Which A/D converter for classical?

[klaukholm]

Originally Posted by Jim Williams

On another front, I just reviewed the JoeCo designs. Those used mid grade AKM converters, not nearly as good as those used in the cheap Alesis HD24XR. The ADC chip they selected does not reach 16 bits of THD quality, very disappointing. The analog opamps are similar to the HD24XR and Radar 96 ADC sections.

I dont get your rant on the JoeCo,
the designer is quite upfront about the ADDA being pretty average.
It is designed to be a rock solid recorder and nothing more.

Pros that get the Joeco for priamry recorder use would most likely be using another front end feeding the digital inputs

[PRH]

Originally Posted by Jim Williams

I found the analog differential opamp from BurrBrown that was used in the EVM to be lacking in transient details and quality. I replaced the analog front end on my EVM. I reset the gain structure for +20dbu = 0 from + 14dbu as I drive it hard with my analog console and mic preamps at +16 dbu.

Jim, are you willing to share a schematic for the modified differential front-end?

Regards, Paul

[Jim Williams]

Originally Posted by klaukholm

I dont get your rant on the JoeCo,
the designer is quite upfront about the ADDA being pretty average.
It is designed to be a rock solid recorder and nothing more.

Pros that get the Joeco for primary recorder use would most likely be using another front end feeding the digital inputs

It's just what I found out about the design and offered my take on it. Why is an opinion a rant around here?

[Jim Williams]

Originally Posted by PRH

Jim, are you willing to share a schematic for the modified differential front-end?
Regards, Paul

Sure, download the PCM4222 pdf data sheets from BurrBrown.
www.ti.com
On page 32 you will see two schematics for the input analog buffer. I used the top schematic as the basis, figure 51.

Change the input 560 ohm resistors to 3.92k ohms. Change the feedback resistors from 270 ohms to 1.21k ohms. Remove the 1nf feedback capacitors. That sets input impedance a bit higher at 3.9k ohms and provides the correct feedback tuning to the LME opamp to set bandwidth at 130 mhz. The stock EVM design sets the input impedance at a very low 560 ohms. Many devices will have trouble driving a load that low which may be why some have sonic complaints. Use a National LME49713MA opamp for U1 and U2. Gain is set for full scale digital 0 at +20 dbu.

Connect a wire from pin 6 of U2, the OPA227UA on the EVM to pin 3 of both left channel LME49713's. Connect a wire from pin 6 of U3, the other OPA227UA to pin 3 of the right channel LME49713 opamps. That provides the 2.5 volt bias to the opamps to center the zero point to 2.5 volts.

[aracu]

Originally Posted by Jim Williams

it's important to seperate the DUT from each other

I assume you mean "devices under test". Well, my interest in the PCM and tests with it were limited to seeing if it could be added to and improve the Sound Devices 744t by bypassing the Sound Devices converters with it.

In this context, first I compared recordings of nylon string guitar. It was
hard to hear the difference between the two different converters.
Then the PCM broke. Texas Instruments sent another free of charge.
For the next tests I used instruments with very high or very low
frequencies. On these tests there was a big, very obvious difference.
The PCM left out a lot of the sound, and the Sound Devices sounded
full and fine as usual.

The tests were limited and there is always a possibility of human error.

[PRH]

Originally Posted by Jim Williams

Sure, download the PCM4222 pdf data sheets from BurrBrown.
www.ti.com
On page 32 you will see two schematics for the input analog buffer. I used the top schematic as the basis, figure 51.

Thanking you, sir!

Jim, a quick follow-on query. You indicated that the bias voltage for the buffered signals is 2.5V. From the EVM datasheet, it suggests that the bias voltage (when the board is jumpered to source Vcc from the on-board 4V regulator) is 1.95V (0.4875 x Vcc). Did you supply a higher Vcc for your build?

Thanks again. This should be a fun project!

Regards, Paul

[Snap]

Thanks so much, Jim. Looking for the parts.

Any suggestions for a good final stereo DAC as well?

[Snap]

The other is a BB EVAL board using the PCM/DSD1792A DAC chipset and National LME49713 transconductance opamps, also direct coupled and biased class A. Super smooth and very revealing. THD is -122 db and noise -129 db, best in class. It's fun listening to old CD's on it, I always hear something new.

Ok, I've found it. Any additional tips on building this one?

[Jim Williams]

Originally Posted by PRH

Thanking you, sir!

Jim, a quick follow-on query. You indicated that the bias voltage for the buffered signals is 2.5V. From the EVM datasheet, it suggests that the bias voltage (when the board is jumpered to source Vcc from the on-board 4V regulator) is 1.95V (0.4875 x Vcc). Did you supply a higher Vcc for your build?

Thanks again. This should be a fun project!

Regards, Paul

Yes, the 4222 is powered via a 3.3 volt regulator so bias will be 1/2 that. The chip can also be run on 5 volts but I run mine at 3.3.

[Jim Williams]

Originally Posted by Snap

Ok, I've found it. Any additional tips on building this one?

Sure, I have the original lab pcb, the new eval pcb's are different with a sub module for the DAC.

The output of the DAC is current output. There is an opamp to convert to voltage. I used the Analog Devices ADA4898-1. That is an extremely low noise opamp with great dynamic specs and a huge open loop gain at 10k hz. There is a 750 ohm feedback resistor, I used a Vishay bulk foil for that critical stage. The feedback cap is a 2200 pf Wima polyprop film. Due to the high output current and low value feedback resistor the CFA (current feedback or transconductance) opamp was not used.

The 2 pole MFB low pass filter was done as designed, except modified for the CFA opamp. I added a 1.21k resistor in series with the inverting input to stablize the LME49713 CFA.

[Snap]

Thanks a bunch!

Sure, I have the original lab pcb, the new eval pcb's are different with a sub module for the DAC.

Not a big issue, isn't it?

[aclarson]

My build seems to have went well, but I'm having a hard time getting it to work with my setup. If anyone could help over at my thread about it, that would be greatly appreciated:

My PCM4222EVM build w/pic. Need some tips...

[matyas]

This thread, interesting as it is, really needs to be separated into multiple threads. All of the stuff about rolling your own converters from eval boards should be put in a separate thread in Geekslutz, where it really belongs.

[Jim Williams]

It's already there, do the search.

[klaukholm]

Originally Posted by matyas

This thread, interesting as it is, really needs to be separated into multiple threads. All of the stuff about rolling your own converters from eval boards should be put in a separate thread in Geekslutz, where it really belongs.

I agree, unless a moderator cleans this thread up it is completely useless.

[Skriabin]

Originally Posted by klaukholm

The design is inhouse at Merging, no DAD involvement.

With that said, one of the DAD designers has given this unit a big thumbs up in my conversations with him.

Remote control from http is brilliant.

The unit is very pricey in a small comfig, but a fully loaded 24IO with micpres is compact and offers a good channel price

We will be getting a unit for a demo as soon as it is available.

So, what did the DAD designers tell you about this new Horus converter/interface from Merging?
And did you already get a unit to demo?

[Plush]

Merging told me that the units will be available next year in the first quarter.

So I am standing by to test the units when they come out. They seem like an excellent and very modern solution.

[klaukholm]

Originally Posted by Plush

Merging told me that the units will be available next year in the first quarter.

So I am standing by to test the units when they come out. They seem like an excellent and very modern solution.

AFAIK the unit is ready to go to production, but they are waiting to release it in conjunction with Pyramix 8, which is the first ravenna enabled release.
Beta testing is likely to commence at the beginning of the new year

[Skriabin]

But will the Horus conversion be of the same quality as the DAD AX24 and EMM Labs?

[klaukholm]

The DA conversion is on paper better than the DAD and the AD is very close.
The AD does not have the gold plated relays the DAD has (cost), but performance is very good.

[Skriabin]

Originally Posted by klaukholm

The DA conversion is on paper better than the DAD and the AD is very close.
The AD does not have the gold plated relays the DAD has (cost), but performance is very good.

So, the AD side should be better on the DAD than on the Horus?
Could the Horus be compared in quality to stand-alone units like Prism Sound, Weiss, Forssell and Lavry Gold?

[David Spearritt]

Originally Posted by Skriabin

Could the Horus be compared in quality to stand-alone units like Prism Sound, Weiss, Forssell and Lavry Gold?

Yes! That's what my mail is telling me.

[Plush]

I am curious to test the new Horus converter because I would like to hear the really modern thinking behind the Claude Cellier product.

Here we still use dCS and the present day Mytek and Nagra converters with VERY good results.

As the folks assembled here know, the dCS never used off the shelf converters (AKM, Cirrus Logic, TI, THAT etc.) and I always thought that that was a design benefit and "feature" that they designed and built their own converters. Now dCS don't make a/d converters any more and the d/a converters they make sell to high end hi-fi freaks for $10,000.

Presently with most makers using chips designed out of house, converter performance is similar on a chip basis. Hopefully not across the board, however, due to the varying design quality (and varying expertise) of the analog stages before and after conversion.

So, getting to grips with a very modern converter helps here to "calibrate" my ear to the latest sound.

Unless that latest sound (from any different company) is mightily different from the UK top range units I'm using now, then there would be little need or requirement to change units.

So that is what my listening test is about.

p.s.--I have yet to encounter any music (including Havergal Brian's Gothic Symphony--done for Naxos by Gunter Appenheimer--Tonstudio van Geest) that has anywhere near the dynamic range of the newly offered converters--last 3 years)

[klaukholm]

Originally Posted by Skriabin

So, the AD side should be better on the DAD than on the Horus?
Could the Horus be compared in quality to stand-alone units like Prism Sound, Weiss, Forssell and Lavry Gold?

You will have to wait until units are provided for real life testing

[Skriabin]

Originally Posted by klaukholm

You will have to wait until units are provided for real life testing

Did you test the Horus interface already?

[Skriabin]

Here it is: the full specs and info brochure of the Merging Horus !!!!

http://www.merging.com/uploads/asset...20-%202012.pdf

[Plush]

Pretty cool stuff for sure. However, I have recently gone to RME Micstasy, Direct Out Technology and RME ADI-8QS conversion along with my older dCS stuff.

The Swiss franc to dollar exchange rate blew it for me with HORUS.

It looks like a very complete system with wonderful specs.

Who will buy one in the USA? I will be curious to watch HORUS.

[sonare]

Originally Posted by Plush

The Swiss franc to dollar exchange rate blew it for me with HORUS.

This is currently 1 SwF = $1.097 Curious what you were hoping for? What is the sticker price on HORUS?

Rich

[Plush]

Hello Rich,

For the system I wanted, I was told it would cost me $15,000 to start out.

No doubt it's a great converter and since I really do like all things Merging, I bet it is fantastic. Broadcasters will take it up as will some government agencies. Some record companies will make the move to HORUS.
Studios will be much slower to buy.

The Swiss Franc is at an all time high. Only through drastic intervention did the Swiss central bank force the Franc back down to its (now still) shockingly high value. The Franc was recently, this winter, over $1.32.

Traditionally the Franc hovered at around .80-.85 cents. At that level, anything Swiss was already very expensive.

So this is just the same as anything European right now. Added expense at a penalty only for the exchange rate. No added value, just empty zeros on your invoice. My recent move for Euro equipment also costs me some air dollars as I call them. Just at a more tolerable and sane level.

I don't usually buy on price, but on good quality. This time around I loaded up on very good conversion, vetted by Deutsche Grammophon. I imagine the Direct Out / RME solution I have crafted is not at the level of HORUS.

However, it IS at the level I require.

It sounds amazing.

[Skriabin]

Originally Posted by sonare

This is currently 1 SwF = $1.097 Curious what you were hoping for? What is the sticker price on HORUS?

Rich

Hi Rich, which converters are you using at the moment?