History Of our Cibalba circuit designs...

The following article is required reading for the next in queue equipment.htm article which goes into depth about reflected impedances and speaker and microphone interfaces. This historic operational education article is helpful in mastering an understanding of how little knowledge of reflective impedances and the associated shifting of currents by inductors and capacitors existed in 1915 to 1925 when tube amplification ruled the world. That lack of interfacing math and science caused a tumble snowball effect. Overcompensation for harmonics became the standardized designer's main goal.



Cibalba Stage And Studio Design Hisory of audio Studio Circuits

We have a long history of designing innovative audio circuits beyond the commerically available quality and risk limits. We think outside the box. We developed a more practical understanding of audio circuits beginning from when we published a javascript crossover for kennedyaudio.com.


Unlike many basement designers, we actually tested the prototype on oscillicope and full power solid state inputs.    That in itself might be surprising, but when you consider that it worked and used nothing but a large array of 6 volt solid conductive polymer capacitors, the REALLY is a surprise. The reason is that standard high school physics text books have been teaching everyone for the past 100 years that a capacitor must be rated at or above the voltage it is being operated at, even if it is in parallel with another capacitor, which for most active devices splits the voltage.               Our effects to investigate truth in assumptions comes from my lifelong work in both politics and technical physics as a quality assurance consultant and inspector of metalwork. In this application the voltage does split according to the laws of Kirchoff, but the capacitors block some current. Electrolytics block almost all in one direction. So, as a blanket cover all mistakes teaching tool, the armchair intellectuals that write books for the teachers union's comfort rather than the student's mastery, in their wisdom, wrote the wrong information for audio technicians into audio text book history.

   Briefly the first breakthrough we made was realizing that DC bias voltage rating for any capacitor is irrelevant if the signal is a normal alternating (AC-like) audio signal. The so-called 'bias' on DC exists in tube amplifiers that are in the plate voltage. The collecting plate or anodes are set to high positive voltage called B+ so that they attract more electrons from the filament or cathode that are excited by the grid which is very near the cathode and has the alternating microphone, guitar, or compressed program signals. Our ability to design crossovers and audio filters was vastly increased, but such basic knowledge can be dangerous as we spent a lot of money trying to get a retail name that would work, only to be denied by the Federal Government because their tradename division considers the 'dark side' of retail stores, even non-chain retailers, to a have sovereign right to any name that sounds remotely like their trade name. But the problem there was that retailers can brag more than one trade name. The store in Florida is known for one name, but the speaker repair affiliates are known by a second name, and it was that second name, speakerxchange, which we tried to get tradename rights for so we could produce product and sell it. However, we only lost after elevating to the appeal level in the end. The government is too entrenched in special interests to allow new entrys into established retailing unless new sales aready exist (like Marijuana?). That is when the idea for an RV park and stage and studio began to condense from the fog of 'Pink Government Corruption as I termed it. #PGC for short.


In the meantime I, the author and owner, needed some new horizons and began repairing what items I could get at a good price on eBay. The eBay market has for a few years, left many orphaned tube amplifiers and transformers up for grabs at less than $200. While that is changing, I started to design using these basic elecments = tubes, transformers, capacitors, switches and jacks, lamps, text plates, potting epoxy and silver solder. Believe me, the costs are prohibitive for anyone readying this with interest in improved audio for private ownership or application in homes and small business. Eventually we discovered many similar mistakes in the audio chain of components that have, by tradition been used. Let me explain how these mistakes were made, rather than launch into a more narrow discussion of the physics behind the electromotive forces involved. There have been since 1915 when the tube amplifier circuit was first retailed, two types of tube amplifiers. The two types are push-pull or pump and single ended. For the moment, let me talk about the time of research between 1915 and 1923 when RCA tried to take over. In that time period the multiplier of signal input to output was more limited than post RCA electronics. That is GAIN was only about 10 to 20 times. Power was all over the map. AM radios did not exist. Power can make a small gain sound loud by feeding more watts (volts times amperes of electrons) to the speakers. Magnets were just beginning to be used so the power also had to make the electromagnet in the speakers work.

This is digressing a bit. The push-pull or pump method uses either one or two active devices to connect the speaker at one pole to power. It works much like a water pump, the only paradigm available at the time. Most amplifiers made and available still today are single ended however. They also use a single pole, but although every conceivable configuation exists, there is no attemp to reduce noise or distortion with feedback or special added circuitry. The single ended amplifiers quickly evolved when radios appeared to use the power output section as a cathode follower configuration to save space and compete in quality where the volume level reached by the preamplifier section was sufficient. The cathode follower acted as an outstanding distortion elimination technique, but it used a power tube intended to amplifier or add gain into a gain reduction device. The triode actually reduces power in the cathode follower because the hot wire element that faraday called the exode (and was criticized for the rest of his life for saying it) is the source of the power going to the speakers. Single ended sounds better by far because it has more second harmonics, or just more harmonic content. And that was our third breakthrough. We suddenly began to understand what all those older designers wanted. They sought pure sound, even if, or maybe especially if, it cost the character, the fingerprints, the subtle nuances of the original signal. So we now had a nitch target to market to - those individuals that wanted to buy a tube amplifier that is allowed to do what tube amplifiers do best. what the older more stable circuit does is to unhance and resonate and fulfill signals beyond the original content. They also are prized in Russia for their military characteristics. Their high volts are solidly driven in many possible ways. They can be made so stable that they operate in space, in high flux environments, even when under nuclear threat conditions.

Enter RCA company with its 1923 'Balanced' design. They sought to make customers flock to their products by making the chassis less dangerous for shock, and using more than one power tube just like the push pull and pump power tubes. It was perhaps the first modern style marketing effort that was nationwide and involved physics applied to general wants needs and desires. A pair of audio tubes connected in push–pull is described in Edwin H. Colpitts' US patent 1137384 granted in 1915, but the term push-pull was introduced in 1923 by RCA along with its 'balanced' terminology, which indicated that the input of the preamp was no longer using a capacitor and sometimes an inductor in series to ground one side of the wire coming from the input. This was done in order to allow easy interfacing of low and high level (not to be confused with low and high impedance but similar if isolation bridge transformers are used) by changing the capacitor / inductor pair. The low level is a milliamp standard, such a guitar or microphone magnetic pickup from .02 to 50 milliamps. High signal became known as line level and is up to 800 milliamps. The standard has a voltage, but it it only relative to running at 800 milliamps limit, so I won't bother with that and end up being what I am so critical of doing in my own science writing.

Now comes the difficult part. How does one describe the advantages and ideas of his new design, without giving away to predatory designers his ideas, especially since nothing has been successful since the 1930's in getting a new design to market? This is just a shot at explaining it, nothing is in order of importance or sound quality. So many things affect sales and popularity, it could amount to the name in the end being radical enough to twist an outdated paradigm or meld with a new popular one. Starting at the beginning, unbalanced circuits almost always have the chassis grounded to some positive or negative voltage. That is you will get a shock of some kind if you touch it. The days when this was considered safe are long gone, as it only takes a few volts across the heart muscle to induce arrest. Secondly, the low and high level inputs need lead to a 4 connection minimum switch, obviously, and if left in parallel the jack itself makes a lot of noise. This is partly because it is impossible to shield all the electromagnetic radiation coming from a transformer tube set, so yes you will hear the hiss always unless there is a switch on BOTH poles. These double pole single throws cost about $160 made in America. The cheaper ones increase their resistance over time, I sure can't figure out why but they just do. Planned obsolescence I think. There must be a standby switch or an inrush current limiter, preferable both to save tube life that you will never know is being worn away without a tube tester. What we have learned about impedance matching must be considered between passive devices and the active one's target and source component. This must be combined with knowledge about the sag of active devices as they get the signal or power. Any discussion of design on the internet will note that you can't just use the same power transformer voltage in several places like it was a wall outlet. Long story short, you end up with over a dozen transformers in order to make the step-down accuratly and not too rapid and avoid using resistors to make it so. Sag is the drop in voltage that occurs at the hot filament when signal draws electrons from it. That sag is what is used in cathode follower type audiophile circuits. We see some problems here. A human voice has no sine waves, which is the traditional design criteria for so-called 'linearity' and 'fidelity'. This is a very recent observation in audio sciences. we use a negative B- as well as B+ bias, which is another shortcut that is often a reductive marketing counter culture modification.

Next in the act of amplification is usually the preampifier. What really happened here in history is that the 12Ax7 double triode in one tube was invented. It runs on 12 volts, which is a very non-standard 12 volt type for tube transformers taps, but common in the automobile's DC system. It sports a gain of 100 times, enough to outpower older preamp and power amp circuits combined. It was sadly given an anode plate component transductance ( a part of the active tube) coupling value of 100 thousand ohms. This of course was done to prevent any backflow of the electrons. Tubes move electrons in one direction through them. The early triode tubes allowed easy backflow but this causes problems as you either vary or want to over power the same circuit. When beam pendodes were developed, they almost always used 12aX7 tube to blast the signal up to line level. This also eliminates that expensive switch.

Perhaps its also impossible to hide the fact thay the Cibalba microphone and analog computing amplifier (when shown) has no preamp but uses only power triodes which run on different power supply levels for each power tube while still retaining the time proved 5AR4 / 5U4 rectifier power tube. These are not ordinary tubes. They are the most expensive tubes for audio ever produced, the 300B, without the pure nickel plate of a 300B and without the rarity and $1000 cost either. They also have three times the voltage tolerance and up to 3 times the output power, depending on how much gain is used they can be quite good as instrument or vocal or other general use amplifiers as opposed to the 300B and 350B which often are used in the 2 watt audio easy listening single ended enthusiast market, most of which is expensive and not retailed but private custom work as a hobby. In defense of hobbies, it is not a fair comparison to say any price is 'high' when you consider how much living goes into just crafting the chassis and other hand built assemblies, components and interfaces of all kinds. The days that go by, the sourcing of rare and exact components; some of which must be previously used because they are no longer manufactured, and of questionable service life, the hand winding of coils that turn out to be just as good as the ones you buy from foreign countries with good reputations, but cost, on average I have noted, 100 times what you can make them for if you spend the time and money, must be taken into the accounting equation. If you wish to ever try this kind of design, I am certain you will come away with a new idea of what is cheap and what is precious and often not replaceable in audio sound systems. I even had a McIntosh MC-30 that needed a few new capacitors, was stolen (never returned by a retail dark side repair man in Dripping Springs, a suberb of Austin, claiming return packing cost burden which is contrary to eBay's returning item policy!) after sending it in to a retail audio store supported by eBay's retail friendly hand licking (feedback for a fee?) editorial legal staff, and after hiring lawyers to write several letters to them and many phone calls asking for support and to at LEAST reinstate my negative feedback to warn others; i.e. it was removed as being too 'nasty' you know. That store, Circle Stereo, is still advertising on eBay to 'rebuild' MC-30 amplifiers, now 6 months after stealing mine. And then would you wonder why an amplifier like this would cost $12K on eBay, that is IF you could buy one. I desinged this and call it 'Mayan'. You would likely see this and other special purpose interfaces at Cibalba stage and studio. There are reasons why microphone inputs do not appear on guitar ciruits, or phono / aux / tape / CD preamp inputs. Briefly it has to do with the ground and if multiple devices or split signal are likely to be needed. Older tube equipment like the Mayan are free from such assumptions and often, related restrictive input signal requirements.





Studio Mic Apparatus Mayan


Addendum:
When mono amplifiers that looked something like the above were first conceived of, they evolved to use a crossover. Their development of ultra-linear feedback from the output transformer in various forms was an attempt to reduce the mismatch loss and return loss, aka 'hybrid balance'. This new design for microphone digital and analog input I call a 'Mayan'. This has to do with its intent to interface to a capacitive load which overlaps the two constant K curves. (below) The crossover allowed more than one speaker to be used, splitting the tone into high and low tone speaker types. The problem is that the reflected impedance with a crossover was very different than for a single voice coil. As recently as today, the loss of wattage is specified in two parts: 1) insertion loss and 2) Crossover loss. The second one, crossover loss is always at least half of the output. The first is supposed to be less than another 1/3 of that first loss. All told, 133% less output required ever larger power draw tubes. In turn, if you read the wattage.htm page at our kennedyaudio.com site, this means negative feedback must keep the output levels equalized. The confusingly named 'equalizer' was a different external band pass filter traditionally used only to boost very high frequencies above the 16 ohm (10K) fidelity front shoulder cutoff. The spectrum equalizer is badly needed whenever the output resistance / impedance of a transformer is higher that the targeted device impedance at that frequency. Otherwise, no signal at all would pass between the devices because almost all the power is reflected back to the source. The negative feedback can be considered an adaptation to loading with more Complex Impedances.
See this page and others for more fidelity or 'audio acuity' background.
There is also more about this trendy fad in design on the kennedy audio buyer's guide page.



Crossover Constant K relected impedance

Commonly, Negative Feedback interacts with reflected load. The reason it always results in half of the signal being lost to heat is shown in the graph below known as the constant K graph. Please do NOT consfuse this older technology with the purely capacitive and pure parallel crossovers that we designed for kennedyaudio and have also put that conceptual interfacing capability inside our mono tube Mayan amplifier(s). The vintage kind of loading assumes that the low frequency pass filter is an inductor and the high pass is a capacitor, introducing phasing instability and losses. The center point is where the capacitive and the inductive coil filters meet each other. The inductance delays current in relation to voltage while the capacitor acts like an accumulator in a plumbing pipe to respond with extra spring loaded impulse, hence it advances phase angles in relation to voltage. 25-30dB superpositional analog attenuation must occur at some points to achieve the illusion of increased audio acuity, advertised as 'hi fidelity' and later stereo HI-FI.
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Our CoCalc free crossover calculator helps folks design speaker control that uses many capacitors for the low pass filter; thus no such crossing notch dropout exists and everything is in baseline phase throughout the spectrum.