Upgrading PLL clock in MOTU 1224

[SonsOfThunder]

Others have said that MOTU clocks are generally poor. Judging by the PLL chip specs, I'd say they're probably right.

To that...I have to say,"whatever".

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.

To this I would say, "Now yer talking and I'm interested!"

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.

I think they are NJM4560 or NJM4580, which aren't so bad IMO. When I got mine, I sniffed the voltages and they were all HIGH and the supplies are basically running free with no regulation. That could be a good easy mod.

Thanks Roger for that info on the Lucid clock. I suppose we'll all be on eBay looking for one of those now! Unless we DIY!!! This sounds like a good easy project and there are plenty of clock schemos for CD players out there that could be modified to suit.

diydiydiydiydiy!
Charlie

 

[Tekay]

Didn't know that the internal clock is that bad?
According to Dave at Motu the internal crystal accuracy is 30ppm on all their units! maybe this only applay on newer units, but the 1224 is on the data list I got!
Old Digidesign 888 is 44ppm, Apogee Rosetta is 22ppm!

 

[dasbin]

Maybe the JRC's aren't so bad, but they're not as good as the OPA 2134's, which I just bought 8 of. Going to replace the Main Out and Headphone Out stages with them.

Regarding the converters, it's not as easy as I thought to drop in the newer replacements. "Pin-compatable" doesn't mean a drop-in upgrade, apparently. So I'm not going to touch them.


So now, I have two questions, both of which demonstrate my utmost newbie-ness to the DIY scene:

1) How do I go about regulating the power supplies?

2) How do I go about modifying a clock meant for a CD player to work? I've checked some of them out, the L-Clock and the Tent XO Clock seem the most promising, but they both seem to be meant to connect directly to the DAC and only provide a single frequency. No idea how to change this. I'd love to give one of them a BNC Wordclock output.

 

[dasbin]

[quote author="Tekay"]Didn't know that the internal clock is that bad?
According to Dave at Motu the internal crystal accuracy is 30ppm on all their units! maybe this only applay on newer units, but the 1224 is on the data list I got!
Old Digidesign 888 is 44ppm, Apogee Rosetta is 22ppm![/quote]

I could be wrong seeing how I know so very little about this, but I don't think the crystal is everything. The PLL chip has a lot to do with it, and even the new version of the super-cheap one that's in there claims 70% less period jitter and 30% less long-term jitter.

I also know that MOTU's are bashed over at Gearslutz.com for their poor clocks. And I also know what I heard with my own ears - with a better external clock, the 1224 sound is improved TENFOLD.

 

[SonsOfThunder]

I don't think the crystal is everything.

I'd agree.

The PLL chip has a lot to do with it

Maybe...but I think I remember there being some other things associated with the clocks output drive and the layout being persnickety. This was where I got my feet wet on DIY (well at least modifying) was CD players and DACs, but its been a while since I've looked at some of the info on clocks.

they're not as good as the OPA 2134

A fellow BB fan! Alright! Those are my fav. I also have a stash of 4134 DIPs :thumb: I can only imagine that you'd also see improvement if you changed the OAs in the I/V convertor on the output of the ADC, but IMO you need something faster...my fav for that is the AD746 but its a tricky beast.

"Pin-compatable" doesn't mean a drop-in upgrade

What are the old/new part numbers again? I can't remember now.

How do I go about regulating the power supplies?

There are a number of ways to do this but basically, you have to find out where the main feed for the OAs is, interrupt that line, and shove in a regulator. Repeat this process for all supply voltages. Do you have yours open right now to measure some voltages? Check the power pins on all the OAs and on the other devices if you wish and let us know what those were again. Is there bypassing at each OA or at least spread around on the PCB? It seems to me, there was not.

How do I go about modifying a clock meant for a CD player to work?

If you only want 44.1, you don't need to mod anything! If you want to add 48k, I'd probably setup seperate oscillators for each, though you could switch some of the components on the PLL to get it to do that. Does anyone here want to open up their Aardsync or Lucid and tell us how they do it? Maybe if you'd like to pursue a DIY clock we'd want to know which devices they use to give us a good starting point on the silicon? Or maybe open a BigBen and peep that!

This is starting to sound like fun!
Charlie

 

[dasbin]

I can only imagine that you'd also see improvement if you changed the OAs in the I/V convertor on the output of the ADC, but IMO you need something faster...my fav for that is the AD746 but its a tricky beast.

For the moment I don't want to touch the ADC OA's. I'm a newbie to ALL of this... this is my first major project... and there are three of those per ADC, and they are TINY as hell. I would surely screw something up. I'm gonna have enough problems soldering in new OA's for the DAC, and they're about 5 times the size. Perhaps in the future.

What are the old/new part numbers again? I can't remember now.

Old: AK4393 DAC, AK5392 ADC
New: AK4395 DAC, AK5394A ADC

There are a number of ways to do this but basically, you have to find out where the main feed for the OAs is, interrupt that line, and shove in a regulator. Repeat this process for all supply voltages. Do you have yours open right now to measure some voltages? Check the power pins on all the OAs and on the other devices if you wish and let us know what those were again. Is there bypassing at each OA or at least spread around on the PCB? It seems to me, there was not.

First, what is a regulator (sorry for my dumbness)? I will pull out the multimeter and attempt to check voltages shortly. Secondly, what do you mean by "is there bypassing?" I'm new!

If you only want 44.1, you don't need to mod anything! If you want to add 48k, I'd probably setup seperate oscillators for each, though you could switch some of the components on the PLL to get it to do that. Does anyone here want to open up their Aardsync or Lucid and tell us how they do it? Maybe if you'd like to pursue a DIY clock we'd want to know which devices they use to give us a good starting point on the silicon? Or maybe open a BigBen and peep that!

OK, let's assume for the moment that I'm content with only a single frequency: 48K. First of all, I'm not looking to DIY an external clock here. I'm looking mod an existing one, that I can buy for a reasonable price, to feed the MOTU. I guess my main question would be, how do I get it communicating with the MOTU as a whole, and not just straight into the DAC/ADC clock inputs? A plug-in to the BNC Wordclock connection would be ideal.

Thanks a ton for your help. As I said, I'll be checking the voltages shortly, and the opamps are on their way. This is turning into a whole 1224 overhaul I agree, it's fun.

 

[dasbin]

For some reason my multimeter is refusing to read DC voltages. I'll have to buy a new one before I can test them.

 

[SonsOfThunder]

I can only imagine that you'd also see improvement if you changed the OAs in the I/V convertor on the output of the ADC

How careless of me...I meant to type DAC here. Sorry! I'll take a look at those data sheets for the DAC and ADC and do some research on the clock thing.

Peace!
Charlie

 

[dasbin]

Ah, now that makes sense... The opamps on the I/V converter are the same JRC's (4580D) although for some reason they have a different configuration number (9012G vs 9015G on the output stage). I ordered enough of the OPA 2134 that I planned to just change them all. Is this a bad idea? They're still significantly faster than the JRC's, which have a slew rate of only 5.

 

[dasbin]

Just got a shiny new multimeter... the opamps are currently receiving a pretty steady 35 volts differential (17 each side). This is quite a bit too high, right?

 

[SonsOfThunder]

the opamps are currently receiving a pretty steady 35 volts differential (17 each side). This is quite a bit too high, right?

No the max is +/-18V so its just below. The thing that I remember is that the voltage of the zener diode in the ckt is higher than this, making it a clamp and not a regulator...dangerous, IMO. Need to take a look at those rail voltages with a scope to "see what we can see."

The opamps on the I/V converter are the same JRC's (4580D) although for some reason they have a different configuration number (9012G vs 9015G on the output stage).

That would be the manuf date code...probably the 12th and 15th weeks of 1990...that's just a guess as to the date.

OPA 2134... They're still significantly faster than the JRC's, which have a slew rate of only 5.

Ya, the 2134 has a slew of about 25, which should give a noticeable improvement. But I think I hear a diff with the OP746...which has a slew of 75! But its not compensated for gains less than 2, which means you gotta play with the feedback a bit to keep it from making funky noises! I've got those in my old modded X-DAC (that originally had NJM5532DD in it) and I think it sounds much "clearer" with the AD746...perhaps it would have been better with Signetics 5532, but I was too too happy with the AD746 to even try.

Keep us posted and I'll dig on those AD/DA spec sheets too!

Peace!
Charlie

 

[dasbin]

I'm trying to get Digi-key to cancel my order of 8 2134's, and just get 2 for the output stage and ignore headphone out (too much trouble), so I can get something better for I/V.

The ones that have me interested are OPA627 (good reports), AD825 (good reports, "detailed" sound probably good for studio), and LM6172 (slew rate of 3000!).

Problems:
- OPA627 is far too expensive, ruling it out immediately.
- AD825 is a single opamp ONLY, so I need 2 each plus DIP adapter
- LM6172, don't know much about... might be taking a risk by trying a drop-in replacement with it

What would you recommend? I just want to drop something in, not fiddle around trying to get it to stop oscillating or fix other problems.

Also I am curious to know why there appears to be a total of 4 dual opamps for the main stereo output I/V, plus 2 more for output stage, plus 2 more for headphone out. I thought that I/V needed only 1 per channel.

 

[SonsOfThunder]

If you don't know how to work the scope and stop oscillation, don't cancel the order for the 2134. As I said

the 2134 has a slew of about 25, which should give a noticeable improvement.

2134 should work well with no other mods. YMMV! I haven't tried it in this box so I cannot "guarantee" it will work.

why there appears to be a total of 4 dual opamps for the main stereo output I/V, plus 2 more for output stage, plus 2 more for headphone out.

It should go like this...DAC chip -> I/V -> Anti-aliasing Filter (Lowpass) -> Output driver. Balanced out obviously takes two OAs per channel. AA Filter is usually 2 OAs by itself...Not sure why there are two OAs for the HP driver...is this two per channel? Perhaps they are running in parallel for more current? Now I gotta drag mine outta the rack and open it!

Eeek!

 

[dasbin]

[quote author="SonsOfThunder"]Perhaps they are running in parallel for more current? Now I gotta drag mine outta the rack and open it!
Eeek![/quote]


I have a feeling that once you find out, you are going to expose my ignorance completely
I have to admit this is really my first serious DIY project and I am picking up terminology, components and circuit functions along the way.. I'm learning fast but I'm still mostly BS'ing my way through it. :wink:


Thanks for the advice, I guess I will just get all 2134's then.
Still interested in learning how to mod a clock to hook up to the 1224.

I have to admit that you, SonsOfThunder, are sort of acting as my 'mentor' here, and for that I am eternally grateful. Obviously, you can stop helping at any point and I won't mind.

Rest assured to the whole community that I will provide any mod results in detail. I think I'm going to do "before and after" loopback recordings as well, so people can listen for themselves.

Thanks again.

 

[aio9]

It's been a while, but I'd like to know the result for this project. Dasbin, can you provide us with some info regarding the result.

Thanks

 

[dasbin]

OK. I managed to obtain a programmed version of the new PLL chip from Cypress, but the MOTU simply wouldn't initialize when it was installed so I had to abandon that idea and put the old one back in.
I've also managed to ruin the Main Outs, I think. I can't find the problem but both the outputs just make this "buzzing" noise no matter what opamps are installed (I put in DIP sockets). I've all but given up on them to tell the truth. Months of frustration! Just too many SMD components on there for me to be likely to find and fix the problem.
I upgraded one of the other output opamps to a AD825 and it actually works. Can't tell a difference in sound though.
I also was brave and upgraded inputs 1&2 to use AD823 opamps, and I think they actually sound better. This is my one real achievement, hah. Don't think it was worth all this trouble though...
Ah well, live and learn.

 

[tony dB]

[quote author="Steve Jones"]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]


Hi Steve,

I have tested, listened and finally bought the Lucid genX. It IS a huge improvement to any DAW, even PT sounded nicer and wider when we clocked it from the Lucid. Compared to Apogee i found the Apogee having a little more low end. Having always enough low in my mixes i went for the Lucid who seemed to have a little nicer topend.

If possible you should try to have them all at your place and compare. btw when i bought the Lucid, the Apogee was 2X the price of the Lucid ... :grin:

Tony.

 

[smilinfu]

Thanks for being brave enought to try! :guinness: :guinness:

 

[Tekay]

Thanx for the tip Tony!

I'm using a Motu2408MK3 now and will soon add a 24 I/O for more putputs so I guess a Lucid GenX 6 will improve my sound too? 1/3 of the price of a Appogee Big Ben!

 

[dasbin]

I forgot to mention that I also got a Genx6... but to tell the truth I can't hear a difference at all I even did some loopback A/B recordings with the internal and Lucid clock as masters, still couldn't hear a difference. I phase-nulled the waveforms and the differences are about 70db down.

Frankly I think the external-clock-improves-any-DAW-quality claim exists mainly in the psychological realm.