spritzer Posted September 11, 2014 Report Posted September 11, 2014 Yeah, clueless people usually do.
purk Posted September 11, 2014 Report Posted September 11, 2014 That's great and a lovely job as well. Credit where credit is due. However you could have had the same physical layout and with some finesse with component values and the transistor used for the Vbe multiplier fixed up the blunder in the original design that has potential to compromise the output stage reliability. Just because Krell designed a potential hand grenade would it be fitting of a clone to leave it that way? I don't want a clone or a clone of a clone. I wouldn't use the circuit Krell used. We are waiting for you to do it and prototype it for us.
grawk Posted September 11, 2014 Report Posted September 11, 2014 yes, no one is stopping you from making a ksa5 derived amp. this wasn't that.
CraigBuckingham Posted September 13, 2014 Report Posted September 13, 2014 (edited) Ok Purk, no need to prototype, it's a just a matter of simple design. See below. Grawk, thank you, I never said I wanted to make a KSA5 derived amp. I actually said I wouldn't use that circuit. I do know what the word "clone" means, however thank you for clarifying what the thread was about. xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx In the original design, if the pot wiper goes open circuit for any reason, such as doing adjustment to the OP (output stage) bias, the OP will go to the maximum bias the Vbe multiplier circuit will allow. As you may know this is not at bad as a 3 terminal pot with wiper connected to the base. For this arrangement a wiper contact failure would result in the OP stage shorting the +ve and -ve rails to each other. I have seen this arrangement in some commercial equipment. At a minimum It generally results in destroyed OP stages. For the KSA5 an open wiper would cause about 500mA current through each OP transistor, however this may not be realised due to the power supply reserve to supply it. If the power supply can source the current it would result in almost 10 watts power dissipation in each OP device. The heatsinks used for the OP devices appear to be Aavid Thermalloy part number 513002B02500G with a thermal resitance of 13.40°C/W. Assuming 500mA bias and 20 volt rails the MJ15030 OP devices would be running junction temperatures 159°C above ambient. This level of heat exceed SOA and would destroy the OP transistors very quickly. Even if the power supply could only supply half the current, 250mA the OP devices would have junction temperatures 80°C above ambient. Whilst inside SOA at 25°C if the amp was in a hot environment it would be running near the limits of the OP device limits of SOA. Here is a modified Vbe multiplier that avoids the flaw in the original design for anyone that is interested. The modified circuit would result in an under biased condition for the OP stage for a wiper failure scenario. It only requires resistor value changes and possible a reverse mounted transistor depending on the type used. EDIT: Correction - mistake made on diagram text. I mistakenly though the base was centre pin. Looks as though the collector and emitter pins would need to be crossed with the MJE15031 PNP and it mounted in the convential way (not reversed). The Toshiba would need to be mounted in reverse and the collector and emitter leads crossed. EDIT2: Updated image text to correct error mentioned in previous edit. (GMT: 01:14 18-09-2014) Edited September 18, 2014 by CraigBuckingham
CraigBuckingham Posted September 13, 2014 Report Posted September 13, 2014 I would just like to add, I thought I mentioned it in my previous post. In my experience good quality multi-turn trimpots like the one used in the KSA5 are usually very reliable on the trimmer contact. Much more so than other types. However, I would always prefer a design that didn't take unnecessary risks.
muskyhuntr Posted October 3, 2014 Report Posted October 3, 2014 A bit more work done on my KSA5. Power supply boxed up and ready to go. I have started boxing up the amp board, but still have lots of work to go. A few pictures. Me
kevin gilmore Posted October 9, 2014 Author Report Posted October 9, 2014 http://gilmore.chem.northwestern.edu/ksa5-12.jpg finally putting it in a chassis
kevin gilmore Posted October 9, 2014 Author Report Posted October 9, 2014 (edited) The idea is to build a whole bunch of different amps in cases that I don't care if they get scratched and then maybe show up at a few meets so that people can hear this stuff and know that all of them blow away most if not all of the current batch of overpriced crap. ss dynalo balanced is done (two of them actually) ksa5 will be done soon. will do the squarewave next. ss dynahi after the squarewave. Pretty sure I can get it in one big hifi2000 box. no, I'm not going to travel with the SS1. It would take up the entire trunk. Edited October 9, 2014 by kevin gilmore
DefQon Posted October 11, 2014 Report Posted October 11, 2014 Would love to see some pics of the SS1, google returns no images besides a few impressions threads on hfi.
aardvark baguette Posted October 11, 2014 Report Posted October 11, 2014 The idea is to build a whole bunch of different amps in cases that I don't care if they get scratched and then maybe show up at a few meets so that people can hear this stuff and know that all of them blow away most if not all of the current batch of overpriced crap. ss dynalo balanced is done (two of them actually) ksa5 will be done soon. will do the squarewave next. ss dynahi after the squarewave. Pretty sure I can get it in one big hifi2000 box. no, I'm not going to travel with the SS1. It would take up the entire trunk. consider some Hello Kitty stickers to prove your point.
GrindingThud Posted October 11, 2014 Report Posted October 11, 2014 consider some Hello Kitty stickers to prove your point.
kevin gilmore Posted October 11, 2014 Author Report Posted October 11, 2014 after the rebuild. icarium posted many before pics. http://gilmore.chem.northwestern.edu/ss1-10.jpg http://gilmore.chem.northwestern.edu/ss1-9.jpg http://gilmore.chem.northwestern.edu/ss1-8.jpg but the thing really is insane for size and weight vs power. its my balanced squarewave boards, and a Chinese remote controlled step attenuator. its hard to tell what it originally was. But I think the following a balanced section with the digital remote controlled step attenuator a balanced section with a goldpoint rotary attenuator a balanced section with knobs on the side for adjusting the output stage bias, something for frequency, and some other unknown knob. there was also a crossfeed knob.
kevin gilmore Posted October 20, 2014 Author Report Posted October 20, 2014 http://gilmore.chem.northwestern.edu/ksa5-13.jpg done (except I'm out of #4-40 nuts, one missing on power supply)
Kerry Posted October 20, 2014 Report Posted October 20, 2014 Nice:) Too many projects in front of this for me. Maybe around Christmas time.
kevin gilmore Posted October 26, 2014 Author Report Posted October 26, 2014 ksa5 boxed up, 2 hours running, 109F at the top of the box.
G600 Posted October 30, 2014 Report Posted October 30, 2014 Will a pair of LSK489 fit in place of LSK389, and will there be an improvement ?
kevin gilmore Posted October 30, 2014 Author Report Posted October 30, 2014 will it fit, definitely, will it work, probably. since its a follower, i doubt there will be even the slightest change in sound. The amp is already very quiet, so might not make much of a difference.
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