+3, no sound from tape at all, with board additions!

For experts to discuss very technical stuff and newbies to ask why the Spectrum they bought off ebay doesn't work.
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ChrisZx
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+3, no sound from tape at all, with board additions!

Post by ChrisZx »

Hello,
I see I'm not the first here with +3 tape loading issues!

I couldn't find my original +3 from back in the day so recently bought one. It all seems to work with the exception of tape loading. In fact, when audio is plugged into the tape socket I don't hear any sound at all through the TV.

I know that the tip of the 3.5mm plug socket is for recording, so am not even using that. Continuity of the socket was ok, but just in case, I soldered a lead direct to the board with a jack plug on the other end. When holding with the board with the socket facing down, the ground is at the bottom, the 'ear' for listening is above right and the output for recording is above left.

Still get no sound through the TV and no reaction at all when trying to load something.

So I had another look and my board has some odd additions - the line from the 'ear' terminal of the socket goes to the plus of C37. On the minus of C37 I seem to have odd additions (I think 1 resistor and 2 diodes) the diodes going from C37 to the middle pin of TR4 and the resistor going off to X3, whatever that does.

Could this 3rd party addition be stopping the sound from getting through? Is that 2 diodes attached to each other in parallel going from C37 to TR4!?

Anyway, here's a pic.


Image
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Re: +3, no sound from tape at all, with board additions!

Post by Guesser »

Those are because it's an Issue 1 board which had errors in the PCB. See here: https://zxnet.co.uk/spectrum/amstradmods/
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Re: +3, no sound from tape at all, with board additions!

Post by ChrisZx »

Ok, so it's normal then. I read just now about T4 being the wrong way round on some +2's. That couldn't be my prob could it? I'm just guessing, I really don't have much of a clue!
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Re: +3, no sound from tape at all, with board additions!

Post by Guesser »

Nah, different board entirely.
Do you get any indication of a loading signal at all? (border flipping between red and cyan). What are you using for your signal source?
You might want to check that C41 isn't damaged. Beyond that you're really getting into "needing an oscilloscope" territory to find where the signal is getting and why it's not loading.
The +3 needs a pretty high peak voltage audio signal in my experience.
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Re: +3, no sound from tape at all, with board additions!

Post by ChrisZx »

Hmm, there's no continuity over C41 (sorry, I thought it was C37 originally).

Maybe I fried that during my earlier attempts with an old mono cable. There is no flipping colour screen, but there was during earlier experiments!
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Re: +3, no sound from tape at all, with board additions!

Post by Guesser »

A capacitor looks like an open circuit to a multimeter, though sometimes if you flip the leads back and forth you can see a bit of charging up and discharging of an electrolytic in resistance mode.

By my simulations the +3 needs at least 1.5 volts peak-to-peak audio signal at the ear input to get any signal through the input amplifier, and probably quite a bit more (like above 2.4 volts) to get something resembling a suitably square signal.
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Re: +3, no sound from tape at all, with board additions!

Post by ChrisZx »

Thanks very much. I don't think I have anywhere near that voltage signal. Checked the laptop output and it doesn't even register anything at the 20v max setting. On 200m there is a little something. I wonder if it might be also partly due to this really cheap lead that I cut off something crappy! I will concentrate my efforts on getting the sound output strong enough first.

I don't suppose you know of a device that is known to kick out that much oomph? I found a youtube vid of a man loading tape games into a +3 using an old iPlayer, but I don't have one of those.

Thanks for your help.
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Ast A. Moore
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Re: +3, no sound from tape at all, with board additions!

Post by Ast A. Moore »

I don’t have a +3, but I do own a +2A, in which I modded the input jack copying the way it is wired on a +3. I can easily load games into it using either my MacBook and my iPhone, even if the volume is not all the way up.

Keep in mind that Apple hardware usually outputs a slightly hotter audio signal than most other computers. Still, I believe you should be getting at least some acknowledgment of the incoming audio from your Spectrum, unless the output of your device is extremely weak. A game may fail to load properly, but you should at least get the border stripes.

To boost your signal, you may want to invest in a small headphone amplifier. You’ll need to look for one that can drive high-impedance headphones (in the 250 Ohm range or higher); not something designed for modern-day wimpy 16–32 Ohm jobbies.
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Re: +3, no sound from tape at all, with board additions!

Post by ChrisZx »

I got out an old cassette player and played a Gary Numan tape through the spectrum, and there was sound at the TV! It was poor quality because the lead is clearly junk. I tried another lead and it was much better and quite loud. I think the main problem must be the poor lead. Better plugs/leads are on their way to me! I think I'll simply disconnect the 'mic' pin of the jack socket as I'm unlikely to ever want to save to tape. I'll also wire up both audio L&R channels to the ring part of the plug, which is correct for the +3.

I'll also dig out an old iPhone and try that as the source. Many thanks.
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Re: +3, no sound from tape at all, with board additions!

Post by Ast A. Moore »

Since I own several Spectrums, I made a universal lead for use with either of them. It has TRS plugs on either end. The sleeve (ground) of each end is wired to the sleeve of the other, but the other conductor connects the ring terminal on one end and the tip on the other. If I’m loading a game into my +2A, the end with the signal wired to the ring terminal goes into the Spectrum and the other end into the source. For any other model, I simply swap the cable ends.

If you have an old tape player, you might simply get away with a cassette adaptor (there are plenty available on the market). It’s also trivial to make one yourself; you just need a tape playback/record head and a cable. I made one when I was experimenting with my turbo loader and it worked a treat:

Image

(I used a set of old earphones so I didn’t have to use up a TRS jack.)
Every man should plant a tree, build a house, and write a ZX Spectrum game.

Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
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Re: +3, no sound from tape at all, with board additions!

Post by ChrisZx »

Interesting contraption.
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Re: +3, no sound from tape at all, with board additions!

Post by ChrisZx »

Nearly there!

I disconnected the 'Mic' pin from the +3 board and isolated that area so that no longer plays a role.

Then, using the tape/CD player that was the most powerful for volume, but this time burned a couple of games onto CD and played them through the Spectrum and 'Buzzsaw' nearly loaded, so I'll play around with volume and stuff.

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