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Marantz 300dc

juanann

juanann

AK Subscriber
Subscriber
Hello ak,

I have some issues with my 300dc amp. Im using a 3250b as my preamp,
when im almost at half way through the volume, the peak lights on the amp
are flashing. Ive checked dc balance, within specs. Tired a different preamp, same results. Changed speakers, no change.

Its sounds great, but the peak lights have never came on before and i have gone over half way point on volume in the past with out issues.

History on amp, all switches cleaned, dc balance set. power filters caps are
original.

Not sure where else to look.
 
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Did you adjust the Gain Controls on the 300DC to full up?
What source are you using?
Where do you have the 3250 Tone Controls set?
Loudness On or Off?
It's normal for the Peak lights to flash at that high an output level.
 
Gain controls are in the middle

source- marantz ipod dock station

tone controls set to flat

loundness on, even off its also lights up

I totally understand its normal for them to flash, im only asking because
it never did that before. i have always left my settings the same.


Thanks for the quick reply also.
 
The same thing happens with my 3200 pre and both 140 amps. With the gain controls on the amp set half way the peak limter lights come on around 1/2 volume. I just turn the gain controls on the amp down enough to get 3/4 on the volume control before the lights come on.
 
Also try a CDP instead of an iPod. Leave everything else as you have it set. Lets see if that helps.
 
Well I tired a cd and same results. I can go 2 to 3 click more on the volume, just past the half way mark and peak lights coming on.
 
The Peak LEDS are telling you something is going on inside the amp.
The 300DC is a Dual Power Supply amp. One channel has nothing to do with the other.

Can you connect a signal source to the Main In jacks and measure ACV at the speaker terminals? Start At 0V and advance the oscillator until the Peak LEDS light. Read the voltage at the Speaker terminals. You'll need a 150W 8 ohm Dummy Load for this test one to the Left Speaker Terminal another to the Right side.

Try this first and see what happens. The next step will be to measure DCV and/or scope out the Peak LED transistors
At what voltage do the Peak LEDs light up?
 
ok ill have to take the amp and put it on the bench for that.

I have my sons football game tonight, so ill check back tomorrow.


Thanks for input jblmar. I read alot of your post on this forum,and i know you have a shop in new york. Thanks alot for your time .
 
Juanann,
You're welcome.
I too have the 300DC. It's a bit strange that both Peak LEDs light as they are independent of each other.
Try flipping the rear AC/DC switch a few times. With the power off. It may be intermittent and triggering the Peak LEDS.That's about the only thing I can think of that's common to both sides of the amp.
Try this, Turn the amp over, remove the bottom panel and play your system as before. Look at and listen to the power switch for arcing. If you don't find a problem there, it may be time to pull the peak Indicator board and check for cold solders and bad or corroded contacts.

When I first designed my fan controller I used an electro mechanical relay. The switching of the relay causes a spark that set off the Peak LEDS (Both channels).
Installing a solid state relay solved the problem.
 
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There is a small PCB on the rear of the amp containing the AC/DC switch. On the board is a 16v/10uF cap (CM03). Replace this cap, it may be the problem.
 
ok so i measured the ACV- 32.3 volts gets me 130.4 watts. thats when the peak lights our on.
alittle underrated then what im used to seeing.

i tired the switch in the back, didn't seem to matter.
next ill check the capicator CM03. i have a telohmike t-5 capicator checker.

ill check that and see.
 
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That might be normal operation of the Peak Lights. They will flash when the amp approaches clipping, not necessarily at hard clipping.
Do you have an oscilloscope to monitor the output? Without one it will be almost impossible to be certain what's going on.
Why not turn the GAIN all the way up (Clockwise) on the 300DC and use the volume control on the 3250 the 'normal' way?
At 130 watts with bass heavy music the amp(s) will produce a higher output than that for a short period (about 5ms) triggering the Peak Indicators. This is normal operation for the 300DC. The earlier 240 & 250 models would clamp these transients. The 300DC design is much better.
The Owners Manual discusses the operation of the 300DC Peak Indicator circuit in detail.
 
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I don't have an o scope, but I do want one. I'm shopping for one.
I guess I can do that. I'll turn the gain full up and leave it and use just the volume on the pre amp. Do u happen to have a copy of the owners manual.
Last time I check on the forum database I only found the service manual.
 
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