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USA - Wide band audio transformer with multifilar winding - Google Patents
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Audio power transformer cross reference pdf download
The present invention relates to transformers, and in particular, to output transformers for use with push-pull vacuum tube audio amplifiers. Audio systems with vacuum tube amplifiers are still commercially available even though most modem audio systems typically use solid state transistors.
Nonetheless, many people still prefer vacuum tube amplifiers because they enjoy the sound produced by the vacuum tube amplifiers, because they enjoy the lights of the vacuum tubes, or for other reasons.
One type of popular vacuum tube amplifier uses a push-pull circuit. In a push-pull circuit one vacuum tube amplifies the positive half of an input signal while another vacuum tube amplifies the negative half of the input signal.
Both halves of the signal are ultimately combined in the secondary of an output transformer. The secondary provides power to the speaker-load typically at high currents and low voltages.
A conventional push-pull output transformer comprises three windings wound around a magnetic core: a half primary winding for each half of the input signal and a secondary winding for the speaker load.
The output transformer has limited the usefulness and applicability of the push-pull amplifier because the output transformer limits frequency response at the upper and lower ends of the audio spectrum, and also introduces notch distortion.
In order for an output transformer to respond properly at low frequencies, a large number of turns in the primary is needed to produce a large inductance. Unfortunately, audio power transformer cross reference pdf download, a large number of turns in the primary increases the distributed capacitance between the windings and also increases leakage inductance, both of which effect high frequency response. Thus, while increasing the number of turns in the primary improves performance for low frequencies, it sacrifices performance at audio power transformer cross reference pdf download frequencies.
Another problem introduced by the output transformer when used in an amplifier operating the output tubes class AB2 or class B is notch distortion. Notch distortion cannot be eliminated by overall feedback. Vacuum tubes in push-pull arrangements such as Class AB, or B are more efficient audio power transformer cross reference pdf download class A amplifiers, but notch distortion can occur at the point where one of the tubes stops conducting and the other tube begins conducting.
Notch distortion is due to imperfect coupling between the two halves of the primary when the impedance of the source of the primary is high. Notch distortion does not usually show up below Hz and becomes excessive starting at about Hz.
InMacintosh disclosed a "unity coupled circuit" that allowed the output tubes to operate in parallel through a bifilar winding, effectively eliminating notch distortion. But, the unity- coupled circuit requires extensive positive feedback to overcome degenerative cathode swings causing problems yet more difficult to solve. Other attempts to reduce source impedance include the single ended push-pull circuit, the Peterson Sinclair circuit, and the Wiggins Circlotron circuit.
Another way to eliminate notch distortion would be to provide a transformer for a conventional push-pull circuit that is tightly coupled between the two half primaries. It is generally felt that a ratio of the open circuit primary inductance to the leakage inductance of 80, would substantially eliminate notch distortion. It is therefore desirable to provide a transformer with reduced leakage inductance that can accomplish this 80, ratio.
Audio power transformer cross reference pdf download windings of the two half primaries are known in the art to reduce leakage inductance, but these bifilar windings have introduced problems into output transformer design. One problem is that high AC potential exists between adjacent wires of the bifilar windings, so the wires must be adequately insulated to withstand the potential. Also, bifilar windings create considerable capacitance between adjacent wires, and that capacitance must be charged in developing potential difference between the wires.
The charging current must be supplied by the output tubes, and this limits the high frequency power output of the amplifier. In a transformer with bifilar primary windings, each winding has capacitance with respect to the two windings on each side of it in the same layer, and also with respect to windings in the layers above it and below it.
Effective capacitance between windings in the same layer may be cut in half by transposing windings of the bifilar pair at every turn. Capacitance between wires in adjacent layers may be reduced by increasing the spacing between layers, but this increases the leakage inductance of the transformer. Thus, in order to improve performance at the upper and lower ends of the audio system and to reduce notch distortion, it is desirable to provide a transformer with sufficiently low leakage inductance i.
In other words, audio power transformer cross reference pdf download, it is desirable to increase coupling between the windings without increasing the capacitance. The present invention is a wide band audio transformer in which the primary and secondary coexist in a multifilar ribbon that is wound around a core side-by-side and layer-by-layer.
The multifilar ribbon consists of several adjacent windings, each winding preferably being made of wire of the same size or gauge. The multifilar ribbon is wound side-by-side through successive layers and then re-enters the transformer structure at the beginning in order to connect each of the primary windings in the multifilar ribbon in series.
The number of series connected primary windings compared to the number of series or parallel connected secondary windings is the turns ratio for the transformer. More than two primary windings are used to prevent the AC potential between adjacent windings in the multifilar ribbon from becoming too high, thus reducing the effects of distributed capacitance. It is preferred that there be 10 or more primary windings in the multifilar ribbon although the invention is not limited to the same.
Several secondary windings are included in the multifilar ribbon to provide enough current handling capacity in the secondary and to provide sufficient coupling between the primary and the secondary. To reduce AC potential differences, it is preferred that the secondary windings be located in the ribbon multifilar adjacent or closest to the center tap of the primary. It is further preferred that the primary windings in the multifilar ribbon be in an order that reduces the AC potential difference between adjacent turns of the multifilar ribbon.
Such a winding pattern can be accomplished by locating each successive winding alternately from the outermost winding inward. Such a pattern also facilitates transformer fabrication because the ribbon only needs to be turned once to make the proper series connection.
The invention results in tight coupling between the windings. This reduces notch distortion and also reduces phase shift. Coupling is improved because the primary and secondary windings are wound side-by-side in the multifilar ribbon. This is in contrast to conventional transformers where coupling is typically increased by sandwiching alternating layers of primary windings and secondary windings. The invention also reduces leakage inductance without increasing distributed capacitance.
Distributed capacitance is controlled by using triple build magnet wire, and thick interleaving material between layers. The use of thick interleaving layers does not affect leakage inductance because coupling is provided by the multifilar ribbon.
Also, capacitance associated with the multifilar ribbon are in series, which tend to substantially reduce capacitance. Furthermore, the effects of capacitance are minimized because the total primary AC potential is divided by the number of primary windings involved. The use of bifilar primary windings in wide band transformers is well known, but these transformers have had problems related to the extremely high AC potential difference between adjacent wires.
In these transformers, ordinary magnet wire wound in contact with an adjacent wire was impractical because of high capacitance. The present invention eliminates this problem because the AC potential difference between adjacent wires in the multifilar ribbon is substantially less, and this allows the secondary to be wound with the primary.
It is, accordingly, an object of the invention to provide a novel and improved wide band high quality audio transformer. Another object of the invention is to provide a push-pull audio transformer capable of reducing leakage inductance without substantially increasing distributive capacitance. Another object of the invention is to provide a transformer that has improved performance at both low and high frequencies. Another objective of the invention is to provide an audio transformer in which the ratio of the open circuit primary inductance to the half primary to half primary inductance is greater than or equal to 80, It is generally believed that such a transformer would reduce notch distortion.
Another object of the invention is to provide a transformer that extends the amount of feedback that can be used, and reduces phase shifts that could cause amplifier instability. The above and still further objects, features and advantages of the invention will become apparent upon consideration of the following detailed description of specific embodiments thereof, especially when taken in conjunction with the accompanying drawings. Referring to FIGS.
The multifilar ribbon contains parallel wires having the same diameter which will constitute the primary and secondary windings of the output transformer A guide is used to guide the wires in the multifilar ribbon when the ribbon is wound around the bobbin to form the transformer The guide has a guide member which has a rectangular slot 22 along its top surface.
The rectangular slot 22 is dimensioned so that the wires in the multifilar ribbon can be aligned single file across the slot The dimensions of the slot 22 should be adjusted depending on the diameter of the wire and the number of wires used in the multifilar ribbon An upper plate 24 can be screwed onto the lower guide plate to clamp the wires of the multifilar ribbon into the slot The multifilar ribbon can then be wound around the bobbin to form the transformer As shown in FIG.
Four layers 28 of 0, audio power transformer cross reference pdf download. A second layer 30 of primary and secondary windings is formed by winding the multifilar ribbon side-by-side around the layers of craft paper The craft paper 28 is an interleaving material separating the first 26 and the second 30 layers of windings.
The layers 28 of craft paper not only separate the windings in the second layer 30 from the first layer 26 but also keep the layers of windings aligned. Another four layers of craft paper 32 are laid on top of the second layer 30 of windings, and the multifilar ribbon is wound over the layers 32 of craft paper to form a third layer of windings Audio power transformer cross reference pdf download layers of windings with interleaved layers of craft paper are wound around the bobbin to obtain a transformer with the proper turns ratio e, audio power transformer cross reference pdf download.
The transformer is used around a magnetic core 80, and it is preferred that the magnetic core have a large cross-sectional area. Referring to FIG.
The beginning end 38 of the multifilar ribbon is turned over so that the windings in the multifilar ribbon 12 are cross connected, audio power transformer cross reference pdf download. The cross connection of the trailing end 36 and the beginning end 38 of the primary windings can be accomplished using a connector 40 as the depicted in FIG.
The cross connection of the beginning end 38 of the multifilar ribbon and the trailing end 36 of the multifilar ribbon for a transformer with a ratio as shown in FIG. The windings in the beginning end 38 of the multifilar ribbon are represented by the top row.
The primary windings are numbered 1, 3, 5, 7, 9, 10, 8, audio power transformer cross reference pdf download, 6, 4, audio power transformer cross reference pdf download, 2 across the top row of the beginning end 38 of windings from left to right. The secondary windings which coexist in the multifilar ribbon are represented by X. Note that the bottom row in FIG. As illustrated, the first primary winding is connected in series to the second primary winding which is connected to the third primary winding which is connected to the fourth primary winding which is connected to audio power transformer cross reference pdf download fifth primary winding which is connected to the sixth primary winding which is connected to the seventh primary winding which is connected to the eighth primary winding which is connected to the ninth primary winding which is connected to the tenth primary winding.
The first primary winding, which preferably connects to a first half primary for a push-pull type vacuum tube audio amplifier, winds around the bobbin several times in each layer e, audio power transformer cross reference pdf download. Each of the primary windings winds around the transformer in this manner and connects in-series with the next highest numbered winding, except for the tenth primary winding which preferably connects in-series to a second half primary in a push-pull vacuum tube audio amplifier after it winds through the transformer The number of series connected primary windings to the number of series or parallel connected secondary windings is the turns ratio for the transformer Enough primary windings must be used to prevent the AC potential between windings from becoming too high so that the effect of capacitance between the windings can be minimized.
Also, there should be enough secondary windings in the multifilar ribbon to provide sufficient current handling capacity and to also provide sufficient coupling between the primary windings and the secondary windings, audio power transformer cross reference pdf download. It is preferred that the secondary windings be wound adjacent to the primary windings which are connected to the center tap 42 or ground to reduce AC potential differences.
The center tap 42 of the primary windings shown in FIG. The secondary windings have been labeled with reference numbers in FIG. The second secondary winding 46 and the third secondary winding 48 are adjacent to the audio power transformer cross reference pdf download primary winding audio power transformer cross reference pdf download should have a low potential because it is grounded by the center tap Likewise, the sixth secondary winding 54 and the seventh secondary winding 56 are adjacent to the sixth primary winding.
The other secondary windings 44, 50, 52 and 58 are located adjacent to the secondary windings 46, 48, 54 and 56, respectively. Note that the secondary windings 44, 46, 48, 50, 52, 54, 56, and 58 are also located so that the distribution of primary windings throughout the multifilar ribbon is symmetrical.
How to wind Fender 5e3 Output Transformer
, time: 21:06Audio power transformer cross reference pdf download
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