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[oleskool]

Could someone help me to understand the different classes of amps? The new class d amps are small , and light. Why? What are the advantages, and disadvantages of the different classes as applied to instrument amplifiers? Also if Fahey sees this post, whatever happened with the possibility of selling the ( if I understood the thread correctly) semi kits for your amps? I think the idea of selling the kits a la carte was a very good idea. I would purchase one. The U.S. needs your product.

[Enzo]

This may or may not help...

The single largest contributor to the weight of an amp is its power transformer.   One cure for that is a switching power supply. Also known as a "switchmode power supply" or SMPS.

We can get into the technology of SMPS elsewhere, but instead of a huge 50 pound hunk of iron, the same power supply can be made for a couple pounds of more complex circuitry.

Power is power.  You can have most any class of amp running on most any type of power supply.  If the amp needs +80v and -80v, you need a dual 80v power supply for it, regardless of class.   I can take a huge boat anchor of an amp like the Peavey CS800, and replace the transformer supply with a switching supply of the same voltage and current and lop 30 pounds off it.  And that is changing nothing on the amp circuits themselves.

Class D amps, and anything digital in the modern market, may very well weigh a LOT less than older amps with similar output, but most of those also have an SMPS inside rather that a transformer.  It is that SMPS that makes it SO much lighter, NOT the class of operation.

Having said that, digital amps can be more efficient than older systems, so you may also get a little weight advaqntage watt for watt, but mainly it is power supply that makes the difference.  For example the old PV CS800 weighed 45 pounds.  Later they made essentially the same amp but with SMPS (CS800S) and it weighed 23 pounds.   Now PV makes the IPR1600 with twice the power output of the CS800, and it weighs just 7 pounds.


ADvantages of class?  I don't even think about class.  If I need a 1500 watt power amp, I look at power specs, cooling needs, eficiency, cost, maybe some other things.  I don;t care what class it is making that power.  I do care that I can have four amps in a rack for under 30 pounds total versus four amps taking up not only twice the rack space but also weighing 180 pounds total.

Think of it this way:  your mom needs a car to go shopping.  She cares about room, number of doors, gas mileage.  She doesn;t care at all if it is fuel injected or has a carbuerator.


Some folks will chat up some class or other in their tube amp.  They prefer class A to class AB or whatever.  In my opinion, most of those folks heard an amp they liked and when they found out it was a class A amp they decided that the class must be why they liked it. Chances are the class had little to do with it.

[oleskool]

Thanks for taking the time to answer. I was really trying to ask what makes an amplifier class a or ab? I can recall something about when current flows. I can't pull up those old brain connections though.

[phatt]

Class A means the *Active* device is conducting for 360Deg of AC cycle.
Class A/B = each *Active device* is conducting for half the AC cycle.

You can also have Push Pull Class A.

Just start goggling relative phrases to what you wish to understand ,, trust me it will be faster learning that way.

As to guitar related sound,,, most of the greatest sounds ever recorded where done with Class A/B output stages NOT Class A.

The triode preamp stages (of classic Valve amps) are of course Class A but the power stages are mostly Class A/B.

Modern SS gear is mostly opamp stuff which are mostly push pull output in both preamp and power stages.

These work in a different manner but the end result can be just as rewarding if you know what to do.

Phil.

[Roly]

The Class of an amplifier tells us over what portion of the signal wave the active device is working.

Class-A - conducting over the entire cycle.  Almost all preamps.

Class-AB - conducting less than the entire cycle but more than half a cycle.  Generally in guitar and similar amps it is not much more than half, just enough to overlap.  Implies two devices sharing the work in push-pull operation.

Class-B conducting for exactly half a cycle.  More efficient than Class-AB but prone to crossover distortion.  Implies two devices sharing the work in push-pull operation.

Class-C conduction for less than a half cycle.  Not used in audio but common in radio frequency applications such as transmitters.  Very efficient but very distorting.

Class-D switch mode between fully off and fully on at very high speed and where the time proportion of off-to-on is proportional to the signal voltage.  Very high efficiency but requires complex circuits and post filters to prevent the high switching frequency getting to speakers, tweeters, or following equipment.

More detail;

http://www.duncanamps.com/technical/ampclasses.html

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

As you will see, a great deal of utter balderdash is talked about amp classes, particularly in Hi-Fi circles, but even in guitar circles for example the myth persists that the Vox AC30 is a Class-A amplifier.

As Phil and Enzo imply, class of operation isn't really all that significant against many other factors.

HTH

[oleskool]

Thanks for the answers guys. I don't know why I ask these questions that end up making me start down a path with many more questions. I came here about to try a simple chipamp. Now i'm about to try a 100w amp. I think i better stop reading and start building.

[Roly]

Why do F1 racing car drivers start out racing GoKarts?

If you want to build a nitro-fueled dragster it's a good idea to start out on something more modest like a lawnmower and work your way up.

There is no reason why you can't get to a 100 watt amp by, say, your forth build, but if you are going to learn by blowing stuff up (and in truth we all did a bit of that in our early efforts) then it's better to blow stuff up that isn't too expensive and won't go "bang" too violently.

Amps can be split into two parts, the preamp before the master volume control, and the main or power amp that follows.  As it happens it is around the master volume control that you can mix and match these two sections.

There is also something to be said for getting a large case and heatsink and starting with a limited build first, then enhancing and rebuilding by stages until you arrive at a very full-blooded guitar amp.  As you upgrade your preamp and power amp your ideas will change about what you want, and gradualism allows room to change your mind in the next stage.

[teemuk]

Class A advantages:
- No crossover distortion
- Less sensitive to effects of heat
- Less sensitive to bias variations
Summary: Advantages that in essence have no concernable benefit in practical applications and that are far outweighted by disadvantages of class-A, such as terribly poor efficiency.

Class B/AB:
- Better efficiency than class-A

Class G/H:
- Better effiency than class B/AB

- Class D and other "switching" classes:
- No crossover distortion
- Better efficiency than other classes

In practice, in a properly designed amp, you won't hear any "tonal" effects of the amplifier's class. Yet, efficient amplifiers tend to run cooler and may even be more compact in size and in weight. If class A has maybe 25% effiency versus maybe 95% efficiency of a class-D you can imagine it kinda has effects on dimensioning the power supply, heatsinks and the robustness of the output devices; things that can weight a lot and introduce notable requirements for the overall size of the unit. The class-D can extract the same output power from less, while less of the power is wasted as heat.

All of the above classes can equally work on a switching-type power supply so let's not go there...

[oleskool]

Yes Roly I understand that it is best to start small. I'm starting even smaller than suggested. I am working on small DC projects on a breadboard just like school. Truth be told the field I worked in required high mechanical skills because, tax accountants, lawyers, schools, and it seems everyone else wants their copy machine working when you leave that day. I didn't do a lot of electronic repair because I was in the field. I would find the problem board, replace it, and have the clients machine up and running in 15 to 20 minutes. I would then take that board to a bench tech to repair at component level. Usually you work your way up from bench tech to field tech. I worked hard in school and when i hired in they must have thought i didn't need to go that route. It was was a blessing because, i made more money, it was a curse because, it made me look at things different. I became complacent doing it the easy way. I also feel i can just jump over the smaller things. The good news is i understand those weaknesses.

Teemuk see that is what causes me problems. If you would not have said class g/h amplifiers i would have stayed on course. I just had to find something about them. I am learning how to design a transformer-coupled class a amplifier ( to make maximum 25% efficiency better) from a book.

To make it worse i just acquired a $40 Hartke b-90 combo amp with no sound out.