Copyright © 1998
Cadman Enterprises Ltd
Welcome to the Graham Slee Audio Products Owners Forum Open to all owners plus those contemplating the purchase of a Graham Slee HiFi System Components audio product and wishing to use this forum's loaner program: join here (Rules on posting can be found here) This website along with trade marks Graham Slee and HiFi System Components are owned by Cadman Enterprises Ltd |
Why Phono Stage Hiss? |
Post Reply | Page 12> |
Author | |
Graham Slee
Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16298 |
Post Options
Thanks(1)
Posted: 15 Nov 2019 at 7:45am |
Anyone getting into vinyl for the first time, or rediscovering it in later years, might be offended by the intrusion of hiss from the phono preamplifier.
CD doesn't hiss, so why should vinyl? Oh, and an old record player didn't hiss either! CD (or other digital music source) doesn't hiss because the music comes off the DAC chip at just the right voltage to match the input of a modern "line-level" input amplifier. The power of computational logic has been employed in both CD (and music file) manufacture, and at playback, to manipulate any noise (hiss) outside our hearing range. Old record players (low-cost "music centres" and "stacking hi-fi") had "rough service" pick-up cartridges to withstand the way in which they were sometimes used. Their ceramic or crystal piezo-electric capsules could also output just the right voltage to match the input of a modern "line-level" amplifier. The type of cartridge used for high fidelity vinyl reproduction on a specialised turntable however, has an output voltage which is miniscule by comparison. Its level must be increased to make it just the right voltage to match the input of a modern "line-level" amplifier. The name used to describe the increase of its output voltage is gain. The amount of gain required is the difference between the right voltage to match the input of a "line-level" amplifier, and the output of the cartridge. Let's say the line-level input requires half a volt, which is 500mV (milli-volts), but the cartridge only outputs 5mV. This will require a gain of 100, because 100 x 5mV = 500mV. The phono preamplifier with this gain of 100 does the job, but also outputs hiss, which, with any good phono preamplifier is indistinguishable whilst playing the music, but you are aware of it whilst it is not, and if you then turn the volume up, you hear even more hiss. Why should this be? A phono preamplifier is simply an analogue amplifier (which also applies tone correction called EQ), which is made of resistive, capacitive, and semi-conducting components, and the resistive and semi-conducting components produce noise simply because of the current that flows in them. Such noise exists in the input of the phono preamplifier, although it also exists in every part of it, the noise that exists at its input is amplified by the same gain (100 in this case) as the signal from the cartridge. Therefore, along with the music, there is this inescapable hiss. The phono preamplifier cannot do the same trick as digital audio - it has no computational logic to manipulate the noise - if it were possible it would have been invented by now, but it hasn't. During the design of the phono preamplifier, the designer does the best to trade-off noise to get a cleaner signal, but there are limits. One can "dig out" the tiniest signal from the depths of noise by dispensing with surrounding frequencies, and this is how medical sensing equipment works. However, for music we do not have this option because we must reproduce every audible frequency, and then beyond that so we have the slew-rate which makes the music "real". All the designer can do is choose the quietest components that will still deliver the musical pleasure we seek. To improve the reality of the music this can mean allowing compromises which make the phono preamplifier slightly more "hissy" than another design. The problem is that fidelity is not the opposite of noise, both mutually exist. As long as the noise (the hiss) does not spoil the rendition of the music, it is all that can be expected. |
|
That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
|
|
patientot
Senior Member Joined: 28 Nov 2018 Location: USA Status: Offline Points: 1523 |
Post Options
Thanks(0)
|
Great write up. I often see people ask about this when coming back to vinyl or just starting up with it.
|
|
SL-1200 MK7 (modified) + Reflex M + PSU-1 used with AT150-40ML, AT VM95ML, Stanton 680mkII + Ogura, and Shure M35X cartridges.
|
|
WigglyWoo
Regular Joined: 23 Sep 2016 Location: Newbury Status: Offline Points: 82 |
Post Options
Thanks(1)
|
I was just asking myself the same question, being the proud new owner of an Accession MC (and new TT)... I'm not new to vinyl but have been mostly digital to-date for a variety of practical reasons and hence used to the silence. The Accession sounds wonderful (and is still burning in) but the hiss did at first have me scrabbling around redressing cables, moving power supplies etc. Of course this did nothing for the hiss and the hum I already had under control...
Going back to my other TT + Reflex M as a benchmark, of course there's the usual analogue hiss but less so because (I'm assuming) MM cartridges have much higher outputs hence much lower gain hence much lower hiss... I feel somewhat foolish having worried about this and wasted time messing around with the equipment positioning and cabling but at least now I understand what's going on
|
|
Solo ULDE; Reflex M; Accession MC+Enigma and other tomfoolery...
|
|
RussL
New Member Joined: 22 Nov 2019 Location: Long Island, NY Status: Offline Points: 24 |
Post Options
Thanks(1)
|
MM gain typically 40dB (100). MC gain typically 60dB (1000) so yes, you’re much more likely to hear some “hiss” when using a MC cartridge with your new Accession. Enjoy.
Russ
|
|
Technics SL-1200Mk.II TT with KAB mods, Grado Gold2 cartridge, Bryston 0.5B phone stage (balanced), Emotiva XMC-1 prepro, Emotiva XPA-1L monoblocks, NHT 2.9 speakers
|
|
Graham Slee
Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16298 |
Post Options
Thanks(1)
|
This video might help some understand noise. It doesn't just apply to op-amps, or non-inverting ones, but this is possibly the easiest to understand.
It will also assist me in explaining why sometimes our assumptions can be incorrect. Edited by Graham Slee - 24 Nov 2019 at 6:37pm |
|
That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
|
|
WigglyWoo
Regular Joined: 23 Sep 2016 Location: Newbury Status: Offline Points: 82 |
Post Options
Thanks(1)
|
Thanks Graham, good to know...
|
|
Solo ULDE; Reflex M; Accession MC+Enigma and other tomfoolery...
|
|
Lucabeer
Senior Member Joined: 24 Jan 2009 Location: Torino, Italy Status: Offline Points: 703 |
Post Options
Thanks(1)
|
Preamp hiss does not bother me at all. With the Reflex M, it is way below the surface noise of the record.
|
|
Post Reply | Page 12> |
Tweet
|
Forum Jump | Forum Permissions You cannot post new topics in this forum You cannot reply to topics in this forum You cannot delete your posts in this forum You cannot edit your posts in this forum You cannot create polls in this forum You cannot vote in polls in this forum |