Hifi-*attenuators*
11 January 2004, 08:33 PM
#2
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I assume you are talking about the "in cable" type of passive attenuators that claim to allow you to operate your volume **** in the middle of it's scale?
If so then I took a look at one recently which claimed to allow smoother sounding audio etc. etc.
There is no question that it followed the hi-fi trend for smoother sounding audio as it rolled off the top end of the audio making it sound, well, relaxed. I suppose it might throw in some harmonics as it goes, in the analogue domain, but I didn't consider that at the time. What it isn't, however, is true to the audio that was recorded. The more relaxed sound may be what you want in which case go for it but don't pay a lot for it based upon it's "hi-fi" qualities. If you want relaxed then a good bottle of whatever takes your fancy might be a better investment with the advantage that once you recover all your audio will still be there in the morning.
I know that in hi-fi there is a movement against complex electronics. When it comes to attenuators most passive, and therefore simple, units are the work of the devil and should be avoided if you want to do the job right.
If so then I took a look at one recently which claimed to allow smoother sounding audio etc. etc.
There is no question that it followed the hi-fi trend for smoother sounding audio as it rolled off the top end of the audio making it sound, well, relaxed. I suppose it might throw in some harmonics as it goes, in the analogue domain, but I didn't consider that at the time. What it isn't, however, is true to the audio that was recorded. The more relaxed sound may be what you want in which case go for it but don't pay a lot for it based upon it's "hi-fi" qualities. If you want relaxed then a good bottle of whatever takes your fancy might be a better investment with the advantage that once you recover all your audio will still be there in the morning.
I know that in hi-fi there is a movement against complex electronics. When it comes to attenuators most passive, and therefore simple, units are the work of the devil and should be avoided if you want to do the job right.
11 January 2004, 08:47 PM
#3
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hmmm,cheers
the advert for the product is very clever,it describes the problem i have perfectly,that the sound is so much better at 10 oclock than it is at 9,but 10 is too loud! sod it,alcohol it is then
i have enough of reading the small ads anyway,the latest i saw was a Russ Andrews CD interconnect which is attenuated,but its just so damn expensive,compared top the others i have (£25 mine,this went for £40 on Ebay)
the advert for the product is very clever,it describes the problem i have perfectly,that the sound is so much better at 10 oclock than it is at 9,but 10 is too loud! sod it,alcohol it is then
i have enough of reading the small ads anyway,the latest i saw was a Russ Andrews CD interconnect which is attenuated,but its just so damn expensive,compared top the others i have (£25 mine,this went for £40 on Ebay)
11 January 2004, 10:03 PM
#5
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A truly attenuated interconnect would just have an in-line resistor to drop the output voltage by e.g. half. If you have say a 10KOhm input impedance on your amplifier, a 10kOhm resistor in the line will drop the signal voltage by half. This should have minimal effect on how "relaxed" or otherwise the sound is. Attenuators including capactive or inductive elements can roll off the treble or the bass, which will make the sound different.
A lot of the reason that most hi-fis sound better at say 10 o'clock than 9 o'clock is because they are louder then! As well as overcoming inertia in the speaker cones, and drowning out background noise, the human ear will pick up the lower level details more effectively if they're a bit louder, within reason.
Having played a bit with the input gain stage in my home built pre-amp (which incidentally upset my dealer by sounding better than his £3500 offering), I can say that the actual position of the volume control for a normal potentiometer is pretty well irrelevant to how things sound, it's purely down to the actual volume levels. Therefore, I'd doubt the claims (although I'm always open to being proved wrong!)
The exception to this rule is some instances where you have a digitally actuated volume control (such as built in to many CD players). You want the digital volume control at full in order to achieve the full bit-depth of the recordings. Therefore, the system will sound better with the CD player turned up to full, and the amp turned down than the other way around.
I know that got a bit scientific, but hope it helps?
A lot of the reason that most hi-fis sound better at say 10 o'clock than 9 o'clock is because they are louder then! As well as overcoming inertia in the speaker cones, and drowning out background noise, the human ear will pick up the lower level details more effectively if they're a bit louder, within reason.
Having played a bit with the input gain stage in my home built pre-amp (which incidentally upset my dealer by sounding better than his £3500 offering), I can say that the actual position of the volume control for a normal potentiometer is pretty well irrelevant to how things sound, it's purely down to the actual volume levels. Therefore, I'd doubt the claims (although I'm always open to being proved wrong!)
The exception to this rule is some instances where you have a digitally actuated volume control (such as built in to many CD players). You want the digital volume control at full in order to achieve the full bit-depth of the recordings. Therefore, the system will sound better with the CD player turned up to full, and the amp turned down than the other way around.
I know that got a bit scientific, but hope it helps?
11 January 2004, 10:06 PM
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Telboy - have generally heard good things about Chord amps, though as always, the proof of the pudding is in the eating - go and have a listen. Have been running Chord speaker cable (Legend bi-wire) myself for a couple of years, although that's going in about a week when my new fancy stuff arrives.
Edit due to my own stupidity.
[Edited by hades - 1/11/2004 10:07:30 PM]
Edit due to my own stupidity.
[Edited by hades - 1/11/2004 10:07:30 PM]
12 January 2004, 06:43 PM
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The problem with a 10K resistor in the signal path is that it forms a potential divider with the 10K (say) input impedance of the amp. But the 10K quoted for the amp will be a nominal value and will very much depend on frequency, that is to say it will change by significant amounts with frequency. It is likely that the 10K quoted for the amp is measured at 1kHz.
This frequency dependence of the amp input impedance causes the "mid-point" of your potential divider to "move about" and so your 1K resistor, which you rightly state has only a resistive component, becomes a frequency dependant attenuator through no fault of it's own. In turn this will have a dramatic effect upon the frequency response of the audio.
It is possible to use a network of resistors, say in a T configuration, to make an attenuator with a more stable performance across a range of frequencies. However, even this will be far from perfect as such a configuration works much better where the impedances are all matched and the input and output impedances are equal.
So, the level passive attenuation of the input of an amplifier is going to vary depending upon the changes in input impedance of the amplifier and those are frequency dependent. As I mentioned this passive attenuation lark is the work of the devil.
Actually, that's not quite true. In a well designed and controlled system, such as the 600 Ohm lines used by BT and other telecoms providers, passive attenuation can work very well. Telecoms signals may pass through many stages of passive attenuation but fairly good frequency responses are possible over a good bandwidth. Once again design flaws in "hi-fi" components let us down and, in the case of i/o design, probably contribute to a significant amount of the differences we hear between bits of gear.
This frequency dependence of the amp input impedance causes the "mid-point" of your potential divider to "move about" and so your 1K resistor, which you rightly state has only a resistive component, becomes a frequency dependant attenuator through no fault of it's own. In turn this will have a dramatic effect upon the frequency response of the audio.
It is possible to use a network of resistors, say in a T configuration, to make an attenuator with a more stable performance across a range of frequencies. However, even this will be far from perfect as such a configuration works much better where the impedances are all matched and the input and output impedances are equal.
So, the level passive attenuation of the input of an amplifier is going to vary depending upon the changes in input impedance of the amplifier and those are frequency dependent. As I mentioned this passive attenuation lark is the work of the devil.
Actually, that's not quite true. In a well designed and controlled system, such as the 600 Ohm lines used by BT and other telecoms providers, passive attenuation can work very well. Telecoms signals may pass through many stages of passive attenuation but fairly good frequency responses are possible over a good bandwidth. Once again design flaws in "hi-fi" components let us down and, in the case of i/o design, probably contribute to a significant amount of the differences we hear between bits of gear.
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12 January 2004, 10:30 PM
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Oh, forgot to say:
Know nothing about Chord. I have a feeling that they use some sort of switched mode power supply though, though that probably isn't what they would like to call it :-)
Hey, as long as it doesn't have a passive attenuator in it then I'm happy :-)
Know nothing about Chord. I have a feeling that they use some sort of switched mode power supply though, though that probably isn't what they would like to call it :-)
Hey, as long as it doesn't have a passive attenuator in it then I'm happy :-)
12 January 2004, 11:14 PM
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Hedgehog, accept what you're saying, yep input impedance will change with frequency, and my comment above was a bit of an over-simplification. But on a car BBS, thought 3-4 pages of technical info on hi-fi would be OTT, so I tend to chop bits out.
I'm probably spoilt as my pre-amp does have a fairly uniform 22k input impedance from sub to supersonic range (and an equally uniform 47K output impedance). Ah, the benefits of building it -properly - yourself
I'm probably spoilt as my pre-amp does have a fairly uniform 22k input impedance from sub to supersonic range (and an equally uniform 47K output impedance). Ah, the benefits of building it -properly - yourself
13 January 2004, 08:54 AM
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TelBoy: Chord amps are very good as you probably already know, it's all in the power supply. Apparently Chord was started by the guy who designed the power systems for the stealth fighter. (The bloke in Audio-T told me that so it must be true!) Far and away the best amp I've heard. It's the next upgrade I'll be making to my home cinema - only the front two channels though! 
13 January 2004, 08:58 AM
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In fact it's Audio-T i'm talking to about them. I sort of made up my mind last night to take the plunge - they certainly seem to have more presence than my current set-up.
Now, which mains lead should i use..???
Now, which mains lead should i use..???
13 January 2004, 03:41 PM
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No audio designer worthy of their job would ever design an input stage whose impedance (in reality just resistance) varied over the audio band, or several octaves above and below, for that matter.
Most amplifier input stages are shunted with a resistor that effectively sets the input impedance. The true imput impedance of the input stage - i.e. without the resistor - will be several orders of magnitude higher.
IMHO, adding a 'passive' attenuator (i.e. some resistors) in front of the input stage will have little effect other than to worsen your signal to noise ratio (even passive components generate thermal noise etc.). If you add excessive resitance, it will, as Hedgehog says, start to roll off the high frequencies because of the amplifier input capacitance. Most amplifier design deliberately shunt the amplifier input with a small amount of capacitance to reduce the input impedance at radio frequencies, i.e. > 100kHz.
Ming.
[Edited by dr_ming - 1/13/2004 3:52:45 PM]
Most amplifier input stages are shunted with a resistor that effectively sets the input impedance. The true imput impedance of the input stage - i.e. without the resistor - will be several orders of magnitude higher.
IMHO, adding a 'passive' attenuator (i.e. some resistors) in front of the input stage will have little effect other than to worsen your signal to noise ratio (even passive components generate thermal noise etc.). If you add excessive resitance, it will, as Hedgehog says, start to roll off the high frequencies because of the amplifier input capacitance. Most amplifier design deliberately shunt the amplifier input with a small amount of capacitance to reduce the input impedance at radio frequencies, i.e. > 100kHz.
Ming.
[Edited by dr_ming - 1/13/2004 3:52:45 PM]
13 January 2004, 05:51 PM
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Now which mains lead should I use?
If you're serious, I could recommend something at a somewhat more sensible price that is a reasonable option with amps at the Chord level, and a very good dealer offering them on "try before you buy".
13 January 2004, 09:43 PM
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Telboy - one with a plug on the end would be your best bet .
Similar to my comments above, any amplifier with a power supply rejection ratio (PSRR) so poor that audio quality is was affected by any 'normal' mains bourne noise, voltage fluctuations etc. belongs in the skip. For the same reason, regulated power supplies are totally unnecessary for a well designed power amp (a pre-amp is a slightly different story). Spend your money on some decent speaker cable and/or interconnects.
.Similar to my comments above, any amplifier with a power supply rejection ratio (PSRR) so poor that audio quality is was affected by any 'normal' mains bourne noise, voltage fluctuations etc. belongs in the skip. For the same reason, regulated power supplies are totally unnecessary for a well designed power amp (a pre-amp is a slightly different story). Spend your money on some decent speaker cable and/or interconnects.
14 January 2004, 12:39 AM
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Whilst I agree with your comments about input impedance, I partially disagree with your comments about mains leads. There's more at work than just mains-bourne noise.
I have been surprised myself (and the dealer I was with) at just how big a difference was heard between a common "value" RF filtered hi-fi 4-way mains block that I owned at the time and the similarly priced one I own now. I find it very hard to believe it was down to the filtering, but the difference was just as marked as the difference with speaker cable / interconnects. I believe the reasoning is extremely similar to the reason that well sorted power supply will make a huge difference to how hi-fi sounds (just look at the Naim upgrade path to demonstrate the relevance of power supplies).
Similarly, I partially disagree with your comments re:regulation on a power amp. IMHO, the goal is to achieve an effective zero Ohm output impedance, to give a perfectly stable and instantly responsive power supply to the power amp output stage. Decent regulation is normally a good means to achieve that end.
Admittedly, you'd need a lot of money and a very serious system to even think about justifying a Nordost Valhalla mains lead at £1500. But the same applies to the matching Valhalla interconnects (>£2k for a 1m pair), or speaker cable (>£8k for a 5m bi-wired/bi-amped pair). In a £100k+ system, it actually makes sense, as much as any £100k system does. For your £70k/week footballers or whatever, it might not be unreasonable, but somewhat out of my (and most people here's) reach.
I have been surprised myself (and the dealer I was with) at just how big a difference was heard between a common "value" RF filtered hi-fi 4-way mains block that I owned at the time and the similarly priced one I own now. I find it very hard to believe it was down to the filtering, but the difference was just as marked as the difference with speaker cable / interconnects. I believe the reasoning is extremely similar to the reason that well sorted power supply will make a huge difference to how hi-fi sounds (just look at the Naim upgrade path to demonstrate the relevance of power supplies).
Similarly, I partially disagree with your comments re:regulation on a power amp. IMHO, the goal is to achieve an effective zero Ohm output impedance, to give a perfectly stable and instantly responsive power supply to the power amp output stage. Decent regulation is normally a good means to achieve that end.
Admittedly, you'd need a lot of money and a very serious system to even think about justifying a Nordost Valhalla mains lead at £1500. But the same applies to the matching Valhalla interconnects (>£2k for a 1m pair), or speaker cable (>£8k for a 5m bi-wired/bi-amped pair). In a £100k+ system, it actually makes sense, as much as any £100k system does. For your £70k/week footballers or whatever, it might not be unreasonable, but somewhat out of my (and most people here's) reach.
14 January 2004, 08:29 AM
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Hades, thanks for the recommendation. In fact it was slightly tongue-in-cheek as hedgehog is a bit sceptical of the effect of mains leads. At the moment all of mine are Kimber Hi-Current PowerKords, but i think i want to try something else.
Well, i'm now the proud owner of a CPA 4000 and two SPM1400E monoblocks, although i don't pick them up for a week or so. You're right about Nordost Valhalla, but at that price i just can't justify it! My next most important component to get right is the speaker cable, as i'm having a new carpet fitted soon and so it's an ideal opportunity to upgrade. Needing it to be flat does restrict my options, but Nordost do make a fine range. At the moment i have Blue Heaven, as i thought Red Dawn was a bit bass-light, but i'm auditioning SPM at the weekend so i'll see how that goes.
Why couldn't i just be satisfied with a £250 Denon midi-system?!
Well, i'm now the proud owner of a CPA 4000 and two SPM1400E monoblocks, although i don't pick them up for a week or so. You're right about Nordost Valhalla, but at that price i just can't justify it! My next most important component to get right is the speaker cable, as i'm having a new carpet fitted soon and so it's an ideal opportunity to upgrade. Needing it to be flat does restrict my options, but Nordost do make a fine range. At the moment i have Blue Heaven, as i thought Red Dawn was a bit bass-light, but i'm auditioning SPM at the weekend so i'll see how that goes.
Why couldn't i just be satisfied with a £250 Denon midi-system?!
14 January 2004, 09:17 AM
#21
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true story.........I've just bought some decent mains leads and interconnects,(Kimber)and decided to turn a chair around to face the speakers and "audition" my new items.Sure enough I am convinced the bass was tighter and treble sweeter,whatever.
I put the chair back and sat on the settee and it sounded different again.
bugger
I put the chair back and sat on the settee and it sounded different again.
bugger
14 January 2004, 05:25 PM
#22
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Telboy - very familiar sounding story. Have got Blue Heaven (mark 2) speaker cable coming, which sounded better with my kit than the Red Dawn (also Mark 2). Couldn't justify SPM reference as by then the cable cost would be just too close to that of the speakers
My recommended option - phone Alastair Gardner at signals . Top bloke, knows his stuff, does sale or return or lends demo cables. Ask him about trying out his "blackcurrent" mains leads, IIRC they're under £100 for an IEC, something like £125 or £150 for a 6 way block. He also stocks the full Nordost range. If you do, mention I recommended him (real name is Phil Elvin), it might just earn me a bigger discount next time I call him!
My recommended option - phone Alastair Gardner at signals . Top bloke, knows his stuff, does sale or return or lends demo cables. Ask him about trying out his "blackcurrent" mains leads, IIRC they're under £100 for an IEC, something like £125 or £150 for a 6 way block. He also stocks the full Nordost range. If you do, mention I recommended him (real name is Phil Elvin), it might just earn me a bigger discount next time I call him!
14 January 2004, 05:34 PM
#24
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i'm now the proud owner of a CPA 4000 and two SPM1400E monoblocks
14 January 2004, 10:18 PM
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will let you know about the Kimber interconnects (PBJ,as they were)
great thread here btw
http://forum.hifichoice.co.uk/viewtopic.php?t=8270
great thread here btw
http://forum.hifichoice.co.uk/viewtopic.php?t=8270
