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Direct DAC to amp & input gain controls.

Nathan_A

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I'm currently playing around with being entirely preamp-less by running a Topping DX3 Pro (v2) in "preamp" mode direct into my Yamaha MX-1 power amplifier.

The input sensitivity of the MX-1 is 1.46V 20k Ohms. The DX3 Pro can easily drive the amp into clipping it seems like considering the 2V output it provides. Currently with this setup I tend to have to run the DX3 Pro at between -45 and -32 db on the digital volume control.

However, the MX-1 has input level controls per channel on the back. Yamaha states that the preference is to run them all the way at the maximum, but I'm wondering if I should trim them down a bit so that the DX3 Pro is operating more between -20 and -5 db on its volume control? Is there any benefit on either end (the DAC or the AMP) to reducing the amp's input sensitivity?

As a complete aside, I was previously running a D50s in the system, and it had some clear benefits that I don't quite understand.

#1 it sounded better than the DX3 Pro. Like the noise floor was lower or something. At quieter volumes everything was clearer on the D50s, and at louder volumes the D50s was less "fatiguing".

#2 the DX3 Pro sends a pop to my amp/speakers when it goes into standby, which concerns me, so I just leave it on 100% of the time to avoid this. The D50s didn't exhibit this behavior.

I moved the D50s back to headphone duty because its screen is way too small to read the volume numbers from several feet away on the couch and it was driving my wife nuts not to have a quick understandable visual indicator, and the DX3 Pro's volume level display is nice and big and clear. So, the DX3 Pro had to go into the main system.
 

Blumlein 88

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I'd probably turn the Yamaha controls to where you mentioned. So that the DX3 is running between -5db and -20 db most of the time. If nothing else, it would reduce the pop thru your system if you did turn the DX3 0ff/on.
 
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Nathan_A

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I'd probably turn the Yamaha controls to where you mentioned. So that the DX3 is running between -5db and -20 db most of the time. If nothing else, it would reduce the pop thru your system if you did turn the DX3 0ff/on.
Any strategies for level matching the input gain controls of the amp other than test tones and an SPL meter? Is there a safe way to do it electrically with a multimeter or something?
 

Panelhead

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You could use REW in RTA mode. Has a signal generator too.
REW is free.
 
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Nathan_A

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Should I expect any negative effects from using the attenuation on the amplifier? HF roll-off, increased distortion, etc.? The input level controls seem like they're very basic, and they're not stepped, so without looking at the service manual I expect they're just little pots on the amp inputs.
 

Blumlein 88

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Any strategies for level matching the input gain controls of the amp other than test tones and an SPL meter? Is there a safe way to do it electrically with a multimeter or something?

Use test tones and measure at the speaker terminals.

Pick -32 db on the DAC. Send a -20 db test tone at 1 khz thru, and measure at the terminals. This is your target voltage.

Turn the pots on the amp all the way down. Raise the DAC to -5 db. Send the same -20 db test tone thru, and raise the amp pots until you get target voltage at the speaker terminals.

Now if this results in the pots being turned way, way down on the amp, you can reduce the DAC to -10 db or -12 db, and raise the pots on the amp back up until you get back to your target voltage. This should be a good workable range.
@Nathan_A
 
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Nathan_A

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@Blumlein 88 I must be doing something wrong, or it's possible my multi-meter isn't sensitive enough.

I ran the 1khz tone through the DAC, left my speakers connected (since the meter won't present a load on its own, and thus the amp won't do anything), set the meter to 200V AC (the lowest AC limit it supports), and tried to take readings off the exposed part of the terminal. The meter readings didn't really budge beyond what they normally bounce around at when poking things before they stabilize.
 

Doodski

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@Blumlein 88 I must be doing something wrong, or it's possible my multi-meter isn't sensitive enough.

I ran the 1khz tone through the DAC, left my speakers connected (since the meter won't present a load on its own, and thus the amp won't do anything), set the meter to 200V AC (the lowest AC limit it supports), and tried to take readings off the exposed part of the terminal. The meter readings didn't really budge beyond what they normally bounce around at when poking things before they stabilize.
The meter frequency response and sensitivity might be at play here. Did you check the spec on the meter frequency response?
 

Blumlein 88

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The meter frequency response and sensitivity might be at play here. Did you check the spec on the meter frequency response?
It wouldn't matter for level matching. Even if a meter were down say 5.4 db at 1 khz, it will be down that amount for all the measurements. So matching the meter result will work just fine. In this case we just want the same level in both channels.

Most even very cheap meters are good for a khz or two.
 

Blumlein 88

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@Blumlein 88 I must be doing something wrong, or it's possible my multi-meter isn't sensitive enough.

I ran the 1khz tone through the DAC, left my speakers connected (since the meter won't present a load on its own, and thus the amp won't do anything), set the meter to 200V AC (the lowest AC limit it supports), and tried to take readings off the exposed part of the terminal. The meter readings didn't really budge beyond what they normally bounce around at when poking things before they stabilize.
Well you probably are looking at a handful of volts. So 200 v AC is too high a scale to be useful. Let me see what else I can come up with. Do you have a smart phone with a sound level meter app on it?
 
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Nathan_A

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The multimeter I keep around the house for handyman-esque tasks is very cheap. I also have an old Radio Shack analog SPL meter that I used to use for calibrating my home theater years ago. I have a better multimeter in storage I am going to try. I can adjust the input levels using the SPL meter with pinknoise tones, but it's... less precise, to put it mildly.
 

Blumlein 88

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The multimeter I keep around the house for handyman-esque tasks is very cheap. I also have an old Radio Shack analog SPL meter that I used to use for calibrating my home theater years ago. I have a better multimeter in storage I am going to try. I can adjust the input levels using the SPL meter with pinknoise tones, but it's... less precise, to put it mildly.
The better multimeter would work. It just needs a scale that is 20 v AC or lower. You are probably only going to see a volt or two at the speaker terminals at these reduced levels. You could use a higher level test tone to get voltage up a little near 10 volts say. But it will be pretty loud and be careful not to blow anything up.

You could use pink noise, but it will bounce around. That Rad Shack meter will do fine. Put it on A wtd, and slow response while using with pink noise.

Same procedure. Dac at -32 db measure each channel individually. That is your target spl. Set amp pots all the way to minimum. Set DAC to -5 db. Bring up pots till you hit target SPL.

You likely could balance channels a bit better once you have it close. Play pink noise thru both channels and tweak the volume pot on one channel until the pink noise seems to come from a spot dead center between the speakers.
 
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Nathan_A

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@Blumlein 88 I was finally able to follow the procedure you originally outlined. I picked up a better multimeter, some banana to alligator cables, and some 100W 8Ohm resistors to act as a dummy load. I was able to correct a minor input level imbalance as adjust the amp input level down to allow using the DAC preout at between -10 and -30 depending on content, time of day, and sleeping status of children.

Thanks a bunch for the advice.
 

Blumlein 88

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@Blumlein 88 I was finally able to follow the procedure you originally outlined. I picked up a better multimeter, some banana to alligator cables, and some 100W 8Ohm resistors to act as a dummy load. I was able to correct a minor input level imbalance as adjust the amp input level down to allow using the DAC preout at between -10 and -30 depending on content, time of day, and sleeping status of children.

Thanks a bunch for the advice.
Glad you were able to get it working the way you wanted.
 
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