Why I enjoy my Luminous Audio passive unit, vs an additional gain stage ( preamp )


This topic of preamp / passive, has been discussed, ad nauseum. So why am I posting this ?, you ask. Why not, as it is still be discussed heavily here, and elsewhere. This is a short story ( lol ), but a quick read, so be patient, and thank you, in advance, for reading. In the early eighties ( I am thinking ’84 ), PS Audio introduced the model IV preamp, which had a button on the left side of the faceplate, that showed...Gain...active / passive. Interestingly, a year or 2 prior, the CD was introduced. Prior to the cd, we audiophiles and music listeners, listened to vinyl, open reel tape, radio ( tuner ) cassette tape, and in my case, worked a bit with microphones, patch bays, mixing consoles, and dabbled in live recording ( early on ). As most of you know about me from my posts here, I own Klipsch Lascalas ( tweaked and modified ). I met Paul Klipsch, and was, from my very early beginnings, a Klipschaholic. My dad had AR3a’s, driven by a Fisher 500C. My music teacher / singing coach, had Klipsch Cornwalls ( the mid and hf horns were vertically mounted, mirror imaged, and were the only pair I had ever seen with this vertical arrangement ), which soon became mine, as he upgraded to the Khorns. My dad no longer wanted tubes, so he purchased a Sansui 8 Deluxe, and I, the 500 C. Wow !. We were both happy. The Sansui was so much a better match for driving his power hungry ARs, and I was happy with my combo ( this was the late 60s already ). Moving along to the CD era, the typical cd player, produced 2 volts output, which was enough to drive most power amplifiers directly ( just needed a way to control volume ). The early cd players, were large and heavy, and they had, as part of their designs, massive transformers and huge, hefty power supplies. Sony, if I remember (and I could be wrong ),was the 1st company, who offered a variable audio output on their players, and we, the equipment consumers, bypassed our preamps, and were running these cd players, even through receivers and integrated amps, that allowed the disconnect between the pre and power sections, going direct into the power amp sections. Getting back to the introduction of the PS Audio model IV preamp, and its gain switch. This began an onslaught of passive devices ( volume controls / switching units ), without a gain stage, to hit the market. Moving along to modern day, there are hundreds of passives available. Some dac manufacturers claim, they can drive amplifiers directly. As it turns out, within the last several years, manufacturers are now producing integrated amplifiers, sans a preamp gain stage, taking the signal of the source ( not just cd players and dacs ), but tuners, tape machines, computers, phones, outboard phono stages, cable and satellite boxes, etc., and driving the power amp directly, without the need for the extra gain stage. What I want to tell you, is this. With the right system ( and I will use my system as an example ), an extra gain stage ( preamp ), does more harm, than good. A longer signal path ( more parts, more wires, more circuits ), can only destroy finite details, can only add colorations, can only add distortions, if GAIN IS NOT NEEDED. I used to feel this is in part, to the very high sensitivity of my loudspeakers, as any of my ( what remains of my collection ) 20 or so power amps, runs them so very easily. However, I have introduced many folks to the passive band wagon, taught them what to listen for, helped them with their systems, and now, enjoy passive listening. With all types of systems. Jumping back to my Luminous Audio unit ( I am using their top single ended model, but they all share similar topology ). This is a fixed series / variable shunt device. What this means is, the signal never passes through the volume control. The signal travels through 1 high quality resistor, and the amplifier’s inputs are shunted to ground, via the potentiometer, itself. The resistors can be selected, as well as the potentiometers, depending on the model, and Luminous will impedance match your particular unit, to match your system. For a nominal fee, it can be sent back to Luminous, and be designed to match with other / different gear. The beauty of my passive unit, is, that I do not " hear it ", in my system. It is NEUTRAL. Another term popularly used, is COLORLESS. How I know this. Using a self modified Yamaha pro amp from my collection, which has input attenuators ( as all pro amps do ), I hear no difference between my dac feeding the amp directly, vs the Luminous in the system ( although, I do hear the additional 1/2 meter Audio Research Litz interconnect, needed, with the passive ). Yes, this cable has a sound ( all cables, ime, do ). I am not getting paid by Luminous, by Klipsch, by anyone, posting this. Lastly, 2 more things. I have heard a few systems, in which an active preamp was beneficial ( the added gain ), but, to my ears, some neutrality was lost. I also greatly believe ( besides the source needing to have the proper output voltage and matching impedance ), the source, whatever it would be ( let’s say a dac ), should have a very hefty, over designed, stiff and well regulated, power supply, as part of it’s analog output section, based on my listening ( many do not ). I am open to further discussions on this matter, invite questions, and share experiences. Enjoy, be well and stay safe. Always, MrD.
mrdecibel
@atmasphere I know you are big on balanced, as this is so very obvious. I AM familiar with balanced systems, for a very long time. As I mentioned recently, I spent some time with the recent Benchmark gear, where we did a shootout with several brands of balanced cables, and they all showed various attributes, weaknesses, colorings if you will, and this included cables made by Benchmark. I am not sure why your insistence of " cables do not sound different ", when they are used in a balanced configuration. Several of us have heard these differences, and easily.......getting back to transformers for a moment. I feel, they are necessary in many instances.....but as a listener, I do not like them, in a home playback system, whenever possible. This is exactly why, you follow your path of OTL amplifiers, as your designs. Yes, it limits their ( OTLs ) use, but imo, transformers are band aids, that are needed in many areas. McIntosh makes fabulous output transformers, and continues to use them in their SS gear. However ( and I might get some backlash from some folks reading this ), my description above in my previous post, is exactly how I hear their amplifiers. Round, rolled off at the frequency extremes, colored, lacking in finite details, and sluggish and slower bass, than most ( why I do not use tube amps )However, I know hundreds and hundreds of listeners who use Mc gear and tube gear, and understand, and respect their decision to use it. Just not my cup of tea, as many, who do not like passive, or horns, etc. So, cables do sound different, whether single ended or balanced, to these ears. Always, MrD.
I am not sure why your insistence of " cables do not sound different ", when they are used in a balanced configuration. Several of us have heard these differences, and easily.......getting back to transformers for a moment. I feel, they are necessary in many instances.....but as a listener, I do not like them, in a home playback system, whenever possible. This is exactly why, you follow your path of OTL amplifiers, as your designs. Yes, it limits their ( OTLs ) use, but imo, transformers are band aids, that are needed in many areas. McIntosh makes fabulous output transformers, and continues to use them in their SS gear.

Apparently I've not made it clear: when the equipment supports the balanced standard, the cable differences are vastly reduced. Its readily apparent from the quote above that whatever product was driving the cables to the Benchmark, while perhaps being balanced it didn't actually support the standard. So you were hearing differences! The standard is also known as AES48. Here's a nice page from Rane that explains more about the standard:https://www.yumpu.com/en/document/read/46700632/rane-note-110-sound-system-interconnection-avw


Line transformers used in balanced line are vastly different than the transformers used at the output of a power amp! The smaller you make the audio transformer (and line transformers are pretty small) the wider the bandwidth that is possible. I would not be surprised to see a line transformer that could do 5Hz to 100KHz. Of course as you point out we are the OTL people, so we came up with a way to support the balanced standard in a **preamp** that not only has no output (line) transformer but is actually direct-coupled.



@atmasphere I will never claim to be as smart as you, but I am sure betting my hearing is as good as yours, and I will leave it at that. Although this thread was about passive vs active, you are making it about single ended, balanced, and balanced standard, AES48. I understand passive has it's limitations, and why you brought all of this up. I do not want to argue with you ( how I miss Almarq ). The entire system used during our cable evaluation was new Benchmark products, from the source to the amps, which I understand to be ( prove me wrong ), the standard AES48. And if I am wrong, so be it. I have been wrong before. So, given the " cable differences might be greatly reduced ", which is your wording, are you suggesting, that differences in cables, under these conditions, are NOT audible at all ? As far as transformers....I understand all that. I still do not like them, in applications that I am speaking. 
BTW...some of the cable brands we listened to were Audioquest, Cardas, Silnote, Kimber, Transparent, WyWires, Shunyata, Belden ( home made ), and the Benchmark cables. 
The entire system used during our cable evaluation was new Benchmark products, from the source to the amps, which I understand to be ( prove me wrong ), the standard AES48. And if I am wrong, so be it. I have been wrong before. So, given the " cable differences might be greatly reduced ", which is your wording, are you suggesting, that differences in cables, under these conditions, are NOT audible at all ?
There are very slight differences between the very best cables and the very worst- not enough to write home about; the balanced standard is very effective!


As best I can make out the Benchmark line drive unit does not support AES48. If a preamp has both balanced and single ended outputs that run at the same time, without a switch to go between the two, then its unlikely to support the standard.

This is because you can't operate both balanced and single ended off of the same output: they are mutually incompatible. What's happening with the Benchmark line drive (which is similar to their other units that make a balanced output) is that the balanced output references ground. That's a violation of the standard (and is quite common throughout high end audio). 

The following article is from the Benchmark website. If you read through it you will see that AES48 is not mentioned, although near the end of the article AES3 *is*; clearly John is familiar with the AES:

https://benchmarkmedia.com/blogs/application_notes/balanced-vs-unbalanced-analog-interfaces


It is also apparent from this article that John knows his stuff! I suspect he is aware that his line stages don't support AES48; otherwise he would mention that somewhere on his site as otherwise he makes all the right arguments supporting differential amplifiers and the like.


Now the argument has been made that if both outputs of the XLR connection reference ground, but the ground currents are identical, then they cancel. This is true but now the cancellation has a number value attached, because in the real world they won't/can't be identical. This is the same argument that some people mistakenly make for an output transformer (driving a balanced line) needing a center tap to reference it to ground. The reason this is not actually a practice is because the center tap can't be perfectly placed and so will degrade the CMRR performance. It also means that there will be ground currents in the cable, and further means that now the construction of the cable has become critical to its sound.


So I'm not doubting what you heard- I've experienced exactly the same thing. I think what's going on here is you were under the impression that the Benchmark line drives support AES48. That would explain about 95% of our exchanges on this thread!


BTW I miss Al too- he retired a few months back and has been far less active here ever since. I really appreciated his comments!