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Master volume and treble loss

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  • Boy Howdy
    replied
    Originally posted by pdf64 View Post
    Err it would be helpful to provide the specifics of the amp you’re asking about
    It's the amp in the schematic I posted, slightly modified.

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  • Boy Howdy
    replied
    Originally posted by vintagekiki View Post
    No treble loss
    Click image for larger version

Name:	MV mod.GIF
Views:	380
Size:	181.7 KB
ID:	920076
    I actually have used that type of master on another amp I have. I wanted to compare the two types. I can't remember what I concluded about the differences, but the single pot version does work well, is cheaper and sounds good. I may just take out the dual master and go with the one pot master.

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  • Boy Howdy
    replied
    Originally posted by Boy Howdy View Post
    As we all know volume controls are very touchy down low on the dial. For a clean sound I'm running at about .5 (that's one-half of one) and it's a bit of a pain to get it just right. So I generally just set roughly where I want it and then use the master volume to control the actual volume.

    I have a Ken Fisher type PPI master on the amp. mod101_ppimv_master_volume_mod.pdf (tubesandmore.com) The problem is that when I turn down the master, I lose treble. So then I have to do this dance of balancing the two volume controls to get the best sound, which defeats the whole purpose of using the master in the first place.

    Can I install bypass caps on the master to recover the lost treble?


    Yeah, I always put a bright cap on the volume control, can't live without it. This time I actually installed a 470K resistor in series with the cap to get it just right. That worked out really well. I get what I want there, as long as I don't turn down the master too low.


    The dual 100K is just what the recipe called for. I didn't give a second, or even a first, thought. . . . Gulp.

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  • pdf64
    replied
    Originally posted by vintagekiki View Post
    No treble loss
    Click image for larger version

Name:	MV mod.GIF
Views:	380
Size:	181.7 KB
ID:	920076
    Did you see the thread where Jon Snell raised the issue of a common mode positive bias caused by the type 3 / crossline master vol? https://music-electronics-forum.com/...olume-question

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  • Helmholtz
    replied
    Originally posted by vintagekiki View Post
    No treble loss
    Click image for larger version  Name:	MV mod.GIF Views:	0 Size:	181.7 KB ID:	920076
    The OT's MV doesn't cause treble loss either (except maybe for some Fletcher- Munson effect at low volume). Don't forget pentode input capacitance is very small.

    And cross-phase MVs cause bass loss at low settings.
    Last edited by Helmholtz; 12-12-2020, 10:57 PM.

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  • vintagekiki
    replied
    No treble loss
    Click image for larger version

Name:	MV mod.GIF
Views:	380
Size:	181.7 KB
ID:	920076

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  • Helmholtz
    replied
    Yes you could.

    But the actual place where treble is lost in the amp is the vol pot and the input capacitance of V1b at low vol settings.
    Have you tried a bright cap of 47p to 150p across the vol pot?

    Also I wonder why you use a dual 100k master pot. That low value loads down the PI output. I would use a dual 470k pot instead and try 100p to 330p bright caps if necessary. But as the MV is within the NFB loop, the bright effect will be small.

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  • pdf64
    replied
    Err it would be helpful to provide the specifics of the amp you’re asking about

    Leave a comment:


  • Boy Howdy
    started a topic Master volume and treble loss

    Master volume and treble loss

    As we all know volume controls are very touchy down low on the dial. For a clean sound I'm running at about .5 (that's one-half of one) and it's a bit of a pain to get it just right. So I generally just set roughly where I want it and then use the master volume to control the actual volume.

    I have a Ken Fisher type PPI master on the amp. mod101_ppimv_master_volume_mod.pdf (tubesandmore.com) The problem is that when I turn down the master, I lose treble. So then I have to do this dance of balancing the two volume controls to get the best sound, which defeats the whole purpose of using the master in the first place.

    Can I install bypass caps on the master to recover the lost treble?
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