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Old 30th October 2004, 10:53 PM   #11
Mr Evil is offline Mr Evil  United Kingdom
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Default Re: PS rejection ratio?

Quote:
Originally posted by Stuart Easson
Hi,

This may be a silly question/statement but...

Isn't it a feature of most 'complex' SS amps that they are quite immune to 'noise' and amplitude changes on the power supply lines?

If you have a PSU rejection ratio thats high enough, can you just change the voltage, leaving the current more or less alone, at it's presumably high level, and not 'hear' anything on the output?

Stuart
That sounds like class G... or maybe class H, they're similar. Good idea, but given the extra complexity in the PSU it seems like it would be better to go to class D instead.
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Old 30th October 2004, 11:17 PM   #12
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Default sorta, maybe, nah, not really...

I think the 'new' PSU is less complex, and essentially more saleable than redesigning a known good topology to a whole new output class. Does anyone know if Krell have done anything but AB amps? my guess is they wouldn't have the same saleability without the heft and huge demeanor...

For most purposes the amp itself doesnt change much here. You have a couple of comparators switching some big solid state devices (fets?), the rails should be already stable, and hopefully you are gonna get it done quickly, preferably before any clip occurs. But if you get it in one or two cycles, I think most people are not gonna notice, expecially if you keep it high for a few seconds or even minutes after. I don't know for certain, but conventional wisdom would suggest low bass being the most likely culprit for inducing clipping, so it's possible you would have a millisec or two after detecting the threshold before the waveform is chopped...

I havent tried it, but it would be interesting to use the clip indicator on, say, an Adcom to drive a servo to increase a variac a volt at a time, and a timer to decrease it, I've only ever done it by hand, never had any bad behavior thus far...anyone wanna make me a servo'ed variac...listening tests anyone?

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Old 31st October 2004, 01:35 AM   #13
markp is offline markp  United States
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It is likely that any audible clip would be masked by the volume level change and it would only happen once at the begining of each loud passage as the supply would stay high as long as the signal was above the threshold and not drop back for a few seconds in anticipation of more peaks.
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Old 31st October 2004, 04:37 AM   #14
jwb is offline jwb  United States
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Quote:
Originally posted by highbias

Does anyone have a KSA 80 schematic they can send me or post here????
Mark
Yep. I posted them last week under "Reverse Engineering Krell KMA 160". The KSA-80 is just a KMA-160 with two channels instead of one. I'm converting two KMA-160s into KSA-80. Although there are a few errors in my drawings, I think you will figure it out and I'll post corrections soon enough.
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Old 31st October 2004, 02:24 PM   #15
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Sorry to say, or happy - depending upon your preferences - that I have yet to hear a Krell that I wanted to own. Which is my bottom line internal reference point for my personal preferences.

Having said that, my experience with the Krells is that the best of the lot that I have heard was the original "Reference" amps. I wonder if anyone knows what (if anything) they did there that made them any different than the amps of that day (I think the KSA-250 era).

Perhaps it was just taking a 250 setting the bias for real class A
and making it mono? Bridged?

ANYONE GOT A SCHEMATIC FOR THEM??

Anyhow, the switching of the rails also requires adjusting of the bias point, so that ur devices are still "1/2 way" on...

The idea of slamming to another rail voltage is *essentially* what Bob Carver did in his amps - but he (cleverly) used a little low power class A amp floating on the switched rails to be responsible for integrating the switch transients and for providing the distortion reduction part and the low level modulation...

made for a lightweight high power package - not particularly good to listen to, but light and high power...

Anyhow, my silly view is that the best thing to do is to *reduce* bias with increased signal, not the other way around...

Preventing a device from turning off is another topic for another discussion...

:- )

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Old 31st October 2004, 03:43 PM   #16
anatech is offline anatech  Canada
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Hi Stuart, Dave
The classic Carver amps use multiple supply voltages and switch them in to the output stage as required. If the switching is fast enough, they pass through the outputs and put a "glitch" on the output waveform. This is very easy to see on a 'scope. Simpler designs exist like NAD and others. The Carver amps also pre-regulate the supplies. The AC is triac phase controlled. The power transformers do not like a sine wave and will draw excessive current. If the triac shorts, or is shorted by technician, the supplies will rise to excessive levels. Boom.

The Carver Lightstar uses a different approach. The mains are running around + / - 125VDC. These are pulse width modulated to deliver voltages that range from + / - 13V ish to "wide open".

The detection speed is such that the off transision is delayed a few mS. This works for full range or bass frequencies. If running mids or highs only, the supplies stay "locked up" and the amp may suffer from thermal runaway. Boom. That's why, if you have Carver amps, use them for full range or bass only.
-Chris
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Old 31st October 2004, 05:34 PM   #17
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Quote:
Originally posted by bear
Sorry to say, or happy - depending upon your preferences - that I have yet to hear a Krell that I wanted to own. ...

Having said that, my experience with the Krells is that the best of the lot that I have heard was the original "Reference" amps. I wonder if anyone knows what (if anything) they did there that made them any different than the amps of that day (I think the KSA-250 era).

Perhaps it was just taking a 250 setting the bias for real class A
and making it mono? Bridged?

ANYONE GOT A SCHEMATIC FOR THEM??

The idea of slamming to another rail voltage is *essentially* what Bob Carver did in his amps -

made for a lightweight high power package - not particularly good to listen to, but light and high power...

_-_-bear

I really liked the KSA-250 and the reference standard amps! I would like to listen to anything better!

the MDA-500 was a KSA-250 bridged mono...

I am looking for a schematic as well and have yet to find one.

the carvers are hard to listen too!!


Quote:
Originally posted by anatech

The classic Carver amps use multiple supply voltages and switch them in to the output stage as required. If the switching is fast enough, they pass through the outputs and put a "glitch" on the output waveform. This is very easy to see on a 'scope. Simpler designs exist like NAD and others. -Chris
The Carvers are fatiguing, you can hear the amp get harsh at some volume levels. thats the switching going on. its subtle but your ears get tired!


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Old 31st October 2004, 07:39 PM   #18
anatech is offline anatech  Canada
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Hi Zero Cool,
I agree with you that the Carvers were fatiguing to listen to. I think they were more into high power in a light package. They were generally reliable in normal situations.

Having said that, I can't listen to early Brystons (like the 4B) or Krell. Not my kind of sound. When you get into a high power design, keeping it sounding good is very tricky indeed.
-Chris
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Old 31st October 2004, 09:37 PM   #19
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zero cool

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Old 1st November 2004, 07:24 PM   #20
K-amps is offline K-amps  United States
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Quote:
Originally posted by Mike Gergen
zero cool

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I own a KSA-250 and recently came to know of the MDA-500 trick, i.e. changing the KSA-250 (250wpc) into an MDA-500 (500w into 1 channel) for free at Krell.

Now what I'd like to know is apart from rewiring the inputs so that one channel gets the differential signal and taking the outputs from the hot sides of both channel (as it in the case of any bridged amp... ) how come krell gets 500 watts from it and not 1000 watts? (because 250 X4= 1000)

In order to get 500 watts, they'd need to reduce the rails by a factor of 1.414x which means they cannot re-wire the Toriod in series either because that would give them a 2X reduction in rails not 1.414.)

Unless the pre-order and install a Toroid with multiple windings, I do not know how they can do it for free....
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