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The making of: The Two Towers (a 25 driver Full Range line array)
The making of: The Two Towers (a 25 driver Full Range line array)
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Old 1st March 2020, 04:48 PM   #5761
wesayso is offline wesayso  Netherlands
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The Xonar ST has a Molex input plug for power:
The making of: The Two Towers (a 25 driver Full Range line array)-st-jpg
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Old 2nd March 2020, 03:10 AM   #5762
fluid is offline fluid  Australia
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Quote:
Originally Posted by wesayso View Post
Koldby did explain it. But what I simply do not understand is why did the schematics show a 6dB gain pré-amp circuit (which is present in the real deal, not in my amp as koldby left that part out) while the amp already has 29 dB gain without it. Is this to be able to adjust the gain with plus or minus 3 dB steps, ranging from +9 dB to minus 9 dB? Something the real deal has as well according to its specs.
The reason the preamp section is there is to cope with a wide variety of sources that put out very little voltage in comparison to a 2V DAC. Kolby built it for a 2V DAC no need for a preamp. Most consumer sources run at -10dBv, then there is the fairly standard 0dBu and the professional +4dBu here is a shot from the sengelpiel calculator showing the RMS and peak values of these standards. We are talking 0.3V to 1.2V RMS. This is why a preamp with gain is needed if you want to get maximum power out of a source with that sort of voltage. These are not unusual so commercial manufacturers allow for them.

The making of: The Two Towers (a 25 driver Full Range line array)-voltage-comparison-png

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Originally Posted by mlee View Post
Regarding amplifier input you only need to know 1 parameter, amp gain. From there you can calculate the required input voltage for required output wattage.

Use maximum wattage required, calculate voltage then use the gain factor of amp to divide that voltage. This will give you the input voltage required to drive the amp to that wattage. Assuming the amp can supply this wattage.

P = (V*V)/R to get amplifier voltage, V. Gain = 20*(log)(V/Vo) = amplifer gain. Calculate Vo. I'd get a dac that can go slightly higher than Vo just to be safe, sometimes when DAC reaches its maximum Vo things get dodgy, depends on the DAC.
This is the same calculation included in the Hypex datasheet, and the answer to it does not make how much single ended voltage is needed any clearer, as the Hypex datasheet say this is differential voltage, so perhaps they are using a combiner with gain to keep the voltage the same after conversion to single ended or maybe they have moved to differential amplification the datasheet is not clear, they use the terminology Hot and Cold to describe the output which is often used with differential signals. So perhaps it does need 2.35V single ended to reach full power but for a different reason.

Without knowing the input stage of the amp or measuring it is hard to guess. Asking Hypex directly would probably clear it up.

Use this calculation for your Goldmund.

350W output at 8 Ohms load needs 52.9V (sqrt of 350x8)
Amp has 29dB gain this is a factor of 28.18

52.9 / 28.18 = 1.877 V Input needed to produce 350W with an 8 ohm load

With a 4 Ohm load it is only 1.32V to produce the same power. The difference is the current needs to be higher to produce the same power with a lower voltage.

Hypex 500W 4 Ohms (sqrt 500x4) = 44.72V / 19.05 = 2.347V same as 2.35V on the datasheet.
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Old 2nd March 2020, 07:44 AM   #5763
fluid is offline fluid  Australia
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Another thing to put it in perspective for the Goldmund is that reducing 2V by -0.75dB makes the voltage 1.82V so it is very close to making 350W at 0dBFs with an 8 ohm load.

This is another reason why the 6dB of preamp/buffer gain is not a bad idea as it allows the reduction in digital level to give some room for intersample overs and still let the amp produce all it can when needed.
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Old 2nd March 2020, 07:49 AM   #5764
wesayso is offline wesayso  Netherlands
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While leaving room for overshoots as stated in their specs?
Quote:
Originally Posted by Goldmund specs
Power
Nominal power : 350 W RMS (2 - 8 Ohms), 175 W RMS (1 - 16 Ohms).
Instantaneous power (8 Ohms) : > 400 W
Maximum instantaneous power : 1000 W
Maximum voltage swing : 70 V peak.
Maximum current swing : 10 A peak.
That's basically the whole idea, as gain is added in a buffer stage, the same gain number (plus the -3 dB I was using) is reduced inside JRiver.
That's exactly what I'm doing with the Atom pré-amp, -6 dB inside JRiver, +6 dB added by the Atom.
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Last edited by wesayso; 2nd March 2020 at 07:53 AM.
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Old 2nd March 2020, 08:07 AM   #5765
fluid is offline fluid  Australia
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Originally Posted by nc535 View Post
I thought it interesting that the D50 performed best on battery power since a switching power supply would otherwise be a primary source of noise. I hope its ability to run off a single 5V supply (USB) doesn't mean its op amps don't have the customary +/-15V supplies.
The D50 comes with a power adapter but it runs at +/-5 V, so no it does not have the voltage swing of 15V opamps but it is using the mobile version of 9038 chip, as it is single ended there is more than enough voltage swing.

Quote:
Originally Posted by nc535 View Post
Hi fluid:
What is your opinion as to dynamic headroom and how does that figure into the discussion?
I'm unsure if you are referring to amplifiers or DAC's now.


Quote:
Originally Posted by nc535 View Post
I guess I've ended up agreeing with your comment. I'm obviously biased in favor of balanced. Its kept me out of trouble more than once and I have an ART Clean Box in daily use between the RCA sub output from an AV RCVR and a pro amp.
Try using a pseudo balanced cable and getting rid of the Clean Box. Unless it is very well designed or you have significant noise problems the result will probably be better or equivalent without it. The balanced receiver by itself can still deliver 40dB of common mode rejection when pseudo balanced instead of 90dB for a full balanced connection. In a home over a short distance is 90dB needed?

If you have a truly differential DAC which most of the best chips are, then to get the best performance out of it a high quality I/V stage is needed the output of this is inherently differential and maintaining that all the way to the amplifier input makes a whole lot of sense as the only thing you need is a balanced connector and an amp with a balanced receiver built in or added.

To convert that differential output back to single ended another opamp combiner is needed inside the DAC which will reduce performance slightly.

Some DAC's built to a budget don't have the full blown I/V stage and do it all with a single opamp which gives a single ended output.

So in my mind at home using balanced or single ended is more about the source you have as it makes sense to use it as is. Adding extra balancing and unbalancing stages makes no sense to me unless noise is an issue.

If the devices are inherently balanced then it makes no sense to use them single ended either
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Old 2nd March 2020, 08:09 AM   #5766
fluid is offline fluid  Australia
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Quote:
Originally Posted by wesayso View Post
While leaving room for overshoots as stated in their specs?


That's basically the whole idea, as gain is added in a buffer stage, the same gain number (plus the -3 dB I was using) is reduced inside JRiver.
That's exactly what I'm doing with the Atom pré-amp, -6 dB inside JRiver, +6 dB added by the Atom.
The power available over the rated power would depend on the the main voltage rails and how much they can supply, if the rails are high enough then those amounts are realistic. Those specs suggest it is current limited rather than voltage limited so lighter loads would let it put out more power.
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Old 2nd March 2020, 03:58 PM   #5767
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Quote:
Originally Posted by fluid View Post
The D50 comes with a power adapter but it runs at +/-5 V, so no it does not have the voltage swing of 15V opamps but it is using the mobile version of 9038 chip, as it is single ended there is more than enough voltage swing.

I'm unsure if you are referring to amplifiers or DAC's now.

If you have a truly differential DAC which most of the best chips are, then to get the best performance out of it a high quality I/V stage is needed the output of this is inherently differential and maintaining that all the way to the amplifier input makes a whole lot of sense as the only thing you need is a balanced connector and an amp with a balanced receiver built in or added.

To convert that differential output back to single ended another opamp combiner is needed inside the DAC which will reduce performance slightly.

Some DAC's built to a budget don't have the full blown I/V stage and do it all with a single opamp which gives a single ended output.

So in my mind at home using balanced or single ended is more about the source you have as it makes sense to use it as is. Adding extra balancing and unbalancing stages makes no sense to me unless noise is an issue.

If the devices are inherently balanced then it makes no sense to use them single ended either
Does it matter if I was referring to amplifiers or DACs? The discussion about precisely how much voltage was needed to drive the Goldmund to its full output was beating with the discussion about headroom. I wanted to know where you stood on the latter. As far as the gain issue goes, I would be interested to know if the absolute peak value out of the DAC is sufficient to drive the Goldmund to its 1000W instantaneous spec rating. Ideally gains would be set so that DAC and Amp would hit their absolute peaks at same input level. Else one distorts before the other and there would be incremental improvement if gain were changed so as to lessen the distortion at the earliest distorting stage.

This brings up the fundamental question I still have after all this time:
Is the e.g. 2V RMS, 5.76 Vp-p rating a maximum undistorted output such that gains must be scaled so peaks never attempt to exceed it?

Since music doesn't have a precisely defined crest factor, adequacy of headroom is always at issue unless we resort to overkill (and maybe even then depending on level of paranoia). That is why I like fully balanced DACs and interconnects and high voltage complementary op amp power supplies, and oversized power amps, and so on.

Is it necessary to go to this extreme? Probably not but I do recall (but haven't been able to find) a post by Tom Danley back in the day where he discussed dynamics and stated the true peak to average ratio for music was a lot more than the 8-12 db crest factor typically quoted for music and systems that provided extra headroom would be perceived as more dynamic. One of the things that distinguish a pro-audio Synergy used in the home is huge amount of headroom. Arrays are similar above their excursion limits and below where combing sets in.

You've convinced me on balanced vs single ended. I could/should have simply cut the shield return inside the XLR end of my RCA to XLR cable (hindsight). I'll do that on the odd interconnect if the need arises in the future but I will keep the bulk of my system as balanced and ground isolated as I can.
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Old 2nd March 2020, 06:09 PM   #5768
wesayso is offline wesayso  Netherlands
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I remember reading that from Tom, wasn't there an old thread on the specifics of what makes a speaker sound dynamic?

Much of my exercise here is just that, trying to create headroom wherever possible. It is why I got a Hypex NC500MP instead of the NC250MP.
It is why I was pretty anxious to see what that Goldmund could do having way more power than the Pioneer it replaced. It blew my mind in our first test, but I did struggle to find that exact ingredient again until recently.

The magic with the arrays is in the midrange, which is where most music lives. If the gain structure is close to right, it can sound clean and feel like there's no limit, effortless. Heck, turning it up does not even get noticed at first if it is a clean sound. Unless you get a reference, for instance trying to talk to the one sitting next to you.

For quite a while I had quite good sound, but less of that effortless feel. This made me search for the reason why, first in processing and more recently in the other parts of the chain.

I guess I would favour overkill as well. Even if we use a fraction of a watt most of the time, it's good to have lots on tap.
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Old 2nd March 2020, 07:20 PM   #5769
wesayso is offline wesayso  Netherlands
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A Test. How much Voltage (power) do your speakers need?

Here is some info on his point of view... I's not the one I was looking for but interesting nonetheless.

I'll refrain from quoting, just follow the link, Tom has been active on that thread. And he has shared his own recordings often to demonstrate dynamic range in recordings and what they can do.
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Old 2nd March 2020, 08:27 PM   #5770
fluid is offline fluid  Australia
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Quote:
Originally Posted by nc535 View Post
Does it matter if I was referring to amplifiers or DACs? The discussion about precisely how much voltage was needed to drive the Goldmund to its full output was beating with the discussion about headroom. I wanted to know where you stood on the latter. As far as the gain issue goes, I would be interested to know if the absolute peak value out of the DAC is sufficient to drive the Goldmund to its 1000W instantaneous spec rating. Ideally gains would be set so that DAC and Amp would hit their absolute peaks at same input level. Else one distorts before the other and there would be incremental improvement if gain were changed so as to lessen the distortion at the earliest distorting stage.

This brings up the fundamental question I still have after all this time:
Is the e.g. 2V RMS, 5.76 Vp-p rating a maximum undistorted output such that gains must be scaled so peaks never attempt to exceed it?

Since music doesn't have a precisely defined crest factor, adequacy of headroom is always at issue unless we resort to overkill (and maybe even then depending on level of paranoia). That is why I like fully balanced DACs and interconnects and high voltage complementary op amp power supplies, and oversized power amps, and so on.

Is it necessary to go to this extreme? Probably not but I do recall (but haven't been able to find) a post by Tom Danley back in the day where he discussed dynamics and stated the true peak to average ratio for music was a lot more than the 8-12 db crest factor typically quoted for music and systems that provided extra headroom would be perceived as more dynamic. One of the things that distinguish a pro-audio Synergy used in the home is huge amount of headroom. Arrays are similar above their excursion limits and below where combing sets in.

You've convinced me on balanced vs single ended. I could/should have simply cut the shield return inside the XLR end of my RCA to XLR cable (hindsight). I'll do that on the odd interconnect if the need arises in the future but I will keep the bulk of my system as balanced and ground isolated as I can.
Yes I think the difference between DAC's and amps is significant in regards to headroom. I typed most of what I am about to write before then deleted it as I thought the discussion was confusing enough at that point but as you asked...

In a digital system there is the theoretical peak of 0dBFS. Nothing should exceed that level to avoid digital clipping which is not a nice sound, sounds like the drivers suspension is broken if there is enough of it.

Due to bad mastering intentionally or otherwise signals can be generated and encoded that exceed 0dBFS. Usually this is the issue of intersample peaks where the interpolation of two samples allows there to be a peak in between them when converted back to analogue. Some DAC's handle this quite well most do not. The simmple solution is to add between 2 and 4dB of digital attenuation in the DAC or before and this problem goes away.

The reason I say there is a difference in headroom is because a digital system should be run as close to it's maximum level as can be to maximise resolution. This is less of an issue in 24 and 32 bit converters because they have inbuilt headroom digitally over what they can realistically reproduce in analogue terms. In the Audioscience review and measurements you will see a linearity figure in bits quoted. The best DAC's are around 20 bit some nudging towards 21 bits. That is the limit of the analogue resolution they can provide and this figure has not improved significantly over time as it is set ultimately by the thermal noise of the resistors in the circuit.

So between 4 and 12 bits can be lost in digital terms without affecting the output.

The second factor that determines the headroom requirement is whether the system is a pure replay system where the peak level can be set or whether it is live or somewhat uncontrolled where performers or inputs can vary beyond the control of the engineer.

Wesasyo and I are using volume levelling in Jriver that he explained well before. The analysis of the files will determine peak and average levels and will work as a sort of intelligent software limiter so the average levels are well controlled but the ultimate peak could still be somewhat variable so the 4 to 10dB digital reduction is sensible. making this back up in analogue gain or adding even more allows the amplifier to produce more power when needed but there will be limits to how much gain makes sense.

So then we get to the question of whether an amplifier can produce enough power to deal with the peak or have enough input voltage to get there anyway. And whether that is going to be a peak or RMS value. I would suggest that when describing instantaneous power that would prefer to peak voltage.

Using the Goldmund specs as an example for 1000W in 8 ohms 89 volts needs to be produced which would seem to exceed the 70V rails by more than is realistic, so 1000W in 8 ohms seems unlikely.

To get 89 volts with 29dB of gain would need 3.17 V which is more than the peak of 2.828 volts that could come from 2 VRMS.

600W in 8 ohms is 69 volts so that would seem realistic which could be achieved with a peak input voltage of 2.45V, which is available from the 2VRMS DAC.

So headroom in an amplifier makes sense too, how much depends on the rest of the system.
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