The name's Dallas and I'm a multi-disciplined engineer in Denver, Colorado. I can handle a solder iron without killing surface mounted bits, build most things out of wood, and I beat/bend/cut red hot iron into hinges and such for sport and to annoy my neighbors. Electronics isn't a total mystery but kits are the way to go for me. I actually learn more and get frustrated less.
1) What is the safe limit on supply capacitance when considering the equipment only?
2) Do coupling capacitors below 0.47uF really need to be matched for human ears even when there is significant low-end signal as well as driver support?
While daydreaming on the final far-future enclosure design for a near-future build, it occurred to me that there could be such a thing as too much supply capacitance. Could this be true?
(By the way, Bob, I'm going to be ordering a ST-70 kit with EL34s and timing relay from you tomorrow. Yeah, that kind of near future build.)
The reason this occurred to me is that I am staring at a rough couple hundred variable frequency drives - some are years old and others new - that are available for me to harvest parts from. I could gather six huge electrolytics in less than fifteen minutes. And, although a six-pack of high-voltage 5700uFs would be visually appealing to the geek in me, I'm not so sure I would want them all collapsing at once into my near-future rig. (Bleed-offs would help.) What would be the point at which there is no longer a benefit in an increased volume of potential? To be clear, I'm not charging the phasor banks on the Enterprise.
And now, a few application notes:
This amp will be driving a pair of (properly refurbished) McIntosh ML-1Cs. I have already finished a did-it-myself version of the MQ-102 (infringement?) to go between a GoodWill-found-and-repaired Rotel 1068 and the future ST-70. (That is, there will be a +13 or perhaps +17dB boost at the far bottom end <200Hz to compensate for the stunningly overdamped woofer.) The end-game is an ST-70-based integrated amplifier with auxillary inputs to an S/PDIF & USB DAC (thanks, AMB); properly scaled mA meter with output [TUBE BIAS] circuit selector switch for biasing; and retro-fitted and re-scaled wattmeters (from an old realistic APM-200 watt meter). It will all be stuffed inside a yet-to-be designed (easy-to-service?) hardwood case paneled with easy-to-read machine etched stainless plates. (Hey, dream big, right?)
That written, a six-pack of beer can -sized polished aluminum capacitors would fit right in... somewhere... I'm certain of it. Unless, I could blow up my living room turning it off.
'Big'(-ish) DC filter capacitors:
This morning I de-soldered four 0.47uF PIO West-Caps from a board and measured them out. They range from 0.465uF to 0.502uF. Am I correct in assuming that these would all make fine coupling capacitors even though their specific values are not 'matched'? It seems the knee frequency would be beyond even the 16-ish Hz my chest could feel at a foot from the ML-1C's woofer at +17dB low gain and pushing an ear-crushing 20watts? (89dB/w/m speakers.)
p.s. thoughts: maybe a pre-amped +17dB at that low of an end might be an issue but I don't know quite yet why... seriously. Time to visit Roger Russel's website for a bit... 35w/channel? I don't really crank the volume, though. 17'x19' room with 8' ceiling, brick/windows/bookshelves on three sides, concrete floor with huge rug and basic furniture, speakers 10' apart centered on the wide side and 3' high stands... anyone else ever get pigeonholed as AADD? Time to bust out the SPL meter and the Adcom 555ii for testing. Oh, and I better put the APM-200 back together; one needs proper data...
Last edited by Dallas on Sun May 03, 2015 5:22 pm; edited 1 time in total (Reason for editing : Clarified circuit for DC mA meter)