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sir sanders zingmore

Gain Structure

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(Note to mods: I put this in the "General" section because I think gain structure applies to all components, analog, digital, amps, preamps, turntables)

 

I note there have been a few posts mentioning gain structure but I thought it might be worth starting a dedicated thread to get all the information in one spot. 

There might already be such a thread but I couldn't find it.

 

Starting with the example of my system.  I have an amp and a preamp both made by the same manufacturer (Sanders Sound systems)

The amp requires 2.2 volts for full output and has a gain of 26dB.

The preamp has a maximum output of 10v peak and has adjustable gain (website says default is +8dB with the ability to go up to 18dB)

 

Maybe my understanding is not correct but why would the preamp have such a large output voltage if the amp only requires 2.2 volts maximum?

Does this mean that the preamp needs to be turned down "too low" in order not to clip the amp? By that I mean, lowering the output voltage of the preamp pushes the signal closer to the noise floor - not desirable

 

 

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The preamp is designed to be used by multiple power amps for starters. No point limiting its use to only the Sanders power amp. In addition, if you have a low voltage signal source, you may need extra gain in your preamp to compensate for it. Even some quiet recordings may be problematic without "more" gain than is necessary to get to maximum voltage required to drive the power amp.

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Posted (edited)
40 minutes ago, Ittaku said:

The preamp is designed to be used by multiple power amps for starters. No point limiting its use to only the Sanders power amp. In addition, if you have a low voltage signal source, you may need extra gain in your preamp to compensate for it. Even some quiet recordings may be problematic without "more" gain than is necessary to get to maximum voltage required to drive the power amp.

Ok so lets say I have a "standard" DAC that outputs ~2V as my signal source. 

In my specific case would I have a better "gain structure" if my preamp's max output voltage was just enough to drive my amp to its maximum output?

Edited by sir sanders zingmore

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3 minutes ago, sir sanders zingmore said:

Ok so lets say I have a "standard" DAC that outputs ~2V as my signal source. 

In my specific case would I have a better "gain structure" if my preamp's max output voltage was just enough to drive my amp to its maximum output?

It does depend, but in general yes. Theoretically you could just not turn the volume control up as much, however "extra unnecessary gain" tends to raise the noise floor of the preamp.

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Gain is conducted in stages. The most common input sensitivities standards are 2V~ (unbalanced rca) and 4V~ (balanced xlr). Amps convert these internally in the form of a buffer board and the better ones offer you select choice of choice of gain.

 

Given how noise, distortion and the dB scale works means you need something magnitudes better performance just so you don't degrade the overall performance. http://www.sengpielaudio.com/calculator-thd.htm

 

Look at the Benchmark HPA4 and AHB2, the line/pre-amplifier is just as costly as the power amp, because it needs to be perform much better than the AHB2 to ensure it doesn't bottleneck the performance of the power amp.

 

I do like the higher line level signals used in pro-audio (12V~ RMS) as stronger voltages are more less prone to interference and hope someday it'll become an official standard. 

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This article gives a good explanation.31250245_ScreenShot2020-07-22at12_02_20pm.png.4d7d8c0621f2d1f18bfb03fe274bc3ad.png

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Just now, kranky said:

This article gives a good explanation.31250245_ScreenShot2020-07-22at12_02_20pm.png.4d7d8c0621f2d1f18bfb03fe274bc3ad.png

That's a screenshot, not a hyperlink ^_^

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Note, you don't need to actually hit your amps input sensitivity unless you really need the extra power. In fact most amps perform better at a lower output. And the hard gain cap provides a nice safety net for your speakers.

 

On 20/07/2020 at 3:06 PM, davewantsmoore said:

Look (Ncore THD+N).

image.png.a4e8aeb85a1fd60be799a3525fc2c9b7.png

 

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59 minutes ago, Ittaku said:

That's a screenshot, not a hyperlink ^_^

Yes I'm slack!!!  but still worth the read.🥺

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1 minute ago, kranky said:

Yes I'm slack!!!  but still worth the read.🥺

A screenshot would take me more time than copying a hyperlink!

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1 hour ago, Essence said:

Note, you don't need to actually hit your amps input sensitivity unless you really need the extra power. In fact most amps perform better at a lower output. And the hard gain cap provides a nice safety net for your speakers.

 

 

In that screenshot I don't see what you mean?

If I read it correctly, the amp performs far worse (orders of magnitude) at low output (say 0.1w) compared to 5w.

 

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1 hour ago, Ittaku said:

It does depend, but in general yes. Theoretically you could just not turn the volume control up as much, however "extra unnecessary gain" tends to raise the noise floor of the preamp.

I guess that's the point I'm trying to understand.

In my specific case, does the fact that the preamp can produce a lot of "extra" volts mean that when I use it with the volume turned down it has a higher noise floor than a preamp that didn't have the 'extra" volts (all other things being equal) ?

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19 minutes ago, sir sanders zingmore said:

In that screenshot I don't see what you mean?

If I read it correctly, the amp performs far worse (orders of magnitude) at low output (say 0.1w) compared to 5w.

 

Yes the best performing region is from 3-10w so you would want to match speaker sensitivity that reaches the majority of your targeted listening spl level within that range. 

 

This kinda applies to your line/preamp, the measured spec is usually done at full output, however quite often you get a window of peak performance at a lower output. 

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25 minutes ago, sir sanders zingmore said:

I guess that's the point I'm trying to understand.

In my specific case, does the fact that the preamp can produce a lot of "extra" volts mean that when I use it with the volume turned down it has a higher noise floor than a preamp that didn't have the 'extra" volts (all other things being equal) ?

Keep in mind the 2v ( listed as a output of as a sensitivity on input) is an average, music will have peaks that can exceed that at high volume settings, and as its all logarithmic the source or preamp need to be able to deliver those peaks well above 2v without distortion or clipping. Its consider an important factor by many and very good preamps and sources often have very high max outputs to ensure liner response at full volume on dynamic material. 

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2 minutes ago, Chill3 said:

Keep in mind the 2v ( listed as a output of as a sensitivity on input) is an average, music will have peaks that can exceed that at high volume settings, and as its all logarithmic the source or preamp need to be able to deliver those peaks well above 2v without distortion or clipping. Its consider an important factor by many and very good preamps and sources often have very high max outputs to ensure liner response at full volume on dynamic material. 

sure, I get that.

But surely if my preamp delivers 6V at a peak on dynamic material, it doesn't matter how cleanly it does this if it's too much for my amp (which only needs 2V input (RMS I know, but that still peaks well below 6v) for max output).

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3 minutes ago, sir sanders zingmore said:

sure, I get that.

But surely if my preamp delivers 6V at a peak on dynamic material, it doesn't matter how cleanly it does this if it's too much for my amp (which only needs 2V input (RMS I know, but that still peaks well below 6v) for max output).

I would expect the amp to have good overload on input as well, especially as their made to work together, there are some components that are not suited to match because of this however

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Guest
Posted (edited)

I just bought an integrated and happy days.

Edited by Guest

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Posted (edited)
1 hour ago, sir sanders zingmore said:

I guess that's the point I'm trying to understand.

In my specific case, does the fact that the preamp can produce a lot of "extra" volts mean that when I use it with the volume turned down it has a higher noise floor than a preamp that didn't have the 'extra" volts (all other things being equal) ?

I think you have it in a nutshell.  The more you attenuate, the greater the proportion of noise in the signal being fed to the following stage.

Edit: This assumes the attenuation is on the input side of  the pre-amp, as it usually is.  If it is on the output then you are attenuating the noise as well as the signal which is the preferable situation and gives the most ideal gain structure.

 

The situation you describe (too much gain in the pre-amp stage) seems to be universal in commercial gear.  And the only explanation I have is that people just expect the volume control to always be in the 20-50% range.  Having the volume at, say, 75% for normal listening just seems to be too weird for people to get their heads around.  And weird is bad and scary and needs to be eliminated.

Edited by RoHo

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23 minutes ago, RoHo said:

Edit: This assumes the attenuation is on the input side of  the pre-amp, as it usually is.  If it is on the output then you are attenuating the noise as well as the signal which is the preferable situation and gives the most ideal gain structure.

I'm not sure I understand what you mean here. The input into my preamp is my DAC which has no means of attenuation - is that what you mean by "attenuation on the input side" ?

 

24 minutes ago, RoHo said:

nd the only explanation I have is that people just expect the volume control to always be in the 20-50% range.  Having the volume at, say, 75% for normal listening just seems to be too weird for people to get their heads around.  And weird is bad and scary and needs to be eliminated.

 

I have zero issue with that. In fact quiet late-night  listening for me starts at around 45% and and "normal" listening is around 60-70 

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1 hour ago, sir sanders zingmore said:

I guess that's the point I'm trying to understand.

In my specific case, does the fact that the preamp can produce a lot of "extra" volts mean that when I use it with the volume turned down it has a higher noise floor than a preamp that didn't have the 'extra" volts (all other things being equal) ?

As I said, "it depends". What it depends on is just how the preamp is designed. I'm not versed enough on preamp design to say for certain, but most preamps will have a higher noise floor if they produce "too much gain" as a match for your power amp at equivalent volumes. A gross generalisation would say that you should only have a preamp that has the minimum necessary gain to just overload your power amplifier.  For preamps with adjustable gain, it's usually recommended to set the minimum required gain for your power amp. When I first got my preamp it had very high gain and the gain was adjustable - the higher I set the gain, the louder the noise floor got for the same volume level, but not all are designed like this. In the interim, Mick redesigned and rebuilt my preamp to have less overall gain and the noise floor fell dramatically.

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41 minutes ago, Fordute said:

I just bought an integrated and happy days.

But surely you still have to care about gain structure for the inputs (DAC, TT etc) into that integrated?

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5 minutes ago, sir sanders zingmore said:

I'm not sure I understand what you mean here. The input into my preamp is my DAC which has no means of attenuation - is that what you mean by "attenuation on the input side" ?

 

 

 

Sorry for the short-hand. Inside your pre-amp is the volume attenuation before or after the amplifier circuit?  Usually it is before.  

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17 minutes ago, RoHo said:

Sorry for the short-hand. Inside your pre-amp is the volume attenuation before or after the amplifier circuit?  Usually it is before.  

Understand now. 
I don’t know. Not sure how I would find out either 

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2 hours ago, Essence said:

Yes the best performing region is from 3-10w so you would want to match speaker sensitivity that reaches the majority of your targeted listening spl level within that range. 

But 3-10 watts is really loud. Even with my low-sensitivity speakers (82.5dB/W/m), it would be uncomfortable for me. According to some back-of-the-envelope math, each speaker puts out 82.5dB at 1m distance when fed 1W. At my listening position (a bit over 2m away) I’d get 1/4 of that, i.e. -6dB. So we’re at about 76dB. Doubling that for two speakers gives me about 79dB, which is about the peak volume (according to mobile phone sound level meters) that I would comfortably listen to. And that’s 1 watt!

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4 hours ago, Essence said:

Note, you don't need to actually hit your amps input sensitivity unless you really need the extra power.

Just as long as  you don't do it by turning down a digital source output too low.    As the signal goes closer to the noise as it gets quieter.    This can be responsible for a lot of peoples gripes with both digital... and with using "big amps on sensitive speakers".

 

3 hours ago, sir sanders zingmore said:

In my specific case, does the fact that the preamp can produce a lot of "extra" volts mean that when I use it with the volume turned down it has a higher noise floor than a preamp that didn't have the 'extra" volts (all other things being equal) ?

No.... not if it is designed sensibly.

 

If it were (most) digital devices.... then, Yes.

2 hours ago, Chill3 said:

Keep in mind the 2v ( listed as a output of as a sensitivity on input) is an average, music will have peaks that can exceed that at high volume settings, and as its all logarithmic the source or preamp need to be able to deliver those peaks well above 2v without distortion or clipping. Its consider an important factor by many and very good preamps and sources often have very high max outputs to ensure liner response at full volume on dynamic material. 

For digital sources..... this is incorrcect   (0dB, is "full scale" = 2v, or whatever)

2 hours ago, sir sanders zingmore said:

But surely if my preamp delivers 6V at a peak on dynamic material, it doesn't matter how cleanly it does this if it's too much for my amp (which only needs 2V input (RMS I know, but that still peaks well below 6v) for max output).

Correct.

2 hours ago, RoHo said:

I think you have it in a nutshell.  The more you attenuate, the greater the proportion of noise in the signal being fed to the following stage.

That depends on how the device is designed.    In a pre-amp, no, not usually.   The noise is attenuated in proportion to the signal.

 

In a digital device.... often yes.... but it also depends on how the output of the digital device is designed.

 

 

2 hours ago, RoHo said:

The situation you describe (too much gain in the pre-amp stage) seems to be universal in commercial gear.

It is almost always, so the preamp is capable of driving something which needs more voltage...... and it doesn't matter (for SNR purposes) if the preamp is turned down some.

2 hours ago, RoHo said:

  And the only explanation I have is that people just expect the volume control to always be in the 20-50% range.

That's not the reason..... I would think in an "ideal world" you would have the use of the whole volume dial.

 

The reason is usually in that range, is that a) the preamp can over drive the power amp .... and b ) most people don't need the full output of their power amp.

 

31 minutes ago, Steffen said:

But 3-10 watts is really loud. Even with my low-sensitivity speakers (82.5dB/W/m), it would be uncomfortable for me. According to some back-of-the-envelope math, each speaker puts out 82.5dB at 1m distance when fed 1W. At my listening position (a bit over 2m away) I’d get 1/4 of that, i.e. -6dB. So we’re at about 76dB. Doubling that for two speakers gives me about 79dB, which is about the peak volume (according to mobile phone sound level meters) that I would comfortably listen to. And that’s 1 watt!

Your mobile phone is not showing you the "peak volume"..... as the meter responds too slowly.   It's showing you more like an average volume.

 

How much above this it really goes, depends on the peak-to-average ratio of the content.    These days a lot of stuff will be << 10dB ...... but it can go up to 30.

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