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Old 18th November 2012, 01:30 AM   #51
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Quote:
Originally Posted by kevin gilmore View Post
2 stacked for balanced much more fun for HIFIMAN HE6 headphones
Does the KSA5 use fully regulated power supplies? The pictures show enough parts for full regulation.

For headphones, has the brain trust agreed upon any favorable reasons for using a balanced amp topology which puts the headspeaker between two output stages, and hence not ground referenced?
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Old 18th November 2012, 06:30 AM   #52
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any thread over at the other place for this mate? i'm interested in the bridged version.

Quote:
Originally Posted by kevin gilmore View Post
Figured i would add a bit on this. As a speaker amp, i did not think it
sounded very good. But as a headphone amp it is absolutely fantastic.
Just for fun, and because after years of trying to buy one, i'm finally doing
a diy version.

Real reverse engineered schematic of the amplifier
http://gilmore.chem.northwestern.edu/ksa5.pdf

virtually identical layout klone board single channel with
much more ground plane.
http://gilmore.chem.northwestern.edu/ksa5.jpg

2 stacked for balanced much more fun for HIFIMAN HE6 headphones
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Old 18th November 2012, 05:49 PM   #53
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There is a thread on Head-case.
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Old 19th November 2012, 08:05 AM   #54
qusp is offline qusp  Australia
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thanks Spritzer, thought there might be, i'm used to calling it 'the other place' when on head-fi, force of habit. really great diy section that over there, much better than head-fi, far fewer nonsense tweaks and ********, but I try to stay away a bit since I have enough 'problems' as it is without adding more stuff I want to build....

nattonrice is a terrible influence, we tend to be a little competitive =) cant beat that man on casework though! hell, I cant beat anyone on casework
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Old 29th November 2012, 12:03 PM   #55
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there are 2 different power supplies

original power supply
http://gilmore.chem.northwestern.edu/ksa5psschemold.pdf

newer supply
http://gilmore.chem.northwestern.edu/ksa5psschem.pdf

we are doing the new power supply board.
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Old 29th November 2012, 01:31 PM   #56
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Hi Kevin,

Voltage reference (12V zener diode) has current bias of ~33mA...way to high. For low noise and low output impedance 1/3 (11mA) is sufficient. Opamp output sits at ~+/-19V7, not a single opamp would like it ... series 12V zener (or 6 x green LEDs) and bypass capacitor at opamp output is an efficient solution.

And one more thing (colleagues of mine with a lot more experience warned me abot that) ... although it does not seem so at first glance, the error amplifier - opamp operates open loop, resistor divider from regulator output to ground does not close the feedback loop... they only polarizes negative input opamp to the desired voltage.
One will need to close the feedback loop from opamp output (or one of the emitters in darlington pass transistors) to negative opamp input.

Otherwise, error opamp will work open loop and whole system will not be unconditionally stable (it can become sporadically unstable), and will largely depend on of the parasitic components that sees opamp negative input (stray capacitance, inductance etc.)

Edit: There aro no AC bypass caps over R8/R9 resistors...also RCRC filter in front of regulator would be nice.
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Last edited by aparatusonitus; 29th November 2012 at 01:39 PM.
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Old 3rd December 2012, 01:13 AM   #57
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correction, the voltage reference is a lm4040-2.5 which results in
16ma.

I'm pretty sure the 2 diode drops of the darlingtons close the loop
and the schematic as drawn matches the pictures of the krell power
supply exactly.

op27 with the supplies as drawn can work up to a 44v pre-regulated voltage.

Last edited by kevin gilmore; 3rd December 2012 at 01:17 AM.
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Old 5th December 2012, 02:30 AM   #58
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All,
I just joined this site today, which explains why I haven't commented earlier on this thread. That, and of course the NDA I signed in order to get and keep my job at Krell.
To answer a few questions that would be easy for someone to figure out if they had the actual unit, yes, it uses 2 pairs of MJF15030-31 output devices per channel. The supply rails were fully regulated (outboard supply with cascaded Zener regulators). The servo op amps were SSM2131s (now obsolete) or OP27s, either of which could live with +/-20~21V rails. (Can't remember which, though.)
The unit did legitimately make more than 5 watts into 8 ohms, but its output impedance was higher than I'd want for driving a complex loudspeaker load. That said, back in the day, Joe Sammut (now of Pass Labs, along with Wayne and, of course, Nelson--a nicer bunch of guys you will not meet) had a KSA-5 at home driving some horns, and he told me it was his favorite Krell amp at the time.
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Old 6th December 2012, 05:30 PM   #59
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Old 6th December 2012, 06:06 PM   #60
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I just joined this site today
The more Krell guys, the merrier.
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Last edited by jacco vermeulen; 6th December 2012 at 06:09 PM.
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