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ZX81 weird tape loading issues

falter

falter

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http://s1381.photobucket.com/user/unclefalter/media/20151116_220046_zpsj9lxoets.mp4.html

I finally decided to see what I could do with my ZX81 using those tape files available online. I converted one to wav, connected my laptop to my ZX81 using an audio cable and tried loading. I had some trouble initially; the audio cables that came with it had some tarnishing on the tape recorder end. I cleaned them up. Anyway, on the first few attempts I got the familiar messed up screen. However on subsequent attempts when I'd type in Load "" and hit enter the pattern wouldbe very different.

I'm not sure if this is due to modifications on this particular unit. This unit I got came in a handmade wooden case with 3rd party keyboard. It was modified for composite video and I further modified it with a different Ferranti chip for brighter video. That said, the first couple of tries it produced the loading video mess I've seen in other videos. Now it does as per the video above.
 
I would have liked to have taken a look at it but by the time I tried, according to Photobucket, the file 'had already been removed or renamed by its owner'

There's a nice redrawn ZX81 schematic here:

http://www.mainbyte.com/ts1000/good_schematic_hi.jpg

This illustrates that the composite video out from the ULA and MIC out to the tape recorder are generated by the very same pin on the Ferranti ULA, but 'EAR' (Audio in) has its own dedicated input pin. So although the composite mod could compromise the unit's ability to save to tape, it's unlikely to have had any effect on the tape loading input.

Can you try it with a tape recorder and a real tape, if available? The volume setting for these was always pretty critical - easy enough to adjust with an old-school rotary volume control but less so with virtual volume controls on PC screens.

If you post one of your WAV files here I'll try to repeat your experiment with a PC and a real ZX81 here.
 
Sure I'll post a file tonight.. many thanks. I discovered one likely issue.. the first game I was loading required 16 ram and this is a stock zx81. Yesterday night I converted a tzx of some 1 breakout game. And the zx81 screen reacted when I played it.. but it only came out to being 17 seconds long and still no dice. So I'm wondering if my issue is the conversions or something. 17 sec seems short even for a 14 program. If I could get a known good wav file I think I could diagnose it better

Regarding volume.. you usually need to crank it right up on these I think?
 
I would have liked to have taken a look at it but by the time I tried, according to Photobucket, the file 'had already been removed or renamed by its owner'
Click to expand...
Photobucket totally bombed until around 12:30 but it's up again.
 
I think very, very few programs will work in 2k. I have volume issues with mine also... seems like I had to run it out of my headphones from my stereo (with speakers turned off). I don't think it ever worked straight out of a sound card for me, no matter the volume.
 
I have a special tone control dongle that fixes most issues with my zx81. That's the trick. I have 3 dozen tapes many work well, keep playing withe the tone
B.
 
falter said:
Regarding volume.. you usually need to crank it right up on these I think?
Click to expand...

Definitely not if you were using a tape recorder, no - a general trick I used to use was to set the tape playing, wait until the data noise started, put the '81 into load mode and smoothly adjust the volume until the thicknesses of the black and white diagonal lines were roughly equal. Then I'd stop the tape, rewind back to the start and put the '81 back into load mode again, this time allowing the program to try to load. The tone ideally needs to be as bright / trebly as possible and with little or no bass, so if you can vary these parameters, all to the good. Also make sure your audio output mixer doesn't have any fancy effects (like reverb!) turned on. The output needs to be absolutely 'dry' (Free of effects).

The thing is, tape recorders have fairly powerful outputs designed to drive (typically) an 8 ohm speaker or earpiece so they have bags of output volume to spare. PC outputs these days are rarely powerful enough to drive speakers directly so quite a few just don't go 'loud' enough to drive the input of an old-school eighties computer. If you look at the 'Ear' input circuit there's a 220R resistor down to ground and a 4K7 resistor going onwards which means that the signal going into the 'Ear' input socket is divided by umm.. roughly twenty before it gets to the input pin on the ULA. I had a similar problem once using an MP3 player to send audio to the ZX81, thinking how cool would that be if it worked... It didn't work, the output just couldn't go loud enough.

If you've got a real tape recorder try writing a short BASIC program

10 FOR X = 1 TO 20
20 PRINT "IT'S WORKING!"
30 NEXT X

Step One: Save that to a real tape recorder and try reloading it from the tape recorder. (Using a short test program like this means you don't have to wait long for it to either work or fail).

If it works, there is a problem with the audio output level from the computer, or with your WAV files.

Step Two: replace the tape recorder with your computer acting as a tape recorder, ie, by using Windows 'Sound Recorder' as a 'Tape recorder'. (The lead you use for this may need to include a DC blocking capacitor / condenser in series with the signal line: the computer will output a DC voltage on the microphone signal terminal to power what it expects will be an electret microphone). When recording, use the computer's microphone input volume slider control in the audio mixer to set the recording level to a sensible level. 'Just below the red level'.

Save the test program to the computer, swap the leads around and see if you can load the .WAV file you just recorded back into the ZX81. If you can, that narrows your problem down to a problem with the .WAV files you are making from .TZX files.

If you can't, that suggests a problem with the audio output levels on the computer.

Please do post one of your .WAVs here so we can have a look / listen to it.
 
Forgot to say: I looked at your video clip. The diagonal lines going in two directions don't look normal to me (I normally only expect to see one set of sloping diagonal lines, but I note you are on the other side of the pond (UK here) so this might just be the difference between what the loading lines look like on a 50Hz screen and what they look like on a 60Hz screen).

The main thing is that the black lines are very thin when they should ideally look around the same thickness as the white bands - this suggests that the audio drive level is not high enough.
 
I should mention, I use a real tape recorder with my ZX81 (T-1000). I bought a new recorder from Radio Shack that is very reliable. Looks like a 70's tape recorder but it's actually new.

For me, the best tape recorders were the Panasonic decks from the 1970's. I still have one.
 
Coincidentally, that (A 'National Panasonic' flat cassette recorder) is what I have always used with my ZX81 / ZX Spectrum as well.

Nice machine, really heavy as the deck mechanism is made almost entirely from metal parts unlike more modern units which used a lot of plastic in the deck.
 
Yah...I remember when I was a little kid, I used to take it with me and listen to Beatles and Billy Joel tapes on long car trips. I don't have that one anymore, but somewhere along the lines, I think when I got my OSI 600 it came with a Panasonic tape recorder.
 
SiriusHardware said:
I had a similar problem once using an MP3 player to send audio to the ZX81, thinking how cool would that be if it worked... It didn't work, the output just couldn't go loud enough.
Click to expand...

The problem here is that the voltage output from the MP3 player is too low for the computer. A transformer suitable for impedance conversion inserted between the MP3 player and the computer will fix this.
 
Cthulhu, agree about your assessment of the problem.

The MP3 player in question was designed for (typically) 32-ohm earpieces designed to be placed inside the ear, so the available power output is minimal. For it to be higher would be dangerous. The nominal input impedance of the ZX81's Ear input is 220 ohm, so it seemed possible that the MP3 player, designed to drive 32 ohms, might be able to develop a higher voltage output across the 220 ohm load, so I tried it. It proved not to be the case.

The only devices which will work reliably are those designed to drive a speaker to room-filling volume, such as old-school tape recorders or stereo amplifiers or similar Hi-Fi stacks. From those, the output from one channel of the headphone socket is usually powerful enough. This is not the case for most PC audio outputs - they have to be plugged into active, internally amplified speakers to achieve the required volume.

There are occasional exceptions: I have a couple of old-school PC ISA Soundblaster type cards which did have onboard amplifers and were link-settable so they could either directly drive passive speakers using the onboard amps, or you could set them into a line-output mode where the output was intended to be fed into amplified speakers or a hi-fi amplifier. The maximum internal speaker output volume on my Dell Inspiron 6400 / 1505 is much, much louder than on any other Laptop that I have seen before or since, but even the phone output on that is not loud enough for a ZX81, I've tried it.
 
Like I said, I use a regular tape recorder myself, but I have seen people (somehow) use a phone to drive the tape input. Not that I think you're addressing me directly, but I do understand about the MP3 or any computer simply does not typically drive enough to be heard without some kind of special dongle or help. I suggest you use a regular nice new tape recorder to eliminate variables from your troubleshooting. It's hard enough to load tapes on an ZX81 with the intended hardware as it is!
Bill.
 
Billdeg. Hi, I was responding both to Cthulhu's comment and yours - He suggested that MP3 players mostly won't be powerful enough (I agreed) and you said that you were aware of cases where people have successfully loaded ZX81s from headphone ouputs - I agree with that too but I think it was probably the headphone output on something more powerful than an MP3 player or a laptop (but as I said, I myself have seen exceptions to this general rule).

Of course it's better to use what the ZX81 was designed to work with (a tape recorder) but the OP's problem is that he doesn't have any actual tapes to use with a tape recorder, he is using audio files made directly from digital snapshots of programs.

The idea that you can play a .WAV file from a digital device straight into a ZX81 'EAR' input is perfectly reasonable in theory, but in practice the most convenient devices for doing this from (Laptops and MP3 players) mostly don't have powerful enough audio output from the headphone sockets.

Here's one left-field idea for Falter: If he has a cassette player but no real tapes to put into it, how about obtaining one of those MP3-to-cassette adaptor rigs which were available a while ago to let you play your MP3 player through an old car stereo? Put the 'fake cassette tape' end of the adaptor into the tape player and plug the 3.5mm plug into the headphone output of the PC. The tape player will provide the necessary amplification and boost the sound coming from the PC up to the necessary level.
 
If for some reason you don't want to take the transformer route then another alternative is to use the headphone output of a portable media player which has been designed to drive high-impedance headphones. These are uncommon, but they do exist and are more likely to be successful at loading software into a ZX81. Why did Sinclair make its input so insensitive anyway?
 
Thanks guys. Definitely seems to be volume that is the issue as suspected. As an experiment I got VLC player on my laptop, cranked it to 125% volume and tried a load. The ZX81 definitely reacts.. but again nothing ultimately happens. I'm assuming I'm not misunderstanding the whole loading process... in videos it looks like you do the load command, play the tape and then when the tape ends the game starts on its own. On mine it just sits at the wavy screen after.

I don't have a tape recorder but I do have an old cassette deck I could try. The only thing I'm wondering about is that deck outputs in stereo and I understand I need a mono cable to make it work?
 
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