Purpose of this Save/Loading device?

Discussions about Sinclair ZX80 and ZX81 Hardware
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Erm
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Re: Purpose of this Save/Loading device?

Post by Erm » Mon Dec 02, 2019 1:46 pm

XavSnap wrote:
Sun Nov 17, 2019 10:32 pm
R1=10k
R2=? (hidden)
R3=1k
R4=100
R5=12 (!)
R6=1M
C1=? (not pol. mylar?)
C2=? (disc)
C3=? (pol.)
Values/locations not checked...
]
R1 is 39k ohms (orange, white, orange, gold)
C1 has "100 µ 1" repeated, (so 100µF I assume)
C2 has "100" on it, so 100 pF I think.
C3, the big one, has "100MFD 12WV" on it. So 100µF. The negative is at the top.

R5 is 330 ohms (orange, orange, brown, gold)
R3 is 10k ohms (brown, black, orange, gold)
I'm Chris, a Brit in Germany (Chr$ on the QL forum).

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XavSnap
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Re: Purpose of this Save/Loading device?

Post by XavSnap » Mon Dec 02, 2019 1:50 pm

Thanks Erm !

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Erm
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Re: Purpose of this Save/Loading device?

Post by Erm » Mon Dec 02, 2019 3:13 pm

I still haven't tried it out yet! I did just feed it with 4.8v and it certainly lights up ok and the load/save switch illuminates different LEDs, so looks ok.
I'm Chris, a Brit in Germany (Chr$ on the QL forum).

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Erm
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Re: Purpose of this Save/Loading device?

Post by Erm » Mon Dec 02, 2019 6:38 pm

It doesn't seem to work. I set it up with the cassette 'ear' lead in a tape recorder and the ZX ear lead going to the MIC-in on a netbook. With Audacity running and it switched to the 'LOAD' position there is a hum with a very square looking wave, even without the tape running. With the tape running the hum changes slightly with tape at full volume, but it doesn't produce anything like a ZX81 data sound.
I'm Chris, a Brit in Germany (Chr$ on the QL forum).

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1024MAK
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Re: Purpose of this Save/Loading device?

Post by 1024MAK » Wed Dec 04, 2019 1:00 am

Here's my take on the board's schematic. I've read between the lines or guessed at some of the component values.
Schematic of unknown tape cleaner
Schematic of unknown tape cleaner
It will convert ANY AC input signal that has sufficient amplitude to a square-wave. Good 0V / ground connections are essential.

Mark

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Erm
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Re: Purpose of this Save/Loading device?

Post by Erm » Wed Dec 04, 2019 9:26 am

The hum it produces (with no input) is certainly a very square wave. What about the cut yellow and brown though, do I need to do anything with those?
I'm Chris, a Brit in Germany (Chr$ on the QL forum).

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1024MAK
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Re: Purpose of this Save/Loading device?

Post by 1024MAK » Wed Dec 04, 2019 12:33 pm

Erm wrote:
Wed Dec 04, 2019 9:26 am
What about the cut yellow and brown though, do I need to do anything with those?
No. I think they may have originally been the power input to the board.

Try the black CR-TB switch in the other position (the one with the two resistors and green connecting wires). And start off with the volume control at one third to half level.

Mark

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Erm
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Re: Purpose of this Save/Loading device?

Post by Erm » Wed Dec 04, 2019 7:24 pm

I did. Also played around with the volume on the source (tape recorder). With the volume right up it does seem to alter the square wave output hum a fraction, but does not resemble ZX81 loading sounds in any way. I wonder if it needs to go louder then? It's a proper old tape recorder that seems pretty loud (well, loud enough to load stuff into a ZX81 with the volume around 80-100%).
I'm Chris, a Brit in Germany (Chr$ on the QL forum).

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