kevin gilmore

that would have to be on an amplifer to amplifier basis. Way too much trouble. you would have though that. But with a low impedance coil and a large magnet structure, the thing has quite a kick. blubliss wants me to find a push pull tube amp. I thought this would be easy, someone had to have a low power push pull tube amp for headphones. Evidently not so easy. The smallest of the atmaspheres might work, There is a cary that would probably work, and a vtl. All 3 of which have stupid pricing for what they are. i'm betting that classic old marantz and mcintosh tube amps are going to sound very nice, especially the mcintosh.

So i have birgir's pair of LCD2's here for extended listening while the transistors are on their way back from england. They sound so dramatically different on all the amps i have tried, And measurements show that these things generate signifant amounts of back EMF, and therefore require an amplifier with a very low output impedance to sound right. OTL tube amps, even the SP extreme perform very poorly on these headphones. The only single ended transformer based amp i have, also sounds pretty grim. Only push pull high bias amps seem to work right. And push pull tube amps also sound really good. Good enough that i will be buying my own pair on monday, and i'll skip the lcd3's for now and get lcd4's later. half an amp at reasonably loud listening levels has been measured with my hall probe. I think that tyll needs a high current buffer amp for his measuring system, because the built in amplifier really cannot drive these kind of headphones correctly. The waterfall and decay plots will change a bunch when done this way.

Yep, according to 6 moons, T amps. On batteries. The batteries are great for high current peaks, but are definitely not as quiet as a good quality regulated power supply. At least the stuff is built better than the rudistor crap, but definitely way overpriced. I've looked into this a bit more, and much of what is inside is actually built by someone else. Both attenuators used are from bentaudio, i recognize the single tube input board, and the T amp board also seems to be one of the standard vendors selling those boards for about $25. Looks like the only thing they actually make is the headphone only output which is one of the national semiconductor lower power gain clone style chips.

And here i thought it was "ERECTOSTATIC"

I can't find the schematic. Seriously. I must have left it at home. Will draw it up again and post soon. here is a fresh version http://gilmore.chem....u/protector.pdf For DC, it triggers on anything over +.5VDC and -.5 VDC Detect time is 75 milliseconds. For AC, at 20hz, it triggers on 5 VRMS.

oops, so i can't spell. I'll fix it later. Its not like its already etched into a front panel. We can adjust the comparator window as necessary, as well as the filter. Ceramic caps up to 4.7uf in that lead spacing i believe. Putting the thing in a small box with a female and male 4 pin xlr's on tails plus a cheap wall brick should take care of those pesky massively overpowered things from my friend in skokie that seems unable to comprehend DC servo's.

Yep, works fine with the dual coil latching 5 volt versions.

This has been needed for a while. For those with problematic DAC's that put out a bit of DC, and balanced headphone amplifiers happy to amplify said DC and produce differential DC on the output... http://gilmore.chem.northwestern.edu/protector.jpg This is the one case where ti kan's protection board does not work, unless you want to use 2 of them.

The test setup already does distortion levels way lower than my 30+ year old measurement system. That is not the point, i can take an lm741 and put oodles of feedback around it and measure .001%. Still sounds like crap. Its the rise time, symetrical slew rates, overshoot, and all those other things that make something sound good or not. These newer chips with real complementary silicon processses really do sound great. The quality of the resistors in the audio path is going to need to be of very high quality. I see that Susumu .1% resistors are now available cheap, i'm going to have to listen to those. To maintain the CMRR on the input stage is going to require very close matching of the resistors. Probably a couple of months away from circuit boards. Then again, maybe sooner. Lil-knight is going to have to do the boards, locally, the prices are way out of line, and the sales tax is also way out of line. As far as i know there are no better board mount xlr connectors made, regardless of price. Everyone uses the neutrik.

these http://www.mouser.com/ProductDetail/Neutrik/NA2MPMF/?qs=sGAEpiMZZMtUKTCHc2CNRBaiw9SrxpJs and these http://www.mouser.com/ProductDetail/Neutrik/NA2FPMF/?qs=sGAEpiMZZMtUKTCHc2CNRAvIKttWysf6

not an engineering drawing. pretty much useless to lay out the board with. why those morons can't post something useful is beyond me. When i asked, i never got the engineering drawing. Measure and post please. more editing, switched to the dip version of the lme49720 so that there is less surface mount work required. http://gilmore.chem....inputboard4.jpg approximate pricing lme49600 need 4 for balanced stereo $10.50 ea lme49720 need 4 for balanced stereo $3.08 each (dip) opa1632 need 2 for balanced stereo $5.88 ea nc3fdh xlr male need 14 for balanced stereo $4.52 each (probably cheaper) nc3mdh xlr female need 4 for balanced stereo $5.55 ea ds2e-sl2-12v relays need 16 for balanced stereo $6.37 ea (digikey) overpriced boards at $37.50 each in quantities of 10 (lil-knight is going to be much cheaper) so about $375 plus resistors plus power supply plus chassis plus plus plus. RK50 (don't ask) my step attenuator (i don't remember how much) arduino (cheap) ...

Nope, not designed for that. I could however change out all the xlr jacks with stacked rca jacks and then change the input amplifier. Then it would be a SE in only, SE out only thing. If there really is interest in this, it would not be too hard as long as i can find a suitable stacked rca jack.

walk in with the el-cheapo transistor tester, test them all, and buy the real ones. Say 50 cents each... Kind of surprised that someone would stock those, and that they were bent into shape like that.

like this ?? http://gilmore.chem.northwestern.edu/inputboard3.jpg I can still add the servo on the input, but probably not necessary. Servo on the output takes care of all issues with DC. Why no one else is doing servo's i just don't understand. Still think that when you need unbalanced inputs, you use the neutrik converters. This way you don't need extra relays and configuration for inputs, and you can change on the fly. The discrete output amplifier is still better, but not by much. The bang for the buck on this one is way high.

so i've been playing with this for a couple of days. The unbalanced and balanced to balanced front end. Its virtually impossible to hear the difference between this and my fully discrete version. To be fair, it does not drive cables as well, and definitely has a higher output impedance, but it is about as simple as it gets. Turns out the rowland criterion preamp uses virtually the same circuit. The 50 ohm output resistors are definitely required if you want to drive 10+ feet of cable without it oscillating. The servo actually is required and i bumped the input impedance a bit to be more friendly to some high impedance sources. (which evidently some others are not paying attention too) http://gilmore.chem....u/ubaltobal.pdf Something like a pair of lme49600's with your favorite choice of opamp in a closed loop configuration as the output amplifiers after the volume control, and you have something super simple to build and way good for cheap. The discrete stuff is still better, especially the output amp, but the chips are damm close. This is the technology texas instruments licenced from nelson pass.

much more suitable for quick go/no go, and for obvious fakes. for critical matching you have to build something custom.

So 70+ horsepower and drum brakes. Yep, definitely a safe item.

sure looks like an early 1950's 1200cc 4 cylinder VW bug engine. About 50 horsepower. Which would make that thing pretty fast and dangerous for its age.

yep, balanced dynalo, same setup as the balanced dynahi. i've been listening to a lot of different configurations, including what has been represented as an identical blowtorch clone with all the exact same parts and values as the original. Blowtorch has almost 2db of unbalance between the + and - output, and it gets worse with low impedance load. Blowtorch also does not drive headphones very well. i did shrink the board to make it fit into a standard chassis. http://gilmore.chem....inputboard2.jpg Its now 12 x 4.5 inches and uses the same neutrik jacks as the T2. Everything in stacks of 2 boards, hole thru the input board to run the control from the bottom board. still no p-channel fet samples as promised by linear systems but i do have a clever way of using the singles fets on a 14 pin dip header with one spreader bar with all 4 glued to it for thermal stability. The thatcorp parts are definitely very low noise.

The stuff sold in the local drugstore is about 3%. You can gargle with it. Although its probably not a great idea. Some of the health food nuts probably disagree. The stuff i have in my basement is 35%. Gets stains out of carpet like you would not believe. Also takes enamel paint directly off of metal. You could probably drink some of the stuff and not die, but it would tear your stomach apart very quickly. Heavy water (Duterium oxide) is definitely a bad idea to drink. I have a bottle of that in the basement too. (not sure why)

Great job. Now time to do up some proper wiring assemblys with the wax coated cotton. Khozmo pot, i sure wish i could get one of those where all the positions actually work.

Should you decide you want to keep the ZD, you may consider replacing those crappy plastic power connectors with the amphenol military things. There is a size that fits the chassis holes directly. About $200 in parts plus the labor to rewire everything.

http://gilmore.chem....du/multiamp.jpg 6.1 x 3.4 inches, 233 holes buildable either super symmetry, which works out great for a gain of one, unbalanced and balanced to balanced converter buildable with john curl jc2 style feedback which works great for gain of 5 or 10 for the output amplifier buildable with the thatcorp quad bipolar input chip, or singles fets thermally glued together. also drives headphones NO PROBLEM. So a full preamp, would be 4 of these boards, plus 2 step attenuators (or balanced pots) and the input switching board. the input board. http://gilmore.chem.northwestern.edu/inputboard.jpg

I'm going to agree that some very low noise jfets are available, and there is no reason to use tubes just to say that you have a tube phono section. If you are going to use some sand, might as well use all sand, and a much lower power supply voltage.

doesn't seem to be the same multi-color thing. But close.