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Gain Structure

wgb113

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Making an active speaker switch to a less-integrated model and will need a preamp as a result. With a mix of consumer/pro gear I'm wondering if someone could explain in layman's terms how to use the specs to guide me in determining the proper gain structure. I'm looking for the best way to have the two sources be as close as possible to each other so that large volume adjustments aren't needed along with minimizing overall system noise while avoiding clipping. Most of the articles I've read are either very product-specific or in the professional realm where a preamp isn't in play. Output and input levels are as follows:

Phono Preamp Output Levels:
Nominal: 2.0V RMS (+6dBV)
Maximum: 6.3V RMS (+16dBV)
Impedance: 200 Ohm
SNR: 107 dB

DAC Output Levels:
Selectable: 0/+1/+7/+13/+19dBu
SNR: +1 dBu: 117dB RMS/120dBA, +7/+13/+19 dBu: 120dB RMS/123dBA
THD+N @ 0 dBFS: -116dB, 0.00016%
Impedance: 200 Ohm

Preamp Levels:
Passive OR:
@ 0dB:
THD: <0.001% at 2V RMS
IMD: <0.001%, CCIR
SNR: >115dB, A-weighted, referenced to 2V RMS
Impedance: 600 Ohm

@+12dB:
THD: <0.002% at 2V RMS
IMD: <0.002%, CCIR
SNR: >110dB, A-weighted, referenced to 2V RMS
Impedance: 600Ohm

Active Speakers:
Sensitivity: 85dB @ 1M free-field
+6dB Setting = 50mV (0dBu/0.775V max)
0dB Setting = 100mV (+6dBu/1.5V max)
-6dB Setting = 200mV (+12dBu/3.1V max)

The phono preamp output levels seem like they're tied to cartridge loading so that's somewhat fixed in that range. The DAC offers some adjustability so I'm guessing that's where I could best get a match between the two but I've also read that you should try to maximize the output of each device (without clipping) so that could cause a mis-match.

Then with 3 selectable options each on the preamp and speakers the speaker manufacturer recommends the -6dB setting for most consumer gear outputs which the preamp is. Is it simply a matter of experimenting with each or can the numbers be a guide?

Bill
 

sergeauckland

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Hi Bill,

Firstly, looking at the active 'speakers, do I understand correctly that they have some sort of volume control, otherwise I'm not sure how the spec relates as 200mV is a long way from 3.1V.

Assuming they do, then I would proceed as follows:-

1) On the -6dB setting, set the loudspeaker's volume control about half-way. If the pot follows the 'normal' 10% Log law, then half way rotation gives 20dB attenuation, so your sensitivity should go from 200mV at full rotation to around 2V at half-way. 2V is a good number for the rest of the equipment.

2) Your Pre-amp will give 2V output, so output volts aren't an issue. Use it on the 0dB setting, or you can go passive provided the cables aren't too long (say up to 5m, 10m if you use low capacitance cables like RG6 or RG59)

3) Set your DAC for +7dBu output as that's almost 2V so you won't clip the active 'speakers even at 100% volume. If you're unhappy not being able to drive the 'speakers as hard as they'll go, then set the DAC to +13dBu output, and you'll have plenty in hand for any digital source that actually leaves headroom, rare these days, although BBC Radio 3 actually does!!

4) Your phono stage is fine, it will drive the 'speakers to full volume.

Looks like you'll end up with a nice system, no excessive gain and so with usable volume control.

S.
 
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wgb113

wgb113

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Thanks for your response @sergeauckland . The speakers have selectable input levels based on the connected equipment, FWIW they're Dynaudio LYD 48. The preamp (a Schiit Freya S) would serve as the master volume control. The 200mV spec was under the speaker's Input Sensitivity section while the 3.1V spec was under the three selectable level section:

Adjusting the Volume
There is a three-position switch that adjusts the input sensitivity for the loudspeaker.
Depending on the output level of your audio mixer, interface, or monitor control system, you can choose a setting that optimizes the gain staging into the loudspeaker.
  • +6dB = 0dBu /.775V max
  • 0dB = +6dBu /1.5V max
  • -6dB = +12dBu /3.1V max
If you are using a professional interface with a max output of +20dBu or more, then a setting of -6dB on the loudspeaker is the most appropriate. If you are using equipment that runs at a consumer or domestic output level (-10dBV nominal), then the +6dB setting is better.

You raise the issue of cables and from Phone Pre and DAC to preamp they'll be 2m, from preamp to speakers they'll be 3m. The cable manufacturer I'm thinking of using offers two options: Belden's 1800F which is low-capacitance or Canare's L-4E6S which has a higher capacitance but also higher common-mode noise rejection. Thoughts on which would be better? Or doesn't it matter at these lengths?
 

sergeauckland

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Thanks for your response @sergeauckland . The speakers have selectable input levels based on the connected equipment, FWIW they're Dynaudio LYD 48. The preamp (a Schiit Freya S) would serve as the master volume control. The 200mV spec was under the speaker's Input Sensitivity section while the 3.1V spec was under the three selectable level section:

Adjusting the Volume
There is a three-position switch that adjusts the input sensitivity for the loudspeaker.
Depending on the output level of your audio mixer, interface, or monitor control system, you can choose a setting that optimizes the gain staging into the loudspeaker.
  • +6dB = 0dBu /.775V max
  • 0dB = +6dBu /1.5V max
  • -6dB = +12dBu /3.1V max
If you are using a professional interface with a max output of +20dBu or more, then a setting of -6dB on the loudspeaker is the most appropriate. If you are using equipment that runs at a consumer or domestic output level (-10dBV nominal), then the +6dB setting is better.

You raise the issue of cables and from Phone Pre and DAC to preamp they'll be 2m, from preamp to speakers they'll be 3m. The cable manufacturer I'm thinking of using offers two options: Belden's 1800F which is low-capacitance or Canare's L-4E6S which has a higher capacitance but also higher common-mode noise rejection. Thoughts on which would be better? Or doesn't it matter at these lengths?
Thanks for clarifying what the 'speakers are. Looking at their spec, the 200mV input is referred to 85dBSPL, not full output, which is achieved with +12dBu (3.1V)

Knowing that, the only thing I would change from my first reply is that I'd try the 'speakers with the 0dB setting, and the -6dB setting, and see which one you prefer. The main difference will be on the usability of the volume control, The -6dB setting will give you more control at lower volumes, the 0dB setting will give you higher maximum volumes. For 'normal' domestic listening, I think the -6dB setting will be more appropriate, as you'll get more control. Considering maximum SPL is 112dB which is BLOODY LOUD!! unless you are in a suitable environment, you're unlikely to need that sort of output.

As to cables, over those sorts of distances it really doesn't matter and as (presumably) you'll be using balanced cables it matters even less.

S.
 
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andymok

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max output gain, and attenuate at the input
start from the very last equipment (ie monitors) and work it backwards


You can also put the range onto a spreadsheet and you'll get the picture
 
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wgb113

wgb113

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max output gain, and attenuate at the input
start from the very last equipment (ie monitors) and work it backwards


You can also put the range onto a spreadsheet and you'll get the picture
It seems my first issue is that they all report values differently, not all dBu. It would seem that I'd set the speaker's attenuation pad to -6dB, use the +12dB out of the preamp, +7dB out of the DAC, and the phono preamp is what it is. Or am I completely understanding this?
 

Blumlein 88

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It seems my first issue is that they all report values differently, not all dBu. It would seem that I'd set the speaker's attenuation pad to -6dB, use the +12dB out of the preamp, +7dB out of the DAC, and the phono preamp is what it is. Or am I completely understanding this?
db is a ratio. So 6 db is twice or half as much. dbu is ranked from a reference level. .775 volts is 0 dbu. So -6 dbu is .3875 volts while +6 dbu is 1.55 volts. It can be a brain twister till you get used to it.
 
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