Question about selecting appropriate phono preamp gain

Discussion in 'Audio Hardware' started by Wounded Land, Sep 20, 2016.

  1. Wounded Land

    Wounded Land Forum Resident Thread Starter

    I was looking at an article on the Absolute Sound's website about finding the optimal amount of gain for a cartridge. The formula they suggest is:

    1. 1 divided by your phono output in volts
    2. take the log
    3. multiply by 20

    I have an Ortofon 2M Blue with an output voltage of 5.5 mV. Going through the calculations above, I end up with a value of approximately 45.

    My questions are:

    1. What do you think about this formula? Do you use this?
    2. My Schiit Mani has gain stages of 42dB and 48dB (the number I calculated was 45). Is it better to go high or low?

    Thanks in advance...
     
  2. russk

    russk Forum Resident

    Location:
    Syracuse NY
    That is what I've always used. This used to be the norm but I think people just forgot about it as LPs moved into the realm of obscurity. My understanding is that your usually ok if you hit within 2db of what you need. I have a feeling a lot of people liking and hating a certain phono pre is more related to how well it accidentally matches their amp.

    As for if it's better going a bit higher or lower that's going to be a mater of personal taste and how your gear behaves i.e. how sensitive it is to overload. You're just gonna have to check it out and pick the one that sounds best to you.
     
  3. beep

    beep Forum Resident

    Location:
    Virginia
    I just adjust mine so it's the same level as my CD player. Seems to work fine.
     
  4. jupiterboy

    jupiterboy Forum Residue

    Location:
    Buffalo, NY
    I've seen that formula before. It doesn't work well for me in real life. I've always found the KAB calc to give a more realistic target.

    KAB PHONO PREAMP PARAMETER COMPUTER »

    It puts your optimum at 35 dB. That seems about right to me.
     
  5. chervokas

    chervokas Forum Resident

    Try 'em both but probably 42 dB gain is more than enough gain for a 5.5mV output cart and the 30 dB setting on that preamp is almost certainly insufficient.
     
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  6. jupiterboy

    jupiterboy Forum Residue

    Location:
    Buffalo, NY
    Too much gain, to my ear, sounds very punchy but flat and you start adding grain to sibilants on hot recordings. Too little gain sounds much better but you lose the punch and immediacy and get more separation, depth—you can hear the size and space of the soundstage.
     
    KT88 likes this.
  7. KT88

    KT88 Forum Resident

    Less is more here. :)
    -Bill
     
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  8. russk

    russk Forum Resident

    Location:
    Syracuse NY
    In the equation 1 represents the input sensitivity of your amp, which is the amount of voltage your amp needs for full output. For that formula to work you need to know your amps input sensitivity, not all amps are 1v. My tube amp is 1.3v to full output. If your running a solid state amp or with a preamp yours will be lower, in the millivolt range usually. If you do this formula right, the answer you get is the ideal.
     
  9. Wounded Land

    Wounded Land Forum Resident Thread Starter

    Thanks for your input, everyone. Interestingly, I e-mailed Schiit to get their opinion, and they suggested the 48 db setting (low output-MM).

    @russk Thanks for your post! I have an NAD 316 BEE. According to the amp's data sheet, it has an input sensitivity of 200 mV (to be precise, it reads "Input sensitivity, rated power"). So running through the following calculation:

    .2/.0055
    take log of result
    multiply by 20

    ...gives me a result of 31 and change. This would imply that I should use the "Decca" mode on the Mani, which provides 30 dB of gain. (What the heck is a "Decca mode", anyway?)

    What do you think?
     
  10. russk

    russk Forum Resident

    Location:
    Syracuse NY
    Yep. The math is good and it also makes sense that 30db would be enough gain with a high output MM cartridge like the 2M Blue and a modern solid-state integrated. I've no idea why they would tell you to use what they themselves are calling the low output MM setting on a cart with a gain of 5.5mv. Weird.

    I'd still play with it a little though. Some people like a touch more gain but the 48 db might cause your amp to clip a bit and sound harsh.
     
  11. Wounded Land

    Wounded Land Forum Resident Thread Starter

    Yeah, I thought it was weird too. Once I get some time this week I'll play with the settings and see what I turn up. Thank you.
     
  12. 5-String

    5-String Forum Resident

    Location:
    Sunshine State
    I wasn't even aware that such a formula exists. This is based on what principle?
    Basically, what I do is that I just use my 60db setting for all my low output MC cartridges.
     
  13. russk

    russk Forum Resident

    Location:
    Syracuse NY
    Anytime. Let us know what you think of the Mani. I've been thinking of picking one up for my amp. With an input sensitivity of 1.3v I'll need the 48db with my 2M Blue.
     
  14. russk

    russk Forum Resident

    Location:
    Syracuse NY
    It's an equation to determine how much gain you need, ideally, to meet a specific voltage based of the output of your cartridge.

    What you do is what most people do, but there's always a way to figure something out with math. :cheers:
     
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  15. jupiterboy

    jupiterboy Forum Residue

    Location:
    Buffalo, NY
    Which math, I suppose, is the question.
     
  16. 5-String

    5-String Forum Resident

    Location:
    Sunshine State
    Yes, what I meant was why multiply by 20 and not by 30 or 15 for instance, what is the principle behind this.
     
  17. jupiterboy

    jupiterboy Forum Residue

    Location:
    Buffalo, NY
    That I can't tell you.

    I do know that my cart is listed at 1.6mV, but many people with better test equipment than I say 2.2mV is more accurate.

    At least the KAB calc tells you what assumptions you are working with.

    Does changing preamp tubes have any bearing on the input sensitivity? IDK

    There are vagaries and language doesn't always help. If I were looking at the OPs post, I might take some wrong ideas about the formula. I've always looked at that formula as a guide, though, so kinda know.

    At any rate, I'm glad I have some gain options, and glad I can borrow from multiple calculations to add to reinforcement to what I hear. 44db gain is not bad with the Denon DL-110.
     
    5-String likes this.
  18. Guildx500

    Guildx500 Forum Resident

    Location:
    California
    You can overload your line preamp if you combine too much cartridge output with too much gain in the phono. It doesn't sound pleasant. But it should be easy to hear. When I did have adjustable gain phono stages I used the least amount I could get away with.
     
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  19. I've tried the KAB method, but my results are somewhat similar to yours. If I recall KAB had my ideal at 58db, which would be -2dbs on my Mac preamp's MC phono stage (it's supposedly at 60db when flat). However, I prefer the sound for the most part when the level is bumped up +4 or 4.5 dbs--particularly for rock. It's got far more bass punch/slam that way and is much closer to the level of the digital inputs.
     
  20. jupiterboy

    jupiterboy Forum Residue

    Location:
    Buffalo, NY
    Lots of people have a similar situation. We all prize different aspects of sound.

    One interesting thing about McIntosh is that some of their phono sections have a gain matching feature so it actively adjusts the gain based on the signal you feed into it so that you never have clipping.

    I usually put on some jazz records where a horn solo gets really hot. If I've got enough gain that those distorted moments in the recording sound worse, I've gone too far.

    On the other hand, I can go a little low and get a really amazing soundstage but lose any punch in the recording.

    Ultimately, it's a bit of a razor's edge, and I try and make sure I'm not trying to fix poor recordings and masterings by pushing too hard or not enough.

    Takes some time.
     
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  21. russk

    russk Forum Resident

    Location:
    Syracuse NY
    Different tubes in the same family have different gain and can change the input sensitivity. Pentodes like EF86 are the highest gain in that family of tubes, the E80f is a great tube but results in a bit of a drop in gain and input sensitivity. Not terrible though. To make things worse, the same type of tubes aren't really exactly the same gain. Take 3 different 12ax7s and odds are they would each differ a bit. That's why I use the formula as a starting point.

    I've played with the KAB calculator once and it's ok. I like the overload function.

    In the end I'm guilty of tuning my system by ear. It's just nice to have something that gets me in the ballpark.
     
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  22. jupiterboy

    jupiterboy Forum Residue

    Location:
    Buffalo, NY
    Ear is the final arbiter. Nothing wrong with that. Why wouldn't it be, it's wired into my brain.
     
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  23. russk

    russk Forum Resident

    Location:
    Syracuse NY
    Measured observation. It's an equivalency formula. In a lab someone once measure millivolts and applied several different levels of gain and measured the corresponding outputs. They compared them and came up with the formula and verified their results by comparing them to the actual physical results.
     
  24. 5-String

    5-String Forum Resident

    Location:
    Sunshine State
    Thanks, it makes sense now.
    I used the KAB calculator and it seems that the optimum gain for my cartridge with 0.5 mV is 56db instead of 60db that I am using now. Although I never noticed any overloading I will drop the gain to 56db and see If I can detect any difference.
     
  25. timztunz

    timztunz Audioista

    Location:
    Texas
    Seems to me that both of these guys are saying less is more, which not normally how I roll. But in this case I think they know what they're talking about and I agree with them.
     

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