Volume pot mod on HRD question

Discussion in 'Amp Central Station' started by dweeb686, Mar 6, 2019.

  1. dweeb686

    dweeb686 TDPRI Member

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    Hey all,

    I have a curious hypothetical regarding the clean channel volume pot on a Fender Hot Rod.

    The stock pot value is A250k. I am going to change this to a B250k, but curious to know what effect using a B500k instead would have on the tone or the way the pot/amp behaves. Thanks for your help!
     
  2. clintj

    clintj Friend of Leo's

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    500k will keep a little more signal going to the next stage in the amp.

    I gotta ask though, why linear? That's going to make the first bit of travel even touchier than it is stock. The stock A15 taper will pass 15% of signal at the midpoint, a B taper will pass 50%.

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  3. dweeb686

    dweeb686 TDPRI Member

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    What kind of effect would that have on a the amps tone? The EQ section would be a little hotter, more sensitive, etc? Just my guess.

    And are you sure it’s not the other way around? The stock, logarithmic pot shakes my house a at 10 o’clock, whereas a linear pot would get me to the equivalent volume later in the sweep, somewhere around 1 o’clock perhaps?
     
  4. clintj

    clintj Friend of Leo's

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    http://www.geofex.com/Article_Folders/potsecrets/potscret.htm

    Discussion of linear vs log (audio) is about halfway down the page. Log comes on slower then builds rapidly at the halfway point. Linear is a better choice if you routinely can run the amp at 3/4 volume or higher now and want finer control in that realm.

    It's the gain structure of the amp that makes the Hot Rods so touchy. Swapping V1 for a 12AY7 or 5751 or simply running a volume pedal in the FX loop to bring down the signal to the power section a little will let you turn the volume up past the super touchy region. And the higher value pot will pass a little more signal to the EQ and later sections, especially at higher volume settings.

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  5. dweeb686

    dweeb686 TDPRI Member

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    Thanks! I’ve done both the 12AY7 swap and volume box in the effects loop. Even went to 6V6Ss in the power section. When I took the back cover off to bias the new power tubes, I noticed that the last guy I had work on my amp changed the Drive channel to a linear pot but left the Clean pot stock. The action on the drive channel is great but I use the clean channel way more and find there to be substantial signal degradation when I put the volume box in the fx loop. Currently, I get no volume until 2, and then by 3 it’s too loud for any sound guy to work with, and by 4 it’s rattling my building. I am determined to have more control over that range!
     
  6. clintj

    clintj Friend of Leo's

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    Well, it's apparent I'm not going to give you the answer you want to hear, so go for it.

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  7. Ess Eff

    Ess Eff Tele-Meister

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    Are you sure you haven't got it all ass-about?
    .
     
  8. peteb

    peteb Friend of Leo's

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    A regular taper pot will give a curved response.


    The audio taper pot changes the response back to linear.
     
  9. dweeb686

    dweeb686 TDPRI Member

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    Yeah, I definitely did have it all ass-about. My bad. I figured I needed the other because of how damn loud my amp was at 2-3, so I was confused. Stupid. Sorry!!
     
  10. dweeb686

    dweeb686 TDPRI Member

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    Just a follow up in my quest to better control the volume of my Deville. I had initially changed my tubes to 12AY7 in V1, 12AX7 in V2 and 12AT7 in V3, with 6V6Ss and a re-bias to 35 for my power tubes. This did take things in the right direction, but out of curiosity I ordered a pair of 12AU7s and stuck them in V1 and V3. This gives me all the control I need over my amp, with the sweep of the clean knob giving me volume for practice level to stage level. I’ve ordered a 12DW7 to test out in V2, but out of the 12AX7, 12AT7, 12AY7 and 12AU7, the AX7 is still the winner as the amount of treble in the drive tone seems to drop disproportionately to the amount of bass, so anything less sounds like throwing a blanket over the amp. Not sure what I’ll find with the DW7 but excited to experiment with it as other people have reported to like it.
     
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