Ultimate matching is curves. You can do gain. Gain is spot curve matching. So use it. Its what you look for to have almost same output in channels. Effective in the second stage mainly. The first stage gets divided a lot by RIAA filtering and the third stage has no voltage gain. Idss must be near enough also not to throw off the DC bias. I hope you understand that ultimate matching efforts are mainly academic sport here and what tolerances are given in the guide are more than good enough practically. I did my prototype on purpose in full deviation by guide standards and by looking to no curves although I could, it ended to 0.3dB output difference between channels only. Many carts will have 1dB+ difference, not to mention vinyl cuts tolerances. The guide is not theoretical, even the proposed gains per cart types and outputs are checked with real cartridges and music records over some builds.
I got 612 mV on my Idss 7,34 and 657 mV on Mikes 7,33. Using alligators and fingers but it was stable on last digit.
Say anything?
For some reason a DCA75 is up flying somewhere between China and Sweden
Salas said:
I do of course. This is all practice and learning for this nerd.
Says they measure like legit fets with natural tolerances. In those that you will find about same vgs off and idss you should find about same voltage gain in amplification simple test rig.
For some reason a DCA75 is up flying somewhere between China and Sweden
Good and practical, but it has tolerances. Its not a Tek or Agilent pro tracer. Ultimately trust same voltage amplification between DCA selected pairs that curves and Yfs it measured look like a good match.
Hi Salas,
I am building mine for 4mV and 5mV moving magnet cartridges. What from the BOM should I consider dropping, and what values would be appropriate for the parts that are variable please?
Also, is there a guide to what input resistance the various Rx switch combinations will produce please?
Thanks for your help
Lucas
I am building mine for 4mV and 5mV moving magnet cartridges. What from the BOM should I consider dropping, and what values would be appropriate for the parts that are variable please?
Also, is there a guide to what input resistance the various Rx switch combinations will produce please?
Thanks for your help
Lucas
Guide says:
"For circa 5mV MM cartridge don't populate Q2,R3, use 91R R2, 5.6K 1W R13, 1.8K R4, for 40dB gain and proper overload margin. Use 100nF C3 only value when with MM.
Choose Q1 between channels from a 10.5-12.5mA range at 5% IDSS pair tolerance."
So make the BOM changes. Use 100pF C2Y straight away as I doubt the RIAA treble will need further taming with MM. Thats the simplest way. No variables.
There is no Rload guide per se just your preferences. Sure thing is you got R1 steady and 4 switched positions paralleling it to take advantage of in various ways. Some examples:
You can use 100K R1 and 33K RX1 47K RX2 91K RX3 330K RX4 so to can go 25K 32K 47K 77K with 1, 2, 3, 4, when that DIP switch position is ON alone and 100K when all OFF.
sBy mixing more than one ON positions you can create many more intermediate values too. Just stick the DMM measuring kOhm across the input when power is down and play the switches. No calculations.
Or just use R1 47K and no switch or RX if you think 47K is all you need. Or use the switch just for CX capacitors. Or use less RX positions and reserve one or two positions for CX. Your TT cable will already have 150pF remember. But read this article first: http://www.tnt-audio.com/sorgenti/load_the_magnets_e.html
"For circa 5mV MM cartridge don't populate Q2,R3, use 91R R2, 5.6K 1W R13, 1.8K R4, for 40dB gain and proper overload margin. Use 100nF C3 only value when with MM.
Choose Q1 between channels from a 10.5-12.5mA range at 5% IDSS pair tolerance."
So make the BOM changes. Use 100pF C2Y straight away as I doubt the RIAA treble will need further taming with MM. Thats the simplest way. No variables.
There is no Rload guide per se just your preferences. Sure thing is you got R1 steady and 4 switched positions paralleling it to take advantage of in various ways. Some examples:
You can use 100K R1 and 33K RX1 47K RX2 91K RX3 330K RX4 so to can go 25K 32K 47K 77K with 1, 2, 3, 4, when that DIP switch position is ON alone and 100K when all OFF.
sBy mixing more than one ON positions you can create many more intermediate values too. Just stick the DMM measuring kOhm across the input when power is down and play the switches. No calculations.
Or just use R1 47K and no switch or RX if you think 47K is all you need. Or use the switch just for CX capacitors. Or use less RX positions and reserve one or two positions for CX. Your TT cable will already have 150pF remember. But read this article first: http://www.tnt-audio.com/sorgenti/load_the_magnets_e.html
Thanks for the great reply, and that article is very useful, especially as he was using my cartridge!
It seems I will be opting for 75R and 400pf loading then, as a base point. I can't hear a jot above 15Khz anyway, so there's not a lot of point worrying about it being there, eh?
Have you tried this test? It's fascinating stuff for for hi-fi obsessives, I'd say...
https://www.youtube.com/watch?v=VxcbppCX6Rk
My kids can confirm that this isn't a hoax - there really are all the sounds on there!
It seems I will be opting for 75R and 400pf loading then, as a base point. I can't hear a jot above 15Khz anyway, so there's not a lot of point worrying about it being there, eh?
Have you tried this test? It's fascinating stuff for for hi-fi obsessives, I'd say...
https://www.youtube.com/watch?v=VxcbppCX6Rk
My kids can confirm that this isn't a hoax - there really are all the sounds on there!
I would try 47K 250pF & 75K 250pF too. Broadband plateaus and valleys have effects to be decided by ear.
When I was 21 I took a test during an acoustics seminar and there were people up to 55 yrs there. We all could hear 15kHz on same volume position with lower bands but no one could hear higher faintly if we would not crank the headphones amp up. The ear goofs at the extremes and needs high SPL. Also the Phons diagrams curiously stop at 15kHz.
Turn on some EQ on a PC replay program, play some music and turn up 15kHz-20kHz. If it will not sound more brilliant then you may don't care.
When I was 21 I took a test during an acoustics seminar and there were people up to 55 yrs there. We all could hear 15kHz on same volume position with lower bands but no one could hear higher faintly if we would not crank the headphones amp up. The ear goofs at the extremes and needs high SPL. Also the Phons diagrams curiously stop at 15kHz.
Turn on some EQ on a PC replay program, play some music and turn up 15kHz-20kHz. If it will not sound more brilliant then you may don't care.