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Can someone explain how amps and preamps/dacs function as a unit please.

direstraitsfan98

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I'm a complete noob and I'm trying to understand something.

I have a dedicated preamp/line stage that I may be looking to replace it with a dac with a built in preamp. It (my current preamp) has got a max output of 16V/8V on it's balanced/unbalanced outputs. I use balanced. My amp has a input sensitivity of 4.2V.

Earlier today, I was playing some classical music and I noticed a couple of things. One, I was seeing peaks on the VU meters just slightly above 45W. So I assume I was using possibly up to 100W of power. Probably closer to 50-60W I suppose. Can't be 100% sure because I wasn't listening 1 meter away, and the speakers specs are 94dB sensitive. Not sure how much volume loss exactly I get listening 8 feet away and my room size.

Anyway, I was thinking of getting a DAC with a volume control and feed my amplifier like that direct. With a voltage input sensitivity of 4.2V, my amp needs 4.2V to get its max rated power, correct? What makes me very confused is when observing the power levels of my amp earlier today, (and, my ears, to make sure I was comfortable with the musical peaks) I had my preamp set to 50 percent. The volume readout is set as a percentage.

If the max output of the preamp is 16V, and the volume was set to 50%, that obviously means the preamp wasn't feeding my amp 8V, right? Wouldn't 4.2V basically blow up my speakers? They're only rated to 300W RMS. And they're 94dB sensitive, so feeding them the amplifiers max rated output of 450W I think would either cause instant deafness, or just blow them up.

I'm sorry if I'm not asking the right questions, approaching this wrong, or not providing enough information. I just want to know if a DAC with a preamp built in would be a feasible solution for me. A lot of the preamps I was looking at have a output of 4V, and I was worried that they won't work well.
 

RayDunzl

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Hmm...

94dB speaker sensitivity
Assume 8 ohms so, @1watt

If 100W, so 114dB SPL
If two speakers make it 117 to 120dB...

Were you wearing hearing protection?

Maybe you are being intentionally vague, but listing the gear you are talking about may be a good idea.
 
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direstraitsfan98

direstraitsfan98

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Hmm...

94dB speaker sensitivity
Assume 8 ohms so, @1watt

If 100W, so 114dB SPL
If two speakers make it 117 to 120dB...

Were you wearing hearing protection?

Maybe you are being intentionally vague, but listing the gear you are talking about may be a good idea.
I don't think it was 100W, probably closer to 50-60W. I don't know how accurate the big blue meters are. I didn't need hearing protection, it was just very brief transiets during classical piece where it swung that high in volume.

I didn't think I needed to explain the chain because regardless of what it was, I think the whole concept behind how the dac preamp stage can drive the amp could be explained just using math. I want to understand that math. The DAC I had my eyes on was the Bricasti M1, but for various reasons I don't think I'll be using anything unless it has a good analog volume pot. I believe the Bricasti has a digital potentiometer. I'm sure if implemented well its great, but I'd rather have a real one. Perhaps that is another question one of you guys could answer to me, if there are any dacs with genuine analog volume implementations, and if that is something I should even give a hoot about.

Anyway, this is all just elementary. I would just like to know the science behind it all. Replacing the preamp is just something I'm toying with right now. I might not even change anything because I'm really happy with the sound. Honest truth of the matter is one of my friends is pushing me to at least consider this change, so I'm doing my best to explore it.

Gears:

Source - Computer (usb direct to the dac in preamp) > McIntosh C53 preamp > McIntosh MC462 power amp > JBL Synthesis 4367 speakers. Room is 10x14, I sit 8 feet away, speakers are 3 feet into my room. I find bass sounds best like this.

Are you running a big McIntosh amp here?
Ye, MC462 amp. Input sensitivity of 4.2V. I did some of my own research and it seems like voltage isn't linear, its logarithmic. I guess I understand that. 2V output on the preamp isn't going to be half the power of 4V. But what really threw me off was the digital volume display on the McIntosh pre, which reads as a percentage. Seeing a percentage just makes me identify that as a linear scale, not a logarithmic. I think that is why I'm so confused. I emailed McIntosh for clarification and I'll report back here what they tell me if you guys are interested.
 
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wwenze

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I thought VU meters usually measure in dB. So halfway mark equals half the dB.

EDIT: Ok wait that sounds weird since dB is a signed value. That's like saying -2 deg C is twice as cold as -1 deg C.
 

Doodski

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Hmmz... Running a DAC straight into the power amp means no pre-amp EQ. That's maybe a bad thing. :D

McIntosh C53 preamp , "Tone controls include an 8-band analog equalizer; each band can be adjusted ± 12dB."

As for the 50% volume indication. It doesn't really tell us what the power transfer is. I'm guessing it's not a real number because if you did put 50% of the output voltage into the amp the amp output would have been max like you said. When dealing with volume controls and indicators it's sometimes not a real indication. If you want a straight DAC signal into the amp then shoot for the req'd input voltage at the amp and watch the output impedance of the pre and the input impedance of the amp to ensure the power transfer is good and there is enough signal at the amp to achieve clipping.
 
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direstraitsfan98

direstraitsfan98

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I thought VU meters usually measure in dB. So halfway mark equals half the dB.
I'm not even sure how it works exactly but it looks like top of the bar reads watts and bottom is in dB. I should read the manual...

Hmmz... Running a DAC straight into the power amp means no pre-amp EQ. That's maybe a bad thing. :D

McIntosh C53 preamp , "Tone controls include an 8-band analog equalizer; each band can be adjusted ± 12dB."

As for the 50% volume indication. It doesn't really tell us what the power transfer is. I'm guessing it's not a real number because if you did put 50% of the output voltage into the amp the amp output would have been max like you said. When dealing with volume controls and indicators it's sometimes not a real indication. If you want a straight DAC signal into the amp then shoot for the req'd input voltage at the amp and watch the output impedance of the pre and the input impedance of the amp to ensure the power transfer is good and there is enough signal at the amp to achieve clipping.
Tone controls shall never be used! I tried them briefly. They aren't completely offensive like the tone controls in my previous preamp, the Akitika PR-101. They seem to be well implemented, but I will bypass them always. I'm also aware that there is a built in roll off under 15hz with this preamp, for turntables, I think. An Itailian hifi magazine mentioned this. I don't think its relevant for me, but for anyone who wants to use the preouts on the C53 for their subs, its something to consider.

I have a feeling that the numbers I am seeing on the digital display are actually a complex sum of a lot of computer controlled stuff going on behind the scenes. The description of how the digital volume control in this preamp is kind of hard to wrap my head around. I guess it doesn't really matter how/why it works per se. I'm sure someone who understands the math will interject at some point and explain away.
 
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Doodski

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This isn't your grandpas old analogue McIntosh that's for sure. So you want to get something simpler, less digital and not software oriented?
 
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direstraitsfan98

direstraitsfan98

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This isn't your grandpas old analogue McIntosh that's for sure. So you want to get something simpler, less digital and not software oriented?
Sorry for deleting that post, I think it was just marketing fluff and wasn't actually relevant to the topic actually. But yeah. What do I want? I don't know. I'm just shooting the breeze right now. Do I want simpler? Yes, probably. I don't think my current setup is even complicated, however. Less digital and software orientated? Maybe. I don't know. If my friend who is pushing me to dump the Mac preamp is any indication, I should throw this thing in the garbage...

This is a complicated subject. I think it comes down to is how well implemented each design is. There are pros and cons for anything. Just because something is more digital doesn't mean its bad, and software you are obviously at the mercy of the programmers skill on implementing the software and integrating on a hardware level. I think a good example of digital volume control done right is certain computer software who's name is escaping me right now apparently has very good digital volume control. I see no reason why a DAC couldn't have their own (complicated?) mathematical formulas used to control the volume digitally. I wonder if the Bricasti M1 is one of those. I've read a lot of (subjective) opinions on other forums with discussions of various dacs that will rob you of bass response, soundstage, etc, because their digital volume controls are poorly implemented.
 

Doodski

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You're making sense. Keep your wants and needs in check. You want a DAC, need a DAC, don't need tone controls and need a volume control. That's pretty straightforward. You might as well get some DAC that's integrated with a pre output and be done with it. Something with a balanced output. There's a wide selection available. You live in a good time for DACS :D You need to make your mind up while you can still return the McIntosh pre amp.
 

solderdude

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It (my current preamp) has got a max output of 16Von it's balanced outputs. I use balanced. My amp has a input sensitivity of 4.2V.

This merely says something about the volpot position in the end.

You can perfecly drive a 4.2V input amp (max output power) with a 16V output pre-amp. In fact it is preferred.
It would be worse if you connect a pre-amp with say 2V output to a 4V input amp.

Reasoning: A pre with 2V out will clip the signal before the power amp does at a lower than expected level. Possible damage to tweeter.
A pre with 4V out is fine because both will clip at the same time (max output power which you should not exceed because... clipping
A pre with 16V out will do the same as the 4V out preamp. The power amp will do the clipping (while the pre delivers excellent signal)
No need to lower the output voltage as most amplifiers will not be damaged by a too high input voltage. Remember your power amp clips and you will hear this.

Never use the max output level of a pre-amp as a power limiter when the signal can clip !
Clipping destroys more tweeters than too much (not clipped) input power.

I don't think it was 100W, probably closer to 50-60W. I don't know how accurate the big blue meters are. I didn't need hearing protection, it was just very brief transiets during classical piece where it swung that high in volume.

No need to worry about peaks in music. 60W or 100W doesn't really matter. That is 60W clipped is MUCH worse than 100W not clipped !
In your case there is no clipping. NO need to worry about peak levels in your case unless max levels of the amp are indicated or you hear distortion.

. 2V output on the preamp isn't going to be half the power of 4V.

A doubling of voltage is a quadrupling of output power (= 6dB) and this is not a doubling of perceived loudness but a clear increase.



My advice: Only buy another pre-amp if YOU feel the need for it, for whatever reason you deem fit. Never buy something because someone else feels you should unless he has compelling technical reasons.

Are you happy with the sound ? Don't need different or more functionality ? then you can keep using the current stuff unless you want to change stuff because of afformentioned reasons or just because you want something different.
 
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Soniclife

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If the max output of the preamp is 16V, and the volume was set to 50%, that obviously means the preamp wasn't feeding my amp 8V, right?
My guess is they are displaying the volume in the same way an analogue would be read, so 50% is half a turn, as most pre-amps would use a log pot that does not tell you much about the output voltage. Think of a exponential graph, the x axis would be how much the volume know is turned, the y axis would be the output voltage.

The RMS DAC would give you the DAC, preamp, adjustable output levels, tone controls and remote control, if this the sort of thing you were thinking about?
 

nm4711

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This merely says something about the volpot position in the end.

You can perfecly drive a 4.2V input amp (max output power) with a 16V output pre-amp. In fact it is preferred.
It would be worse if you connect a pre-amp with say 2V output to a 4V input amp.

Reasoning: A pre with 2V out will clip the signal before the power amp does at a lower than expected level. Possible damage to tweeter.
A pre with 4V out is fine because both will clip at the same time (max output power which you should not exceed because... clipping
A pre with 16V out will do the same as the 4V out preamp. The power amp will do the clipping (while the pre delivers excellent signal)
No need to lower the output voltage as most amplifiers will not be damaged by a too high input voltage. Remember your power amp clips and you will hear this.

Never use the max output level of a pre-amp as a power limiter when the signal can clip !
Clipping destroys more tweeters than too much (not clipped) input power.



No need to worry about peaks in music. 60W or 100W doesn't really matter. That is 60W clipped is MUCH worse than 100W not clipped !
In your case there is no clipping. NO need to worry about peak levels in your case unless max levels of the amp are indicated or you hear distortion.



A doubling of voltage is a quadrupling of output power (= 6dB) and this is not a doubling of perceived loudness but a clear increase.



My advice: Only buy another pre-amp if YOU feel the need for it, for whatever reason you deem fit. Never buy something because someone else feels you should unless he has compelling technical reasons.

Are you happy with the sound ? Don't need different or more functionality ? then you can keep using the current stuff unless you want to change stuff because of afformentioned reasons or just because you want something different.

+1

Another reason I can think of is digital stored music with a lot of headroom. With this music you will never get the power out of your amp, if your DACs output matches the amps sensitivity, unless you apply gain in the digital domain, wich could cause clipping of the DAC in songs without this headroom.
Or if you do some DSP stuff you maybe also need some headroom in your analog domain.

So yeah, I would also keep this headroom.
 

Frank Dernie

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A lot of well recorded classical music has the average level very low to allow the peaks to be real and without compression.
It is almost the opposite of loudness wars in pop music.
I find that some of my best classical recordings need a volume control setting 10 to 20 dB higher than I listen to pop music but the crescendi are realistic rather than crushed.
The level meters are around -20 to -40 dB a lot of the time, whereas with most pop recordings they vary from 0dB to -10dB (so much for needing a SINAD of 120dB!)
 

briskly

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Clipping destroys more tweeters than too much (not clipped) input power.
I have seen this assertion many times but never seen it tested. I find it difficult to believe.
Suppose you have a square wave, which has less dynamic range and more HF power than any other truncated waveform. The power of each harmonic rapidly converges to zero (1 watt, 1/9, 1/25, 1/49, 1/81, . . .) Tweeters are often much more sensitive and efficient than woofers, especially when horn-loaded(waveguide). A resistor network and highpass filter are used to attenuate the tweeter response in general and particularly reduces the input power of the strongest first few overtones.
 
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LTig

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I have seen assertion this many times but never seen it tested. I find it difficult to believe.
Suppose you have a square wave, which has less dynamic range and more HF power than any other truncated waveform. The power of each harmonic rapidly converges to zero (1 watt, 1/9, 1/25, 1/49, 1/81, . . .) Tweeters are often much more sensitive and efficient than woofers, especially when horn-loaded(waveguide). A resistor network and highpass filter are used to attenuate the tweeter response in general and particularly reduces the input power of the strongest first few overtones.
In the 70's I've seen several fried tweeters in bigger bookshelf 3-way speakers after abuse in a private rock disko when driven by insufficient powerfull (< 100W) stereo amplifiers.
 
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In the 70's I've seen several fried tweeters in bigger bookshelf 3-way speakers after abuse in a private rock disko when driven by insufficient powerfull (< 100W) stereo amplifiers.
The key word there being "abuse."
If a high-power amplifier were substituted and the system driven at the same SPL the tweeters would have fried just the same. (More than likely.)

Dave.
 
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