PLEASE NOTE: This article has been archived. It first appeared on ProRec.com in May 2000, contributed by then Contributing Editor Bill Park. We will not be making any updates to the article. Please visit the home page for our latest content. Thank you!
I can’t remember the first John Hardy M-1 advertisement that I saw. It seems as if that smallish ‘The John Hardy Company’ ad has always graced the back pages of the trade magazines that I read. I remember thinking that this simple little draftsman-like line art drawing could not possibly induce anyone to purchase the product, and the paucity of accompanying information did not help.
Little has changed over the years. The ad has gotten a little larger and contains a little more information, like the fact that they take credit cards now. But it is still a simple black line drawing of the front panel of an M-1, with one knob, one meter, and three switches. I remember thinking, “Doesn’t look like much to get excited about.” Then I started to read the posts and recommendations about it.
There used to be an active community of recording engineers, technical engineers, producers, mastering engineers, the occasional artist, and a lot of coders at a particular spot on line. I became a member about ten years ago. What I liked about that forum was that if you had a question about how something was done on a particular current monster hit album, you could usually get a full rundown on the whole process from the guy who did it.
I often saw John Hardy mic preamps being recommended on that forum whenever the question came up. Any other mic preamp was usually a second choice, after the M-1. Time after time I would read, “We have two…” “We have four, and want four more…” being written by names that also appeared on CD liner notes in my collection. Maybe there was more going on with the M-1 than I first suspected…
So I tried to find one used. I couldn’t. People who buy them never sell them. To this day, I have only seen one for sale. It was on auction at ebay, and sold for just a few dollars shy of what a new one cost. I am also the King of the Discount Deal. I’ll make 500 phone calls trying to save $5, and I will talk to every salesman that I can find until I manage to get the product at the price that I want to pay.
There is no discount on a John Hardy M-1. Since he can sell them as fast as he can push them out the door and they are a proven product of superior quality, he doesn’t have to discount them. There are no big sales commissions or markups in the way that his business is structured. This is the first piece of equipment that I have paid full retail for in 25 years.
John Hardy was also a member of this on line community. I don’t remember if he joined later, or had been there as long as I, but we’ve been exchanging e-mails for several years now. I spoke with him recently about his company, his products, and his design philosophy.
John, you have been around so long that we just take it for granted that you have always been here. How did the company get its start?
The John Hardy Company was officially incorporated in January of 1980. The M-1 came out in 1987, and that is when the M-1 line-art ads started. The 990 op-amp came out in mid-to-late 1979, prior to the official incorporation of the company. Advertising for the 990 started around then.
My first mic preamp card was the MPC-500C, a retrofit for the stock mic preamp cards in the MCI 500C and some of the 500D consoles. It came out in 1981. My 2nd mic preamp card was the MPC-600, a retrofit for the stock mic preamp cards in the MCI 600 series consoles, about 1983 or 1984. In 1986 I released my 3rd mic preamp card, the MPC-3000 card, a retrofit for the stock mic preamp cards in the Sony MXP-3000 consoles. All of those cards are still available. In fact, I revamped and updated the p.c. board and circuit design of the MPC- 600 and MPC-3000 cards last year. All three of those cards have the same basic ingredients as the M-1: The Jensen JT-16-B mic input transformer, the 990C discrete op-amp, and the total absence of coupling capacitors in the signal path. I have a great DI box that I bring in from Germany (The AMB Tube Buffered Direct Injection Box).
I’d like to get back to the capacitor issue in a moment. But speaking of Jensen, I know that you had an involvement with Deane Jensen. How did that happy collaboration occur?
I manufacture the Jensen Twin Servo 990 Mic Preamp. This product came about at the request of Deane Jensen. He originally had a mic preamp being built for him in 1986, known as the Boulder Mic Preamp. The M- 1 came out in 1987, and I made certain to show it to Deane on a trip to the west coast. In 1988 Deane decided to cancel the Boulder preamp product, and he then asked me if I would be willing to build his concept of a mic preamp using the M-1 package as the foundation. I was honored to do so, and the result was the Jensen Twin Servo.
The main difference between the M-1 and the Jensen Twin Servo is that the M-1 uses one 990 op-amp per channel, while the Jensen Twin Servo uses two. There are tradeoffs in each approach. The Jensen Twin Servo offers somewhat less distortion and wider bandwidth at maximum gain than the M-1 because the gain is split between two 990s. But the M-1 can handle higher maximum input levels than the Jensen Twin Servo (+12dBu vs. +6dBu) because the minimum gain of the M-1 is 12dB, compared to 18dB for the Jensen Twin Servo. I originally made the Jensen Twin Servo exclusively for Jensen Transformers. For the last two years or so, I have been selling the Jensen Twin Servo directly.
Now for the electronics lesson. Let’s talk about the role of capacitors in a modern mic preamp.
It might help if you understand what a capacitor is. A capacitor is simply two conductors (plates) separated by an insulator (dielectric). The dielectric could be mylar, polycarbonate, polypropylene, Teflon, air, a vacuum, etc. A capacitor allows AC voltages to pass through, but it blocks DC voltages.
Capacitors have a problem known as dielectric absorption, where a small portion of the signal that passes through the capacitor is absorbed by the dielectric of the capacitor, then released a short time later. This can smear an audio signal.
So the idea is to design an audio circuit path with no capacitors? Then how do you prevent the flow of DC?
There are various ways in which unwanted DC voltages can creep into the audio signal in audio equipment. Those DC voltages must be minimized. The traditional way to do this is to send the audio signal through a capacitor. Unfortunately, there is the smearing effect due to dielectric absorption. Some capacitors are much better than others in this regard, but the best approach is to have NO capacitors in the signal path. This requires different methods of minimizing the unwanted DC voltages.
All of my mic preamp products employ two methods of minimizing the DC voltages without sending the signal through any capacitors: Input bias current compensation circuitry, and DC servo circuitry. The input bias current compensation circuitry injects a very small amount of current into the inverting and non-inverting inputs of the 990 op-amp. This nulls out the small amounts of input bias current that flow from those inputs, reducing unwanted DC voltages at the input side of the 990. The DC servo circuitry constantly checks the output of the 990 for the presence of DC voltage. If any DC voltage appears at the 990 output, the DC servo circuit sends a correcting voltage back to the inverting input of the 990 to null it out.
Well, I can see one problem right off the bat. How do you deal with phantom power when you are blocking the DC flow?
Mic preamps have an additional DC voltage problem: the +48VDC phantom power supply. It must be allowed to travel back to a condenser mic to provide power, but not forward into the amplifier circuitry of the mic preamp where the high voltage could cause damage. There are two ways to block this voltage: capacitors or transformers. Transformerless mic preamps have to use capacitors to block the phantom power supply, with the side effect of smearing from dielectric absorption. A mic preamp with an input transformer does not need capacitors to block the +48VDC because a transformer inherently blocks DC voltages *without* the problems of dielectric absorption.
So, the argument is: Which is better, capacitors or transformers? It depends on the amount of dielectric absorption in the capacitor vs. the degree of nonlinearity in the transformer. I use the very best of the Jensen mic input transformers, the JT-16-B.