Meridian Unplugged - Powered by MrTechGuy.co.uk Forums Discussion Meridian - Systems Which DACs are used on the Meridian 861?

Sorry if this was already asked but I couldn't find the information anywhere.

I would like to know who is the manufacturer of the chip? I believe it's a bitstream DAC right?

I believe my 568.2 had Crystal DACs so my *guess* would be Crystal. Also keep in mind that circuits around the DACs (as well as processing) are just as important as the DAC itself. The OA13 DAC card is a killer.

Keep in mind that 861 has several DAC boards.

See the Price List over on the wiki for the different DAC boards. There are also older ones not listed.

http://meridianunplugged.com/wiki/index.php/Price%20Lists

Crystal? I see...so it seems it is indeed a bitstream DAC alright. I was curious because of the alleged superiority of the multi-bit DAC over the bitstream ones, but sadly (or not) this is the path followed by the vast majority of manufacturers including even on the high end.

I know it`s true what you said, in fact a wonderful DAC by itself won`t make a wonderful sound, but I also believe that having the best components all together can never be considered a disadvantage. It would be interesting to know if Meridian did change the DAC from the OA12 to OA13 for instance.

I read a very interesting paper although very technical and in the final conclusions the author wrote: "… The multi-bit converter is the most
straightforward method but carries a penalty of accuracy which implies higher cost."
Now the question here to me is what 'straightforward' means under this context. Is it better or just simpler to implement regardless of cost?

This is the paper I found:
http://www.essex.ac.uk/ese/research/audio_lab/malcolmspubdocs/C58%20Techniques%20in%20DAC.pdf

The 568.2 has Analog Device AD1852 DAC's. They are 24 bit DAC's.

That's what JK's review said in Widescreen review.

Ron

c'mon gents, someone open up their 861 and take a gander!

mine's stuffed in a rack, so that's a PITA to do...

doody.

Ron,

The reviews I've seen say Delta-Sigma DACs. The data sheet on the AD1852 also says Delta-Sigma.

WikiPedia says Delta-Sigma are 1-bit dacs.

What does a MultiBit or 24Bit Delta-Sigma (or Sigma-Delta) mean? Is it two stages of conversion?

Seems like Delta-Sigma (or Sigma-Delta) and MultiBit is an oximoron.

Hi Guys,

Really long post, but there's a lot of info. Sorry.

A multibit converter is the simplest to explain, and the simplest to draw, but pretty much the hardest to make. Each bit in binary is worth twice the one below it. A multibit converter is often made of an R-2R ladder, so every bit gets through a resistance proportional to its value. This gives you a current or voltage proportional to the whole lot. The problem is that you have to make a buffer and resistor accurate to 0.5 * the top bit / 16,777,216 for each of the 24 bits to get 0.5 LSB accuracy. Transistors are easy in silicon, resistors are hard. Even if you achieved it, you'd have to then achieve it across temperature.

Any inaccuracy in the resistors and buffers leads to that bit having the wrong value, which can lead to a non-monotonic DAC (a bigger number should always lead to a bigger output, but for some values it's smaller). Really bad.

A Delta-Sigma uses a multibit DAC, but run at a higher speed to get the effect of a slower but more precise DAC. I used a Burr-Brown with a 4 bit multibit DAC ran to emulate 24 bits. Imagine a 2 bit DAC running this sequence:

3, 3, 2, 3

If you analogue filter it to slow it down you end up with a value somewhere just above 2.75, which the original DAC couldn't have achieved.

Take that to extremes and you could have a 1 bit DAC running many times faster. This is bitstream or DSD.

I'd argue that there are really two categories - full multibit, then Delta-Sigma (which includes 1 bit/bitstream/dsd as a special case) as well as more standard multibit/DS implementations.

Cheers,
Mark.

Some more information I found concerning Sigma delta modulation:

"When sigma delta modulation is used for audio signal processing, limit cycles in the output may result in idle tones that are audible to the listener. We show that a multibit implementation of a modified first order sigmadelta modulator may produce an effective, stable chaotic modulator that accurately encodes the input and prevents idle tones."

Full article here:
http://www.elec.qmul.ac.uk/people/j...-Multibitchaoticsigmadeltamodulation.pdf

I think the difference between 1 bit or multi-bit sigma-delta is explained by this paragraph:

"A multibit implementation may offer increased resolution in the quantization. For an n bit first order modulator, the quantized output can assume one of m=2n states."

P.S. sorry if I forgot to thank you Mark.

No need Cochinada, and thanks for the links to the articles - very interesting (But I'll be first to admit to skipping the maths!).

I think it is a Analog Devices DAC on a OAx2 and a OAx3

One thing seems almost certain: it's a bitstream DAC.

568.2 / 861v4 / G68 / DSP5200 all use the Analog Devices AD1852.

From a manufacturing perspective they appear to have standardized on one DAC across their product line. Benefits are twofold.

First, you get economy of scale from a purchasing perspective -- you buy more units at a time and your per unit price is lower. Second on the manufacturing end the use of one DAC part removes the potential for a manufacturing error. Whether they are building 861 D/A cards, G68s or DSP loudspeakers they all use the same DAC. No chance for error. With multiple DAC parts in use it would be relatively easy to make a mistake by putting the wrong DAC into the production line.

Cheers,