That assumes input stage Johnson noise is dominant. In many designs (e.g., Joachim's or syn08's), one can reduce input stage noise to below the intrinsic Johnson noise of the source, so the 3dB penalty is moot. In other designs (like mine), those analyses are not valid.
May be an important precision must be recalled here... We are speaking of two different things. The balanced nature of the cartridges AND the use of the current mode instead of the voltage ! Even there are some "current preamp" on the market (for example 47Labs, the various Dynavectors, the ESE Nibiru, Jean Hiraga's DIY) the balanced version of this current preamp is rare !...
Then, most of the drawbacks of the balanced voltage preamp don't apply to the current mode preamp. The amplification in current mode, for example, does not require any impedance matching.
Then, most of the drawbacks of the balanced voltage preamp don't apply to the current mode preamp. The amplification in current mode, for example, does not require any impedance matching.
This would not be the case.
Nearly all high performance DAC chips these days are balanced OP. They do
this specifically to get very low distortion figures through cancellation of
(some of) the even order components.
WRT all of those opamps, one of the best upgrades you can do to most fully
balanced voltage OP DAC's is throw away the whole back end and use a
VHQ line OP transformer such as Jensen or Cinemag.
Then you get a true galvanically isolated, bal or unbal OP - just like in
studios in the old days when they made great sounding recordings 🙂
Terry
I finally got my lightspeed working
I finally got my lightspeed working and it sounds amazing. I used Quanghao's pcb of Salas's Low Voltage Shunt Regulator circuit to power it.
My wife is also amazed at how good my stereo sounds now.
Thank you George, Salas and Quanqhao for providing these circuits and pcb.
I finally got my lightspeed working and it sounds amazing. I used Quanghao's pcb of Salas's Low Voltage Shunt Regulator circuit to power it.
My wife is also amazed at how good my stereo sounds now.
Thank you George, Salas and Quanqhao for providing these circuits and pcb.
Oh great - a Lightspeed post at last !!
It's been all about cartridges, balanced stuff and pro audio recently.
Nice one Kerux - congratulations.
I'm recently a convert too and I'm still delighted with mine.
It's a big upgrade.
Your power supply sounds interesting - I'll check that out🙂
Andrew
It's been all about cartridges, balanced stuff and pro audio recently.
Nice one Kerux - congratulations.
I'm recently a convert too and I'm still delighted with mine.
It's a big upgrade.
Your power supply sounds interesting - I'll check that out🙂
Andrew
Andrew;
Check out dvb-projekt's Salas shunt regulated boards for powering the Lightspeed
Attachments
I bought my matched ldrs from a friendly person on this board. costs are a premium but it saved me many grey hairs.
I actually have the case now and most of the small bits and pieces. As soon as I manage to free up some time I'll start assembly. 🙂
(Three projects running in parallell and my classes at the local techical university keep me quite busy.)
I actually have the case now and most of the small bits and pieces. As soon as I manage to free up some time I'll start assembly. 🙂
(Three projects running in parallell and my classes at the local techical university keep me quite busy.)
Kerux,
Nice job. Got pics?
Was at a friends house yesterday. He had been a DJ for a jazz station in Louisiana for several years back in the 80's. I've not met anyone with that many records/cds. "3000 more records out in the garage" he says. Jeeeeez!
Anyway with a LS in his system for the first time his words were "are those MY speakers?" pretty much what his wife said. The difference was huge. Fun times.
He had a Melos pre in there when I arrived which also sounded incredible, not equally incredible but I am predjudiced towards LDRs of course, but it was quite a different sound. I wouldnt mind trying that pre in my own system from time to time.
Uriah
Nice job. Got pics?
Was at a friends house yesterday. He had been a DJ for a jazz station in Louisiana for several years back in the 80's. I've not met anyone with that many records/cds. "3000 more records out in the garage" he says. Jeeeeez!
Anyway with a LS in his system for the first time his words were "are those MY speakers?" pretty much what his wife said. The difference was huge. Fun times.
He had a Melos pre in there when I arrived which also sounded incredible, not equally incredible but I am predjudiced towards LDRs of course, but it was quite a different sound. I wouldnt mind trying that pre in my own system from time to time.
Uriah
George, for a balanced setup I would rather use a simple shunt setup (two fixed R in series + single shunt LDR between the two "sides").
Using series/shunt LDR (i.e., mkII) IMHO is NOT a good idea, any attenuation unbalance among the two "sides" will screw up the balanced environment.
That solution would certainly be easier. I dont think George was recommending the solution he posted but simply giving the guy what he asked for. Its really hard to perfectly match up as many LDRs as are necessary for balanced, the reason for the Valium. Your solution might be worthwhile of course impedance is all over the place that way, but with a powerful CDP output and a real high input impedance on the amp it might not matter much. Why not use LDRs as the set resistance resistors?
A much simpler way to build a balanced attenuator is to use "floating balanced" (see figure)
Using this method, you'll save one LDR per channel, less headaches for their matching and their driving !
The series LDR must match very accurately.
This could be done with a switched resistor stack. A two pole 6 position switch each feeding a fixed resistance into the respective LEDs would achieve the separation that could allow for very accurate trimming of the LED resistors.
The shunt LDR is the continuous Volume controller and does not need to be matched.
However, I proposed something very similar in another thread and was referred to D.Self for why this shunt version of a balanced volume controller is not as good as it can be. I can't recall the details but the argument against seemed valid to me.
If you can accept or overcome Self's argument, then this would be very simple to implement.
This could be done with a switched resistor stack. A two pole 6 position switch each feeding a fixed resistance into the respective LEDs would achieve the separation that could allow for very accurate trimming of the LED resistors.
The shunt LDR is the continuous Volume controller and does not need to be matched.
However, I proposed something very similar in another thread and was referred to D.Self for why this shunt version of a balanced volume controller is not as good as it can be. I can't recall the details but the argument against seemed valid to me.
If you can accept or overcome Self's argument, then this would be very simple to implement.
Well, there are two possibilities here :
- if no match at all is performed, a separated left and right control could deliver the correct balance,
- if a stereo control is used, a balance correction is mandatory.
As for all LDR, the major drawback is to ALWAYS deliver the CORRECT current to LED to be sure to get the correct value for the resistor. This remains true for all series and shunts components. Using resistors to control them may be one solution, but it is a "fixed" method (excepted if the resistors could be replaced by real adapted values). A best approach is to be able to correct the currents for any divergence of these resistor values, from time to time, either manually or automatically, ...
