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Old 28th March 2008, 08:50 PM   #1961
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The innards represent another dimension of system engineering level. Know what eee'e doing ?

PFC dept with lid off in lower rt'hd corner with large storage electy'tics. LH side AC in. rest upwards with sig in.

richj
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Old 28th March 2008, 09:58 PM   #1962
Jeb-D. is offline Jeb-D.  United States
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Very nice Rich. The THD and power is very impressive. I hope your design uses NFB, because if you got those THD numbers without it, that means I have to go back to school
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Old 29th March 2008, 07:49 AM   #1963
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Jeff, yup quite right.
The output transformer quality is vital in this design and a custom part was used extending to 15Hz and 50Khz at 250W. The 15Hz 1.4% 2nd harmonic criteria was used in determining low end core size.This took some time to optimise and was done by brain and calculator and alot of emails. The tricky part is to keep the upper frequency response up. What alot of folk donít realise is as the size goes up, the problem with the anode to UL tap leakage inductance gets progressively worse and to avoid ringing various snubber networks are used and snubber dissipation gets higher je the size. Yet circuit is stable with global 36dB nfb. Despite the lower working Z with parallel p-p, size is the biggest penalty with electrical parameters, more copper implies higher internal Cís and the conflict with leakage inductance grows. Facit, donít go for a montrous large design unless one really knows what one is up against.
20dB global nfb used. Used 10 ohm in each cath leg which reduces IM thd. By far the most influencial component in nulling thd is a pot in the driver stage anodes. (per Williamson) This tweak ensures optimum harmonic null.
Another issue with power. Most transformer manufacturers ignore insulating the screws through the transformer E&I laminations, the eddy currents from stray leakage inductance is quite high and with a case to case s/c or within the lid of a drop-through types acts as a part shorted turn. This will waste considerable power and make the screws (M6) to get quite hot.. The photo shows a fiber washer insulating the lid. This even applies to the output transformer. The difference between doing it and not doing it amounts to about 50W wastage on a 650W core !!
There is alot of detail which in other designs wouldnít be apparent. Fuses against fire are obvious. This requires sensing circuitry if e.g the neg bias fails. Mains transformer windings are all sep fused except 6.3V 35A winding which has thick enough wiring on a short to blow the mains fuse. The only way to ensure sensible AC line input fuse rating is to use an input soft-start ballast which will drop out & reset on a cycle per cycle basis on intermittant mains contact.
One soon realises the conjestion and lack of physical space gets used up. photo of pfc section. The copper 6.3V busbars can just be made out 15% down from top
richj
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Old 30th March 2008, 03:27 AM   #1964
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Default Karna Power Supply

My Lynn Olsen Karna power supply.

Electraprint power transformers, Hammond chokes, ASC oilers, and 6DE4 dampers.
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Old 30th March 2008, 03:29 AM   #1965
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It's kind of heavy.
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Old 30th March 2008, 03:42 AM   #1966
JoshK is offline JoshK  Canada
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Nice! I see you put both channel's PSU on one chassis. I thought about that. I started building my PSU chassis last weekend. I opted for seperate chassis and didn't put things so close together because I am not so sure I'd get the layout so well done that I could get away with such close quarters.
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Old 30th March 2008, 04:42 AM   #1967
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Very clean!

Is the wood Wengae (or Wenge) ?
Nice dense wood, good for musical instruments.

Are the caps painted or something more serious?

Does the dual PS feed a similar dual-amp-in-one chassis?

Love those amphenol connectors! Lately I've been favoring the Bendix style bayonets.

Cheers!
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Old 30th March 2008, 01:15 PM   #1968
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Very perceptive - Wenge it is. Careful with those slivers; they are brutally painful.

Caps are just the typical ASC motor runs, painted black. The amps proper will have their own local sets of caps as well.

I plan on monoblocks for the amplifiers for an overall three chassis design. This will give me plenty of room to provide magnetic spacing between the filament transformers and audio transformers. For the record, the reason for two IEC inlets is NOT for the two power supplies. One inlet feeds both power supplies in complete. The other inlet is dedicated for the DHT filaments, and will be supplied from a regulated source to variac. That way, I can play around with the voltage on the filaments easily. I also like the idea of the high common mode and differential mode filtering the Sola ferroresonant transformers give me. From what I understand, Lynn is preferential to a filament supply somewhere around 109V.

I'll post a shot of the guts when ready. Just a few more solders to make.
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Old 30th March 2008, 08:38 PM   #1969
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Guts.

Just have to land the copper bus to the Amphenol, and she's done.
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Old 31st March 2008, 09:16 AM   #1970
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Quote:
Originally posted by zigzagflux
Guts.

Just have to land the copper bus to the Amphenol, and she's done.

Can't make it out...youv'e gotton away with a part empty box ?

richj
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