DAC 4Vrms out to AMP 1.4Vrms in? Question on setup.

[Tachyon88]

Thought I would start here first, maybe I should ask this in the crown 2502 thread ? Brand spanking new to this, I have no experience with any equipment, other than my su-8 and thx 789.....Looking to buy Buchardt s400 and crown 2502 amp. Will hook up to smsl su-8 balanced DAC from PC.

PC>optical in DAC> balanced in AMP> speakers.

The DAC's balanced output is 4v rms and the amp's input sensitivity is 1.4v rms....the amp does not have gain, rather it's attenuation. I think I remember reading that the amp's max attenuation is 0db.

Question. When initially setting up the best noise to signal ratio, should I have source and dac volume 100% and start from 0 on the amp and attenuate the knob to the loudest comfortable listening level ? OR should I have the amps attenuation maxed out to begin with and raise my source/dac's volume from there ?

I hope I am clear, just not sure I fully understand what I am reading or what the best approach would be. Thanks for your time.
Quick reference
AMP https://www.crownaudio.com/en/product_documents/5055568_xlsdc2_mnl_print_050615-pdf-188f6caf-1d35-476c-85d1-14e7374821fd
DAC http://www.smsl-audio.com/Upload/download/20181220152119868.pdf

 

[Wayne A. Pflughaupt]

That amp’s gains read from 0 at minimum (counter-clockwise) to 10 at max, which is unusual. Typically on pro amps 0dB is full clockwise and the numbers show increasing negative values going counter-clockwise, with full counter-clockwise being a high number: -60 dB or something similar.

Assuming the source / DAC is clean at 100% output (it might not be), you don’t want to start with the amp gains maxed out, too. That could blow the speakers. So, start the amp at full counter-clockwise and increase to your maximum listening level.

Regards,
Wayne A. Pflughaupt

 

[Tachyon88]

That amp’s gains read from 0 at minimum (counter-clockwise) to 10 at max, which is unusual. Typically on pro amps 0dB is full clockwise and the numbers show increasing negative values going counter-clockwise, with full counter-clockwise being a high number: -60 dB or something similar.

Assuming the source / DAC is clean at 100% output (it might not be), you don’t want to start with the amp gains maxed out, too. That could blow the speakers. So, start the amp at full counter-clockwise and increase to your maximum listening level.

Regards,
Wayne A. Pflughaupt

Hi. Yes, I think I will start the amp's at zero with source at 100% and turn the amp up to the loudest listening levels for me.

I dont fully understand the science of it all. Without attenuation the max input signal is 1.4Vrms, so if I decrease the "gain" I would be further decreasing the input signal that is already lower than the output signal coming in ?

 

[RayDunzl]

I dont fully understand the science of it all.

The amplifier has gain. It multplies the input voltage by some constant factor to create the output voltage.

The "volume" or "gain" knob adjusts the level of the voltage that is input to the amplifier stage.

XLS2502 has 32.64 dB gain (per some random web page)

1.4Vrms sensitivity x 42.85 = 60V output

60V out to an 8 ohm speaker = 450W

XLS2502 spec:

Close enough.

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You reduce the input voltage with the knob, you reduce the output voltage.

The knob adjusts a "voltage divider".

The amplifier section is a voltage multiplier.

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Attenuate the input by 12dB:

1.4V / 4 = 0.35V

Multiply by gain factor:

0.35V x 42.85 = 15V = 28W output into 8 ohms

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That's the "science", unless you want more.

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Calculations:

http://www.sengpielaudio.com/calculator-gainloss.htm

http://www.sengpielaudio.com/calculator-ohm.htm

 

[Tachyon88]

@RayDunzl Thanks for the information. I will study it more.

 

[Jimbob54]

If the DAC has a remote, I'd start at around 85% or so of the DAC volume (26/30 is a favourite position of mine) then turn your amp up to a nice sounding volume with just a touch of bite, then down one notch . Sit, enjoy and if you want to nudge it up or down for track/ mood, use the remote on the DAC.

 

[Wayne A. Pflughaupt]

I dont fully understand the science of it all. Without attenuation the max input signal is 1.4Vrms, so if I decrease the "gain" I would be further decreasing the input signal that is already lower than the output signal coming in ?

It’s not all that complicated, really. The 1.4 v rating merely reflects what it takes to drive the amp to its maximum output. If you feed it a hotter signal, such as with your DAC, the front-panel gain controls attenuate the signal to an appropriate level. That’s all there is to it.

Regards,
Wayne A. Pflughaupt

 

[Tachyon88]

It’s not all that complicate, really. The 1.4 v rating merely reflects what it takes to drive the amp to its maximum output. If you feed it a hotter signal, such as with your DAC, the front-panel gain controls attenuate the signal to an appropriate level. That’s all there is to it.

Regards,
Wayne A. Pflughaupt

Ya, that does sound simple, I was thinking that since the input signal is so much higher, turning down the gain would decrease the amp's 1.4v input further, thus creating a greater disparity. Well, now I wait for this stuff to come in.

 

[Tachyon88]

If the DAC has a remote, I'd start at around 85% or so of the DAC volume (26/30 is a favourite position of mine) then turn your amp up to a nice sounding volume with just a touch of bite, then down one notch . Sit, enjoy and if you want to nudge it up or down for track/ mood, use the remote on the DAC.

Hi, yes it does. I'll give it a try when the gear comes in. Thanks !