MC452 protection mode one channel?

marcus_ec

New Member
I'm from Sweden so I'll try spelling correctly.

I own an MC452 where the right channel plays higher according to the vu meters. I have always thought they are incorrectly calibrated and have not bothered me. But yesterday, I was home without wife :) I played really loudly and then the right channel began to go into protection mode. The diode began to flash.

Are there any bias adjustments or anything else on the MC452?
Where do you set the meters (calibration)?
Is there any service manual to download?

I have tried switch signal cables on the right & left channel and tried other speakers on the right channel. I have provide an application on my phone that measures decibel. But they seem to play as high both of them.

Some tips on troubleshooting?
 
Did you switch the whole signal cables between left and right, or just changed the connections left and right at one end?

If you changed the whole cables between left and right I suggest instead to cross connect the outputs of the preamp to the inputs of the amplifier (connect preamp left > amplifier right and right>left). The cross connection should help check if the difference is the amp or something upstream.
 
May sound like a silly suggestion, but have you checked your preamps balance control?
 
Yesterday I tried more ...

Tried to change signal cables
Cross the signal cables
Tried other outputs (pre out) I have 3 pcs on my preamplifier.

Tried xlr and rca
Tried other speaker cables

It is a Lyngdorf DPA-1 preamplifier. Never touched the tone controls and I double-checked. It's a digital preamplifier.
Checked my signal chain (htpc)
Tried other digital inputs.
Always the same! Right channel VU meters always higher.
Checked with decibel meters. 0-1.5db difference, within the error margin ... application in the phone.

I own a multimeter, can I measure the speaker outputs voltage or something else?
 
I believe your preamp's room compensation circuit is asking one channel to ask for more power than the other. This would most often be to compensate for more bass boost needed in one channel.

By feeding it's right channel into the amps left input this could be confirmed.

If you still believe it is the amp you will need to bring it to a tech who has the correct test equipment to load the amp and test and adjust it under high power situations.
 
If the Lyngdorf has balanced ouputs. They wire their XLR lugs to iec standard. So pins will not align one to one with the MC452. The inital MEN220 had similair full balanced issues running with Quad balanced amps If I Recall another poster on AA forum having early adopter issue. . Required MEN220 fix. Suggest you use unbalanced RCA outs, contact Lyngdorf for rewire of cables. I had issues interfacing a TDAI with the Lyndorf microphone until rewiring my US XLR Balaned interconnect to iec standard.

The Room Perfect also will run channel imbalance compensation for room issues. I can’t imagine that overheating the MC452.

The original MEN220 was based off Lyndorf RPA-1 design technology. So issues the early ones had with QUAD balanced amps makes sense.
 
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Yesterday I tried more ...

Tried to change signal cables
Cross the signal cables
Tried other outputs (pre out) I have 3 pcs on my preamplifier.


Tried xlr and rca
Tried other speaker cables

It is a Lyngdorf DPA-1 preamplifier. Never touched the tone controls and I double-checked. It's a digital preamplifier.
Checked my signal chain (htpc)
Tried other digital inputs.
Always the same! Right channel VU meters always higher.
Checked with decibel meters. 0-1.5db difference, within the error margin ... application in the phone.

I own a multimeter, can I measure the speaker outputs voltage or something else?

I would say you have an issue with the amplifier as you say no matter what you do, its always the same.

I think you will need to get the amplifier to a technician.
The MC452 is a current model so the public will not be able to obtain the service manual/Data.

It will need to be put on a load bank and subjected to proper tests.
 
Now I'm 100% sure. I connected the laptop 3.5mm to the 2 rca straight into the power amplifier without speakers and tested with 1khz test tone and the right channel plays higher anyway... damn boring! 1h drive to nearest servicecenter.
 
I believe your preamp's room compensation circuit is asking one channel to ask for more power than the other. This would most often be to compensate for more bass boost needed in one channel.

By feeding it's right channel into the amps left input this could be confirmed.

If you still believe it is the amp you will need to bring it to a tech who has the correct test equipment to load the amp and test and adjust it under high power situations.
Also selecting Room Perfect bypass will also level meters output imbalance.
 
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If the Lyngdorf has balanced ouputs. They wire their XLR lugs to iec standard. So pins will not align one to one with the MC452. The inital MEN220 had similair full balanced issues running with Quad balanced amps If I Recall another poster on AA forum having early adopter issue. . Required MEN220 fix. Suggest you use unbalanced RCA outs, contact Lyngdorf for rewire of cables. I had issues interfacing a TDAI with the Lyndorf microphone until rewiring my US XLR Balaned interconnect to iec standard.

The Room Perfect also will run channel imbalance compensation for room issues. I can’t imagine that overheating the MC452.

The original MEN220 was based off Lyndorf RPA-1 design technology. So issues the early ones had with QUAD balanced amps makes sense.

Something seems amiss because IEC, AES, and the MC452 all indicate the same wiring for XLR, having pin 2 "hot".
 
So the meter is out of calibration, but this would not be why the one channel goes into PG earlier than the other...that would have to be either a higher signal level going into that channel or a issue with the amp or speaker load.
 
So the meter is out of calibration, but this would not be why the one channel goes into PG earlier than the other...that would have to be either a higher signal level going into that channel or a issue with the amp or speaker load.
It could be Room Perfect has EQ'd the two sides differently in the low end, my Room Perfect does that, takes a cut out of the side thats nearer the corner of the room, obviously something bass related going on it can detect, so when I am watching the level indicators on my Sub amp (the Macro-tech) it shows level on the left channel before the right channel.
This could be happening in this case perhaps. Or there is a fault with the 452? Needs to plonked on the bench and tested...
 
Something seems amiss because IEC, AES, and the MC452 all indicate the same wiring for XLR, having pin 2 "hot".
Nope, nothing amiss.
The MC452 needs a true balanced input, a great number of "balanced" outputs are not truly balanced and in the case of a pin2 hot scenario, pin3 can still be referenced to ground. You cannot run this with a quad balanced McIntosh, you will short the negative side out.
The quad balanced amps are fully balanced all the way though, they operate above ground and are fully floating, in a similar way a fully floating bridged amplifier works.
 
Nope, nothing amiss.
The MC452 needs a true balanced input, a great number of "balanced" outputs are not truly balanced and in the case of a pin2 hot scenario, pin3 can still be referenced to ground. You cannot run this with a quad balanced McIntosh, you will short the negative side out.
The quad balanced amps are fully balanced all the way though, they operate above ground and are fully floating, in a similar way a fully floating bridged amplifier works.

That is a different matter than the pin 2 vs pin 3 hot thing eluded to by the references to IEC and "US" balanced connections. That was the point of "amiss".
 
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That is a different matter than the pin 2 vs pin 3 hot thing eluded to by the references to IEC and "US" balanced connections. That was the point of "amiss".

@kevzep is right. The DPA-1 is culprit.

Here is an old post I found elsewhere explaining how Lyngdorf wired there XLRs and the OP’s preamp DPA-1, RP-1 and original MEN220 design, which was circuit similar to RP-1, before MEN220 XLR fix, original balanced wiring causes overheat of the McIntosh Quadbalanced Amps. So @marcus_ec you most likely damaged your MC452 Use unbalanced outs in future or custom XLR.

In conversation with two different people at McIntosh, including one of the engineers who helped develop the MEN220, I was told that connecting the MEN220 outputs to a fully balanced power amplifier (MC402, MC501, MC1201, MC1.2Kw) should only be done using unbalanced interconnect cables. It was explained to me that the balanced outputs on the MEN220 are not true balanced outputs. In other words, the wiring of the three balanced output pins is not standard. Normally, pin #1 is ground/shield, pin #2 is (+) signal hot, and pin #3 is (-) signal cold. It was explained to me that the MEN220balanced output pins are wired where pin #1 is ground/shield, pin #2 is (+) signal hot, and pin #3 is ground/shield. In other words, pin #1 and pin #3 are both connected to ground. There is no (-) signal cold on #3 pin, which is normally the inverted audio signal. Even though it is a balanced output connector, it is wired as an unbalanced connection that delivers only the (+) hot, and ground, the same signal found on the unbalanced output.
 
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It's good we now have a proper explanation of the problem. My previous point, again, is that the original explanation of IEC vs. "US"* balanced wiring in fact had zero to do with the problem.

*"US" balanced wiring is a misnomer. Pin 3 hot was used a few mfg. but was never a US standard.
 
Getting back to the OPs possible issue.....

I believe no overheating was observed.....just one channel PG light came on earlier than the other and his one meter reads higher.

If the problem switches channels when he swaps the preout right to left and left to right I would suspect the EQ differences between channels....if it does not switch I would suggest a bench test to compare actual output under load and recalibration of the meters.

Meter calibration is easy.....checking the early onset of PG is not.
 
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