[aos]

Thomas, you can always design a PCB and have one of those express stores make it for you. You can expect to need one revision before you finalize it. It is not that expensive but "expensive" is relative.

I have a question, do R2R chips need separate digital filters? You would need to use latest BB chips since PCM63 is now obsolete, plus it is huge and does need filter from what I've seen. Of course, my preferred configuration - which would be CS8414 + CS4390 + AD823 + EL2001 is also quite, quite obsolete even though I do have enough parts to make it.

 

[thomas]

yep i was thinking of surfboards or the Soic- dip converters, but i was worried that they would add parasitic effects that would compromise performance? I guess i should give it a try....

I guess the prices at the PCB manufacteres are very resonable for what you get, but it is quite expensive for a DIY project. I was thinking of getting a simple etching tank and use it with copper boards and resist pens, would it be worth the effort/cost for what i'm doing?

aos-

traditionally, R2R chips have been used with external digital fiters (usually oversampling filters) before the dac and analog filters after it. But the latest audiophile trend seems to be removing all filtering and oversampling, and just use reciever-->DAC--> I-V--> output stage. The theory behind it is that you're ears act as a strong low pass filter, so it really doesn't matter if there's tons of noise at 25khz +, since you can't hear it. And removing the filters will remove any artifacts/distortion/jitter they produce in audiable frequencies. I think layout becomes even more important with these designs, as that noise could cause lots of problems in the analog stages if its not designed properly.

Rick told me that there will be tons of out-of band noise and crap if you look under the a scope, but it will sound amazing...

 

[Joobu]

If you use surfboards without the SIP pins, they're just the SOIC pattern with several other pads for other components. If you use surface mount components (caps, resistors) there's actually less parasitics. You can even put all the surfboards on a copper ground plane.

 

[aos]

Ok, so what's the current R2R Burr-Brown DAC?

 

[thomas]

BB has a few out right now, their best are the 20 bit PCM1702 (available in DIP) or the 24 bit 1704 (SOIC only). They actually use 2 DACs per channel to eliminate the LSB glitch, like the PCM63.

I think the 1704 would be great with your 96/24 DAD, or possibly with an interpolation filter?

There's also the PCM56 (and the parallel input 54 +55) which is much cheaper than these DACs.


BTW, although digikey is out of stock of the 63's, the do list an estimated arrival time (october-november)... if its true, then it'll probably the last chance to pick them up...

 

[aos]

Thanks thomas, I'll try to add 1704 these to an order I did on Friday (not to Digikey, to some place cheaper). I'll get some lower grade for experimenting and higher grade for final.

Interestingly enough, PCM1704 accepts only 24 or 20 bit words. It won't accept 16 bits. So I guess zeros must be passed for the lower 8 LSBit's, and I'm not sure if receivers will do this...

 

[eric343]

Have you guys tried ordering the out-of-stock chips as engineering samples? When I was *desperately* in need of an opamp for one of my Cmoys TI was kind enough to send me one, a few months before Digi-Key got them instock. Standard warnings about not overusing the "free sample" service apply.

By the way, how do you guys solder SMD stuff? My soldering iron is *way* too big...