Where to insert Baxandall tone stack in 5F10 circuit?

Discussion in 'Shock Brother's DIY Amps' started by OahuClay, Oct 16, 2019.

  1. OahuClay

    OahuClay TDPRI Member

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    building a 5f10 and wanting more than the standard "tone"control, the Baxandall or James tone stack looks pretty nice.Where would you insert this in the circuit? Specifically for the 5F10 circuit Baxandall_Tone_Stack_Layout.png
     

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  2. sds1

    sds1 Tele-Afflicted

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    I think you would insert it directly after the first stage, with output of the tone stack leading to the volume pot.

    But keep in mind the tone stack will be significantly lossy compared to the tweed tone control. You will be hitting grid of the next stage with less signal. This is a big change to the amp beyond just the filtering.
     
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  3. Wally

    Wally Telefied Ad Free Member

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    I have no idea, but what that 5F10 is in essence is a 5E3 with fixed bias.....or a 5F11 or 6G2 Princeton without the bias vary trem....and I would not change a thing about it. Ommv.
    Sometimes simpler is better, ime. is there enough gain in that single input preamp gain stage to work with the Baxandall? I have no idea. The AMPEG Gemini uses that tone circuit, but it follows the second gain stage in that amp.
    I have an Alamo fury that I believe runs a Baxandall.....I’ll have to refer to the badly drawn schematic I did because there is no known schematic for this amp the Fury runs a 7199 preamp stage, though.....think EF86...a pentode preamp. I need to find that schematic I drew!!, I drew it up because the treble pot response is what I am used to...but the Bass pot sweep does a very strange thing.

    maybe this bump will get someone with more insight on this to respond.
     
  4. Ten Over

    Ten Over Tele-Meister

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    You would have no choice but to put it between the first and second stage. The negative feedback is inserted at the second stage, so putting the tone control after the second stage would put it within the feedback loop.
     
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  5. Teleguy61

    Teleguy61 Friend of Leo's

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    You would certainly lose a lot of gain.
     
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  6. Wyatt

    Wyatt Tele-Afflicted

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    It goes in between the 1st and 2nd Stages

    • From the 6AT6, the signal goes through the .02 MFD coupling cap and then to the "Input" as marked on the James tone stack diagram in the OP
    • The "Output" on the diagram would run to the Volume pot (like on an Orange) and then to the grid of the Driver Stage
    There will be insertion loss (which may be fine if you want a mellower, clean amp like Ampeg) and I don't see an easy way to recover from that. We can't add a cathode-bypass cap to the Driver Stage, it would ground out the NFB loop as well. We could just remove the NFB, but that doesn't so much as add gain as changes the amp to a more aggressive behavior — more excited, less polite. If using a 12AX7 instead of a 6AT6, we would consider the leftover triode as a cathode follower to drive the tone stack or a recovery gain stage after it.

    Ampeg did it two ways...

    1. gain stage > tone stack > gain stage > volume > long-tail PI (with NFB)
    2. gain stage > tone stack > gain stage > volume > pentode driver stage (with NFB) > cathodyne PI
     
    Last edited: Oct 17, 2019
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  7. OahuClay

    OahuClay TDPRI Member

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    plenty of valuable info here, thanks much, I'm building this on an aluminum chassis and utilizing extra parts so its not like im messing up a nice fender clone kit, I have a 7199 tube as well as plenty of 12ax7's so changing out the first stage isn't too far fetched, the 7199 seggestion interests me, I'll have to pull an ampeg schematic, I may try it "as is" first though and give it a listen, all sugestions appreciated, thanks!
     

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  8. Wally

    Wally Telefied Ad Free Member

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    Oahu, the Ampeg Gemini uses a 7199, but it is not used in the preamp. So, I don’t think that will be much help to you.
    I have a little Caliphone unit that uses the 7199 pentode section as the sole input preamp gain stage and the triode for the driver, iirc. It is a grainy, rich sounding little amp...people wonder ‘what is THAT?!?’ That schematic might be of interest?? Let me look for this hand drawn schematic for this Alamo Fury I drew up. It may be of even more interest?
     
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  9. FenderLover

    FenderLover Friend of Leo's

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    James and Baxandall are NOT the same, though they look similar on paper. The first post is a James and is mislabeled. Ampeg never used a Baxandall circuit that I know of, it was James. Baxandall is a James circuit in a feedback loop. James was 1949 and Baxandall was 1952.

    James uses log pots and unequal C and R values, and is lossy in its center (flat) position. Blackface type of lossy if the bass and treble are turned down. Baxandall uses linear pots and equal value caps and resistors for top and bottom of the circuit. It's center position has unity gain.

    To be honest, either circuit is going to change the nature of the amp in terms of gain, but maybe that's what you're after. If you are just looking for more EQ control, try a bass cut/Vol between the first two stages, and a treble cut after the second to preserve the circuit gain and the nature of "tweed".
     
    Last edited: Oct 18, 2019
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  10. OahuClay

    OahuClay TDPRI Member

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    Well, I tried it with the stock circuit and then installed the james, it certainly did cut the gain, although it sounds good to me and the tone stack does give me some eq, I may take out the 6at6 and install a 12ax7 though so I can get the gain back up.
     
  11. Wally

    Wally Telefied Ad Free Member

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    The 6AV6 has a triode with an amplification factor of 100.
     
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