Hi everyone. I have a Marantz 300DC with a Marantz 2245 serving as the pre-amp. The 300DC is hooked up to a pair of JBL 240Ti's which are 8 Ohm with 89 dB sensitivity. With the gain knobs turned at the half-way points (12 o'clock) and the -20 dB meter range button pushed, the power meters are barely twitching with the volume knob on the 2245 at 10 o'clock. Is there something wrong with the power meters or am I just not listening loud enough? I live in an apartment, so I don't like to really crank the volume - but I feel, with how large the bass drivers are on the 240Ti, that they should be sucking up enough power to make the meters dance even at the -20 dB meter range engaged.
Register to hide this ad
Nyjblbob
Hooked on Horn's and Tubes. Go big or go home
Do the meters move w/o the -20db range engaged?
Based on what I observed at -20 dB, switching to -10 dB, then 0 would mean I would have to really crank up the volume to see them move, which is something I have not tried yet because it would be too loud for an apartment setting
How beefy of a resistor would it have to be?You could build a couple of 8ohm load resistors and connect them in place of the speakers. Then you can crank it up as much as you want and not disturb the neighbors.
Your amp is 152 watts/channel
You would need an 8-ohm resistor that can handle at least 200 watts if you plan on driving the amp at full power.
Here is an example from Digikey (although this one is 10% -- you may want a 5% or 1%):
There is also this type, but you probably need a heat sink to attach this to (need to look at the datasheet).
This is from the Marantz 300DC instruction manual:
Looking at the front panel it looks like the push buttons are Off, 0, -10, -20 dB, so I'm a bit confused (probably a sign error in the manual). Anyway, you should be able to drive your inefficient speakers to 1.5W with the meter range set to 0 dB. This makes some sense since you selected -20 dB and barely saw the meter moving... because it is 75W to 0dB and 150W to +3dB. I think the knob setting is the amount of attenuation added to the meters... so at the highest power output 20dB of attenuation is added to the meters so you don't peg them. Comments?
You would need an 8-ohm resistor that can handle at least 200 watts if you plan on driving the amp at full power.
Here is an example from Digikey (although this one is 10% -- you may want a 5% or 1%):
There is also this type, but you probably need a heat sink to attach this to (need to look at the datasheet).
This is from the Marantz 300DC instruction manual:
Looking at the front panel it looks like the push buttons are Off, 0, -10, -20 dB, so I'm a bit confused (probably a sign error in the manual). Anyway, you should be able to drive your inefficient speakers to 1.5W with the meter range set to 0 dB. This makes some sense since you selected -20 dB and barely saw the meter moving... because it is 75W to 0dB and 150W to +3dB. I think the knob setting is the amount of attenuation added to the meters... so at the highest power output 20dB of attenuation is added to the meters so you don't peg them. Comments?
Last edited:
Why don't you unplug your speakers and crank it?
I think you're just listening quietly.
Also really should sell the 2245 and get the matching pre, or at least a dedicated pre. The 300DC is much much different and better than the 45.
I think you're just listening quietly.
Also really should sell the 2245 and get the matching pre, or at least a dedicated pre. The 300DC is much much different and better than the 45.
Wow! Thanks for all that info! That is odd that the manual contradicts what's actually on the unit. I looked up some YouTube videos on the 300DC and there were a few videos where the person would cycle between the three meter range states, and it showed that at a constant volume, the -20 dB state showed the most movement in the meters. When the -10 dB button was engaged, there was less movement, 0 dB even less. So I'm wondering if maybe perhaps the wiring got mixed up? I know that the unit I bought was serviced in the past. But also, it really could just be that I don't listen loud enough.
Klipsch efficiencies are usually in the high 90's, right? How loud are you playing them - i.e. volume and gain knob location?
If I unplug the speakers and crank it, wouldn't that strain the amp? Due to the nature of the output being AC, it would still see a capacitive load instead of a perfect open circuit, right? I'm just basing that on my limited knowledge of electronics so not sure if entirely true or not.
I wouldn't be able to let go of my 2245 - it holds too much sentimental value. But I'm open to getting a dedicated pre. Which one was usually paired with the 170/300DCs?
With the speakers disconnected or speakers switched off, current would not be drawn from the output transistors in the main amplifier since you do not have an 8 ohm load connected. That is why amplifier power testing is performed with a high-wattage, 8 ohm power (wire wound) resistor load which is a substitute for the speaker load.
Also, from the 300DC Service Manual Alignment Procedure section:
This seems to say that the 0dB setting is used for high output and the -20dB is used for low output which is different than my previous manual excerpt and that your original post using the -20dB setting should be for low power? Who knows?
Last edited:
Interesting, maybe when the amp was serviced, some of the voltages got knocked out of spec. That could be another thing I could check out