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Have Passive Preamps Finally Come of Age?

Back in the late 90s (eons ago) I tried a variety of passive preamps (PPs). The most musical was an autoformer, but back then my system was not balanced. For the last decade I have been using active preamps, both tube and solid state, but finding a quality balanced preamp under $4K is damn near impossible. Enter the Parasound P5 (2.1), which in addition to having balanced I/Os, it has a separate bass management circuit (MSRP $1095), and I was hoping it would provide better control over the built in class D plates incorporated into my 2 SVS powered subs, whose volume controls are STUPIDLY sensitive: when barely cracked from zero they overwhelm. Alas, no bueno. 

Recently i watched a PS Audio YT video that was emphatic about NOT connecting powered subs with interconnects; instead he recommends speaker cables piggybacked off the main systems amp/s. I had a spare set of DIY flat copper cables, and was shocked how much better they sounded, but doing so did not change the  volume control problem and unfortunately this id not bypass the SVS amps whose class D chips are now ancient. Thinking there could be an impedance problem led me to revisit PPs.

I sold my P5 and was using the XLR outs from my Oppo 105 (upgraded power supply and IEC/wiring to the power supply) direct to my Emerald Physics 100.2SEs (class D). The noise floor dropped tremendously, allowing me a much better view into the music. My Core Power Technologies 1800 PLC had more than a little to do with this, but...  

Days of PP research later, I came across LDRs, which seem like the ultimate PP option, but XLR versions are ~ $2K and up, with the Tortuga coming in at $2700, seems like a true SOTA bargain, just not in my current budget. Scouring the' for sale' sites I came across a Hattor XLR (MSRP $995) which was in my price range. Hattor's www had links to 2 reviews both were extremely positive: one used it in combination with a class D amp. Bingo! I snapped it up.

It arrived late yesterday, although Hattor's www pictures look awesome, they do not compare to seeing and touching it. The metal carrying case was an indication of the designer's dedication. This is an etremely well made piece of kit, but how does it sound? Alas it came with no manual and Hattor's site does not have a PDF. How hard can it be to hook up? Well, after a couple scary minutes, I discovered that it would not light up until I connected the 105. 

Stone cold, the first thing that shocked me was a further reduction in noise floor and an incredibly wide and deep sound stage, but as can be expected, it was dry. Fingers crossed, in about a half hour I began to be rewarded with texture as well. Tis only got better as the night wore on

I hope somebody chimes in with their Tortuga experience, or any other high quality PP information.that goes under the reporting radar. 
tweak1
georgehifi's avatar
georgehifi
4,966 posts
 
With a 3 foot high quality cable (which would have 300pf) in such cases you would have a roll-off that is very real world.
Totally false and misleading.
A 10kohm passive pre which the Lightspeed is also, has a worst scenario output impedance of 2.5kohm.
This together with Ralph’s example of 300pf for a meter of interconnect, will give a high frequency -3db roll off point of 212kHz!!!! (bat hearing territory)
With 2mts of the same interconnect (which btw is not low capacitance) the -3db is still 106kHz!!!! faster than any transformer output tube amp.

You are kidding yourself calling this "very real world". (Just product protection mode from what I see with these sorts of comments)

Cheers George
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atmasphere's avatar
atmasphere
7,068 posts
 
If the passive has a 10K impedance maximum George's statement is true.

Apparently not all Lightspeed controls have such a low impedance; we had one here that was much higher. So the model you get can have a big effect. Also, 300pf is a low value even for a 3 foot interconnect (A 6 foot cable will double that capacitance), although low capacitance cables are available that are much lower.  Its my recommendation that such cables (such as are used for phono cartridges) be used unless a lower value of passive control (such as 10K) is employed. Keep in mind though that not all sources are happy driving a 10K load (which may well be in parallel with the input of a solid state amp, resulting in an even lower impedance) so its best also to check with the manufacturer of the source component to insure that it can drive such a load successfully.
georgehifi's avatar
georgehifi
4,966 posts
 
Most good interconnects are 100pf per foot or less your citing of 300pf for a mt, is for a reasonable low capacitance interconnect and all my figures above in my last post are correct, and I have always stated so from the first Lightspeed built, and to use good quality interconnects that are 100pF per foot or less.
What you stated is a total falsehood and misleading.
With a 3 foot high quality cable (which would have 300pf) in such cases you would have a roll-off that is very real world.

Apparently you had either clone or a faulty one or just BS’ing, and if your going to start on my product then you’ll receive the same.

As for impedance matching, I have also always stated from the first one built that an output to input (Lightspeed to amp) impedance ratio should be 1:10 or higher, and have never said that it or any other 10kohm passive would be happy into a 10kohm amp input impedance.
And that sources should have a low output impedance <500 ohms, not like most tubes sources have, very few like the Herron phono stage are fine.

As I still believe these falsehoods are of someone in product protection mode, and to be honest I don’t blame you, threads like these cheap passives are a killer for $$$K preamp sales, and OTL’s can only drive so much, unless aided by Zero band-aids, of which I’m also anti.
atmasphere's avatar
atmasphere
7,068 posts
 
Hmm. George, I'm not worried about it- I simply acknowledged that you were correct yet you're still going off. If anyone seems in damage control mode, its you right now. Just calm down.

You'd have to imagine that I'm well aware of what our amps can and can't do; our amps don't use feedback, so speaker choice is important. But the flip side of that has consistently been that if the speaker requires the amp to have feedback, it also has no chance of sounding like real music (I can outline exactly why easily enough). So I just vet each sale to make sure the customer is going to have a success. Works pretty well- that's why we're one of the older manufacturers in high end audio- 42 years in about 10 days. 

I don't remember which customer lent us the Lightspeed, but we had it for a week. As passives go, it was one of the better ones we checked out. If you are on a budget and have only high level sources, its not a bad way to go. IOW like any passive it can do well but not state of the art; plain and simple. That's why I'm not worried; passives are just a little too simple to do everything correctly (the better your system gets, the easier this is to hear). Cable control and buffering the source to prevent distortion are two example of why and I can name more.

Now that's not an insult, its just a statement of fact. State of the art nearly always costs more and that shouldn't bother you.

BTW, your comment about headroom in preamplifier and source design is still false and no amount of remonstration on your part will change that. I chose not to continue that bit but you insist on attacks. Just calm down and it will be OK.

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