kevin gilmore

you forgot the dn2540 cascode on the 10m90s

updated board file, 10k input resistors added (optional) and 25k changed to 17k cfaelectrostatschem2-4 - CADCAM.ZIP

the neutrik jacks i used in the diy t2 are actually 4 wires. the connector shell is a seperate wire. i put in a jumper to chassis ground for that wire.

relays are dual coil latching. so 2 might be tricky. 3) lots and lots of cheap transistors. best to go with the "B" versions, matching is always better. 4) 50k attenuator NOT NEEDED. thats the point. there is no commercial product with an output voltage that will saturate the input. 5) very much like the ayre kx-r. individual resistor goes between the 2 pins. for increased gain should you want or need it. schematc shows everything at 0db gain.

only need one power supply for both channels and its not a lot of power. also runs whatever microcontroller you decide to use.

possible final version, 4 inputs and the xlr jacks correctly located preamp2025i - CADCAM.ZIP

this version should be compatible with the amb lcduino software with no changes. preamp2025h - CADCAM.ZIP

soren asked for the board with onboard grlv preamp2025g - CADCAM.ZIP preamp2025g.PDF

for clarity this board is mono. 2 required for stereo. boards stack. needs arduino software, or equivalent programable controller.

board file and schematic preamp2025f.PDF preamp2025f - CADCAM.ZIP

actually the bryston uses that scheme.

the idiot at eddie current was big on that circuit. and did that on his electra. and then tried to get too much gain out of it. and the tubes went into saturation and then you have to hand pick the tubes etc. biggest problem with that one is the 100k pot starts off with 2nv of noise all by itself.

its not obvious what this is? first stage is the input section from the uberamp 2. current mode voltage gain. (not that you actually need voltage gain) differential input, differential output. then balanced step attenuator. constant input impedance load. output stage is the same input section with the darlington input removed because its not needed and some of the cascoding removed because its also not needed, tied to a voltage buffer. many of the expensive preamps out there convert everything to single ended internally to save on parts and board space. this is balanced from input to output. and 6db or more less noise. many features of preamps of the past include things that are no longer useful. so they are removed. like tape out and second zone. seriously i have never heard of anyone actually using second zone. and except for the really expensive ages old professional gear, there are no tape machines with balanced inputs. maybe the new revox has balanced inputs. so consider it as a balanced buffered volume knob. turns out the signal to noise boost really is audible. krell fpb600 vs mc611. more than 12db signal to noise boost on the mc611 partially because of the low input impedance and rail to rail input buffer.

finally. higher signal to noise ratio, more than 110db. takes signals up to 20 volts peak to peak unbalanced, 40v peak to peak balanced. no input attenuator that adds noise for those stupidly high voltage dacs. ( requires 30v power supplies) (volume control in the middle) thd about .005% no feedback. work in progress 4 layer board. preamp2025f.PDF

thorens td125 with sme type 3 tonearm. mcintosh c26 preamp mcintosh 2105 power amp teac reel to reel. classic stuff then. classic stuff now.