Lawrence001

Optimal pre amp volume.

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I got this in my daily PS Audio blog email, I think it has some truth, although whether you believe in true bit perfect/lossless digital attenuation is another matter...

"Most preamplifiers have a zone on their level controls where they sound best; typically higher on their dials.

Finding that perfect spot on the dial isn’t too hard, but getting there can be because much depends on the loudness levels of the source and the sensitivity of the speakers.

Most sources don’t have level trim controls to help match their gains to the rest of the system.

If you have a DAC, like our DirectStream, then it is an easy task to set the gain to match the sweet spot on your preamplifier. For example, depending on the system I am using, I like to set the DirectStream at around 80 on its level control. This places most tracks in the upper 40s and 50s on the BHK preamplifier, and the softest tracks bumping into the high 70s.

It’s tempting to think preamps sound the same at any level setting, but it isn’t true. Not for most preamps, anyway.

Finding just the right spot on the preamp level dial can bring hours more enjoyment to your system."

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Suspect it has more to do with the speaker/room optimal volume...

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Super Dealer

Yes and the ear’s relative insensitivity to low frequencies.

Keith

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But he's referring to attenuating the input level to counteract the higher preamp volume level so that you achieve the same SPL. I imagine he would measure the SPL to ensure they're the same volume.

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Super Dealer

Variable analogue output , from a dac for example is a good idea, allowing you to use more of the volume knob.

Keith

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3 hours ago, Lawrence001 said:

Most preamplifiers have a zone on their level controls where they sound best; typically higher on their dials.

Hi,

Yes - if you read Doug Self's book on active filters etc., the higher output increases the S/N, for a low THD too - opamps assumed.

From my interpretation, there are many aspects of engineering that are never discussed, yet have an effect on the audio signal, and vice versa.

As per other threads, there seems to be a perception that digital volume controls are bad, but no actual data provided to back up the claim. I disagree with this - there is no discussion of people saying they can hear the negative effect, on the wider forums etc, nor in the hifi magazines.

Then there are analogue chip based volume controls - these introduce significant THD at high frequencies, yet i have never seen a report in a hifi magazine, nor on a forum, where people have complained about the sound of these. Their noise effect is significantly greater than a digital volume control.

It depends on the setup, but setting the output from the digital volume controlled device to a maximum with analogue components following, ensuring that this produces the maximum output- then add inline analogue attenuators - should provide the best sound. Again, it depends on the equipment - the opamp in the digital volume device - which one is used, performance profile etc.

Regards,

Shadders.

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So where I'm coming from is, if you don't have a variable digital output, is inserting a high quality attenuator between the dac and the pre going to sound better? Intuitively I would have thought no, but if the benefit of using the higher volume on the pre outweighs the loss of transparency/bass extension/whatever of the passive then it might be worth a try.

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4 minutes ago, Lawrence001 said:

So where I'm coming from is, if you don't have a variable digital output, is inserting a high quality attenuator between the dac and the pre going to sound better? Intuitively I would have thought no, but if the benefit of using the higher volume on the pre outweighs the loss of transparency/bass extension/whatever of the passive then it might be worth a try.

Hi,

No - it depends.

If you have a fixed output DAC, and the output is high, which for a preamplifier will significantly overdrive the amps (pre and power) with the preamp volume at maximum, then an attenuation device will help. Since for analog potentiometers, the lower volume setting will have channel mismatch.

If the volume from the DAC only requires a small amount of volume reduction on the preamp from maximum, then no attenuation required. 

The strategy is to have the highest signals as possible in the chain to ensure the highest S/N ratio, without overdriving the amplifiers, or such that they generate higher THD at normal listening levels.

Regards,

Shadders.

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Hi,
No - it depends.
If you have a fixed output DAC, and the output is high, which for a preamplifier will significantly overdrive the amps (pre and power) with the preamp volume at maximum, then an attenuation device will help. Since for analog potentiometers, the lower volume setting will have channel mismatch.
If the volume from the DAC only requires a small amount of volume reduction on the preamp from maximum, then no attenuation required. 
The strategy is to have the highest signals as possible in the chain to ensure the highest S/N ratio, without overdriving the amplifiers, or such that they generate higher THD at normal listening levels.
Regards,
Shadders.


If I had a high output (as in 2v) dac I would never use the pre amp at full volume. Most active preamps I've used require a level between 0 and 2 for most of my listening, near 0 late at night.

I wouldn't use a resistive pot, I was thinking a stepped attenuator with high quality resistors.

The point of the article was I think to say that having the highest possible input level is not necessarily the best strategy as the pre doesn't sound as good when attenuating lots.

It might be that a bit more THD which you say will be the result actually makes the pre sound more "lively" but I'd be surprised if an experienced amp designer like Paul would fall for that trap.

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Posted (edited)
19 minutes ago, Lawrence001 said:

If I had a high output (as in 2v) dac I would never use the pre amp at full volume. Most active preamps I've used require a level between 0 and 2 for most of my listening, near 0 late at night.

I wouldn't use a resistive pot, I was thinking a stepped attenuator with high quality resistors.

The point of the article was I think to say that having the highest possible input level is not necessarily the best strategy as the pre doesn't sound as good when attenuating lots.

It might be that a bit more THD which you say will be the result actually makes the pre sound more "lively" but I'd be surprised if an experienced amp designer like Paul would fall for that trap.
 

Hi,

What i said was that for a fixed high output DAC, is that with the preamp and power amp outputing the maximum level with the volume turned up to its maximum on the preamp, then this is optimal. If the preamp at its maximum setting is severely overdriving the amplifier for the fixed DAC output, then an attenuator is optimal.

The step attenuator - only possibly if the power amplifier is sensitive, such the output of the DAC fully drives the power amplifier. There is the issue that the step attenuator input impedance can change with volume setting, so this may be an issue on loading the DAC output.

There is a difference between sounding good (subjective) and not generating more THD due to component mismatch or overdriving the system. Not sure who "Paul" is, but the issue is, do you want the system to reproduce the signal with minimal distortion or with added distortion. It is a subjective preference, and maybe people should recognise that is what they like. The statement from the article you posted :

"Most preamplifiers have a zone on their level controls where they sound best; typically higher on their dials.Finding that perfect spot on the dial isn’t too hard, but getting there can be because much depends on the loudness levels of the source and the sensitivity of the speakers."

The key statement is "they sound best" - opamps (DAC output, preamps) generally perform optimally with the maximum voltage rails, and high output voltages (lowest THD and highest S/N). What you seem to be referring to is liking distortion as sounding lively. OK - that is your preference, but we do need to define what other people mean by the sweet spot.

Regards,

Shadders.

Edited by Shadders
Clarity.

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Super Wammer
2 hours ago, Lawrence001 said:

The point of the article was I think to say that having the highest possible input level is not necessarily the best strategy as the pre doesn't sound as good when attenuating lots. 

Apart from a Music First Audio TVC maybe? 

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Apart from a Music First Audio TVC maybe? 
Actually I've got a Django with the same trafos so why am I worrying...

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The problem is two fold

First with old pre-amps (pre CD) it is likely the line stages are 125mv and it depends on the design as to what the upper level of input is before the line stage goes into distortion.  However, that is not the problem that was being addressed (I think).

Second (the problem being addressed) is that a pre-amp may have a high output (say 2 volts) but the power amp may have a requirement for only 1 volt or less to provide full output.  So if that is the case then it is unlikely you will ever get the pre-amp to anywhere close to 12 o'clock and it varies from virtually no volume level to too loud (due to the volume control travel being so small to accurately give a gentle level increase).  Also if the pre-amp is operating with the volume control hardly on, it is not performing to its optimum.

I had that problem with my SP9 into my Hafler (the SP9 provides nearly 2 volts, even with the circuit board user setting to provide a lower output).  I rectified the situation by fitting two rothwell type attenuators between pre and power.  Now the usable volume range on the pre is from 9 oclock for low volume to 2pm for max volume ... whereas before attenuation I was stuck between zero (about 7 o'clock) to 10 o'clock.  So now the pre-amp is performing at its peak levels and I have a nice wide range on the volume control to set listening levels required.

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22 minutes ago, uzzy said:

Also if the pre-amp is operating with the volume control hardly on, it is not performing to its optimum.

I believe this is the issue being discussed in the blog and that's what I'm trying to get a better understanding of. So for a given output, say 0.2v, is it better if this comes straight from the dac and is attenuated by the pre amp volume level at a low setting, or attenuating the input into the preamp, either directly within the dac, or, if you don't have digital attenuation, then by using a passive pre or attenuators, and using a higher volume setting in the pre itself.

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Posted (edited)
17 hours ago, Lawrence001 said:

I believe this is the issue being discussed in the blog and that's what I'm trying to get a better understanding of. So for a given output, say 0.2v, is it better if this comes straight from the dac and is attenuated by the pre amp volume level at a low setting, or attenuating the input into the preamp, either directly within the dac, or, if you don't have digital attenuation, then by using a passive pre or attenuators, and using a higher volume setting in the pre itself.

Most DACs give the same output as a CD (2 volts or thereabouts) as far as I am aware.  If you have variable output then try it on a lower setting but in my experience I also found with my pre that without attenuating between pre and power I was too "loud" on all sources with little movement on the volume control of the preamp.  

As to sound quality I can say that in my experience it improved things with the attenuators due to balancing the output of the pre to the power amp.  I should add that  my first course of action was to attenuate between CD and preamp but realised that it needed to be pre to power so slipped the attenuators over to that formation. 

You need to check the manufacture specs of your preamp to determine if you should reduce the output of the dac to preamp.  Most preamps today are designed to work on about 2 volts on line stages so if that is the case with your preamp then reducing output of the DAC is not ideal, however, if you are using an old quad preamp where it is expecting about 120 millivolts on the line stage then you need to attenuate between the dac and the preamp (IMO) the technical boffins in here will no doubt lend their expertise.

Edited by uzzy
correction
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