Yamaha TX7- Owned from June 2000- June 2002, Bought and sold for $75
The TX7 is basically a DX7 stuck into a heavy, weird-looking, and indestructible plastic box. The voice architecture is the same but there are a few differences otherwise: Only the "function" parameters (portamento, mono/poly modes, tuning, mod wheel/foot pedal/breath controller/aftertouch destinations, etc.) can be edited from the panel. The front panel only has a (very cryptic) 1x16 display and a row of green buttons. Also if what I've read is true the outputs are noisier than the DX7. They are indeed quite noisy, though not awful. Also there is no cartridge slot and no pedal or breath controller inputs, just midi in/out/thru, a tape dump port (which uses a custom connector), and a mono output. Anyway on the plus side the function settings are stored on a per-voice basis instead of globally, but if you dump the patches using DX7 software you'll lose it all (I found out the hard way). The TX7 represents the cheapest entry into the world of 6-op FM out there, if you can stomach the added noise and lack of editablility (most people use patch editors anyway- I don't- I found it to be a pain to do it like that and that's largely why I sold it). It probably doesn't need to be stated here but I'm going to describe the voice architecture anyway. There are 16 voices (monotimbral), each consisting of 6 sine wave oscillators (called operators). There are 32 algorithms which define how the operators interact with each other (modulator and carrier combinations). Basically the amplitude of one operator modulates the phase of the next operator in the chain and this changes the waveform. Each algorithm contains a feedback loop too where an operator can modulate itself or the last operator in a stack can modulate the first one- Single-operator feedback loops make saw waves and pseudo-resonant filter sweeps, multiple-operator feedback loops make interesting distorted textures and odd rhythmic sounds. Higher feedback levels lead to aliasing and chaos. Each operator can be tuned from 1/2 to 32 (as in the harmonic series) and detuned to non-integer frequencies, or can be put into a fixed frequency mode. Fixed frequency operators are not affected by the keyboard or any pitch modulation. In fixed frequency mode an operator can be tuned to sub-audio frequencies, and when used as carriers they produce a very interesting chorusing style sound. The oscillators can be set to synchronize with every note-on or run freely. Each oscillator has its own 4-stage envelope where all the rates and levels can be defined- much more interesting than simple ADSR envelopes. They can also track the keyboard (keyboard rate scaling) and they all have independent velocity sensitivity (but unfortunately this is positive only and there are no selectable velocity curves). There's also a global pitch envelope. There's a single LFO which can modulate the pitch of all operators or the amplitude of each operator independently. The amplitude/frequency modulation amounts can be controlled independently with the mod wheel or pedal or whatever. The LFO has sine, triangle, square, saw up, saw down, and noise waveforms and can go pretty fast. It has a delay parameter and can be set to restart on note-ons or run freely. There are also interesting keyboard level scaling curves for each operator. It is possible to pick a key for each operator as a break point and set the curve for each side- positive or negative, linear, logarithmic, or exponential, with controls for depth- if that makes any sense. Then there are controls for portamento (which can also be set to glissando), and controller destinations, mono/poly modes, etc. There is only room onboard for 32 patches.
Sound-wise it is capable of some incredible things- lovely bell sounds, bass sounds, pads, and the best chaotic noise patches outside of modular territory. The problem is that programming good sounds takes a lot of patience and knowledge of how it works. So most people tend to just use banks programmed by other people. There are thousands of banks out there, and I've gone through a few but I've found that most are pretty awful. So I mostly stuck to programming my own sounds.
The DAC is 12-bit 28KHz (I think, don't quote me on that) so there'a a good amount of grit and aliasing to the sounds. Later models like the DX7II and TX802 used 16-bit 44.1KHz DACs so there is less aliasing and noise, but a colder sort of sound. Which one sounds better is a matter of preference, but I think I like the aliasy stuff more.
The inside of the TX7 is pretty packed. Inside this thin little module are two boards, one for the CPU and one for the sound generation, plus a switching power supply. The CPU is a Hitachi HD63A03. The sound generation board contains two main chips that do all the work: the YM2129 EGS chip, which calculates the envelopes, and the lovely ceramic and gold-packaged YM2128 OPS chip, which is the FM part (by the way OPS is the type of FM chip- yamaha had a whole range of them, the OPLL being the lowest and I think the OPS was the highest. Some of the PSS and PSR keyboards used OPL chips and the 4-operator synths used the OPN chip). The DAC is a BA9221.
There are key-combinations to display the backup battery level and possibly other things but unfortunately I forgot what they are.
Overall the TX7 is a nice module, and the cheapest source of 6-operator FM synthesis. But it is pretty noisy and there are better options out there (TX802) for a bit more money.
pictures: unfortunately I don't have any good ones of the outside...
sounds:
TX7-1- This nicely demonstrates the kinds of noises FM synthesis can make, and there's a similarly noisy demo here.
links:
There are many good Yamaha FM-related things to be found here: Dave Benson's DX7 Page. I strongly reccomend the "How to Program the DX7" article featured near the top of the page.
Yamaha has user manuals for nearly all of their products available here: Yamaha Manual Library (English)
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