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

Showing 6 responses by almarg

almarg's avatar
almarg
9,670 posts
 
Jay23 8-3-2018
I was referring to George and Ralph’s technical discussion on the last page (3), and not the whole thread and topic.
Sorry I misunderstood. Upon re-reading that page of the thread I believe you are referring to statements by Ralph such as:

Atmasphere 7-27-2018
If the circuit only has to do 2 volts but can make much more, its distortion can thus be kept extremely low- to the point that its difficult to measure.

This is why many active preamps have such low distortion, because they are operated well below their limits. This is just good engineering.
and by George such as:

Georgehifi 7-27-2018

Any source that has been designed to give out 2v has been done so to be done to do so in it’s most linear state, you would be a fool to do otherwise, unlike what Ralph will have you believe.
On that particular point I agree with Ralph 100%. And in fact a very common means of assuring that "any source that has been designed to give out 2v has been done so to be done to do so in it’s most linear state" [quoting George] is to design in exactly the manner Ralph described, providing a good deal more voltage swing capability than will actually be necessary. Also, consistent with that, a few posts prior to their exchange on that issue I had commented as follows:

Almarg 7-27-2018
... 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

almarg's avatar
almarg
9,670 posts
 
Notwithstanding the hilarious frequency response claim, I’m pretty sure the internal wiring to and from the internal portions of the RCA input and output jacks of the attenuator is likely going to be more bandwidth limiting than any external RCA interconnect(s).

While I’m not familiar with the internal construction of George’s Lightspeed attenuator, I would expect that what limits high frequency bandwidth is the low pass filter formed by the interaction of the impedance "looking back" from the junction between the series and shunt LDRs and the capacitance "looking forward" from that point.

Given the far greater length of an interconnect that would be usually be connected to the output of the Lightspeed, compared to the length of the wiring between the LDRs and the output of the device, that capacitance will almost invariably be dominated by the capacitance of the interconnect. Hence the statement I quoted above appears to me to be incorrect, and George’s statement that "interconnects are the determining factor here" is likely to be correct.

Perhaps, though, the statement I quoted above was intended to refer to the bandwidth of the interconnect in itself. If so, under any reasonable circumstances involving a home audio system I would expect that number to be so high as to be irrelevant to the bandwidth limitation imposed by the interaction of the capacitance of the interconnect and the Lightspeed’s impedance that I referred to.

Regards,
-- Al


almarg's avatar
almarg
9,670 posts
 
Jay23 7-27-2018
@almarg

Pick a side!

As I mentioned earlier I haven't taken the time to read the first couple of pages of this thread. And my usual tendency is to not take sides in traditional debate topics such as active vs. passive, tubes vs. solid state, vinyl vs. digital, R2R vs. delta-sigma DACs, etc., because it seems clear to me that any of these alternatives can work very well or very poorly depending on the specific designs, system matching, and user preferences. In other words, I consider myself to be a pragmatist.

In case it's not clear, though, all of the comments I have provided in this thread have been entirely consistent with what Ralph has said on the same issues. And in fact I rarely disagree with Ralph about anything.

Regarding George, I have both agreed and disagreed with him on numerous occasions in these forums, but always in a mutually respectful manner. One of the disagreements occurred in the recent thread where the Herron/Lightspeed/Gryphon combo he referred to above was discussed.

Regards,
-- Al
almarg's avatar
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
almarg's avatar
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


almarg's avatar
almarg
9,670 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
More to discover