DX7 noise and opamps (was

[Barry Klein]

To: synth-diy at horus.sara.nl

 Ju> No problem for bright sounds, but very annoying if you want to
 Ju> program dark and mellow sounds. Wurlitzer Piano - what a
 Ju> wonderful Wurlie I had on my DX-7, even with the typical
 Ju> distortion on every individual note - but it was drowned in noise.
 Ju> You can make things a *little* better by tweaking the trimpot
 Ju> in the DAC section, to optimize linearity. But even then ...

Yes this is where the problem is - in the LF-only types of sounds
the noise really pumps up.  I did try tweaking the DAC pot but it
was already set pretty well.  The problem isn't really just because
of the 12 bit resolution per se (my P2000 is fine and its 12 bit too)
but I think is really due to the conversion design.  The amplitude
could be higher through the chain but it wouldn't cut the noise down
great enough to be worth tweaking.  Could maybe pop some newer DAC
chip on the digital bus but I'm not that ambitious - even if it
worked much better who else would do it?  Very few.

 Ju> I remember the headphones output being even more noisy than
 Ju> the FM process. This was the only chip I replaced when I used
 Ju> to own a DX7. I *think* I used a 5534 there, which can drive 600
 Ju> Ohm Headphones very well. But I don't remember the details.

I was going to suggest this particular chip as I thought I had
remembered seeing it used for a headphone amp.  I run the DX7 through
my SE70 though so I won't worry about it.

Barry

... Elect. Music, Photography, Bubble Machines, Stunt Kites, Elect. Design

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