Source of 200ohm speakers?

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Erm
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Source of 200ohm speakers?

Post by Erm »

Does anyone know of a source for the 200ohm speakers like those used in the Issue 1 and 2 Spectrums? The newer (Issue 3 and later) 40ohm speakers are easy to find as new versions, but seemingly less so for the 200ohm.
I'm Chris, a Brit in Germany (Chr$ on the QL forum). https:\\QXL.WIN < QL related collection.
Moggy
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Re: Source of 200ohm speakers?

Post by Moggy »

200 ohm sounds more like a piezo than a speaker, googling "200 ohm piezo" throws up quite a few answers.
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1024MAK
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Re: Source of 200ohm speakers?

Post by 1024MAK »

I would suggest upgrading the circuit to the issue 6A board standard, then you can use a 40Ω speaker.
Issue 6A ear/mic/speaker circuitry
Issue 6A ear/mic/speaker circuitry
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Erm
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Re: Source of 200ohm speakers?

Post by Erm »

It certainly looks like a speaker in that it has a coil/magnet and membrane. It's just one that I'm fixing up to sell, so an entirely new circuit is probably overkill, and perhaps a non-beeping Spectrum might actually appeal to people that like to shoot-things-up in the dead of the night or whatever (you can't actually turn the speaker off normally of course).

Electronically, is it viable/what would happen if I used a 40ohm speaker with a resistor added to bring it up to about 200 ohm resistance?
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XavSnap
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Re: Source of 200ohm speakers?

Post by XavSnap »

Hi,

In case of 40ohm speaker, the resistor will pull up the ZTX450 main currant and will destroy it by overheated.

You had to make a serial pod made with five 40ohm speakers… :oops:
Or add a 150 ohm resistor.

8-)

Wiring diagram:
5speakers.jpg
5speakers.jpg (28.97 KiB) Viewed 9580 times
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1024MAK
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Re: Source of 200ohm speakers?

Post by 1024MAK »

The reason that Sinclair changed the circuit (which occurred from the issue 3 board, but the schematic is wrong) is because the sound output was too low (too quiet).

If you use a less sensitive speaker, such as a 40Ω one, and then wire a resistor in series with it, you will only end up making it even less loud! In fact with a 160Ω resistor, more power will be wasted in the resistor than used in the speaker! :(

Changing to the later circuit just involves removing diode D10 and replacing it with a transistor and some patch wires.

Mark
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Erm
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Re: Source of 200ohm speakers?

Post by Erm »

1024MAK wrote: Wed Feb 05, 2020 9:01 pm Changing to the later circuit just involves removing diode D10 and replacing it with a transistor and some patch wires.
Oh yes, so it does! I only need to pinch the 9v from somewhere. I'll give that a go then.
I'm Chris, a Brit in Germany (Chr$ on the QL forum). https:\\QXL.WIN < QL related collection.
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1024MAK
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Re: Source of 200ohm speakers?

Post by 1024MAK »

XavSnap wrote: Wed Feb 05, 2020 8:15 pm Hi,

In case of 40ohm speaker, the resistor will pull up the ZTX450 main currant and will destroy it by overheated.
Xav, the issue two circuit does not use a transistor:
Issue two ear/mic/speaker circuitry
Issue two ear/mic/speaker circuitry
And the speaker is a higher resistance type.

Mark
ZX81 Variations
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XavSnap
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Re: Source of 200ohm speakers?

Post by XavSnap »

:oops:
So we cannot have a DOLBY 5.0 standard on the Spectrum.
it's really sad...
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Erm
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Re: Source of 200ohm speakers?

Post by Erm »

Sorted. Half neatly done - but it doesn't matter as it's hidden by the heat sink. I stole a TR7 from a parts only Issue 6 board.

Thanks Mark and Xav for your comments.
I'm Chris, a Brit in Germany (Chr$ on the QL forum). https:\\QXL.WIN < QL related collection.
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