LB: The Phonatic provides a wide range of choices with regard to gain, impedance, and capacitance. How is this implemented?
MK: All gain ranges and cartridge loading R & C is set with .0025” square pin headers and shunt/jumpers. These are sturdy gold plated posts and tight tolerance shorting caps located on the motherboard. Honestly, it’s pandemonium when you first try to set the board for your cartridge, but we do include an Excel program to show your options and a diagram to help with jumper locations. The R/C loading jumpers include spring loaded finger jacks (also gold plated) for those fanatics who wish to load with exotic resistors and/or caps, or use values different from the jumper selectable ones included on the board.
In anticipation of your next question, we could have used DIP switches, which are easier for the consumer and less expensive for the manufacturer, and they were in our original design until I read of the possibility of internal resistance changes due to spring stress and high spots developing over time. True, this may take a decade or more to happen; it may be less time than predicted. Either way I didn’t want to take that chance. The pin headers can be easily cleaned and back to being as good as new, even after decades of use. And I anticipate the Phonatic being out there as long as vinyl is still played by styli.
Could I have located the jumpers in a more convenient location such as outside the box, or in a grouping accessible through a door? Yes, but not without compromising the audio quality! Perhaps falling into the category of “disadvantages of opamps” is the inconvenience of having to open up the case to set gain, but many non opamp designs also require this and too, many other designs that employ the switches outside for convenience are adding noise by extending the wires connecting the switches to the PC board. Plus there’s the additional solder, joints and possibility of RFI and EMI induced into these wires.
They say it’s asking for trouble to encourage the consumer to open the case, and many manufacturers void the warranty if you do, but the truth is that audiophiles love to “improve on the original design” by going inside and arbitrarily replacing or adding components. My best defense is to build a sturdy well-designed piece that can withstand even the clumsiest and most careless albeit good intentioned consumer.
Recently my house was directly hit by lightning. Several pieces of audio and video gear had holes blown in the metal chassis. Others were incinerated. A well-known $12,000 power amp was damaged but continued to produce music, somewhat reluctantly, though. The Divinitive sustained minimal damage, and the Phonatic survived unscathed. I frequently forget to discharge myself of static electricity before touching the stereo (it’s a good testing procedure) and so far (years) there hasn’t been a failure. All I can say is that I hope that those with Miracle Audio products will have the same experience. Time will tell.
LB: Let’s turn now to the Divinitive linestage. An ever-increasing number of DACs now include volume controls, and great strides have been made in controlling volume in the digital domain. Along the same lines, some audiophiles opt to use passive linestages. Putting aside for a moment those of us who have analogue sources, why does one need an active linestage?
Volume control technically has nothing to do with gain. Gain depends upon active circuitry, which may generate noise and distortion along with the gain. A volume control is just a potentiometer (“pot”), or stepped attenuator. A better name for a pot might be unstepped attenuator. The key word is “attenuate” or to lessen. Pots and stepped attenuators only decrease volume from the maximum level created by the active circuitry. Therefore, technically even active preamps have passive attenuators. (Except in some rare cases where a switch with resistors is part of the active circuitry such as controlling gain directly in a feedback loop of an individual stage.) Analog pots decrease analog signal and noise levels created by analog gain circuitry, and digital pots do the same for digital circuitry. The big question for me is “How well does your digital volume control / gain circuitry on your DAC perform when driving a power amp?” You cannot answer this question simply, as there is a whole set of answers; these include all the permutations of all volume levels at all frequencies at all changes in dynamics (both fast and slow), and of course for all power amps being driven. This assumes that at some point you will want to evaluate another power amp and want the DAC to be the only variable in the chain. The same applies to devices (volume controls) inserted in between the DAC and power amp.
Let’s take a quick look at all volume controls that can stand alone or be an integral part of an active component such as a DAC, CD or DVD player, or linestage pre.
I. Stepped attenuator
Price is $100 to several $1000’s.
A. Series type. It has switch contacts in audio path. Each successive attenuation step adds another resistor into the chain so at soft levels you are listening to all the noise of up to 23 contacts and resistors.
B. Ladder Type. Overall resistance gets greater as levels get softer but the number of switch contact points and resistors remains the same — usually 3 R’s and 2 contacts per channel, per step.
With only 24 steps you usually get a comfortable listening level falling somewhere in between steps (Murphy’s Law?) or you have –3dB steps at the extreme settings with –1 or -2dB in the middle settings. If you prefer you can have 48 steps with all the additional resistors, contacts and noise that accompany its double price tag. With both types, overall impedance with respect to ground changes slightly from step to step, but is usually fixed at 10K, 25K, 50K…100K so you really should optimize your attenuator for both your front end and your amplifier: Change either and you may need a different impedance attenuator for maximum efficiency and sound quality.
II. Autoformer (auto transformer)
Price $300-$10,000
There are many windings of wire around E-lams. Switch contacts add windings into the audio path as levels get softer. Overall impedance changes may be necessary as components change but some manufacturers allow for “butt gap” stacking. (Look it up.) The lower priced ones come with all the potential to limit transients and dynamics for which inductors are known. They really need to be highly shielded and kept far away from large transformers and magnets. And just for fun, try to get some gain from these and watch their performance degrade.
III. Step-up transformer (passive gain)
Price $300-$10,000
Use this instead of an active MC phono stage, but don’t be surprised when they exhibit the same slow response to transients as your autoformer with either added noise or rolled-off highs depending on the ratio of the windings and the loading impedance of your cartridge. One that sounds good with a 100-ohm cart will most likely sound terrible with a cart requiring a 2K loading.
IV. Digital IC
Price $2-$15
IC (integrated circuit)-based chips usually manipulate volume while in the digital domain, but there are some that contain VCA’s (voltage controlled amps) or DCA’s (digitally controlled amps) that pass an analog signal level in response to an analog (perhaps switched resistor or potentiometer) or a digital encoder. These volume controls are usually found in your basic appliance store electronics, TV’s, phones etc., and can sound fine when properly implemented with excellent power supplies. Technically, since they require power (though unity gain configured) one might consider these to be active devices. Your DAC may contain one or more of these to control volume.
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After reading that you would think everybody needs to hear these speakers & amplifier.