2. amps-preamps
  3. 136322-2546

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
teo_audio
2,197 posts
 
It will also pass clean 1080p component video or coaxial 24/192 digital & DSD.

It might also pass a couple of amps of current at ~12vdc. All with the volume wide open, of course. High current DC and high MHz AC capable, all in the same box.

Let me rephrase that a bit. (deleted my above prior post) Wrote it too fast and slightly incomplete. Some capacity for AC, as in HF alternating current. More like ’RF capable’, would be the better analogy. Lowe current, low voltage, but Radio Frequency. Similar in bit bandwidth, as well. Very high bit bandwidth, essentially.
tweak1 OP
3,645 posts
 
lartecafe

"SHOULD BE SIMPLE"?

First, my mnd is officially blown after replacing my Emerald Physics 100.2SE monos (with upscale fuses) with an Audio Alchemy DPA-1, (125w @ 8 ohms)  Having  2 Gain options are crucial in my case; seems my Hattor Passive needs the extra 6db to come on song, otherwise, meh! I am told AAs preamp/dac sounds as good as Constellations 1.0 @ ~ $2700 with external power supply, which is said to be essential

I suggest you read Absolute Sound reviews of the Constellation 1.0  Preamp ($9000); itself a lower cost version of their Inspiration preamp ($24000) and the Tortuga LDRXB passive $2695 vs the rest of the simplistic passive world. Not hatin, just sayin

Replacing resistor ladders with LED light tech requires an entirely different (and more complex) approach to passives. It's hard or me to imagine being "that' must better than my Hattor, but.... 

LDRs are not the easiest components to work with notwithstanding their superior sonic qualities. Their challenges are twofold. First, the relationship between LED current (light intensity) vs. resistance is inherently nonlinear. Secondly, even with LDRs of a given make and model there's considerable variance in this nonlinear relationship from one individual LDR to the next. To implement a reasonable stereo attenuator with LDRs means you have to use 2 per channel. Given both their nonlinear behavior and individual variances, you soon realize that you first have to test each individual LDR and record its current vs. resistance curve. All of that data goes into our LDR database where at any point in time we usually have test results for over 100 LDRs which we haven't already used. We've developed sorting routines that process this data to tell us which next 4 LDRs are most closely matched. If we decide those 4 aren't sufficiently close, we'll test another 50-100 LDRs and add them to the database, then re-run the sort until we get satisfactory matches.

So your advice is at best archaic, or limited to your investigations


celander's avatar
celander
1,503 posts
 
@teo_audio  I presume you’re discussing the Liquid Pre. 
tweak1 OP
3,645 posts
 
George, your info would be spot on IF the AA did not have 2 gain options (I was unaware how valuable that is). I didn't try the base gain until late last night: where did the music go? I quickly reengaged the + 6dB and viola. Im a very happy camper again. And I am not abe to use (and not missing) my 2 SVS Ultra powered subs, which is more evidence of the EP/Hattor mismatch

Eventually the Hattor will go to a new home, to be replaced by either an AA DDP-1 (but I don't need either the dac or the headphone circuit) and if the dac is better than in my Oppo 105 I'm guessing I would need to switch it in/out when listening to non SACD format:and if so, no bueno, but I think I can get one with power supply in the $1500 range. If so, I probably will. So far the Tortuga LDRxB is at the top of my wish list, but it's $2700. I could stretch to half that amount, but don't see that happening :(.

I decided against the Nord for several reasons

* it would take 3-4 weeks and I was music-less
* it had tons more power than my 94dB KCIIs need to jump out of the speakers, and my new speakers are 96db
*  the AA was almost half of the Nord price

Thanks again, though
celander's avatar
celander
1,503 posts
 
@georgehifi I agree with your assessment of impedance mismatch between the Hattor passive (unbuffered) preamp and the choices of amplifiers that tweak1 selected. 

@tweak1 You initiated this thread discussing passive preamps, yet you have nearly changed everything downstream to accommodate it (that is, the Hattor passive unbuffered preamp). This includes a new amp, a different set of speakers and ditching your powered subs. I respectfully disagree with your assessment that a simple gain switch will rectify the impedance mismatch George referred to. Just for kicks, why not obtain his suggested amp to audition? You’ve changed so much already; one more audition won’t be much work. And don’t be afraid to liberate yourself from the need of a class D amp, unless you are worried about electric bills. There are a lot of good design topologies that will likely bring smiles to your face when mated into your system.

Trying is the pudding of life. And I know you at least enjoy trying new gear!  

Just my two cents!! Enjoy the music!!  
More to discover