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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
celander's avatar
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celander
1,036 posts
 
Ugh....
This is from Wiki:

“In a home audio system, the term ’preamplifier’ may sometimes be used to describe equipment which merely switches between different line level sources and applies volume control and possibly tone control circuits. Such equipment prepares the signal before amplification but, in fact, no actual amplification circuitry may be involved.”

In professional lore, this definition is usually used, as no phono stage is included in a professional mixing console. 

The term “line stage” was created to alert the home audiophile of the absence of a phono stage in the box. But the converse isn’t necessarily true in the case of a preamp. 
tweak1 OP
870 posts
 
The reason behind my question had to do with better design and higher quality parts making for  a better end product than in ages gone by

In my case, the missing ingredient was not understanding the importance of impedance matching in order for them to get along with the amplifier/s. This tidbit alluded me then and now, as electronics is foreign to me
celander's avatar
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celander
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@tweak1 Agreed regarding impedance matching. My ATC active monitors have built-in amps having an input impedance of 10-kOhms. While this is typical for pro amp gear, it’s on the low side for consumer gear. And the adage of sticking with gear from the same manufacturer is wise advice with regard to ATC. Their preamps have output impedances set at 10-Ohms. (Typical pro preamps have output impedances of 600-Ohm or less, so I gather.)
tweak1 OP
870 posts
 
All prior comments were when using my Oppo 105  either direct for SACD/DVD-As, or as a transport, after getting the Audio Alchemy DDP-1 DAC/PRE

A couple days ago I decided to dust off my Pioneer PD 65 CD player (inverted platter) Stage 3,modified over a decade ago by Musical Concepts; with outboard power supply: it is a CD player with optical output

After a brief warmup, the music is so much richer, adding texture to the entire musical spectrum

My Hattor does not provide for toslink,  so it was a good thing I bought the AA DDP-1, or I would have never known what I was missing with the Oppo

Hattor definitely going up for sale now


 
atmasphere's avatar
atmasphere
7,068 posts
 
And Al, a source that gives out 2v is always going to give it out, even if you shunt half of it to ground because you don’t need it, because you have more gain to make it back up in the active preamp.
So the distortion from the source "whatever it is remains the same", it does not change because you’ve decided not to use half of it and shunted the other half to ground.
If anything shunting more of it to ground "could" make it distort more.
Not all volume controls shunt signal to ground. The traditional volume control does not shunt any at all. But there are shunt-style controls and they have been around for a while. They rely on a resistor (usually of significant value) to be always in series with the source (meaning that the resistor affects the sound if not carefully chosen), so that when the volume control is shunting the resulting output, the source will not distort or be bandwidth limited (IOW not significantly loaded).

Now if the shunting element is the same value as the series element, the signal loss will be 6db, as the the output voltage will be cut in half (at full volume). With most passive systems this sort of loss is unacceptable- so the shunt portion of the circuit (the actual control) is often much higher than the series element; as much as 10 times higher.
The question then is - what is the value of the composite control? For example George has stated quite often that his controls are "10K" (10,000 ohms). If its a shunt-style system as one might infer from the above quote (since many controls don’t shunt the signal at all), then is he stating that the series element is 10K? That would allow for the minimum value that the source (DAC or CDP) would be 10K. This would imply then that the *actual* control is considerably higher.

At any rate, the statement in the quote above is problematic. The designer of a passive control I would **assume** would not want to give an active preamp an edge over his product by loading the source in such a way as to increase its distortion! If this point is ignored by some passive designers, it may explain why good active line stages can easily outperform passive devices in some cases.

FWIW, no *active* preamp loads a source in the way George describes; the volume control (if at the input of the preamp, which is a good place to put it) is chosen to be a value such that no source of any type will be challenged by it!! Again, this is just common sense engineering (much like the built-in headroom that all competent preamps and sources have), and I hope that this is obvious to anyone reading these words.
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