Protection mode issue on integrated amplifier

I'm currently running my Marantz PM8004 integrated amp as a preamp with a NuForce STA200 power amp. When I'm done listening I noticed that when I power off the NuForce (not sure what I should power off first) the Marantz goes into protect mode for around 20sec, after that it goes back into regular power on. Should I be powering off the preamp before the power amp?

 

Power off the Marantz first. It’s reacting to a spike of some sort from the NuForce.

 

Thanks Agitater! Do you have any experience with the NuForce STA200? I just got this one a couple days ago from Audio Advisor. Wanted to give an audition.

 

I've had only audition experiences with the NuForce DDA120 integrated and a couple of other NuForce products. I am not personally a fan of the sound, but the DAC implementation in the DDA 120 was surprisingly good at the price.

 

Thanks. Looking forward to comparing against the Marantz which I’ve been enjoying for the past 4 years.

 

That's not good advice. While it is unknown why the Marantz is going "protected mode" if it doesn't have speakers hooked up to it, the noises and pulses that come out of it while turning it on or off could go through the power amp and damage speakers. Always power amp is the last thing to be turned on and the first to be turned off.

1: Ensure you are using only "Pre-out" connectors on the Marantz, not "power amp direct" RCAs, which work the opposite way.
2: Press Speakers A/B on Marantz until speaker outputs are turned off (or pick other speaker outs if they don't turn off)
3: You might need to insert a set of shorting/grounding plug RCAs into "power amp direct", to ensure that the unused Marantz' amp part never gets any spurious signals from having it's input unconnected.

 

Yes, I'am using the pre outs. I just turned all speaker outputs off and it is still going into protect mode.

 

Protect mode can be triggered in the amplifier stage from DC output being detected on the speaker wires, and turning off the amp may dump a power surge into the power cord or grounding, which is picked up in the Marantz' unconnected amp.

I think the solution to this inconvenience will be to get (or make) a set of RCA shorting plugs and plug them into the "Power amp direct" inputs.

If you have an extra set of RCAs, plug one end into this input, and then pack aluminum foil between the center pin and ground shield with a little screwdriver on the other unconnected end to short it out - if that solves this problem, you can order something more elegant.

 

The Marantz PM8004, like many other integrated amps, does not like shorting plugs of any kind. I think that using them on a PM8004 might be ill-advised, and could cause damage (or trigger protection mode, or blow the Marantz fuse eventually).

The protection circuit in the PM8004 is something that prevents damage to components within the Marantz internal power supply when an abnormality such as an overload or excess voltage occurs for any reason. That means either the NuForce is kicking something back at the PM8004 through the pre-out connection, or something has gone wrong with the Marantz. Nothing to do with the Marantz power amp section in the OP’s pre-out setup.

The NuForce is not exactly an example of top-of-the-heap engineerng, but it’s nowhere near junk either. So it’s not really clear that the NuForce is absolutely the culprit.

For the time being, as a test, the OP should connect his speakers directly to the Marantz again. Run it conventionally for half an hour, listening to music. Then turn off the system. If the PM8004 still goes into protection mode, it means there’s a problem with the Marantz and it will need to be serviced.

 

I’m gonna try this next, I’ll report back. Funny thing is I haven’t really compared the two amps yet. If I don’t find the NuForce satisfying I can just return it. Hopefully my Marantz is ok.

One more thing, the protection mode kicks on even after a cold power off. Meaning I turn the NuForce on than the Marantz. As soon as I turn off the NuForce the Marantz goes protection.

 

Marantz PM8004 is fine, no protection mode after connecting my speakers and listening for 30min. Powered off as normal. Powered right back on just as normal.

 

That means either the NuForce power amp you’re auditioning is misbehaving or the cables you’re using to connect it to the Marantz are suspect.

 

I’m gonna give different interconnects a try. Right now using Blue Jeans LC-1. Have some Audioquest lying around I’ll try

 

If there are gain adjustments on the NuForce and they’re set all the way up, back them off equally to 70% (approximately) and see if that resolves the problem.

 

After presumably not hearing the Marantz on its own for a while, what did you think of the sound? I haven't heard either but would be surprised if the Marantz + NuForce combination was definitely superior to just the Marantz.

 

I've had mine for maybe two weeks now, broken in, and the level of detail it reveals is unreal. I hear something new in every album I listen to. No preamp issues with the Onkyo P3000R.

 

There are no gain adjustments. In fact I had to lower the gain of my phono preamp from 66db down to 56db, I’m running a low output moving coil. At 66db, my stylus was actually skipping at certain points with the volume at a decent level which is louder than normal for me. Once lowered to 56db, which is still fine due to the NuForce having such high gain it didn’t skip anymore and a bit quieter.

Very quickly in between connection changes I played the same piece of music and to be honest, the NuForce just seems louder. I’m not gonna jump to that conclusion until I can do a fair comparison but all these bugs I’m having is kinda making me not optimistic. I only jumped on the NuForce due to the closeout prices. I got this one for $449 demo. I really enjoy my Marantz, the original plan was to upgrade to a Yamaha A-S1100 or used A-S2000 or maybe a used McIntosh 6300 or 5200 and also maybe a Marantz Reference piece.

 

If you're interested in McIntosh integrated amps without autoformers, I'd actually go a bit older with the 6500. I (and most critical reviews it seems) finds the 6300 and 5200 sound great at low volumes but kind of wear out with more complex music and/or higher volumes. Not the amp for a metal head.

 

I got the Nuforce on sale, and it replaced a Marantz MM7025. I figured I'd keep whichever amp I was most pleased with, and sell the other. It will be the Marantz that I sell. Not that it's a bad amp. Not even close. But where the Nuforce wins is soundstage and imaging. It's more three-dimesional and deeper.

 

I used to have the five channel version of the MM7025. I'm not surprised you're selling it. My impression of it was basically the receiver portion of an A/V amp put in its own box because separates are cool.

 

A shorting plug does nothing to the input other than tie the input level to 0 volts. It ensures that there is no voltage potential between ground and the input signal, voltage that the amplifier replicates 100x louder and which might put the amp into protect mode.

Doesn't hurt this amp, and in fact, we'll see it doesn't do anything ... unless you do something else.

The problem with this amp: The internal amplifier is not isolated from the preamp out jacks, unless you also engage the "P. Direct" feature on the front panel.

Here is a block diagram of the output stage. I've also confirmed how it works in the schematics:



I made a big red arrow that shows how any spurious signal from the NuForce input jack upon power off is fed back into the Marantz' internal amplifier. There is no buffer that prevents signal from going backwards. The NuForce is surely doing something that has either a DC component or clips the internal Marantz amp, either will send it into protect mode.

The solution to this is to:

1> engage the P. Direct Switch on the front panel,
2> use shorting plugs on "power amp direct" (you can use a 47K short if you don't like a true short)

That engages the processor-controlled switch (a relay) that you see pictured right after the big red danger arrow, isolating the Marantz amp from both the internal pre, and anything injected via "pre out". Then the Marantz amp is instead only connected to the Power Amp Direct input, where we connect a shorting block to ensure the amp is given no signal.

You can also connect Y RCA connectors from the pre out to both the Marantz and NuForce amps at the same time to run them both. However, the turn off issue would likely return from garbage going "out" the NuForce input.

Addendum: Protect circuits on amplifiers "listen" to the output after the amp chips. If they detect something abnormal, they shut down the whole amp. DC voltages (frequencies below 1Hz) are abnormal and will trigger protection, as it might also indicate a chip gone bad. I've even had clipped MP3s set this off. It doesn't take much voltage.

 

No doubt the NuForce lacks a bit of engineering sophistication. As well, the OP must make sure that P. Direct mode is engaged. Hopefully, he’s got everything sorted out now.

 

Whether one amp is louder than the other at a given preamp volume control setting is irrelevant, and it’s not a measure of amp quality. How one amp sounds to you, compared to the other, at identical volume levels is what matters.

Put on a test record, dig out an inexpensive Scosche SPL meter, play a test tone on the test record and set the volume at a certain level, and mark it with a piece of masking tape. Listen to a piece of music you know well. Then change amps, play the same test tone, and using the meter again set the volume to the same level as you did for the first amp. Mark that level on the piece of masking tape too. Then play the same record again and make notes about the sound. Switch amps, adjust the volume level according to the mark on the masking tape, play another record you know well. Repeat the process until you have a winner. That’s a sensible and reliable way to help make a decision.

Make sure you remember to switch the Marantz into P. Direct mode when using the NuForce.

 

I always use Source Direct (that is what its called) on the Marantz. I also swapped out interconnects between both and the Marantz still goes into protect mode. I have not done the shorting method for the Direct Amp Input but will try the home remedy later. I do not have a test record but I can rip my Stereophile Test Cd which has test tones and I do have a Radio Shack SPL mater which I use for my home theater. I can just listen to my digital files between amps.

 

"Source direct" bypasses the tone controls. That's not what we want to test.

Press the power amp direct button on the front.



Just having that mode engaged may solve the issue where the the Marantz goes into protection when you turn off the power amp first (as you should always do).