Jad Freer Sisma Mega Thread.

[gtirard]

I hope my lack of written english did not sound unrespectful. I don't feel there's anything "invalid" in your feelings about the amp and I welcome any kind of feedback, there is a good amount of personal taste happening. I just felt to stress the importance of trying the amp in a real setting, a rehearsal could be enough too.

My feedback is based on rehearsal and gig experience, in particular my comment about "slam and heft".

 

[12bass]

I hope my lack of written english did not sound unrespectful. I don't feel there's anything "invalid" in your feelings about the amp and I welcome any kind of feedback, there is a good amount of personal taste happening. I just felt to stress the importance of trying the amp in a real setting, a rehearsal could be enough too.

Some years ago I tried out a Euphonic Audio amp at rehearsal, my first experience with Class D. Spent some time playing with the EQ, but never could get it dialed in the way I liked. Even my fellow band members noticed the difference and didn't think it sounded that great. Guessing it was mostly a voicing issue, rather than the power section.

That said, I've spent quite a bit of time focusing on the sound of various components and pretty much everything affects the sound in some way, including the power amp. I visited the NRC acoustic laboratory in Ottawa in the late 80s, where a number of famous Canadian speakers were tested and refined. My engineer friend told me that they generally considered amplifiers to be essentially transparent, though later on I worked at an audio store and actually compared a variety of amps and noticed differences that were far from subtle. I'd expect that if there are differences to be heard between the Sisma and WD-800 power sections, they might become more apparent at gig volume. It's great to get these sort of comparisons too, as a way to check perceptions and compare with others.

 

[DJ Bebop]

My feedback is based on rehearsal and gig experience, in particular my comment about "slam and heft".

The closest I got to a gigging volume was using my old PA booming out some music and playing against that. The only “big” cabinet I had on hand was an old Peavey 1820 and that was goofy. Not a real test of quality, it was loud. I find the Sisma gets loud and full sounding. I like it, it is toneful and rich. I'm not good with my words.

 

[DJ Bebop]

I'd expect that if there are differences to be heard between the Sisma and WD-800 power sections, they might become more apparent at gig volume.

Are you familiar with the WD 800?
I'm not saying that the Sisma and WD sound exactly the same but there are some similarities and I was surprised that some of heft was in the preamp as I switched the Sisma preamp into the WD power amp.

 

[Boneless]

Just for a data point, the response of the WD power amp is exactly as I intended it to be, which is also based on the Walkabout that it’s inspired by.

Since I have many commercially successful class AB/G/H and class D amps under my belt, I have never been limited by one class or another. I can achieve exactly the same results regardless of class (and have done exactly that).

The perception of “heft” is very much in the preamp and surrounding signal processing IMO and IME. If one “class” of power amp doesn’t have the performance, it’s not because of the class but because of limitations on the designer’s ability.

TBH, I do believe that you *can* do things with a traditional class AB (or G, or H) amp that don't come as easy with a class D amp, also because the most rational way to implement a class D amp is to use a ready-made module. Take the 800RB, for instance. Its power amp has a clear "tone" of sorts, even without using the boost control (which is a simple JFET amplifier). Many people do find that its successors still don't sound the same, even when following the manufacturer's recommendations to dial in that kind of tone, and I believe there is some truth to this. FWIW, I did some tests by recording the signal both from its DI and from the power amp (with an external DI) and there is a clear difference, and it's not only about an EQ of sorts (the boost stage is in series with the preamp and it does have its own filtering). Can this difference be replicated before the power amp? Of course it can. But maybe it isn't worth it?

(Of course, most of the time tonal difference are deliberate. But sometimes it is a deliberate choice not to go through the complications of replicating 1:1 a tone of a different "technology" and just go with something else).

 

[12bass]

Are you familiar with the WD 800?
I'm not saying that the Sisma and WD sound exactly the same but there are some similarities and I was surprised that some of heft was in the preamp as I switched the Sisma preamp into the WD power amp.

Not 100% sure I've played through one (few are ever found in stock here), but I have listened to quite a number of recordings of the WD-800 and have tried the D-800/+ and TT-800. Noticed a bit of recognizable baked in tone that sounded quite nice to my ears, subjectively better than the voicing of the D/TT amps. I would expect that the majority of the voicing differences come from the preamp sections, so I don't find your results that surprising. Might expect some differences between the two once the amp section starts to get pushed near its limits where behavior is more non-linear.

As I said, I like these sorts of comparisons, swapping pre/power amps and listening to the similarities and differences. Another interesting one is when I had an SWR pre/power amp rig for a few days, with the Grand Prix preamp; it sounded surprisingly thin/scooped to my ears and it took me a while to dial the "heft" in where I liked it. I generally prefer to have a solid fundamental with fairly open upper harmonics... unless running distorted. The DP-3X has been a whole other tone warping exercise and is anything but clean and flat, but it works and sounds pretty darn cool. Different tools for different tones....

 

[Jazzdogg]

While a rehearsal or a gig is best, it isn't necessary to see if an amp has potential. A lot of amp decisions are made on less, your amp should be ready to compete on less than a full-blown gig or even a rehearsal. Again a lot of purchases and continued use are made with less, sad but true.

View attachment 5468054

Personal taste is what it's all about, always, can't change that!

Heft, slam. There, I said the words!

Which WD800 settings bring the heft and slam, DJ? Can the two heads be tweaked to sound comparable in the heft and slam department?

 

[DJ Bebop]

Which WD800 settings bring the heft and slam, DJ? Can the two heads be tweaked to sound comparable in the heft and slam department?

I don't know anymore
I don't even know what heft and slam mean.

Maybe HPF off or completely counter clockwise. Maybe a little boost in the Bass or a little dip in the passive mids. Damping on low, or on high. Master volume up to a gig volume, I don't know.

 

[DJ Bebop]

TBH, I do believe that you *can* do things with a traditional class AB (or G, or H) amp that don't come as easy with a class D amp, also because the most rational way to implement a class D amp is to use a ready-made module. Take the 800RB, for instance. Its power amp has a clear "tone" of sorts, even without using the boost control (which is a simple JFET amplifier). Many people do find that its successors still don't sound the same, even when following the manufacturer's recommendations to dial in that kind of tone, and I believe there is some truth to this. FWIW, I did some tests by recording the signal both from its DI and from the power amp (with an external DI) and there is a clear difference, and it's not only about an EQ of sorts (the boost stage is in series with the preamp and it does have its own filtering). Can this difference be replicated before the power amp? Of course it can. But maybe it isn't worth it?

(Of course, most of the time tonal difference are deliberate. But sometimes it is a deliberate choice not to go through the complications of replicating 1:1 a tone of a different "technology" and just go with something else).

I think to my ear, in fact, that is what has happened to the WD 800 with its class D power section. There are some things that have been done around and maybe in the class D power section to give it a sound like the Walkabout amp it was reimagining. Part of that gives the class d amp a power tube response and feel and with some dynamic processing that also adds a power tube-type breakup when pushed. Not the type of thing typical of a class D amp.

The preamp voicing was tailored to sound kinda like a Walkabout, not a Sisma so there is that difference but they do share the same or similar tone stack, the Braxandall tone EQ which is common in hi-fi equipment and some bass amps like the B-15. So to my ear again, the WD performs differently than all the class D amps I've played through. Realizing I don't have an extensive experience with a lot of different amps over the years others, like yourself have had!

 

[Boneless]

I think to my ear, in fact, that is what has happened to the WD 800 with its class D power section. There are some things that have been done around and maybe in the class D power section to give it a sound like the Walkabout amp it was reimagining. Part of that gives the class d amp a power tube response and feel and with some dynamic processing that also adds a power tube-type breakup when pushed. Not the type of thing typical of a class D amp.

The preamp voicing was tailored to sound kinda like a Walkabout, not a Sisma so there is that difference but they do share the same or similar tone stack, the Braxandall tone EQ which is common in hi-fi equipment and some bass amps like the B-15. So to my ear again, the WD performs differently than all the class D amps I've played through. Realizing I don't have an extensive experience with a lot of different amps over the years others, like yourself have had!

You can, if you want, implement a soft clipper/saturation circuit in an intermediate stage between the preamp and the power amp. Or at the end of the preamp. To tell the truth, these tube emulation circuits not on the power amp will never really "behave" like a tube amp into an output transformer etc. because there are a few things that give a tube amp its sound (for instance, its high output impedance, the interaction between cabinet and amp, the presence of the output transformer, etc.) that, placed before a traditional "clean" power amp, will get you sort of there but not quite. But this is more significant on guitar than bass, anyway. And you could also mimic (at least part of) this with a filter bank and a "speaker calibration" feature, if you really want. (I wonder if this is what the calibration function on the new Boss amps does).

 

[DJ Bebop]

You can, if you want, implement a soft clipper/saturation circuit in an intermediate stage between the preamp and the power amp. Or at the end of the preamp. To tell the truth, these tube emulation circuits not on the power amp will never really "behave" like a tube amp into an output transformer etc. because there are a few things that give a tube amp its sound (for instance, its high output impedance, the interaction between cabinet and amp, the presence of the output transformer, etc.) that, placed before a traditional "clean" power amp, will get you sort of there but not quite. But this is more significant on guitar than bass, anyway. And you could also mimic this with a filter bank and a "speaker calibration" feature, if you really want. (I wonder if this is what the calibration function on the new Boss amps does).

The WD also implements a three-position damping control, low, mid, and high to bring that tube feel and reaction between the power amp and speaker, the interaction you are speaking about. A tube power amp exhibits a low-damping state, that is the tube power amps feel and responce people expect and associate to a tube power amp.

I admit I don't know all the particulars. @agedhorse does as he is the creator of the Subway line and the WD 800.

There are a lot of great amps out here

 

[Boneless]

Without a speaker calibration feature, you can mimic that "tube feel" with a preset EQ. On bass it works better than on guitar, IMO, for a number of reasons (guitar speakers *tend* to have a bit more variability when it comes to speaker resonance, for instance, and also with certain bass reflex speakers the lower damping of a tube amp can make the cabinet overly resonant). You can also do this with mixed mode feedback, but this is a bit safer on "guitar" power levels.

 

[DJ Bebop]

Without a speaker calibration feature, you can mimic that "tube feel" with a preset EQ. On bass it works better than on guitar, IMO, for a number of reasons (guitar speakers *tend* to have a bit more variability when it comes to speaker resonance, for instance, and also with certain bass reflex speakers the lower damping of a tube amp can make the cabinet overly resonant). You can also do this with mixed mode feedback, but this is a bit safer on "guitar" power levels.

The damping control is not a preset EQ on the WD. To the overly resonants in a reflex speaker, the beauty of the three-position damping control on the WD

A speaker calibration feature? I’m only familiar with speaker calibration for balancing speaker in live PAs and studio monitors. Again though I obviously don’t have the experience some have.

 

[Jim C]

So something I tried was, running the send from the Sisma into the return of my Mesa WD and the WD send into the Sisma return.

I was a bit surprised by the results. The Sisma I assumed that the big thick sound would be in the class G power amp section as that was touted as a difference to class D. But I found that sound was present in the preamp as it ran into the WD class D power amp, it kinda sounded like the Sisma by itself.

Similar take going the other way, I found the WD preamp going into the the Sisma class G power amp, it kinda sounded like the WD by itself.

There are no doubt some nuances I might be missing in my comparison but overall that is what I found fooling around. The differences were more subtle than striking. But they are there.

Anyway…

Having just spent at least 5 solid hours running the same Ampeg tub pre into 3 different MI amps (as well as PA style rack mount amps) I can tell you there can easily be a difference in tone. I will follow up in my thread but the bottom line is a new Traynor SB500, an SWR SM400, and to a slightly lesser extent, a GK MBF800 can all sound close.
The difference is how hard you drive the pre-amp. I was originally gain matching by leaving the pre-amp volume set at about 12:00 and using the amps output control to gain match. This did not work well and tone suffered.
By adjusting the pre-amp output and power amp output, (gain matched by ear), I could get much closer in overall tone.
I'm finally confident that I can get great tone with the Traynor and ordered a rack shelf.
Honestly, just a small change in the pre-amp volume could really change the overall tone.
My concclusion is these MI amps are much more fussy about how hard they are being driven for clean, full, 3-D tone. I did these tests over about 6 days to avoid ear fatigue and frustration and am confident in my results.
And, as expected, the PA style amps (CA6 and Ampeg SVP1600) sounded the same and great with the same 12:00 pre-amp output setting.

 

[agedhorse]

The WD also implements a three-position damping control, low, mid, and high to bring that tube feel and reaction between the power amp and speaker, the interaction you are speaking about. A tube power amp exhibits a low-damping state, that is the tube power amps feel and responce people expect and associate to a tube power amp.

I admit I don't know all the particulars. @agedhorse does as he is the creator of the Subway line and the WD 800.

There are a lot of great amps out here

There's a lot going on circuitry-wise in the WD (and all of the Subway amps), the results speak for themselves. The WD was intended as an updated, upgraded replacement to the Walkabout which can no longer be manufactured due to critical components no longer being available. It was never intended to sound like the Sisma (which obviously wasn't on the market when the WD was released).

The damping factor on the WD (in the low and medium positions) is considerable lower on the D-800/800+ which are equal to the high position. Some players really prefer low damping, some prefer medium damping and some swear by high damping, nobody's right or wrong in their preferences.

 

[DJ Bebop]

The damping factor on the WD (in the low and medium positions) is considerable lower on the D-800/800+ which are equal to the high position.

Did you mean:
The damping factor on the WD (in the low and medium positions) is considerable lower than the D-800/800+ which are equal to the high position.

 

[agedhorse]

Did you mean:
The damping factor on the WD (in the low and medium positions) is considerable lower than the D-800/800+ which are equal to the high position.

Correct.

 

[DJ Bebop]

Correct.

 

[DJ Bebop]

So I’ve been having major plumbing problems here at my house and I was very frustrate. I got a call from a guitarist friend of mind that was having a GTG yesterday and invited me over for a little jam session. Took the Sisma with me and gave it a whirl. Bass, drums, guitar, keyboards. We played at a house party, tavern level volume.

I played with the gain and master volumes, high master for a clean gain structure, then high gain lower master volume to get into more harmonic texture and then tried some heavier grind, and more use of the LPF. Love the lower gain fat warm tone. I thought me playing with more grind was goofy as that is not my thing but it was quite good and convincing without any pedals. I felt the amp had more going on pushed, more organic response and give. The lower volume settings were very filling and buttery. Noted had a lot of weight and staying power. A lot of power and character in this amp.

 

[gtirard]

So I’ve been having major plumbing problems here at my house and I was very frustrate. I got a call from a guitarist friend of mind that was having a GTG yesterday and invited me over for a little jam session. Took the Sisma with me and gave it a whirl. Bass, drums, guitar, keyboards. We played at a house party, tavern level volume.

I played with the gain and master volumes, high master for a clean gain structure, then high gain lower master volume to get into more harmonic texture and then tried some heavier grind, and more use of the LPF. Love the lower gain fat warm tone. I thought me playing with more grind was goofy as that is not my thing but it was quite good and convincing without any pedals. I felt the amp had more going on pushed, more organic response and give. The lower volume settings were very filling and buttery. Noted had a lot of weight and staying power. A lot of power and character in this amp.

Exactly my thoughts, and I like the way you say it.