Help in Measuring RCA Voltage

[ElStevO]

Hello folks. First post. I think you have a really neat forum here and appreciate it. After reviewing some info here I have recently purchased an amp: SY-DAP2002 - 4ohm (TPA3255). I needed to get this giant NAD356BEE off my computer desk and back in the living room. That's why I bought the above amp and it is a rather strong amp. Kinda strange how strong it is really for the size. After reading, here, about the amp's 1V input design I wanted to test some RCA outputs of my audio singal (from PC) to make sure I'm feeding it what it needs and not inducing clipping. I'm new to voltmeters so, let me put that out there first. But I don't understand why I cannot get a voltage reading from an RCA that is being pushed signal from my computer and am here for help. So, Spotify is playing a song that is going from PC to amp via RCA. While song is audibly playing, I unplug the RCAs and try to measure the output. The voltmeter is on the DC setting and I have tried both the 2V setting and the 200m volt setting and I get nothing. I'm using the probes on the RCA shield and the RCA tip to try and get a reading and I get zilch. I have tried both polarities (red to RCA cable tip; black to tip/black to shield; red to shield). Sorry to come in with problems before introduction.

I have an affection for audio. I have had a LOT of amps/receivers. Went through a vintage phase. Actually kinda miss my Sansui G701. Had a lot of different setups. Have messed around with acoustic treatments. Really just enjoy my music. The current speakers being driven on my computer desk are Ascend Sierra 2s.

 

[RayDunzl]

You are measuring DC with the meter.

Music is a kind of AC, and the DC average of it approaches 0V.

Use an AC scale on the meter.

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It might be better to use a known steady test tone to measure whether or not clipping might be occurring.

Music signal is a constantly changing peak voltage, you'll just get an average on the meter using it for the test.

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Music signal vs Test Tone:

 

[ElStevO]

Thanks for the reply Ray. Still nothing. Maybe I should make a video and put it on Youtube so you can advise. It must be something simple. I'll get back to this a little later.

 

[sergeauckland]

A multimeter won't work measuring music signals, as it is designed for measuring steady mains voltages of low frequency. Music signals have such a lot of variation and the meter does a lot if averaging that you won't get anything sensible that way.

If you play a steady tone, say 400Hz at a reasonable volume, you might measure 100mV or so on the RCA outputs. You really need an oscilloscope to do what you're trying to do.

S

 

[raindance]

If it clips and you can't hear it, you've got much bigger problems.

 

[voodooless]

There can be a lot of things wrong here. The obvious ones are already covered: set the meter to AC, and use a test signal: sine @ 400 Hz should be okay.

Next check that you have the correct inputs on the meter: there is often a different set for measuring current or voltage.

Finally: how are you measuring? We’re does the red wire go? Where the black?

 

[solderdude]

Show a picture of the AC voltmeter.

 

[ElStevO]

Show a picture of the AC voltmeter.

 

[voodooless]

Next check that you have the correct inputs on the meter: there is often a different set for measuring current or voltage.

This!

 

[raindance]

You've got it set to measure current. So all you're doing is shorting out the RCA. Move the red lead to the correct terminal !!

 

[ElStevO]

Well well well....looks like somebody doesn't know how to use a voltmeter lol. I misread the manual. Thought it said that other port only went up to 200 mV, but it is 200 mA.

I measured .012 VDC and .2 VAC off the recommended 400 Hz test tone. I tried a 60hz wave and got a .9 VAC. .4 VAC on a 40 Hz. .8 VAC on a 20 Hz. The purpose in all this is I was curious what my computer is putting out the analog side because that amp I purchased is designed for 1V signal. I guess this is a bad way to test for that.

 

[LTig]

View attachment 123483

This is not sensitive enough to measure low level AC. The lowest sensitivity is 200 V AC and you need at least 20 V, better 2 V. With 200 V the readings are very imprecise.

 

[LTig]

Well well well....looks like somebody doesn't know how to use a voltmeter lol. I misread the manual. Thought it said that other port only went up to 200 mV, but it is 200 mA.

I measured .012 VDC and .2 VAC off the recommended 400 Hz test tone. I tried a 60hz wave and got a .9 VAC. .4 VAC on a 40 Hz. .8 VAC on a 20 Hz. The purpose in all this is I was curious what my computer is putting out the analog side because that amp I purchased is designed for 1V signal. I guess this is a bad way to test for that.

You're measuring current, not voltage. Set the switch 2 steps right of 'off' and plug the red cable into the middle connection ( one down compared to your photo).

 

[solderdude]

This meter won't show correct low AC voltages because of the way it is constructed (as LTig already explained) and why I asked for a picture of the meter.

It is fine for measuring 10VAC to 240VAC (when you have the red lead in the middle socket) but it will give incorrect values at anything below a few Volt. The reason is that the AC measuring setting is simply a DC meter with a single diode in it which drops about 0.5V across it so from 0 to 0.5VAC it will show nothing. When there is 1V in reality it may show 0.5V or so. Doesn't matter at 110V whether or not it shows 110 or 109.5 but it does with low AC voltages.
Also fine for measuring DC voltages, resistors and batteries. NOT for low AC voltages nor AC currents.

Get a better one. Such a better meter should have ACV settings like 2VAC, 20VAC etc..

 

[ElStevO]

Ok, got a sweet, sweet question. Condition: I play a song from my iPhone 11 via bluetooth, full volume on phone and amp, which means it should not exceed the amp's 1V signal design (right?), and output measured 100 dBA and was NOT clipping. Question: Now, let's switch over to RCAs coming from my computer to the amp, PC is at 100% volume, but the amp volume is rotated to achieve 100 dBA, would that garauntee that I am not clipping? I feel like I will have to clarify something....rolling the dice.