Didn't know where to put this thread because it's not only in solid state amps but in old tube receivers too. I remember from childhood that my dad's stereo sounded very warm and full. At that time I had a more modern stereo Japanese set that had a much more 'neutral' or 'thin' sound. His receiver was Saba Meersburg circa 1973 with only 8 Watts per channel (while I had more than 20Watts at my disposal).
It's only now that I have the same age as my dad then, that I long for that more coloured warm sound. I discoverd that the Meersburg only sounded that good with its own FM radio, not with a line source. With the benefit of hindsight I now suspect (can not find the circuit for free) that a form of loudness or contour was built into the preamp circuit. It was not possible to listen without loudness, it just worked all the time without you knowing it. The more volume you got (the higher you cranked up the volume pot) the more linear the curves got.
I'm researching this topic a bit. What amps and receivers did this trick? Was it a European thing? Apart from Saba I found the Tandberg amps from the 60ties and early 70ties did this into their designs. It's no coincidence then that a lot of Tandberg fans find the older models sounding like full-blooded tube amps.
Here are some clippings from a service manual of a Tandberg receiver early 70ties. PS look at the treble and bass curves, these are measured with the volume pot cranked up at 100% because only then was the inbuilt loudness correction effectively put off. The circuit shows a special kind of volume pot with the an extra loudness tap (see other posts).
After this periode also Tandberg did it the neutral way and only had loudness as a separate feature that could be put on or off. Most of the time this new loudness facility is way too heavy. In the early days it was about a boost of around 5dB @ 50Hz but later it got 10dB or more so making it useless.
Still later we don't see even tone controls in audio equipment anymore. It has to be straight and lineair for some reason.
I'd like to know more makes, designs etc that have this inbuilt loudness correction built into the amps. Right now I'm building my own to relive the old days of my dad's stereo.
It's only now that I have the same age as my dad then, that I long for that more coloured warm sound. I discoverd that the Meersburg only sounded that good with its own FM radio, not with a line source. With the benefit of hindsight I now suspect (can not find the circuit for free) that a form of loudness or contour was built into the preamp circuit. It was not possible to listen without loudness, it just worked all the time without you knowing it. The more volume you got (the higher you cranked up the volume pot) the more linear the curves got.
I'm researching this topic a bit. What amps and receivers did this trick? Was it a European thing? Apart from Saba I found the Tandberg amps from the 60ties and early 70ties did this into their designs. It's no coincidence then that a lot of Tandberg fans find the older models sounding like full-blooded tube amps.
Here are some clippings from a service manual of a Tandberg receiver early 70ties. PS look at the treble and bass curves, these are measured with the volume pot cranked up at 100% because only then was the inbuilt loudness correction effectively put off. The circuit shows a special kind of volume pot with the an extra loudness tap (see other posts).
After this periode also Tandberg did it the neutral way and only had loudness as a separate feature that could be put on or off. Most of the time this new loudness facility is way too heavy. In the early days it was about a boost of around 5dB @ 50Hz but later it got 10dB or more so making it useless.
Still later we don't see even tone controls in audio equipment anymore. It has to be straight and lineair for some reason.
I'd like to know more makes, designs etc that have this inbuilt loudness correction built into the amps. Right now I'm building my own to relive the old days of my dad's stereo.
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My HK Citation I has a loudness switch and a tapped pot so it decreases as you turn up the volume control. I know that HH Scott and Fisher tube equipment also had this. There was one tube pre-amp that I had in the 70's that had a loudness switch and a loudness level control so that you could adjust the loudness vs volume effect to match your speakers efficiency, unfortunately I do not remember who made it. I am not sure if I remember any solid state amps or pre-amps that still had this function after 1972.
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So as I understand: you could choose to have loudness on or off? I am looking for amps that have it hidden under the roof (without you knowing it's on all the time).
In effect all amps from mid 70ties to mid 90ties had a (rather useless) loudness buttion on it, that's not special.
What was special about the HK that it had a tapped pot in conjunction with on/off.
Having a loudness tap on the volume control results in poorer tracking between channels.
With a switched resistor control, loudness compensation can be added with no penalty,
if the internal connection is brought out. Better circuits have separate volume and
loudness controls anyway, so controls without taps can be used for these. See for example
the ARC SP3 preamp. https://www.psaudio.com/pauls-posts/loudness-button/
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I am providing a slight EQ to all inputs except AM and Aux/CD on my rebuilt SX-780.
FM requires a 4th order filter to remove 76khz stereo carrier ( 4 x 19khz ) and a bass boost of about 2 db at 35 hz to sound great.
turntable: MM cart plus preamp = RIAA curve
Iphone: again an FM like boost to the deep bass region
Loudness contour lowered to +6 at 30 hz +4 at 10khz
Tube preamp before and after volume / balance / loudness stack.
70w amp freq response 20 - 20khz +-0.05 db all controls flat aux input.
FM requires a 4th order filter to remove 76khz stereo carrier ( 4 x 19khz ) and a bass boost of about 2 db at 35 hz to sound great.
turntable: MM cart plus preamp = RIAA curve
Iphone: again an FM like boost to the deep bass region
Loudness contour lowered to +6 at 30 hz +4 at 10khz
Tube preamp before and after volume / balance / loudness stack.
70w amp freq response 20 - 20khz +-0.05 db all controls flat aux input.
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FM stereo has a suppressed carrier at 38 kHz and a pilot tone at 19 kHz. RDS and some American equivalent of it (RBDS?) have a suppressed carrier around 57 kHz. I have no idea where you get 76 kHz from.
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Why does having an on/off-button make the loudness control rather useless? Or do you consider the button itself useless?
In any case, a tapped volume potmeter with an RC network connected to it has for quite a long time been the most common way to make a loudness control. You find it in many old radios from the 1950's, for example.
The fact that it's on/off itself is not what makes it useless, it's as stated above the way it's most of the time implemented. Where (as far as I've seen) old fashioned inbuilt controls are rather mild with boosts of around 5dB, the loudness-button-amps are most of the time 10db or even more and that't too much most of the time to sound any good.
Yes, that's what I've seen indeed. But I can see only a few examples of transistorised units and they seem to be only built around the 70ties and from European brands (I only know of receivers by the way). I've found Saba and Tandberg, but guess the same applies for Grundig, Blaupunkt and the like.
The catch is that I never knew these units didn't use flat amplifiers. I assumed that putting the bass and control sliders into mid position meant 'straight amplification'.
OK, that makes sense. I think any loudness control that doesn't give the listener the possibility to set the amount of compensation is flawed. What you try to correct for, is the difference between the shapes of the equal loudness contours ( Equal-loudness contour - Wikipedia ) at the level used for recording or mastering and at the level used for playback. As the levels used for recording or mastering are generally unknown and may vary a lot depending on the type of music, the most practical way to deal with this is to give the user control over the amount of compensation. A compensation of 10 dB up to 40 Hz is about correct when the playback volume is 20 dB below the mastering or recording level.
I had an old Mitsubishi receiver that I used for a few years. It had 5 or 6 loudness settings selected by a rotary switch. It was a passive network driven by a basic discrete circuit. It worked pretty well. It was a decent receiver until one of the power amp modules burned up, taking a speaker with it.
I have a Nakamichi receiver (circa 1995) that has a variable loudness control. It is a passive circuit buffered by op amps. It works very well.
I've seen tons of loudness controls; most bad, some not too bad. I have visited this topic several times and have not come up with a satisfactory circuit. I have some fresh ideas and hope to revisit it soon.
I have a Nakamichi receiver (circa 1995) that has a variable loudness control. It is a passive circuit buffered by op amps. It works very well.
I've seen tons of loudness controls; most bad, some not too bad. I have visited this topic several times and have not come up with a satisfactory circuit. I have some fresh ideas and hope to revisit it soon.
Back when I first started messing with this stuff as a kid with my first stereo amp (Heathkit AA-29), at first the loudness button seemed to do too much to be useful. I soon figured out that the loudness curve was not constant, and did indeed decrease as the master volume slider position increased, essentially flattening out again at about 75% or so, can't remember exactly.
The problem of course was that the preamp/amp combination had a fair bit of extra gain in the design, as most do, presumably to cover all the possible combinations of peripheral gear. This negated the usefulness of the loudness feature (at least in my case), since it was way too loud at 75% volume.
My solution was to add a second stereo volume pot between the preamp output and the power amp input, to adjust down the gain of the system until the volume slider position (and loudness contour) was more calibrated to the actual SPL produced by the system as a whole. This wasn't perfect of course, but it was close enough that I was able to just leave the loudness function engaged most of the time.
I only ever saw one commercial product that seemed to address this problem directly out of the box; a large Kenwood stereo receiver owned by a friend. It had a normal volume control with switchable loudness contour, but there was also a second concentric volume knob that allowed a straight system gain calibration. I always thought that was a pretty smart feature, and wonder why it wasn't more popular.
Funny thing is, I only ever bothered with all the above with that very first system. With all subsequent setups, I just haven't thought about loudness compensation very much. And with my current all-digital rig, I'm not even sure how or if I could implement such a thing.
The problem of course was that the preamp/amp combination had a fair bit of extra gain in the design, as most do, presumably to cover all the possible combinations of peripheral gear. This negated the usefulness of the loudness feature (at least in my case), since it was way too loud at 75% volume.
My solution was to add a second stereo volume pot between the preamp output and the power amp input, to adjust down the gain of the system until the volume slider position (and loudness contour) was more calibrated to the actual SPL produced by the system as a whole. This wasn't perfect of course, but it was close enough that I was able to just leave the loudness function engaged most of the time.
I only ever saw one commercial product that seemed to address this problem directly out of the box; a large Kenwood stereo receiver owned by a friend. It had a normal volume control with switchable loudness contour, but there was also a second concentric volume knob that allowed a straight system gain calibration. I always thought that was a pretty smart feature, and wonder why it wasn't more popular.
Funny thing is, I only ever bothered with all the above with that very first system. With all subsequent setups, I just haven't thought about loudness compensation very much. And with my current all-digital rig, I'm not even sure how or if I could implement such a thing.
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I once had a Braun valve amplifier that also had two cascaded volume controls, one with flat response and one with loudness control.
Any chance you remember type and year of this Kenwood receiver? It looks like a smart solution.
I've been Googling awhile, but haven't been able to find it. (It's been almost 40 years since I last saw it, sorry.)
On the other hand, It would be pretty easy to do what I did with my Heathkit. I added my gain control to the back panel and wired it internally, but it could also be built into a separate little box and plugged into the preamp out / power amp in jacks that many receivers had back in the day. All you need is a 10K, 25K or 50K stereo pot wired as a voltage divider; taper isn't even that important in this application.
This passive control would of course provide only variable attenuation, not gain; but it's more likely that you'd be correcting for too much gain instead of not enough, so that's likely not a problem either.
On the other hand, It would be pretty easy to do what I did with my Heathkit. I added my gain control to the back panel and wired it internally, but it could also be built into a separate little box and plugged into the preamp out / power amp in jacks that many receivers had back in the day. All you need is a 10K, 25K or 50K stereo pot wired as a voltage divider; taper isn't even that important in this application.
This passive control would of course provide only variable attenuation, not gain; but it's more likely that you'd be correcting for too much gain instead of not enough, so that's likely not a problem either.
Another approach is to simply make a tone control that follows the differences between equal loudness contours. The bass part of the Viddeleer tone control (developed by L.V. Viddeleer in the 1940's) matches the ISO-226:2003 contours quite nicely when you change the time constant L1/(R8 + R9 + R10 + R11 + R12 + R2 + 1/gm) to 430 us. The attached curves are for a 430 us time constant, with the resistors split up a bit further to give 3 dB steps and with infinite C2 and C5. "Gewenst bij -10 dB" means desired with 10 dB attenuation. Mod 6 is the transfer with the control set to +6 dB, mod 9 set to +9 dB and so on.
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By taking the dual circuit and swapping some parts, you can make a variant that you can implement with op-amps and a capacitor rather than an inductor. A disadvantage is that the switching arrangements get more complicated.
Sure.
I had experimented with variable loudness circuits that emulated commercial designs; the better ones I've seen were passive networks buffered on both sides with op amps. My results were surprisingly disappointing. Although I figured it out I have had to move on to other projects for the time being.
My new scheme involves putting a loudness contour network inside the feedback loop of an inverting op amp circuit. The center of the network will be connected to the non inverting input with a potentiometer. This circuit will be similar to custom speaker compensation circuits, which I have had great success with. The big difference is the potentiometer.
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