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Old 30th November 2007, 08:39 AM   #1931
AndrewT is offline AndrewT  Scotland
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Hi Harry,
the operating current for each of the FETs is half the CRD current which is specified @ 3mA. Leaving 1.5mA per device.
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Old 3rd December 2007, 03:42 AM   #1932
Harry3 is offline Harry3  Australia
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Thanks guys. When I went home and had a look at the circuit diagram it was soooooo obvious.

On another note - I measured a few of the resistors that I had soldered onto my board the previous night and could not believe that the meter reading was all over the place. It varied like it does when you put it across a cap. When I turned over the board I noticed that there was green corrosion on some of the gold tracks where the flux had been. I rang the guy who sold me the "silver" solder and he told me that they use a aggresive flux and I should clean the board with water after soldering. The resistor readings went back to normal after the wash.
I think I might go back to using the old solder with lead.
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Old 3rd December 2007, 04:10 AM   #1933
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Quote:
Originally posted by Harry3

I think I might go back to using the old solder with lead.
This will for sure make it sound better, but only if you use magic rocks and the $500 wooden knob...



http://cgi.ebay.com/4-Western-Electr...QQcmdZViewItem

Bob G.
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Old 3rd December 2007, 04:32 AM   #1934
Harry3 is offline Harry3  Australia
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I donít believe in any of that stuff!
I usually sacrifice a chicken before turning on a new amp.
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Old 3rd December 2007, 04:54 AM   #1935
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I'm just wondering, I've got a pair of KSA100 boards and I'd like to use them to build a KSA50 if possible. Should I just built it like a regular KSA100 but with reduced bias and a power supply suited to KSA50 rail voltages? Building a real KSA100 would not only bankrupt me but would be much more power than I need. In fact, I barely need more than 15 watts...I wonder why I bother...anyway I had planned to use five pairs of MJL21193/4, TO-3P per channel.
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Old 3rd December 2007, 06:14 AM   #1936
PWatts is offline PWatts  South Africa
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You cannot build a true KSA50 with these boards, the circuit design is different in quite a few key areas. You can halve the output transistors and halve the drivers and halve the total bias (or just halve the bias), but you would end up with a low-biased-KSA100 and not a KSA50. Whether a 50W-biased KSA100 would sound better than a true KSA50 is open for debate, any takers?
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Old 3rd December 2007, 08:58 AM   #1937
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I have been carefully examining the schematics of both amplifiers to the best of my non-engineer abilities and it seems reasonable to think a KSA-100 running at 50 watts per channel might be at least as good as a true KSA-50 clone. Unlike the KSA50 it has two sets of drivers, something that stood out to me. I wanted to use ten devices per channel, but this will mean one set of drivers is driving two pairs while the other drives three. Is this going to cause a problem? I need to use at least eight devices anyway because I am using plastic case transistors. I could not find any decent TO-3 heatsinks.

Also, I have asked this question in the KSA-50 thread several times before and rather frustratingly, never gotten an answer. I would like to use a capacitance multiplier power supply as described by Rod Elliott here. This will not only allow me to use a four-secondary(4x 39-0-39) transformer which I can get for a good price, but also I will have the only Krell clone to have anything other than an unregulated power supply. Not true regulation but it avoids a lot of regulator headaches. I read some posts in the KSA-50 thread where a CRC PS was being discussed. Some comments by AndrewT indicated that much of the KSA-50's 'slam' comes from large capacitor reserves. As the main capacitor banks are going to be isolated from the output by the capacitance multiplier the same way they would have been isolated by the resistors in the CRC supply, I'm a little worried that I'm going to lose this subjective 'slam' because I won't have more than 15,000uF per rail on the multiplier's output i.e. the first place the amplifier dips into for current reserve. Actually, Mr. Elliott says that exceeding 4700 uF on the multiplier supply's output is not recommended due to high charging currents, but I have to ask the dummy's question: What will be the consequences of using 15,000 uF caps on the power supply output? 4700 uF simply doesn't seem like enough reserve for this much iron. Will I need even more? Can I use more?. The supply is originally designed to power a JLH style Class A amp, but those don't push nearly the kind of power a KSA-50 does so I need to adapt it to its new environment.

thanks

Oh, and I updated the KSA-100 wiki to include a link to the KSA-50 wiki and since we didn't have one, there is now a Krell-o-Tracker for KSA-100 builds. Please post your information on the wiki!
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Old 3rd December 2007, 09:17 AM   #1938
PWatts is offline PWatts  South Africa
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The similarity between the 50 and the 100 is pretty much the input and its zener regulation, bias, driver and output topology, which is pretty basic and shared by many other amplifiers.

The rest is quite different with the mosfets, current regulators and cascaded predriver stage.
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Old 3rd December 2007, 10:26 AM   #1939
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Would there be any reason for a 50 watt KSA-100 clone to sound grossly inferior to a real KSA-50?

Mostly I am wondering about the power supply issue.

Thanks
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Old 3rd December 2007, 11:29 AM   #1940
AndrewT is offline AndrewT  Scotland
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Hi,
The Capacitance multiplier gets different reviews depending on who's listening and what type of amplifier is being supplied.

It would be a worthwhile experiment to listen to the KSA50 on simple and rCRC and CMult supplies to hear the differences.

The really big advantage of the multiplier applies to ClassA amps where significant mains ripple gets past the first stage capacitance and can give rise to hum on the output when signal levels are low.
Output impedance is not as low as a regulated supply and this may affect the way the KSA50 sounds.

If you were to separate the supplies for the voltage amp from the driver and output stage then rail hum problems disappear.


I think and may still try a dual driver version of the KSA50 using the output stage of the KSA100 as a reasonable way to go.

It would be possible, but wasteful, to convert the 100PCB to 50duty by linking across the omitted components.
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