Are passive volume controls totally transparent?

[Miguelón]

this is around 10x bigger than the typical output impedance of an active device.

Got it, thanks!

Double happy of having bought my Ifi Zen DAC, has an analogue volume knob and an output impedance of 200 Ohms.

 

[antcollinet]

has an analogue volume knob

Which is fine - but in most cases not audibly superior to digital volume control. Despite the claims of IFI.

 

[solderdude]

Impedance of cables is expressed in ohms per meter? Or per feet?

Cable impedance is the characteristic impedance which is only important > audible frequencies.

Often wire resistance is given in ohm/km.
Capacitance and inductance per meter or foot.

 

[Miguelón]

Which is fine - but in most cases not audibly superior to digital volume control. Despite the claims of IFI.

In fact, I realized I don't need it (and agree, seen a little bit on the marketing side).

Genelec G Three can be reduced by 10 dB with one of its dip switches, then resulting in 86 dB @ 0 dBu.

Actually I can playback at reasonable dBFS and bypassing the analogue attenuator of the Ifi

 

[Miguelón]

Cable impedance is the characteristic impedance which is only important > audible frequencies.

Often wire resistance is given in ohm/km.
Capacitance and inductance per meter.

Humm, according to the matemathical telegraph model, the inductance and capacitance per meter will begin to have importance in the line if the output impedancd of the attenuator is high. Is not my case, but in the case of the 5k passive device can become audible.

Cable impedance is the characteristic impedance which is only important > audible frequencies.

Often wire resistance is given in ohm/km.
Capacitance and inductance per meter.

In the given expression capacitance and inductance per lenght can impact charscterisric impedance of the line.

I didn't run any calculation yet because have not inductance and capacitance values and their impact in impedance is also frequncy dependent...

 

[Holmz]

Impedance of cables is expressed in ohms per meter? Or per feet?

Either.

I see, impedance is not dependent on lenght in usual distances, is a charachteristic value.

Why the lenght does matter in XLR balanced signals? Is the combination of the attenuator plus the cable lenght that can cause alterations?

XLRs are more immune and better. I thought you might be using RCAs, but clearly the link showed XLRs.

I recently red about the common wire ground (L+R signal) resistance combined with R out and amp resistance can affect soundstage but I thought was only for headphones.

I have a quite particular output, Pentaconn balanced but this means that ground wire is shared by both channels. But my cables are 10 feet

If you are not turning the thing way way down, then it should be OK.
I would start with one device, and a single stereo amp and a single speaker.
If you can get that to behave how you want, then it should bode well for the second speaker being added in.

Probably makes as much sense to just use a beefier amp than biamping, but active XO have some advantages..

 

[Miguelón]

Either.


XLRs are more immune and better. I thought you might be using RCAs, but clearly the link showed XLRs.


If you are not turning the thing way way down, then it should be OK.
I would start with one device, and a single stereo amp and a single speaker.
If you can get that to behave how you want, then it should bode well for the second speaker being added in.

Probably makes as much sense to just use a beefier amp than biamping, but active XO have some advantages..

I'm using XLR, WiiM RCA doesn't sound good in my home setup, I think either is a bad unit or I have issues with the electric installation because the differenece between both lines are too much high as expected.

 

[solderdude]

In the given expression capacitance and inductance per lenght can impact charscterisric impedance of the line.

For analog audio and interlinks only the capacitance is of importance in combination with the output resistance of the source (or the output resistance of the attenuator which varies per setting).
A simple 1st order (6dB/oct = 20dB/decade) low-pass filter is formed.
When the cutoff frequency comes near 50kHz there can be measurable differences in phase and amplitude response bordering on being detectable in direct comparisons.

Ohmic resistance is not important not even for longer lengths.

 

[Miguelón]

A simple low-pass filter is formed

Yes, this is what I learned from your contribution and other members help, and I wrote in my "acknolewdgement" message.

I think you should know how much myths and wrong posts exist on some audiophile sites around the line transmission, when I came here I had to re-learn all again.

And finally all can be mostly resumed in that inoffensive and gently roll-off, except for some really highly unmatched amps-preamps-source lines, or interferences.

Not only ASR is a source of learning pleasure, but it saved me hundreds of euros I don't have

 

[solderdude]

The main problem with passive volume controls is that the output resistance of the attenuator varies and so does the cut-off point.
It is 'worst' at -6dB attenuation (half the input voltage) and thus that is what is used to calculate the worst case.
For linear potmeters this is the half-way setting but linear controls are only suited as 'gain control'. For volume control (semi) logarithmic controls are used and the -6dB point is usually around 75% of the total 'travel'.

Assuming the output resistance of the source being very low compared to that of the atttenuator you can set the R value for calculation of the -3dB frequency for the formed low-pass to 1/4 of the input resistance of the attenuator.
So a 10k potmeter has worst case 2.5k in resistance (at -6dB setting) and will be lower on either side of that volume setting meaning the -3dB frequency point will be higher.

For capacitance one should use the capacitance of the used cable length... so 10m with 220pF/m = 2200pF (2.2nF).

f(in Hz) =1/( 6.28 x R(in ohm) x C(in farad) ) when the found worst case frequency is above 50kHz you're safe.

 

[Miguelón]

The main problem with passive volume controls is that the output resistance of the attenuator varies and so does the cut-off point.
It is 'worst' at -6dB attenuation (half the input voltage) and thus that is what is used to calculate the worst case.

Assuming the output resistance of the source being very low compared to that of the atttenuator you can set the R value for calculation of the -3dB frequency for the formed low-pass to 1/4 of the input resistance of the attenuator.
So a 10k potmeter has worst case 2.5k in resistance (at -6dB setting) and will be lower on either side of that volume setting meaning the -3dB frequency point will be higher.

For capacitance one should use the capacitance of the used cable length... so 10m with 220pF/m = 2200pF (2.2nF).

f(in Hz) =1/( 6.28 x R(in ohm) x C(in farad) ) when the found worst case frequency is above 50kHz you're safe.

Thanks, this is very pracitc to know worst case and accptable case scenario.

What about gain input? Switching -10 dB sensitivity reduction on the amp input has less inpact or equal than at the middle or source output?

I suppose by intuition that is better, because the attenuator is on lowest impedance or not needed and there's no more elements on the line after reduction.

 

[solderdude]

Thanks, this is very pracitc to know worst case and accptable case scenario.

What about gain input? Switching -10 dB sensitivity reduction on the amp input has less inpact or equal than at the middle or source output?

I suppose by intuition that is better, because the attenuator is on lowest impedance or not needed and there's no more elements on the line after reduction.

That totally depends on where in the circuit this is done. Usually this is not done directly at the output of a source nor by changing the input resistance of a load so is independent of the cable parameters.

Using an external attenuator (resistor divider) of course will but the output R to use in the formula is not 1/4 but 1/5 of the input resistance for a -10dB attenuator

 

[Miguelón]

That totally depends on where in the circuit this is done. Usually this is not done directly at the output of a source nor by changing the input resistance of a load so is independent of the cable parameters.

Using an external attenuator (resistor divider) of course will but the output R to use in the formula is not 1/4 but 1/5 of the input resistance for a -10dB attenuator

I don't know where is the attenuartor implemented, in Genelec G Three the amp is on the speaker, but I imagine that this means nothing. Subjectively sounds better when activate the -10 dB input gain reduction on the speaker and the "fixed" switch on the DAC preamp side, than if I go full sesnitiviy
on Genelecs and use the "variable" switch in the DAC with the volume pot.

Also this can be meaningless, just personal prefernce or purely psychological

 

[dualazmak]

Am I correct? What software should I use to see the harmonics?

I am sorry for my being late in noticing and responding to your early inquiry in your post #7.
And, since I have not yet fully reviewed the discussion after that until now on this thread, please forgive me if your above inquiry has been already well responded on this thread.

Just for your possible reference and interest, "to see", i.e. visually observe, the harmonics tones, I usually use 3D (gain-Fq-time) color spectrum given by Adobe Audition (I use ver.3.0.1) with proper/adequate "spectral control" parameters.

You would please find many of such 3D color spectrum examples in the posts on "Reference Quality Music Playlist" under the thread entitled "An Attempt Sharing Reference Quality Music Playlist: at least a portion and/or whole track being analyzed by 3D color spectrum of Adobe Audition".

In this my post, please let me copy-paste three typical examples of such 3D color spectrum of solo violin music (ref. here #643), cello music (ref. here #644), and female vocal (ref. here #639);

Ref. here #643

Ref. here #644

Ref. here #644

Ref. here #639

 

[dualazmak]

Even though I also use rather "affordable" Behringer ECM8000 measurement microphone (specially selected unit in 2008, ref. here #813 and here #819), recently I could fortunately cross-calibrate it and found it has still-nice/acceptable flat Fq response all the way through 15 Hz to 25 kHz, as shared here #831 on my project thread.

You (we) should be careful enough about Fq response of our individual measurement microphone(s) as I shared this diagram in my post there #831.

 

[Miguelón]

Even though I also use rather "affordable" Behringer ECM8000 measurement microphone (specially selected unit in 2008, ref. here #813 and here #819), recently I could fortunately cross-calibrate it and found it has still-nice/acceptable flat Fq response all the way through 15 Hz to 25 kHz, as shared here #831 on my project thread.

You (we) should be careful enough about Fq response of our individual measurement microphone(s) as I shared this diagram in my post there #831.
View attachment 434720

I saw other mic calibration, frequently show some deviations on the mid-high region, but for instance I'm only correcting some modes and just the 2500 Hz dip that appears on 8030C Amir measurements

 

[JRR]

So do I understand this correctly that having 25’ before and 3’ after the XLR POT would be a non issue?

 

[DonH56]

Attenuator Bandwidth

This article is to explore how line-level attenuators might affect the signal bandwidth. An attenuator is to reduce the signal amplitude from a source before it is applied to the next component. This could be between a DAC and preamp, or between preamp and power amp. Etc. The reason is usually...

www.audiosciencereview.com

 

[Blumlein 88]

So do I understand this correctly that having 25’ before and 3’ after the XLR POT would be a non issue?

Yes, keep the length from passive volume output and the input of speaker or amp short. No problems.

 

[Holmz]

Yes, keep the length from passive volume output and the input of speaker or amp short. No problems.

And the lower the volume is turned down the worse it performs.
If one is going to really turn it down super low, then a preamp is a safer option.