Asheville, Walnut Cove, Biltmore Forrest and Western North Carolina’s Audio and Home Theater specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

All in one

As the team has been working on getting Stellar products up on the website (hopefully sometime next week) a thought occurred to me I hadn’t yet expressed.

Stellar’s Gain Cell DAC, the wonderful new piece designed by both Bob Stadtherr and myself, is really two products in one box. A cutting edge Sabre based DAC and an analog preamplifier. Bob designed the DAC and controls, I designed the Gain Cell which is the heart of the analog preamp.

Together these form the basis of the Stellar control center which we call the Gain Cell DAC. What I had neglected to write about was the design imperative we started with—build a single device that bettered the performance of either standalone component.

Readers of this blog will know that a few years back I relented my stance on DACs directly feeding power amplifiers. Once it had been demonstrated to me that an analog preamplifier inserted between the DAC and power amp improved sonics—a lot—I became a convert. With caveats. The main one being the quality of the analog preamp. Only a very small handful of analog preamps made the DAC sound more magical. Others of lesser quality clouded the DAC’s beauty.

The fact we were able to design and package two components together whose synergy bettered their standalone performance is a testament to a lot of hard work. That we pulled this off at anything less than a few thousand dollars is a miracle.

Fortunately for me, most of that work fell on Bob’s shoulders. Not my own, lazy bones.

Thanks, Bob.

Asheville, Walnut Cove, Biltmore Forrest and Western North Carolina’s Audio and Home Theater specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

Paul had posted a picture recently of a PS Audio CD spinner that they had taken in on trade for their new version, called the Perfect Wave Memory Player.

The previous owner of this unit had taken all these steps to try and reduce the amount of EMI, otherwise known as electro-magnetic interference, inside the unit by wrapping everything, including all the internal wiring, in some sort of EMI blocking  tape.

It looked funny to me and not something I would do. Why? Because a competent electronics designer takes these things into account when they design and voice a piece of audio gear.

Did what this guy did, do any good? Who knows, although I’m pretty sure the owner thought so.

Here’s Paul.
Invisible gremlins

If you’re making a horror film the best gremlins are visible. Even the most terrifying invisible threats eventually make themselves known so viewers get their money’s worth. But “seeing” audio problems isn’t all that easy for designers.

In a practical sense we can see neither the good nor the bad that impacts audio. Music is invisible.

Perhaps it’s more accurate to suggest there are the generally accepted causes that we metaphorically “see”, and the less accepted we do not. We can’t see germs with our eyes, but their impacts are felt none the less.

One gremlin is EMI (Electro Magnetic Interference). We take great pains to guard against this invisible enemy. Shielded wires, balanced cables, Mu metal, all exist to combat EMI’s evil. It’s easy to recognize when a hum or buzz has been eliminated by better shielding.

Far less noticeable is EMI’s impact on digital audio, a subject our wizard, Ted Smith, has been schooling our team on.

It turns out that many of the improvements in sound quality attributed to lower jitter tweaks find their roots in EMI reduction.

Our research and learning curves march forward. As we learn more specifics I’ll keep you posted.

 

 

 

Asheville, Walnut Cove, Biltmore Forrest and Western North Carolina’s Audio and Home Theater specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

From Paul…A shorty…
Perfection’s curse

When we become aware of better, we’re automatically aware of worse. Differences are magnified by extending boundaries.

Where once I might have been just fine with this or that, being exposed to better lowers tolerance for worse. Food is a great example.

Next week I travel to Las Vegas for the annual CES where eating has become something of a challenge. Most of the high-end food choices in Vegas have been institutionalized—homogenized—to the point of off-putting to me.

I understand that as a vegetarian living in a meat-consuming world I am always a pain in the kitchen’s butt. I get that. But it doesn’t mean the food quality has to be dumbed down to the point of mere acceptance vs. enjoyment.

The same is true for hi-fi.

Once you get exposed to better, it’s hard to go back to worse.

Asheville, Walnut Cove, Biltmore Forrest and Western North Carolina’s Audio and Home Theater specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

From me…
We recently completed an AV system that was installed by a guy from Charleston, SC, in Lake Toxaway, NC. The system was interesting, but all sorts of questionable design choices, which had served the owner well enough, but with problems and Charleston a long ways away, he turned to us.
 
We replaced a old Niles amplifier that has been powered on 24/7 for the past 8 years and a pair of outdoor speakers that for some reason were used in this very nicely furnished Guest Living Room.
The homeowner, by the way, is a very nice man and grateful that we would take over the servicing of his AV needs.
 
This design certainly isn’t the way I would have done it, but we replaced things the way I suggested with a Yamaha Aventage amp, Martin Logan Motion speakers, a new Sony Bu-Ray player for streaming and a new ProControl Universal Touchscreen remote control and it works beautifully. It’s a lot easier to control and also sounds a lot better…A whole lot better.
 
As an example of what some installers do and what we are faced with when we take over an install we did not do, I have one more story to tell about this install.
 
In a different location in this large, beautiful home, the owner has an old URC iPod dock which hasn’t been made of many years now.
 
While simply plugging in a new Blu-Ray player we set up for him, his dock lost power and appeared to be dead. He asked me what I did. I told him not enough to have done something like that. Truth is, I did….
 
We pulled this iPod dock from the cabinet and plugged it in elsewhere and it powered up fine. We then tested the outlet it was plugged into and sure enough, it was dead. We went to look at the circuit breaker box (twice), but no breakers were tripped, nor were there any GFI’s tripped.
 
Bryan took a look in the bottom of the cabinet where all his stuff is plugged into and spotted a white two conductor cord, which didn’t match any of the equipment inside the cabinet. He jiggled it and all of a sudden the electrical outlet flashed on an off.
 
The original installer, should have simply run an extension cord from the iPod dock to the bottom of the cabinets, where his equipment is plugged into the surge suppressor. Easy enough and the correct way to do this..
 
Instead, because he apparently really likes to hardwire stuff, he cut the end off of some electrical device, like a lamp cord, and connected the bare wire end directly to one end to the electrical outlet and plugged the other end into the surge suppressor. It worked, but the wire he used was two conductor, with a two prong connector, while the outlet was a grounded outlet.
 
It quit working because the two blades on the plug had become too too flat over the years to continue making contact with the electrical outlet inside the surge protector.
 
By me simply plugging in one component into the same surge protector that powered the outlet he installed, this was enough to make it quit working. So, considering this out of the scope of our work for the day, we simply widened the two blades to make better contact and it started working again.
 
Apparently the original installer does million dollar jobs and while I’ve done great work on the opportunities I’ve had, I wish I had a few more of those opportunity like this job here. However, this market is different…Yes…different….
 
Happy holidays everybody.

Asheville, Walnut Cove, Biltmore Forrest and Western North Carolina’s Audio and Home Theater specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

More on how PS Audio is controlling volume in their products these days.
The Gain Cell

The critical nature of a preamplifier’s heart and soul, the volume control, has vexed designers concerned with sound quality for years. Time and again we face the dilemma posed by it: What’s the best device possible for the smallest degradation? Turns out, the answer to that is no device.

Instead of compromising audio quality by inserting an attenuator in a purely analog preamp, better results are obtained by eliminating the device altogether. Instead, it is possible to reduce a preamp’s essential elements from three to two by varying the gain of the output stage, rather than attenuating the signal into a fixed amplifier.

But how do you design a transparent sounding gain-variable output stage in a preamp? You turn to the recording industry who has wrestled with this problem for years.

In the heyday of analog mixing boards, (they’re mostly digital now) engineers faced the same problems as we in audio: How to remote control potentiometers without sacrificing audio quality. They first used motors. It didn’t take long before that solution became unwieldily so they turned to something else. A variable gain amplifier. Based on an older circuit design known as a Gilbert Cell, this unique amplifier topology uses multiple differential pairs in a balanced configuration and a voltage to vary the gain. According to Wikipedia, “The Gilbert cell was invented by Howard Jones in 1963 but usually attributed to Barrie Gilbert (before joining Analog Devices) in 1968.”

My first experience with this unique topology was gratifying. I had long wondered what sonic compromises might be attributed to this device and set about testing a number of them. At the time I was interested more in sound quality than functionality (they all worked well for gain setting—not all sounded good). I wanted to find a Gilbert Cell that had the sonic richness and transparency I insisted upon to go into one of our products. None lived up to my expectations until our chief engineer, Bob Stadtherr made a suggestion to me. “Maybe it’s not the cell but the way you’re using it.”

Aha! Of course. It took me six months of hard work to design a fully balanced input to output amplification stage whose gain could be varied by simply changing a voltage, but hard work was rewarded with amazing sonic performance.

And thus, the Gain Cell was born.

You’ll be reading much more about this sonic wonder in the next few weeks as we launch the Stellar Gain Cell DAC for beta testing next month.

Stay tuned.

Asheville, Walnut Cove, Biltmore Forrest and Western North Carolina’s Audio and Home Theater specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

This is interesting to me as I think the way PS Audio controls gain, which is the volume control in their BHK Signature preamp, is truly different and the main reason is resolves such incredible, focused detail.

Is it perfect?

No……

The BHK Signature preamp depends on the quietest of tubes and even then, you hear a click or two as you turn the preamp “up”. These are the couple of relays that are part of the volume control.

We really don’t turn these things “up”. We really just lessen the amount of attenuation, as it always wants to play full blast. Kind of like a horse wanting to run and us pulling back on the reigns. Volume controls pull on the reigns of the preamp. Amps are a bit different, depending on what type of output stage they sue.

I can say with great certainty, that this preamp is as transparent a preamp as I’ve ever heard and I’ve heard a bunch and owned a bunch.

Now, from Paul.
Shortening the path

I’ve been writing a very long series over these last days. The path to understanding and appreciating volume controls in preamplifiers.

Without hesitation I would maintain their design and implementation remains one of the bigger challenges in high-end audio when sound quality is the primary concern.

To date we have covered many ways to control level: pots, stepped attenuators, light dependent resistors, and transformers. All have one thing in common. They require extra parts in the signal path.

The best volume control would be no volume control.

As I have written over the years, we designers can rarely make things better—though Power Plants would refute that. Generally we do our best to cause less harm and the ubiquitous volume control is a great example. No volume control element of any design can improve the signal. Best you can hope for is as little damage as possible. But what if we could eliminate the extra circuitry in the signal path altogether?

Control the volume without an additional element?

This is where an idea I came up with years ago comes into play. Instead of adding a pot, or attenuator in series with the signal, would it be possible to simply change the gain of the amplifier within the preamp? In fact, it is, but it turned out that’s not an easy thing to do well.

All active preamplifiers have an amplifier at their heart. Generally low gain, these amplifiers are the core of any device.

Remember back to the first post in this series? There I described simply the internals of a preamp.

  • Input selector
  • Volume/balance control
  • Gain stage

The question I had asked myself was simple. Instead of a three element design might it be possible to eliminate the middle and create a two element design?

  • Input selector
  • Gain stage

In so doing we obviate the problems associated with the volume balance control. Because if you don’t have one to muck up the sound, you’ve scored!

I’ll delve deeper starting tomorrow.

 

Asheville, Walnut Cove, Biltmore Forrest and Western North Carolina’s Audio and Home Theater specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

More on volume controls and in particular, the one inside the BHK Signature preamplifier.
Removing limitations

I had written in yesterday’s post the limitations of 30 or so steps of mechanical stepped attenuators concerns the switch itself. It’s near impossible to add too many more switch contacts in the small space available.

The limited number of steps isn’t the only drawback. Adding remote control requires a motor to do the turning, and we’re still stuck with large level jumps between steps.

But the idea of using individual resistors to control level in steps is still a great sounding option. How to get more steps when mechanical means don’t permit it?

Eliminate the restriction of the mechanical switch.

If you’ll recall our first posts on input selection in a preamp you’ll remember we had this very same problem. Mechanical input selectors are hard pressed to be remote controlled. We use an electronic switch instead. A relay, or its FET equivalent.

Once you figure this little gem out—using an electronic switch instead of a mechanical one—a new world of possibilities come into play. You’re no longer restricted on the number of steps and remote control is a cinch. Two birds with one stone and you’ve not sacrificed anything.

This is what we do in the BHK preamplifier and how we achieve 100 steps in 1/2dB increments. A combination of relays and FET switches control expensive, great sounding resistors to control level. The results are near perfect.

Still expensive and challenging for designers to build and implement, but problems solved.

I was going to move on and write how similar results can be achieved without such expense—the innovations of the new Stellar Gain Cell DAC—but many have asked for one more post about outlier technologies for level changing: light resistors and transformer level shifters.

Tomorrow.

Asheville, Walnut Cove, Biltmore Forrest and Western North Carolina’s Audio and Home Theater specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

More on volume controls and the BHK preamplifer has a great one.
Getting it just right

We covered what a stepped attenuator is and how it works in yesterdays post. The mechanical versions of this complex volume control are not used much anymore because of their many limitations: restricted number of steps, inability to use a remote control, expensive to build, big jumps in level between steps.

To make an effective volume control you need to control a great deal of range. Most designers want to cover at least 70dB from loudest to softest, but 50dB is the practical minimum.

If you’re going to divide the control into steps you don’t want the steps to be too big. Imagine trying to get the level just right and each step is a giant change in volume. To be usable, we recommend that steps be no great than 1/2 dB—the protocol we adhere to when building our own stepped attenuators (like on the BHK).

I had previously mentioned the physical limitations of building a mechanical switch mean that few have greater than 30 steps. If each usable step is 1/2dB; and you need to cover 50dB; and you only have 30 steps…

You see the problem.

Which is why most mechanical attenuators have larger steps. 1dB is common, but we’re still 20 dB short of the minimum required.

Enter the audio taper.

It turns out our ears are less sensitive to volume changes at lower listening levels. This allows the designer to have large jumps in volume at the softest end of the control, and finer increments at the upper end. Pots, attenuators, and all manner of level controls use a tapered response when adjusting volume. Bigger jumps at lower levels, smaller at higher.

The BHK Signature preamplifier uses a stepped attenuator too. Unlike the restricted mechanical ones we’ve discussed so far, the BHK has a whopping 100 steps and 1/2dB increments!

How the hell did we do that when mechanical switches are limited to 30?

 

Asheville, Walnut Cove, Biltmore Forrest and Western North Carolina’s Audio and Home Theater specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

Paul continues to write about volume controls, called potentiometers.

I’ll post this as volume controls are very important to the sound quality of high end audio components and is one of the reason PS Audio’s BHK preamplifier, as well as preamplifiers from Rogue Audio, Herron Audio and others sound so good.

I’m not sure how much more I’ll post on the subject, as it can get complicated, but for today, it’s easy peasy.
Other choices

A pot, or potentiometer, serves as a volume or balance control in a preamplifier.

It’s essentially a resistor, but not a very good sounding one.

And resistors all have a sound to them.

When we choose resistors to build products we pay close attention. After all, the entire signal is forced through these devices, one after another. Their cumulative sonic impacts can be significant. In each of our products we listen test resistor types to find the best match within budget. This includes not only the types of resistor construction, but even the brand. They all sound different.

It’s therefore easy to imagine that when it comes to the volume control, where the entire signal is forced through, it’s really important to put your best foot forward.

And that foot isn’t necessarily a pot. There are other, better sounding alternatives.

The first we’ll look at is called a stepped attenuator. These are found on more expensive products because they are typically hand built with expensive parts.

A stepped attenuator is like an input selector switch, a subject we’ve previously covered in the past few days.

I’ll go into some depth on stepped attenuators tomorrow.

Asheville, Walnut Cove, Biltmore Forrest and Western North Carolina’s Audio and Home Theater specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

From Paul explaining different volume controls and how they work. Everything that plays audio, including cell phones, iPods, iPads, etc. have volume controls..
Since pot’s legal…

Couldn’t resist the headline opportunity. Actually pots, the volume kind, have been legal since they were first developed, though some would suggest they ought to be banned for the damage they do to sound quality.

Like everything in audio quality matters. Pots never make something sound good, only less bad. Let’s take a look at some of the variations. Pictured here are two extremes. A Penny and Giles potentiometer which will set you back several hundred dollars, and a cheesy one that costs less than a dollar.

Simply inserting one for the other will have noticeable sonic differences. Few audio manufacturers can afford a couple of hundred dollars in their bills of materials, and they actually don’t need to. Penny and Giles are used in the recording industry on older analog consoles, rarely on hifi equipment. Instead, there are a number of lower cost alternatives that sound equally good.

At the heart of these volume controls is a simple resistor, stretched out and contacted with a tensioned piece of metal known as the “wiper”. The wiper is what slides across the resistive element and picks off a part of the resistor. Here’s what a pot looks like inside and how it works.

Looking at the diagram, A is where the original signal is placed. B is connected to ground. W (the wiper) is the output of the pot that feeds the next stage or even directly a power amplifier.

When you turn the volume knob on your system up and down, the wiper rubs against different sections of the resistor. Closer to one end of the resistive element (A) there is no resistance, thus we get full volume. At the opposite end (B) there is much resistance, and the volume is decreased until we get all the way to ground and there is zero.