MSB Overdriving Amp Input?

[Bretson]

Hi Guys,

I have been trying to work through something. I have an MSB Discrete with 2 psu's and love the overall build and design. The SQ is also amazing and the unit itself is rock solid in operation. I have found however that it doesn't play nice with all amplifiers.

I recently picked up a TAD M2500 amplifier and connected it as usual and the amp immediately went into protection mode. I thought at first that i was merely sent a dud but then i figured i would experiment a bit. It seems to be working when connected to anything other than the MSB. This is not the first time i have had this happen either. I have also had a Vitus ss010 do the same thing. When connected to the merason dac1 mk1, there was no issues. When connected to an Auralic Vega G2, no issues. When connected to the msb in amplifier mode, it immediately went into protection mode. when in integrated mode, it was strained and when turned up, it shut down also.

Amps that i have in house that work well with MSB:

Burmester 036 (The best sound of all pairings imo)
Pass Labs 30.8 (No bass in this pairing)
Luxman 590aii
Audionet WATT
MSB S202 (Excellent sound also, but not as good as burmester)
Vinnie Rossi L2iSE

Amps that go into protection Mode:
Vitus SS010
TAD M2500

Maybe i have some electric gremlins in my house but i also tried connecting the Pre output of the Vinnie Rossi into the burmester for fun and it sent it into protection mode. Synergy is obviously key here but its not obvious to me how to diagnose this ahead of time prior to purchasing. Has anyone else run into this? Specifically with MSB.

 

[mtemur]

I’m not sure but I’m guessing it can be due to negative and earth connections. If TAD 2500 has a floating negative and MSB doesn’t may cause shorting amp’s negative to ground. Most amplifiers have negative connected to ground, especially single ended amps, but some have floating negative, same as positive.

 

[Bretson]

Just to update this thread for anyone who is interested. I contacted MSB regarding this issue and they kindly helped me through it.

It turns out that some amps with XLR inputs may opt to put the third pin of the xlr input to ground. They indicated to me that this is predominantly in single ended amps.

They indicated that if this is the way the amp is wired, that the DAC will push DC into the amp. This is what i experienced on the Vitus SS-010 (amp mode) and the TAD M2500. Both amps went into shutdown when connected directly to the discrete.

I have tried other preamps between the dac and amp but it honestly sounds best direct form the DAC to a suitable amp in my experience.

So, unfortunately the MSB Discrete is not universal to use with all amplifiers. I'm not sure if this is the case with their other DACS, but you could reach out to them to find out if you might have compatibility issues. They mentioned that i could use some XLR to RCA adapters but that it essentially negates the point of their output design.

 

[exupgh12]

TAD is a Japanese company, there for isn't the hot wire 2 and 3 (+\-) in XLR connector is opposite to what you find from US\European products ?

 

[Bretson]

TAD is a Japanese company, there for isn't the hot wire 2 and 3 (+\-) in XLR connector is opposite to what you find from US\European products ?

Somebody else will have to answer this one.

 

[GSOphile]

My Esoteric Player has a setup option that will let you specify which output XLR pin (2 or 3) you want to be hot.

 

[MarkusBarkus]

...Luxmans were the same...you could invert the XLR pin map.

Couldn't you have someone make up a set of XLRs with the pins changed? Would that work?

 

[DonH50]

DC was my guess... An XLR has pin 1 to shield (ground), pin 2 is signal (+), and pin 3 is signal (-). Some European and Japanese equipment flips pins 2 and 3 but that is only a signal inversion not related to this problem. The problem is that that XLR signal output may be DC coupled, swinging about a common-mode voltage other than 0 V (ground). If you use one output, it still swings around a (large) DC offset, and not ground.

From a source the usual convention is to connect output pin 2 to RCA center pin and output pin 1 to RCA ground for a single-ended input. Connecting pin 3 to ground shorts one side of the driving component's output to ground ;some tolerate that, some do not. Either way, there is no guarantee of 0 V average (DC) level from the balanced XLR output whether connected differentially or single-ended -- it depends on the bias and common-mode level of the output stage. Not usually a problem if the next stage's input is AC coupled, but can wreak havoc if DC coupled. And pin 1 does not always work, either, since it may create a ground loop depending upon the input circuit of the receiver. A transformer or active device (e.g. DI box) to convert the differential XLR output to single-ended RCA is the best solution.

If the polarity inversion bugs you, you could just swap the +/- speaker cable connections at the amp outputs or speaker inputs.

IME/IMO/FWIWFM/etc. - Don

 

[Bretson]

Hi All,

Thanks for your input and Don, thanks for the additional background.

After following up with MSB it was suggested by them that I could try using some xlr to rca adapters. I asked them at the time if this would negate the point of running a balanced output and they agreed it more or less does but i could see if it works.

I went to Blue Jeans Cable and had them make up a set of adapters in the conventional orientation. The setup more or less mirrors what Don indicated in his overview.

Balanced to Unbalanced Audio Cables at Blue Jeans Cable

When i hooked them into the system, there were more interesting things occurring.
I plugged the adapter into the RCA input of the TAD M2500 and it was an immediate loud pop of the speakers and almost a full volume surge. I immediately unplugged the amp fearing serious damage to the amp, speakers or both.

The strange thing was that using the adapter like this stopped the amp from going into its protection mode. Typically the amp will indicate power with an amber light and if it is in fault it will flash red. With the adapter in place it just sounded like a dead short. I'm not sure what the mechanism for this would be that it would prevent the bypass.

Fortunately, everything seems to be working fine. Plugging an Auralic Vega DAC into the amp direct using xlr to xlr and rca to rca and things all seem functional but I'm not sure if there is any unseen damage.

Don, you mentioned a transformer device for RCA. I have just looked at MSB website again and they actually make such a device but it is seemingly only compatible with their Reference and Select DAC. I will reach out and see if this can be used for the discrete as well.

I am actually brining in the partner TAD C2000 pre as i want to see if this is unique to the pairing with the amps only. I'm assuming the wiring of the TAD pre in would be the same as its partner amp?

Given the results so far is there any cautionary measures before plugging the Discrete into the Preamp? The TAD is said to be able to accept up to 15V to its inputs but says nothing of dealing with DC being pushed into it.

Thanks

 

[Bretson]

Well today i brought in and connected the TAD c2000 Preamp. Hooked it between the discrete and the m2500 and everything is singing lovely with no problems. I was nervous to hook it up given the pops and bangs i had been getting going direct.

I checked the xlr orientation of the TAD equipment and it is conventional wiring. Anyways, it is a mystery to me why the dac can not run direct to the amp in this case but all is well in audio land this friday.

I tried the internal dac of the c2000 and it seems quite nice for it is but it gives way to the msb in every category.

 

[DonH50]

Well today i brought in and connected the TAD c2000 Preamp. Hooked it between the discrete and the m2500 and everything is singing lovely with no problems. I was nervous to hook it up given the pops and bangs i had been getting going direct.

I checked the xlr orientation of the TAD equipment and it is conventional wiring. Anyways, it is a mystery to me why the dac can not run direct to the amp in this case but all is well in audio land this friday.

I tried the internal dac of the c2000 and it seems quite nice for it is but it gives way to the msb in every category.

The preamp is probably AC-coupled, blocking the DAC's DC component that was causing the problem.