kevin gilmore

I've been looking at various different interfaces (knobs, buttons, remote control...) and i think i have decided on this as the complete interface. With the remote control and touch options. SparkFun Electronics - Active Matrix OLED 2.4" with Touchscreen Reasonably priced, active matrix OLED, built in i2c drivers for the preamp control stuff, and IR input. Single part complete controller. Any comments??

Output impedance is less than 1 ohm. Should drive anything.

better at 1.7mb http://gilmore.chem.northwestern.edu/baseboard3-3.jpg bigger at 6.5mb http://gilmore.chem.northwestern.edu/baseboardpro.pdf both smaller than the above version. Now for the important stuff. charles hansen says he found a non-multiplexed vacuum fluorescent display for use in his preamp, he says it generates way less digital hash. Which certainly makes sense. Anyone have any idea who makes his display. its 1 line of 16 characters, and is VF. Power supply coming along nicely. lm317/337 in first stage, same thing as current limiters in second stage, third stage will either be series regulated, or shunt regulated, have not decided yet. All the resistors will be the surface mount thick film, vishay or equivalent, completely non-magnetic and non-inductive. (and not super cheap, but not super expensive either)

how i hate photoshop. If anyone has any better ideas to take a multi sheet pdf and stack the pages with some transparency to make something that shows up without being 10mb... http://gilmore.chem.northwestern.edu/baseboard3-1.pdf

uploaded struts spreadsheet. http://gilmore.chem.northwestern.edu/t2parts3as.xlsx

Except when bridged is used as balanced. Lets take the input of the T2 for example. The two hot wires both go to seperate deck on the attenuator. The other end of each of the attenuator decks is ground. Therefore a truely balanced 2 wire input signal coming from a transformer has both wires referenced to signal ground thru the resistance of the pot. Now the T2 also as a switch that can tie pin 1 to signal ground. For hum and noise reasons signal ground IS NOT chassis ground. Chassis ground is strictly tied to earth safety ground. If you want to you can drive the T2 with an unbalanced signal by using one of the neutrik unbalanced to balanced converters. In which case rca ground is tied to both pin 1 and pin 3 inside the connector. For this you have to set the switch to connect pin 1 to circuit ground. The same thing is exactly true for the input of the preamp. Now the output of the preamp should be considered as a bridged output referenced to signal ground. In which case only 2 wires are needed to drive the input of a transformer. The problem comes in with the input compliance with respect to ground. In this case chassis ground. transformers are good for at least 100 volts of compliance, most solid state gear can handle less than 15 volts of compliance. the RSA protector for example is a bridge output amplifier.

The preamp in question is both balanced and bridged. It will take a 2 wire balanced input. It will take a 3 wire balanced input. It will take a 2 wire unbalanced input. It will output both 2 and 3 wire balanced output. And 2 wire unbalanced output. Same as krell and ayre, and levinson. The T2 will take a 2 wire balanced input. But because there are only balanced input connectors, pin 1 is connected to signal ground so that you can supply an unbalanced input. Clear as Mud!

The aluminum is recycled. Still it takes lots of energy to melt the stuff down and re-purify and recast. At the prices ayre is charging, he probably does not make too many of those things. They sure are nice however. The blowtorch's were also machined out of a solid block of metal. and then they still have an end plate. What a complete waste of materials.

I have studied the JC design for many moons. I have synthesized it over and over and tweeked it over and over. Which is how i improved on the original. Nope, not using the renasys devices Yes i certainly am going to use the lsk389 and lsj109 My version swings 8 volts peak to peak (unbalanced) from +/-20 volt power supplies. (may go to 24 volt supplies) At 8 volts peak to peak the second harmonic is down 81db. The 3rd harmonic is below the 120db resolution of my instrument. At 2 volts peak to peak (unbalanced) the thd is about .005% I know how to get the second harmonic down another 4 or 5 db. But as many already know, its the sound that i'm after, not the numbers. The problem with cmos switches is well... they are cmos switches. I know that levinson uses cmos switches in their silly priced preamp, on an arlon board. But i think that gold cross point relays sound better. I was planning on using the omron small signal relays. But sealed reed relays would be better, but are also much much bigger. Will see what i can get to fit. Yes i think i have a pretty good servo. And its not in the audio path anymore. Although you might argue that the common mode servo in JC's original is not in the audio path because it is DC, except when you go balanced input. I've pulled out my schematics for my phono stage from 30 years ago. I'm pretty sure i can source equivalent parts for everything, so at some point there will be a phono stage. OH look, there is the lsk389 and lsj109 again... An exact copy of the vendetta phono preamp should be a snap. But in a seperate box with a seperate power supply. .2 pitch OK, glad you said something now because i'm going to start laying out the board tomorrow. Can't wait to see the price on teflon or arlon circuit boards. Just wait till you see how silly the power supply is going to be.

Invert phase, sure why not, the blowtorch had it. Just 2 more relays... Maybe we can get to 50 pieces per board and get a price break.

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)