kevin gilmore

that's the 4th wire, and very few people actually ever wire that. Although mikhail was famous for tying pin 1 and pin 4 to chassis ground which caused all sorts of trouble in his balanced creations. Now most of you probably do not know how the krell preamps actually work. The volume knob is totally faked. It is tied only to a stepper motor which is monitored for current spikes as you rotate the knob. So the cpu counts the pulses and programs a relay controlled attenuator. The remote control makes the stepper motor move which moves the knob which the cpu counts pulses and programs the attenuator. I could do the same thing with a motorized RK27. But instead of using the pot to actually control the audio, the pot goes to the cpu which measures the single analog voltage and then drives the relay controlled step attenuator. Similar to what justin does in the pico except with relays instead of cmos switches.

I really like the idea of switching all 3 wires of a balanced, and 2 wires of an unbalanced input. More relays. In fact an extra input relay that loads the input with something like 10k might be a good idea too. There is a rumor out there that the RK50 is soon to be discontinued. In which case maybe the P&G might be the next best thing. Last i checked those were upwards of $700... Or the relay step attenuator.

So after a successful T2 project, it is time to tackle something i've been playing with on and off for quite some time. The KGITSOJC The Kevin Gilmore in the style of John Curl preamp. Now if you want to read over 700 pages of babble and bullshit, you can go over to diyaudio and read the two threads. But suffice it to say that the Blowtorch circuit sounds very good, but JC is of the opinion that only 2 people in the world are capable of building and getting the thing to run. I kind of disagree with that because i have one exact copy of the blowtorch amplifier running right next to my version. He has some reason to say this, parts matching is ultra critical, including matching 4 resistors to better than .01%. Not something a DIY type would want to do. And besides the unbalanced to balanced performance of this amplifier leads something to be desired. Plus there are 2 opamps directly in the signal path. Its time to make a couple of changes. I've made a better version. Critical parts matching is a thing of the past. And the servo is outside of the signal path. Performance in the unbalanced to balanced mode is much better. And the sound is absolutely identical. Unlike the T2 however, the rest of the design is not as obvious, nor is the way to build it. To save space on the back panel I could just do balanced inputs, then for unbalanced inputs use the neutrik unbalanced to balanced converters. What do you think about this? Or would you prefer 4 unbalanced inputs and 2 balanced inputs? In which case what kind of rca input blocks should i use? I'm going to stick with the neutrik nc3fdh for the balanced, they are way easy to use. I've been talking to ti khan about integrating his attenuator project into this. What do you think about this, or do you people prefer some kind of real attenuator? (rk50 et all) Would anyone be interested in stacking more than 2 channels of this. Say 8 channels for the ultimate in surround sound preamplification? Before i start laying out the board, i kind of need to know what people really want.

Otari, Ampex, Studer, and Nagra. Those are really studio machines, and very few made it to homes. A long time ago i had an 8 channel ampex. Took at least 2 people to move it around. Like the Eidiphor i had, it was completely useless and took up way too much space. Very hard to find pre-recorded R2R tapes these days, and the price is silly if you do. So if you are going to be doing live recording you are going to have to get one of the new all digital things with the built in hard drives. And again, not really suitable as a recordable media device for home use.

yep. But things have changed. I'm not sure anyone needs a tape loop anymore. Certainly not for a real tape machine of some kind. And if they do, its unlikely to be balanced. So a full feature preamp these days is a lot different than they were 25 years ago.

The final resistors came in today, and the T2 is now 100% complete, all parts including standoff's mounted, and most of the screws in the chassis... But in the last hour, i got the prototype of the NEW preamp running. First time. Got to lay out the board. Does unbalanced to balanced, and balanced to balanced with no more than .02db error, and FR of DC to 200khz... Desperately need to test with lsj109's... Been a very productive few weeks.

You don't need a leaf spring. It only moves 270 degress... Four turns of wire around the thing connected to the shaft and to ground, and you are done. I've actually seen this done a few times.

you are going to want some ultra low capacitance cable. 2534 is not that by any means. If you are already using an adapter then recabling with the stax cable would be the best idea. Otherwise if you need the sennheiser connector you are going to have to buy the replacement part directly from sennheiser.

The idea on the DACT is to make an aluminum angle bracket, and secure it to the hole provided in the circuit board.

For those doing the DACT instead of the RK50, here is the howto mouser part number 517-647-07-36 unsolder the pins from the DACT. cut the above pins into 3 pin pieces bend the above pins approprately to fit. Use 2 bars of metal (or whatever) .280 inches to space the thing off the board, then solder. http://gilmore.chem.northwestern.edu/dactmtg.jpg

Massive connectivity problems between NWU and the rest of the world for about 30 minutes. Everything should be OK now.

updated schematic with all decoupling caps. http://gilmore.chem.northwestern.edu/t2schem.pdf text list of parts for power supply http://gilmore.chem.northwestern.edu/t2schempower.txt

Wrong you are... Stax's first commercial product was made in 1950. 4 years before i was born.

when i was 21, a lot of stuff was still tubes. power fets did not exist. Things like 2sc3675 and 2sa1486 did not exist. Capacitors of equivalent value were 4 times the current size.

I multitask very well. If i was just 21 years old again, the whole thing would have taken only 2 months. (subject to availability of parts)

i added an extra battery to the schematic, output a bom, multiplied everything by two and this should be the right number of resistors and values http://gilmore.chem.northwestern.edu/t2schem.txt someone please verify.

updated BOM's there are a total of 11 x 8 pin dip sockets. http://gilmore.chem.northwestern.edu/t2parts3.xls http://gilmore.chem.northwestern.edu/t2parts3cgeditv2.xls i decided not to use the split fork turrets, but they are still on the bom. Also the holes for the feet are #10. Should i ever get those rubber things from craig@eddiecurrent I have a DACT in house from justin, i'll show people how to fit it in a few days.

i'm going to import whatever i come up with and then machine it with the 3d mill with a micro engraving bit. I showed an example a while ago...

I was planning on machining it into a chicklet. (a 1 inch x 1 inch square made out of something interesting like pure silver)

Show me what you got...

I think we have a winner... That should get past you know who...

And it needs to be a shallco for historical reasons !

I can't believe i got it done in 8 months. In fact i can't even believe i got it done. And no magic smoke or parts flying across the room. And i only got bit by the high voltage once, because i was working when i was way too tired. Never ever am i going to do something this massive again. Estimate of at least 500 hours in this. Well the hollowed out brick is going to be a one off.... although the boards will be available... I see the beginnings of smoke rising from california Need to find some 64 position balanced shallco's. NO shorts, NO socks, NO underwear... Lets go Native.

Anyone want to design a logo for the T2?? Could include the head-case logo as part of it...

Somewhere on my site is a picture of the monster motor driven variac that drives the transformer. So not only is it isolated to something like 110 db, but the voltage is stable to better than 1%. I also have this thing, which i use to drive other parts of the house. http://gilmore.chem.northwestern.edu/equiinside.jpg