Does anyone have a genuine Covox Speech thing for photos? (I'm making a replica)

Discussion about old sound cards, MIDI devices and sound related accessories.

Does anyone have a genuine Covox Speech thing for photos? (I'm making a replica)

Postby Kahenraz » 2018-9-07 @ 05:19

I'm trying to make a replica Covox Speech thing and I'm getting conflicting information on that resistors were used:

viewtopic.php?f=62&t=51483&start=20

From what I can make out, the resistor is 10uF in yours, keropi. However it sounds like a 80~100uF would sound in dreamblaster's. Why do you think?


Most circuit diagrams for the Covox suggest a 10 ohm ladder but this document says 7.5 ohm:

http://kb.gr8bit.ru/GR8BIT-KB0010-Addin ... 102013.pdf

And Beegle seems to think that the Dreamblaster uses even higher resistors.

I've ordered various parts to try but I'm not sure how this will affect the exactness of the replica. How will different resistors change the sound?

And does anyone have a genuine Covox Speech thing who can provide a photo of the circuit board to see the original design? Or better yet, a photo and confirmation with a multimeter.
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Re: Does anyone have a genuine Covox Speech thing for photos? (I'm making a replica)

Postby Tiido » 2018-9-07 @ 10:26

Lower values will result in less thermal noise (hiss) as will use of metal film resistors over carbon ones but they'll also result in higher loading on the IO and that can result in distortion due to IO drivers no longer putting out flat levels and also various digital noises getting exaggerated due to non existent PSRR in digital bits. I have used 20kohm and 10kohm resistors on an LPT DAC I built a decade gao and on my sound card I used 2kohm and 1kohm.
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