high pitch frequency on motu 896mk3 hybrid inputs

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Discussion related to installation, configuration and use of MOTU hardware such as MIDI interfaces, audio interfaces, etc. for Mac OSX
Klaus
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Re: high pitch frequency on motu 896mk3 hybrid inputs

Post by Klaus »

Yeah, they have confirmed the issue...
Let us know...

Best

Klaus
maaaquemeseyo
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Re: high pitch frequency on motu 896mk3 hybrid inputs

Post by maaaquemeseyo »

We’ve send ours to the dealer. You can even hear the high pitch tone physically in the unit if you approximate your ear to the 896.
The tone is in stand alone mode, usb mode and firewire and I’ve checked with Bruel 4006 and Sm 58. Long and short cable throws, mogami.
Just waiting. :boohoo:
Klaus
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Re: high pitch frequency on motu 896mk3 hybrid inputs

Post by Klaus »

maaaquemeseyo wrote:We’ve send ours to the dealer. You can even hear the high pitch tone physically in the unit if you approximate your ear to the 896.
The tone is in stand alone mode, usb mode and firewire and I’ve checked with Bruel 4006 and Sm 58. Long and short cable throws, mogami.
Just waiting. :boohoo:
Thanks :D

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Klaus
Spencil_Splodge
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Re: high pitch frequency on motu 896mk3 hybrid inputs

Post by Spencil_Splodge »

It has been suggested that only a few people have actually 'reported' the issue to Motu - I would suggest, if you haven't already done so, that you raise a TechLink with Motu directly (i.e. report the issue) to ensure the number of people experiencing the issue is representative! This might help their developers focus their efforts...

Thanks,

Spence.
Spencil_Splodge
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Re: high pitch frequency on motu 896mk3 hybrid inputs

Post by Spencil_Splodge »

Also, I have started another thread in the Windows section...

http://www.motunation.com/forum/viewtop ... 14&t=49160

...as this is not OS specific (I am using Windows myself) and I want to increase awareness and get people reporting the issue to Motu.
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wylie1
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Re: high pitch frequency on motu 896mk3 hybrid inputs

Post by wylie1 »

Just thought I'd post to see how this gets resolved.
I was looking at picking one of these up but I think I'll hold off a bit.
MacPro 3.2 ghz 8 core 12gig,DigimaxFS, 2408mk3,8Pre,828mk3,Ozone5,MachFive3, BFD2, Sampletank2,DP8.+,Sampletron,Nectar,Central Station,D5s,Q10s.plus stuff.
Spencil_Splodge
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Re: high pitch frequency on motu 896mk3 hybrid inputs

Post by Spencil_Splodge »

Can't blame you!

I'm still working with Motu tech support to get an answer, and they in turn are waiting upon the developers to a) find the cause and b) come up with a solution.

Thanks for the post, I'll point out that this issue is stalling sales - might up the priority further ;-)

Spence.
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wylie1
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Re: high pitch frequency on motu 896mk3 hybrid inputs

Post by wylie1 »

Looks like as great unit plus all the new Cuemix stuff.
Let us know what happens.
MacPro 3.2 ghz 8 core 12gig,DigimaxFS, 2408mk3,8Pre,828mk3,Ozone5,MachFive3, BFD2, Sampletank2,DP8.+,Sampletron,Nectar,Central Station,D5s,Q10s.plus stuff.
Spencil_Splodge
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Re: high pitch frequency on motu 896mk3 hybrid inputs

Post by Spencil_Splodge »

It *is* an amazing unit - very impressed, generally!

But, this issue is a show-stopper for me as it ruins live and recorded material at modest gain settings (the required gain for a dynamic mic). Without this issue, the preamps in my opinion are actually pretty good.

Spence.
midnight_engineer
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Re: high pitch frequency on motu 896mk3 hybrid inputs

Post by midnight_engineer »

Okay... I agree with original poster. Without any input, at max gain, I get broadband noise. Hook up a good low impedance source and I get less broadband noise but the whining is clearly evident on the headphones. My source was a Shure SM7b in an anechoic chamber.

Crack the case. Very helpful to have an good o-scope with high impedance probes. Using an ac-coupled setting, the whine is found riding on the 3.3,3.8 and 5 V dual header jumpers between the main board and the PS, about 60mV worth. Apparently, noise is an unexpected interaction effect between the main board draw and the power supply. Initially, I tried decoupling filtering between the ps and main board but that didn't work at all. I was only able to change the frequency of the whine, not eliminate it.

The main board is much newer but MOTU uses a 3rd party power supply (or it is some older MOTU PS) as it is marked with a 2006 design date. They may not enough info on that PS to fix this on their own. If they do, then they could offer an alternative fix on either board.

I have terminal cancer and can't wait so I plunged on. It took fifteen man hours to research and trace the 3rd party power supply design and then I fixed mine. I forwarded introductory info to motu last week and have not heard back. I'm not sure how to proceed without a motu response. I'd like motu to acknowledge and test as well as verify that my mod creates no other issues. All of these units are under warranty so I suppose I willingly voided mine. I haven't burned my repair in yet so I suppose that might be my next test.

Anybody local to Maryland is welcome to visit. Worst case, I could offer info or a repair service to folks. It takes less than an hour per unit to repair. The fix is component level requiring SMT skill and equipment.

I'm also doing a preamp opamp upgrade using an LME part later this week. After that upgrade, I'm withdrawing to record with this fine device.

Regards,
M.E.
Klaus
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Re: high pitch frequency on motu 896mk3 hybrid inputs

Post by Klaus »

Thanks ME
I'll PM you

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Klaus
Spencil_Splodge
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Re: high pitch frequency on motu 896mk3 hybrid inputs

Post by Spencil_Splodge »

Hi midnight_engineer,

Thanks so much for posting this detailed information. I'll also post this information to Motu on my TechLink (crediting you of course!) - I had a suspicion it might be the PSU, although I was hoping it wouldn't be!

My hardware engineering friends at work (I'm a firmware guy) suggested the use of the o-scope but I didn't want to open the unit! Hopefully, given the level of detail that Motu now have in regards this issue (and the man hours saved their end) they might honour your warranty :) - it's just as well brave people like you exist otherwise this issue would drag on for a long time.

Finally, I'm very sorry to hear of your illness, I hope you can now at least get plenty of music creation/recording/mixing time in without needing to fix issues with equipment. I wish you all the best in this respect.

Best Regards,

Spence.
maaaquemeseyo
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Re: high pitch frequency on motu 896mk3 hybrid inputs

Post by maaaquemeseyo »

Where’s the product manager?. Yeah! Wanna hear you here!. You know for and explanation and so... :dance:
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HCMarkus
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Re: high pitch frequency on motu 896mk3 hybrid inputs

Post by HCMarkus »

Midnight Engineer... I don't own the unit in question, but your response is much appreciated, and (I believe) completely in the spirit of what James is tryiong to accomplish with this board.

Not to mention above and beyond the call. You rock, and I wish you the best.

maaaquemeseyo, this is not a MOTU-sponsored board, so a product manager is unlikely to appear here. You may wish to contact MOTU directly.
midnight_engineer
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Re: high pitch frequency on motu 896mk3 hybrid inputs

Post by midnight_engineer »

I called MOTU on Feb 8th and talked to a service rep and he said he would forward the message that I had solved my noise issue. To date, I have received no call back. Also, I posted a techlink on Feb 9th on MOTU’s site which remains "unread" to this day, Feb 27th. I said I would wait two weeks in a prior PM, so off we go….

Me, and a great friend, modified my unit on Feb 7th. I've been running it off and on for hours at a time over the past several weeks with no problems. The mod appears to work. I’m passing this on just in case I happen to pass on.

BACKGROUND: The Power Supply Board (PSB) is distinct from Main Board (MB). Utilizing a low impedance Shure Sm7b placed in an anechoic chamber, approx 60mV of 1500-1600 Hz AC shows up on several of the dual header jumpers between PSB to MB, those specifically labeled 3.3, 3.8 and 5. All of these pins have actual DC slightly higher than labeled. I assume this provides headroom for downstream regulation on the MB. The PSB corruption is easily audible at high gain thru the headphone jack and is recorded.

My power supply board is labeled "PS-3501" rev4, layout dated as 2006. The PSB is a pulse-width modulated switcher with error feedback wherein the dc output is continuously compared to a reference and pulse width is adjusted accordingly. In this case, the PSB utilizes an optical coupler, precision reference, and amplifier in one handy chip.

http://www.fairchildsemi.com/ds/FO/FOD2741A.pdf" onclick="window.open(this.href);return false;

The 896mk3 PSB closely resembles the "typical application" in the data sheet. Be cautious studying this datasheet as my cohort noticed that Figures 7 and 8 have the opamp pins incorrectly labeled. I could easily examine the PSB feedback oscillation with an ac-coupled scope probe on U1 pins 6, 7, and 8. Pins 6 & 7 exhibit a sinusoidal waveform and Pin 8 is asymmetrically compressed. Since we only want pure dc out of the PSB, this feedback signal needs to be clean and, ideally, it should only waiver as the MB load rapidly varies. From my experience, the layout of the PSB should have the compensation network much closer to the chip. Component changes or a new layout would be a “better” fix but at least there is an “easy” fix , we need to simply add a part.

SOLUTION: A very similar chip is shown in

http://www.scantec.de/uploads/media/Fly ... ration.pdf" onclick="window.open(this.href);return false;

Specifically, Figure 3 “Control Loop Section at the Output” provides for an additional capacitor. The cap connects between pins 6 & 7. We added a X7R 4700pF, 10%, 50 Volt capacitor to PSB U1. We used a small surface mount part but you can use anything non-polarized that will fit nicely - a 1206, 0805 or even a thru-hole part. Adding this cap lowers the oscillation amplitude on pins 6, 7, & 8 and moves the dominant frequency to well over 300kHz which is well above Nyquist frequency for the highest onboard sample rate. Better yet, the oscillation is NOT AT ALL EVIDENT on the PSB to MB jumpers due to the existing output filtering and so it can only be found on the feedback network after the mod.

PHYSICAL IMAGE: http://s1095.photobucket.com/albums/i46 ... gineering/" onclick="window.open(this.href);return false;

Regards,
ME
Last edited by midnight_engineer on Tue Feb 28, 2012 1:57 pm, edited 1 time in total.
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