Class D vs Class A or A/B

[ThisBass]

The topology of the svt power amp section is a combination of:
solid state distortion
and
clipping due to line transformer power capacity.

The combination of both is a very special thing.
Most of all times (in 99%) this legendary grunge provides a plenty of feeling and very enough loudness in any situation on stage.

Last night the situation was different.
The grunge that is deriving from the svt solid state distortion is an increase of frequency content in the essentially lower mids.
But the svt distortion (or establishment of new frrequencies) is a symmetrical one.
I never had problems with this behavior before, but I had last night.

 

[ThisBass]

And how would that have solved your problem? IMO, this has more way more to do with room acoustics and cabinet design, than it does the topology of your amps power section.

The cab design was done by myself.
Btw I was a little bit surprised (here on talkbass) to recognize that other prof design folks had the same idea like I do.

 

[seamonkey]

The topology of the svt power amp section is a combination of:
solid state distortion
and
clipping due to line transformer power capacity.

The combination of both is a very special thing.
Most of all times (in 99%) this legendary grunge provides a plenty of feeling and very enough loudness in any situation on stage.

Last night the situation was different.
The grunge that is deriving from the svt solid state distortion is an increase of frequency content in the essentially lower mids.
But the svt distortion (or establishment of new frrequencies) is a symmetrical one.
I never had problems with this behavior before, but I had last night.

You will not get agreement on this forum about the svt solid state components.

If you have oscilloscope traces, and spectrum analysis I'd like to see them.

 

[ThisBass]

You will not get agreement on this forum about the svt solid state components.

If you have oscilloscope traces, and spectrum analysis I'd like to see them.

I don't have any need to beg for agreement.
I Know what you don't know.

 

[fdeck]

You will not get agreement on this forum about the svt solid state components.

If you have oscilloscope traces, and spectrum analysis I'd like to see them.

In particular, you won't get agreement from me.

We've been through this. Work out the input sensitivity of the SVT power amp circuit, from the schematic, and compare it to the forward voltage of the diodes.

 

[agedhorse]

The topology of the svt power amp section is a combination of:
solid state distortion
and
clipping due to line transformer power capacity.

The combination of both is a very special thing.
Most of all times (in 99%) this legendary grunge provides a plenty of feeling and very enough loudness in any situation on stage.

Last night the situation was different.
The grunge that is deriving from the svt solid state distortion is an increase of frequency content in the essentially lower mids.
But the svt distortion (or establishment of new frrequencies) is a symmetrical one.
I never had problems with this behavior before, but I had last night.

I offer you this to think about...

Could the legendary grunge possibly be due to the overall amp design, the particular voicing and the stages that offer distortion combined with the particular voicing of thise stages?

There's a heck of a lot more to the sound of an SVT than "solid state distortion" and "clipping due to line transformer power capacity". In fact, you have probably named two of the least influential components to an SVT's legendary grunge. Even the speakers commonly used with an SVT set-up are IMO way higher on the list.

 

[ThisBass]

I offer you this to think about...

Could the legendary grunge possibly be due to the overall amp design, the particular voicing and the stages that offer distortion combined with the particular voicing of thise stages?

There's a heck of a lot more to the sound of an SVT than "solid state distortion" and "clipping due to line transformer power capacity". In fact, you have probably named two of the least influential components to an SVT's legendary grunge. Even the speakers commonly used with an SVT set-up are IMO way higher on the list.

I start with the power amp stage.

compered to a SS power amp stage by moderate loudness it is hard to separate the svt from SS. I hear the difference but the difference is marginal.

In the "cranked" position the difference is more audible.
The svt performs more smooth to the sound whereas SS drives the clipped content harder to the ears.
But without the two diodes (the SS distortion) the svt power amp performs clipped content very similar like a SS amp.

Never the less the svt power amp is a little bit different.
The combination of both give the svt power amp the basic sound.
But the pure svt power amp alone provides not the legendary svt grunge at all.

The svt preamp sounds like it is, normally.
The power supply for the preamp hangs on the the line transformer supply for the power amp.
In the cranked gain position all the voltage rails get down and impact directly the supply for the preamp.
The sound performance of the preamp "changes" direct proportional to the power needed at the output.
Explained in different words. Voltage at the anodes goes down and ....yes you know what I mean

The separated combination of both the svt preamp and svt power amp sounded different.
Even they where just the same, but the preamp had an independent supply.

 

[R Baer]

All of this bagging on various this and that type of power supplies and power amps without the qualification that there are some very reliable SMPS/class D amps on the market and some very unreliable class AB amps on the market.

I think that before dog-piling on a particular topology, you might consider that the pro audio world at the highest level has shifted almost exclusively to SMPS/class D (with some exceptions) and the reliability is BETTER than with many of the older amps. This is the world that I come from, and I have designed products using both types of amps over the years. I don't dislike class AB, I don't dislike line frequency power transformers (there you go Bob ) but I also understand that it's beneficial to many players to shed the size and weight (especially international touring players who fly with their amps).

Hey Andy, I know sometimes it comes across as my opinion that class A/B is somehow superior to class D, but that's not the case. For the moment, I still prefer class A/B, but I have nothing against class D. I find the technological possibilities fascinating and I'm sure we will have a class D at some point. The advantages are simply too big to discount and class D opens up a world of possibilities that you just can't achieve with a larger, heavier amp. That said, I still love me a big 'ol lead sled and I don't mind schlepping one around.

Do I think that class D will replace all larger class amps just because of it's size and weight advantages? Not at all. There are all types of players out there with a wide variety of personal preferences in their gear, so I think there's room out there for just about anything that is well built and sounds good. Just like basses. Some guys won't give up their '60's P-bass for anything, while other guys would rather play a bass with carbon graphite necks and optical pick-ups.

 

[Duke21]

There's also another issue here that the class D, class A/B conversations never seem to touch upon, and that is the power supply topology. When are talking about class D, as it applies to the modern micro bass heads, we are generally talking about an off the shelf class D amp that has been mated to a SMPS. On the other hand, most people talking about class A/B are typically referring to a class A/B amplifier that is mated to a more traditional transformer based power supply.

So really, IMO, these threads debating the merits of either topology also need to include a discussion on how the various types of power supplies affect the overall feel and tone of your amplifier. We did some experimenting using a few different switch mode power supplies in the Valkyrie and I can say that in my experience, there is definitely a difference in how the amplifier behaves and sounds based on the power supply method used to feed the amplifier section. In the end, we stuck with a heavy toroidal transformer, not because it was "better", but because I preferred the amp, as a whole, with that type of power supply. It's kinda of like comparing stainless strings to nickel strings. Sure they both do the same thing and your bass still sounds like your bass, but there are differences there that are easy to perceive and people will logically choose one over the other based on personal preferences.

This question about matching power supply to a power amp is very interesting. Almost all class D amps have SMPS while only a few like Markbass II and III are class AB with SMPS.
One interesting all tube head is the Peavey VB3 which have SMPS. Does this head have very different sound then the VB2 which is a classical design?

A good example of a class D amp which excels in testing (BGM test) is the Orange BT500 which if I remember right scored over 900W burst and well over 500W RMS. So this head have SMPS which is able to deliver a lot of reserve. Does the BT500 use the same SMPS as the BT1000?

 

[Duke21]

You will not get agreement on this forum about the svt solid state components.

If you have oscilloscope traces, and spectrum analysis I'd like to see them.

He he,
You are Bingo on this issue. Personally I've no idea how the SVT poweramp distort, but accusing an all tube SVT with SS distortion is a risky thing on this forum.

 

[Calaverasgrande]

I start with the power amp stage.

compered to a SS power amp stage by moderate loudness it is hard to separate the svt from SS. I hear the difference but the difference is marginal.

In the "cranked" position the difference is more audible.
The svt performs more smooth to the sound whereas SS drives the clipped content harder to the ears.
But without the two diodes (the SS distortion) the svt power amp performs clipped content very similar like a SS amp.

Never the less the svt power amp is a little bit different.
The combination of both give the svt power amp the basic sound.
But the pure svt power amp alone provides not the legendary svt grunge at all.

The svt preamp sounds like it is, normally.
The power supply for the preamp hangs on the the line transformer supply for the power amp.
In the cranked gain position all the voltage rails get down and impact directly the supply for the preamp.
The sound performance of the preamp "changes" direct proportional to the power needed at the output.
Explained in different words. Voltage at the anodes goes down and ....yes you know what I mean

The separated combination of both the svt preamp and svt power amp sounded different.
Even they where just the same, but the preamp had an independent supply.

that might explain some sag/compression, but I think more of the SVT tone is in the EQ section, which is pretty much unique to that amp.

 

[Calaverasgrande]

IMO it is never possible to play "clean" and with a "hint of overdrive" twice at the same time.
Btw the definition what is "clean" at all is a very confusing story.

I can assure you it is quite possible. My "clean" is another players "dirty". Yet when I am playing with the band you would be hard pressed to be able to tell that I am not playing entirely clean until the guitars drop out.

No it is not. Some times the average is the same, probably most of the time the average is a little less.

In general the distorted signals sound louder by the same average.

I suppose you balance both "sounds" to the same loudness.
The distorted sound average will then probably be smaller.
The peaks/transients are reduced anyhow.

I can tell you from my work as a sound engineer that distorted/overdriven bass DOES have a higher average level. conversely clean bass has a much higher peak to average ratio.
It is easy to see this by the metering on a desk when you have DI (before the amp) and mic signals.
Or when you have the same two signals in your DAW you can see the clean signal has 10-15db difference between peaks and average signal level. Where the overdrive/distorted signal has 1-3 db or almost none.
The DAW's representation will show a solid sausage where the overdrive bass clip is. It will show a bunch of peaks and valleys where the clean signal is represented.
Though with some fuzz type effects you will encounter an odd PWM type effect where the average IS much less than the peak level. But this is unique to the "synthy" sounding fuzz pedals such as the Death by Audio "Fuzz War" and several other boutique makers.

And actually I tend to roll of the top on my distortion pedals and boost quite a bit to get some of that lost bass back. A problem that almost all bassists who use distortion encounter.
[/QUOTE]

 

[ThisBass]

I can assure you it is quite possible. My "clean" is another players "dirty". Yet when I am playing with the band you would be hard pressed to be able to tell that I am not playing entirely clean until the guitars drop out.


I can tell you from my work as a sound engineer that distorted/overdriven bass DOES have a higher average level. conversely clean bass has a much higher peak to average ratio.
It is easy to see this by the metering on a desk when you have DI (before the amp) and mic signals.
Or when you have the same two signals in your DAW you can see the clean signal has 10-15db difference between peaks and average signal level. Where the overdrive/distorted signal has 1-3 db or almost none.
The DAW's representation will show a solid sausage where the overdrive bass clip is. It will show a bunch of peaks and valleys where the clean signal is represented.
Though with some fuzz type effects you will encounter an odd PWM type effect where the average IS much less than the peak level. But this is unique to the "synthy" sounding fuzz pedals such as the Death by Audio "Fuzz War" and several other boutique makers.

And actually I tend to roll of the top on my distortion pedals and boost quite a bit to get some of that lost bass back. A problem that almost all bassists who use distortion encounter.

[/QUOTE]

I understand what you try to point out.
All the things you argue are understandable.

I considered in the mean way the average, or average power.

P(avg) = SQR(Vrms) / R

I don't know if there is a desk on the market that draws True Vrms signal levels.

But I would not even going to try to calculate any P(avg) or Vrms amount from the reading of a desks level meter.

 

[ThisBass]

I can assure you it is quite possible. My "clean" is another players "dirty". Yet when I am playing with the band you would be hard pressed to be able to tell that I am not playing entirely clean until the guitars drop out.

As I pointed earlier, the definition "clean" will be a gas when expressed by musicians feeling.

To exhaust the full power of an amp with any bass guitar it is necessary to clip the signal for a duration of many seconds.
Clear audible clipped sound for a duration of many seconds can never be a "clean" one.

 

[Calaverasgrande]

As I pointed earlier, the definition "clean" will be a gas when expressed by musicians feeling.

To exhaust the full power of an amp with any bass guitar it is necessary to clip the signal for a duration of many seconds.
Clear audible clipped sound for a duration of many seconds can never be a "clean" one.

who said you needed to exhaust the full power of the amp in order to achieve overdrive or distortion? There are literally thousands of pedals that let you have overdrive and distortion at levels far below power amp clipping.
There are also a number of amps that have preamp gain/master volume arrangements which allow you to derive an overdriven sound from the preamp, while keeping the power amp clean.
This is essentially the Mesa Boogie gimmick. Heavily saturated pre driving a clean power amp. Though that is speaking of their guitar gear, their bass gear is similar.

 

[ThisBass]

He he,
You are Bingo on this issue. Personally I've no idea how the SVT poweramp distort, but accusing an all tube SVT with SS distortion is a risky thing on this forum.

Here in Germany some other well skilled tube amp tecs/engineers know it all.
But there is normally no big discussion about it.
Because it is as it is, and it is therefore no need to raise discussions for nothing.

The power amp "grunge" sound can be simulated a bit when silizium diodes are combined with z-diodes.
However the result of the simulated sound will never be exactly the same like the svt. The whole svt power amp is needed if it shall sound like svt power amp. No doubt about it here.
But the relationship is audible.

I used an improved schematic of it in a SS amp for a couple of years.
I was often asked if the SS has tubes inside.

 

[ThisBass]

who said you needed to exhaust the full power of the amp in order to achieve overdrive or distortion? There are literally thousands of pedals that let you have overdrive and distortion at levels far below power amp clipping.
There are also a number of amps that have preamp gain/master volume arrangements which allow you to derive an overdriven sound from the preamp, while keeping the power amp clean.
This is essentially the Mesa Boogie gimmick. Heavily saturated pre driving a clean power amp. Though that is speaking of their guitar gear, their bass gear is similar.

I thought there was some discussion about burst ability/capacity vers. continuous ability of any amp.
The basic approach was,
do all bass players have more benefit with continuous?

If the answer is considered as yes, what have I to do to exhaust this benefit.

I don't think about effects just this moment.

Btw the boogie's invention of two times kathode basis stages in serial are very great. An essential invention that is basic in the meanwhile in most of all tube guitar amps.

 

[MAMMOTHvolume]

The topology of the svt power amp section is a combination of:
solid state distortion
and
clipping due to line transformer power capacity.

The combination of both is a very special thing.
Most of all times (in 99%) this legendary grunge provides a plenty of feeling and very enough loudness in any situation on stage.

Last night the situation was different.
The grunge that is deriving from the svt solid state distortion is an increase of frequency content in the essentially lower mids.
But the svt distortion (or establishment of new frrequencies) is a symmetrical one.
I never had problems with this behavior before, but I had last night.

I really don't agree with this at all. Have you ever had an svt on a scope? The driver stage would only clip before the power amp stage if there was something very wrong with it and the driver stage has alot of juice to it and will stay clean for a decent time after the power amp clips.

transformer contributes to the sound but not with clipping, but it is designed in a way to tame high frequencys

 

[ThisBass]

I really don't agree with this at all. Have you ever had an svt on a scope? The driver stage would only clip before the power amp stage if there was something very wrong with it and the driver stage has alot of juice to it and will stay clean for a decent time after the power amp clips.

transformer contributes to the sound but not with clipping, but it is designed in a way to tame high frequencys

The power amp measures appro 360 Watt at 4 Ohm at 100Hz sine wave.
Signal is scoped until the output signal is at the edge of clipping.
Vrms measured with Fluke 185. The Tectronix TX3 is just the same like Fluke 185.

Using scope channel #2 and trace the signal on the grid of V1 explains the impact of the diodes.

The VAC readings in the brackets of the original schematic draw don't reflect exactly the real behavior of the amp.
Neither for power or for pre.

I played a VR version with 610 cab a couple of month ago.
A brand new amp standing in a musicstore.
It was a funny thing.
I was able to predict the vr clipping edge and sound ...


I know the common recommendation for measurements is 1kHz.
...but I play bass guitar!

 

[seamonkey]

The power amp measures appro 360 Watt at 4 Ohm at 100Hz sine wave.
Signal is scoped until the output signal is at the edge of clipping.
Using scope channel #2 and trace the signal on the grid of V1 explains the impact of the diodes.

The VAC readings in the brackets of the original schematic draw don't reflect the real behavior of the amp.
Neither for power or for pre.

I played a VR version a couple of month ago.
Brand new amp in a musicstore with 610 cab
It was a funny thing.
I was able to predict the vr clipping edge and sound ...


I know the common recommendation for measurements is 1kHz.
...but I play bass guitar!

It would be great if you could post some scope pictures.

There's this book, I'm too cheap to buy it. Local libraries don't have it. I'd be curious what he has to say. Sound out is what I focus on, however it is achieved.

Invalid Link Removed
"The Ultimate Tone Vol. 3" Kevin O'Connor.
Chapter 12: SVT
SATISFACTION 12-1
Electronic Irony 12-1
Traditional Fixes 12-3
NOT SO "SUPER" 12-4
Power Amp Overview 12-4
Other Oddities 12-8
OUTPUT STAGE & SUPPLY 12-9
The Hard Way... 12-9
Toroidal Option 12-12
Or, the Easy Way... 12-12
A Universal Alternative 12-14
Ideal Power Supply 12-14
CHASSIS SELECTION 12-14