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Vernier scale

Discussion in 'Amp Central Station' started by Larry F, Aug 9, 2018.

  1. Larry F

    Larry F Doctor of Teleocity Vendor Member

    Nov 5, 2006
    Iowa City, IA
    I remember using old scopes and oscillators that allowed for course/fine scaling using either two separate knobs or one dual-concentric (if that's the term) knob.

    I am sure that my question has been asked/answered before, but thought I'd check here. Why can't an amp master volume control only have one knob? Why not a vernier knob, also? We all know what it is like to dial in an amp at super-low levels smoothly, without seeming to jump between levels.

    The amp I'm using is an ODS type, where changing the level of any knob other than the master volume often changes the sonic character, whether intentional or not. There are a number of different ways of controlling OD.

    I'm upstairs at 1:00 AM, trying to work with a new guitar, but at a level that won't wake my wife. I've been doing this kind of thing for years, and really wouldn't mind having a vernier knob for the master volume. Is my thinking unrealistic, impossible, etc.? I'm hip to the many ways of controlling loudness, but in this one instance, I'd really like a vernier knob. Even if I have to get a plastic knob and tape it to the amp.

    To be clear, I'm thinking of having the master volume at, say, 2, but wanting it at 2.2 or whatever is desired but unobtainable with the master volume knob.
     
    AAT65 and 24 track like this.

  2. Anode100

    Anode100 Friend of Leo's

    May 9, 2014
    Behind my beard.
    That would make perfect sense.

    A more direct solution would be to have a multi-turn pot in place of the regular 270 degree pot.

    Sure, you'd have to (literally) wind your amp up to 10, but for those of use who don't gig at the 'Enormodome' every night, it would be *very* useful.
     
    AAT65 likes this.

  3. 24 track

    24 track Doctor of Teleocity Silver Supporter

    Nov 6, 2014
    kamloops bc
    I built an Iso box for that reason, a 50 watt amp doesnt even begin to play untill you approach headroom , I also have a 5 watt beltone and a 15 watt beltone and run them through the iso box so i can play at night, interesting design for an amp Larry
     

  4. RLee77

    RLee77 Friend of Leo's

    May 15, 2016
    Silicon Valley
    It would be pretty simple to put a pot inline with the normal pot, like 1/10 the value, for fine tuning. Easier to install a multi-turn drop-in replacement as Anode suggested. You might even find a dual concentric pot of the right values needed, which would probably be the best case scenario.

    For example, you could do it with a pot like this, if your volume was a 500k: https://www.allparts.com/EP-4585-000-CTS-250K500K-Concentric-Pot_p_1443.html

    The top section would be your fine adjust, using just two terminals, with a resistor paralleled to lower the 250k to around 30k to 50k, and this would be put inline with the hot terminal of the 500k.
     
    Last edited: Aug 9, 2018

  5. chezdeluxe

    chezdeluxe Poster Extraordinaire Gold Supporter

    Age:
    68
    Dec 29, 2007
    Brisbane Australia
    My guitar has a volume control.
     

  6. Anode100

    Anode100 Friend of Leo's

    May 9, 2014
    Behind my beard.
    :D:D

    ...which changes the way the amp reacts, sadly.

    If you want 'that tone', sometimes, your guitar has to be on 10.
     
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  7. AAT65

    AAT65 Friend of Leo's

    Two nice ideas, IMHO!
     

  8. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

    Age:
    66
    Mar 2, 2003
    Lawndale CA
    Are you talking about a "fine tuning" volume control because you can't control loudness jumps with the standard pot?

    Why not do what a huge number of players do and use amps with much lower output for home situations? When you use the master on an ODS-type amp like that I don't see how you can even drive the speaker(s) enough to get full frequency response.

    It just seems like "too much amp" for the situation.

    since the '70's I (and many other players) have used an amp with the lowest output for a given situation, cranking the amp and using the guitar controls as the "drive throttle". When a good tube amp is driving hard (with output appropriate for the venue, home, studio, whatever) you find the guitar controls actually don't need to be dimed for the best sound.
     
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  9. Larry F

    Larry F Doctor of Teleocity Vendor Member

    Nov 5, 2006
    Iowa City, IA
    This isn't what I'm talking about. Sorry if you misunderstood my post.
     

  10. Old Tele man

    Old Tele man Friend of Leo's

    May 10, 2017
    Tucson, AZ
    Usually the "vernier" was a function of the KNOB assembly, which was geared to turn the pot shaft at a slower rotation than the KNOB was being rotated.

    There are also 'multi-turn' (10:1, etc.) pots available if you search the major electronics suppliers.
     

  11. dsutton24

    dsutton24 Doctor of Teleocity Gold Supporter

    Dec 29, 2010
    Illinois
    Two thoughts:

    You can buy little planetary drives that can be connected to a regular potentiometer, variable capacitor, or variable inductor, basically anything with a shaft that fits the drive. The drive puts out, say, one turn for every ten turns of the knob. There are various ratios available.

    Secondly, modern audio taper pots are pretty crappy things. They usually consist of three or four linear segments and only sort of approximate a logarithmic taper. True logarithmic taper pots can be had, but they're hugely expensive.
     
    RLee77 likes this.

  12. RLee77

    RLee77 Friend of Leo's

    May 15, 2016
    Silicon Valley
    This is very true. What this means is that turning the existing volume pot extremely gradually with a 10:1 ratio may not even help the "volume jump" issue, because even the smallest increment in conductive material ends up being a big jump in resistance.
     

  13. peteb

    peteb Friend of Leo's

    Apr 25, 2003
    Cascadia
    Trying to put together a basic signal generator has taught me more than I expected.



    Last week I did the dual pot vernier scale on my basic signal generator that started out as only one resistor, one capacitor, one transistor and one audio transformer. I needed to set the level low, like 20 mV. I noticed on my kit generator, that I could not get to work, that it had course and fine adjustment for frequency.


    To set the level I added in a 50k pot in series with a 1 k pot. It totally worked. I was able to dial in very close to 20 mV.





    Someone has to offer a stacked pot with one much higher value than the other. They could even pre wire them in series and all one would have to do is install it just like a single pot.
     

  14. Paul in Colorado

    Paul in Colorado Telefied Ad Free Member

    Mar 17, 2003
    Fort Collins, CO

  15. schmee

    schmee Friend of Leo's

    Jun 2, 2003
    northwest
    Fill us in, because I don't understand what you are trying to accomplish either. I thought you were looking for a fine adjustment volume control, but apparently not. (Not being rude, I really dont!) :>)

    "To be clear, I'm thinking of having the master volume at, say, 2, but wanting it at 2.2 or whatever is desired but unobtainable with the master volume knob."


    "Are you talking about fine tuning volume control?..." No
     

  16. schmee

    schmee Friend of Leo's

    Jun 2, 2003
    northwest
    You can mod the volume pot so it spreads the volume of say 2-4 over the whole dial 1-10. Is that what you want?
     

  17. dogmeat

    dogmeat Tele-Holic

    Age:
    67
    591
    Oct 12, 2017
    Alaska
    another possibility is 2 pots in parallel. they would have to be higher ohm. maybe 2 different values you could play them off eachother
     

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