Wiring Up A 3 Band Marshall Tone Stack From Scratch?

Discussion in 'The Workbench' started by RickyLee, Jun 12, 2010.

  1. RickyLee

    RickyLee Well-Known Member VIP Member

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    OK fellas. I am finding conflicting info and diagrams/schematics on the net for this. On some I am a bit confused on the pot lug numbers/landings. This is going in place of my '69 Traynor Custom Reverb YSR-1's 2 band EQ (Bass & Treble) which I thought was a Baxandall tone stack until I got inside and traced it out. From what I can make out of what is in this Traynor is that someone in this amps Dirty Past tried to do a cross between a Plexi and a Blackface two band style, maybe using a resistor on the back of the bass pot as a fixed mid control. But after tracing it out, it just does not make sense on a few of the connections compared to what I am seeing on the web.

    So . . .

    I am going to gut the tone stack and start from scratch. I was figuring going with a Plexi era stack - I will be adding either a 50K mid pot or 100K mid pot (I totally dig my Jubilee's tone stack!). I can always tinker with the cap values and slope resistor later.

    There are quite a few of you VERY SMART FELLAS on here that I know I can trust (You Know Who You Are!) to give me the right info!

    I also picked up some optional push pull pots to possibly do the "lift the tone stack for a boost" mod.

    :headbanger:
     
  2. Wilder Amplification

    Wilder Amplification New Member

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    The "lift the tone stack" boost may work great with a pre-phase inverter master, but with a PPIMV it didn't work all that well simply because the PI was already being distorted to shit.

    Here's a simple layout for that type of tone stack using stock Marshall values. Pots are shown as you're looking at them from the back.

    [​IMG]
     
  3. jcmjmp

    jcmjmp Well-Known Member

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    Wilder pretty much gave you the info you were looking for but in the future, you can get layouts online in a bunch of places. Metroamp and Ceriatone both have them, as does Weber.
     
  4. Joey Voltage

    Joey Voltage New Member

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    In a passive network it is more correctly referred to as a james, but the schematic I have doesn't show it as a james either. I would say it is a bit more similar to a bandmaster, than a james.

    It is hard to know what was done without seeing the corrections thatyou drew out, do you have a schematic of the corrections you can post?


    there are a couple of things to keep oi mind, the source impedance from which you will be driving the stack, which may not make it react the way you are hoping it will. I also wouldn't go too crazy on the mid pot depending on what you decide on for the slope, as the pot and slope sets your "normal" pass band (it's not really a mid control"), and raising it too high may rob both your treble and bass frequencies of range.


    gotta go, in dutch with the girlfriend!
     
  5. Lane Sparber

    Lane Sparber Well-Known Member VIP Member

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    Hey, Ricky!

    This sounds like a COOL project! I'd just like to add that simply copying a Marshall tone stack in and of itself will most likely NOT give your Traynor a more "Marshally" tone. That all depends upon the surrounding circuit topology (e.g. component values, gain levels, transformers, etc.). I'm not sure if that "Marshall" sound is what you're going for, but I just wanted to put it out there for you in case you wind up disappointed after installing the new tone stack. It WILL sound great, just don't NECESSARILY expect "instant Marshall" simply by copying the tone stack.

    PLEASE let me know how it goes, as I'm really curious as to how this will sound. Best of luck!

    Cheers!

    -Lane
     
  6. Wilder Amplification

    Wilder Amplification New Member

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    Exactly. A BIG part of that Marshall sound is the way they drive that tone stack with a gain stage DC coupled to a cathode follower buffer stage.

    Lots of guys who mod amps pull the whole "Oh I can add another gain stage to your Marshall without adding a valve" BS. Then they go and convert that gain stage/DC coupled cathode follower into a gain stage and plate feed the tone stack! Once you do that you take the thing out of "Marshall" territory as that particular valve/surrounding circuitry plays a big part in what gives Marshalls their "Marshall" sound. I never did understand why they do that.
     
  7. JohnH

    JohnH Well-Known Member

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    I can't add to the discussion, but if you want to understand the differences resulting from various component values, the Duncan Tone Stack Calculator is a great free app:

    TSC

    There are several basic tone stack types modelled, including Marshall. You can move sliders to see the frequency response, and double-click components to get the option to change them.

    cheers

    John
     
  8. RickyLee

    RickyLee Well-Known Member VIP Member

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    Thanks for all the replies fellas!

    I should have gave you guys some more info in the beginning regarding where this amp's circuitry is at. I have two of these YSR-1's. This is the second one that I just recently got. It is aprox. a '69 model. All original Hammond Transformers - has the choke and reverb Xfmr. Xfmr's and potentiometers have a mix of '66 & '68 date codes.

    My first/other Traynor YSR-1 is all stock and unmolested. Has the Baxandall/James type tone stack and from what I can tell is probably a 1970 model.

    Now, this 2nd one '69 model has some things going on in the preamp that I did not expect to see. It was "supposed" to be stock - no mods, but I only paid $320 for it, so I am not complaining. The second preamp tube V2 is setup as a cathode follower and the tone stack has been changed. So that is really the only difference. Strange thing is that internally, those two changed areas look as if it was done that way from the factory. I can not find any info verifying this could have been the case though, and I don't mind anyway.

    I guess I need to make it clear that I am in no way chasing the Plexi tone with this amp or the Marshall tone in general. So, that being said, that will help you guys in giving me advice for what the best option would be for me choosing a tone stack type.

    There is no master volume at all on this amp. Channel I is stock with it's - I am guessing here - 4 meg pot? Actually I am thinking both volume pots are 4 Meg? I have not verified this yet though. Each channel (same input layout as a Marshall model 1987/1959 4 inputs ) has the stock High/Low inputs with the 68K grid resistor pairs. Each "channel" goes through one triode/gain stage of V1. 100K plate resistors for both triodes V1A & V1B. Both V1 triodes had the shared 820 ohm/250uF cathode/bypass cap, but I set Channel II V1B up with it's own 3K ohm/.47uF cathode and bypass cap and I removed the bright cap on the back of the volume pot for Channel II ( I first tried lowering that bright cap to a 120pF Silver Mica, but it was still too icepicky in the 'Ol Ears! ).

    Then each channel/first gain stage goes on to .022uF coupling caps, then on to their volume pots then the channels join together via 100K mixing resistors. Then onto V2 setup to a Marshall spec'ed cathode follower. Then on to the tone stack - which is in parallel to the reverb circuit from what I can tell, but I have yet to officially trace out the entire reverb circuit. But everything else seems to be stock. The phase inverter matches the YSR-1 Jan 13 1967 schematic. I might change the driver section to Marshall specs. What do you guys think??

    Oh yeah, I did notice that this amp has the 100K NFB loop resistor, but does not have the .1uF cap in parallel with the 4.7K fixed "Presence" resistor.

    So, with all that info given, let me know what you think would be the best match for the tone stack setup. This just has the two band Bass & Treble, but I am adding the Midrange control. Like I said before, I am not worried about chasing another model of amp's tone and Mojo, as this amp already has it's very own unique tone and Mojo goin' on already. My other YSR-1 is stock with the Baxandall/James similar tone stack, and so there is no need or desire to put this one back to match that one. I am using an ABY switch to jumper the channels as well switch between them.

    I am noticing a bit of channel bleed going on also. Is this common to the 4 hole input two channel setup?
     
  9. Lane Sparber

    Lane Sparber Well-Known Member VIP Member

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    Ah! I think I'm picking up what you're putting down now! :)

    I can only tell you what I would do in your shoes, so please take the following with a grain of salt. ;)

    As you have a circuit there with some unusual elements, I feel it would be hard for me (and possibly any other tech here) to predict with 100% certainty what any given tone stack would sound like in your amp. Consequently, I feel that it's your EARS that will need to guide you here. I would start by installing the classic Marshall tone stack Wilder outlined above, and then see how it sounds. You can always alter it later - as there are a wide range of acceptable pot and cap values that would work in your amp. For a basic example of this, classic 60s era Fender tone stacks (for the most part) had a .1uf bass cap, a .022 OR .047 mid cap, and a 250pf treble cap instead of the 22n/22n/470pf array in the diagram above. Once the new tone stack is in and working, EXPERIMENT if you're not happy. Be careful at getting TOO extreme with your values, as if you go too far, the amp can become unstable and "motorboat" or have any number of weird things happen. Even if you DO go too far, you an always come back by putting the most recently changed part back in. Just play for a while AFTER EVERY MOD and listen to what your good ol' EARS tell you to do! :fingersx:

    I hope this helps!

    -Lane
     
  10. MajorNut1967

    MajorNut1967 New Member

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    thats wrong it should be a 22k pot for the mid and a 220k for the treble on a real Marshall!
    LOL:fingersx::lol::naughty:
     
  11. MajorNut1967

    MajorNut1967 New Member

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    Joey it ain't more Bandmaster, where the tap on the treble pot? Come on you have to do better then that jeez!
     
  12. Joey Voltage

    Joey Voltage New Member

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    I don't know man, thats really generalized! It's the CF itself and how it is driven, not how it drives the TS (the two are related depending on use but that is beyond the scope of the OP's question), and the way it does it changes with topology and the amount gain/gain stages the circuit utilizes. For example, throw another gain stage with significant gain in front of a 2203, you are now driving the cathode follower differently than that 2203 was, so it's not reacting the same, or sounding the same, or driving the tone stack the same as it would in a typical marshall (what ever that means), it is sounding and doing something different. so the statement might work for discussion a specific model in question (i.e. the use of a CF in a 2203 really adds to make up the sound of the 2203 circuit), but is not the sole thing that makes a marshall sound like a marshall!, nor is throwing it at the end of every circuit going to make it react like it does in a 2203, or a 1959.

    Again Jon you are really kinda polarizing this issue a tad too much, and closing yourself off to the big picture, or other pictures rather.

    I can think of many reasons not to do it depending on topology of the mod.... sometimes it just doesn't sound good in conjunction with other stuff that is going on, i.e the use might sound dense and muffled, or mushy. Alot of the times, if not most of the time, you would not be able to tell just by playing an amp whether it has one or not. and if you were getting a killer hotrodded marshall tone out of a particular amp, and then had the revelation that it doesn't have a CF, would that automatically kill the marshall vibe it had?
     
    Last edited: Jun 14, 2010
  13. Joey Voltage

    Joey Voltage New Member

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    I didn'tsay it was one, but it could have been the scheme I was looking at, It looked closer to that than a James at first look, you got a link for a good scheme?
     
  14. MajorNut1967

    MajorNut1967 New Member

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    Let me open my amp I get it for you.

    I really like the Baxandall tone stack my self almost zero loss through it and you can punch down the 1K down below the floor, since I'm a mid hater.

    Here Joey



    [​IMG]
     
  15. Joey Voltage

    Joey Voltage New Member

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    Thanks for doing that Major!, that is definitely a James stack. and not what I was looking at for sure, I will redraw what I saw because it is a little hard on the eyes, and post it up, but it is weird, it looks like two shelving filters, probably to give the impression of a boost in high/lows rather than sounding like cut in either band to make the other sound more prevalent, and is probably what Ricky was looking at in his.

    I honestly don't have much experience playing with a James/bax, so I don't really have an opinion either way on them, A lot of people either love them or hate them, but I have always been curious about them. I might try it in a build just to see how it sounds though..probably more useful and less subtle than a FMV for some things.
     
  16. Joey Voltage

    Joey Voltage New Member

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    Here this is what I was looking at in the scheme, I redrew it to make it easier to read. I didn't include the 100K source at the stacks input, but it won't work right without it (one), and it is plate driven

    [​IMG]
     
  17. RickyLee

    RickyLee Well-Known Member VIP Member

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    Good stuff fellas!!

    Yeah Joey, I will try to check that out against both my Traynors - mainly my '70 unmodded one. I read some threads on the net that stated that the Custom Reverb had the Baxandall tone stack.

    It is back to the good 'Ol work week, so when I can make some time I will take a look at what you guys posted vs. what is in the supposed Bax Traynor.

    As the for the other Traynor that I started this post about, I need to have the time to play the amp as it is now and have a real good listen. Then change it over to the 3 band somewhat Marshall style tonestack and have another real good listen to see the changes. Really, I am just looking to have the midrange control added for now. Then some other tweaks will come later. But to be honest, the amp sounds good as it is at the moment after the few minor tweaks I made. I am just getting a bit obsessed with having a midrange adjustment. LOL

    Maybe I can add a presence pot in place of that fixed 4.7K resistor? The .1uF cap that should be parallel with the 4.7K resistor shown on the schematic is missing. Or I might try the resonance mod.

    Lots of ideas going through my head . . .


    P.S. Can you guys point me in the direction of some links that give a decent explanation of how the tone stack actually works it's magic? I am still learning quite a bit, and capacitors and high pass low pass filters is a subject that is just not sticking into my memory bank.

    Thanks once again to all of you - and GOODNIGHT!!

    :cheers:
     
  18. Joey Voltage

    Joey Voltage New Member

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    Your "unmodded" one most likely has the James stack that Majornut posted from his YSR, the one you suspect that was modded from the factory probably has what I posted, they probably revised the model at some point


    I'll see if I have anything specific, but TS are not really all that difficult to understand the function of, as the are just usually a string of simple high pass, and low pass filters lumped on top of each other, and most of the time, with the exception of the james/bax, are pretty interactive with each other.

    EDIT: In fact lets make this a learning exercise, and we will take the two band one I posted as an example because it will be easy to understand. I will make some thing up for you, and hopefully this may help you out
     
    Last edited: Jun 14, 2010

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