Digital preamp designs?

i am sure you lot have seen this a thousand times, but i was wondering if anyone has some links to wesites for hi-fi preamps with digital control front end.

I was after projects/products etc, anything so i cn build up some ideas. i have spent hours going round on blind links and circles.

I know u guys are helpful and resourceful. Also, i know there was a chat about redesigning the site, and i was wondering if any 1 is in favour of a digital thead. it could include DACS, CD/DVD stuff, DSPs, digital controlled amps/preamps, class D, etc etc (hopefully WITHOUT purists saying that anything digital is crap)

TA TA
 
Helix said:
i am sure you lot have seen this a thousand times, but i was wondering if anyone has some links to wesites for hi-fi preamps with digital control front end.

I was after projects/products etc, anything so i cn build up some ideas. i have spent hours going round on blind links and circles.

There are several commercial preamps that have serial connections (RS-232), so that a computer can control them. You can also find preamps with LOTS of digital inputs. Finally, there are preamps that convert all analog audio to digital. Which of the above are you looking for (or is it something else)?

I know u guys are helpful and resourceful. Also, i know there was a chat about redesigning the site, and i was wondering if any 1 is in favour of a digital thead. it could include DACS, CD/DVD stuff, DSPs, digital controlled amps/preamps, class D, etc etc
The suggestion has already been made. Please check out 'http://www.diyaudio.com/forums/showthread.php?threadid=495'. If you have other suggestions, that's a good place to put them.
 
Really need to bump this up...

I spent last weekend playing with a new mix desk (Klotz) connected to a digital database of music (thousands of tracks). Way too cool. I really want to build something like this for my house, but I realize that it quickly becomes a computer too. Which is what these mix desks are - a computer connected to a SAN and a router.

I just want one for home. For a price that an actual human can afford.
 
i'm all for a digital thread!

Although my website is currently frozen, I have a number of digital projects in the works, one of which is a multi-channel preamp with digital volume control and input selection. Now, exactly how I'm going to do the volume control I don't know yet, but the CS3310 is a strong candidate *if* i can be convinced that it's as good as a discrete stepped attenuator...
 
By far the best method is by using a 32 bit DSP; this way you can effect volume by multiplying each incoming sample by a fractional value number or using a shifter to multiply or divide the sample by a power of 2. Somewhat exotic, for DIY'ers I'm afraid...

Gordon

PS; the CS3310 is a very acceptable alternative as well...
 
Haldor,

I must admit that I haven't seen this particular project, I don't check all the audio or DIY websites you know. It sounds to me though as a very ambitious project. What I meant with "an exotic project" was that I expect that only very few DIYers have the knowledge to succesfully complete such a project. It requires a lot of digital system design and programming knowhow, and yes, some financial resources too.

To get back to the original question of designing a digital frontend, I have to admit that I'm definitly in favor of that. Digital frontends provide a flexibility that only the most eleborate analog frontends can offer and, when executed with great care, should be able to sonically top everything. However, in my view there is no such thing as a separate digital frontend. I would like to use the immense computational power of the present generation of DSP's to filter (upsample) the datastream, provide volumecontrol and if wanted tone control. Followed by a conversion to the analog domain with the very best converters, this type of machine would be a upsampler/frontend/D-A converter all roled into one. So far, i haven't seen any of this in a commercial offering, which is not surprising of course; the big names in high end sell all of these things as separates. So basically, this is my view on all of this, knowing that it's far off into the future ...

Gordon
 
One problem that we have to fight

will be the content producers - read record companies. And we are not even in the game yet.

I want, no need, to be able to get to those bits without any other junk thrown in. There should be no reason that I can't use the straight rip of the song, store it in my computer based system, then play it out as I like. I don't want to transcode it - it leaves digital artifacts in the sound. No D to A back to D. We are going to have a fight - they want us not to have straight access to those bits. The Satellite Radio companies basically had to swear to never give anyone digital outputs to the radios - only analog. So you say, re-sample them. Nope. These signals have been compressed to within an inch of their lives before they were broadcast - very agressive codecs. You do another encode and it is unusable in our world - it simply sounds like crap - too much information has been lost and too many artifacts have been created. The record companies want us to get one play, and only one play.

What if we want to build digital speakers that use inboard DAC's/amps to build just the right signal for each driver? It will not be able to play the new radios, both sat. based or the new ground based Digital Radio, IBOC.

The problem is that the record companies are so afraid of people ripping them off, they have gone stupid. I know that in one case, they forced a broadcast system to actually buy a plastic CD for every song going in their database, even though they were buying them pre-ripped from another company. They just did not want to store the 20,000 CD's (yep, that is a correct number - its a big database - more than 25terabytes spinning on harddisks). They were willing to pay a fee, even more than they would by buying them. Nope, the record companies insisted that they buy and hold each and every CD - and you cannot imagine the hassle they had to go through to be able to prove that they never stored more than ONE copy of the song anywhere in the system, and that NO ONE would have the ability to burn a CD in the system.

Now they are throwing in digital junk to try to stop copying. It is useless - the pirates can beat it easily and the semi-computer literate will be able to too. And we need to fight it, as music lovers. We know that it can be heard, perhaps not on your boombox, but in our systems, where we up the sample, play with the bits and then play it with good equipment, you can hear this junk. Some classical music will be unlistenable - instuments that have a natural high freq. ring are nightmares for digital. Encode decode twice and the artifacts are at higher levels than the orginal signal. It might not matter to the mass market, who thinks a MP3 from Napster is OK. It matters to me. I think it matters to the people who would read this - music is what got us this addiction. We have to make our voice heard or we won't have digital based music we can stand to listen to.

[RANT MODE OFF]
 
Gekko:

If you want the digital processing you just described (upsampling + volume control), you can just use the standard digital audio chips. AD1896 will give you superb upsampling to 24/96 (with the side benefit of excellent jitter rejection), and the DF1704 includes digital attenuation. However, there is a caveat: too much digital attenuation, and you start losing data resolution, and hence all the benefit of doing it in the digital domain. One way of acheiving excellent volume control is to use the DF1704 to do attenuation in 0.5 dB increments down to -5.5 dB, then use an R-2R stepped attenuator with relay control, which gives 6dB steps. This hybrid volume control gives precise 0.5dB steps without ever going below 23 bits resolution... Now, to control these chips along with the relays, you just use a PIC or Atmel microcontroller (which is cheaper and easier than you may think)...
 
[RANT CONTINUED]

...here's my 2 bits:

SACD is evil. yep. Why you ask? ...because the DSD format removes (or severly curtails) any ability i previously had to digitally process the music. You see, digital signal processing likes to handle data in the PCM format... real numbers you can play with. But DSD is just a mash of 1-bit noise, and a good deal of DSP has to take place to extract useable data from that bitstream... so add more digital manipulations and some decent resolution loss if you want to do something digitally with this stuff.

Now here's something even funnier: SACD can dramatically reduce the cost of a CD player by moving all the digital filtering and delta-sigma modulation (normally done by chips inside your cd player) into the studio. So now, your CD player just has to spit out the bitstream to a very simple DAC chip. Say goodbye to audible differences between different DAC chips and digital filters, and say hello to higher-priced equipment. Of course, the manufacturers will say that the higher price is justified by the higher quality of output, but I know that the chipset will actually costs much less than a conventional CD player... (at least if SACD ever becomes the new standard).

This is just one example of a disturbing trend I have noticed where big companies are pulling the wool over consumer's eyes and selling less for more under the veil of "high tech". As we move into the age of sophisticated electronics, new products are consistently moving farther and farther beyond the comprehension of the consumer (and, notably, court judges...), and so it is increasingly easy for corporations to pull this kind of stunt whereby the consumer only sees the end result, and can be heavily influenced by marketing propoganda.

Thanks for tuning in.

[Edited by hifiZen on 09-10-2001 at 11:26 PM]
 
WOOOW - ok let me play historian!
Back when I suggested this the digital pots were a bit poor for precision audio work. We were experimenting with relay attenuators. Then the PGA2310 came out which was designed for good audio use. There were a bunch of project here using it, including one I made myself.

A guy called Dale, with the name of harvardian here made a kit or a 'volume purchase' project for people to buy in. It was all modular and open source with boards to fit together either a PGA or relay controlled pre-amp. It had the name of Apox and was really inspiring to me at the time:

Remote relay volume control kit.

Sadly the website is gone now....
 
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