Grimm Audio MU2 "Major Dac"

WLP3 said:

Adjusting the volume level made a difference. I learned a couple of things yesterday: The volume level of the MU2 is best controlled via Roon. Roon adjusts the gain of the unit based on the volume level on the Roon slider. I have set mine to 92 in Roon which corresponds to 0db on the MU2. For whatever reason, before I rebooted the unit I was able to have two volume levels, one on the MU2 and one in Roon. Since reboot I adjust the volume level in Roon and it automatically adjusts the gain on the unit.

Secondly I found that using the control disc to navigate to the power button on the screen does not completely turn the unit off. It puts in into standby mode. To completely turn the unit off you have to go to standby mode initially, presumably, and then use the small button on the back to turn off the unit. That is not intuitively obvious. There should be a standby symbol on the screen rather than the international symbol for on/off. My unit was running sluggishly before I rebooted and now it is running much faster. I must have cleared out the cache or something.

I think a contributing factor, or perhaps the main factor, for the crispiness may be coming from the input tubes. I also recently changed the input tubes to PsVane "Cossor" 6SN7 carbon balls. They sounded fantastic when they were installed, but they might be losing their mojo. They probably only have 100 hours on them. I think the soundstage may be narrowing and there is not the layering that I had when they were brand new. Could they be causing some sibilance?

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GHasley said:

Do you have other tubes? That's an easy thing to check. I'm glad you have the settings properly set now and I'm certain you will get things sorted on the tube front. Are your Roon settings for the MU2 properly set for the Major Dac? On the MU2 have you set it for the 8fs and 3db headroom setting?

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WLP3 said:

I have a new pair of Tung Sol 6SN7 GTBs that I can try. Perhaps the PsVane tubes are still not broken in? I am used to the input tubes typically breaking in in about 50 hours or so. I will swap out.

I believe that I am properly set up on Roon/MU2 for using the volume control on my amp. I believe it is set for line level now.

I am not aware of the headroom setting on the MU2. I have heard of it for the MU1 but I am not aware of that setting being available on the MU2.

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GHasley said:

I have a MU1 and I'm not at home so I am going off of memory. Have you set your default volume to -8db or whatever it is you've decided is proper? I know there are some boxes to check for the upsampling which allow you to choose no, 2fs, 4fs and I believe the MU2 has 8fs. I dont recall if the MU2 has the 3db headroom setting but the MU1 does. ALso, if you are using Roon to adjust volume then you are using the Grimm volume control right? ANyway, I would try to find unity gain on your Trafo and set that volume to that setting. I would then only use the Grimm volume as its likely a higher quality, more transparent analog volume control than the Trafo.

As far as tubes, I would not be much help in that regard. Even though I have an all tube setup I just dont have experience with the new production tubes you mention nor how act/react in the Trafo circuit. I can tell you in my experience if it has sonic problems at 20 hours it will have sonic problems at 200 hours.

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WLP3 said:

I don't think that the MU2 has the oversampling settings that the MU1 does.

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Kal Rubinson said:

None that I could find but, of course, it also has no digital output.

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WLP3 said:

I don't believe that it does. I have found a difference in sound when selecting fixed volume from the device setup within the volume button in Roon vs device volume. Selecting device volume in Roon is brighter than having fixed volume selected in Roon. Very different sounding. If I am using the volume control on my amp, what should Roon and MU2 be set at? I would guess that Roon should be set at fixed? What was the designers intention? I may need to contact Grimm.

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GHasley said:

The designers intent was for the all-in-one server/streamer/dac/fully analog preamp to drive an amp direct or an integrated amplifier.

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GHasley said:

Within Roon, you should select “device volume” and use the volume control on the MU2 to control the system volume.

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WLP3 said:

I reviewed the documentation, and it is quite explicit about selecting device volume. Very different sound. I’m not sure that I like it…much brighter

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GHasley said:

One of the interesting challenges for us as we upgrade components is to do so in a manner where these upgrades, for better or worse, are identifiable to a particular component. A cursory review of the thread indicates you have a couple of changes going at the same time and it can be anxst inducing to chase down a root cause for changes you hear. I know I've driven the dealers with whom I've purchased a bit crazy over the years. In your case you have tube changes and of course the MU2 which potentially displaces a myriad of components. Hang in there.

You've mentioned your interconnects that you love but perhaps (and I apologize, I havent read the entire thread) sharing your system before the MU2 and the system today, perhaps then we can assist more effectively. The amp manufacturer will be able to tell you approximayely where unity gain is on the dial of your particular amp. Likely between noon and 3 on the dial but email them Im sure they can help. Good luck.

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GHasley said:

One of the interesting challenges for us as we upgrade components is to do so in a manner where these upgrades, for better or worse, are identifiable to a particular component. A cursory review of the thread indicates you have a couple of changes going at the same time and it can be anxst inducing to chase down a root cause for changes you hear. I know I've driven the dealers with whom I've purchased a bit crazy over the years. In your case you have tube changes and of course the MU2 which potentially displaces a myriad of components. Hang in there.

You've mentioned your interconnects that you love but perhaps (and I apologize, I havent read the entire thread) sharing your system before the MU2 and the system today, perhaps then we can assist more effectively. The amp manufacturer will be able to tell you approximayely where unity gain is on the dial of your particular amp. Likely between noon and 3 on the dial but email them Im sure they can help. Good luck.

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GHasley said:

One of the interesting challenges for us as we upgrade components is to do so in a manner where these upgrades, for better or worse, are identifiable to a particular component. A cursory review of the thread indicates you have a couple of changes going at the same time and it can be anxst inducing to chase down a root cause for changes you hear. I know I've driven the dealers with whom I've purchased a bit crazy over the years. In your case you have tube changes and of course the MU2 which potentially displaces a myriad of components. Hang in there.

You've mentioned your interconnects that you love but perhaps (and I apologize, I havent read the entire thread) sharing your system before the MU2 and the system today, perhaps then we can assist more effectively. The amp manufacturer will be able to tell you approximayely where unity gain is on the dial of your particular amp. Likely between noon and 3 on the dial but email them Im sure they can help. Good luck

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WLP3 said:

Thanks very much for your reply.

Thanks for your response.
My system is:

Grimm MU2
(Previously Gold DS10 EVO with PSU 10 EVO pow
Tchernov Ultimate Slim RCA ICs
Trafomatic Rhapsody 300B PSE Int
Amp (20w/chan)
Emission Labs 300B Mesh (x4) approx 160 hours
Psvane “Cossor” 6SN7
Tchernov Reference DSC SC speaker cables

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WLP3 said:

Yes I understand that, but it is not clear in the manual how it should be configured. When selecting the fixed volume setting in the device settings in Roon creates a completely different listening experience. It is like I am listening to the MU2 for the first time. I have contacted Grimm about what the settings should be for controlling volume through your amp or preamp.

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aangen said:

I have my MU2 feeding my preamplifier. In this case I find fixed volume the best way to go. You don't have to fix it to 100%, you can roll it back from 100% and see if that is better or not.
When using the MU1 as a Preamp, fixed volume would be wrong. You would use the MU2 to control volume.
As far as letting Roon control volume, no thank you.

I tried using the MU2 as a Preamp, plugged directly into my Gryphon Apex Amp with Stealth V17 Sakra LE cables and it performed very well. But playing through my Gryphon Commander Preamp is better still. I suppose that isn't a surprise.

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PYP said:

There is no choice for the oversampling rate for the MU2 as there was for the MU1 where you feed different DACs. Grimm has already given us the best choice for their DAC.

As far as I know, as mentioned, Device Volume must be chosen within Roon's audio device setup whether you use the Roon slider bar to communicate the volume setting of the MU2 (the MU2 does the volume control). Then, in the web interface, you can choose (or not) the Fixed Volume option. It seems to me that you can "Fix" the volume level where you want to. If you choose 0db (as recommended), that setting appears on the Roon slider bar control as 92.

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• Keep Roon in "Device volume".
• Set the MU2 to "0 dB" on the MU2 display (note it can go to +8, but these levels can cause internal clipping).
• Then select the "fixed volume" option in the MU2 GRUI web interface (it adopts the current volume setting)

WLP3 said:

I have asked the question about proper settings for use of volume control on an amp or preamp and Eelco Grimm responded with the following:

If you prefer to use the volume control of your amplifier, you should use the following setup:

• Keep Roon in "Device volume".
• Set the MU2 to "0 dB" on the MU2 display (note it can go to +8, but these levels can cause internal clipping).
• Then select the "fixed volume" option in the MU2 GRUI web interface (it adopts the current volume setting)

This setup will offer you the most transparent result.

That being said, I recommend to try the MU2 volume control once (and use a fixed setting on your amplifier). It is of a quite special quality...

FYI…

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