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Post by jimwilliams on Oct 13, 2013 12:47:38 GMT -6
You need a decent bench fitted with the basic tools. A meter and scope are necessary. A graphical analyzer in either hardware or software is also needed to test and "verify". You can use a soundcard and freeware or spend $15,000 on a new Audio Precision 2600 rig. Look for cheap, accessable test gear and tools at: www.mcmelectronics.comIt's not much fun working on your gear if you can't figure out how to fix your mistakes.
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Post by jimwilliams on Oct 13, 2013 12:40:26 GMT -6
I just build my own here. I have a couple of racks with them. I use a quality opamp, a CFA from National, the LME49713. I used Harris current buffers, the 5002's. Those are very linear, highly regarded and add 500 ma output current. No caps are used in the system, all direct coupled, no phase shift, zero degrees from 20~20k hz, THD is at .0006%, IMD is at .0002%. Slew rate is 2000v/us. Bandwidth is approximatly 30 mhz. Noise sits at around -110 dbu, not too bad. I used a quality power supply design and huge caps everywhere on the power supplies.
It has enough power to hurt tracking drummers. Usually I start off at around 2o'clock and wait....wait....wait... for the drummer to feebly request, "is it possible to turn the cans down"?
It's so damn clean some don't ask, they never heard their drums sound so open and clear. It does have a useful effect, great drummers start doing "dances" on the cymbals and stuff, all excited by these new sounds they're hearing when they play.
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Post by jimwilliams on Oct 13, 2013 12:27:31 GMT -6
The "Silent Knight" is based on THAT Chips throughout, THAT1512 pre. The National Opamp doesn't color, too. So it will be just quiet, crisp, clean and transparent gain. Heard those chips already when they came up. BR Martin You can also order it with Audio Upgrades PIP modules installed in place of the mic pre chips. That offers lower noise, faster slew rate and greater bandwidth, along with .0002% IMD and .0006% THD.
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Post by jimwilliams on Sept 24, 2013 9:18:00 GMT -6
You still have all your old favorites to listen to. I have so much here I really don't need to find "new music". It's far more fun making crappy new music than it is to listen to it.
The catalogs are your friends. When the new batch start making music back up to that level I might give it a listen, otherwise I have over a thousand CD's to keep me entertained.
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Post by jimwilliams on Sept 23, 2013 17:50:38 GMT -6
Parts Express has low cost sub kits with pre-cut MDF cabs. 8, 10, 12 and 15". I would do the 15" and use their dual voice coil 15" sub. I use a dual voice coil 15" sub and love it with my 8" JBL's. Got to get my 25 hz's.
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Post by jimwilliams on Sept 23, 2013 17:46:07 GMT -6
Jack an oscillator into the front end and trace down the circuit with a scope probe. Where the signal stops or goes off is where the problem lies...
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Post by jimwilliams on Aug 9, 2013 9:35:52 GMT -6
Savor the moment. Take your time.
Stop to smell the roses.
There is plenty of time if you don't make a mistake rushing.
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Post by jimwilliams on Aug 4, 2013 12:12:48 GMT -6
Without a boatfull of cash to get paid for it, ITB mixing/tracking can be 'non-inspiring'. For you that do that, I have a couple of questions:
1. Do you ever listen to music after a long day "at the office"? 2. Do you ever take the old lady out for music or dancing, after a long day "at the office"? 3. Do you prefer to come home and bury your head in a pillow?
I had a couple of PC's that gave me headaches. Solved that out in the desert with a few 5.56 NATO rounds.
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Post by jimwilliams on Aug 4, 2013 12:03:55 GMT -6
How about some real info on it? What did they do, what converter chips are used, the usual stuff "under the hood".
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Post by jimwilliams on Aug 4, 2013 11:57:51 GMT -6
Better hope Bob Filner doesn't sign up. Not much chance considering how few women there are here.
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Post by jimwilliams on Aug 1, 2013 10:12:30 GMT -6
I still do output biasing on selected opamps stages. Using a current source to 'turn off' one of the complimentry output devices does force the class A/B output stage into class A operation, up to about +6 dbu. Of course, the opamp selected must be able to drive that load as well as the signal load combined. Don't try this with a TL072 opamp. Tests on the Audio Precision analyzer show no increase in any form of THD with this technique and a capable device. Most folks like the effect, especially in critical stages like stereo sum opamps. Yes, the power supply must be capable but adding a couple of ma to the opamp isn't going to overheat anything nor burn up a signal trace. Older fast opamps had various THD problems. Those have been resolved with newer devices. Symetrical CAD design has lowered DC and AC errors to almost unmeasurable THD, some as low as -154dbu. Open loop gain is now around 90 db at 10k hz further lowering THD, especially in the upper octaves where older opamps ran out of loop gain. That is 50 db more OLG than an 072 opamp as an example. Any audio person with some chops and a wee bit of curiosity ought to check some of this stuff out, these arn't "your father's opamps". If you don't have the funds, get them sent to your door for free. Sign up at www.ti.comand www.analog.comand get some free opamps and try them out. You may be in for a suprize.
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Post by jimwilliams on Aug 1, 2013 9:28:24 GMT -6
I love our southwest deserts, but wait until October before I venture back out there. You get 'conditioned' to the 72 degree lifestyle here in San Diego. I would melt out there now. Lots of amateur astronomers are found just east of here up on top of Palamar mountain, next to the "big boys" with the 200" telescope.
Why not Tape Op Con in May or something?
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Post by jimwilliams on Jul 31, 2013 9:45:35 GMT -6
The first version of these IC mic preamp chips was the SSM2015 made by Dan Parks of SSM audio back in the early 1980's. That was used in the Symetrix SX202 and many others. It was replaced by the SSM2016, used by AMEK in the 2520 console. SSM was bought by PMI and later sold to Analog Devices. Dan has long since left but his SSM brand lives on with the SSM2017 and the newer SSM2019.
I make the PIP here, the "Plug in Preamp". It's a small pcb with 20+ discrete parts made to sub those chip preamps. It does have superior noise, THD and bandwidth specs and slew rate is much higher. These are much lower noise than a 150 ohm resistor residing at -132 db EIN at 50 ohms.
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Post by jimwilliams on Jul 31, 2013 9:33:14 GMT -6
IME opamps handle DC just fine, many are designed for precision DC operation. They don't like exceeding the maximum specs. I come from the era of analog computing. Those used opamps to shove DC around. They were tube opamps back then, changed to SS in the mid/late 1960's. The IC's came out in '68 with the LM101.
If pots had a hard time with DC then all those dbx compressors would have failed many years ago. They still operate just fine today moving DC up and down. If you have more than a few millivolts of DC going across a pot, you will hear that as scratch. Using low bias current precision opamps will eliminate the bias current noise when turning a pot, fet opamps are the lowest.
Small amounts of DC can be delt with by a cap, a trimpot or a servo. Modern low offset, precision opamps eliminate the need for those older generation fixes. Yes, the sonics of an electrolytic cap are determental to quality audio. Those that have experienced a direct coupled, capacitor-free audio system already know this. A bipolar el cap is also no fix, it may block DC from both directions but you pay by running the signal through two back connected el caps, doubling the losses. Bipolar caps are not available in low impedance 105 degree formulations either. If you need to use one you are better off using two higher quality el caps wired back to back. 105 degree el caps will last longer as well.
Here are some opamps that will allow direct coupling in many circuits: LME49720/10 OPA1611/12 OPA1641/42/44 AD8597/99
Besides power rail decoupling, any feedback resistor above about 3k ohms will generate stray capacitance that will lead to ringing or oscillations. A small cap across the feedback resistor usually fixes that.
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Post by jimwilliams on Jul 30, 2013 11:30:27 GMT -6
You also must calibrate the SPL outputs to precisly match the mains speakers. A miss set sub is worse than no sub.
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Post by jimwilliams on Jul 30, 2013 11:00:19 GMT -6
Set the meter to DC volts, 200 mv setting. Connect the black probe to ground. Place the red probe on the output pin of the opamp, pin's 1 and 7 for a dual, pin 6 for a single. Observe voltage and polarity.
If below 2~3 mv, usually it's safe to remove the el cap. If higher, observe polarity. Be sure the + pin on the cap is facing the positive DC and vice-versa.
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Post by jimwilliams on Jul 30, 2013 10:55:03 GMT -6
Apex 460 = $189
Microphone Parts rk-12 capsule, $99
The knowledge to optimize the cathode follower circuit = priceless.
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Post by jimwilliams on Jul 30, 2013 10:51:05 GMT -6
Impedance is the resistance you get from your wife.
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Post by jimwilliams on Jul 30, 2013 10:50:04 GMT -6
Have you heard the Distressor? That one sounds digital harsh to me. The Expressor is smooth as silk next to one of those.
Perhaps that Expressor had a misfiring opamp in it or the THD trims are off.
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Post by jimwilliams on Jul 30, 2013 10:45:57 GMT -6
Liked those in the early 1970's, until they blew up (everyone's else's amps were louder). These days, not enough top end definition and nothing below 55 hz. They sound rather middy to me now. And those rattles, no good for recording with those problems Played with a fellow with a SVT for years. One day we connected an outboard preamp to the power amp input jack. Then we heard all that deep low end the guitar preamps in the SVT roll off (at 90 hz according to my R/C calculations). Yes, I've rebuilt it to get that missing depth, it was a PITA as I had to add additional B+ filter caps and resistors. The player ended up selling the head and he used an old beat up modified Sunn Colosium head I bought used for $125. That brain did an honest 40 hz, no problems. It beat bringing a Fluke meter to every gig to set bias on the SVT.
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Post by jimwilliams on Jul 30, 2013 10:43:46 GMT -6
Liked those in the early 1970's, until they blew up (everyone's else's amps were louder).
These days, not enought top end definition and nothing below 55 hz. They sound rather middy to me now. And those rattles, no good for recording with those problems
Played with a fellow with a SVT for years. One day we connected an outboard preamp to the power amp input jack. Then we heared all that deep low end the guitar preamps in the SVT roll off (at 90 hz according to my R/C calculations).
Yes, I've rebuilt it to get that missing depth, it was a PITA as I had to add additional B+ filter caps and resistors. The player ended up selling the head and he used an old beat up modified Sunn Colosium head I bought used for $125. That brain did an honest 40 hz, no problems. It beat bringing a Fluke meter to every gig to set bias on the SVT.
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Post by jimwilliams on Jul 30, 2013 10:32:14 GMT -6
I've used a 15" floor firing subwoofer for about 20 years now. It's connected passivly to my modified JBL 4408A speakers. It has a 2 meter sized cab, no vents, a special dual voice coil subwoofer that does 25 hz and a custom passive crossover set to 90 hz.
Smaller subs don't have the excursion to reach 25 hz. Most of them have a bump at the roll-off point as well. Sloppy bass can be more of a problem than not having enough.
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Post by jimwilliams on Jul 30, 2013 10:26:56 GMT -6
My sister in law teaches at Beserkly. Her hubby is a noted local jazz sax player and sax tech.
They are planning to move here in North San Diego County, tired of the summer heat and winter snow.
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Post by jimwilliams on Jul 30, 2013 10:22:49 GMT -6
You can hear .002% THD and a very low .0005% IMD? Got to get you into Sterophile's record review section. BTW, you are the only one in over 20 years that said it imparts a digital harshness. Are you using analog tape tracks or, perhaps a digital converter or DAW? It will reveal warts too. I suspect your converters may have higher THD specs than this compressor.
A guy at the Record Plant said it best:
"It's like there's a little man inside running a fader up and down who's smarter and faster than we are".
I use 5 here myself. a couple are rebuilt with large torriod power transformers,heavy heatsinks and very high current .9 nv noise opamps. I often insert them and ask if anyone can tell. They can't.
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Post by jimwilliams on Jul 30, 2013 10:11:15 GMT -6
You can check self noise by wiring a 150 ohm metal film resistor inside an XLR connector from pin 2 to pin 3. That eliminates mic noise, acoustic noise, etc.
There are also several variants to those chips that are pin compatible. There is the original discontinued SSM2017, the improved replacement, the Analog Devices SSM2019 (my fav of the chips) and the that Corp. 1510. Get that one from Mouser. You can sign up at Anlog device web site and get free samples of the SSM2019. Same with TI and BurrBrown.
The low cost kit from SCA also has balanced output drivers and some DC servos to eliminate some electrolytic blocking caps, a good platform to 'experiment'.
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