ZX81 audio.

[marste]

@Freya : is ZN428 is a nice chip, but is "era compatible"? Seems to me that is a product of the 90s more than the 80s...

With the solution of MAK you should add really just a bunch of resistors and you can go with a single widespread 74hct377! More, with a simple DPDT switch in the middle of the R2R ladder the interface can go from a mono 8bit audio to a stereo 4bit one still with the same components!!

Anyway the interfaces with both ICs can be made compatible, we should just agree on the address line to use for the out instruction!

And, more important, since they are already existing on spectrum, we should have trackers ported to the ZX81!!

[Moggy]

We have had an AY tracker for ZX81 for the last 12 years and very good it is too but admittedly no sample tracker..

This thread has all the information....

viewtopic.php?f=6&t=556&hilit=ay+tracker

[1024MAK]

The ZN428 is a Ferranti semiconductors product, and is quite old, so certainly existed in the 1980s. See the dates at the end of this data sheet. Of course, it would not have been cheap…

Mark

[marste]

The ZN428 is a Ferranti semiconductors product, and is quite old, so certainly existed in the 1980s. See the dates at the end of this data sheet. Of course, it would not have been cheap…

Then we can design two absolutely compatible boards to choose from!

Is bus signal A5 good to go (meaning there are known/common interfaces using it already)?

[Freya]

It definitely is from the 80's and I think it would have been cheap considering the high quality output.
This was the chip at the heart of both the specdrum from Cheetah (The PCB of which is pictured in my earlier posting)
and the ram music machine.

The SpecDrum was actually one of the cheapest add-ons for the spectrum at 29.99.
This was crazy cheap when you consider what a drum machine based around similar technology would cost but then again with a drum machine you are paying for a new computer all over again. Another advantage of the specdrum was you could load new sounds into it too.

At $3 it's not the cheapest silicon but for a dac that seems a good price to me.

and it is authentik of the era which the edge connector on that PCB proves!

I'm not sure what went on with this chip. Ferranti actually described it as being designed for 8 bit computers but I'm not sure it got any use in any except as expansions. Having marketed it for 8bit computers perhaps nobody wanted to use it with a 16bit computer??
Dunno?

Anyway the sound is very nice for the price.

[Moggy]

Didn't realise The Specdrum used this chip, checked my own and yes there it is.

I agree it was a cheap way into auto rhythm when you consider a Linndrum in the 80's was retailing at over 5 grand (US)!

[Moggy]

There is a source for them here but a bit expensive.

https://www.silicon-ark.co.uk/zn428d-8- ... by-plessey

[Freya]

and here it is for $2.73 with $1 shipping but why not make an offer and see if you can get one or a few for a cheaper price?


https://www.ebay.com/itm/253704143993?_ ... 101224.m-1

[Freya]

I think it is a real shame the 128k spectrum had the AY chip instead of this Ferranti DAC.
The audio would have really been something then!

[McKlaud]

It might be an overkill but AD makes/made some interesting D-A converters like:
https://www.analog.com/media/en/technic ... d7228a.pdf
or
https://www.analog.com/media/en/technic ... AD7801.pdf

The second one might be an alternative to the ancient ZN428D.