Upgrading PLL clock in MOTU 1224

Hi guys.

I have a MOTU 1224. The clock is the weakest point - the converters are actually very good for their day: AK5392 ADC's, AK4393 Main DAC.
I don't have a very good understanding of how clock is derived in units like the MOTU - if it is generated by the DAC or by a seperate chip. I found a programmable PLL generator chip on the board (Cypress CY2081) but its data sheet doesn't specify any usage for audio - perhaps it is just being used for the FireWire-like interface? In any case, the CY2081 is an older chip, and has been superceded by what seems to be the superior and possibly pin-compatable CY22381. I am considering swapping this one in.
Could someone explain what this PLL chip is likely being used for, and what my DIY upgrade options might be? Thank you.

You normally use PLL chips if you need to generate more than one frequency- is that the case in this converter?

If you only need a single frequency using a crystal oscillator like I have done on my ADC board (see here: http://stiftsbogtrykkeriet.dk/~mcs/ADCon2_small.jpg) is probably the best way. Unless you want to buy one of the expensive audiophile/phool clocks. They are better, but I don't know how much difference it makes in the real world?

TI makes some PLL clock generators. I have a board designed around the PLL1708 here somewhere, but I haven't assembled it yet... Have a look here: TI PLLs

Best regards,

Mikkel C. Simonsen

Hey mikkel

I have a board designed around the PLL1708 here somewhere, but I haven't assembled it yet...

Click to expand...

Be interesting to peep that if poss For the adc/dac box Im undergoin the PLL1700 seemed to be the one of choice. How are you controlling the PLL? via an AVR chip? I guess u got a flash control brd n all that too eh... :thumb:

[quote author="daArry"]Be interesting to peep that if poss For the adc/dac box Im undergoin the PLL1700 seemed to be the one of choice.[/quote]
I was told to use the PLL1708 instead of the PLL1700, because of the better specs. You can see the schematic here: http://stiftsbogtrykkeriet.dk/~mcs/Clock_sch.gif and the PCB layout (double size!) here: http://stiftsbogtrykkeriet.dk/~mcs/Clock_pcb.gif

I could probably get the board assembled and tested next week, but I can't find a 27MHz crystal anywhere. Can somebody here help?

How are you controlling the PLL? via an AVR chip?

Click to expand...

No, using a 8051 type chip as always... The clock board is for my HDRec project, so the clock will be controlled by the same control panel the operates the recording board and the ADC/DAC etc. I currently use an Atmel AT89S51 chip, but I will run out of code space soon and replace it with an AT89C55. The code I write could be used on any 8051 compatible chip if you don't like Atmels...

I guess u got a flash control brd n all that too eh... :thumb:

Click to expand...

Que?

Best regards,

Mikkel C. Simonsen

This particular PLL chip is capable of generating 3 different clocks at once, and as far as I can tell, all are being used. I'm guessing one is being used for the DAC/ADC's, one is being used for the FireWire-like (AudioWire) interface, and the other for the AES in/out. So it is not so simple as taking out the PLL chip and putting in a single crystal oscillator.
It MIGHT HAVE BEEN as simple as taking out the PLL chip and replacing it with the new version (70% less jitter - that's why I want to change it), but this particular chip is programmable and has been programmed a certain way for the MOTU. In this case it was factory pre-programmed so I can read the numerical programming reference (614), but that is only available when you buy quantities greater than 10,000. My only other option would be to get the new version PLL chip and a programming board ($500). Which is of course ridiculous.

So I think I will change the focus of this project somewhat. How about a high-quality stand-alone clock generator with Wordclock output? My assumption would be that this isn't a very complicated DIY project, though it would be my first digital one. Where the heck do I start?

looks great..again :grin:

ut I can't find a 27MHz crystal anywhere. Can somebody here help?

Click to expand...

Rapid Electronics here in the UK has em...50p each (+vat) I'll be doin an order n/w and will be gettin a few...

Que?

Click to expand...

Its all good. You answered in the prior paragraph.

Your HDRec project seems to be coming together nicely I must say! And the modular format is very handy indeed - Well done :guinness:

dasbin:
Can you confirm the clock problems or is this just a feeling/thought? I have a 1224 myself. You do have choices to use the internal clock or the clock on the PCI-324 if you think that one is better. The easy solution is to pump an external source into the WDCLK input. Here are some ideas:

http://www.diyhifisupply.com/diyhs_cdxo_dac.htm
http://members.chello.nl/~m.heijligers/DAChtml/PLL/PLL1.htm
http://www.anidian.com/audio/pdf/clock.pdf
hth!

Peace![/url]

S of T has a good point, it may be easier to provide clock through the BNC connector, because the problem with modding word clocks internally is that without some really expensive test gear it can be hard to tell if you are making progress or sliding backwards.

[quote author="SonsOfThunder"]dasbin:
Can you confirm the clock problems or is this just a feeling/thought? I have a 1224 myself. You do have choices to use the internal clock or the clock on the PCI-324 if you think that one is better. The easy solution is to pump an external source into the WDCLK input. Here are some ideas:

http://www.diyhifisupply.com/diyhs_cdxo_dac.htm
http://members.chello.nl/~m.heijligers/DAChtml/PLL/PLL1.htm
http://www.anidian.com/audio/pdf/clock.pdf
hth!

Peace![/url][/quote]

Others have said that MOTU clocks are generally poor. Judging by the PLL chip specs, I'd say they're probably right. Additionally, I've heard some samples of a 1224 clocked internally vs. clocked by a Big Ben... no comparison... having a good external clock puts the MOTU up there with the big boys.
Thanks for the links BTW. I'll check them out and maybe build something.

Next upgrade: DAC and ADC chips. There's a pin-for-pin replacement for the DAC, should be incredibly easy. Also, the current ADK flagship ADC is "semi-pin compatable" with the ones in the 1224... with a bit of research and a few modifications, this thing will compete with an Apogee

Big Bens are expensive, but by all accounts awesome. Has anyone tried the Lucid Technology word clock generators? They don't have the features of the Apogee, but are more within my price range. Currently I clock my 2408 II via BNC from my 02R, but I don't know what the clock in the console is like, except that I haven't noticed any problem with imaging etc. It can be hard to tell subtle issues unless you have a reference to compare to.

[quote author="SonsOfThunder"]dasbin:You do have choices to use the internal clock or the clock on the PCI-324 if you think that one is better. [/quote]


FYI, I just checked the PCI-324, and it uses the exact same clock (CY2081 SC-614) as the 1224, except it only uses 1 of the clock pin outputs as opposed to all 3 on the 1224.

[quote author="dasbin"]Next upgrade: DAC and ADC chips. There's a pin-for-pin replacement for the DAC, should be incredibly easy. Also, the current ADK flagship ADC is "semi-pin compatable" with the ones in the 1224... with a bit of research and a few modifications, this thing will compete with an Apogee [/quote]

I have a 1224 as well and a 24i. Let me know if you do the DAC/ADC convertor upgrade. That sounds like fun!

I'm looking for an external clock as well. Got my sites set on an Aardsync.

I also think I'm going to upgrade the opamps on the main DAC. They're some really cheap JRC's. Should also be an easy switch. I'll let you guys know what I do.

Thank you! Looking forward to it!

ouaaww! this forum is great!
Well, here's my question : I can't find 27Mhz at the local shop here too, so I try with a 26.985Mhz... and it doesn't oscillate! I tried with a 12Mhz and a 24Mhz and the same problem (oscillation on only one pin of the xtal, and at 666Khz). So this is because I didn't use a 27Mhz???
Oups! it's for a pll1700 chip (maybe I should use the pll1708...)

It sounds like a different problem. The PLL chip can't read what frequency is written on the xtal :green:

You either have some other problem in the circuit, or the crystal could be the wrong type. There are series resonant and parallel resonant crystals as well as overtone crystals...

Best regards,

Mikkel C. Simonsen

[quote author="daArry"]Rapid Electronics here in the UK has em...50p each (+vat) I'll be doin an order n/w and will be gettin a few...[/quote]
Please order a couple of them for me also - I guess they are standard HC18 (or whatever) crystals and not a strange SMD type?

Best regards,

Mikkel C. Simonsen

I guess they are standard HC18 (or whatever) crystals

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Indeed they are... :thumb:

thank you mcs to not joke with the 666Khz (smash and daarry told me to bring it to the local church... I don't think this is the solution! lol)

Well, I know that the pll don't read the value... I'll try more now, but maybe I use to small caps (10pF), let's try with 33pf.

[quote author="pilo"]I'll try more now, but maybe I use to small caps (10pF), let's try with 33pf.[/quote]
I normally use 27pF. 10pF may be too small. Check the datasheet of the crystal (it you can find it) for the recommended value.

Best regards,

Mikkel C. Simonsen