Right, Joachim. Everyone, what we are designing is a GENERIC phono, line stage, PROPERLY ENGINEERED, but not perfect in sound reproduction, any more than an early VW was the ultimate car for the Autobaun, off road, or to pull a trailer. The early VW was designed to take 4+ people from point A to point B. And do it, without too much difficulty, cost, or fuel consumption. Correct me on this, if I am wrong.
THIS preamp is designed to be SIMPLE, RIAA accurate, and BULLET PROOF with regards to normal operation. Nothing more, nothing less.
THIS preamp is designed to be SIMPLE, RIAA accurate, and BULLET PROOF with regards to normal operation. Nothing more, nothing less.
Post 7420If that is true then i eat an elephant but it may well be.
If -3 dB @ 10Hz is the goal then i stand by the original values plus the 1uF cap.
Yes, this is a Volkverstärker and that designed by an american ! I call that progress of the forth order. 😉
I redid the simulation on the RIAA. Actually for 10Hz -3dB we come by with a 0.33uF cap.
There is a slight 0.5dB lift in the fundamental tone area. The forth pole is at 1.55usec not far from the infamous "Neumann Pole" of 2.2usec.
There is a slight 0.5dB lift in the fundamental tone area. The forth pole is at 1.55usec not far from the infamous "Neumann Pole" of 2.2usec.
No need to worry too much about ultrasonic response, IN THIS CASE, the Shure or its equivalent cartridge will roll of virtually EVERYTHING above about 25KHz, in any case.
I think perhaps some shunt capacitance @ the input ......
I would suggest ......
>-------------2.2k------------->
47k ......................100pF
>------------------------------>
with a fet input opamp the input capacitance is intrinsic
the 2.2k pronounces the input capacitance (dynamicness and all)
which is quite pleasent
I'm suggesting a series resistor with the input
and a shunt capacitor if the opamp is bipolar
I would suggest ......
>-------------2.2k------------->
47k ......................100pF
>------------------------------>
with a fet input opamp the input capacitance is intrinsic
the 2.2k pronounces the input capacitance (dynamicness and all)
which is quite pleasent
I'm suggesting a series resistor with the input
and a shunt capacitor if the opamp is bipolar
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The Shure V15 is no more. The best cart. they make at this time is the M97xE.
I found the price to be something under 90,-€ in Germany.
Here is the Users Guide.
http://www.shure.com/idc/groups/tech_pubs/@global_managed/documents/webcontent/us_pro_m97xe_ug.pdf
They spec. the frequency response as : 20Hz - 22kHz
I found the price to be something under 90,-€ in Germany.
Here is the Users Guide.
http://www.shure.com/idc/groups/tech_pubs/@global_managed/documents/webcontent/us_pro_m97xe_ug.pdf
They spec. the frequency response as : 20Hz - 22kHz
Just for completeness here is the schematic of what we have so far. I took the freedom to call it "The Beatle".
What could be the PSU ? Is LM317, 337 too expensive. Maybe fixed regulators with cap multipliers ?
What could be the PSU ? Is LM317, 337 too expensive. Maybe fixed regulators with cap multipliers ?
Looks pretty good, a few too few parts and few too many parts, but OK in general. The best approach would be fixed 3 terminal regulators, for minimal current loss, and perhaps using the power supply rejection of the quad op amp to advantage. An in-between cap multiplier would lower the power supply noise considerably, but would anyone actually hear or even measure the difference in the phono or line stage? That is worth looking into.
A preferred config for this would be a dual opamp for the output amp and another dual for the input stages. The output stage carries the largest currents, and if you use a dual for one channel (or a quad for the total) the output stage currents can couple to the input stage amp through common supply wiring inside the chip (the bondwires). You don't want those output currents to couple into the sensitive input stage, even with the high PSRR.
jan didden
jan didden
Yes, that whould be better and single ones may be better still but it would break the boundary set by JC to make the preamp as cost effective as posible. I misunderstoud that goal in the beginning.
Can we utilize 150 ~ 180pF for the "exotic" cables? Do we still need R13 after the low pass filter, I think we can remove it.
Yes, crosstalk in the region of 130 dBs is measurable. But who cares? No need to be grumpy just because it is not your fav opamp.
There are at least 3 better reasons to use two duals instead of a quad:
1. Easy to test the design with other opamps.
2. 2 duals are cheaper than a quad (just checked at Mouser)
3. Duals are more available than quads
And since the required real estate only slightly increase, my choice would be two duals.
But I am still concerned about the output stage gain (I never give up, do I 😀 )
My comfy listening level is in the 75 - 85 dB SPL region. This translates to less than one watt from each power amp. With a power amp output of 3 volts and a gain of 20, the preamp output level is 150 millivolts. A gain of 5 in the line stage takes this down to 30 millivolts from the vol pot. With an input level from a digital source in the 1-2-3 volts region, my vol pot will be around the 9-o-clock position. Here the level adjustment is very course and the channel balance is poor.
Well, MY solution is the read the spec sheet for the OPA4134 and NOTE the optimum position of the individual channels for optimum separation for normal operation, which may WELL BE something other than phono, most of the time, the phono being added as an engineering exercise, AND to play your late uncle Marvin's jazz records that were kindly donated to you after his passing, or an equivalent situation.
The choice between two duals and 1 quad is a small one. Either will do, depending on how sharp your pencil is, but it was the very idea of making an entire preamp with a phono stage in 1 CHIP was the source of this design exercise, as it first came to me 45 years ago when I was still a student, living on limited income, and I kept hoping that op amps would finally improve to this point. It took awhile, but now it has been done on paper.
Perhaps we should next make something that will sound 'better' (for some reason beyond engineering) have more useful features, or really show off our engineering talents.
For example, this morning, when my associate arrives, we well be testing my latest phono preamp prototype. It is a 2 stage all discrete design, except for the multiple servos, that are surface mount on the back of the board. There are over 50 active jfets that you cannot buy in the open market, easily, anymore, per phono channel. This is your Bugatti or Bentley, with the V12 engines and dual turbos.
Yes, there is room in the world for this too. Everything, in between, is a compromise of some sort.
Perhaps we should next make something that will sound 'better' (for some reason beyond engineering) have more useful features, or really show off our engineering talents.
For example, this morning, when my associate arrives, we well be testing my latest phono preamp prototype. It is a 2 stage all discrete design, except for the multiple servos, that are surface mount on the back of the board. There are over 50 active jfets that you cannot buy in the open market, easily, anymore, per phono channel. This is your Bugatti or Bentley, with the V12 engines and dual turbos.
Yes, there is room in the world for this too. Everything, in between, is a compromise of some sort.
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