Barry
29-11-2010, 17:59
I was prompted to start this thread by being reminded of a slightly sexist cartoon showing the difference between an audio amplifier built for men and one built for women. The ‘man’s’ amplifier had just had one control – an on/off switch, whereas the ‘woman’s’ amplifier was festooned with all manner of controls – allowing complete control of every thing and everything! Clearly the ‘joke’ was that men know exactly what they want without fuss, whereas women can’t make up their minds and need to be able to make all sorts of alterations. Whether you think the joke sexist or not, or even funny or not, is not really important - though it did cause one member to leave as he could not see the ‘knowing’ humour. What is important is whether the controls fitted are sufficient and useful. This is the area I want to explore, express my take on it and open it up for discussion.
A Bit of History
In the early days, audio preamplifiers (or ‘control units’ as they were then called) came with a comprehensive range of controls. This was due partly to the lower standard of audio quality that could be wrought from disc (vinyl!), tuner or from tape, compared with what we enjoy today, and partly due to the un-standardised replay characteristic used; each record company had its own replay characteristic and it wasn’t until 1955 that the RIAA equalisation response was devised and adopted internationally.
Preamps in those days had tone controls, usually just bass and treble affecting the frequency range from ~ 1kHz (or, in those days 1Kc/s) upward or down with a massive +/-12dB amplitude range. Most preamplifiers used the feedback circuitry devised by Peter Baxandall to implement these tonal adjustments. Some, usually of American manufacture, even had a third centre or ‘presence’ tone control. Apart from the tone controls there were often various filters, both low-pass (called ‘scratch’) and high-pass (called ‘rumble cut’), and of these, the former might have a range of ‘turn over’ frequencies as well as a range of filter slopes! But we’re far from finished: the choice of inputs a preamplifier could handle might include two pick-up inputs (this was in the days where a serious audio enthusiast would have two decks; one to play the new fangled vinyl ‘microgroove’ and one to play 78s) a choice of pick up cartridge equalisation, loading and sensitivity (for various type of pick up: moving coil; fixed coil and for the less well off, the ceramic cartridge), as well as a tuner, microphone, tape line output and even one for direct connection to a tape head. And on top of all this, with the advent of stereo and the necessity to use two channels, the preamp would have a balance control, and switching for mono (one channel only), mono (split between both channels), stereo and stereo reverse (for those who having got their left- and right-hand channels mixed up and couldn’t be bothered to swap the speaker connections!). Not surprisingly, the preamps were festooned with controls – this was man’s stuff: women "needn’t worry their pretty little heads" with all this complicated stuff; or so the thinking went at the time and quite the opposite of the joke of the cartoon I alluded to above.
http://i780.photobucket.com/albums/yy88/barrydhunt/IMG-1-1.jpg?t=1291039803
A Rogers 'Master Mk II Control Unit' (Photo: advertisment in HFN/RR)
In the late sixties a new facility appeared on preamp fascias – the ‘quiet’ or ‘loudness’ switch. Despite the contradictory labels, this facility was designed when one wanted to listen at low volume, late at night. It was however an example of woolly thinking. The idea was to be able to listen at low levels and yet not loose detail at the frequency extremes. To do this, the switch introduced an overall attenuation of 15 - 20dB and then imposed a frequency correction according the ‘equal loudness’ contours derived by Fletcher and Munson or by Robinson and Dadson.
The human ear only has a relatively flat response at around the 120 phon level (120dB above the threshold of hearing); at other levels below this very loud volume level, the ear’s response is far from flat. Yet this is what we are all used to and the brain allows for it. Adding bass and some treble boost just makes everything sound ‘wrong’ and false. Not surprisingly this facility didn’t last long.
Preamplifiers offering this facility included the Sugden C51 and the Radford SC24.
“The Less is More”
In the ‘70s a new way of thinking came about. By now the quality of record reproduction had improved enormously, most enthusiasts opted for a magnetic (electrodynamic) cartridge and of course there was the universal replay characteristic. This meant that tone controls were called upon less frequently and the use of filters even less. Some amps retained the selection between mono and stereo replay, and virtually all amps had a balance control. However all this little-used circuitry was still in the signal path and the possible effect of this circuitry to the degradation of the signal quality was considered; only a few amplifiers (the Quad and Hafler 101 for example) had a ‘cancel’ control, whereby the tone and filters could be switched out of the overall signal path. If this extra circuitry wasn’t wanted or wasn't being used, why pay for it to be included in the first place?
One of the first in the vanguard of these minimalist preamps was the Naim NAC12, seemingly following the maxim: “the less is more”. The NAC12 only had three knobs: one to select the input; a balance control and of course a volume control. The unit did not even have an on/off switch: power was derived from a Naim power amplifier, which had its own switch. Naim later claimed the removal of unnecessary circuitry was done with sound considerations in mind, however early literature suggests tone controls were not fitted as the preamp was intended to be used with a multi-channel graphic equaliser! However such was the influence of the ‘Young Turks’, that other manufacturers followed suit and offered minimalist designs. The Americans were doing the same, however the Japanese continued to provide a full range of facilities (these could however be switched out if unused).
http://listeninn.com/catalog/imagemagic.php?img=images/Used-Pre-Amplifiers/Naim-Audio-NAC12.jpg&w=430&h=430&page=popup
Naim NAC 12 preamp. (Photo: listeninn.com)
The trend for minimum control was maintained by the likes of Meridian and Creek, and later by Onix and Cyrus. The only deviation from this paring down of controls occurred around the ‘90s with the introduction of an ‘absolute phase’ switch, and on some of the more specialist preamps, comprehensive cartridge impedance loading and sensitivity adjustments appeared on the fascia rather than being hidden away within the interior of the preamp.
The introduction of an ‘absolute phase’ switch is interesting. It first appeared on American preamplifiers, such as the Mark Levinson ML26S
http://i780.photobucket.com/albums/yy88/barrydhunt/800px-No26s_front1.jpg
Levinson ML26S preamp with balance controls, mono/stereo switch and an absolute phase polarity switch. (Photo Wikipedia)
It is usually assumed that audio reproduction systems are wired so the correct absolute phase is maintained from microphone through to speaker. This means that explosive sounds, such as those from wind instruments and percussive instruments such as a kick drum, initially creating a local compression of the air, will be so reproduced via the recording process and replay system so that the loudspeaker cones or diaphragms move outwards towards the listener producing the same local air compression. It is a moot point whether the initial transient of a plucked or bowed string causes an initial compression or rarefaction; it all depends on the microphone placement, if at all. Note this has nothing to do with the two speakers being ‘out of phase’. In the latter, when fed with equal signals, one speaker will move out, the other moves in; completely destroying the ability to produce a central acoustic image and hence incapable of presenting a stereo image.
Now it is not obvious that the correct absolute phase is important to some people; especially so as some amplifiers are inverting while others are not. The situation is further confused with the use of multi-miked recordings; not all of the microphone channels may be in phase with one another. And furthermore the situation can easily vary track to track on a recording. So for people who like to worry about these things, an absolute phase switch is provided so listeners can change the polarity disc-to-disc and even track-to-track (rather like some enthusiasts obsess over VTA for vinyl reproduction).
Meters, the good the bad and the ugly
A very few preamps came with level meters; the Levinson LNC was one such. Usually meters are reserved for situations where monitoring of the signal level is important such as when recording onto tape, or to aid optimum tuning of a VHF tuner by maximising signal level and minimising channel in-balance.
Generally power amplifiers have very few controls. Sometimes there may be a switch to change the damping factor (though I can’t see the purpose for this) and if a valve amplifier, there may be a speaker impedance selector switch since the feedback is taken from the secondary of the output transformer and depends on the nominal impedance of the speakers used. There may be controls for the occasional re-biasing of the output valves if auto biasing is not used, and for this a milliameter may be fitted, as they were on early Marantz and Audio Research designs.
In the early ‘70s a new feature appeared – meters, which indicated the actual power being delivered to the speakers. I believe the first to do this was Phase Linear. I also suspect that this was a marketing ‘gimmick’, intended to show off the very high power capability of these amps (200 or 300W per channel). It no doubt appealed to the ‘macho’ enthusiast for whom “size is everything”. And to force this message home, the meters were big, butch and beautiful. Add blue to that list and we’re talking McIntosh, who have become obsessed with adding their pretty blue meters to just about everything – including a meter to indicate the speed (rpm) of their turntable!
Aesthetics aside, these meters serve absolutely no useful function. Their ballistics have to be such they respond to transients and yet need to have a slow decay so that transient indication can be read, or at least inferred. Amusing they may be, and reassuring to those who have doubts about the size of their equipment, but then just having 300W written on the fascia (in “large friendly letters”) would do just as well. No, ultimately they are distracting – once noticed, you spend all your time transfixed, watching then bob up and down and find yourself no longer listening to the music. I remember the Harrison Chapman S200 integrated amplifier that had a power level LED bar-graph display fitted. Audio dealers just loved to play you a dynamic record loudly so as to ‘impress’ you with the dancing LEDS. Sigh!
My summary
From the above you will have already got an idea of what I think are necessary and useful features. I’ll run through them and state whether I would want them on my amplifier.
1 Input selector
Obviously essential and should cater for a minimum of five inputs: CD, tape (either cassette or reel-to-reel), two cartridges (either one each MC or fixed coil) and radio tuner. A couple of ‘auxiliary’ inputs would also come in handy.
2 Input sensitivity and impedance loading
Often rudimentary adjustments can be made within the preamp, but I would like to see these adjustments made possible on the fascia of the amplifier, or at very least from the exterior (as in the Quad 44). The adjustment of input and output levels is especially useful when tape dubbing, or when connecting external gear via the tape circuit.
3 Volume control
Obviously essential, but should be of sufficient quality such that the two channels track one another to within 0.5dB. It should ideally have an ‘off’ setting when no output is available (a feature the Quad 44 does not have). For those volume controls using a stepped attenuator, some indication of the attenuation level in dB relative to full output is useful, but not essential.
4 Balance control
Essential, either as a single control or as two separate level controls, the latter once set being left alone. If manufacturers insist on using two separate volume controls, please make them concentric and friction-coupled so that once set, the two can be turned as one, i.e. the friction coupling has to be stiff. Separate volume controls are the spawn of the devil and have no place in this world (so no Levinson ML7 preamps for me). So called 'true' dual-mono designs are no excuse for dual volume controls!
Why do I want a balance control? Well even though ones system may be entirely symmetrical, ones listening room is not. At the moment I’m using a Levinson ML28 preamp, which does not have a balance control. To get around this I had to spend much time altering the position of one speaker a few mm at a time to achieve balance!
5 Stereo/Mono switch
Also essential in my opinion, but only if you have several monophonic vinyl records that are in poor condition. There is nothing worse than listening to a record with a nice central image, only to have asymmetrical noise, clicks and pops coming out of one speaker or the other. Switching to ‘mono’ places these distracting noises in the centre where they tend to be 'buried' under the music, and if not buried as such, are a lot less distracting.
It is not important that switching should provide for single channel mono only – that really is for purists.
There is absolutely no need for the so-called ‘stereo reverse’ option. That is for users who are too lazy to sort out the left- and right-hand channels.
6 Tone controls
Not necessary, though I have to admit I have found the ‘tilt control’ available on the Quad 44 and 34 preamps (and also I think on the 66) to be occasionally useful. What this ‘tone’ control does is described very well by the name; the entire frequency response can be tilted up and down a dB or two, with the pivot at around 1KHz. On early versions of the 44 the range was +/- 2dB, this later being increased to +/-3dB as it was on the model 34. Frankly this is too much – I have found +/-1dB to be sufficiently useful; any more then one should look elsewhere for correction. I have a couple of rather ‘thick’ sounding LPs that can be ameliorated by tilting up the response by -/+1dB.
7 Filters
These are unnecessary, either as high-pass or as low-pass. The high-pass or rumble filter is redundant as any turntable worthy of the appellation “hi-fi” or “transcription” will have sufficiently low levels of rumble.
Low pass filters are not sufficiently sophisticated to be of help. Some of the best were fitted to Quad preamps, but even for these to have any effect on tape hiss or scratches intrude on the music too much. Also steep roll off filters can cause too much phase shift, which will affect the music.
8 Quiet or loudness control
Utterly useless – fortunately this so called facility disappeared in the early ‘70s.
9 Absolute phase control
I do have a Levinson ML26 that has this feature. I have only played with the control and have to say that I couldn’t really hear any difference apart from the understandable momentary change on switch over. To comment on its usefulness I would have to do more of a controlled test.
10 Power meters
Of absolutely no use whatsoever; inaccurate and distracting - regardless of their colour!
So that’s my very personal take on it all. What are yours?
A Bit of History
In the early days, audio preamplifiers (or ‘control units’ as they were then called) came with a comprehensive range of controls. This was due partly to the lower standard of audio quality that could be wrought from disc (vinyl!), tuner or from tape, compared with what we enjoy today, and partly due to the un-standardised replay characteristic used; each record company had its own replay characteristic and it wasn’t until 1955 that the RIAA equalisation response was devised and adopted internationally.
Preamps in those days had tone controls, usually just bass and treble affecting the frequency range from ~ 1kHz (or, in those days 1Kc/s) upward or down with a massive +/-12dB amplitude range. Most preamplifiers used the feedback circuitry devised by Peter Baxandall to implement these tonal adjustments. Some, usually of American manufacture, even had a third centre or ‘presence’ tone control. Apart from the tone controls there were often various filters, both low-pass (called ‘scratch’) and high-pass (called ‘rumble cut’), and of these, the former might have a range of ‘turn over’ frequencies as well as a range of filter slopes! But we’re far from finished: the choice of inputs a preamplifier could handle might include two pick-up inputs (this was in the days where a serious audio enthusiast would have two decks; one to play the new fangled vinyl ‘microgroove’ and one to play 78s) a choice of pick up cartridge equalisation, loading and sensitivity (for various type of pick up: moving coil; fixed coil and for the less well off, the ceramic cartridge), as well as a tuner, microphone, tape line output and even one for direct connection to a tape head. And on top of all this, with the advent of stereo and the necessity to use two channels, the preamp would have a balance control, and switching for mono (one channel only), mono (split between both channels), stereo and stereo reverse (for those who having got their left- and right-hand channels mixed up and couldn’t be bothered to swap the speaker connections!). Not surprisingly, the preamps were festooned with controls – this was man’s stuff: women "needn’t worry their pretty little heads" with all this complicated stuff; or so the thinking went at the time and quite the opposite of the joke of the cartoon I alluded to above.
http://i780.photobucket.com/albums/yy88/barrydhunt/IMG-1-1.jpg?t=1291039803
A Rogers 'Master Mk II Control Unit' (Photo: advertisment in HFN/RR)
In the late sixties a new facility appeared on preamp fascias – the ‘quiet’ or ‘loudness’ switch. Despite the contradictory labels, this facility was designed when one wanted to listen at low volume, late at night. It was however an example of woolly thinking. The idea was to be able to listen at low levels and yet not loose detail at the frequency extremes. To do this, the switch introduced an overall attenuation of 15 - 20dB and then imposed a frequency correction according the ‘equal loudness’ contours derived by Fletcher and Munson or by Robinson and Dadson.
The human ear only has a relatively flat response at around the 120 phon level (120dB above the threshold of hearing); at other levels below this very loud volume level, the ear’s response is far from flat. Yet this is what we are all used to and the brain allows for it. Adding bass and some treble boost just makes everything sound ‘wrong’ and false. Not surprisingly this facility didn’t last long.
Preamplifiers offering this facility included the Sugden C51 and the Radford SC24.
“The Less is More”
In the ‘70s a new way of thinking came about. By now the quality of record reproduction had improved enormously, most enthusiasts opted for a magnetic (electrodynamic) cartridge and of course there was the universal replay characteristic. This meant that tone controls were called upon less frequently and the use of filters even less. Some amps retained the selection between mono and stereo replay, and virtually all amps had a balance control. However all this little-used circuitry was still in the signal path and the possible effect of this circuitry to the degradation of the signal quality was considered; only a few amplifiers (the Quad and Hafler 101 for example) had a ‘cancel’ control, whereby the tone and filters could be switched out of the overall signal path. If this extra circuitry wasn’t wanted or wasn't being used, why pay for it to be included in the first place?
One of the first in the vanguard of these minimalist preamps was the Naim NAC12, seemingly following the maxim: “the less is more”. The NAC12 only had three knobs: one to select the input; a balance control and of course a volume control. The unit did not even have an on/off switch: power was derived from a Naim power amplifier, which had its own switch. Naim later claimed the removal of unnecessary circuitry was done with sound considerations in mind, however early literature suggests tone controls were not fitted as the preamp was intended to be used with a multi-channel graphic equaliser! However such was the influence of the ‘Young Turks’, that other manufacturers followed suit and offered minimalist designs. The Americans were doing the same, however the Japanese continued to provide a full range of facilities (these could however be switched out if unused).
http://listeninn.com/catalog/imagemagic.php?img=images/Used-Pre-Amplifiers/Naim-Audio-NAC12.jpg&w=430&h=430&page=popup
Naim NAC 12 preamp. (Photo: listeninn.com)
The trend for minimum control was maintained by the likes of Meridian and Creek, and later by Onix and Cyrus. The only deviation from this paring down of controls occurred around the ‘90s with the introduction of an ‘absolute phase’ switch, and on some of the more specialist preamps, comprehensive cartridge impedance loading and sensitivity adjustments appeared on the fascia rather than being hidden away within the interior of the preamp.
The introduction of an ‘absolute phase’ switch is interesting. It first appeared on American preamplifiers, such as the Mark Levinson ML26S
http://i780.photobucket.com/albums/yy88/barrydhunt/800px-No26s_front1.jpg
Levinson ML26S preamp with balance controls, mono/stereo switch and an absolute phase polarity switch. (Photo Wikipedia)
It is usually assumed that audio reproduction systems are wired so the correct absolute phase is maintained from microphone through to speaker. This means that explosive sounds, such as those from wind instruments and percussive instruments such as a kick drum, initially creating a local compression of the air, will be so reproduced via the recording process and replay system so that the loudspeaker cones or diaphragms move outwards towards the listener producing the same local air compression. It is a moot point whether the initial transient of a plucked or bowed string causes an initial compression or rarefaction; it all depends on the microphone placement, if at all. Note this has nothing to do with the two speakers being ‘out of phase’. In the latter, when fed with equal signals, one speaker will move out, the other moves in; completely destroying the ability to produce a central acoustic image and hence incapable of presenting a stereo image.
Now it is not obvious that the correct absolute phase is important to some people; especially so as some amplifiers are inverting while others are not. The situation is further confused with the use of multi-miked recordings; not all of the microphone channels may be in phase with one another. And furthermore the situation can easily vary track to track on a recording. So for people who like to worry about these things, an absolute phase switch is provided so listeners can change the polarity disc-to-disc and even track-to-track (rather like some enthusiasts obsess over VTA for vinyl reproduction).
Meters, the good the bad and the ugly
A very few preamps came with level meters; the Levinson LNC was one such. Usually meters are reserved for situations where monitoring of the signal level is important such as when recording onto tape, or to aid optimum tuning of a VHF tuner by maximising signal level and minimising channel in-balance.
Generally power amplifiers have very few controls. Sometimes there may be a switch to change the damping factor (though I can’t see the purpose for this) and if a valve amplifier, there may be a speaker impedance selector switch since the feedback is taken from the secondary of the output transformer and depends on the nominal impedance of the speakers used. There may be controls for the occasional re-biasing of the output valves if auto biasing is not used, and for this a milliameter may be fitted, as they were on early Marantz and Audio Research designs.
In the early ‘70s a new feature appeared – meters, which indicated the actual power being delivered to the speakers. I believe the first to do this was Phase Linear. I also suspect that this was a marketing ‘gimmick’, intended to show off the very high power capability of these amps (200 or 300W per channel). It no doubt appealed to the ‘macho’ enthusiast for whom “size is everything”. And to force this message home, the meters were big, butch and beautiful. Add blue to that list and we’re talking McIntosh, who have become obsessed with adding their pretty blue meters to just about everything – including a meter to indicate the speed (rpm) of their turntable!
Aesthetics aside, these meters serve absolutely no useful function. Their ballistics have to be such they respond to transients and yet need to have a slow decay so that transient indication can be read, or at least inferred. Amusing they may be, and reassuring to those who have doubts about the size of their equipment, but then just having 300W written on the fascia (in “large friendly letters”) would do just as well. No, ultimately they are distracting – once noticed, you spend all your time transfixed, watching then bob up and down and find yourself no longer listening to the music. I remember the Harrison Chapman S200 integrated amplifier that had a power level LED bar-graph display fitted. Audio dealers just loved to play you a dynamic record loudly so as to ‘impress’ you with the dancing LEDS. Sigh!
My summary
From the above you will have already got an idea of what I think are necessary and useful features. I’ll run through them and state whether I would want them on my amplifier.
1 Input selector
Obviously essential and should cater for a minimum of five inputs: CD, tape (either cassette or reel-to-reel), two cartridges (either one each MC or fixed coil) and radio tuner. A couple of ‘auxiliary’ inputs would also come in handy.
2 Input sensitivity and impedance loading
Often rudimentary adjustments can be made within the preamp, but I would like to see these adjustments made possible on the fascia of the amplifier, or at very least from the exterior (as in the Quad 44). The adjustment of input and output levels is especially useful when tape dubbing, or when connecting external gear via the tape circuit.
3 Volume control
Obviously essential, but should be of sufficient quality such that the two channels track one another to within 0.5dB. It should ideally have an ‘off’ setting when no output is available (a feature the Quad 44 does not have). For those volume controls using a stepped attenuator, some indication of the attenuation level in dB relative to full output is useful, but not essential.
4 Balance control
Essential, either as a single control or as two separate level controls, the latter once set being left alone. If manufacturers insist on using two separate volume controls, please make them concentric and friction-coupled so that once set, the two can be turned as one, i.e. the friction coupling has to be stiff. Separate volume controls are the spawn of the devil and have no place in this world (so no Levinson ML7 preamps for me). So called 'true' dual-mono designs are no excuse for dual volume controls!
Why do I want a balance control? Well even though ones system may be entirely symmetrical, ones listening room is not. At the moment I’m using a Levinson ML28 preamp, which does not have a balance control. To get around this I had to spend much time altering the position of one speaker a few mm at a time to achieve balance!
5 Stereo/Mono switch
Also essential in my opinion, but only if you have several monophonic vinyl records that are in poor condition. There is nothing worse than listening to a record with a nice central image, only to have asymmetrical noise, clicks and pops coming out of one speaker or the other. Switching to ‘mono’ places these distracting noises in the centre where they tend to be 'buried' under the music, and if not buried as such, are a lot less distracting.
It is not important that switching should provide for single channel mono only – that really is for purists.
There is absolutely no need for the so-called ‘stereo reverse’ option. That is for users who are too lazy to sort out the left- and right-hand channels.
6 Tone controls
Not necessary, though I have to admit I have found the ‘tilt control’ available on the Quad 44 and 34 preamps (and also I think on the 66) to be occasionally useful. What this ‘tone’ control does is described very well by the name; the entire frequency response can be tilted up and down a dB or two, with the pivot at around 1KHz. On early versions of the 44 the range was +/- 2dB, this later being increased to +/-3dB as it was on the model 34. Frankly this is too much – I have found +/-1dB to be sufficiently useful; any more then one should look elsewhere for correction. I have a couple of rather ‘thick’ sounding LPs that can be ameliorated by tilting up the response by -/+1dB.
7 Filters
These are unnecessary, either as high-pass or as low-pass. The high-pass or rumble filter is redundant as any turntable worthy of the appellation “hi-fi” or “transcription” will have sufficiently low levels of rumble.
Low pass filters are not sufficiently sophisticated to be of help. Some of the best were fitted to Quad preamps, but even for these to have any effect on tape hiss or scratches intrude on the music too much. Also steep roll off filters can cause too much phase shift, which will affect the music.
8 Quiet or loudness control
Utterly useless – fortunately this so called facility disappeared in the early ‘70s.
9 Absolute phase control
I do have a Levinson ML26 that has this feature. I have only played with the control and have to say that I couldn’t really hear any difference apart from the understandable momentary change on switch over. To comment on its usefulness I would have to do more of a controlled test.
10 Power meters
Of absolutely no use whatsoever; inaccurate and distracting - regardless of their colour!
So that’s my very personal take on it all. What are yours?