Hi, clever bods! these are probably dumb questions, but I need to know the answer(s)...
I have a Yamaha AX-490 that has no listed Vrms spec for inputs. The specs sheet says 150mV/47 K-ohms 'sensitivity'. I am guessing this is not Vrms, as at 0.9Vrms from my MiniDSP it sounds quiet and flat (compared to input not via the MiniDSP).
Is there any way to calculate/guesstimate the appropriate Vrms level for input to this unit?
Also, I am getting a Marantz PM5005, which says it has an input sensitivity of 200mV/20 K-ohms, but also says it has an S/N of 103db (2V input, Rated output). I am guessing this means it is best at 2Vrms. Am I correct?
The Marantz specs seem to hint at Vrms being a different animal to input sensitivity expressed as mV/k-ohms, but I don't really understand this stuff very well. Help!
I have a Yamaha AX-490 that has no listed Vrms spec for inputs. The specs sheet says 150mV/47 K-ohms 'sensitivity'. I am guessing this is not Vrms, as at 0.9Vrms from my MiniDSP it sounds quiet and flat (compared to input not via the MiniDSP).
Is there any way to calculate/guesstimate the appropriate Vrms level for input to this unit?
Also, I am getting a Marantz PM5005, which says it has an input sensitivity of 200mV/20 K-ohms, but also says it has an S/N of 103db (2V input, Rated output). I am guessing this means it is best at 2Vrms. Am I correct?
The Marantz specs seem to hint at Vrms being a different animal to input sensitivity expressed as mV/k-ohms, but I don't really understand this stuff very well. Help!
The voltage will almost certainly be RMS, as that is the normal way to specify AC voltages. What you may be confusing is 'input voltage for maximum output power' and 'input voltage for some standard (smaller) output power (possibly 1W?)'.jinja said:
No. It means at 2V input it will have s/n of 103dB. At lower inputs it may have worse s/n; at higher inputs it may have better s/n. The details depend on the exact gain distribution through the amp.
You may have misunderstood, or they may have misunderstood.
Specifying 'sensitivity' as mV/K-ohms is misleading - it seems to imply some sort of division is taking place! Sensitivity should be specified in mV or V (as appropriate) - in both cases an RMS figure would be normal. As a separate matter, the input impedance can be specified as something like '20k' or '47 000'. "K-ohms" are not an internationally recognised unit, although most people will recognise what they are trying to say.
Ah, OK. I understand that it is a measurement of 'sensitivity'
Then how do I know what would be a good input range for the Yamaha, for instance? What specs. should I use to calculate the max. or a 'good' Vrms level to send to it from, for example a miniDSP?
Or can I ONLY calculate this using test equipment? (which I don't have)
Thanks!
Then how do I know what would be a good input range for the Yamaha, for instance? What specs. should I use to calculate the max. or a 'good' Vrms level to send to it from, for example a miniDSP?
Or can I ONLY calculate this using test equipment? (which I don't have)
Thanks!
It doesn't specify a maximum input (unless I'm missing something), that's why I am asking. The Yamaha AX-490 specs can be seen at the end of the pdf here. The Marantz PM5005 specs are on page 41 of the pdf here.
How to calculate, and what details I would use/need for this calculation is also what I was asking.
Any ideas would be appreciated. Thanks!
How to calculate, and what details I would use/need for this calculation is also what I was asking.
Any ideas would be appreciated. Thanks!
Input sensitivity (like 150 mV) denotes the minimum input level required to achieve full rated output power with the volume cranked all the way up. So it's a good idea if nominal input level were at least as high as that. The nominal consumer audio level used to be considered 300 mV.
I would suggest trying to obtain input levels such that a comfortable listening volume ends up in about the 10 o'clock position of the amplifier's volume pot. Channel imbalance should be low by this point, and there should be enough volume to spare if need be.
While I cannot find any schematics for the AX-490 anywhere, I assume it'll be similar to the AX-590. In this one, any input but CD connects to the volume pot, so the overload limit would be given by the pot's power handling (>10 Vrms, typ). In practice, you would be bothered by irritating channel imbalance long before this point.
The CD input is different since it adds about 10 dB of voltage gain - another 10 dB gain block after the volume pot is then bypassed in CD-Direct mode, which results in almost as much reduction in output noise, making even sensitive horn speakers happy. (The articles section of this site contains something on gain staging if you're interested.) In fact, the '590 makes use of two NJM2068s in parallel for this, with each having to drive about 1k5 worth of feedback network up to 6 Vrms for a 2 Vrms input. (I presume the '490 will only have one opamp.) Maximum permitted input level is less than 3 Vrms before things start to clip.
This input stage is a good example for misguided overdesign because:
1. the noise even of one opamp stage would be entirely swamped by source noise in practice (or have you ever seen a CD player remotely approaching 130 dB SNR at 2.0 Vrms out? Input noise sims at ~0.55 µV!), and both are reduced to inaudible levels by turning down volume, and
2. the '2068 won't be too happy (distortion wise) having to drive that kind of load at that kind of levels, which should be measurable. (The "CD" input should better be called "anything but CD", which is a bit ironic - it would be a good match for up to ~1 Vrms from a soundcard or portable device.)
IOW, they designed for low noise where it was not necessary and only puts an undue strain on the opamp output. I would resize the feedback network from 1k/470 to more like 1k8/1k or 2k2/2k2 (some reduction in gain isn't a bad idea, since CDs have become so much hotter in level since the early '90s that people often have to turn the volume way down and then run into channel imbalance issues).
As for the problem in question - is the MiniDSP output 0.9 V nominal, or 0.9 V full-scale? In a DSP setup, you always tend to leave some processing headroom (staying anywhere from 3-10 dB away from full-scale), and overall gain from input to output may vary according to how the DSP is set up. Next step would thus be finding out what input-to-output gain of the MiniDSP is, what sort of input levels it'll handle and what its maximum output is.
I would suggest trying to obtain input levels such that a comfortable listening volume ends up in about the 10 o'clock position of the amplifier's volume pot. Channel imbalance should be low by this point, and there should be enough volume to spare if need be.
While I cannot find any schematics for the AX-490 anywhere, I assume it'll be similar to the AX-590. In this one, any input but CD connects to the volume pot, so the overload limit would be given by the pot's power handling (>10 Vrms, typ). In practice, you would be bothered by irritating channel imbalance long before this point.
The CD input is different since it adds about 10 dB of voltage gain - another 10 dB gain block after the volume pot is then bypassed in CD-Direct mode, which results in almost as much reduction in output noise, making even sensitive horn speakers happy. (The articles section of this site contains something on gain staging if you're interested.) In fact, the '590 makes use of two NJM2068s in parallel for this, with each having to drive about 1k5 worth of feedback network up to 6 Vrms for a 2 Vrms input. (I presume the '490 will only have one opamp.) Maximum permitted input level is less than 3 Vrms before things start to clip.
This input stage is a good example for misguided overdesign because:
1. the noise even of one opamp stage would be entirely swamped by source noise in practice (or have you ever seen a CD player remotely approaching 130 dB SNR at 2.0 Vrms out? Input noise sims at ~0.55 µV!), and both are reduced to inaudible levels by turning down volume, and
2. the '2068 won't be too happy (distortion wise) having to drive that kind of load at that kind of levels, which should be measurable. (The "CD" input should better be called "anything but CD", which is a bit ironic - it would be a good match for up to ~1 Vrms from a soundcard or portable device.)
IOW, they designed for low noise where it was not necessary and only puts an undue strain on the opamp output. I would resize the feedback network from 1k/470 to more like 1k8/1k or 2k2/2k2 (some reduction in gain isn't a bad idea, since CDs have become so much hotter in level since the early '90s that people often have to turn the volume way down and then run into channel imbalance issues).
As for the problem in question - is the MiniDSP output 0.9 V nominal, or 0.9 V full-scale? In a DSP setup, you always tend to leave some processing headroom (staying anywhere from 3-10 dB away from full-scale), and overall gain from input to output may vary according to how the DSP is set up. Next step would thus be finding out what input-to-output gain of the MiniDSP is, what sort of input levels it'll handle and what its maximum output is.
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No, that really is how CD-Direct works with these Yamaha amps (up to AX-596 and A-S700) - take away 10 dB after the volume pot, add 10 dB before the volume pot (only at CD input). Result, overall gain is the same, but output noise floor goes down by almost 10 dB. The CD input amp has to handle pretty high levels though, as described.
It does get a bit dumb in non-CD-Direct mode, where the amplified CD input is immediately attenuated again in order to be compatible with the other inputs - worst of both worlds, so to speak.
Of course a CD player is easily the loudest source these days, but remember this series came out in '95, when average CD levels were a fair bit more reasonable still. And with CDs being the best medium available to the general public, having a dedicated higher-performance CD input made sense. They also had entirely dropped 4-gang volume pots by this series (AX-1070 still had one, as did AX-1050 and AX-750) and probably wanted to offer something to make up for it.
Hi,
Well i'm bemused. I used to make 7dB attenuator leads for non
CD amplifiers and your description doesn't follow all line inputs
being 150mV sensistivity, at all, I severely doubt your idea
10dB is added to CD before the volume pot, very pointless.
Or your assumption the noise floor is improved.
rgds, sreten.
Well i'm bemused. I used to make 7dB attenuator leads for non
CD amplifiers and your description doesn't follow all line inputs
being 150mV sensistivity, at all, I severely doubt your idea
10dB is added to CD before the volume pot, very pointless.
Or your assumption the noise floor is improved.
rgds, sreten.
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sgrossklass...thanks...interesting stuff...unfortunately, I do indeed have the 490, not the 590, so most of your hypothesizing is moot in my case... re. the minidsp...it likes to be set at the higher 1.9Vrms input setting for my input source (a mixer unit which is showing good levels at this input...i.e. entering 'orange' on the VU fits well with a -3 to -6 db channel in on the MiniDSP VU). The other available input setting is 0.9V which is just way to low for my source. I'm thinking I probably need the minidsp balanced 2x4 which also gives a 1.9Vrms output (instead of ONLY a 0.9Vrms), but I would like to know how to calculate a 'safe' Vrms output for both amps I mentioned (which I can then set on the MiniDsp by doing a Vrms to -db calculation and adjusting the line out level of the miniDSP accordingly, I guess)...though going by these discussions, my gut feeling is tending towards 'set it at what sounds right' and don't worry too much about the amp (but probably worry more about the 20 watt speakers I'm going to connect to the Marantz)...cheers!
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measure it.
Get a fixed frequency onto a CD and then use a CD as your Sourfce.
Pano started a Thread to give guidance on maximum power and in there, there are two fixed tones for testing.
Put in you CD and set to play.
Measure the output voltage of the CD.
Connect that to the amplifier. Set the vol pot to about 25% rotation. Power on and measure the output voltage.
Keep turning up the vol pot till the output measures 26Vac (=85W into 8r0).
You now have the input voltage and the output voltage and can determine the Gain when the vol pot is in that position. It might be @ 60%, or 70%, or whatever.
If your CD player has a variable output adjustment, then you can get better.
This time set CD adjustment to minimum. set amplifier to maximum.
power on and measure the output. Increase the CD player output gradually until the amplifier output reaches 26Vac.
Now disconnect the CD player and measure the CD player output.
That Vac will be the input required by the amplifier to reach maximum output.
You will need a DMM that can be set to 200.0Vac & 20.00Vac & 2.000Vac
Get a fixed frequency onto a CD and then use a CD as your Sourfce.
Pano started a Thread to give guidance on maximum power and in there, there are two fixed tones for testing.
Put in you CD and set to play.
Measure the output voltage of the CD.
Connect that to the amplifier. Set the vol pot to about 25% rotation. Power on and measure the output voltage.
Keep turning up the vol pot till the output measures 26Vac (=85W into 8r0).
You now have the input voltage and the output voltage and can determine the Gain when the vol pot is in that position. It might be @ 60%, or 70%, or whatever.
If your CD player has a variable output adjustment, then you can get better.
This time set CD adjustment to minimum. set amplifier to maximum.
power on and measure the output. Increase the CD player output gradually until the amplifier output reaches 26Vac.
Now disconnect the CD player and measure the CD player output.
That Vac will be the input required by the amplifier to reach maximum output.
You will need a DMM that can be set to 200.0Vac & 20.00Vac & 2.000Vac
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Of course you need to know - what it is, that you need to know. 
As Andrew said, take a look at my voltage thread. It may not tell you what you are asking for, but it will tell you something, at least.
- Do you want to know how much input voltage it takes to get your amp to clipping?
- Do you want to know the maximum voltage you can input, then turn down with the volume control?
- Do you want to know what voltage will blow up the inputs?
- Perhaps all of the above?
As Andrew said, take a look at my voltage thread. It may not tell you what you are asking for, but it will tell you something, at least.
As has been pointed out, all voltages are RMS (Root Mean Square) unless otherwise specified. If peak voltage is intended, which it never is, the spec will say so.
<< ... has no listed Vrms spec for inputs... >>
Yes it does. It's 150mV.
Or actually the spec correctly stated is, "Input Sensitivity/ Impedance: PHONO MM = 2.5mV/47 k-ohms, CD etc. = 150mV/47 k-ohms"
Taking the CD spec, 150mV/47k is a statement of two unrelated specs. The 47k means the amp has a Zin (input impedance) of 47k, which is a semi-standard Zin.
The 150mV sensitivity means your AX-490 will develop its full rated wattage output with an input of 150mV. Of course that's with everything cranked up to 100%, which is not how you'd run.
However, unless you're a studio engineer it's not usual to care one way or another about this 150mV figure. What you do is turn all the volume controls down to zero, plug things together, and turn everything on. Then you creep the volume controls up and see what happens. It's generally desirable to run volume controls in the middle third of their rotation, if possible.
Your owner's manual states that "Pure" or "Direct" switches simply bypass the tone controls, which is as usual.
Just to ramble on a bit, the 150mV figure tells you that no separate preamp is needed because one is built into the AX-490. The classic "true audiophile" setup is a preamp in one chassis, having volume and tone controls, and selector switches. The preamp has a line level output which feeds an amplifier in another chassis. The amplifier might have just a volume control, or perhaps no controls whatsoever. The amplifier would have a line level input jack, and would develop it's rated output with a line level input.
Your AX-490 simply has the preamp and amp built into one chassis, that's all. It works the same way, you just have one less chassis to put on a shelf somewhere. All of the controls are actually for a preamp section inside the chassis, which feeds a separate amplifier section in the same chassis.
The amp section still needs a line level input to develop its rated output. The preamp section does deliver line level to the the amplifier section, but itself needs only 150mV to output line level.
So what is line level? It really doesn't matter because audio output levels vary all the time. Are you listening to a flute solo, or a full symphony orchestra with cannon fire--or heavy metal? Japan says one thing about line level, Korea says another thing, India has ideas of its own.
Still, you do need some kind of planning figure, and "line level" is that figure. I personally use the classic "line level = nominal one volt" rule. "Nominal" meaning vaguely in that vicinity, more or less.
By the way, we are clear on terminology? This 150mV = 150 millivolts = 0.150 volt. To raise this to a line level of 1 volt the AX-490 preamp section has a maximum gain of about 7, or about 17dB.
.`
Thanks folks!
Thanks to everyone, for helping out a real newb when it comes to considering anything other than connecting stuff and seeing what happens!
There's some really useful info. in this thread (for me). I particularly like AndrewT's notes on measuring, and I will defo. check out those related threads. Looks like I need to get some new batteries for my DMM (which will read up to 600V AC).
I'm currently, slowly, amassing the bits and bobs needed to move from a single amp with average speakers to an active x/o (miniDSP) to 2 amps feeding 2 separate pairs of speakers (including a pair of Alpair 7.3s in the pensil 7.3 design). I don't really know what I'm doing, but I'm having a lot of fun thinking about it! Will let you know how it goes.
Thanks again for all the useful input [sic.]
Thanks to everyone, for helping out a real newb when it comes to considering anything other than connecting stuff and seeing what happens!
There's some really useful info. in this thread (for me). I particularly like AndrewT's notes on measuring, and I will defo. check out those related threads. Looks like I need to get some new batteries for my DMM (which will read up to 600V AC).
I'm currently, slowly, amassing the bits and bobs needed to move from a single amp with average speakers to an active x/o (miniDSP) to 2 amps feeding 2 separate pairs of speakers (including a pair of Alpair 7.3s in the pensil 7.3 design). I don't really know what I'm doing, but I'm having a lot of fun thinking about it! Will let you know how it goes.
Thanks again for all the useful input [sic.]
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You can always look up the service docs of any Yamaha integrated amp if you don't believe me - HFE has a whole bunch, for example. AX-590 up, AX-492 up, AX-496 up, AX-497, A-S700. Circuitry may differ a bit (opamp vs. discrete, a bit more or less gain) but the basic scheme is always the same.
For the sensitivity spec, it does not matter how gain is distributed inside the amp, only the sum counts. You can shift part of that gain around however you please, and the spec doesn't change one bit. Obviously relative levels in the individual stages do change, which can be used to tweak the noise vs. distortion / level handling tradeoff in practice.
And that brings us to your attenuators. These absolutely make sense when either you've got a case of touchy or unbalanced volume pot syndrome (not uncommon with modern-day CDs - early ones tended to be about on par with vinyl, but levels have gone up by ~10 dB since then), or (much more rarely) the input buffer / amplifier has relatively modest level handling. For traditional amplifier concepts with the volume pot up front, input level handling tends to be bombastic (you can calculate for yourself what a 50 or 100 kOhm pot typically rated at 50 mW can take).
Vpk vs VM
Vpk you mean Vpeak this inculde the Vdc ?
VM is Vmax without a Vdc component
Vpk you mean Vpeak this inculde the Vdc ?
VM is Vmax without a Vdc component
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