I fear you're right with your -10dB. Too long time in studios ? i was thinking of all this the semi-pro equipment at 0dBu (775mV).
The shame for me is I designed several consumer integrated amps, long time ago, and they were, indeed at -10dB.
la vieillesse est un naufrage.
Hi Tryphon,
Good consumer trumps "Pro-sumer" every time. Professional also trumps "Pro-sumer". It seems that the Pro-sumer tag gives those designers artistic license to do their own thing.
I spoke french better in high school than now. I wouldn't call myself able to understand it, but my oldest daughter is officially Bilingual English and French. I'm proud of her accomplishments.
In high school I had a choice to make. Drop French, or one of my technical subjects. The French prof. was upset because I was apparently doing very well. Something had to give, and it was my languages that took the hit. Looking back on it, there was no other decision that could be made. Had I been able to carry French as well, it would have opened doors for me as it has for my daughter.
-Chris
Good consumer trumps "Pro-sumer" every time. Professional also trumps "Pro-sumer". It seems that the Pro-sumer tag gives those designers artistic license to do their own thing.
I spoke french better in high school than now. I wouldn't call myself able to understand it, but my oldest daughter is officially Bilingual English and French. I'm proud of her accomplishments.
In high school I had a choice to make. Drop French, or one of my technical subjects. The French prof. was upset because I was apparently doing very well. Something had to give, and it was my languages that took the hit. Looking back on it, there was no other decision that could be made. Had I been able to carry French as well, it would have opened doors for me as it has for my daughter.
-Chris
I had in mind a "control" reflection off a stationary part of the drive unit as well as off the cone. Not a trivial thing to implement and I am no expert but workable in principle, I reckon. A couple of phase detector circuits.
I suppose a problem may be where on the cone or VC to measure displacement. Considering resonance patterns and break-up modes and such. It may be that the existing back-emf method sort of averages all that out in a convenient way that a single laser point would not. Interesting.
For example, say you could measure the displacement of the back edge of the VC tubular former. This would be in error if the VC did not move in exactly one axis. If it tended to yaw and pitch an error would occur. I don't know how large this error is in practice. So multiple points might be needed or some other solution.
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When I was in junior high I took French. A few foriegn exchange students came over for a few weeks of class. None of them could understand my teacher. Who do you think knows more French, you or I, Chris?
Later I had math with the same teacher in high school. I got a C, and never could understand anything from her. Her and another teacher couldn't give me any kind of formula for finding square root... Last year of high school I got an A with no effort at all, and could have got 100% if I corrected some stuff; which was more like writing it out instead of writing calculator programs that did everything for me - they always got mad at me for that. In retrospec I should have been selling calc programming. Their fault for telling me about the program stuff...
Later I had math with the same teacher in high school. I got a C, and never could understand anything from her. Her and another teacher couldn't give me any kind of formula for finding square root... Last year of high school I got an A with no effort at all, and could have got 100% if I corrected some stuff; which was more like writing it out instead of writing calculator programs that did everything for me - they always got mad at me for that. In retrospec I should have been selling calc programming. Their fault for telling me about the program stuff...
And remember dB has to be relative to something. Reference levels when setting gain structures in a system are often for convenience referred to as the "0 dB" level, but they are almost never actually are 0 dB electrically relative to a voltage, current or power. (0 dbV, dBI, dBW)
In the consumer unbalanced signal world that 0.316 V reference for "0 dB" is electrically -10 dBV.
In the pro balanced world that 0.775 V reference for "0 dB" reference level is 0 dBm (1 miliwatt), into a 600 ohm load. However the most common reference "0 dB" in the pro world refers to an electrical 4 dBm or 1.23 V. In broadcasting 8 dBm is sometimes used as the reference "0 dB" which is 1.95 V...all voltages historically measured when driving a 600 ohm load, but now usually measured open circuit.
Cheers!
Howie
Hi Howie,
Yes, you're exactly right. I think that dBu is referenced to 1 volt, isn't it? Or was that dBV? They aren't power relationships, so circuit impedance isn't involved. It is the dB that is a ratio that requires a reference.
dB in my lab still throws me as it is referenced to 50 ohms. I'd rather deal in voltages instead of trying to reset my head from 600 ohm to 50 ohm. A little 75 ohms are thrown in for good measure. I imagine that the 50 and 75 ohm references are second nature to you.
-Chris
Yes, you're exactly right. I think that dBu is referenced to 1 volt, isn't it? Or was that dBV? They aren't power relationships, so circuit impedance isn't involved. It is the dB that is a ratio that requires a reference.
dB in my lab still throws me as it is referenced to 50 ohms. I'd rather deal in voltages instead of trying to reset my head from 600 ohm to 50 ohm. A little 75 ohms are thrown in for good measure. I imagine that the 50 and 75 ohm references are second nature to you.
-Chris
Did you mean the 0dB "operating level" ?
To resume:
dB fs (full scale): digital clipping.
0 dBm : 1mW under 600Ω (soit 0,775V).
dBu : Electrical level relative to those 0.775V
dBV : Electrical level relative to 1V.
Consumer use, as the line reference level: -10dBu (0.316V)(I stay corrected)
Semi-pro, often: 0dBu. (0.775V)
Pro: +4dBu : (2.28V)
Analog out of digital equipment, often +2.2dBu (= 0dBV)
For digital, the reference is usually set at -18dB fs in Europa, -20dB fs in USA, in radios, i have seen: -16 ou -14 ou -12 dB
This time I hope i made no mistake.
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Right, I don't think people here understand the economics of the consumer market at its lowest level.
I agree, I remember some huge efforts to suppress as much straps as possible during printed circuit design for economical reasons.
To come back to this levels discussion, i wonder why it was decided to set those -10dB for consumer products. Was-it decided at the age of germanium transistors that had low collector emitter max voltage ? Was-it to allow the use of low voltage batteries ?
Anyway, as most of the power amps have an input sensitivity between 200mV and 1.5V for max power, all this is insane.
Hi Scott,
That is something I'm well acquainted with. At least I no longer have to try and eek out a living fixing consumer equipment that no one wants fixed to begin with. But this is at the finished goods level, not the parts level you're at where you have to try and hit some kind of target cost. (who figures out what the part should sell for anyway?)
-Chris
That is something I'm well acquainted with. At least I no longer have to try and eek out a living fixing consumer equipment that no one wants fixed to begin with. But this is at the finished goods level, not the parts level you're at where you have to try and hit some kind of target cost. (who figures out what the part should sell for anyway?)
-Chris
Hi Tryphon,
I think the signal levels for the tape buss on DIN connectors is lower, isn't it? I'm thinking the 5-pin DIN plug as we know it.
-Chris
Probably because when you figure out the peak to average levels, the peak levels might clip at normal internal signal levels. I've never sat down to figure out what the gain budget was, but I think this level has been with us for a long time. Maybe early Dolby chips running on a single supply cast the level in stone. Everyone else just followed along.
I think the signal levels for the tape buss on DIN connectors is lower, isn't it? I'm thinking the 5-pin DIN plug as we know it.
-Chris
Or home bodged
Well this knuckle dragger is putting an ADC in his phono stage. That runs 'odd' levels of +15dBu FS so neither fish nor fowl*. At the DAC end I'm running as hot as I can reduce gain on the power amp to cope with. Not yet ideal, but I'll get there. The work done recently here on high gain preamps so the power amp can effectively be reduced to a power buffer is intriguing, but the right answer is still to put the DAC in the power amp IMO. Worthy of discussion though.Obviously the knuckle draggers who still use analog sources will have to figure out their own solutions, (I'm kidding, of course
Chris: FWIW dB in the voltage domain still gets me, I am far happier with proper 10logx power relationships ref 1mW from all my years with RF.
*And in true 'knocked up by the summer student' style I think that 15dBu is in fact wrong as the numbers don't stack up for the ADC input.
Hi Bill,
Well, for me, I was comfortable with the dBm at 600R, then I edged into the world of RF. First with tuners, then with instrumentation needed to work on them. Then I was plunged into the 50R world of lab equipment. At the end of the day, my own lab is on a 50R standard with adapters between the 75R and 50R equipment.
Normally I'm only concerned with ratios between two points at the same impedance. That's fine, but shifting between instruments at different impedances, like an audio generator. One referenced to 600R, the other to 50R, gives me headaches.
-Chris
Well, for me, I was comfortable with the dBm at 600R, then I edged into the world of RF. First with tuners, then with instrumentation needed to work on them. Then I was plunged into the 50R world of lab equipment. At the end of the day, my own lab is on a 50R standard with adapters between the 75R and 50R equipment.
Normally I'm only concerned with ratios between two points at the same impedance. That's fine, but shifting between instruments at different impedances, like an audio generator. One referenced to 600R, the other to 50R, gives me headaches.
-Chris
MSB big class A amps:
XLR Input 40K Ohm Balanced
10Vrms Maximum
Switchable +16dB or +22dB Gain
RCA Input 20K Ohm single-ended
10Vrms Maximum
+22db Gain
MSB Select DAC
XLR Analog Inputs
100kΩ Balanced
12Vrms Maximum
XLR Analog Outputs
3.57Vrms Maximum (Digital Input)
12Vrms Maximum (Analog Input)
XLR Input 40K Ohm Balanced
10Vrms Maximum
Switchable +16dB or +22dB Gain
RCA Input 20K Ohm single-ended
10Vrms Maximum
+22db Gain
MSB Select DAC
XLR Analog Inputs
100kΩ Balanced
12Vrms Maximum
XLR Analog Outputs
3.57Vrms Maximum (Digital Input)
12Vrms Maximum (Analog Input)
While I have the greatest respect for MSB, especially their D-A converters, the set gain of their power amps is not typical. It is probably meant to interface with their D-A system.
Usually, TODAY, we use the THX gain specification of 28.3V or so for power amps. We try to reduce the preamp line gain, these days to 10dB or so, with the phono specs usually 40dB for MM, and 60dB for MC. Over the years we have increased the voltage gain in power amps for convenience. This is because with a voltage gain of 28.3, 0.1V in gives 1W/8ohm out, and 1V gives 100W/8ohm, and finally 2V gives 400W/8ohm. This is a comfortable range for almost all preamps to drive, an it is a convenient reference for determining speaker sensitivity.
On another topic, have any of you out there tried the Analog Devices ADA4625? It looks like it would be very good for audio, even if they do not recommend it specifically for this.
Usually, TODAY, we use the THX gain specification of 28.3V or so for power amps. We try to reduce the preamp line gain, these days to 10dB or so, with the phono specs usually 40dB for MM, and 60dB for MC. Over the years we have increased the voltage gain in power amps for convenience. This is because with a voltage gain of 28.3, 0.1V in gives 1W/8ohm out, and 1V gives 100W/8ohm, and finally 2V gives 400W/8ohm. This is a comfortable range for almost all preamps to drive, an it is a convenient reference for determining speaker sensitivity.
On another topic, have any of you out there tried the Analog Devices ADA4625? It looks like it would be very good for audio, even if they do not recommend it specifically for this.
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