Dynamic Headroom: Where is the limit? - Page 8 - diyAudio
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Old 24th July 2002, 05:05 PM   #71
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Hmmm. Its alot to read but I suspect you have misinterpreted what is being calculated and what is resultant on the media. We agree that for all practical purposes there is a maximum "raw signal" of around 90dB so it is entirely possible that the numbers you are quoting are "pre-production" and not what is on the final recording. I think what is being described is the process of setting a maximum spL of 103dB with an 83dB sound floor set to 0dB. The real question now is: What is actually meant by the "peak to average" reference if not to describe the dynamic range?
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Old 24th July 2002, 05:26 PM   #72
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Nania,

The article on level has a good explenation of "peak-to-average". Also at the end of the article on compression, there is a list of recordings that Katz considers to be exceptional for their dynamic quality. Each of these recording were recorded with 0VU greater then 75db.

Since we agree on the headroom limit of less then 20db, the question still remains, how far below 0VU does the recorded music extend? My guess is somewhere between you and I.

The link to Stereophile give an indication of this, but I must admit, the recording was not through a mixer and it was only a single note.

I, like you was hoping that this was a more important issue to others. I still believe it is.

Rodd Yamashita
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Old 24th July 2002, 06:35 PM   #73
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roddyama
Did you notice on the list of recommended CD's the monitor gain number? Could this be the recommended minimum spL to hear the whole dynamic range or the gain required above the ambient noise?
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Old 25th July 2002, 02:50 AM   #74
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Nania,

I believe that the "monitor gain" setting is the 0DBVU setting of the monitor during the recording process. That would be set at a level the same number of db above the noise floor. The actual dynamic range would be the -XXdb (below 0VU = to the monitor gain setting) that they managed to record. They do not give this number. This is the missing piece of information that we need to determine the real dynamic range of the recording.

Rodd Yamashita
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Old 8th January 2006, 11:55 PM   #75
rmihai is offline rmihai  Canada
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This was an EXCELLENT thread years ago.

I am curious what your opinions are about it after 3 years.

As long as I measured "dynamic headroom", in my system, with all kind of recordings (SACD, DVD-A, CD, DVD-V, LPs) never ever went over 30db.

It seems that there is a confusion between SPL and dynamic range. SPL can go to 120db. But show me a recording with a change in dynamic range of 80db and I will eat it.
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Old 9th February 2009, 04:27 PM   #76
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Quote:
Originally posted by djk
"The NAD spec of having a 6 dB headroom is the marketing and sales department's way of saying that the amp has a lousy power transformer that sags badly, and low power rated output transistors."
Nothing could be further from the truth than the above statement. For people with an open mind I will try and explain some of the NAD design. But load the Nelson Pass patent first, I will refer to it later.
http://patft.uspto.gov/netacgi/nph-P...number=5343166
How does the NAD power envelope amplifier work? What trade-offs did they make?
The schematic for the 100W NAD power envelope amplifier looks almost like a Bryston 3B or an Accuphase P300, but with a tiered power supply. Cross coupled dual differential inputs, fully complimentary from input to output. But with a high voltage tier.
I have bench tested the 100W NAD with both channels driven at 8R with a 1Khz sine wave and got 360W/ch RMS. After a couple of seconds at this level the RayChem PolySwitch opens up and shuts down the high voltage tier. With the high voltage tier shut down the amp will do 100W/ch RMS.
As long as the peak to average ratio in the program material is better than about 6dB the high voltage tier will be available. Even highly compressed rock music meets this requirement.
Money is saved compared to a 400W amp in that the transformer and heatsink is sized for a 100W amp.
The downside is some noise where it switches to the high voltage tier.
There are ways to eliminate the switching. See the Pass patent. While the NAD used a hard switch for the high voltage tier, the Pass works like a normal amplifier up to the tier, and then cascodes itself for the rest of the swing! The higher voltage tier operates in a linear, rather than a switched mode.
Let's do some bench racing. You own some inefficient speakers like the B&W 801s that need 300W/4R to make them get up and go. Well class A is OK if you have $1,000 for heatsink. What about AB biased 10W into class A? OK, our supply voltage is +/- 57V to do 300W/4R, a brute force unregulated supply with lots of filter caps and a big low voltage transformer. Say 40-0-40 at 1KVA with 120,000F filter capacitance (one 30,000F per rail, per channel. To put this in perspective, an Adcom GFA555 puts out 325W/4R with a much higher +/- 75V and half the filter capacitance with only a 700VA transformer). 10W/8R is 1.58A peak, or 360W at idle for a stereo amp. This is a LOT of heat. A normal 300W stereo class AB amp would only have to get rid of about 240W of heat (60% efficency) at full power.
Now let's add a +/- 12V tier. With our same 1.58A bias we now only have 76W of heat for the stereo amp at idle! At full power the efficency would be about 70%, so we could either reduce the size of the heatsink, or choose to increase the class A power point a little higher.
I think one IRF 640/9640 pair in the TO247 package would do for the 12V tier (no matching dozens of transistors), and I would use two pair MJ21193/21194 for the cascode. The Apex jr 37-37-37-37 at 1KVA would be just right for the main rails, and for a stereo amp the low voltage tier need only be 3A or so.

I was researching possible upgrades/modifications to my NAD 2600A, and came across this gem of a thread!

I was listening to some of my favourite music just now, got a bit carried away with the volume knob, and suddenly no bass! Looked at the amp rack, the red 'protection' light on the NAD was 'ON'. (2600 bridged mono, driving my 8 ohm 15 inch sub). Quickly turned the volume down, and the light went off after a few seconds, and everything was fine. I think i just found the limit of the mighty 2600!

Was reading the earlier posts about the NAD power envelope circuit, with dual voltage rails, and how the PSU sags when loaded. So the 150W RMS for the 2600 is from the lower voltage rails?

How does the protection circuit come in for the 2600? When the PSU voltage rails sags excessively, or due to output current limiting?

Is there any way to mod the 2600 to improve the performance? IE, what is the weakest link now? More capacitance in the power supplies? Larger transformer? Or it is limited by the output transistors?

I'm not looking to up the continuous power rating, more like the dynamic headroom, so i was thinking along PSU capacitors upgrade. Currently, think there are 2x 10,000uF 120V and 2x 10,000uF 80 V capacitors.

Thank for the input and comments!!
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