Article: Variable Gain Volume Control

[Ryan Berry]

On 9/19/2020 at 1:38 PM, rhmmmm said:

I love Ayre and I particularly enjoy my VX-R/Twenty amp, however for less cost, I decided to pass on the KX-R/Twenty Preamp in favor of upgrading my MSB Premier DAC to an MSB Reference DAC with the optional preamp constant impedance passive volume control. It also includes analog inputs so completely negates the need for an external preamp as my only other source is a turntable.

 

Hoping that Ayre releases some newer and innovative high end components that compete with this or surprise us in other ways. A great volume control is *necessary* but the KX-R/Twenty is 6-7 years old or more and Ayre’s needs to innovate to catch up or even remain competitive in the market. 

 

Hey Rhmmmm, appreciate the response.  In all reality, we're still waiting for someone to catch up to our 6 year old design. :)  But seriously, when we last upgraded the KX-R, back in 2014, we weren't sure if there was a way to make it any better.  The KX-R has a special story as Ariel mentioned in a PWA video...when Charley and he finally nailed down the design of the original KX-R, we were left with a preamplifier with 0.00X distortion with zero feedback in the circuit.  Charley was so excited, he called up John Curl to tell him what he was able to do and John couldn't believe him!   

 

It's hard to make lightning strike twice...the KX-R was largely considered the best preamplifier on the market by almost anyone that had heard it and improving it was not going to be a small task.  We were really lucky when we started playing around with the diamond circuit design and the AyreLok power regulation we're using today.  After getting the first prototypes done, Charley and I looked at each other and knew we had something almost immediately.  It's pretty rare in our design process for that to happen and the KX-R Twenty was born.  

 

My point is that newer is often not necessarily better.  A great example are the Toshiba JFETs Ayre uses in its circuit design to this day.  The parts were discontinued by Toshiba over a decade ago, yet there has yet to be a replacement anywhere in the market that can touch what they are capable of.  Still, we always keep looking for new ways to do things or further improve our greatest achievements.  We're as much hobbyists as anything and love finding better ways to do something.

 

Cheers,

Ryan

[Ryan Berry]

10 hours ago, manueljenkin said:

Is this an attenuator (active resistor, JFET based) at the output stage of the amp? Or is it in the input stage of the amp? Or is this actually acting as a gain control directly on the amp?

 

Also, am I looking at the correct references: https://en.m.wikipedia.org/wiki/Voltage-controlled_resistor

 

Hi Manuel,

 

The VGT is a variable gain amplifier stage, so closest to the third option. 

No, a voltage controlled resistor is effectively what is happening in a JFET, like those we use in our products, but they are not part of the volume control for us.  The VGT uses a mechanical switch and motor to select different resistors for each volume level, which changes the gain stage's output level.  It's tricky to work with as it has quite a few moving parts that need to work perfectly together to behave properly...one of the reasons other companies tend to avoid a switch like this.

 

Cheers,

Ryan Berry

[Ryan Berry]

22 hours ago, rhmmmm said:

My point is that this is solving a problem I simply don’t have. I don’t know anyone else that has a problem that is solved by a $25k 8-input analog preamp. 
 

I need a high quality volume control and I have 2 sources. One that is digital and itself has a variety of digital inputs, and my ARC phono pre has 2 inputs. I simply don’t see the value in paying $25k for a volume control and 6-7 extra inputs plus taking up unnecessary rack space when the dollars can be used more wisely somewhere else. 
 

The innovation and market catch-up I refer to and suggest to Ayre in my original post is in digital and other green/white space you currently aren’t covering or aren’t covering as well as competitors. For example, where are the highest-end digital Ayre “R” components? Why not use the great volume control and other tech in a newer flagship component that addresses problems people have *now* in the streaming age? You said yourself the KX-R Twenty hasn’t been updated since 2014. Everyone is staying at home right now and the stock market is up, the time is right for a new, innovative product drop in the *highest-end* Ayre range. 
 

 

Ah, I see.  Well, if we were to equate the KX-R to simply a volume control, then can see your point.  However, the unit does much for for the system than simply throwing in a gain and offering input selection, which I think is something you have to live with to appreciate.  Were I able to just use the digital volume control in my QX-5 and be happy, for example, I certainly would and free up the rack space.  But once I pull the KX-R out, everything is considerably less for the loss of the piece.   For what it's worth, the difference between putting 2 inputs and 6 inputs on a preamp is only a matter of how much space you have on the back and not really a significant cost difference...so a 2 input preamp won't cost 1/4th the cost of an 8 input, for example.  I sometimes wonder why people don't put in as many as they can on an analog preamp considering the price difference is so negligible.  With how the KX-R works, you wouldn't really gain anything in being able to reduce the size either, I have to say.  The inputs really came after the audio design and Charley and Ariel did some pretty impressive work with what they fit into that chassis. 

As far as an R-series DAC, well, there's a bit more to that story.  Frankly, the QX-5 could have easily been an R-series DAC considering what is inside a unit, and it would have been easy to slap it in a solid billet chassis and overcharged to get it up to a nice $20k+ price point, but it's not who we are.  It would likely have been reviewed just as favorably if not more so to the $30k-$50k DACs the QX-5 is now and it would have sold fine.  However, there were several key pieces of technology (mainly around the streaming end) that simply wasn't available until about a month ago that we'd consider necessary to put into a DAC at that price.  So the QX-5 was initially designed with an R series DAC in mind...multiple transformers to isolate every portion of the circuit, custom-designed oscillators, price-no-object sort of design, but that design ended up going into the QX-5 instead until the outside technology could catch up to what we wanted to see.  Part of Ayre's ethos is to do what we feel is right and act as we'd wish a company to treat us, and slapping a large price tag on a unit that didn't check all of the boxes for us didn't work for the team here.  In the end, it ended up making a QX-5 a product that was better than we may have designed if we went in with the mentality to make something under a certain price...a good problem to have and a big reason the QX-5 reviews so favorably.  Happily, the missing pieces have finally been falling into place and we can revisit the design along with the ideas that DIDN'T make it into the QX-5.  We know some more tricks since then as well, so I'm sure there will be something coming that will satisfy that market.

As I said in another post that had a bit of negative attention: I still believe that streaming is in it's relative early stages as far as where I can see it going.  As time goes on, I am sure we'll see better and better technology come available to us.  It's only now getting to the point that I'm even satisfied with what we can do.   I'm really looking forward to the time that I'll be blown away by it.

Cheers,

Ryan