Tube power stage vs Class-D (effective power)

[Japhet]

In my (limited) experience, I'd say that the volume delivered by a valve amp is more 'linear' than SS or class D. In other words, 8 is much closer to twice as loud as 4. Class D amps that I've had tend to get more 'shouty' without getting much louder whereas valve amps keep the inherent sound, albeit with a bit more drive, as they get pushed harder. These are my layman's terms which might work for some.

[Bill Fitzmaurice]

4 hours ago, Japhet said:

8 is much closer to twice as loud as 4.

It is if you do it right. Our hearing is logarithmic. It takes ten times the power/a 10dB increase in level to sound twice as loud. To account for that volume controls are also logarithmic, commonly referred to as audio taper pots, as opposed to tone controls, which are usually linear taper pots. I've seen amps that used linear taper volume controls, and the result was not linear. But it has nothing to do with the amp class.

[agedhorse]

2 hours ago, Bill Fitzmaurice said:

It is if you do it right. Our hearing is logarithmic. It takes ten times the power/a 10dB increase in level to sound twice as loud. To account for that volume controls are also logarithmic, commonly referred to as audio taper pots, as opposed to tone controls, which are usually linear taper pots. I've seen amps that used linear taper volume controls, and the result was not linear. But it has nothing to do with the amp class.

Often this is done intentionally, to give the impression that the amp “gets louder” more quickly as the control is turned up. This comes at the penalty of usability and control. It’s more common in lower quality, lower priced amps, but not always.

[Tech21NYC]

13 hours ago, agedhorse said:

There are a couple of reasons for using a 200 watt module… the first being that the amp is not operated at 4 ohms, therefore the rated power is only 100 watts. The second reason is for duty cycle management combined with the modeling algorithms, specifically relaxing the compression and

limiting attack time versus how hard the amp is driven. There’s a ton of stuff going on under the hood.

Actually it is. From  the spec sheet. 

 

Wattage

200W into 4Ω (Simulates 85W Tube Amp Performance) 

Speakers

Two - 12" Jensen® N-12K Neo

Total Impedance

4 ohms

 

It makes sense. You want more available headroom when using the SS amp vs the tube amp. Coming from the sound reinforcement side of things the basic rule of thumb was always doubling the amount of power in relation to speaker wattage. ie 1000 watt of speakers use at least a 2000 watt power amp. I found this out the hard way by constantly blowing tweeters in my PA tops because I was using an underpowered power amp. With musical instrument amps it usually goes the other way. A 300 watt SVT is paired with an 800 watt 8X10.  A 100 watt Marshall will be used with a cab rated at 200-300 watts.

 

Of course this begs the question what is accomplished with with all that complex stuff under the hood? A lighter, less expensive amp that has more flexibility and no maintenance other than software updates. The repair and reliability is hard to quantify at this point. Digital amps usually can't be easily field serviced. If the processor goes out it needs to be replaced etc. We do some repairs on the Class D power amp modules in our amps but it's usually more cost effective to replace the module.  While tubes became an obsolete tech in the 1950-60's and have their own set of drawbacks they are still being made. The original Line 6 AxSys 212 which came out in 1996 is no longer supported by Line 6 and can be very difficult if not impossible to repair and yet my '66 Fender Bassman lives on. 

 

 

 

 

[Tech21NYC]

8 hours ago, Japhet said:

In my (limited) experience, I'd say that the volume delivered by a valve amp is more 'linear' than SS or class D. In other words, 8 is much closer to twice as loud as 4. Class D amps that I've had tend to get more 'shouty' without getting much louder whereas valve amps keep the inherent sound, albeit with a bit more drive, as they get pushed harder. These are my layman's terms which might work for some.

 

You have it backwards. SS amps are more linear. What you are describing is the tube amp starts to saturate and "compress" more when turned up. That provides a bit of a cushion to the sound whereas the Class D amp will just get louder. With SS amps there is no output transformer. The wattage changes with impedance. See the specs for our 1000 watt Class D dUg Ultra.

 

1000 Watts RMS minimum, @ 4Ω

600 Watts RMS minimum, @ 8Ω

300 Watts RMS minimum, @ 16Ω

 

Many commercial SS amps are rated at 2 Ohms because that's the biggest number. The only time I ever blew up a power amp was running at 2 ohms. 

 

 

[itu]

2 hours ago, Tech21NYC said:

Many commercial SS amps are rated at 2 Ohms because that's the biggest number. The only time I ever blew up a power amp was running at 2 ohms.

It may be easier to understand, that when impedance diminishes, current rises.

 

When current - and temperature - rises, cables and components have to be larger in diameter, or they melt.

 

An 8 ohm cab is usually the safe choice. Works with tubes/valves and SS, and everything. But as long as people believe that watt equals loudness instead of dB, they want lower Z, and literally hotter amps.

[agedhorse]

A quality power amp designed for 2 ohm operation should have no problem driving 2 ohm loads with no reliability issues, I have been doing so for >30 years. 

[agedhorse]

3 hours ago, Tech21NYC said:

Actually it is. From  the spec sheet. 

 

Wattage

200W into 4Ω (Simulates 85W Tube Amp Performance) 

Speakers

Two - 12" Jensen® N-12K Neo

Total Impedance

4 ohms

 

It makes sense. You want more available headroom when using the SS amp vs the tube amp. Coming from the sound reinforcement side of things the basic rule of thumb was always doubling the amount of power in relation to speaker wattage. ie 1000 watt of speakers use at least a 2000 watt power amp. I found this out the hard way by constantly blowing tweeters in my PA tops because I was using an underpowered power amp. With musical instrument amps it usually goes the other way. A 300 watt SVT is paired with an 800 watt 8X10.  A 100 watt Marshall will be used with a cab rated at 200-300 watts.

 

Of course this begs the question what is accomplished with with all that complex stuff under the hood? A lighter, less expensive amp that has more flexibility and no maintenance other than software updates. The repair and reliability is hard to quantify at this point. Digital amps usually can't be easily field serviced. If the processor goes out it needs to be replaced etc. We do some repairs on the Class D power amp modules in our amps but it's usually more cost effective to replace the module.  While tubes became an obsolete tech in the 1950-60's and have their own set of drawbacks they are still being made. The original Line 6 AxSys 212 which came out in 1996 is no longer supported by Line 6 and can be very difficult if not impossible to repair and yet my '66 Fender Bassman lives on. 

 

 

 

 

Other ware some models that used the same module operated at 8 ohms with lower rated power. 
 

Much of the emulation/simulation involves significant dynamics processing which limits the power into their respective rated loads. Otherwise those poor speakers would fail at an unacceptable rate. It’s a combination of both approaches depending on the specific product. 
 

Active power management while maintaining musicality is a game changer. I remember when such adaptive algorithms (including dynamic HPF’s, adaptive multi-band compressors/limiters, dynamic crossover points, HF lift circuits (came into existence in the pro audio world in products like Meyer, Renkus Heinz, Appogee, etc), they are now ubiquitous in today’s pro audio products at all levels. That’s one reason why reliability has dramatically improved.