Rowland --- older amps vs the newer models?

sirspeedy, the model I have is the original model 8 with the choke power supply( single chassis).
I have heard the switch mode power supply and still prefer the choke. Jeff once told me that the choke was in his opinion the way to go, but that he had to change it due to the far east market complaining of hum. (Which I do not have any problems with in the US.) I also heard the battery power supply version,and it too seemed to be lacking in dynamics compared to my choke version.

Davey,your one chasis version is a superb amp,as my friend has it.My amp,as I've explained,is the original 8t circuitry,with the second chasis acting as the switch mode.I really don't know about the newer amps,and the ICE units within,but as per two conversations with Jeff Rowland,he stated to me that this configuration(my two chasis model,as upgraded to Switch mode)had 3 advantages,over the single chasis model,and was "logically superior",as it should be.First,the PS is isolated on a separate chasis,a good thing.Second there is NO filtering,due to the switch mode's usage.Thirdly,the A/C coming out of the line is converted to pure D/C,for quieter operation.These are Jeff's words,to me.Believe me,my friend's one chasis unit is superb,but you cannot convince me that I was originally duped into paying so much more for the two chasis model.That was actually the case as compared to the orig battery,which was quiet,yet rather WIMPY.This new version,of 8t circuitry,coupled with the second chasis acting as the external Switch mode PS,is a whole different ballgame.Better frequency extremes,and a much better sense of dynamics,as compared to the battery.Also,it seems STILL quieter than the original battery.That being said,and to be honest,I'd have gone with the single chasis unit,if I'd have known that it was actually superior to the ORIGINAL battery unit.It was,and IS,THAT GOOD!Best regards!

Well, I can not speak for Jeff, but YES! If you can tolerate the weight, the mechanical hum (damn hard to get rid of it), not to mention that you can't place it near the anlog front-end (electrical hum), then I would concur that choke inputs are better.

Why?

Lots of reasons.

One, current peaks on the transformer are much lower. This helps to reduce gabage created by the recitifiers switching on and off.

Two, it adds ripple reduction. Back when all we had was tube amps, with wimpy little filter caps, we had to use choke input supplies. Somehow, things still managed to sound good. Right?

Yeah, I know.....only two reasons. Yes, but. There are sublte interactions between transformer VA rating and core utilisation, peak charging curents, filter cap size and ESR/ESL, that can not be easily explained. (Trust me, ok?) You could spend a lifetime building amps, and not be able to explain or predict how it all works.

Anyway, the Far East market is very demanding. If Jeff said that his agents there kvetched about hum, then I would take that as gospel.

As for batteries:

I know it sounds counter-intuitive, but batteries sound noisy. I realise in many circles that is the hot mod of choice, but listen to one long enough, and you will concur. Sure, no 120 Hz ripple, but that may be its only advantage.

I believe the SMPS that Jeff uses employs a technique called "power factor correction". To the user, how it actually works should not be important. What should be important is that it should reduce noise generated in the AC/DC process.

Ar t, that's a good description of the differnces between choke and other power supplies. Oddly, I am not bothered by the weight, of course it helps that my brother helps me lift the darn thing.
Regarding the hum, I have always taken care to support the amp on a good amp stand( zoethecus) and to make sure that it is not close to any analog devices. Also, I know that if i.e. a low powered halogen is on in the house that that will be a major source of hum.
The top plate mod is a very good mod for this amp though, because the choke seems to need an extreemly rigid chassis.
sirspeedy, in truth, I have not heard your version of the amp( only the single chassis version, which as I stated above, the choke is better IMHO) I would think that a dual chassis design with power supply in seperate chassis would be beneficial.
Have you A/B'ed your current amp against the single chassis choke of your friend.Does he have top-plate mod, because if not he should be recommended to get it.

Have any of you guys ever compared something like the 8T or 9T to a current Krell cx amp?