Why Phono Stage Hiss?
Printed From: Graham Slee Hifi System Components
Category: Turntable Audio
Forum Name: High Fidelity Turntable User
Forum Description: Technical Q&A, hints and tips
URL: https://www.hifisystemcomponents.com/forum/forum_posts.asp?TID=4824
Printed Date: 27 Mar 2026 at 4:02am
Software Version: Web Wiz Forums 12.01 - http://www.webwizforums.com
Topic: Why Phono Stage Hiss?
Posted By: Graham Slee
Subject: Why Phono Stage Hiss?
Date Posted: 15 Nov 2019 at 7:45am
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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 park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Replies:
Posted By: patientot
Date Posted: 15 Nov 2019 at 2:05pm
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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 VM610 MONO, AT VM95ML, Stanton 680mkII + Ogura, and Shure M35X cartridges. |
Posted By: WigglyWoo
Date Posted: 23 Nov 2019 at 7:51am
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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... |
Posted By: RussL
Date Posted: 24 Nov 2019 at 5:37pm
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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 |
Posted By: Graham Slee
Date Posted: 24 Nov 2019 at 6:35pm
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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. ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: WigglyWoo
Date Posted: 24 Nov 2019 at 7:17pm
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Thanks Graham, good to know... ------------- Solo ULDE; Reflex M; Accession MC+Enigma and other tomfoolery... |
Posted By: Lucabeer
Date Posted: 25 Nov 2019 at 7:46am
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Preamp hiss does not bother me at all. With the Reflex M, it is way below the surface noise of the record. |
Posted By: Graham Slee
Date Posted: 26 Nov 2019 at 5:30pm
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So, did anybody see his "deliberate" mistake? If 1k has noise voltage of 4nV then 100k is 100 times 4 = 400, not 40. However, it serves the purpose of informing us what the input noise is. Now, in a real amplifier the input isn't grounded like what's shown in the video - it has a source, and that source has impedance, and that impedance is its driving impedance (not to be confused with recommended load impedance). The video looked at fixed resistors, but impedances are AC resistances which appear in sources and might not look like fixed resistors, but are there nonetheless. An MM cartridge is roughly 1k at 1kHz and some as high as 3k. Therefore we can add 4 to 12 nV of noise to the input. The phono stage might have 1k of series resistance with its input prior to its "load capacitor" to aid radio rejection - that adds another 4 nV. At 20kHz a MM cartridge impedance is closer to its matching impedance (47k) and so, as a source, it becomes noisier; but because of the spectral spread (the frequency response) being "corrected" by the RIAA EQ, the noise doesn't rise rapidly at high frequencies. It is because of the EQ that multiplying out the noise voltages by the square root of bandwidth (20kHz being 141) does not give us the correct noise answer. So does more gain equate to more noise? In one way it obviously does, but then in another it doesn't. It will obviously be dictated by the noise of the source, and if that source's impedance is substantially lower, then a higher gain might not lead to more noise. We can see in the Accession specifications that the difference between MM and MC versions is only 1dB, yet the MC has 20dB more gain. ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: RussL
Date Posted: 27 Nov 2019 at 11:14pm
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Hi Graham - thanks for posting the educational video and your further clarifications above. I guess my thinking intuitively that 60dB vs. 40dB automatically means more noise at the output is not necessarily correct. You've certainly proven that with your Accession design. Great work. 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 |