Phaez SIBLY Tone?

Discussion in 'The Squawk Box' started by 8len8, Jan 24, 2014.

  1. 8len8

    8len8 Senior Member

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    I've had a Phaez SIBLY for a couple years now, and it's just too midrange sounding for me these days (the cab and guitars sound fine with my other amps).

    Anyone with a SIBLY every tweaked the tone stack? It doesn't look like the typical Marshall/Fender stack. I emailed Randy about it, but he doesn't have enough bandwidth to answer all my questions.
     
  2. V2

    V2 V.I.P. Member

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    What are the values in your amp?
     
  3. darkbluemurder

    darkbluemurder Senior Member

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    The pictures I have seen show a 250pf treble cap, a 82k or 100k slope resistor and 22nf caps for bass and middle (but that's a guess only since they are the same size). Pot values were 250kB treble, 500kA bass and 50kB middle.

    You could change the treble cap to 150pf or 180pf for less midrange and a brighter tone. Likewise, if the treble cap in your amp is a different value, just use a slightly smaller one (e.g. have a 500pf, try a 330pf or 270pf).

    Cheers Stephan
     
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  4. 8len8

    8len8 Senior Member

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    My problem is that I can't even locate the slope resistor. The tone stack doesn't seem to be wired like a typical one.
     
  5. darkbluemurder

    darkbluemurder Senior Member

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    Can you post a picture, please?

    Cheers Stephan
     
  6. V2

    V2 V.I.P. Member

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    A photo would seem necessary...
     
  7. NYC LP player

    NYC LP player Premium Member

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    I'm no amp pro but I do know Randy can mod it his JTM version failry easily

    [ame]http://www.youtube.com/watch?v=dEs9FnoBVoI[/ame]

    I inquired about a SIBLY/JTM switch but it doesn't sound possible
     
  8. 8len8

    8len8 Senior Member

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    Here's the tone stack pic.

    Pots from left to right: Mid, Bass, Treble, Gain. There just aren't as many R's and C's around the pots as I'm used to.

    [​IMG]
     
  9. V2

    V2 V.I.P. Member

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    [​IMG]

    Follow the wires to and from the Rs and Cs in the yellow oval. The R looks to be a 43k slope resistor. I certainly see two brown caps, and I bet there is a dark silver mica cap as well.

    Meet your tone stack. :)
     
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  10. 8len8

    8len8 Senior Member

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    That's where I get confused. Here's where things go:

    [​IMG]

    That doesn't match the "typical" tone stack wiring:

    The Tone Stack Explained in English for Humans | Pick Roar

    That resistor you mention doesn't go near the Treble pot. Also, in the picture you can see there are actually 2 caps mounted to the treble pot, which look like part of the tone stack.
     
  11. V2

    V2 V.I.P. Member

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    There will be jumpers from the various TMB pots (and no doubt your boost pot, although I don't know what that does). C3 is probably your treble cap, and so if it connects first to the boost pot, there is probably a jumper that takes it to one of the outside terminals of the treble pot.

    Same with C1; it goes to the mid pot, but there is very likely a jumper wire from that terminal over to the bass pot.
     
  12. 8len8

    8len8 Senior Member

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    The Boost pot controls the amount of even vs odd harmonics generated by the amp (a Randy feature).

    I do show that C1 goes to both the mid and bass pots.

    C3 doesn't go anywhere near the treble pot. I've beeped it out with a meter, and there's nowhere near a short between them. Several 100's of Kohms.
     
  13. V2

    V2 V.I.P. Member

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    so is the boost pot to the left of the pots in the photo:

    boost (not shown), mid, bass, treble, gain?

    I'd like to see the wiring for the boost, mid, bass, and treble pots.

    Assuming the second-from-the-right pot is labeled treble, where does the wiper (middle) wire go to?

    Assuming the left-of-the-photo pot is labeled boost, where does the wiper (middle) wire go to?

    My current thinking: the left-of-the-photo pot is the treble pot; the second-from-the-right pot is the boost pot.
     
  14. 8len8

    8len8 Senior Member

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    It says in the post with the picture which pot is which. "Pots from left to right: Mid, Bass, Treble, Gain."


     
  15. V2

    V2 V.I.P. Member

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    a couple of notes:
    - that post doesn't say which pot is the boost. Is it to the left of the Mid pot?
    - the pot labeled Treble might not actually be the treble.

    So I suggested that you follow the wiper wires from each of those two pots to find out what they are. The treble pot wiper will likely be tied directly to the Master volume (if you have one). Is either of those pots connected to the master?
     
  16. 8len8

    8len8 Senior Member

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    I was hoping to not have to do too much wire tracing because a lot of the wires go under the power supply circuit board :). I'll take a closer look at things over the weekend. Like I mentioned, I beeped out the stack and it doesn't math the typical wiring so I assume this'll get interesting.
     
  17. V2

    V2 V.I.P. Member

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    set TMB and boost all at minimum. Depending on the wiring, you may hear nothing or some signal (I bet nothing).

    Now what happens when:

    1. you crank the pot labeled Treble? Do you hear high frequencies or nothing?

    2. Set everything back to zero and then crank the boost pot. Do you hear high frequencies or nothing?

    Edit: I'm 99% sure the pot next to your gain pot is BOOST. So doing #1, you will likely hear nothing because the tone stack pots are all at zero, and doing #2 will give you high frequencies if it is the actual Treble pot.
     
  18. 8len8

    8len8 Senior Member

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    Here's the more detailed schematic of the Tone Stack.

    [​IMG]

    I just marked the V1 and V2 connections with arbitrary pin names so you could see which tone stack components shared a V1 or V2 connection.

    Like you said, it's starting to look like the Boost and Treble pots are mis-marked :).

    Like you recommended, I ran some tests with the Boost and Treble pots.
    - When I turn down the Treble+Mid+Bass pots there's still a small signal coming through. - When I turn down the Boost+Mid+Bass pots there's no signal that comes through.

    The Treble and Boost pots have a similar impact on tone, although the Boost impacts higher frequencies. Neither completely kills the signal if turned all the way CCW on its own.

    In Randy's words, "Yes the boost on the front is like a HF peaking circuit, or cut if all the way left. It can change the nature of the distortion by going very asymetrical all the way right, and more symetrical all the way left. But to maintain the same level of distortion you would have to adjust the gain pot also. I find it pretty useful, and will be offered on most of my amps".
     
  19. V2

    V2 V.I.P. Member

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    Good first attempt at drawing out a schematic! I think there are probably some errors, but not to worry - its a difficult task. It think it would be easier if you took a look at an existing schematic and tried to match up some of the main components and circuits. It also extremely helpful to read books on what these different circuits do; then you can look at something and know what is going on very quickly.

    R5 is the treble in the tone stack. If you measure resistance from its outer terminals, you should find 250k ohms. And with R5 set at noon, you should measure 125k ohms. That would mean R5 is a linear 250k pot (like most treble pots).

    Your mid pot might be either 50k (linear) or 100k (log). In either case, try setting it below noon if your sound has too much mids. Also keep in mind that the treble pot (R5) and the mid pot are highly interactive. If you turn up the mids near noon, the treble might have to be turned down, at least at home.

    Your tone stack also needs a connection to ground. This is usually done from the 'right' terminal of the mid pot. The Master and mids grounds are often connected, as are your R4 and R6. Check to see if that goes to a ground rather than to a pin on the V2 socket.
     
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  20. 8len8

    8len8 Senior Member

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    Thanks for the help. I've actually played guitar for over 30 years and been an electrical engineer for about 20 years :). I was just being lazy and didn't want to have to dig too deeply into learning the ins and outs of tones stacks. Now that I know the Treble and Boost pots are switched I can dial in a lot better sounding tones (until now I was always setting Treble to 0 thinking that was Boost).
     
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