[sdiy] Parallel 8 Bit DACS?

[rsdio at sounds.wa.com]

Thanks for bringing up this thread again. I'd intended to comment  
when it first came up.


The Texas Instruments THS5671A 14-bit DAC runs at 125 MHz, and has  
both +/- outputs. They're current outputs, so you'll probably need  
current-to-voltage conversion. As with any parallel input DAC, you'll  
want S/H on the output to de-glitch.

The counter design is straightforward and very appropriate.

I'd recommend the following:

Oscillator -> Binary counter -> EPROM -> DAC -> S/H

... with appropriate logic to tie the S/H timing to the oscillator to  
keep everything in sync.


Flash EPROM will work, provided that you select parallel address /  
data designs. That's probably obvious, but there are a lot of serial  
Flash chips, and those won't really work well for a drum machine  
without a bit of extra logic for the serial-to-parallel conversion  
(unless you also have a serial DAC that is compatible).

Personally, I'd select the Flash first, then read its data sheet  
about programming. You might want a CPU on your drum machine to  
handle MIDI and sequencing, so that CPU could potentially have  
firmware that can program the Flash without attaching something like  
the PIC style programmer you're talking about.

There are lots of hex file formats, and they can easily be converted.  
The real challenge is the electrical requirements of the Flash  
according to its programming needs. If the electrical part doesn't  
match up, then it doesn't matter how similar the file formats are.  
Regarding the file format, you could design your own MIDI format for  
loading the data into your CPU for programming into each Flash.


There's probably a lot of magic, possibly due to happy accidents of  
imperfect technology from the old days that we've all grown fond of.  
Sometimes the most accurate design for audio quality is missing that  
certain grunge, aliasing, or distortion.


Are you thinking of a single voice or several?

Brian


On Dec 8, 2013, at 14:41, Jack Jackson wrote:
> To my answer my own question, the DAC0800 was used in the rare  
> Solton Programmer 24:
>
> http://soundsofthedot.com/images/Programmer-24_Schematics.jpg/ 
> page-4.jpg
>
> ----------------------------------------
>> From: jackdamery at hotmail.co.uk
>> Date: Wed, 20 Nov 2013 13:35:45 +0000
>>
>> I'm investigating the world of drum machines and EPROMs. I quite  
>> like the idea of a DAC with parallel inputs and +/- output as per  
>> the DAC0800. I can't find any implementations of it though, apart  
>> from the datasheet. First question:- Is there a similar DAC that  
>> might better suit this purpose?
>>
>> As far I understand it, a fairly standard implementation for a  
>> drum machine would be an oscillator driving a parallel-out binary  
>> counter fed into an EPROMs address inputs with the EPROMs outputs  
>> fed into the the DACs parallel inputs. Like so:
>>
>> Oscillator -> Binary counter -> EPROM -> DAC
>>
>> Second question, in terms of EPROMs I believe it would be easier  
>> to use a Flash EPROM, which is electrically erased and programmed  
>> (as explained on this page: http://www.arlabs.com/help.htm ).  
>> Could one use a PIC style programmer to programme these? The Linn  
>> drum .bin files I found online seem to contain HEX code as you  
>> would programme a PIC IC with.
>>
>> Last question: Is there any magic to using this topology, and also  
>> analogue VCA and filtering, over using samples of original drum  
>> machines?
>
>