ODP: diy GM synth

[Mikko Helin]

So you think (at least Roman) that this could be a feasible
project idea? Of course I meant that the manufacturing of 2-
sided board is difficult at home, not the designing of it.

I think the converters may be any brand, anything we could find
easily, if the quality is good (>90 dB THD). A $2 DAC is not
expensive if there are enough people buying the 50 pieces
($100), which is enough just for 25 synths. The SAM9773
chip is 31.60 USD /piece in France, I didn't get any
other prices (for bigger quantities). I don't know
if the price includes the VAT (in EU you don't have
to pay extra VAT if it's already paid, or you may pay
it in you own country). If it's impossible to find a
DAC all could get, we could just put the I2S headers
there for interface to separate DAC board (which
could also be a s/p dif transmitter). Then the hard part
seems to be the soldering of the  TQFP package.
The pins are nom. 0.65 mm apart from each other.
Any ideas for solve this problem?

They (Dream) also have evaluation kit for 9773 for
$125. It fits into standard waveblaster connector.
Maybe there wil soon be commercial card based
on this chip with lower price.


-Mikko



-------------------------------------------------

find my comments below
Roman

> The Crystal chip is quite limited, IMHO. It even lacks the portamento
> switch (though there is the mono mode)
	[Roman Sowa]  
	Yeah, it's simple, but nice

> . More interesting chip is
> the Atmel/Dream SAM9773, which implements Roland's GS mode
> with tweakable filter cutoff etc. (you can use pitch bend midi
> messages for less zippery realtime control of Fc). It's also
> got 20-bit I2S output.
	[Roman Sowa]  
	coooolll!

>  It needs the opto + 9.6 MHz crystal
> or oscillator, which I haven't found yet. Could we design
> our own pc-board for that chip, and order some chips
> from Dream? Could this be the first digital synth-diy list
> project synth? 
	[Roman Sowa]  
	Good idea

> We would need a pcb manufacturer (was there an 
> inexpensive place in Poland?),
	[Roman Sowa]  
	Yes, there is.

>  also some DAC's (see below). 
> You can use two DAC's for 4-channel output in SAM9773, so you 
> can route some MIDI channels to front DAC and some other
> to rear DAC. To get most of the 20 bit DNR it would be
> better to design a two-sided pcb, which is diffcult to
> do at home.
	[Roman Sowa]  
	No, it's nooot...
	Think as those PCBs would be already made, and cheap
	(well, by making PCBs at home I mean designing them,
	since they are made by this cheap manufacturer anyway)

>  The chip itself is in TQFP80 package,
	[Roman Sowa]  
	I'm not gonna solder it. Do you? I once did 0.65 lead pitch TSSOP
	and I felt like it was beyond my limmits, but TQFP could be even
0.5mm

>  and 
> CS4334 in 8-pin 150 mil SOIC case (smaller than CS4331).
> CS4340 is in 16 pin 150 mil SOIC case, it may be better
> choice as we don't have to order 300 chips.
	[Roman Sowa]  
	As for DACs, I wouldn't stick to Crystal if they were too expensive
	or hard-to-get-in-small-qty. No need to deny, I like An*l*g D*v*c*s'
chips.
>  
> I'm going to ask the prices for the Dream chip, let's
> hope it's not too much.
> 
> 
> -Mikko
> 
>