Electrical signal experts, help me figure out this connection problem

mantis

Active Member
I'm still puzzled by this:

DAW Soundcard->marantz 2230->amp->speaker-> Good bass levels
DAW Soundcard->amp->speakers-> anemic bass levels

I can't find ANY information on such a situation, it seems nobody else notices this...

The amp input specs are:
input impedance: 50,000 ohms
input sensitivity 97mv/W

The soundcard output specs are only given as:
• Line level 8 x 1/4" TRS Jack
• Nominal output level 0dBFS = 16dBu, electronically balanced
• All outputs are useable as monitoring outputs

The 2230 specs are:
-input impedance: 100,000 ohms

So whats going on? Its an impedance problem of some sort, but I can't figure it out. Any help would be greatly appreciated, Ideally Id like to just run the damn thing straight to the amp but I can't because of the no bass problem :(
 
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The Marantz receiver/preamp probably has a loudness control that is boosting the bass, I'd suspect.

When the sound card is connected directly to the amp, you are not getting this loudness contour effect. The signal is "flat" so to speak.
 
What amp? I'm confused. Are you attempting to use the Marantz receiver as a pre-out to a seperate power amplifier?
 
The Marantz receiver/preamp probably has a loudness control that is boosting the bass, I'd suspect.

When the sound card is connected directly to the amp, you are not getting this loudness contour effect. The signal is "flat" so to speak.

no, its not "loudness" or the bass knob, and I would have reported a treble boost if that were the case.
 
no, its not "loudness" or the bass knob, and I would have reported a treble boost if that were the case.

Afaik, impedance issues typically affect the high end.

With a 50k input impedance on the amp the sound card would need to have exceptionally high output impedance to cause an issue.

The rule of thumb I've seen is a minimum of 1:10 impedance causes no issues...meaning the card would need output impedance ~5k ohms or higher to be a problem.

Positive you don't have a connection wrong causing an out-of-phase issue?
 
Afaik, impedance issues typically affect the high end.

With a 50k input impedance on the amp the sound card would need to have exceptionally high output impedance to cause an issue.

The rule of thumb I've seen is a minimum of 1:10 impedance causes no issues...meaning the card would need output impedance ~5k ohms or higher to be a problem.

Positive you don't have a connection wrong causing an out-of-phase issue?
yep, I've run them mono and they are putting out less bass for sure.
 
That input sensitivity of 97mV/W doesn't seem quite right.

The GFA-2 is 100wpc, yes?

If so, wouldn't 97mV/W mean you'd need 9.7V input for full power? Seems awfully high unless I've misplaced a decimal or something.
 
thats not it. There has got to be something fishy going on here- what does 16dbu mean anyway?!?! how can I measure the output impedance?
 
I ran a 1khz sine generator at -0.1db with the gain maxed and I measured voltage between the hot and cold and I measured 4.3 V so I'm guessing thats pretty close. Can I use this info to determine impedance?
 
Unless you have a program in your computer that allows you to adjust seperate bass & treble, Your soundcard is putting out a line level (flat) signal as mentioned above.

When using just an amplifier (no controls) connected to the soundcard, you are just amplifying the line level (flat) signal.

When using a preamp connected to an amplifier, the preamp gives you the added bass & treble control. When using a receiver or integrated amplifier, you get the options of being able to adjust the bass & treble control.

Maybe I'm wrong with what you are asking, but I have a computer program that puts just a line level output to my 1/4 inch headphone jack. With just an amplifier (no controls), it sounds like crap with no bass and tinty mids & highs. When I add an integrated, it has the controls which boosts the DB level so it sounds just great.
 
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no, this is flat for both. NO BOOSTING.

I think I figured out why... I could be wrong but I have a feeling the output impedance is really really fuggin high on this soundcard...

Tell me if I did this right.

I put out a constant 1k sine wav at -0.1dB at the max output of hte soundcard... which measured 3.9V, so I ran it through a variable resistor set at 100k ohms, and the resulting voltage measurement was 3.1V

I plugged that into the equation found here:
http://www.zen22142.zen.co.uk/Theory/inzoz.htm

so I measured 25.8k ohms output impedance is that right?!?!
 
What's the model of the soundcard in use? Generally, these use a balanced output on either a Tip-Ring-Sleeve/TRS format or on an XLR format. In both cases, this is usually about 600 ohms output impedance to drive a 600 ohm line into some other balanced inputs.

If you're running these into either the Marantz or the Adcom, then somewhere along the line the balanced is being converted to unbalanced RCA connections. How is this being done?

Cheers,

David
 
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