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
Post removed 
almarg's avatar
Ag insider logo xs@2x
almarg
9,670 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


unsound
7,329 posts
 
Some amps require more than 2 Volts input for full output.
almarg's avatar
Ag insider logo xs@2x
almarg
9,670 posts
 
Very true, Unsound. For example most and perhaps all Pass Labs amps have the same gain (26 db), which means that as the power capability of the various models progressively increases progressively more input voltage is required for them to reach their rated maximum power. Consequently the X600.8, for example, has a specified sensitivity for full power of 3.46 volts.

Although if a Redbook source provides balanced outputs, those outputs may provide maximum voltages in the area of 4 to 5 volts (i.e., 2 to 2.5 volts or so for each signal in the balanced pair of signals), which would still be enough to clip that amp.

Best regards,
-- Al
atmasphere's avatar
atmasphere
11,772 posts
 
Many amplifiers overloaded with 2 volts ? Are we talking about power amplifiers being overloaded, or preamplifier sections being overloaded ? 30 volts output ?
Al did answer this, I hope its now clear.
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.
George's statement here is clearly false; it doesn't appear that he's trying to mislead so much as he seems to have no idea of what he's talking about.

As I said before, active preamps are often built to produce far more output than is asked of them so that distortion at their normal operating range of less than 2 volts will be devoid of distortion. Most sources like CD players have a similar overload margin built in to them as well for the same reason, despite the maximum output being the Redbook spec.

The amount of overload margin used in a vinyl cutting system is even higher, to insure that its impossible to overload the cutter or the cutter amps. IOW, the inclusion of overload margin in audio products is a common practice among competent designers.


More to discover