Big problems with my Preamp...

[Mozhoven]

Hello all,

I recently purchased a older Marantz AV600 premap on Ebay. The preamp was delivered today. Cosmetically it seems fine, but I'm having some major
issues with its functionality - perhaps you can help.

My major problem is no volume control (via the volume knob that is). I am playing my cd player through the CD input. I can control the volume via the "input level" knob on the front, but the main volume knob does nothing. It's as though I am running my monoblocks from the line out jacks.

My second problem is erratic sound. Sometimes it will sound quiet so I will turn up the"input level" to the 12 o'clock mark for a normal listening level and then will attempt to tweak the volume knob only to have it blast me and I am forced to turn it off. When I turn it back on it'll be normal again, but play out of either the left or right channel only. There seems to be no rhyme or reason to which it plays on.

My connections are good and as well as are the components. Here is what I'm running on it
(and where it is connected to)

*2 - Marantz MA500 Monoblock Amps (connected <Front> outputs on the <Audio
Out> jacks

*Marantz 4300 CD Changer (connected to <CD>

*Pioneer C503 DVD Player (connected to <LD>

I also have the whole D-bus remote system hooked up daisy-chain style (doesn't seem to be
working either, but I may not have the sequence done right yet)

I don't know if it matters or not, but in the lower right corner I see <L> and <R> blinking erratically - almost like the signal is bad. This happens with both the DVD and CD player.

I haven't been able to find a manual for it online, but something seems very wrong here.
I have used this same setup with two Yamaha preamp/receivers and another Marantz
preamp/receiver with no problems what-so-ever.

Am I doing something wrong? Please let me know your thoughts.


I contacted the seller about the problem and he says it worked perfectly for him in is music studio using active monitors.

I'm not sure if it was there before or not, but the back left edge (bottom) is dented about 1/4". It doesn't look catastrophic by any means, but am wondering if this sort of problem can arise from shipping mishandling.

Just to make sure my cables aren't bad, I hooked it up to my old preamp it it worked flawlessly.

The sound discrepancy is really baffling though. It'll play quietly out of both speakers, but one more than the other. Then, after bumping up the volume knob (with no change in volume) it will suddenly become very loud, but in the other speaker. It's as though the processor is confused about how to decode the signal.

I'm only using the Stereo setting, but it does it in all the DSP modes.

-Jeremy

 

[Spasticteapot]

First, try disconnecting the D-bus system. I don't really know how it works, but my experience with computers has taught me how you should always disconnect a component from the rest of the system to see if the problem is external.

Second, check if there's a "tone direct" switch or anything similar to that. It's not likely, but you could be bypassing some bits of the pre-amp.

However, it really sounds to me like you've bought a lemon.

 

[Mozhoven]

Ok,

I decided to take a look inside it to see if there is anything obviously wrong. I imagine the circuits look good - if I could see them!

There must be a 1" layer of dust on all the boards, no to mention the dirt and crud on the RCA jacks.

So, I blew out everything, made sure all the cables were plugged in well, and then used electronics cleaner on the jacks. Bingo - she works like a charm.

The only problem I have now is when I use the volume knob, I here an audible "click" through the speakers (only when the music is quiet). Is there something I can do about this?

 

[infinitesymphony]

Quote:

Originally Posted by Mozhoven /img/forum/go_quote.gif Ok, I decided to take a look inside it to see if there is anything obviously wrong. I imagine the circuits look good - if I could see them! There must be a 1" layer of dust on all the boards, no to mention the dirt and crud on the RCA jacks. So, I blew out everything, made sure all the cables were plugged in well, and then used electronics cleaner on the jacks. Bingo - she works like a charm.

It's strange how that works... Dust is the leading cause of electronics heat death; maybe it's possible that the dust was shorting out some connections if the dust was made of conductive material?

Quote:

Originally Posted by Mozhoven The only problem I have now is when I use the volume knob, I here an audible "click" through the speakers (only when the music is quiet). Is there something I can do about this?

Probably not--this is one of the downsides of using a digital volume control. There are no analog potentiometers to get gunked up, but each volume 'step' instantly ramps up the volume to the next level, which causes a slight click. It's usually more noticeable at higher volume settings.

 

[Mozhoven]

Ah, that makes sense. It's funny how some "problems" are ok if they aren't "problems" to begin with. As long is it can't be (or supposed) to be fixed, I'll be contented.

Actually, with it working and not having to hound the seller for a refund, I'm quite happy. It sounds very nice and finally completes my studio setup. No more Craigslist/Ebay prowling (until next month)

I do have one more question about the preamp. On the display it has a "L" and "R" that light up in the lower right corner. They flicker constantly seemingly corresponding with the output to the left and right channels. This makes sense as sort of poor-mans graphical display, but it is rather annoying. They flicker so rapidly it looks like that part of the display is burning out or something. Is this normal? The preamp sounds fine and the display in general is strong and bright; it just seems odd that Marantz would build in such an uncouth feature like that.

Your thoughts?

 

[infinitesymphony]

That display is probably meant to show the number of channels in the source material, which is common on home theater equipment. You'd probably see 5.1 channels with a typical DVD.

Regarding the flickering, that doesn't sound normal--I haven't heard of it happening before. The electronics that control that part of the display might have been damaged, but who knows, that flickering might be on every model. Any chance you could guess the cycles/sec (Hz) of the flickering? Most CRT computer monitors run at 60 Hz (the frequency of North American power) and some people find that to be unacceptably slow.

 

[Mozhoven]

I would say the flickering is definitely slower than 60 Hz. I know it's a silly comparison but you know when, in a movie, a bomb explodes in a room full of electronic equipment, and in the aftermath there are various flickering screens/buttons? It's erratic like that, but it does correspond with the music somewhat. They don't light up at all during silent passages.

Another thing is there is an <Input Level> knob on the bottom control compartment. The higher I set that knob, the stronger the flickering L & R is. Not sure if that helps.

Speaking of that, what is the optimum setting for that <input level> when using 2 monoblock amps (150 watt)? I have it set on 12 o'clock right now, but every so often I see the "PEAK" light appear between the L & R.

 

[infinitesymphony]

Quote:

Originally Posted by Mozhoven /img/forum/go_quote.gif I would say the flickering is definitely slower than 60 Hz. I know it's a silly comparison but you know when, in a movie, a bomb explodes in a room full of electronic equipment, and in the aftermath there are various flickering screens/buttons? It's erratic like that, but it does correspond with the music somewhat. They don't light up at all during silent passages. Another thing is there is an <Input Level> knob on the bottom control compartment. The higher I set that knob, the stronger the flickering L & R is. Not sure if that helps. Speaking of that, what is the optimum setting for that <input level> when using 2 monoblock amps (150 watt)? I have it set on 12 o'clock right now, but every so often I see the "PEAK" light appear between the L & R.

Oh, weird, I hadn't heard of a preamp doing that before. Basically, the flickering is showing you the strength of the signal input for a given channel, which would be handy for troubleshooting purposes (i.e. I should be hearing left-surround, is that channel getting any signal?).

Since it's a preamp, the output level will be variable. Unless the power amps clip easily with a certain level of input (not likely), you'll only have to worry about the input level at the preamp. The input level knob controls the volume of an incoming source, for example a CD player. One way to set the level would be to play a steady 1 kHz, 0 dBFS (full-volume) test tone and set the input level to just under clipping (which I assume is what the peak indicator is measuring). The idea is maximum volume without clipping for each step in the chain.

Or, you could just some loud/heavy music and set it that way. Just keep an eye on the meter and be sure that it isn't clipping, and after a while you'll never have to think about it again.

The benefit of having an input level adjustment is that it allows optimal gain staging, since different gear often outputs at different levels. For example, two CD players might require totally different settings, and one might be loud enough to clip the preamp if the input level is all the way up.

 

[Mozhoven]

Thanks again for the wonderfully detailed explanation. It's makes more sense now. As for the flicker lights during normal use, I'll just keep the cabinet door closed!