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Fender Ramparte - Schematic

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

  1. Cleeve

    Cleeve Tele-Holic

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    That cathode magnatone feedback rig i think used to be pretty common in old record players and radios, it's main aim is to use as few parts as possible to have at least some feedback for noise reduction. Feedback in tube amps is mostly about noise reduction, where in solid state stuff the whack transfer characteristics require feedback for more reasons.

    I could possibly find in my textbooks the math to apply, but it would take way less time to just temporary solder a wire jumper or two and see what happens.

    The best tone stack solution I believe for this simple amp would be any one-knob tone put just before the power tube grid. Maybe even just a high cut, just like a guitar tone control.
    The way to control the amp then is turn it up till the bass falls apart, turn the guitar up some then use the amp tone to shave off the harsh highs when distorting hard, then turn the guitar down some for good clean or crunch, and have some volume knob left for solos or something. The old way of things!
     
  2. GERPUD

    GERPUD TDPRI Member

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    If the NFB is for noise, it won't help after the mods I've done on the power supply because it is silent now.

    For cap C4, correct me if I'm wrong:

    Cool side frequency response:
    1/(2*3.1416*470k*0.022u) = 15hz
    Stock hot side frequency response:
    1/(2*3.1416*250k*470p) = 1354hz

    To get 15hz, i would need C4 be equal to 42nF. The closest standard is 0.047uF.

    To be able to put a smaller cap, (0.02uF) in C4, I could inverse R32 and C4 and get the same frequency response. Or maybe it is a good idea to cut the bass a little bit for drive channel...
    I may try also 0.0047uF to cut bass at 135hz.
    What do you think?

    I was wrong when I thought changing C20. This is a 10hz high pass filter...
     
    Last edited: Mar 1, 2015
  3. Cleeve

    Cleeve Tele-Holic

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    The feedback will do more than reduce noise, it will help clean things up and change the overdrive character of the output, but I don't know if the result will be subjectively better or worse.
    Worth experimentation i think.
    You've got me looking for a Ramparte, but I need more practice on guitar not a tenth amp!
     
  4. GERPUD

    GERPUD TDPRI Member

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    I found an other funny thing on that amp that could be improved:
    Output impedance of V2-A (second hot channel preamp stage -of three) varies form 570k to 770k depending on the cool pot position.
    I've tested it, and the amount of drive of the hot channel can be modified using the cool volume pot!
    The Hot channel as much less drive when Cool volume is at 0 instead of 9.
    Pretty odd!

    I also asked on Ampgarage forum what could be the purpose of C23, C24, R33, R34, R35.
    http://ampgarage.com/forum/viewtopic.php?p=334185#334185
    Some guys are saying it may be a noise power supply cancellation.
    In my case, this network doesn't make any difference.
    Pretty odd also. It takes a fair amount of place on the PCB.
     
  5. GERPUD

    GERPUD TDPRI Member

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    Ok, for those still interested in the modification of this amp, here a summary of my previous mod + new some mods, with schematic.

    https://app.box.com/s/7ap8vihwtzx06qeiao3mz1kpg0sa8h0x

    - Changed the speaker for Eminence V128

    - Added a filtering stage (47uF+4F choke)

    - Added a standby switch (right after the choke, not shown on schematic)

    - Removed: C6, C23, C24, R34, R35.
    They were probably there to cancel the noise. Not needed anymore with the choke.

    - Removed: C19
    Much clearer overdrive

    - Replaced C4 from 470pF to 2200pF
    More bass on the drive channel. I'v tried 3300uF but it was too much for my taste. Didn't like the distortion on the bass. To me, 2200uf is right on.

    - Replaced R7: from 390 to 450k to fit a KT66 Gold Lion.

    - Cut the PCB after R19, added a 1M load resistor, replaced R19 to 150K.
    This is to separate the drive channel to the clean channel.

    - Removed R16, and used to pins to separate the clean channel from power section.

    - Removed C25, I needed a place to connect the master volumes, and this cap was not usefull. I was a 70hz high pass. It is now 15Hz high pass. Didn't changed the sound at all.

    - Removed C18
    Needed because the gain of the cool channel was to high after the other mods. This droped also the gain of the drive channel, this is why I replaced R19 and put 1M load resistor...

    - I added two master volume. The two 500k pot are wired in parallel from point 5 to ground. They replace R24.

    - I added a DPDT switch for channel switching. Fist pole is for channel switching, second pole is for master volume switching.

    Other mods: Spring retainer for KT66, one coat of lacquer, Gold Lion in V1, JJ in V2, replaced all tone cap with Orange Drop (because I like the color!)

    I must say, this amp now ROCKS!!. I removed Ramparte Logo because it is not a Ramparte anymore...
    The clean gain gets the sound from very clean to light crunch. The drive channel get the sound from light crunch to moderate-heavy overdrive. So it can be used as two overdrive at different gain. Very unique!

    - I'm now planning replacing the DPDT switch by a 5V relay controled by a foot switch. Footswitch will use the Hot input no longer used. This is why I removed R2.
    - With C18 removed, I'll be able to try NFB loop. I'll also try to add a Presence and Resonance control...I'm waiting to receive some parts and material...
     

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    Last edited: Mar 9, 2015
  6. GERPUD

    GERPUD TDPRI Member

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    Ok, now I'm done.
    Here's the final version:
    - 3 channels Clean/Drive/Drive
    - Three gain settings clean/drive/drive
    - Two master volume Clean/drive
    - Footswitch with DEL and manual control witch toggle switch

    The two drive channel have the same gain pot (the max is the same for both), but maximum gain is way enough for me. (i just added a pot parallel to the Hot Pot).
    The clean gain is really interesting. Low gain give plenty of headroom, increasing the gain compress the sound, and even more give a light distortion. I can use on of the drive so get a clean boost, or two overdrive.
    This is very flexible.

    I hope this can help someone!
     

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  7. 356user

    356user NEW MEMBER!

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    hi, your mods are great but probably to advanced for me as I'm new to this. I would be more than happy just to get rid of the noise.I know its basic but could you tell me how to install a choke and filter cap?
     
  8. GERPUD

    GERPUD TDPRI Member

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    Adding a choke is not easy since you have to modify the PCB path from behind (putting the amp completely apart).
    Maybe you should only try to take the OT away from the PT, and add a cap in C15. That may help for sure.
     
  9. peternortoft

    peternortoft NEW MEMBER!

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    Ramparte vibro champ on steroids

    Thank for all the inspiration in the thread.

    My take has been to rebuild the Ramparte using the vibro champ schematics (AA764), substitution of 6V6 with the rampage 6L6 circuit

    remarks:
    1. turn the OT 90 deg and move so it is in symmetry with the PT ( -| if you know what I mean )
    2. decreased the grid voltage to be 2 volts below the anode
    3. installed a choke (4H/20 mA) after the cap.
    4. added 2 * 65R/100uF after the choke
    5. cleaned up the ground circuit
    6. chassis ground by the input jack
    7. two vibro speeds via simple switching between 560k/3M3 instead of 3M RA pot (hard to find)
    8. implemented on/off/on switch for standby
    9. implemented a volume/tone instead of the tremble/mid/bass

    fun ahead:
    1. feedback on/off
    2. feed vibro osc from separate R/C
    3. master volume after V1b
     
  10. GERPUD

    GERPUD TDPRI Member

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    Great crazy idea!
    I could, in fact, be done. Good idea if you prefer the vibro over the overdrive.
    It's a way of turning a 300$ amp into a 1000$ amp (but with a bigger speaker and more output)

    Give us picture once it is done!

    I've done a bit more experimenting:

    - I've used Eminence Wizard Speaker instead of V128. The Wizard is the most efficient speaker available. Huge difference! Made that amp much louder. I also love the frenquency response. Very transparent, bright, not harch, great bass and punch. It got me more sound out of this tiny amp.

    - The negative feedback loop is really an improvement to me. I got more headroom and better frequency response. I've put a variable resistor with on/off switch. I'm using NFBL all the time now. Simple mod that gives big results. A 50k resistor should be fine instead of the 100K pot I've used.

    - As mention in an other post, the OT of this amp is 7k5 on the primary. It would be perfect for a single 6V6, but it's a little hi for a single 6L6.

    Comming up:
    - I've ordered Edcor gxse15-8-5k. I'll be able to try a lower primary resistance. I should gives a bit more power/headroom, maybe smoother. I'll see.
    - With gxse15-8-5k I'll be able to add a ultralinear switch. I have no idea of the result compared to the NFBL. I'll see...
    - I've ordered a new PT. I'll be able to try KT90.
     
  11. axplanck

    axplanck NEW MEMBER!

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    That's what I was going to say....

    Hi, I am on my very first post here, and I am very happy to know this forum exists.

    My brand new Ramparte HUMS like a M**F*** at 120Hz, and I am very interested to fix that. I bought it yesterday on sale and can't return it - so I am in for the fix.

    But one mod at a time for me, I bought it because I liked the sound, and even thought the mods sound good, I am really going after the hum first.

    After reading this thread I bought a couple of caps and I have ordered a choke, will be here in a few days or a week.

    I know you are really more interested in tweaking than fixing a design error, but you all seem very knowledeable, and I understand close to half of what you say, mostly. But - if I could ask for a couple of clarifications, if you don't mind:

    1) rotating the OT (output tube I am pretty sure) - meaning removing the tube socket from the chassis and reinserting it so the OT is - well - maybe 90 degrees rotated from its original position? (I haven't opened up the amp yet, I have not even owned it for 24 hours yet!)

    2) MOVING the OT means punching a new hole in the chassis six inches away, and relocating the socket...? By this time, I am really hoping this socket is connected with wires and not directly soldered to PCB traces....!

    3) Installing the choke sounds like the most effective fix, but it requires mods to the PCB including trace cutting - -well, I can do that, I am good at soldering, but figuring out where on the PCB the cuts are made....I could probably do it but that would, I am sure triple my time of completion. Is there a photo of this mod that would be a good guide to the procedure?

    4) I am a bit confused by the "replace C16 (or is it C15) with a 47mf cap, or a 94mf cap" - I found a 100mf, any reason that won't work? As far as the location of this cap, I see a new cap (CXX1) next to the choke on schem rev1 - is that the recommended location? Somewhere in this thread someone recommends soldering a 47mf cap on in parallel with another cap - oh here it is -
    I am pretty sure you mean C16 here, right? because C15 is up near one of the PTs and is a very small capacitor......anyway, a bit more clarification on this and I will right there!

    Anyway, thanks for posting so much work, and if you can lead me (and probably others) just a little bit more specifically, we will be quite grateful!!

    thanks
     
  12. GERPUD

    GERPUD TDPRI Member

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    That's right. I didn't do only rotation, (also put it away of 6in) so I don't know how much it work. Some say it does the job.
    If only doing the rotation, no mod on the wires is required. If putting the OT 6in away, you will need to increase the length of the primary wires.

    It have connectors everywhere, but you need to take the pcb out of the case to drill new holes. Other solution would be to use metal screw instead of nut and bolts.

    The choke is a very good solution. You need to cut the pcb from behind. You can drill holes for the OT at the same time.
    From the original schematic, the first filtering cap is C15. The cap could be increased or double (in parallel). The schematic says 17uF, but I my original amp this cap is 47uF. Probably an error in the original schematic. Maybe they also made this amp with 17uF and this is what you have...When adding a choke, I added the capacitor after it and before R27. In my case, I have C15/47uF - 4H choke - 94uF - R27.

    I didn't know anything about amps before buying this amp. I also only wanted to only fix the hum when I opened the back first... I ended up to almost rebuild completely this amp.

    It is a great learning amp:
    - Not too costly so if you scrap it, you're not wasting too much money
    - Not too complicated. (no effects, no integrated circuit, one voltage (+ heaters), no relay, no switch, no tone stack, no fx loop, no reverb, only one input...) It is easier to physically understand.
    - Lot of issues to fix and to work on while learning!

    In my opinion, the drive channel is not very nice and not bedroom friendly. If you're not using it, I highly recommend the negative feedback loop:

    - Remove C18
    - Connect a 50k resistor from Pin 3 of the power tube to pin 8 of V2-B (or use 100K pot)
    - you may have to flip the two primary wires if the sound is more treble and feedback after the mod.

    This mode reduce the gain of V2. It will change the drive channel a lot. It may be ok, but it will improve the clean channel a lot.
    - the volume will be more usable because the preamp gain will decrease
    - It will improve headroom
    - It will improve bass response.

    I say it again: the speaker is crap! Put an other one!
     
    Last edited: Jun 16, 2015
  13. axplanck

    axplanck NEW MEMBER!

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    Thanks very much, GERPUD....

    .....hopefully I can prepare the patient for surgery this week.
     
  14. GERPUD

    GERPUD TDPRI Member

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    So I replaced the stock 7.2k primaty OT with a 15W 5k primary.
    The 15W is way bigger and heavier.

    As I was expecting, the amp sounds huge! It's loud! WOW!
    More bass, probably louder/more headroom but hard to do A/B testing.
    It is definitely a bit smoother, rounder, more neutral, thicker, deeper and louder bass, a tiny bit less treble. That's because it was even punchier, tight and crisp before.
    It has an impact on the NFBL. The 50k value sounds a bit dull. Sounds better when increasing it to 75k.
    The stock OT was adding more colour to the sound. I read somewhere that 7.2k should be more "in your face". That could be true.

    It's hard to give better explanations...

    At this point, I think it may be a matter of taste. Some would say it's an improvement, other will say it's different. To my tastes, it is an improvement.

    With a lot of gain, I'm able to get a more "heavy rock" sound. Before it was more "rock and roll".
    I think it is more flexible and polyvalent now.
    Clean, it's definitely thicker.

    I get more rattle from the furniture in the room!
     

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    Last edited: Jun 16, 2015
  15. PurpleStrat

    PurpleStrat Tele-Meister

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    Your really making this look fun. If I did not already have to much on my plate I would want to get one and join in!
     
  16. GERPUD

    GERPUD TDPRI Member

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    Can it get crazier?

    And now with a homemade pine cabinet with Celestion Blue...

    Also, I added a Ultra Linear switch to experiment with the third wire on my new primary OT. I did not like it. It gives about the same result that the NFBL but it is not adjustable. I loose to much of the snap and punch, loose a bit of the bright sparkle. It tame the bass. So basically, more dull. May be better for smooth music or jazz, but I still get that sound from the adjustable NFBL.
    I'll just tape that wire in the back of the amp...
     

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    Last edited: Jun 18, 2015
  17. Joshbailz

    Joshbailz TDPRI Member

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    Any chance you could repost your most up to date schematic, the previous link doesn't work anymore :(.
    Thanks
     
  18. GERPUD

    GERPUD TDPRI Member

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    Check this link for the tone mods:
    https://onedrive.live.com/redir?resid=1BA261969B7CDB86!156&authkey=!AHNSWm3EUty_HnM&ithint=file,pdf

    This schematic does not show the negative feedback loop. So you must add a 100k pot between pin 8 of V2-B and tip of speaker plug. Highly recommend.
    For the footswitch:
    https://onedrive.live.com/redir?resid=1BA261969B7CDB86!157&authkey=!AO9P_AgyeMOJ3kk&ithint=file,pdf

    This does not show the choke. Basically, I've put a filtering caps (2x47uF) and a choke (4H) before B+ on the power supply schematic.

    I've put a standby switch on the choke. Would be better on the AC current since it is popping when I cut power.

    I've undone the mod for KT66 and used back the 6L6GC. I was loosing power with the KT66 and was running this tube too hot. With the OT at 5k, the 6L6 is now smooter so no need for the KT66.

    If I'd had to do it again, I would only do the power supply mods, OT replacement, and clean channel mods and use overdrive pedals. The overdrive channel mods and footswitch is a lot of work...

    Hope it helps.
     
  19. Joshbailz

    Joshbailz TDPRI Member

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    Thanks, i am going to move the OT away from the PT and rotate it too. I'm slightly confused about the caps used for the filtering stage and position of choke, have you added the choke after the rectifer, then added a seperate 47uF cap before B+then added 1 47uF in parallel with (C15) the 47uF cap that is already there. On my schematic B+ comes before C15 so i thought B+ gets filtered by the PT? WHich would then make me think i just add one 47uF cap in parallel with C15 but place the choke before these 2 caps?

    Hope that makes sense............
     
  20. GERPUD

    GERPUD TDPRI Member

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    You need a filtering cap before and after the choke to make a PI filter:
    https://www.google.ca/webhp?sourcei...BCA558CA558&ion=1&espv=2&ie=UTF-8#q=PI+filter
    You basically add a PI filter before B+ (cap (2x47uF) - choke - B+ - C15(47uF)). The PI filter is made with a choke instead of a resistor (like C15-R27-C16).

    Instead of just moving the OT, I strongly suggest to also replace it with a 5K primary OT of at least 10W. You will get more headroom, and smoother tone. The amp will sound bigger.
     
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