Impedance differences

November 28, 2021
 by Paul McGowan

If you double the input impedance of your power amplifier from, say, 30kΩ to 60kΩ you're not going to hear a difference.

Yet, double the input impedance of your phono amplifier and you'll hear a change.

What's different between the two?

In the first case of doubling the amp's input impedance, we won't hear any difference because nothing in this chain affects frequency. The amp's input impedance must be high enough to not load down the preamp, but aside from that, not much else matters.

That's not true when it comes to a device such as a phono cartridge. Here the small coil generating the voltage feeding the phono preamplifier is part of what we refer to as a tank circuit—a tuned inductive network where the frequency response is a function of impedance and capacitance.

Think of it like a filter where the resulting output is dependent on the values of the elements that make up the network: coil, cap, resistor.

It is natural to assume that if the impedance setting of one element within our system matters, then it stands to reason all must.

Hopefully, it helps to have a short little explanation like this to set the record straight.

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43 comments on “Impedance differences”

  1. I think it should be mentioned that impedance matching options is a matter for MM, not MC cartridges, as for MC the impedance values would have to be very high to influence frequency response and therefore having negative impact on phase etc. (so far my humble knowledge).

    But anyway still not fully sure about the goal of today’s post.

      1. I have an MC cartridge and my phono preamp has multiple impedance Dip switch settings at its inputs. These small switches match the cartridge loading to the preamp and you can fine-tune the characteristic sound by carefully adjusting these switches for repeated listening until you get the musical results that sound to what you are listening for.

  2. Optical cartridges and a laser turntable both do not require such settings for tuning the sound.:-) However in order to fully get the sound quality buried in the grooves a hell of steps for fine-tuning is necessary. And don’t forget the impedance of the tonearm cable and super-clean and tight connections. The biggest trouble with vinyl records: too often the center-hole is not centered!

  3. I never understood any of this component matching impedance loading stuff. Fortunately my Devialet software has a long list of cartridges for the internal phono preamplifier and it does the settings. My external phono preamplifier doesn't have any dipswitches to change loadings or output so there is nothing to fiddle with, thank goodness.

    I suspect it is this sort of electronics stuff that puts off the average bloke from buying component audio. In the old days (the 1990s, possibly recent memory for many audiophiles) integrated amplifiers had inputs marked CD, tuner, phono etc. and there was nothing to worry about.

    1. My current integrated amplifier, built in 2019, has 4 inputs & none are marked 'Phono'.
      I'm interested in the one marked 'CD'; for all intents & purposes the others don't exist.

      1. Have a look at the back of the new Exposure 3510.

        A popular brand that’s been making very high quality sensible hifi for almost 50 years.

          1. It's been decades since I saw anything with tape in and out sockets. When it was reviewed it was referred to as a 1980s throwback, which it is, but it's a high quality unit. There are optional DAC and phono modules.

      2. Seems like your preamp is a line stage only but you’re not playing vinyl so it doesn’t really matter. I can’t speak to the CD input part of your comment.

        1. Basically yes, I'm using it as a line stage only. However, it offers a rare pre-amp feature that works well for me. The line outputs offer full range bandwidth for the main power amp, but also offer an electronic crossover HP to the mains and LP to a sub, with independent adjustments on the HP/LP ranges between 50Hz-250Hz!

          At my selected "HP/LP integration of 50Hz", the monitors have a Seamless bandwidth hand off to the powered sub, allowing the main high-pass power amp an extra 6 to 10db of headroom to power the monitors!! Overall, the large soundstage is effortless with a no-point-source presentation from 18Hz to 28kHz (monitors/sub totally disappear)!!

  4. It’s the software that costs more money for vinyl than CD.
    The respective hardware can range from $600.00 for a basic CD player,
    $900.00 for an acceptable basic t’table to dizzying heights for either.
    Still, everything costs money, time and effort.
    Just enjoy what you can afford.

  5. I’ll leave the component impedance matching up to the designers. If what is designed doesn’t match up well with what I have then I’ll move on.

    If I ever start spinning vinyl again then I’ll start ensuring the proper impedance match, azimuths, tracking weights, speed of rotation, etc. All the stuff I threw out of my mind to make room for formats, clocks and digital jitter. 😀

  6. Paul,

    I am confused with your message today, potentially by a typo.

    In opening you state: “If you double the input impedance of your power amplifier…”

    But then you go on to state: “In the first case of the preamp feeding the amplifier…”

    Is it amp, pre-amp, or both?

    Not trying to be an ass pointing out errors. Genuinely confused.

    1. Sorry about that. Not a typo but assumed folks would figure their amps were fed with something - in this case a preamp. Let's assume in all cases the amp's fed with a preamp and the preamp always has a low output impedance.

      Now we're just talking about the amp and its input impedance. Same applies. Regardless of whether the amp has an input impedance of 20kΩ (or double that) of 40kΩ, there won't be any sonic difference.

    2. Much more important in relationship to matching the pre-amp to amplifier is not it's impedance, but it's sensitivity. These should be matched. If you saddle a pre-amp that outputs 1V/0dB, and your amplifier's input is rated at 1.4V/0dB then the pre-amp doesn't provide enough signal voltage to ever drive the amplifier to 0dB. At that point the input resistance on the amplifier has to be decreased in order to maintain proper bus gain structure. In the professional amplifier realm, you can find many that have settings to match this 0dB reference level. Not so much in the consumer products out there today.

  7. Just as important, if not more, is the capacitance of the connecting cables. Especially on those pre-amps that have no pre-selector to set or change it's capacitance. Matching the cable's overall impedance/capacitance to the input stage of the pre-amp, is vital to keeping the RIAA curve correct.

    For example, I had someone come to me concerning his new Technics SL-1200 which was replacing his old Mk1, and complained at how the replacement left his collection sounding quite poor in comparison. Upon investigation the provided cable from Technics on the new table was well over 300pF, where the original Mk1 was only 50pF per foot, which had threw the curve well out of balance. The pre-amp was designed to 47kΩ/150pF. After utilizing a cable much closer to 50pF per foot, all was well. Just sayin'

    1. I don't use a turntable, so all my experience is with analog interconnects after a DAC. Two analog interconnects that sound phenomenal in my system between DAC and preamp and between preamp and amps are: Stealth Indra (1m) and Tara Labs Zero Evolution (1.5m). Ironically, the Indra has one of the highest capacitances in the industry for a high-end cable: 165 pF (but far lower than the 300 pf cable that plagued your acquaintance's system). The penalty with the Stealth is a slightly rolled off very top end, but other qualities of the sound are superior to what I hear from most of my other interconnects. The Tara Labs Zero Evolution has one of the absolutely lowest capacitances in the industry: 2.5 pF. It is the best sounding cable in my system, with the AudioQuest Fire a close second. Though I typically just run an interconnect pair straight from my DAC to the amps, when I do use a preamp, having the Indra or the Fire in combination with the Evolution is very satisfying. Capacitance is important, but other characteristics of the cables, such as their construction and materials, are probably more important to superior sound.

      1. In voltages found at the MM phono cartridge levels, (generally 1.5mV to 3.5mV) it is much more sensitive to the capacitance of the cable due to the way the RIAA curve works. At line level, while important, it's not as critical due to how it works.

        1. Yep, that was Paul's point as well. I was trying to illustrate your and his point by giving examples of how capacitance is not as big a factor in non-phono line level interconnects. In my last sentence I should have said "line level cables" instead of "cables" to avoid any misinterpretation.

  8. I'm glad people have not given up on the phonograph. More audiophiles are realizing that there's something amiss in digital though it's hard to pinpoint what it is. But whatever it is it's not missing in well recorded vinyl.

  9. Paul, it is likely my lack of understanding electronics, but I'm confused.

    You stated, "nothing in this chain affects frequency". My understanding is the preamp output should be matched with the amp input to avoid higher frequency roll off. For example, the output from a tubed preamp/line stage will result in a roll off if the amp input is say 30 ohms or lower. Something like 50 ohms or higher is needed to avoid frequency impacts. I believe solid state preamps/line stages may have an output which is not affected by the lower amp inputs. Is this correct?

    1. It can be confusing. And when you write 30Ω you actually mean 30kΩ (1000 Ohms with the k).

      The rolloff in frequency you're referring to if the input impedance of the amp is too low is found in the bass (not the top need). This s because the output coupling capacitor of a tube preamplifier needs to look into a higher impedance.

      That said, as long as there's a good 10X or more difference between the output impedance of the preamp and the input impedance of the power amp you should be ok.

  10. This topic of impedance has been on my mind for the last week in the context of the power chain.

    Sadly, my aging ears have developed a sensitivity to my audio system that can lead to tinnitus and even something like hyperacusis if certain components are not right. Since I upgraded my system to BHK components and a DSD DAC two years ago, I've had one P600 in my system, but only for the source components and the preamp. Ten days ago, I was excited to dig out my second P600 Power Line conditioner, which gave me enough power to hook my amps up.

    It was a huge improvement. OMG, I've never had such a good sounding system! But it was bittersweet: since my listening session, I've had elevated tinnitus, which has been taking its time dying down, so I've been giving my ears a break and haven't listened since. Unless I can eliminate the cause of the tinnitus, I'm going to have to take the P600s out of the power chain for the amps, which kills me. (The volume didn't seem overly loud when I was listening.)

    I know the P600s lower the impedance of power to the amps, but why would this translate to tinnitus at the same listening volume? Any ideas or suggestions? (I've been thinking of going back to stock power cables between the P600s and the amps, instead of my PS Audio Lab Cables. Might that help?)

    I don't want to make a substantial downgrade to the sound of my system, but if my ears demand it, I must obey. And that's what I'm about to do.

    1. Tinnitus has several ways of happening to a person. It’s not only about high volume levels. It could start from medication’s and there may be other reasons as well. I suggest that you do some research on the Internet and definitely consult an ENT physician.

      1. Thanks for your advice, Stimpy. I appreciate it. I think I understand tinnitus and hyperacusis pretty well, though. I didn't listen to my audio system at all for almost ten years because of hyperacusis - or something like it - and during that period I did tons of research and saw lots of doctors. In the end, I think an old DAC (a dCS Elgar!) was probably the culprit.

        I'm pretty confident that my reaction to my recent listening session was because the P600s fed the amps. My only reservation is that I also cleaned the contacts on my connectors, and my speaker cables and connectors badly needed cleaning. That might have been a factor, too.

  11. If you stick with an established manufacture then picking the right phono preamp ( or phono stage ) for your cartridge is not so much about impedance as it is about gain. The line inputs ( i.e. a CD, Aux, tuner, etc. ) on preamps, integrated amps and receivers want to have signals that are about 1 volt to operate at there best. Electromagnetic cartridges ( which is what MM and MC cartridges are ) produce about 5 mV ( MM ) to 1 mV ( MC ) to 0.2 mV ( low output MC ). The phono preamp has to supply enough gain to make those mV outputs ( millivolt which is 1 thousandth of a volt ) into 1 volt signals. Thus for the cartridge outputs listed above you would need at gain of 200, 1000 and 5000 to get each output to 1 volt.

    Most phono preamps have their gain listed as so many dB. Here is a list of gains for some typical dB gains: 44 dB = 160, 54 dB = 500, 65 dB = 1780 and 73 dB = 4470. I actually use a cartridge with a 0.2 mV output and a phono preamp that has a gain of 54 dB or 500. 500 times 0.2 mV is only 0.1 volt. Thus, I use a step up transformer ( SUT ) that has a gain of 10 to get the desired 1 volt signal.

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