Homebrew Drum Computer - test-drb@ccmp.vtda.org

14 Dec 2007

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Subject: Re: Homebrew Drum Computer
   From: Jules Richardson <julesrichardsonuk at yahoo.co.uk>
   Date: Fri, 14 Dec 2007 08:19:06 -0600
     To: General Discussion: On-Topic and Off-Topic Posts <cctalk at
classiccmp.org>

Robert Nansel wrote:
  Certainly I could trash a few old cassette decks,
or even get some 
 floppy R/W heads to experiment with audio recording tape super-glued to 
 a soda can, but I really want to get at least the performance the old 
 machines could produce, so that means a reasonably fast drum RPM, 
 somewhere around 6000 RPM, say. 
Very interesting project.  Won't standard tape heads only work reliably if the 
magnetic material's passing by at quite a narrow range of speeds, though? 
Google suggests that's 1 7/8" per second, which isn't very fast at all - a 
drum that can do a few tens of RPM seems possible, but 6000?? 
Correct, there is a relationship between gap width and media speed.
I've used casette heads to 10ips but above that there are problems.
one is the total inductance of the winding limit the upper frequency 
reponse (used as saturation recording head) to around 40khz and thats
pushing it.

Allison

...

If I've got my numbers right, a small 6" drum has a diameter of approx 19"
and 
at 6000rpm will take 1/100 seconds to do a single revolution. That's 1900" per 
second past each head - roughly 1000 times the typical operating speed of a 
cassette deck.

Build several low-speed soda can drums - equivalent in number to the word 
length of your machine, then read/write data in parallel... (OK, that's a 
humourous suggestion, but it wouldn't surprise me if someone hasn't tried it)

cheers

Jules 