Final November, inside a “microphone fundamentals” writeup of mine, I discussed that an Audio-Technica AT2040 dynamic microphone I’d just lately acquired had required extra sign boosting forward of its connection to my audio interface gadget:
Whereas somebody with a extra booming voice than mine may be capable of sustainably drive a dynamic mic to enough output ranges, my comfortable speech wasn’t up for the duty, even when I cranked the audio interface’s preamp enhance setting to the max (which might degrade SNR, after all)…that’s, until I shouted, which undoubtedly wasn’t pure, to not point out unsustainable. That’s after I found I wanted a “pre-pre-amplifier” (my wording), a widget which can be a requirement for equally low output ribbon microphones.
Such gadgets sit in-between a dynamic or ribbon microphone’s output and the audio interface or different related gadget’s microphone enter, boosting the degrees to condenser microphone equivalents. They’re subsequently generally known as in-line preamps; you’ll additionally generally see them referred to as “activators”. The nifty factor about them is that they’re “fueled” by the identical phantom energy that might usually drive a condenser mic however gained’t move that DC on to the dynamic or ribbon mic, which doesn’t want it and will the truth is be broken by it. Well-liked activators can price effectively over 100 {dollars}; mine set me again lower than $40 and works effective.
Ever since I wrote these phrases, I’ve been curious to see what’s inside considered one of these gizmos. Sadly, there’s no apparent strategy to get to the inside of my first-purchased “activator”, offered by an organization referred to as Manayo (right here’s one other view of the gadget):
and I wasn’t keen to bust it within the means of busting inside it. Fortuitously, fortune extra just lately smiled upon me in not less than three other ways: I bought my arms on one of many extra “fashionable” activators; it didn’t price me the standard “effectively over 100 {dollars}” (solely a bit greater than $40, given its “open field” standing claimed by eBay retailer TradePort USA); and courtesy of two visually uncovered Philips head screws, the route contained in the gadget was seemingly apparent, painless, non-destructive and absolutely reversible to the practical authentic situation. Behold Triton Audio’s FetHead, considered one of a dozen conceptually associated merchandise supplied by the producer:
(extra movies from the corporate right here)
Look carefully and also you’ll see the letters “Ge” subsequent to the product title. Your highschool chemistry reminiscence hasn’t failed you but; they certainly stand for “Germanium”. This proliferation of the FetHead product basis…effectively…I’ll let the producer clarify:
FetHead Germanium is top quality in-line microphone preamplifier. It supplies a punchy and direct, ‘bigger than life’ germanium sound for dynamic and ribbon microphones. Sounding full and wealthy it’s harking back to a lot larger priced classic gear, making FetHead Ge’s fascinating coloration a very welcome addition to (interface) preamps which sound quite impartial. Our FetHead Germanium makes use of tried and true FET expertise mixed with a hand chosen “New Outdated Inventory” Germanium transistor to ship 29dB’s of germanium flavored enhance.
Germanium transistors have been extensively utilized in earliest transistor designs by Neve, EMI, Telefunken, and Fairchild, and have developed a fame for a decidedly classic mojo that is still wanted in the present day. We created a novel hybrid circuit that consists of low noise JFETs and a hand-selected ‘new outdated inventory’ germanium transistor to take full benefit of the “Germanium” sound and on the identical time obtain the identical sonic high quality we’re identified for. A low impedance output buffer supplies output drive to lengthy cables.
Fact be informed, I purchased two FetHead Germaniums, each on eBay from TradePort USA, each marketed as “open field”, and each priced at simply over $40. One in every of them, nonetheless, exhibited an audible “hissy” background noise “ground”, repeatable throughout the a number of microphones and audio interfaces I attempted it with. Person discussion board discussions revealed that this was a identified subject: see, for instance, this firm consultant’s publish in that very same dialogue thread:
The transistors we use in our FetHead Germanium are chosen and examined by hand.
Subsequent to that we pay attention to each single FetHead Germanium earlier than it’s shipped.
Sadly, as a result of we use a ‘new outdated inventory’ germanium transistor, in uncommon events the transistor can go incorrect over time.
Subsequently we give a lifetime guarantee on the NOS germanium transistor.
Please contact us straight at contact@tritonaudio.com to get a alternative unit.
The “lifetime guarantee” promise can be documented proper on the firm web site’s product web page. Alas, my repeated efforts to contact Triton Audio through e-mail went un-responded; maybe the “lifetime guarantee” is simply legitimate for the unique product proprietor? Conversely, to TradePort USA’s credit score, they did reply to my outreach (promptly so, the truth is) and supplied a full refund, together with selecting up the tab for return transport. The opposite unit, which I made a decision to maintain and whose internals I’ll be sharing with you in the present day, remains to be a bit “hissy” in comparison with its inexpensive (new) Manayo predecessor showcased in November, however not egregiously so…but, not less than…
A couple of fundamentals earlier than continuing with the dissection: first, the XLR connector:
The male connector proven at proper is the variant coming out of a microphone; XLR enter connectors constructed into audio interfaces are of the feminine taste. XLR cables subsequently are sometimes male on one finish and feminine on the opposite, as are the FetHead Germanium and its ilk. Right here’s a related Wikipedia quote:
The usual sign movement for audio in XLR connectors is that the output is a male connector and the enter is feminine. In different phrases, the pins on the plug level within the route of sign movement. Phantom energy, if used, originates from the socket and flows into the plug, (the wrong way to the sign and the conventional route for energy circuits). The voltages of microphone and line stage audio indicators aren’t hazardous.
On this explicit software, connections are these days (however weren’t all the time) standardized as follows:
Previous to the introduction of this commonplace, the wiring of pins 2 and three various. The pin 2 “scorching” and pin 3 “chilly” conference was sometimes utilized by European and Japanese gear producers, however American firms used pin 3 “scorching” and pin 2 “chilly”. This precipitated issues when interconnecting gear with unbalanced connections. The pin 3 “scorching” conference is now out of date however remains to be discovered on classic gear.
Balanced audio connections, referenced within the earlier desk, are additionally one thing I’ve mentioned earlier than. In that earlier evaluation, my major focus was of their (theoretical, not less than) capability to maximise audio high quality by the digital-to-analog conversion and amplification hyperlinks of the audio processing chain. Nonetheless, I additionally famous:
In {many professional} audio functions, indicators are routed from place to position through balanced cables in an effort to cut back widespread mode interference from radio frequency (RF) noise sources like fluorescent lights and motors. As a result of the voltage developed on the transmission line from RF interference is equivalent on each regular and inverted sign conductors, and since the balancing transformers solely permit present movement when the indicators are opposing, the widespread interference sign is canceled out.
That’s the first motive for XLR connector (and related balanced cabling) utilization in this software: to cancel out widespread mode interference picked up by lengthy cable runs performing as RF antennae.
Now a bit about phantom energy, whose traits and (specifically) limitations have been behind a lot of the curiosity impetus that compelled (propelled?) me to actualize this teardown’s aspiration. Right here’s the introductory abstract from Wikipedia’s matter entry:
Phantom energy, within the context {of professional} audio gear, is DC electrical energy transmitted by microphone cables to function microphones that comprise lively digital circuitry. It’s best generally known as a handy energy supply for condenser microphones, although many lively direct bins additionally use it. The approach can be utilized in different functions the place energy provide and sign communication happen over the identical wires. Phantom energy provides are sometimes constructed into mixing consoles, microphone preamplifiers and comparable gear. Along with powering the circuitry of a microphone, conventional condenser microphones additionally use phantom energy for polarizing the microphone’s transducer aspect.
As famous right here, and as my last-November treatise additionally described, the presence of externally utilized phantom energy (alternatively self-powering through an AA battery, for instance) is important for correct condenser microphone operation. Conversely, nonetheless, dynamic and ribbon microphones don’t want phantom energy. In truth, until they’re deliberately designed to ignore it, they is likely to be broken by its presence. For the reason that FetHead Germanium is particularly meant to be used with these precise two varieties of microphones, such pass-through prevention is an inherent facet of its design. This attribute is akin to that of the corporate’s Phantom Blocker, which does solely what its title implies, not additionally boosting the sign, versus the FetHeat Phantom, which delivers decreased enhance for an already gain-rich condenser mic however passes phantom energy on to the mic along with utilizing it to gasoline itself.
And the way a lot “gasoline” does phantom energy supply an activator-plus-mic combo? Right here’s Wikipedia’s tackle the subject:
Most microphones now use the P48 commonplace (most accessible energy is 240 mW). [editor note: that’s 5 mA max at 48 V]. Phantom powering is just not all the time applied appropriately or adequately, even in professional-quality preamps, mixers, and recorders. Partially it is because first-generation (late-Nineteen Sixties by mid-Nineteen Seventies) 48-volt phantom-powered condenser microphones had easy circuitry and required solely small quantities of working present (sometimes lower than 1 mA per microphone), so the phantom provide circuits sometimes constructed into recorders, mixers, and preamps of that point have been designed on the idea that this present could be enough.
The unique DIN 45596 phantom-power specification referred to as for a most of two mA. This follow has carried ahead to the current; many 48-volt phantom energy provide circuits, particularly in low-cost and transportable gear, merely can not provide greater than 1 or 2 mA complete with out breaking down. Some circuits even have important extra resistance in sequence with the usual pair of provide resistors for every microphone enter; this may occasionally not have an effect on low-current microphones a lot, however it may possibly disable microphones that want extra present.
1-2 mA isn’t a lot, particularly together with any inefficiency inherent in voltage down-conversion (48V isn’t a typical IC provide voltage, in spite of everything). So, one may assume that the circuitry contained in the FetHead Germanium could be scant and primary, excessive MSRP apart. Let’s see.
Right here’s the packaging that my gadget got here in:
And right here’s what it appears to be like like exterior of its cardboard tube however nonetheless inside its snazzy material baggie, as normal (for these teardowns) additionally accompanied by a 0.75″ (19.1 mm) diameter U.S. penny for dimension comparability functions:
Free as a chook, however nonetheless coin-accompanied (the FetHead Germanium is 3” lengthy, 0.86” in diameter and weighs 0.12 lb):
An preliminary have a look at the opposite aspect reveals the aforementioned screws, which I promptly eliminated:
Let’s look first on the “feminine” finish, i.e., the gadget enter, fed by a microphone output:
The connector slips proper out of the chassis:
“Chassis floor (cable defend)” pin 1, referencing the sooner Wikipedia-sourced diagram and accompanying desk, is soldered to the black wire, whereas “Optimistic polarity terminal for balanced audio circuits (aka “scorching”)” pin 2 is soldered to the pink wire. Pretty rote to this point, proper? Rotate the connector a bit, nonetheless, and issues get extra attention-grabbing:
Be aware that pin 1 can be hardwired to each pin 3 and to the protrusion that finally ends up being screw-connected to the chassis. Right here’s one other perspective:
My trusty multimeter confirmed 0 Ω resistance between all three, in addition to (a little bit of foreshadowing) pin 1 of the male XLR connector on the opposite finish:
Sure, of us, it’s true: my workplace go-to is an oldie-but-goodie analog Radio Shack unit:
Right here’s extra from Wikipedia on this explicit facet of the design:
Pin 1 has all the time been floor and/or defend if the cable is shielded, and plenty of connectors join it internally to the connector shell or case. Though coated in trade technical requirements, there may be nonetheless some disagreement on one of the simplest ways to deal with the usage of pin 1 for grounding (earthing). The principle controversy is whether or not the shell of the connector ought to be related to pin 1 or the defend, or left floating.
AES requirements…suggest that shells of cable-mounted connectors ought to by no means be related to pin 1 or the defend, as a result of inadvertent contact of the shell with one other grounded floor whereas in use can create undesirable present paths for fault present, probably inflicting hum and different noise. Then again, gear containing lively circuitry ought to all the time have pin 1 related to the conductive enclosure of the gear as shut as potential to the purpose the place the sign enters the enclosure.
The argument facilities on the radio frequency shielding supplied by the shell of the connector, which can be decreased whether it is left floating. An alternate answer is to attach the shell to pin 1 and the defend by a small worth capacitor, offering RF shielding however permitting little or no audio-frequency present to movement. This functionality will be constructed into a set jack or a cable terminated with XLR connectors.
Onward to the opposite (male) finish, aka the FetHead Germanium output:
As soon as once more, aided by needle-nose pliers to clamp onto one of many XLR pins, the connector pulled proper out. Listed here are penny-inclusive and penniless (as a result of I couldn’t determine which I preferred higher) views of either side of the PCB:
together with two edge views:
I didn’t do any desoldering or different additional disassembly as a result of I didn’t need to probability rendering the FetHead Germanium nonfunctional. And I’ve by no means claimed to be an analog engineer; the world of “1”s and “0”s is the place I really feel most snug. So as a substitute of (woefully, inevitably) additional pontificating, I’ll simply direct you to the feedback in your ideas on components choice, general design, and the like. I’m clearly not eliminating the gadget, and it’s straightforward to re-disassemble to the purpose the place I ended right here, so I’m comfortable to do additional (nondestructive, thoughts you) evaluation in response to reader requests. And to additional pique your curiosity, I’ll shut with two different movies on different Triton Audio gadgets which (amongst different issues) concerned teardowns; I’ve conveniently initiated playback on the factors the place disassembly begins:
FetHead (a fair extra easy design, it appears):
FetHead Phantom (word on this case the three wires–pink, black, and blue–working from the feminine XLR connector on one finish to the circuitry connected to the male XLR connector on the opposite finish):
—Brian Dipert is the Editor-in-Chief of the Edge AI and Imaginative and prescient Alliance, and a Senior Analyst at BDTI and Editor-in-Chief of InsideDSP, the corporate’s on-line publication.
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