Which Loader For You? – The Cassette Gazette Page 11
The Cassette Gazette was a 1983 one issue advertising newsletter that was a joint production of Lemons Tech and KWIK Software. The Gazette described the products sold by the two companies, mixed in with operational advice and interesting facts about using cassettes with your TRS-80. It appears to have been written by Wayne Lemons, the founder of Lemons Tech. The Gazette is reproduced here page by page with permission from Wayne Lemons' family.
Which Loader For You?
Here is information, perhaps in a different form than otherwise presented, that should help you better decide which of our products can best suit your needs.
Model LL-1 and L80M are signal powered loaders, that is, the output signal from the cassette recorder (CTR) itself supplies all the power the loader circuits use. Of necessity a certain level of output signal is required before the loader can work reliably. For this reason the LL-1 or L80M are recommended only for use with the Radio Shack CTR80 or CTR80A. They will, however, work with CTR41 and CCR81 if you make simple solder-in modification in the CTR41 and a resistor and capacitor in the CCR81. These parts and modification instructions are included free with your order… please note on your order blank if you need them.
If you do not wish to open your recorder and make these modifications then we recommend you buy the PLUM. This has the same kind of very reliable loader circuit but in addition has a built-in amplifier to boost the output signal when used with CTRs that have weaker output than the CTR80/80A. (Of course, it works with the CTR80/80A too.) In addition, the PLUM has special limiting circuits so FSK signals such as used in the Model III/4/100 and in the Color Computer load without volume juggling also. Because it can handle both pulse (Model I and Model III low speed) and FSK (Model III/4/100 and CoCo) the PLUM may be used for making CTR-to-CTR tapes copies of programs if you wish.
In addition the PLUM, like the L80M, has built-in audio monitoring. But, unlike the L80M, it also has a built-in motor pushbutton… this lets you override the remote motor jack in both the PLAY or RECORD mode merely by tapping a button. For example, suppose you have saved a program and your CTR is still in the RECORD mode… by just tapping the PLUM button you can move the tape forward an inch or two putting a silent gap between that program and the next one you want to record. This silent ‘marker' gap of course makes it easy to find the program later and the big news is that you had to pull no plugs to do it! We also recommend this tap of the switch at the end of the program so as to move the tape out from between the capstan/pinch roller pressure which, if you forget to release the PLAY button, can sometimes cause a “pinch hit” at the end of a program.
Further, if you want to find where a program begins or ends, with your CTR in PLAY you can advance the tape with the pushbutton while listening to the PLUM’s audio monitor. Quite obviously when the sound starts or stops you know you have found the beginning or the end of a program.
An LED lamp, with automatic polarization sensing, lights to show when the motor is turned off or on, either by you or by the computer. In addition this circuitry tends to “soften” the turn-off surge of the motor so that there is almost no danger of putting a ‘hit' on the program due to spurious motor noise currents when you move the tape. (There is no such protection if you move the tape by pulling the remote plug and reinserting it.)
The PLUM uses a single standard low-cost battery power supply. (No messy line cords to plug in or get tangled up in other wiring.) There is no manual off-on switch… instead the circuit itself automatically senses whether you are loading a program. If you are, the circuit automatically turns on. When the load is finished the battery current stops immediately. For this reason you may expect up to a year or more from one 50-cent battery… a battery you can buy at any drug, grocery, or electronics supply such as Radio Shack.
More About Why Our Loaders Work
Without question the Model I TRS-80 is the most critical of all the TRS-80s to load. The reason is that it uses a pulse system… not that a pulse system is bad, per se, but because audio cassette recorders are not designed particularly to handle pulses. A pulse is a signal that turns on then turns off (see Fig. 3, page 8) and there is a silent space between one pulse and the next. Any pulse processed through a tape recorder tends to ‘ring', that is, it does not stop instantly but obeys the idea that something in motion tends to stay in motion. What occurs is a false or ringing pulse generated following the true pulse. The greatest difference between the true and the false pulse is that the false pulse is not quite so large. Unfortunately, though, if you turn the CTR volume just slightly too high, the false pulse gets large enough to trigger the computer latches. Quite obviously a “stray” second pulse is going to create either a checksum error or garbage in the loaded program.
But turning the volume down is not good either since almost any tape has audio variations on it, and if you turn the volume down the least bit too far you can be almost certain there will be a weak pulse somewhere on the tape that won’t trigger the computer’s cassette latch. That is why you have to ride such a thin line when loading programs into many Model I computers. (Late Model I’s and all Model III’s were improved in the ROM routines by making the SET pulses occur sooner thus making the ringing less apt to intrude into the RESET territory and as a result load volume was and is somewhat less critical, but you still have to set the volume control rather critically unless you use one of our loaders.)
Our loaders solve the problem of ringing by the simple expedient of suppressing it before it gets to the computer. And since the suppression works at high volume levels you can turn the CTR volume full up and leave it there because you have not only eliminated ringing but at the same time any weak pulses on the tape are now more than ample level to trigger the SET latch of computer.
These two factors working together automatically is why, with a loader, you may well be able to load tapes that are virtually impossible to load in any other manner. So reliable and consistent are our loaders that you can reasonably expect, and almost never be disappointed, to load every loadable program the first time everytime!
But this is not just advertising hype. We guarantee YOUR satisfaction. We guarantee that our loaders will work for YOU. If they don’t do what we say all you need do is return without physical damage anytime up to 30 days after you receive it and you’ll get your full purchase price refunded, no questions asked.