What will raising the Va of atransformers provide?

Dcarol, why do you think it does not? A true chass A amp draws 4 watts ALL THE TIME for each watt of output. So a 100 watt a channel amp will draw a constant 800 watts from the wall. An AB amp idles at a few watts and rarely draws its maximum current. Therefore the transformers in an A amp have to be up to ALWAYS supplying full current as opposed to doing it once in a great while. It is obvious that class A amps require more robust parts to deal with the constant heat generated; they actually run cooler at full output than at idle. Class A amps never see a sharp increase in current draw because they are already drawing their maximum; how then would bigger transformers improve the performance? Yes you could increase the power rating but that would mean everything else would have to be bigger also. I thought the origional question was just changing the transformer and I have seen nothing in what you said to convince me that it would.

Stanwal

high-end audio reproduction doesn't work like that. If it did work the 'theoretical way' then a bigger power supply or larger VA rating on a transformer on a preamp would do absolutely nothing!

As we all pretty much know though, it does make a difference.

Your calculations do not take into account instantaneous/ transient current draw - the current draw during fast, large musical passages which happen in a few milliseconds. This is where a larger VA rating is needed. If you have ever built an amplifier whether Class-A or AB and calculated the exact power requirements and even been generous adding an extra 1.4 multiple, you will still hear an improvement doubling the VA rating.

If the theory and maths could explain everything then how does high-end audio work? Theory and maths does not explain differences in audio nor does it explain the reason why a larger supply helps the audio reproduction in just about every piece of audio equipment. Ask any audio designer...he'll/she'll be able to get so far but then after that it's all 'guess work'.

stanwal: I thought the origional question was just changing the transformer
Dirk: Changing the transformer to something larger is changing to a larger VA rating.

It is your original explanation to class-A and AB that is questionable. Class-AB 'varies with demand' and Class-A 'runs at full power' and also the idea that they are all large and expensive - they are not all large and expensive.

I'm not asking you to take anything I say onboard, just that it is not as simple as you make out - if it was then we would all have the same system.

Dcarol, it appears that you are not addressing Stanwal's point about a class A amplifier. I agree with him- if the transformer for such an amplifier is up to the task in the first place, a larger transformer is not going to make a difference, high end audio or no. If the transformer is not up to the task, then the amp is either not class A or its one with a reputation for eating transformers. In any case it may be moot as a class A amplifier is 'high end' anyway...

Unless you are upgrading and altering the circuit designs within your amp, the new transformers must have the same turns ratio for voltage in and out. In other words, whatever the original input and output voltages are in your current transformer, that is what it must be for your new transformers.

This comment is not entirely true. Power transformers can have voltage drops across their windings, a lot has to do with the internal temperature rise of the part during operation- transformers with more temperature rise have higher internal voltage drops. If you go with a transformer with more VA, you may well have to *reduce* the turns ratio to obtain the correct output voltages under load.

In any case, while on the surface it might appear to be a simple upgrade, the fact of the matter is that doing such a change is an R&D project and should be viewed in that light, especially when the initial results fail to satisfy :)

I might add that I was one of the origional Krell dealers and have also sold Class A amps from Musical Fidelity and Stax. I had a preamp with a custom power supply using 2 Avil Lindberg torrodial transformers and very large caps built in the early 80s; my ASR Basis phono stage uses a 50 lb power supply and my MF Kw line stage weighs 50 lb or so and will put out 50 volts. I also use an aftermarket PS for my MF V-DAC. I am well aware of the importance of power supplies; my point was that JUST the subistution of bigger transformers in a design that already had adquate ones was not a guarentee of better sound. As Atmasphere points out it is a lot more complicated than just making a simple subistution.

Atmasphere is correct. I was describing transformers whereby you want the same rail voltages and are just swapping transformers with one with higher VA ratings, but the voltage in/out (turns ratio) is the same. If you change the turns ratio from the original transformers without playing with the power supply circuitry, your power supply rails voltages will be different. Guys, and ladies, "always on" describes that the device is always turned on. it does not mean that it is biased towards full output capability. You can bias where the devices are "just" turned on (class A) or you can bias where the devices are cooking at full rated current output (full power class A). If I bias a 100 WPC amp on at 25 WPC, it is biased class A at 25 WPC, but it is still class A. Just not 100 WPC class A.

enjoy