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5881 Tweed Princeton #2

Discussion in 'Shock Brother's DIY Amps' started by jsnwhite619, Mar 26, 2021.

  1. jsnwhite619

    jsnwhite619 Friend of Leo's

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    That actually makes a lot of sense.

    I also finally ordered a Cannabis Rex today. I was trying the 1258 because I had just gotten it for another project when he asked me to do this, so I said, "Great, I already have a speaker we can use." I used a C-Rex last time and loved everything about it. There's a harshness that I just can't get rid of this time, even with humbuckers cranked. There's always a painful treble end that I've never dealt with before, so at this point I'm attributing it to the speaker. Absolutely loved it in my 5e3 clone, but I just don't think it's 100% working for me in this case.

    So, with that said, I'm just going to work on the cabinet until it arrives, and leave anymore circuit tweaks until I have the C-Rex and mounted in this cabinet.
     
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  2. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Well, the C-Rex arrived today, and BINGO! It solved everything I have been fighting with the 1258. The upper mids & and treble was just painful before with the 1258, but all that's taken care of now. Easter kept me out of the shop all weekend with family and cooking, but I hope to knock out a good chunk tonight to finish the rear panels and cover the baffle. If I'm lucky I can get the first coat of shellac on there tonight.

    Anyway, now I know - what I already knew - the Cannabis Rex is a great option when a 1258 is too bright.
     
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  3. Mongo Park

    Mongo Park Tele-Afflicted

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    Very underrated speaker the Rex is one of my favs.
     
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  4. jsnwhite619

    jsnwhite619 Friend of Leo's

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    It seems to be an almost "unspoken" favorite. When you look for reviews on forums like this, it seems to have as many or more detractors as fans. But, several times I've found "Favorite speaker for XYZ" polls on the same forums, and it's often a top 3 contender. Maybe the people who don't like it are just more vocal about it? Anyway, it arrived today from Sweetwater with my little bag of candy, and I have it mounted in an extra cabinet right now wearing in a little, but I already know that this is what I was missing after just 5 minutes with the amp & guitar through it.
     
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  5. Tele Slacker

    Tele Slacker Tele-Meister

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    Jason, thank you for documenting all of this. Enjoy the banter and learning. Definitely thinking about building the champ/Princeton “louder” but not a 5e3. All of this is appreciated!
     
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  6. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Thanks! I ought to be wrapping this thing up in the next couple days, and will be getting some real sound clips done with a mic this time. Got the cabinet 95% done tonight, probably have everything put together tomorrow.
     
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  7. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Thanks! You have some really great demos as well! I've actually been reading about the Framus mod - and your clip on youtube - and was curious - with only one hole for a pot, would you rather have the Framus or the tone control? I'm leaning toward trying the Framus because the low strings are just too boxy/mid sounding in overdrive, even with a 12ay7 in there.
     
  8. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Ok, I tried the Framus setup. It certainly works, and I think is a step in the right direction, but the shelf is wrong. My Les Paul really has the "cocked-wah" sound right now. Any suggestions on the capacitor values to play with to move the notch?
     
  9. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I think I'm calling it on this one, unless someone spots something I missed or didn't try. At this point, there's still blocking distortion when the Humbuckers are cranked and I'm listening to the mic, but at the end of the day, it's still mainly a Tweed Champ, so I may just have to accept it for what it is. I'm going to try and remember everything I've tried on this amp.
    • 2.2k bias resistors
    • 1.5k bias resistors
    • 220k plate resistors
    • 82k plate resistors
    • 100k plate resistor
    • .047uf coupling cap
    • .0022uf coupling cap
    • 2uf & 25uf bypass caps on V1 A&B
    • Framus mid cut control
    • Legend 1258
    • Cannabis Rex
    • A few different NFB values
    • 12ax7 & 12ay7
    • separate inputs - 34k & 68k
    • My grandmother's kitchen sink... :D

    2.2k bias & 220k plates: nothing but fuzz and zero headroom.

    82k plate with 1.5k bias: The last place I'm 50/50. I currently have 100k plate resistors in it and 1.5k bias just to try it with a standard common value & with the 12ax7. Every guitar player is going to be able to put their hands on a 12ax7 at most any time, I already know he has no other amps with a 12ay7 in it, so why make this one setup specifically for it if I don't have to? That being said, as was discussed in my thread last year, I think there is huge potential in further experimenting with ideal bias and plate voltage scenarios with 12ay7 tubes. It's hard to explain, but with the higher plate voltage with the 12ay7 it really sounded good.

    .047uf cap - I used it last time and it worked fine for single coils, but obviously allows too much bass with humbuckers

    .0022uf cap - sounded like a cocked wah pedal on the bass E & A strings. Very woody, but very mid focused

    Framus mid cut - it certainly worked, and the C-Rex may not help, but it again had a cocked-wah tone

    2uf & 25uf bypass caps - I went around the world with these, and I seemed to prefer the bypass to be in the second stage. It's currently set with no bypass in V1a, and 2uf on V1b. It seemed to help keep the overdrive cleaner than having it on the first stage, even by itself.

    1258 speaker - painful upper mids and treble, clean or dirty. Great with my 5e3, but it was just too bright for me in this.

    Cannabis Rex is the speaker to stay.

    I think I have 2.7k & 5.6k NFB resistors in it now, switchable. I stole the Blackface Champ & Princeton style NFB with a 47r tail resistor and the second stage bypass cap. On my db meter with the amp cranked, the NFB cuts approx. 2dB off of the total output at the same cranked volume. Another fact on that -- it really doesn't get any louder after that halfway up the dial point. Dirtier, more feedback, more distortion, but watching the meter - yes, it's an actually meter, not a phone app - there isn't an actual output difference between 6-12. Just "more" of it, maybe?

    The separate inputs both have 1M input resistors, there is a definite cut between #1 & #2, so in the stock Fender setup, the lack of 1M on #2 seems to dull the treble a bit, but the actual input difference is certainly there solely based on the grid stoppers. That being said, I may play with #1 and increase it a bit and see what it does. I'd wondered about a single 34k "hot" input, and a 50k pot on #2 that would simply allow you to adjust the grid stopper resistance to suit your taste...still seems worth pursuing. Also, with the separate inputs and some playing with values, an A/B box could allow a lead/rhythm option on a single channel 2-knob amp. ;-)

    So, there it is. If anyone has any suggestions on curing blocking distortion in a Champ, I'd love to hear it. Otherwise, since the high powered Champ/Princetons seems to be gaining popularity around here, maybe this will save some collective time.

    Recorded about half an hour of playing earlier, still have to go through it and edit it out. Will post when done.
     
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  10. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I forgot pictures.

    IMG_20210408_205550392_HDR.jpg

    IMG_20210408_205541609_HDR.jpg
     
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  11. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Quick clip, but it's enough to tell me I'm going back to the 12ay7. This is with the 100k plate resistor, but it sounded even better before with the 82k and and extra 30v-40v on the plate. But it's still a lot better than the 12ax7, so that's settled.

    This is with my Pearly Gates in a Les Paul. Amp was probably on 8-9 range... and loud.

     
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  12. jmp81sc

    jmp81sc Tele-Meister

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    sounds great, and thanks for documenting all of your experiments. I'm also a fan of the CRex with the 5F2a, especially with single coils.
     
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  13. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I think I'm going to try that. I considered it in the beginning b/c the Blackface dropping resistors are only 1k -> 10k. I know I have a 10k 3W on hand. I may just tack on another 22k in parallel and see what happens, then fix a 10k if I like it.
     
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  14. cobaltu

    cobaltu Tele-Meister

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    If the "boxy" mids bud you there might be an easy solution. I too never really liked the mids of the 5f2 variant I have, until I changed the bright cap to a lower value. The stock 500pF is pretty heavy in the low mids. Which is why people tend to crank that control, to increase the highs more and get more presence. I lowered the cap to 180pF myself but anything around 250pF would be great. This does change the frequency range of the control - higher in frequency - so it won't quite behave the same way. You'll probably keep the control lower but it will help alleviate the congestion.

    The Framus could also work but it will change the gain structure of the preamp more, and is more complicated.

    If you want to play around with tone stack curves, there is great phone app called "Tonestack Kit" that seems to work pretty well. It has the 5f2-a tonestack in it. There is a free version that has a limited number of the them, but if you pay ~$4 for the full version, I think it might be worth you while.
     
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  15. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Well, I swapped the second power resistor from 22k to 10k, and that basically solved all my problems. The higher voltage sounds way better with humbuckers. The Tele is actually pretty clean with this amp, but as I've learned, a 2 knob amp isn't exactly the picture of versatility. As it stands, the 12ax7 with single coils gets mostly to the 12ay7 sound with humbuckers. So, it's not a flip of a switch, but a single tube swap gets both into equal territory. I made a demo with my Blues Driver tonight - sounded great in the room, but awful on the playback. Way too thin. My experience with microphones is that they usually hear things a lot differently than I do. I only did one take and didn't play with mic placement, but it turned out to be a bit of a wash.

    Even though I can't get a demo yet to really sound like what I'm hearing in the room, the Les Paul with 12ay7 and the 10k dropping resistor is going to wind this up I think. I have a new 12ay7 on the way. Only one I have right now is a 5-6 year old EH that has seen to much use to send with the amp.

    I really thought about starting out with Blackface AA764 specs with a 1k and 10k resistor lineup, but went with the Tweed 10k & 22k. I left the first 10k, but changing the 22k to 10k made a huge difference.

    Also, in the end, this is the first time I've used the OT. I used ClassicTone last time, and I have to wonder how much this massive Hammond is playing into things with not saturating at all and passing full bandwidth. Would the 1258 been a better match with the ClassicTone OT vs the Hammond? Who knows? But, I think this one will be heading to Mobile by the end of the week.
     
  16. Mongo Park

    Mongo Park Tele-Afflicted

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    So another one in the rear view mirror, well done man and an interesting read.
    So same amp same builder same
    speaker different sound must be the iron you started with or who knows. Course different tunes make a difference as well I find. One tube sucks and another glorious yet the tube that sucked really sings in another amp, all part of the fun.
     
  17. jsnwhite619

    jsnwhite619 Friend of Leo's

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    One big difference was the humbucker setup. I looked up his pickups, and they are all in the 9k-10k+ range, so I had to go way beyond the last one to have any chance of things holding together. Also, I built the last one around MY Tele, and a local guy I know heard it and fell in love with it - he plays a Strat. If this had been another single coil guitar build it would have been done two weeks ago. Focusing this one humbuckers really drove home for me how clean a "dirty" amp has to be. The Tele has some great cleans on it now. That's when I tried the 12ax7 in it and the Tele sounds more like the Les Paul. The Les Paul with the 12ax7 is just beyond my preference, but who knows what he'll like. I'm pretty positive that I'm more discerning in what I'm looking for than most people are expecting to hear. I thought about lowering the bias, but the voltages are pretty high already, so I don't think I'm going to do that.

    I think that I'm going to need to switch to a Brown/Blackface style amp/chassis next time with individual bass/treble controls. I love the Tweed cabinet style, but a 6G2 chassis with T/M/B tone controls would be perfect for this and my Harvard based College Dropout. It just turns my guts to pay as more for two faceplates as the entire welded steel chassis costs. But, a real EQ control would be a huge game changer.

    Side note, I played with my A/B/Y box today and the split inputs are handy. You get the hot #1, lower #2, then hit the switch and run both of them together.
     
  18. NTC

    NTC Tele-Holic

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    Can you post a final schematic? I have stuff to make a similar amp and would like to have a quick reference of where your corciit ended up.
     
  19. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Ha. Funny enough, for everything I did and tried, the only real end changes from the Fender schematic that matter I think are
    • increased filtering
    • be sure to use power/bias resistors to handle the 5881
    • use the AA764 NFB circuit. I preferred the bypass cap on the 2nd stage only with the humbuckers. Last time for single coils, I liked it better on the first stage.
    The end goal was finding that balance point for the humbuckers & bass response. I wonder what a smaller OT would do for possibly saturating sooner and cutting out some of the unwanted frequencies?

    Anyway, for all that I tried, that NFB change is the only thing that wasn't related to handling the bigger tubes.
     
  20. jsnwhite619

    jsnwhite619 Friend of Leo's

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    This is the amp on 4, 6, and, 8 with a 12ay7. I'm flipping through the pickups as I go on each section.

     
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