Technically there may be little, but it is the difference between someone trying the concept and not!
Personally I want to try the zero cap load idea and there is the possibility of some external noise being reduced. Don't know till you try it. Which I generally do, build everything and try it before deciding. The little 9V impedance converter with 4 RCA's worked very well so I suspect little is gained but then the other guys claim otherwise.
Sticking with the no user mods at all idea you are left with doing it at the exit point of the TT, also why did the other guys do it in a way that makes you use their cart? You still need an XLR dongle for the phantom powered version.
Yes of course, you should try everything.
Removing the cable capacitance means that the FR drops at an earlier point, but now at 6dB/oct and will have to be corrected somewhere else.
The effect is most likely a larger FR after correction, but who knows ?
Much better to predict and supported with real life measurements comes from loading the Cart with a 75usec pole, making the whole cable capacitance issue practically unimportant.
Because it is so simple to implement with a single resistor, that would be my first step before making the next step in connecting an "active cable" to the Cart.
It would be most interesting to see how your recording Moving-Magnet Head Amp - without RIAA
would look like with the 75usec Cart termination and at the same removed from the digital filter.
Just an idea ?
Hans
There are no filters at all in that recording, it is a constant velocity sweep, no RIAA, and flat preamp. I expect you would see an added 75us pole so maybe there is enough resolution to see if it behaves exactly as a 75us pole.
We are not going to extract useful information if we don't keep track of ALL the conditions for any data presented.
Starting to do a list for a mouser order to start prototyping things and a really silly question. What voltage rating do I need for the 47uF caps? Mk1 eyeball suggests they will never actually see 48v across them but may have missed a start up condition.
O.k. No filters involved and constant velocity on disc.
An inverse 75usec filter after D/A conversion could then be used to correct the 75sec Cart termination and see whether it makes a difference with the 47k terminated and not filtered recording.
Still quite a bit easier to do than to make an "active cable" ?
Signal will be attenuated above 1Khz and so will the noise, but as long as it all stays above the noise level of your straight amp, you could have something nice to compare.
Hans
Please don't forget the caps charged to 48V suddenly applied via hot plugging. I have toasted at least one field recorder this way.
I'm actually starting to put the mouser order together for testing this. I may wuss out and do a lot in through-hole to start with as I'm too out of practice dead bugging SMD.
Got one of my usual spectacularly dumb questions. Why the 31k2 resistors. That's an E192 value which seems a little specific?
Got one of my usual spectacularly dumb questions. Why the 31k2 resistors. That's an E192 value which seems a little specific?
Scott will find this funny. Chatted with my Technics owning Guinea Pig (ToGP). ToGP was horrified even by the idea of a headshell mounted doohickey so I'll make him one that goes at the mixer end. I reckon you could build the circuit into an XLR connector if you were more delicate than I am.
Tonights Dumb question(tm) on the balanced version. How matched do the FETs need to be and what needs to be matched. I realised I have a number of LSK170 about to come free which would make initial lashups easier.
If your doing source followers with a relatively large drop on the source resistors you don't need to worry much about it.
Thank you. I thought that was the case, but wanted to double check before I unsoldered the wrong FETs 🙂
Hi Bill,
You may also want to include a rectifier or two. Phantom-powered toys not only get hot-plugged, but a lot of recent gear provides a switch for the 48V -- and it won't always be a nice, polite 2 volts-per-second ramp.
Such fun discovering this project and getting caught up. Hope I'm not too late for your Mouser order.
Regards,
Rick
You may also want to include a rectifier or two. Phantom-powered toys not only get hot-plugged, but a lot of recent gear provides a switch for the 48V -- and it won't always be a nice, polite 2 volts-per-second ramp.
Such fun discovering this project and getting caught up. Hope I'm not too late for your Mouser order.
Regards,
Rick
Umm -- come to think of it, maybe just a 15 or 18V zener from Q1* emitter to ground should be adequate for both ramps.
* referring to the 2nd schem, Hans' post #156
All the best,
Rick
* referring to the 2nd schem, Hans' post #156
All the best,
Rick
Rick, all my projects are slow time at the moment around other things at the moment so nothing missed out. As soon as I get something working will go off to my test subject to see if he can get it to work without breaking it and likes it. This will be the balanced version.
Rick,
I fully agree with the 18V zener on the SE version.
The diff version already has a zener, no accidents waiting to happen over here.
Hans