thanks for the heads up Mark. Good to know, since i haven't ordered yet. I have had to spread out the cost of tis project because my wife seems to think that her entire wardrobe, including shoes, needed to be replaced when I took a new job last May. She's done her best to keep me from buying parts for months. So, you really think the the rail would be too low at 35v, huh? Well, the cost for 30-0-30 is so little more that it doesnt matter, and as discussed way back in the thread, I can always take a bit of the winding off to lower the rail. But it seems that nobody has had probelmes using the higher rails, I just thought that it increased dissipation quite a bit.
Googler,
It will be a tad bit low with 120 volt AC input. I am sure because I have two of the 25-0-25 400 VA trannies here powering my KSA-50. I get +/-34.5 volts under idle load which is 400 mv across the .68 ohm resistsors. These are fine for 4-8 ohm soeakers but they'll crash at lower impedances... which the amp is capable of provided there is enough power supply. In LuckyLindys amp we used Anatek's next size toroid up which I believe was 28-0-28 volts. I am having LuckyLindy confirm that for me tonight. With that tranny and 120 volts you will get +/- 40 volt rails under idle load.
Mark
It will be a tad bit low with 120 volt AC input. I am sure because I have two of the 25-0-25 400 VA trannies here powering my KSA-50. I get +/-34.5 volts under idle load which is 400 mv across the .68 ohm resistsors. These are fine for 4-8 ohm soeakers but they'll crash at lower impedances... which the amp is capable of provided there is enough power supply. In LuckyLindys amp we used Anatek's next size toroid up which I believe was 28-0-28 volts. I am having LuckyLindy confirm that for me tonight. With that tranny and 120 volts you will get +/- 40 volt rails under idle load.
Mark
Hey Mark-
Pardon my ignorance, but you mentioned
"These are fine for 4-8 ohm soeakers but they'll crash at lower impedances..."
Why would it crash and not just deliver more current if your transformer and parts (transistors and such) can handle it?
Grant it 200 watts Class A into 2 Ohms contineous would be quite painfull in domestic use.
Pardon my ignorance, but you mentioned
"These are fine for 4-8 ohm soeakers but they'll crash at lower impedances..."
Why would it crash and not just deliver more current if your transformer and parts (transistors and such) can handle it?
Grant it 200 watts Class A into 2 Ohms contineous would be quite painfull in domestic use.
The two Anatek's were a pair of 500 VA 31-0-31V
transformers.
Price was $118 shipped ground from East Coast to West, last September, 2005
Working very well.
Lyndon
Salt Lake City
Alta Ski Base: 118"
More snow and powder expected this weekend!
Sundance Film Festival!
We got it on in the West, baby!!!
transformers.
Price was $118 shipped ground from East Coast to West, last September, 2005
Working very well.
Lyndon
Salt Lake City
Alta Ski Base: 118"
More snow and powder expected this weekend!
Sundance Film Festival!
We got it on in the West, baby!!!
Thanks for posting that info from your transformers Lyndon!
Yes, as long as your power supply can do it the amp also can..... I have found the 25-0-25 400 VA trannies to be very marginal in performance. Going to the 31-0-31 provided that extra bit of performance margin one would expect from a Krell. Also as long as +/- 40 volt rails is safe why not extract the last bit of perfromance one can.
Mark
Yes, as long as your power supply can do it the amp also can..... I have found the 25-0-25 400 VA trannies to be very marginal in performance. Going to the 31-0-31 provided that extra bit of performance margin one would expect from a Krell. Also as long as +/- 40 volt rails is safe why not extract the last bit of perfromance one can.
Mark
Hi,
for ClassAB the norm is about 1.5VA times the output power into your normal load impedance, i.e. 28Vpk=20Vac into 8r = 50Watts.
This needs about 75VA and 2*25Vac transformer. There is much opinion on the 1.5VA times figure and most ClassAB amps will work either side of this ratio.
For ClassA the norm is 6VA times the output power etc. for the same example as above 28Vpk into 4ohms =100Watts and needs about 600VA and 2*25Vac transformer. It also needs the smoothing capacitance factored up by about the same ratio.
Now that maybe explains some of the increased cost of ClassA cf. ClassAB
A 400VA transformer will not break/blow up/overheat on a 4ohm load but it would not be optimal for this low load. I know that the KSA50 and the Klone are very tolerant of a wide spread of load impedance, but I would suggest that 400VA is optimised for either 8ohm or 6 to 8ohm speakers. It will drive 4 to 8ohm speakers adequately but you may be able to obtain slightly improved performance by re-optimising some of the amplifier components and by the time you apply 4ohm speakers then I would certainly recommend re-optimising components and/or component numbers to suit. Your transformer selection is just the first stage of this process.
for ClassAB the norm is about 1.5VA times the output power into your normal load impedance, i.e. 28Vpk=20Vac into 8r = 50Watts.
This needs about 75VA and 2*25Vac transformer. There is much opinion on the 1.5VA times figure and most ClassAB amps will work either side of this ratio.
For ClassA the norm is 6VA times the output power etc. for the same example as above 28Vpk into 4ohms =100Watts and needs about 600VA and 2*25Vac transformer. It also needs the smoothing capacitance factored up by about the same ratio.
Now that maybe explains some of the increased cost of ClassA cf. ClassAB
A 400VA transformer will not break/blow up/overheat on a 4ohm load but it would not be optimal for this low load. I know that the KSA50 and the Klone are very tolerant of a wide spread of load impedance, but I would suggest that 400VA is optimised for either 8ohm or 6 to 8ohm speakers. It will drive 4 to 8ohm speakers adequately but you may be able to obtain slightly improved performance by re-optimising some of the amplifier components and by the time you apply 4ohm speakers then I would certainly recommend re-optimising components and/or component numbers to suit. Your transformer selection is just the first stage of this process.
AndrewT said:
From the bare minimum in class AB to a generous powersupply in class A, hardly objective !
Good class AB amplifiers have a much bigger transformer, and really good class A amplifiers have been built with much smaller ones. One of those used to be on permanent exhibit in the Museum of Modern Art in New York.
I can name a few 100 watts in 8 Ohms class AB amplifiers that have 1.5kW transformers.
My rule of thumb: if you can afford it, take the biggest one you can get. (for women, check the bra size)
googler said:
With an idle dissipation of 136 watts plus about 14 watts in other losses (nice round number), you are looking at about 150 watts of dissipation and at 8 ohms you will be within this figure.
The 400va might let you pump out about 150 watts into 3 ohms or so with those rails and overall dissipation might peak at 250-300 watts or so, So overall you are still below the 400va rating of the trafo.
If you "had" to strech it, I suspect your 400va would work just fine even working both channels as Trafo's usually can deliver 2x the power on short term basis.
So unless you plan to run 3ohm sinewaves at clipping for extended periods of time, you might be ok.
Having said that, I would use 2 of those, i.e. 1 per cannel, but thats me and Jacco!
Jacco, tell me that you were not thinking about Gengis's avatar when you wrote that last sentence.
It's all i can think about. 
Main benefit of big transformers is the ability to keep voltage level up when the impedance drops.
That used to be the single territory of US amplifiers, output voltages as flat as a pancake throughout the impedance and phase plain thanks to giant toroid transformers.
Smaller transformers will deliver the VAs they are rated for and even much more for short periods, but the voltage will be sagging as the output increases.
Whether that is of importance is questionable, my electrostats are amplifier killers and 20 volts continuous is all they need. I've heard those on a KSA50 a century ago when i could not afford either of them, i gathered the KSA50 has 400VA transformers, did not sound like they were out of gas to me.
Main benefit of big transformers is the ability to keep voltage level up when the impedance drops.
That used to be the single territory of US amplifiers, output voltages as flat as a pancake throughout the impedance and phase plain thanks to giant toroid transformers.
Smaller transformers will deliver the VAs they are rated for and even much more for short periods, but the voltage will be sagging as the output increases.
Whether that is of importance is questionable, my electrostats are amplifier killers and 20 volts continuous is all they need. I've heard those on a KSA50 a century ago when i could not afford either of them, i gathered the KSA50 has 400VA transformers, did not sound like they were out of gas to me.
jacco vermeulen said:Pavel,
we all know you are a heavyweight.
All of us DIY jokers have to compensate one salami for the other, it's even worse during the winter season.
Just a thought, i drive a huge car.
Well the more commonly accepted connotation of the "Salami Phenomenon" is guys driving the Z3... and thats a small car! I guess you are ok in your big Salami. (even after you factor in water shrinkage.)
kmj said:Page 3?? come on
How's the parts GB going?
I have sent out US kits and I am waiting for them to check through them to ensure they are correct before I send any out of country.
Has anyone rx'ed their kits yet, and did they check through them for accuracy?
EDIT:
I have the rest packed and addressed sitting on my kitchen table awaiting the green light...