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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
kosst_amojan
2,095 posts
 
@mrdecibel 

He doesn't know what he's talking about. No good amp designer builds an amp that really peters out at it's rated power. You overbuild the amp, set the gain conservatively, and then brag how your amp gets .00X% distortion at "rated power" with 1.5V input. That's what Nelson Pass does all the time! It takes WAY more than 2 volts to break down a typical small signal audio JFET. 
almarg's avatar
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almarg
8,673 posts
 
Many amplifiers overloaded with 2 volts ? Are we talking about power amplifiers being overloaded, or preamplifier sections being overloaded ? 30 volts output ? Now I am confused.
I haven’t read most of this thread, but regarding your comment I’ve seen preamp output voltage specs confuse a number of people here in the past. The 30 volt number Ralph referred to, and other preamp output voltage specs that are greater than a few volts, represent their maximum output voltage **capability.** Everything else being equal, the higher that number is the better (within reason of course), as a higher number will provide more margin relative to the output voltages that are actually required from the preamp in normal use.

Actual output voltages higher than a few volts (in many cases something like 2 volts) will not occur in normal use, as they would drive nearly all amplifiers into clipping, and perhaps damage the speakers as well. Not to mention driving the listener out of his or her chair and toward either the volume control or the nearest exit :-)

The actual output voltage provided by a preamp will correspond to the input voltage the source provides to it at any instant of time (which will vary with the volume of the music, of course), multiplied by the gain of the preamp (expressed as the ratio of output voltage to input voltage), and reduced by the amount of attenuation the volume control provides at the setting being used (relative to its maximum possible setting).

Regards,
-- Al
georgehifi's avatar
georgehifi
4,966 posts
 
@mrdecibel

Simply: With the sources feeding them, preamps active or passive giving out UP TO a clean 2v to an amp that only needs 1v in to give it’s rated output before clipping, there NO USE at all for those same preamps active or passive to be able to give 10v 20v or 30v output.

Cheers George
kosst_amojan
2,095 posts
 
Huh.... looks like the Aleph L runs runs 30 volt rails to get upwards of 10 volts output. With...... MOSFETs!

If no amp ever made required more than 2 volts to utilize it's full power, why's Nelson Pass build nothing but pre-amps that give you at least 9.5 dB and at least 5 volts output? He certainly isn't the only one. All kinds of reasons why, too. 
almarg's avatar
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almarg
8,673 posts
 
All kinds of reasons why, too.

I would think that one reason, in addition to providing overload margin per se, is that if a preamp’s output stage is just operating over a small fraction of the voltage range it is capable of operating over, the result in many and perhaps most cases will be that linearity and hence distortion are a bit better than if it were operating closer to its limits.

Regards,
-- Al


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