Built in head amp?

September 23, 2017
 by Paul McGowan

Head amps are devices used to separately amplify moving coil cartridges to the same level as moving magnets. They can be built from active electronics with power supplies or simple step-up transformers. They are needed because moving coil cartridges typically have outputs thirty times lower than their moving magnet brethren. Why they are separate has always been intriguing to me.

Moving coil cartridges have been around for many decades. I think it was in the late 1940s that Danish company Ortofon started selling moving coils, but for the most part, turntables and records were played primarily on moving magnet cartridges. From my memory, it wasn’t until the 1970s that moving coil cartridges like the famous Koetsu made their presence known and the need for head amps became the hot ticket for manufacturers.

PS Audio made its first head amp, the MCA, in the late 1970s. Not long after its introduction we also outfitted our preamplifiers with the ability to play moving coils without aid of a separate head amp, but that was rare.

Ron, from Hayes, Va., asked me a good question about head amps in this video about reducing vibrations. “Why don’t they just build head amps into the turntable’s headshell?”

This is a great idea because it eliminates the need for separate boxes, power supplies, connecting cables. But that’s also the problem. Unless the head amp is a passive transformer, you still need most of that stuff to make the circuitry work. Moreover, most head amp manufacturers aren’t the ones building turntables, arms, and headshells.

But the notion of miniaturizing the sensitive electronics that provide gain to these low output moving coil cartridges is certainly food for thought. Perhaps a better place to put a head amp is at the base of the turntable itself—where the tonearm mounts to the table. There we can have power and space to make this happen without the added weight of the head amp electronics.

What’s stopping us? I suspect if you ask most turntable manufacturers why they don’t include a built-in head amp I’ll bet you’ll get one of two answers: we don’t do electronics or, the more practical of them all, audiophiles don’t want any sort of built-ins.

Separates are, after all, what distinguishes many of us from the crowd.

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33 comments on “Built in head amp?”

  1. From my point of view the most meaningful integation/outboarding decision to save cost for separate cabling & chassis would be:

    Headamp and phonostage inside the preamp, power supply outside of the preamp. Most separate head- or phonoamps are so big that they couldn’t be placed nearer to the turntable than the preamp anyway.

  2. I recently purchased a stand alone MC step up transformer for my very low output MC cartridge setup. It’s performance is far beyond any phono preamp that had it built in. I was shocked by how good it is. I had never thought of a standalone one in the past, so I hadn’t really researched them.

    The alarming aspect for me was that it needs no power supply. It has one set of RCA inputs and one set of RCA outputs. I’m sure it’s not alarming for those with an EE background, but the the fact that it performs that function so phenomenally well with no power supply is majical.

  3. Linn, who make a well-known turntable, supply an internal phono-stage that I understand is very popular.
    https://www.linn.co.uk/hifi-separates/turntables/phono-stages
    I was of the view that with the minute voltages coming out of my Koetsu Urushi Gold I needed a very good phono amp and the thinking is that valves are preferable, so I had a pimped up one of these (pimped for both m/m and m/c inputs, line in and volume control, so effectively a phono passive pre-amp):
    http://www.artaudio.co.uk/vinyl-one-phono-stage/
    As can be seen at the bottom left of the photo with the lid off, the M/C inputs plug straight into the back of a pair of Sowter step-up transformers. The unit was exceptionally good, a design decades old with high quality components. It did take up a lot of space, as Paul suggests. My all-in-one unit also facilitates both m/m and m/c inputs (my turntable has two arms, m/c for stereo and m/m for mono) and the phono stage is a 2″x2″ card programmable for the specific cartridges working in the digital domain, and sounds just as good.
    In theory it would be very easy to take this approach – an A/D converter and digital phono stage – and built it into the base of the turntable, but I wouldn’t like to be the marketing man trying to sell a turntable with a digital output.

    1. About 30 years ago in the days of separate head shells, my friend Murray Zeligman designed a head amp in the head shell. Basically it was a set of FETs embedded in the head shell for cooling the devices. And, I think, mainly for fun he included a set of red LEDs to indicate it was on which he would demonstrate in a dark room. Too bad he didn’t have the finances to produce it.

  4. If the sound of these cartridges is so exquisite and the cartridges so absurdly expensive, why wouldn’t the cartridge manufacturer build an amplifier for his cartridge with a line level output?

  5. Paul,

    Try reading Calvin and Hobbes. You might learn something: https://i.pinimg.com/originals/ca/95/5e/ca955ee1fee632a28c4c36228fc88646.jpg

    The moving coil cartridge was invented by Joe Grado in the ’50s.

    The biggest reason not to put the head amp in the headshell is that it would significantly increase the moving mass of the tonearm. (Although some tonearms have been built with electronics in the headshell anyway. There’s always dumb people in the audio business.)

    1. Except Ortofon was apparently selling moving coil cartridges the decade before. From the quick search I did “The first Ortofon cartridge, the MC Mono-A cartridge was developed by Holger Christian Arenstein in 1948”.

      I know Joe was credited with its development, but I believe that to be inaccurate.

      1. Hello Scott,

        Thank you for correcting both Paul and I. The accurate answers are that the mono moving coil cartridge was patented in January 1914 by the German F. Schrõter, and that the stereo moving coil cartridge was patented in 1931 by the British Alan Blumlein. According to US patent law, a working model must be built – one cannot patent a theoretical idea. I would assume that the same is true for patent laws in other countries as well.

        This changes a lot of preconceptions and false claims. It is similar to the fact that the JFET was invented many years prior to the BJT (standard transistor).

        Thanks,
        audio_truth

        1. The U.S. Patent Office has not required working models since no later than 1890. The following is from their web site:

          Models, Exhibits, and Specimens
          Models or exhibits are not required in most patent applications since the description of the invention in the specification and the drawings must be sufficiently full, clear, and complete and capable of being understood to disclose the invention without the aid of a model.
          A working model, or other physical exhibit, may be required by the Office if deemed necessary. This is not done very often. A working model may be requested in the case of applications for patent for alleged perpetual motion devices.
          When the invention relates to a composition of matter, the applicant may be required to furnish specimens of the composition, or of its ingredients or intermediates, for inspection or experiment. If the invention is a microbiological invention, a deposit of the microorganism involved is required. to disclose the invention without the aid of a model.
          A working model, or other physical exhibit, may be required by the Office if deemed necessary. This is not done very often. A working model may be requested in the case of applications for patent for alleged perpetual motion devices.
          When the invention relates to a composition of matter, the applicant may be required to furnish specimens of the composition, or of its ingredients or intermediates, for inspection or experiment. If the invention is a microbiological invention, a deposit of the microorganism involved is required.

          1. Hi Scott,

            Thanks again for the accurate information. Perhaps you should be writing these columns. “Scott’s Posts”? Or at the very least Paul should send them to you for fact-checking before posting them with errors.

            Cheers,
            audio_truth

    1. Ceramic cartridges have an inherently higher output and don’t need an extra amplifier stage.

      The output of magnetic cartridges vary with the velocity of the stylus, so everything else being equal, there is more output at high frequencies. Ceramic cartridges are sensitive to the amplitude of the motion and will have greater output at lower frequencies.

      Since records are produced to have a tipped up response when played back by a velocity sensitive cartridge, phono stages have an EQ circuit (typically using the RIAA standard) to restore flat response. The inherent response of the ceramic cartridge more or less achieves the same result naturally.

      1. I seem to remember that the first cartridge I ever used was a Decca Deram ceramic, and there was a ‘standard’ RC coupling to connect them to a phono input and appear approximately like a magnetic cartridge. I saw a reference to that fairly recently, and I am going quietly nuts trying to remember where.

  6. Paul, I understand you try to simplify your posts to keep them brief, but sometimes that results in misinformation being conveyed.

    As you certainly know, not all moving coil cartridges have low output. I believe a common identification of low output is less than 1.0 mV and several models are higher than that. Conversely a handful of MM cartridges are classified as low output. So maybe it would have been better/more accurate to simply refer to low and high output, without getting into coil/magnet design.

    Also, as audio_truth mentioned, an important reason not to consider building a head amp into the headshell would be the increased mass. But I agree, locating the head amp or even a complete phono stage at/near the base of the tonearm makes a certain amount of sense.

    1. I agree and there’s always a risk in giving short all inclusive answers to complex questions. There’s conversely risk in turning away readers with too much information.

      I suppose it’s a balance between the two that I seek. I don’t always succeed.

      Of course there are high output moving coil cartridges.

      One of the reasons I suggested a better place to put the electronics or transformer for a step up device was at the base of the tonearm was to avoid the obvious problem of weight/mass in the headshell – though if you look at the link paulsquirrel posted you can see an actual circuit with what I suspect is almost no mass at all. Pretty cool.

      In any case, this is all just food for thought.

  7. The moving magnet and moving coil cartridges work on the same principle. The only difference is that in one the coils are fixed to the cartridge body and the magnet is moved by the stylus and in the other the magnets are fixed to the cartridge body and the coils are moved by the stylus. Because powerful magnets can be very small, light, and machined with great precision, output and stylus compliance can be high and dynamic mass can be low. This requires less amplification and lower tracking force than Moving Coil cartridges. Because of their high mass, coils in MC cartridges tend to have relatively few turns and therefore low output. At one time replacement styli for MC cartridges could only be installed at the factory or an authorized service center.

    The audiophile choice has for the past few decades been the moving coil type anyway. This makes no sense to me. Publications for hobbyists no longer report any of the pertinent measurements of phonograph cartridges. Early Ortofon cartridges had a poorly damped mechanical peak in the top audible octave. This gave them a bright sound. Some moving magnet cartridges had the same problem. Audio Technica was unbearably bright to my ears. Low end Pickering cartridges were often selected for high end phono consoles and portables to compensate for their poor treble performance.

    Grado pioneered what he called the moving iron principle. I never researched it but my guess is that this is a variable reluctance type where the stylus modulates ferrous material in the magnetic circuit altering the magnetic flux and may not even be magnetic itself. Both magnets and coils would be fixed to the cartridge body. Grado describes this as a “flux bridge generator” which would be a good way to explain this principle. It is neither an MC nor MM type.

  8. The thought that having a separate head amp separates one from the crowd is not right. Head amps are a necessity for MC cartridge owners. Also no two head amps sound the same. They can vary from just so so to ear openers to jaw droppers take your pick. Transformers can sound different from active circuit head amps. Tubed units sound different from solid state ones. All transformer head amps do not sound the same. A few can sound astounding. I have heard two such units. They are in a class by themselves. All tubed units do not sound the same neither do all solid state units. A really good unit can not be miniaturised enough to fit in a head shell. Chips are not as good as discrete parts. And when it comes to audiophiles who also happen to be the majority of good head amp users one size fits all is a no no. They are just too discriminating when it comes to sound.This rules out head amps built into the turntable. Lets not forget compatibility with individual systems. These are the real reasons for not having built in head amps. Yes they will be fine in mediocre systems where not very much is expected from the system. Regards.

  9. @ those who know: What’s the reputation of step up transformers in opposite to active MC amplification as in most phono stages? Is it similar to active/passive preamps?

  10. These days, with SMT parts, it should be possible to make a FET head amp *first stage* in half a square centimeter, weighing well under a gram. This could be part of the headshell or even the cartridge body. The power source and maybe an output stage could be below deck.

    But I don’t expect any manufacturers to jump on this.

  11. Moving coil and moving magnet cartridges generate a similar amount of energy. The discriminating factor is 1,000:1 difference in impedance, which means roughly 30x less voltage and 30x more current. This gives a big advantage to PNP transistor inputs in Common Base configuration. Tube MC amps have to have transformer front ends because the voltage noise is too high, with ~1MOhm plate input impedance.

    It also means a good pair of transformers on the front end has the best noise performance since no amplification devices have balanced current and voltage noise at 30 Ohms. This strengthens the case for having the cartridge manufacturer supply the transformers and head amp circuit since they can be tuned to flatten the system frequency response wiht minium phase degradation the same way as an active ribbon microphone. I have a Denon transformer pair in a cylindrical case that came with my MC cartridge.

    Even these very low level transformers will not fit in the size and weight constraints of the headshell, but that is not critical because of the low impedance output which shunts electronic noise pickup.

  12. Back in 1978 I was searching for a cartridge to bring my LP’s to life. I tried an Empire,
    Sure V15 type 3, and an ADC XLM. All were returned within a day or so to a very understanding dealer. I finally found a Denon 103C which was packaged with a cheap SUT. -That did it for me, No more moving magnet cartridges. The transparency of the moving coil was addictive.

  13. Very thought provoking comments regarding headamp utilization / integration into tonearm head shells. I am working on a design to incorporate the front end of a Linear Technology smd chip into the head shell end of a tubular tonearm attached to linear tracking mechanism. The larger discrete components will be embedded into tubular length and distributed to balance weight at the points of inertia with components sealed in dampening material. Arm will be constructed of carbon fiber to reduce ringing. Linear tracking will employ horizontal delrin rod which will be suspended in two porous carbon air bearing bushings. VTF will be accomplished using a similar principal utilized in Bruce Thigpen’s Andromeda TT. The associated wiring for circuitry will be attached to a chuck which will positioned horizontal and behind the tonearm. The chuck will be driven by servo motor controlled by sensor mechanism which evaluates groove spacing density on opposite side of lp to provide ideal tangency of wires with tonearm. This should eliminate the torsion on wires as arm tries to move in relation to stylus. Other design implementations will be employed but this is getting a little too lengthy for now. Thanks for the great discussions!

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