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Old 16th March 2013, 05:33 PM   #8461
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Hey guys I have been reading up on all of these. The Krell I showed is the only populated board version. No trans for any. But antek can supply the simpler ones for the hiraga's. There is also a hi end Marantz clone kit on offer.

For bass the most promising one after contacting jim's audio and asking. He suggested class ab. There is a few different nap 140 kits. This one below at a guess seems the best kit going on parts quality alone. Sanken or Toshiba output trans can be optioned? any advice of the best choice there?

What appeals to me is that it can make 60 or 80 watts from a 24 volt single rail. Its a hi feedback amp so good damping factor. And I have some BIG sla's I can run them off. Naims are known for there rythme. I am currently building a little 23$ naim preamp kit just for fun as it turned out.again battery feed.

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As for the krell Since no one has any knowledge of this particular kit. I am to scared yet. Or as they say a wise man knows his own limitations or some thing like that. I am definitely building a Hiraga. not sure if it will be the 8 or the 30 yet. I have a pair of 18 0 18 trans which are not quiet suitable for either amp 12v for the 8 watt and 35v for the 30 watt. But the Hiraga will be all out fullrange quality amp. oil signal caps power supply chokes etc. Thanks for you help guys.

Last edited by fatbattery; 16th March 2013 at 05:36 PM. Reason: again spelling:|
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Old 18th March 2013, 06:31 AM   #8462
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Ok I bought two. The cheapest guys are these. I have dealt with them before. He recons they are tested.


YJ KSA50 Class A Mono Amplifier Board New | eBay
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Old 18th March 2013, 09:53 AM   #8463
AndrewT is offline AndrewT  Scotland
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Hi Fat,
A pair of 1943/5200 biased to 1.9A shared between them is going to run mighty hot.
Probably too hot for these 150W plastic packaged devices.
Try starting out with a device bias of 100mA and test the amplifier thoroughly.
Increase the bias in 100mA increments after satisfactory 24hrs at the previous bias level.

I suspect you will be OK upto ~500mA device bias, for a total bias of 1A.
This will give ~2Apk of ClassA current into your load.
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Old 22nd March 2013, 12:09 PM   #8464
neychi is offline neychi  Croatia
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“Nothing about the Krell KSA-50 sounds “vintage” in any way” by Ken Kessler – TONEAudio magazine – december 2012 | Dé Durob Audio blog – Le Blog de Durob Audio
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Old 2nd April 2013, 09:19 PM   #8465
henryve is offline henryve  South Africa
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I've been running my KSA50 now for a while in the nude whilst I am finishing my case. I have been checking the temps regularly and it may seem that I have more heatsink than I bargained for. I am currently running my bias at 325mV per Re. My Re = 0R5. Since I have 3 pairs it gives my Iq = 650mA per pair for a total Iq of 1.95A.

I am measuring temps of 45 degrees C after 2 hours on my sinks at Ta = 22 degrees C. Shall I increase my bias? And to what Iq? As stated previously I am using the MJL1302A/MJL3281A pairs in the TO264 package which is a 200W device. My rail voltages under load is 38.4V. I suspect that I have another 5 degrees C to play with here. I am staring at the datasheets but really have no idea which curve to use as guidance.
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Old 2nd April 2013, 10:20 PM   #8466
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Hi Henryve,

Since 2 x Iq is peak Class A current, you can presently drive a (~36 / ~4) ohm load -> ~9 ohm to full class A power. if you have a great power supply and the rail voltage doesn't drop as the idle current goes up you can decide when you have enough based on your chosen speakers impedance...I don't think there is much to be gained from more bias than can be used in your driving the speakers (in Class A), but I'm sure many would think there is no such thing as too much.

...and don't forget to allow for whatever ambient temperature extremes apply in your locale.


Stuart
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Old 4th April 2013, 02:40 PM   #8467
alibear is offline alibear  United Kingdom
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Hi all, glad to see the thread is still running.
I am still playing with the KSA and I am trying to use a seperate supply for the front end up to but not including the drivers. I am using Jans PCB's.
When I use just one supply for the entire channel all is good with the offset showing just a few mV at switch on that falls within a couple of seconds to zero, and when the supply is turned off there is a small rise and then it falls again.
When I use the second supply for the front end the offset at switch on starts at about 500mV and rapidly drops to zero but on switch off the offset hits about 1.9V and takes a very long time to drop to say below 200mV.
The supplies I am using are just rectifier and capacitors, not regulated.
I have tried putting bleed resistors (4.7k) across the caps but not much difference. By the way i am using +-42V for supply voltage
Any suggestions, what am I doing wrong.
Thanks
Alan
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Old 4th April 2013, 02:54 PM   #8468
henryve is offline henryve  South Africa
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Which caps are you using on your secondary supply for the front-end? I am using 10 000uF 63V Epcos Sikorels and don't see any of these types of issues. I am using the PM boards BTW.
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Old 4th April 2013, 07:49 PM   #8469
alibear is offline alibear  United Kingdom
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Hi Henry ve, thanks for your reply. At the moment I am only experimenting with using a seperate supply for the front end so it consists of a 30-0-30 transformer, two bridge rectifiers and 2 2000uF caps. If it makes an audable difference powering the front end seperatly then I will use a regulated supply.
By the way I forgot to mention that input is grounded and output has no load on it.
I have not yet tried it with music playing, but after the initial turn on period the offset stays very stable and once it has reached operating temp. the bias is also stable.
On a different subject I thought I read a post from Stuart Easson about emiter resistor values and I think he advises that if extra output pairs are used the value should be chosen to equal the original Krell value of 0.5 ohm.eg. the more output pairs the higher the Re should be. Unfortunately I have not been able to find the post again, so I might have dreamt it. Do you know if too many output pairs are detremental to sound quality. The reason I ask is that my heatsinks are drilled for six pairs of TO3's per channel complete overkill I know, but it would fill up all the holes.
Thanks
Alan
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Old 4th April 2013, 08:21 PM   #8470
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Hi Alan,

You did not dream it, and more output transistors with higher Re is good for keeping the gain of the output stage high and the sharing closer to equal.

Your summary is quite correct, if you have twice as many output transistors I'd recommend Re be twice as large, ie the paralleled value of all the Re should match that of the original you are cloning.

HTH

Stuart
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