Tonal changes linked to volume control settings; can it really be so?

[Neil McCauley]

Hello. In summary, should the tonal characteristics of an amp be consistent across at least 80 percent of its volume control range?

Let me explain if I may. I've heard tell of a person – and he might not be the only one – who while using a sophisticated integrated amp (the brand is irrelevant in this context I think and might be a distraction from the core issue) notices a change of tone that is linked to the volume. Thus, apparently, he is struggling to achieve concurrently the volume he likes plus the tone he likes. He can achieve one, or the other – but not both. This is particularly apparent on well-recorded solo instruments and female voice.

A lack of bass at low volumes isn’t the issue here though. It’s tonal characteristics in the low mid to top spectrum.

Room acoustics must of course play a part but it seems not to be the most significant contributor. I don't have the details re this and so can't elaborate.

Frankly I've not experienced this in the audio world but … I am well aware of it with my bass guitar rig inasmuch as with the gain and vol controls on my SWR BabyBlue combo amp, I get the precise tone I want (Epiphone Jack Casady) at one particular setting on the guitar volume bass control. This is with me leaving the guitar bass controls untouched. Apparently most musicians experience this; it’s commonplace.

Perplexed, I spoke to a well known designer of studio systems. This volume versus tone issue is, again, frequently encountered in that world.

While I've yet to confront this on my modern home system I think (and I use the word advisedly here) I hear it via some of my vintage amplification.

Has anyone here experienced something similar? Thanks. Howard.

[Marco]

Hi Howard,

You may have noticed that a new sub-forum has been opened for your use in the name of LFD4U, see here: http://theartofsound.net/forum/forumdisplay.php?95-LFD4U

Please open it by posting there. Cheers! :cool:

Marco.

[Neil McCauley]

Hi Howard,

You may have noticed that a new sub-forum has been opened for your use in the name of LFD4U, see here: http://theartofsound.net/forum/forumdisplay.php?95-LFD4U

Please open it by posting there. Cheers! :cool:

Marco.

Thanks Marco. Will do, probably tonight. Got your emails and thanks. Been heavily distracted for most of today battling server issues. Sometimes I seriously wonder about online technology, I really do.

[Marco]

Lol - no worries... I wasn't sure if you knew what required doing. Don't get me started on technology! :eek: ;)

Marco.

[zanash]

may be connected or may not be ....I've often experienced the effect where some rooms need a certain lvl of sound to sound good. Its almost as if the sounds been sucked out quicker than the rooms filled .......thats as nr as I can create an analogy. You purposely refrained from mentioning the brand ......if its the amp that should be simple to test. if its got its own headphone socket a revealing pr of phone should easily pick up any tonal change when using the volume pot.

[Neil McCauley]

may be connected or may not be ....I've often experienced the effect where some rooms need a certain lvl of sound to sound good. Its almost as if the sounds been sucked out quicker than the rooms filled .......thats as nr as I can create an analogy. You purposely refrained from mentioning the brand ......if its the amp that should be simple to test. if its got its own headphone socket a revealing pr of phone should easily pick up any tonal change when using the volume pot.

Headphones? BRILLIANT idea. Thank you. I wish I'd thought of that. I hope the anonymous chap might by chance be reading this. Hope so. If he hasn't got a headphone jack then he could use a pair of vintage STAX earspeakers where the energiser takes its power from the speaker terminal outputs.

[YNWaN]

There are a bunch of things that could be happening. Room interaction is certainly one of them. However it could also be the way the volume control has been implemented. Also, some low powered amps (valve) go into clipping very early but do so in a forgiving manner and people often prefer the sound like that. The ear itself is a tone control of sorts - as the level goes down so mid range sensitivity of ones hearing increases and the frequency extremes decrease - hence the reason for the old 'Loudness' button that raised bass and treble for low volume listening.

[Yomanze]

Hello. In summary, should the tonal characteristics of an amp be consistent across at least 80 percent of its volume control range?

Let me explain if I may. I've heard tell of a person – and he might not be the only one – who while using a sophisticated integrated amp (the brand is irrelevant in this context I think and might be a distraction from the core issue) notices a change of tone that is linked to the volume. Thus, apparently, he is struggling to achieve concurrently the volume he likes plus the tone he likes. He can achieve one, or the other – but not both. This is particularly apparent on well-recorded solo instruments and female voice.

A lack of bass at low volumes isn’t the issue here though. It’s tonal characteristics in the low mid to top spectrum.

Room acoustics must of course play a part but it seems not to be the most significant contributor. I don't have the details re this and so can't elaborate.

Frankly I've not experienced this in the audio world but … I am well aware of it with my bass guitar rig inasmuch as with the gain and vol controls on my SWR BabyBlue combo amp, I get the precise tone I want (Epiphone Jack Casady) at one particular setting on the guitar volume bass control. This is with me leaving the guitar bass controls untouched. Apparently most musicians experience this; it’s commonplace.

Perplexed, I spoke to a well known designer of studio systems. This volume versus tone issue is, again, frequently encountered in that world.

While I've yet to confront this on my modern home system I think (and I use the word advisedly here) I hear it via some of my vintage amplification.

Has anyone here experienced something similar? Thanks. Howard.

Good evening Howard,

Nice to see you back on the forums.

In response to your question I am in a listening environment where I often need to listen at ultra-low volume. I use a Krell KRC-3 preamp, which has a unique volume control in that 300 different attenuation values are chosen from a combination of precision resistors. Far far more flexibility than a stepped attenuator.

All potentiometers have issues with channel imbalance and tonal issues at very low volume - subjectively it's like you need to turn the wick up a bit for it to open up - however, as it gets louder the issues even out and balance improves. Stepped attenuators don't offer fine adjustment but do offer proper channel balance. The Krell KRC-3 is uncanny in its ability to have no change of timbre, tone or soundstage at different volumes, just sounding 'louder' or 'quieter'.

Thus, absolutely, volume control can have a fundamental impact on audio qualities *especially* at low volume and especially when dealing with potentiometers & 'pot sound'. It is extremely difficult IMHO for HiFi to sound open and alive at low volumes.

At medium to higher listening levels the issues are far less relevant.

Best regards,

Neil

[struth]

certainly when using my Proarts as monos, I find the balance control on each amp has differing effects at different levels, so this may have some connection. I actually find it very usefull to aid my speakers do full justice to themselves.

[Neil McCauley]

Good evening Howard,

Nice to see you back on the forums.

In response to your question I am in a listening environment where I often need to listen at ultra-low volume. I use a Krell KRC-3 preamp, which has a unique volume control in that 300 different attenuation values are chosen from a combination of precision resistors. Far far more flexibility than a stepped attenuator.

All potentiometers have issues with channel imbalance and tonal issues at very low volume - subjectively it's like you need to turn the wick up a bit for it to open up - however, as it gets louder the issues even out and balance improves. Stepped attenuators don't offer fine adjustment but do offer proper channel balance. The Krell KRC-3 is uncanny in its ability to have no change of timbre, tone or soundstage at different volumes, just sounding 'louder' or 'quieter'.

Thus, absolutely, volume control can have a fundamental impact on audio qualities *especially* at low volume and especially when dealing with potentiometers & 'pot sound'. It is extremely difficult IMHO for HiFi to sound open and alive at low volumes.

At medium to higher listening levels the issues are far less relevant.

Best regards,

Neil

Thanks Neil. Good points. The chap in question (I'm getting closer to have a direct rather than indirect dialogue) has his tonal 'issues' at around one third up from zero rather than at low spl. Intriguing.

[Neil McCauley]

There are a bunch of things that could be happening. Room interaction is certainly one of them. However it could also be the way the volume control has been implemented. Also, some low powered amps (valve) go into clipping very early but do so in a forgiving manner and people often prefer the sound like that. The ear itself is a tone control of sorts - as the level goes down so mid range sensitivity of ones hearing increases and the frequency extremes decrease - hence the reason for the old 'Loudness' button that raised bass and treble for low volume listening.

Thank you. Interesting re tube devices. I hadn't thought of this. Suddenly I feel a little nostalgic for my Manley Shrimp.

[Yomanze]

Thanks Neil. Good points. The chap in question (I'm getting closer to have a direct rather than indirect dialogue) has his tonal 'issues' at around one third up from zero rather than at low spl. Intriguing.

Yes, probably his preamp has a potentiometer and there's some issues with the tracking somewhere.

[Hipper]

Would this have anything to do with Equal Loudness Curves (ELC), often called Fletcher-Munson Curves?

https://en.wikipedia.org/wiki/Equal-loudness_contour

Whilst ELC apply to frequencies, tone (or timbre) is formed by a number of frequencies (harmonics) and the ratio of these will vary at different volumes according to those curves.

If this is the cause then it is not the amp's volume control but the listeners interpretation. I should also point out that these curves are averages of different listeners and so shouldn't be taken too literally for interpreting how you hear.

There was a type of equaliser, called TACT, that is no longer in production, that could employ ELCs as you changed the volume. Maybe there are other products that do this, such as software.

[SPS]

There is a fair chance the issue could be the power supply modulatation, in every amplifier the power supply has an imprint of the signal on it, as the volume increases so does that imprint, and in the case of most amplifiers each channel has an increasing amount of the other chanel on it, that usually causes cancellation as the signal voltages are added together on each chanel,
This causes a lack of resultion, changing the sound, and is always volume related
It is a big issue in valve amps especially SE, as their normally high resultion highlights this , and the likes of rock music causes alot more modulation than simpler music, so at higer volumes simple music sounds good and rock can struggle, resulting in a blurred sound

It is a bigger issue with pa kit, bands tend to sound best without going through a mixing desk and keeping all the instruments seperately amplified, but as ever it depends on the quality of the equipment used

Cheers...

[Neil McCauley]

There is a fair chance the issue could be the power supply modulatation, in every amplifier the power supply has an imprint of the signal on it, as the volume increases so does that imprint, and in the case of most amplifiers each channel has an increasing amount of the other chanel on it, that usually causes cancellation as the signal voltages are added together on each chanel,
This causes a lack of resultion, changing the sound, and is always volume related
It is a big issue in valve amps especially SE, as their normally high resultion highlights this , and the likes of rock music causes alot more modulation than simpler music, so at higer volumes simple music sounds good and rock can struggle, resulting in a blurred sound

It is a bigger issue with pa kit, bands tend to sound best without going through a mixing desk and keeping all the instruments seperately amplified, but as ever it depends on the quality of the equipment used

Cheers...

Thank you. This is most helpful. Interested parties, do watch this post because .... there may be a solution in the wings using an optical servo system. Here's what I've been told so far:

"The volume control is done with a Photovoltaic Resistor a large LDR is used on each channel this help to reduce the noise and increase the balance between them. Green Leds are used as the light source this produce less noise then red Leds and has 570nM light spectrum and the LDR is about the same at 575nM this helps with the matching."

[SPS]

Thank you. This is most helpful. Interested parties, do watch this post because .... there may be a solution in the wings using an optical servo system. Here's what I've been told so far:

"The volume control is done with a Photovoltaic Resistor a large LDR is used on each channel this help to reduce the noise and increase the balance between them. Green Leds are used as the light source this produce less noise then red Leds and has 570nM light spectrum and the LDR is about the same at 575nM this helps with the matching."

The LDR can cause channel imbalances but that alone should not affect the tone by any amount
I have used one in my system, many people report an improvement to the sound,
But unfortunately on my (high resolution) system it produced clear audible distortion .. I would not use one

[Ali Tait]

Measurements that were made bear this out-

http://www.audio-talk.co.uk/phpBB3/viewtopic.php?f=9&t=5720&p=120711&hilit=ldr#p120711

[Yomanze]

Classic case of "fixing" a problem (switch contacts and wipers) and introducing new ones in the process.