Tape recording levels

General discussions related to the Altair 8800 Clone

Tape recording levels

Postby mail@gabrielegan.com » May 22nd, 2018, 3:13 pm

Inspired as ever by Mike's videos, I've been trying to get an Altair to save and load data from a reel-to-reel tape recorder, in my case an Akai 4000DS. The Akai has phono inputs and outputs on the back and also a Microphone input and a Headphone output on the front panel. I am able to save BASIC programs to tape -- I know they're there because I can listen to them as audio recordings -- but I can't get the Altair to load them back. I suspect the problem is the signal levels.

The Akai has VU meters on the front, and I've been setting the record level so that the signal takes the needle to the top of the white zone (up to 0) but not further right into the red zone (above 0). I adjust the playback to get the same level. Does that sound about right to anyone? I can do this via the phono or Mic/Headphone sockets and the result is the same in each case: it records okay and plays back giving what seems to my ears like undistorted reproduction, but the Altair just ignores the recording so that CLOAD "T" in BASIC just hangs.

If I switch out the Akai reel-to-real tape recorder and try a cheap mono audio-cassette recorder with Automatic Volume Control using the Microphone and Headphone sockets, it all works fine: there is nothing to set for recording and the playback at about one-third maximum volume enables the recorded BASIC file to be reloaded.

Anyone know if there any diagnostics I can try to see if I've got the levels wrong? I have a modern digital multimeter but don't know how to use an oscilloscope. (This might be the time to learn!)

Regards

Gabriel Egan
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Re: Tape recording levels

Postby AltairClone » May 22nd, 2018, 3:26 pm

If the tape deck is stereo, make sure it is recording and playing back on whichever channel ends up on the tip of the phone plug to/from the Altair.

You can also run GENTEST and CASTEST to help set levels (in the http://altairclone.com/downloads/cassette_interface/ folder) as detailed in the Altair Clone Cassette Interface manual (http://altairclone.com/downloads/manual ... Manual.pdf).

Mike
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Re: Tape recording levels

Postby TomXP411 » May 23rd, 2018, 10:08 pm

:) This sounds familiar. I did the same thing with a TASCAM digital recorder.

I found that the tape adapter can handle a fairly wide range of volume levels - and definitely use the cassette tester that Mike mentioned. It was very helpful when I was setting up my system.
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Re: Tape recording levels

Postby mail@gabrielegan.com » May 28th, 2018, 6:44 am

I THOUGHT I'd seen somewhere a manual specifically for the Clone Cassette Interface, but I failed to file it away correctly and I've been working from the original Altair Cassette Interface manual, which is much less helpful than's Mike manual. Got the correct Clone Cassette manual now, and will use the CASTEST and GENTEST routines as advised. Will check signal at plug-tips too. Much obliged.

Regards

Gabriel
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Re: Tape recording levels

Postby mail@gabrielegan.com » May 28th, 2018, 4:21 pm

Sorry, quick follow up question . . .

I notice in the videos, Mike, that you unplug and replug the audio cable from the cassette recorder each time you switch from recording onto cassette to reading from cassette. And the original 88-ACR manual says "Be sure that only the 'Play In' or the 'Record Out' of the 88-ACR is connected at any one time; never both" (p. 70). I guess then this matters, but it's a rule I overlooked and I been using two cables--one for 'microphone' and one for 'speaker'--at the same time to save the hassle of switching over. Might I have damaged the Altairs I did this on? (It's force of habit: on the 8-bit home computers using cassette recorders in the 1970s that I'm familiar wite, like the Sinclair ZX80/ZX81/ZX Spectrum, we routinely left both cables plugged in at once).

Regards

Gabriel
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Re: Tape recording levels

Postby AltairClone » May 29th, 2018, 11:48 am

There is not an electrical issue with the Altair Clone cassette interface with having both cables connected at the same time, so no damage will occur to the equipment.

I have not dug into the reason the original manual states that only one cable should be connected at time, but I imagine it was due to feedback issues that affected operation depending on the recording equipment being used.

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Re: Tape recording levels

Postby toml_12953 » May 29th, 2018, 9:18 pm

AltairClone wrote:There is not an electrical issue with the Altair Clone cassette interface with having both cables connected at the same time, so no damage will occur to the equipment.

I have not dug into the reason the original manual states that only one cable should be connected at time, but I imagine it was due to feedback issues that affected operation depending on the recording equipment being used.

Mike


I know that on the TRS-80 with Radio Shack recorders, there was a ground loop that caused hum if both were connected at the same time.
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Re: Tape recording levels

Postby TomXP411 » May 31st, 2018, 6:06 pm

Also, some recorders have a "monitor" feature that lets you hear the recorded audio through the earphone jack while recording. I don't know how the ACR and associated SIO handles that, but I could see it conceivably causing problems with certain hardware configurations.
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