class D amps?

Yes, many different classes; Class A, Class B (rare), Class AB1, Class AB2, Class C (RF use), Class D and other less standard "Classes" of operation.

 

Switching PSU, Vs old fashioned, HEAVEY, transformer. Class D saves, on weight, heat, power consumption.

Wow, valve pre, and plenty of class D power, in a sub four pound package. Thank you for giving me GAS.

 

Other than the power handling, how does the sound of one of those compare to the old iAmp350?

 

Amp classes are not descritions of the power supplies.

 

+1, nor does amp class affect tone. Ideally a power amp is totally neutral where tone is concerned; a power amp that colors tone might be considered defective. OTOH some small/lightweight power amps also have 'lightweight' power supplies, and that can cause them to run out of steam, especially in the lows.

 

Hi.

Even though I know that quoting wikipedia is considered lame and noobish, guilty as charged.

http://en.wikipedia.org/wiki/Electronic_amplifier

Regards
Sam

 

Class does affect tone unless you are outputting a very small %age of the possible output. You get into not-quite- & then non-linear parts of the transistor (or FET, MOSFET, tube) curve.

 

I've been kind of a 'class D' fanatic for many years. By that, I mean I've been drawn to amps that happen to have class D power amps since they were for the most part smaller and lighter. However, as mentioned above, the real driver of 'small and light' is the power supply. A switch mode power supply is what makes the Genz amp you reference so small and lightweight. The Class D power amp is also smaller and runs 'cooler' than the typical class A/B used in solid state bass amps also, so when you combine class D AND switching power supplies, you get the little tiny form factor.

Per Bill F's comment, a number of years ago, there did seem to be some 'low end' issues with some executions of bass heads with switching power supplies. There were a few companies (Epifani and EA) who had a somewhat unusual combination of class D power amps and toroidal power supplies, which I assume was an attempt to reduce the size somewhat via the class D power amp, but still keep the 'balls' in the low end that the SMPS power supplies available at the time didn't seem to deliver. Both these companies are now (from the pre NAMM announcements) going to full class D/SMPS designs.

Markbass does the opposite with some of their amps. They use a class A/B power amp with a switching power supply in amps like the LMII. Even though power amps aren't supposed to color the sound, darn it if the don't seem to. Virtually ever execution of class D amp I've experienced has a bit of upper mid spike and an uber clean sort of vibe. Who knows... maybe that's a voicing decision versus the technology, but you can hear it, for example, in the F1 (class D/SMPS) versus the LMII (class A/B/SMPS) voicings (they use the same pre and power supply).

That was a long winded way of saying that the recent batch of ultra-light SMPS amps have all the balls (in general) of their older, heavier cousins. Of course, just like with 'traditional' heavier bass amps, some executions are better than others. There is no reason to either choose or not choose an amp anymore IMO based on type of amp and power supply. It's all about if it delivers your sound. There is (again IMO and IME) no general level of 'better or worse' any more to my ear between amps with these different components.

 

That's a matter of whether you're running the amp within its limits. The classic definition of the perfect power amp is a straight wire with gain. OTOH many hi-fi afficionados of Class A, SET and so forth rave about the 'warmth' of those amps, and that indicates they're anything but neutral. To each their own. Class A does have the advantage of keeping your house warm on a cold winter's night, though.

 

Amp class can very well affect the tone. One reason the Class A topology is so often touted is its extremely low distortion (at the expense of efficiency).

A lot of the early tube amplifiers got their tone when cranked because the power amp tubes would start distorting.

 

I think we agree there are gross non-linearities as you approach the 'power supply borders' of signal swing, but the 'normal' range has non-linearities. Not large, but there.

 

Global feedback (properly applied) is a tool that is used to reduce these factors to very, very small degrees. Start with a good design, then apply global feedback to linearize it even more.

Side note... of course a poor circuit or a good circuit with poorly executed feedback is probably what's responsible for a lot of bad products out there over the years. In attempt to polish a turd, feedback was applied indescriminately which caused even more problems than were solved IMO.

 

This doesn't come into play for class-d, akaPulse Width Modulated (PWM) amps. The output devices in class-d are either fully on or fully off.

 

The amps with the lowest measured THD in the industry are class-d amps.
http://www.newclassd.com/index.php?page=10

But face it, we're talking signals from basses slabs of wood or plywood, and going into imperfect speakers both of which are going to add "distortion" more than ever comes through any pwer amplifier of any class (driven within measurements)

 

Class A without feedback can be very high distortion. Thart's one appeak of class A tube voltage gain stages in guitar amps.

One thing that's significant about low feedback class A stages, they tend to overload in a fairly graceful and pleasing way. Another appeal for guitar players.

 

Amp class doesn't affect tone unless the design is deficient or has deliberate abnormalities.

 

+10^21

Most popular bass guitar amplifiers, come with deliberate abnormalities in the amplitude response.

Most Pro amps will not/or should not unless they are defective.

I personally like to have control over my abnormalities (eq and effects) before they reach my amplifier/head. And not dictated to me from the get go.

Antone

 

IMO their are positives and negatives to each approach (i.e., an integrated head versus a PA type power amp and pre). As one who has gone both routes, there is a certain beauty to a well integrated head, with the pre and power amp designed to work together in a very musical way. I've experienced too many 'pre/power' amp modular rigs that just seemed to perform under expectation (not sure why.. gain matching, not optimal hi pass filtering of the deepest low end, whatever).

I have no problem these days finding a very transparent platform to play through in two rack spaces are less!

 

Ken, though I'm using separates for reasons of specialization I much agree. A lot of the heads not only have good power sections but the preamps are arguably as good or better at what they do as separate units and for a fraction of the price - and size/weight performance benefits once two chassis and a rack are considered.