very midsy (never really understood the accusation that the SWR heads are too scooped, I'm always cutting something in the mids with my 350).

 

[Al Kraft]

On my Bass 350, I tended to use the AE at about noon to 1 or 2 o clock. It does seem to fatten things up but after a certain point is probably less effective/desirable.

This is exactly what I observe as well (beefier gain in the pre-amp circuit) and is totally consistent with (what I believe to be reliable) frequency vs knob position plots for the Aural Enhancer that I have seen.

 

[Thir13teen]

The good news is that I've seen them used and in good shape for only $200 which is quite the steal if it comes to your needing and wanting another.

I just received my SWR SM-400 for $174.99 and it came in a giant SKB case. It was kept in a rack case the entire time so visually - it looks like it's 1-4 yrs old (I got it at Guitar Center). Plus I have a 45 day window to bring it back should I not like it and/or it conks out and quits working. Hard to believe that they retailed for $1299.99 back in the day.

 

[Roxbororob]

I just received my SWR SM-400 for $174.99 and it came in a giant SKB case. It was kept in a rack case the entire time so visually - it looks like it's 1-4 yrs old (I got it at Guitar Center). Plus I have a 45 day window to bring it back should I not like it and/or it conks out and quits working. Hard to believe that they retailed for $1299.99 back in the day.

Wow great deal! Enjoy.