Trying to understand input/output voltages

[imdamo]

Hi! Question if I may..

So I notice the two common gain settings on power amplifiers (26.5db/20.5db) are said to be ideal for 2v and 4v inputs respectively..

If my DAC outputs 4 volts over XLR into a preamp with 18db (7x) gain (XLR), then full preamp output would be about 28 volts (if i understand correctly).

Even with the lower power amplifier gain setting of 20db, that's about 280-volts, or 19,600 watts over a 4 ohm load.

Now, I know that can't be right, but I don't know what I'm missing.

Can anyone help explain how preamps with 4-volt XLR inputs are supposed to work with typical 20db gain power amplifiers?

[Guest]

This might make it clearer, or not: https://www.audioholics.com/audio-amplifier/amplifier-voltage-gain

The gain on an amplifier is usually set to drive the amp' to full power with a full theoretical voltage input from your preamp. So the 26.5dB gain means that when the RCA's get a 2V signal (it's not really 2V but let's go with that), then your amp' will be a full volume. You are not really going to be driving an amplifier with a preamp that has 18dB of gain at full volume on the preamp as the amp' will be far into clipping at that point. 

 

Edited June 22, 2023 by Deepthought

[aussievintage]

2 hours ago, imdamo said:

If my DAC outputs 4 volts over XLR into a preamp with 18db (7x) gain (XLR), then full preamp output would be about 28 volts (if i understand correctly).

 

Why do you need to amplify the DAC output?  Is it not already sufficient to drive the power amp directly?  If you must use the preamp for control reasons, turn it down so it has about unity gain.  

[imdamo]

On 22/06/2023 at 12:58 AM, aussievintage said:

 

Why do you need to amplify the DAC output?  Is it not already sufficient to drive the power amp directly?  If you must use the preamp for control reasons, turn it down so it has about unity gain.  

 

I suppose I don't really have a need for pre-amplification, but I would like one for control reasons, and also like the idea of trying different preamps and seeing what they do to the sound. Trying to find the right tone for me, personally. A fools errand perhaps, but my question is adjacent to this. 

 

In looking into preamplifier I've noticed 12db of gain is pretty common. What I don't understand is how that is practical in really any audio system. Especially one with XLR inputs. 

 

From what I understate, standard voltage over XLR is about 4-volts. Power amplifier sensitivity is usually around 4 or 5 volts too.. So when is there ever a need for an XLR preamplifier? 

 

I feel like I must be missing something. Or is everyone just using the first 20 percent of their volume knobs? 

[imdamo]

On 22/06/2023 at 12:43 AM, Deepthought said:

This might make it clearer, or not: https://www.audioholics.com/audio-amplifier/amplifier-voltage-gain

The gain on an amplifier is usually set to drive the amp' to full power with a full theoretical voltage input from your preamp. So the 26.5dB gain means that when the RCA's get a 2V signal (it's not really 2V but let's go with that), then your amp' will be a full volume. You are not really going to be driving an amplifier with a preamp that has 18dB of gain at full volume on the preamp as the amp' will be far into clipping at that point. 

 

 

Thanks deepthought. 

 

This seems to confirm to me that most any preamplifier with XLR inputs will produce a voltage way beyond clipping point on most any power amplifier.

Why would they be designed this way? 

Is there a way to use XLR preamps and still maintain a full range of motion on the volume knob? Doesn't leaving the preamp turned right down to avoid clipping defeat the purpose of the preamp? 

[aussievintage]

21 minutes ago, imdamo said:

 

I suppose I don't really have a need for pre-amplification, but I would like one for control reasons, and also like the idea of trying different preamps and seeing what they do to the sound. Trying to find the right tone for me, personally. A fools errand perhaps, but my question is adjacent to this. 

 

In looking into preamplifier I've noticed 12db of gain is pretty common. What I don't understand is how that is practical in really any audio system. Especially one with XLR inputs. 

 

From what I understate, standard voltage over XLR is about 4-volts. Power amplifier sensitivity is usually around 4 or 5 volts too.. So when is there ever a need for an XLR preamplifier? 

 

I feel like I must be missing something. Or is everyone just using the first 20 percent of their volume knobs? 

 

In the situation described, I would suggest decreasing the output voltage of the DAC, or your preamp, to a point where it allows a useful control range on your preamp. 

 

I think in many instances people do end up with too much gain in their systems, and so need to take steps to manage them.  I always put input level controls on the power amps that I build, so I can adjust their sensitivity so that any preamp volume control  has a useful range.

[imdamo]

21 minutes ago, aussievintage said:

 

In the situation described, I would suggest decreasing the output voltage of the DAC, or your preamp, to a point where it allows a useful control range on your preamp. 

 

I think in many instances people do end up with too much gain in their systems, and so need to take steps to manage them.  I always put input level controls on the power amps that I build, so I can adjust their sensitivity so that any preamp volume control  has a useful range.

 

That sounds logical. My DAC does have a volume knob. 12db gain of 1 or 2 volts would be far more manageable. 

 

Are there any quality losses associated with running a DAC at say 25 percent of full output? One would assume it would still output the full digital bit depth, but attenuated in the analog output. I suppose it depends on the DAC. Mine is an smsl su-9, but I am prepared to replace it if there are others that run better at low voltages. 

[georgehifi]

On 22/06/2023 at 6:04 AM, imdamo said:

So I notice the two common gain settings on power amplifiers (26.5db/20.5db) are said to be ideal for 2v and 4v inputs respectively..

 

Simple, forget all your other numbers you posted up.

If the lower gain of (20.5dB) gets you "loud enough" for your "loudest listening" use it, as you just add more noise by using the higher gains for nothing. 

 

Cheers George

Edited June 23, 2023 by georgehifi

[aussievintage]

8 hours ago, imdamo said:

 

That sounds logical. My DAC does have a volume knob. 12db gain of 1 or 2 volts would be far more manageable. 

 

Are there any quality losses associated with running a DAC at say 25 percent of full output? One would assume it would still output the full digital bit depth, but attenuated in the analog output. I suppose it depends on the DAC. Mine is an smsl su-9, but I am prepared to replace it if there are others that run better at low voltages. 

 

Seems the designers made allowance for your situation.  I just read this in a review "SMSL also included options to put the SU-9 in fixed output mode, as well as the preamp mode with 99 volume level steps." here  https://headfonics.com/smsl-su-9-review/

[imdamo]

So it's completely normal for preamps to be putting out amplifier destroying voltages?

Everyone just attenuates their DACs to compensate? 

 

If anyone here uses an XLR preamp I'd love to hear how they manage their gain staging. 

[imdamo]

1 hour ago, georgehifi said:

 

Simple, forget all your other numbers you posted up.

If the lower gain of (20.5dB) gets you "loud enough" for your "loudest listening" use it, as you just add more noise by using the higher gains for nothing. 

 

Cheers George

Yes, but my concern is too much volume, not too little. 

[georgehifi]

5 hours ago, imdamo said:

Yes, but my concern is too much volume, not too little. 

@imdamo Ok if the lowest gain setting is still too much you need attenuation plugs like the "Rothwell" analog attenuators. 

http://www.rothwellaudioproducts.co.uk/html/attenuators.html

 

Or better for noise, if using an active preamp that has gain, sell it and use a passive pre instead, probably sound better for it.

Cheers George

Edited June 24, 2023 by georgehifi

[Addicted to music]

15 hours ago, imdamo said:

So it's completely normal for preamps to be putting out amplifier destroying voltages?

 

yes.

 

15 hours ago, imdamo said:

 

Everyone just attenuates their DACs to compensate? 

 

That will depend on what your set up is, not everyone runs the same setup.   

 

15 hours ago, imdamo said:

 

If anyone here uses an XLR preamp I'd love to hear how they manage their gain staging. 

I prefer to use XLR, it has multiple advantages over RCA and with the gear I have that supports XLR just sounds better.     Your equipment don’t have to be fully XLR designed,  any amplifier will benefit if it supports XLR.   Your DAC chip outputs pins are  differential +/- outputs, the RCA goes though a separate conversion stage that gives output respect to ground.

[georgehifi]

7 hours ago, Addicted to music said:

23 hours ago, imdamo said:

So it's completely normal for preamps to be putting out amplifier destroying voltages?

 

yes.

 

 

Yes it is normal, but also stupid, because of.

1: Higher gain higher noise/distortion

2: If analog, the resistive track of the volume control is more in the signal path when it's lower in it's travel and less likely to be channel balanced.

3:  If digital, then volume can "bit-strip" more if it's lower than at close to full up. (read below how Wadia got around this)  Maximum gain setting links for the output opamp feedback circuit is the way to go.

(if you don't need an active preamp with gain, get rid of it for a passive, or go direct and use the dac's volume if it has one.) 

Cheers George

 

 

 

 

Edited June 24, 2023 by georgehifi

[Addicted to music]

31 minutes ago, georgehifi said:

 

 

Yes it is normal, but also stupid, because of.

1: Higher gain higher noise/distortion

 

agreed but you don’t have a choice.   also depends on the amplitude.  
The smaller then signal such as from a MM or MC,  are plagued with thermal noise because youre in the micro to milli volt region,  you’re safer when digital as its larger amplitude: 2V plus.   

 

40 minutes ago, georgehifi said:

 

 

Yes it is normal, but also stupid, because of.

 

2: If analog, the resistive track of the volume control is more in the signal path when it's lower in it's travel and less likely to be channel balanced.

 
if you use ordinary prehistoric mechanical wipers,  it’s one of the most destructive devices to effect SQ and it wears from day one of use.    
 

43 minutes ago, georgehifi said:

 

 

Yes it is normal, but also stupid, because of.

 

3:  If digital, then volume can "bit-strip" more if it's lower than at close to full up. (read below how Wadia got around this)  Maximum gain setting links for the output opamp feedback circuit is the way to go.

 

 

 

This is only in the digital domain: software control,   There are many ways to do volume and this far better than any prehistoric mechanical volume potentiometer or optical means.   Volume control chips uses digital to control it the analog domain to 0.25db accuracy, it’s contactless and last the life of the product without maintenance 

 

 

 

52 minutes ago, georgehifi said:

 

 

Yes it is normal, but also stupid, because of.

 

(if you don't need an active preamp with gain, get rid of it for a passive, or go direct and use the dac's volume if it has one.) 

Cheers George

 

 

 

 

 

Agreed, if it was possible

[georgehifi]

3 hours ago, Addicted to music said:

This is only in the digital domain: software control

 

Many of today sources and dacs have digital domain controled volume, and they do "bit strip" if you go below a certain level.

 

I heard my MSB discrete R2R dac loose detail on it's digital domain vc if I went below a certain level, that's why I changed the output opamp's gain in it (lower) like the Wadia does above https://tinyurl.com/2ncpdsv6 , so then I'm up at "75" on the digital vc for normal level, like I just did before getting much more efficient speakers.

 

If you can't do this and you don't use a preamp then you have to use either the Rothwell attenuators on the dac's analog output or go to extremes, get the power amps gain lowered, or less efficient speakers  

 

Cheers George     

Edited June 25, 2023 by georgehifi

[Addicted to music]

9 hours ago, georgehifi said:

 

Many of today sources and dacs have digital domain controled volume, and they do "bit strip" if you go below a certain level.

 

I heard my MSB discrete R2R dac loose detail on it's digital domain vc if I went below a certain level, that's why I changed the output opamp's gain in it (lower) like the Wadia does above https://tinyurl.com/2ncpdsv6 , so then I'm up at "75" on the digital vc for normal level, like I just did before getting much more efficient speakers.

 

If you can't do this and you don't use a preamp then you have to use either the Rothwell attenuators on the dac's analog output or go to extremes, get the power amps gain lowered, or less efficient speakers  

 

Cheers George     

 

Agreed.

 

there is differences in software domain and at the DAC chip feature which just does it by bit  stripping.  I found I like the convenience with a PGA2310, digitally controlled analog domain, just more detailed!  usually critical listening will tell you this is better,  but if you just want to throw some sound in the room, either of the above will suffice!   As long as there isn't any contact wear.

[imdamo]

On 24/06/2023 at 10:48 PM, Addicted to music said:

yes.

 

That will depend on what your set up is, not everyone runs the same setup.   

 

I prefer to use XLR, it has multiple advantages over RCA and with the gear I have that supports XLR just sounds better.     Your equipment don’t have to be fully XLR designed,  any amplifier will benefit if it supports XLR.   Your DAC chip outputs pins are  differential +/- outputs, the RCA goes though a separate conversion stage that gives output respect to ground.

 

Does your volume control knob ever go beyond a quarter turn or so? Do you use a preamp?

 

On 25/06/2023 at 6:36 AM, georgehifi said:

 

 

Yes it is normal, but also stupid, because of.

1: Higher gain higher noise/distortion

2: If analog, the resistive track of the volume control is more in the signal path when it's lower in it's travel and less likely to be channel balanced.

3:  If digital, then volume can "bit-strip" more if it's lower than at close to full up. (read below how Wadia got around this)  Maximum gain setting links for the output opamp feedback circuit is the way to go.

(if you don't need an active preamp with gain, get rid of it for a passive, or go direct and use the dac's volume if it has one.) 

Cheers George

 

 

 

 

 

Turning down my DAC output seems logical, but how do I know if my DAC is doing its attenuation in the digital or analog domain? 

There is no mention of this on the website or in the manual (smsl su-9).

[imdamo]

I find it a little concerning that this is the norm. Lots of people have kids, or in my case, drunken house guests. It's common for someone to think 'Oh man I love this song' and turn up the volume. If I have a preamp controlling volume and a DAC turned down to keep the voltage at safe levels, then all it takes is one well intentioned house guest to reach for the wrong knob and boom, lethal voltages to the power amplifier and lethal wattage to the speakers. 

That is for the most part why I'm finding it hard to belive that this is the accepted normal behaviour of high end equipment. 

[georgehifi]

1 hour ago, imdamo said:

Turning down my DAC output seems logical, but how do I know if my DAC is doing its attenuation in the digital or analog domain? 

There is no mention of this on the website or in the manual (smsl su-9).

Seeing it goes in 0-100 in single steps and is able to be switched off then chances are it's a digital domain volume control. (send email to the manufacturer to be sure)

 

47 minutes ago, imdamo said:

If I have a preamp controlling volume and a DAC turned down to keep the voltage at safe levels, then all it takes is one well intentioned house guest to reach for the wrong knob and boom, lethal voltages to the power amplifier and lethal wattage to the speakers. 

Then forget the preamp, use the dac direct into the poweramp/s for a better sound, and keep the remote in your pocket.

 

Cheers George 

[aussievintage]

2 hours ago, imdamo said:

to reach for the wrong knob and boom, lethal voltages to the power amplifier and lethal wattage to the speakers. 

That is for the most part why I'm finding it hard to belive that this is the accepted normal behaviour of high end equipment. 

 

To be clear, those theoretical wattages you were calculating just can't happen as it is all limited by the power supply voltage and current capability in the power amp.  Take your rail voltage , square it, and divide by nominal speaker impedance, and the attainable power will be somewhat less than roughly that. 

 

 Turning the sound up full briefly (and it will be brief as they (or you) will quickly turn it down again), will not instantly blow everything up.

[imdamo]

On 27/06/2023 at 10:04 AM, aussievintage said:

 

To be clear, those theoretical wattages you were calculating just can't happen as it is all limited by the power supply voltage and current capability in the power amp.  Take your rail voltage , square it, and divide by nominal speaker impedance, and the attainable power will be somewhat less than roughly that. 

 

 Turning the sound up full briefly (and it will be brief as they (or you) will quickly turn it down again), will not instantly blow everything up.

 

Valid point. Calling these preamp voltages gear destroying really isn't fair. But as far as I understand, it does still mean we are operating in the first 20 percent of the motion of the volume knob. Why not have less sensitivity and keep the full range of control?

 

I think there is a good chance my calculation of the output voltage of a typical preamp is also incorrect, as I'm using online calculators but don't fully understand what I'm doing. Or do those numbers sound accurate?

[aussievintage]

2 hours ago, imdamo said:

Why not have less sensitivity and keep the full range of control?

 

That's what I recommend.

 

2 hours ago, imdamo said:

I think there is a good chance my calculation of the output voltage of a typical preamp is also incorrect, as I'm using online calculators but don't fully understand what I'm doing. Or do those numbers sound accurate?

 

They vary widely.    

[Addicted to music]

On 27/6/2023 at 7:31 AM, imdamo said:

 

Does your volume control knob ever go beyond a quarter turn or so? Do you use a preamp?

 

Yes it does.   I use a preamp that has a PGA 2310 chip that digitally control volume from 0-99 steps.
 

 

On 27/6/2023 at 7:31 AM, imdamo said:

 

Turning down my DAC output seems logical, but how do I know if my DAC is doing its attenuation in the digital or analog domain? 

There is no mention of this on the website or in the manual (smsl su-9).

I can guarantee that your SMSL SU-9 is controlling volume using the volume control in the ESS3098 dac chip.   If SMSL was using a digital controlled analog volume chip they will boast about it on there marketing like they have on some of there more expensive dacs.   That’s not a bad thing, as I’ve said, you do away with channel balance issues and wear and tear on contacts from day one that isn’t mentioned on most discussions, that’s the real evil in degradation.   
 

Here’s a video on volume control by Mark Mallision from ESS.   It’s interesting on the figures and the resulting FFT on noise.   Even though he saids digital doesn’t compare with a typical volume pot, pay attention to what he saids about what they discover on the simulation especially when they physically adjust it to the centre.    He also mentions thermal noise that he didn’t really delve into due to allocated presentation time and had to move onto the following topic.