The Jensen JT-11SSP-7MPC comes to mind. Line input rather than line output is good for this application. (Shielding differences.) The JT-11SSP-7MPC has lower distortion at a given output level in general than the JT-123-SLPC and it’s high end peaking is more controlled (important in this application.)
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Just want to try and explain why this can achieve what it has achieved. Just my opinion, of course.
The D/A conversion process has been highly optimized here and is as simple as can be. Aside from the fw aspect I mean. Here’s the chain- well defined, well buffered bit stream bits are fed into a small passive low pass filter. Then very simply, out comes the analog signal we want. No switches, no glitches, no stair steps, nada.
Also this D/A converter has no power supply nor considerations thereof… it is self contained and fully open loop and thus no closed loop IMD… it has low impedance through it. It’s just a dumb servant here that puts out what it’s supposed to, no more, no less.
If that filter performs such that it has no overshoot or ringing and it simply goes to the point that it’s being told by the bit stream density (and quickly), no more, no less then it is not adding or subtracting anything from our desired signal.
For now, we then create a balanced output stage via the highest quality sound transformer we know of. We hear the results of the above.
Further improvements might come from using very transparent output caps. Only the best will do here. Most are not up to the task we need here- I’ll say that I do know firsthand at least one solution that can work, I spent well over a year and thousands of my own dollars finding what does work up to our level for signal coupling.
Even better IMO, switch to a bi-polar PSU and then we no longer need transformer or caps. Our low impedance D/A converter can drive the line directly with no DC offset issues. That IMO would be the ultimate in terms of clarity and transparency here
I sort of tried this early on and yes, I recall it was in fact much better sounding- much more direct connection clarity. Not a surprise, to me at least. Post was referring to “look ma, no transformers” or similar. In that case the DC blocking was already in my preamp which allowed the test; so another pair of DC blockers would be redundant.
Below is the simulated step performance through the whole chain, from bit buffering through the current iteration LPF to the D/A output. Please feel free to discuss what is unlikeable there.
T
Very much looking forward to hearing it! I note with interest that the pin layout for the XS4400 looks at first glance to be the same as that for the Jensen you mention…
Tho the transformers fit in the same mounting holes, the windings are pinned out differently 
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Ah, nuts.
Check out the Cine-mag mu metal I posted above?
Update- sorry, it does not appear to be pin compatible.
T
Here are some links that at least start I think:
No transformers early test: Modding the DirectStream DAC - #2111 by Turbotk
Modding the DirectStream DAC - #2112 by Turbotk
Vocm mod: Modding the DirectStream DAC - #2674 by Turbotk
Modding the DirectStream DAC - #2685 by Turbotk
Change OA circuit to perfect step response: Modding the DirectStream DAC - #2835 by Turbotk
Modding the DirectStream DAC - #2836 by Turbotk
Swap OA to higher perf versions: Modding the DirectStream DAC - #2726 by Turbotk
Modding the DirectStream DAC - #2858 by Turbotk
Final approach- convert the OA to bit buffers: Modding the DirectStream DAC - #2889 by Turbotk
Final approach- passive LPF D/A: Modding the DirectStream DAC - #2976 by Turbotk
Modding the DirectStream DAC - #2996 by Turbotk
Bybee Purifiers: Modding the DirectStream DAC - #2998 by Turbotk
Recs: Modding the DirectStream DAC - #3002 by Turbotk
Some results: Modding the DirectStream DAC - #3015 by Turbotk
Modding the DirectStream DAC - #3027 by Turbotk
A sample of it playing after Bybee install: The Griot- first tune with Bybees in place-WhatsApp Video 2022-05-30 at 7.20.34 PM.mp4 - Google Drive
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Turbotk,
It’s just a 14 hr drive from Atlanta. 
I woulld gladly pay you a visit, if I lived in Texas. Very interesting what you’ve done and it’s great that you are able to enjoy positive results from all that work.
Thanks Turbo!
That is Hot Rodding at is core. Make it (any machine) better than it was with aftermarket high performance parts.
I dont know a thing about the insides of these pieces so I need to lean on others with the right skill set but they have not let me down yet.
TurboTk, Would you mind sharing the parts cost of your modifications. Thanks.
You nailed it Baldy- in fact that was my former life (before deep dive audio), extreme power adder drag racing 
I know some of the folks on Street outlaws for example; my good friend’s brother got punched in the face on Tee-Vee there lol…
EFI programming and calibration and engine controls were (are) my specialty 
Got to do it professionally for a few years as well, working on advanced emissions research projects for the DOE, EPA and the CARB for example Even did a huge project helping decipher hundreds of pages of engine control code for the worlds largest automaker (in the land of the rising sun perhaps?). Back when engines had transitioned to drive by wire throttle and there was creeping up this odd problem of mini-vans and such running away and powering their way over cliffs or into deadly accidents… No, no, it was simply a floor mats issue peasants 
Ahh those were indeed blessed, fun days… Man, don’t get me started…
T
Kneeling behind car launching at Clash of The Titans in 2005. We qualified #3 in the July heat that day with only v6 powah (twin turbo w/ FAST EFI) vs numerous Goliaths (it went 7.99@185)
Back to Clash again in 2008. Standing behind new much louder, much faster car (>2500 hp on gasoline). All out Procharged BBC w/ FAST EFI. Mid 4’s @ 170’ish (1/8th mile) on some initial test passes. Yeah, we were all over procharged combo long before it became ultra trendy this year with the No-Prep Kings and Americas List crowd
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Wayne, thank you so much. I wish we could get together. Anyone else out there closer?
Parts cost- well the transformers are the major cost. Worth it though for what you get, IMO. Think I paid near $200/ea for these amorphous w/ pure Cu. But high nickel (mu metal) core are lower cost than amorphous and I think they sound pretty close.
Speaking of, IMO its likely very important to not distort lower freqs, because all the distortion tones generated (D2, D3, …) are then right up into the mid range, exactly where we do not want them. Seems pretty clear to me at least that unwanted low level tones in the midrange would muddy the effective noise floor. Meanwhile we are doing all this work to try and achieve remarkable “low noise floor clarity”, yet M6 steel core generally specs near an order of magnitude higher low freq distortion vs high nickel core (or amorphous).
Otherwise, its just a handful of SMD passives for the other mods. The Vocm mod, good through hole audio caps for that can be had for around a buck ea I think. It can be done with caps only on R_B in the image. I put caps on both R_A and R_B but don’t think doing R_A brought much further advantage really.
My DS uses 2 OA/channel to save time/effort on these changes. Per Ted they do need to be on different bit trees to be able to use the latest fw. You can do 1 OA/channel for initial testing. I also cut each OA loose from the main output net so I could wire directly to trafo and to output. If you wanted, rather than cut traces you could instead just keep the OA output RC off the output pads somehow. And yes, 4 OA/chan would reduce the output impedance, which we might want to put into play if (when?) we move to a bipolar PSU and no trafo, no caps
I think for most to get top-notch sound it would be these 3: more transparent trafos, Vocm mod; very nice improvement. But then much better still, change OA circuit filter topology as well. I think these 3 would serve most quite well and not that difficult really.
The optional Bybees, they are pricey- Cu small bullet Purifiers were $100 ea (x4).
Pondering now maybe putting together a 2nd unit and send it out on a (shipped) walkabout tour?
*PS if anyone knows of a reasonably priced unit available please let me know.
T
Turbo @Turbotk , Are you close to DFW? TX is a whole country in size. Lol
Although my preference is for road/circuit racing, I enjoy watching those guys on street outlaws too. Pretty awesome cars and cool that you were a part of those cars and the technology. I will continue to watch with interest how your work eventually turns out with the DS DAC. Awesome, keep going.
Well, it’s not too far really… If the will is there we could find a way.
T
Wonderful fun!
All of my racing experience is road courses, but I have taken some runs down a drag strip. Take my times and subtract a second or so and one has a rough idea of what the car can actually do.
Now I see where the Turbo name comes from 
We used to make ProCharger mounting pieces for The Supercharger Store in Tucson until the owner retired a couple of years ago.
We also circle track raced for 40 years or so before everybody got too old and broken down to do it anymore. Sold everything in 2015-16.
It was a lifetime of fun though. Too many stories to start here and I don’t regret any of it. Based on the costs to race at the regional level these stereo bits are small change.
Small world indeed.
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If you are a pioneer, let’s have our own design and special production.
conductor, and if we choose the core. For example, in edcor
@Turbotk , @tedsmith
or someone who knows can make an adapter card that will mount the lundahl transformer to the analog card
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