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Fender Ramparte - Schematic

Discussion in 'Amp Tech Center' started by GERPUD, Feb 8, 2015.

  1. GERPUD

    GERPUD TDPRI Member

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    Hi everyone,

    The Fender Ramparte schematic is not available anywhere, so I've tried to draw it myself. The goal is then to be able to modify it.
    I'm very not experienced with electronics, I did not have access to the back of the PCBs, so there is probably few (maybe a lot) a errors.
    I did my best to draw it as best as I could, but I would need help to correct it. Hopfully, It will then serve other people.

    So, could you point out to me where the schematic is likely wrong from your experience? I'll try to triple check the highlighted sections.

    Thanks for your help!
     

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  2. Wally

    Wally Telefied Ad Free Member

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    GERPUD, is FEnder unwilling to send you the schematic??? That would be a rare thing, ime.
     
  3. Cleeve

    Cleeve Tele-Holic

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    I wrote to fender via email asking for the Vaporizer schematic and they sent it to me, maybe they'd do the same for the Ramparte.

    I see no glaring errors on your drawing, I'd add either the graphic symbols for plate, grid, screen and cathode on the tubes, or at least the Pt1, Gt1, Kt1, etc.

    What program did you use to draw that?
     
  4. GERPUD

    GERPUD TDPRI Member

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    I used DipTrace.

    I just wrote to Fender. I'll wait for their answer. Anyway, I've done it. It should be close to what I did, with a better tube symbol...

    But you can imagine that I did not made to complete schematic only to kill some time. The goal is to understand the amp to be able to make some mods.

    I made a schematic with some mods. I'll like to have you comments and advices on them. All the mods are physically "easily" doable. I'm waiting advices or comments before doing theses mods, so none of them is done now.

    Of course, I put a new speaker. Otherwise, this amp would have gone back right away in the box straight to the store...

    Mod #1: To fix a really bad noise issue. I added a filtration stage with a choke. I'll also move the OT away from the PT, add a standy switch for muting

    Mod #2: For the coolness. Changed the cathode resistor to fit a KT66. (I did this mod).

    Mod #3: For more control. I put a master volume before power tube. Could R20 be removed with a pot? (easier to do)

    Mod #4: Add a "Hum balance Pot". I saw that on other schematic. It is supposed to help to reduce the hum. I don't know if it is really usefull. Any advice or comments?

    Mod #5: Channel foot-switch. To be able to use both channel.

    Other mods that that I'm not desided or don't know how to do them:
    - Tone caps with orange drop. Some info say it's good, other say it's useless...
    - Master volume for drive (and separate master volume for clean). I have no idea how to do that....

    Comments, other ideas??
     

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  5. Cleeve

    Cleeve Tele-Holic

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    Your schematic looks good- I'm sure it took much effort- I have trouble just drawing mine with a pencil! I modified a 5 watt crate amp that was otherwise hopeless with it's noise and odd overdrive. The single ended output configuration probably won't benefit from a hum balance in the heater circuit. I found the crate needed a bit of negative feedback like is used in the Fender Champ to tame the hum. The way I see to try it here on your schematic is remove c2 from the cathode of the driver tube and connect a resistor from the cathode to one of the speaker terminals. Connecting the resistor to one of the terminals will reduce gain and hum and be the right one, connecting it to the other one will cause the amp to oscillate, so use the other one! As to what resistor value, that will have to be determined experimentally, starting with something like a 47k- working to find the compromise of best hum reduction verses keeping enough gain in the driver/output stage. Here's the champ- http://www.thevintagesound.com/ffg/schem/champ_5f1_schem.gif As to master volume- R20 should stay, but R24 can go, I'd use a 100k pot configured as a variable resistor, so the output of the driver tube is loaded down forcing distortion in the driver. Fully up, the master volume is just a 100k resistor as if no change from stock, but turned down, the driver tube is running into a near short at low master volume settings, causing the tube to distort. Matchless does this with their master volume.
     
  6. Telenut62

    Telenut62 Poster Extraordinaire

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    Your standby switch is not in the best position.....

    ...A switch will lead a happier life in an AC circuit rather than a DC circuit, because direct current will sustain an arc across the switch more easily, as the switch is opened, and arcing wears away the switch contacts. For this reason, putting the switch before the rectifier is to be preferred.
    Switching DC is also more likely to cause audible pop sounds in the speaker. If you already have a problem with switch pop then it can sometimes be fixed by adding a diode after the switch, so the switch only handles pulsating DC rather than pure DC.....

    http://www.valvewizard.co.uk/standby.html
     
  7. Abu Twangy

    Abu Twangy Friend of Leo's

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    As a Ramparte owner I'll be interested to hear how the mods work out. I use an A/B box for switching between the Cool and Hot channels
     
  8. GERPUD

    GERPUD TDPRI Member

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    I'll try to put the standby switch before rectifier.

    I'll remove the Hum balance pot as suggested. I don't even understand what it does exactly.

    For the master volume I'm not sure how it works exactly:
    As the value of R24 decreases, the power tube will distort?? That is the opposite of a volume function?? This amp is way to loud when it sounds good. The goal is to set the gain with cool pot or hot pot, and then decrease the volume with the master pot. So, if a put a 1M pot, I should be able to get zero volume (when 1Mohm) to distortion (when 0ohm)??
    I'm not familiar with tubes, but with opamp, we divide the input voltage to decrease the opamp gain. I was expecting some kind of voltage divider before the driver tube. This is why I've draw the master pot in this configuration. The gain of the "fender -champ" schematic you refer is the way I put my master volume. http://www.ax84.com/static/sel/AX84_SEL_101004.pdf is also putting the master volume the way I did.
    So, I don't understand what exactly having R24 variable would do...

    Other question:
    What would sounds better:
    - Decrease volume before driver tube or
    - Speaker soak (resistive load (with or without bright cap))??
     
  9. GERPUD

    GERPUD TDPRI Member

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    I've only changed the speaker and the cathode resistor yet.
    This discussion is on the planning of the other mod. I just want to make sure that my mods will work before doing them.
     
  10. Cleeve

    Cleeve Tele-Holic

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    Tubes have high output impedance compared to op amps and the output can be attenuated by having the tube drive into a low impedance. The point of a master volume is to simulate the distorted sound of the driver tube driving the power tube grid positive relative to the cathode. When the driver tube tries to make swing the control grid positive relative to the power tube cathode, that grid begins to conduct current and presents a low impedance to the driver, which can only drive a wee little current. Unlike an op-amp, the driver tube won't be harmed by driving an impedance mismatch, as the currents are so low- the plate load of the triode is usually 100k or so, so the resistor just fails to drive that part of the wave, thus, distortion.

    By attenuating with the master volume as a variable resistor, the overload sound happens at a lower volume. With the master volume configured as a potentiometer, it pretty much just attenuates the volume without the distortion happening at all.
     
  11. GERPUD

    GERPUD TDPRI Member

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    So, from what you explain, the variable resistance (R24) will do more or less overdrive of the driver tube without a volume variation?
    Isn't going to be tricky to set the volume and drive with a gain pot before and a variable resistor after the driver tube?
    In practical therms, I would set the volume with the cool/hot pot, and then the drive of the driver tube with R24?
    Would it give the same results with setting the gain with the cool/hot pot, and then the volume with a potentiometer? (replacing R24 with a 100k pot, so full volume = stock, 0 volume R20 is connected to ground). I was on the impression that it is the standard way for gain/volume control. One preamp gain and one power tube gain.

    Thanks for the info, very interesting!!!
     
  12. Cleeve

    Cleeve Tele-Holic

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    Sorry my previous answer was rushed by an appointment!
    The r24 as variable resistor will still cause volume variation, all the way to zero when the control is turned all the way 'down' because with the wiper connected to the driven end of the potentiometer resistance, the driver tube will be feeding into a short to ground, so the power tube will get no signal.
    Turn the master up just a wee bit, say so that 1k of resistance is between the wiper and ground, then the load presented to the driver tube is 1k, where if the wiper was not connected to the driven end of the pot, the driver tube would be seeing whatever the full resistive path of the potentiometer is, 100k if it's a 100k pot.
    If you have a 100k or similar pot laying around, it should be easy to tack solder some leads across r24 and experiment with both methods.

    So if you wanted a distorted sound late at night without the police coming, turn up the preamp gain and the master volume down, just as you have come to expect.
    With the master configured as a potentiometer, the distortion from zero of the master on up as you increase the position will stay the same as the volume gets louder until you start to overdrive the output tube, then the loud distortion from the output section will be dominant just as it was before the master volume.

    With the master configured as a variable resistor to ground in place of r24, the distortion will be possibly a lot at low master volume level, then cleaner possibly as it goes on up until like in the above description the output section begins to distort as it would have before the master volume mod.

    So i'm saying the potentiometer connection only attenuates what is going to the output tube, the variable resistor connection attenuates and induces distortion in the signal going to the output tube.

    In pratical use, you'd set both the preamp gain and the master volume up till you hear something, if it's too distorted and not loud enough, turn up the master and turn down the preamp gain. If it's too loud and clean, turn the master down and the gain up.

    Here's an example Matchless with master volume-
    http://www.mhumhirecords.org/DIYpages/schematics/SpitfireSchematic.bmp

    This Matchless is push pull so the master volume is connected across the opposite phases of the drivers balanced signal, accomplishing the same thing as a single variable resistor would do between the single drive and ground of a single ended champ like circuit.
     
  13. GERPUD

    GERPUD TDPRI Member

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    Ok, great! I understand.
    I've look to different schematic and both ways seems to be used. (it should be a 100k pot in my first example)
    For instance, Fender Blues Deluxe is using variable resistor for gain and volume, and they put the potentiometer for the hot rod deluxe for both gain and volume!

    I'll try both, not a big deal.
    When I'll do the footswitch mod, I think I will also add a second master volume. One for each channel. It would be easy to do with a DPDT relay...

    For the other mods, I wonder if it will make a big difference in the Hum if a filtration stage is added before the OT. There is a lot of design with only a cap for the OT supply.

    Is anybody would say that changing cap for Orange drop is an upgrade or a waste of time.
     

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  14. Cleeve

    Cleeve Tele-Holic

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    The orange drops won't make any difference, besides being orange!
    The variable resistor in your second drawing should have the wiper connected to the other end of the resistance, rather than to the ground-connected end.
     
  15. GERPUD

    GERPUD TDPRI Member

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    I saw that on your example, but, to me, it does the exact same thing?! (it just reverse the action of the pot)
    The picture show the blues deluxe that is connected like I did.
    That's what I thought :)

    Any comments on the filtering stage?
     

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  16. GERPUD

    GERPUD TDPRI Member

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    error...
     
  17. GERPUD

    GERPUD TDPRI Member

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    Rev1
    I've added missing components, and removed Mod 2 because it was already there...
    There is probably other errors, but this version is better.
    If you find any section/component that doesn't work, tell me so I double check.
     

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  18. Cleeve

    Cleeve Tele-Holic

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    Look good, the only thing I wonder about is C25 and C9, C9 is redundant there in series with the smaller C25.
     
  19. GERPUD

    GERPUD TDPRI Member

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    You are right.
    Both cap are the same, 47nF, but they are in series as illustrated

    Is it normal that the only coupling cap on the Hot channel is 0.47nF??
     
  20. Cleeve

    Cleeve Tele-Holic

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    You mean C4? It's ok but I don't see how it can be a .47.nf and be connected with C19 as a 1nF going to ground. Could it be a .47uF instead of nF?
     
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