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Modified Harvard build

Discussion in 'Shock Brother's DIY Amps' started by jsnwhite619, Mar 3, 2020.

  1. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I had a thread going about the layout and design, but figured I'd start a new one now. After the weekend, only thing left to do was install the transformers that came in today. So, I did. New tubes are in the mail, but I pulled everything out of my 5e3 to try it out. 325v secondary PT biased around 65% here @ approx. 380v B+ I think. Plate to cathode was 375v I know. I think the B+ rail went 380v, 375v, 300v and the V1 cathode was 1.5v. A 5u4 is on the way, but I'll just have to see where that ends up.

    I plugged into a cabinet with my old Warehouse Veteran 10 from several years ago. The lowest powered speaker I have right now, but it sounded pretty dang good. It stays pretty clean up to the 7-8 range, then the overdrive really starts to kick in. Even on 12 it stays together really well and doesn't get too mushy. I just went and checked, and the last time I turn it up for the video takes it to 12 until the end -- that's where the knob is since I turned it off. Chassis is open & face up toward fluorescent lights, but still pretty quiet considering. I can't wait to try it through a stronger speaker & with my Les Paul.

    I have to redo the input jacks, but I'm 99.9% sure I know what is wrong and was grounding it out. Going for a single/parallel Marshall style, but one was dead silent until I clipped the jumper, now both are identical inputs and both work fine.

    Hammond 290AX PT, Hammond 1750E OT.

     
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  2. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I was right - got the inputs sorted out. It's too late to do anything more than make sure they are working, but that's solved. Even at super low volume I see what people mean when they say parallel gives a thicker tone. I think I'm going to like it turned up.

    To be clear, the video above was just a normal Fender #1 input sound. Now, #1 is the hotter parallel input, and #2 will be the same level as a regular Harvard #1.
     
    Last edited: Mar 3, 2020
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  3. Nickfl

    Nickfl Friend of Leo's

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    Sounds good!

    You should post a link to the thread about the layout and design for reference so people can say what the modifications you made were.
     
  4. printer2

    printer2 Poster Extraordinaire

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    When I get back to it...


    You say you want to try a stronger speaker than the Vet 10, Do you feel it won't take a good pounding from the amp?
     
  5. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Oh, no, I'm not worried about the speaker. I still like it. I've just turned around on what I like about certain speakers now from what I used to be. I still appreciate the attenuator qualities of less efficient and lower wattage speakers. And I like the sound of the Veteran. But, I've really grown to love what a strong, powerful speaker can do for an amp. That's how I've gotten into my Eminence kick I guess.

    Sent from my moto g(6) using Tapatalk
     
  6. printer2

    printer2 Poster Extraordinaire

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    OK, got it. I have a couple and have not used on in a 15W amp yet and am putting together one. I didn't know how well it would take the power.
     
  7. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Always heard they rate conservatively. As in, their 20 watt speaker is good for a 20 watt amp, knowing that it will exceed 20 watts. But, I've never tried to blow one.

    Sent from my moto g(6) using Tapatalk
     
  8. jsnwhite619

    jsnwhite619 Friend of Leo's

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    A quick demo with a Tele & the Ragin Cajun. Starts at Volume on 4, then to 8 when it gets a little dirtier, then on 10 around 5:50 mark. The first .02uf coupling cap has a .047uf tacked on it to see how it does. It sounded a little thin before, so I added it. I think swapping the .02uf for just a .047uf will give the lower level warmth I want and reduce some of the fuzz when it's completely cranked.

    Oh, yeah, I have a name for my dirty Harvard -- College Dropout. :cool:

     
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  9. sleazy pot pie

    sleazy pot pie Tele-Afflicted Gold Supporter

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    That sounds great. I finally understand what people mean when they say break up that doesn’t fall apart.
    That’s one college drop out that still gets an A
     
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  10. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I know the soundcloud links don't work on mobile versions, so I did a Youtube video for it.

     
  11. cobaltu

    cobaltu Tele-Meister

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    If you want to do that, it might help to approach it from the other end - attenuating treble. If you haven't already, adding a grid stopper to the phase inverter would be a good idea, especially if this amp is meant for overdrive (cathodyne PIs are not famous for taking OD gracefully). ~470K ohms should be a good staring place.
     
  12. jsnwhite619

    jsnwhite619 Friend of Leo's

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    The demo clip had a 100pf ice pick cap on the NFB because it was pretty bright, and it's going to stay I think. I tacked on the .047uf cap with the .022uf to see how that sounded, and now I've got the single .047uf for the first coupling cap. I also made the board with extra eyelets to play with that grid stopper value. It had a 220k in the demo, and I've now swapped it for a 470k. Haven't tried it cranked again yet though. Also, from your advice in the layout thread, I went with a .01uf phase inverter input cap. I also added 470R screen resistors since the demo. Bias for the recording was around 65%, but I haven't played around with it enough yet to see what I like between hot/cold bias.

    New tubes should be here today, and I have a 5u4 as well as a 5y3 to try. That's why I went with this PT because it has a 3A winding. The Princeton Reverb I built last year with a 5u4 had the best cranked tone with my Les Paul I've ever heard I think. Same transformers on it as this. I know there's other differences, but I'm going to try it out and see. I stuck a GZ34 in there, but I couldn't adjust the bias cooler than 80% and I didn't plan on using it anyway, so I didn't change the resistor to accommodate it.
     
  13. jsnwhite619

    jsnwhite619 Friend of Leo's

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    470k grid stopper in place & .047uf coupling cap on V1; Tele with 12AY7. Volume on 10 in the parallel input. I really think that cleaned up the overdrive. Still on the fence about the .047uf. Adds the nice Fender warmth at lower level, but might be getting too wooly cranked up... 6 of one, half dozen of the other.

     
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  14. cobaltu

    cobaltu Tele-Meister

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    I dunno if you changes anything else b/w the two recordings (settings, mic placement, other components) but it definitely lost some 'fizz'. Less 'hairy' and more focused.

    This has inspired me to add a grid stopper on my recent 5e3 build. I was going to add it during initial construction, but just forgot about it. However I thought that the amp has a certain 'edginess' with the tone above ~7.5, especially on the bright channel. That PI grid stopper might just be the trick.

    Do you have and up-to-date schematic for this build?
     
  15. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I think the bigger grid stopper and the screen resistors were the only changes. That and a 12ay7 on the last one vs 12ax7 on the first. I am loving the parallel inputs. I've always liked a 12ay7 more than a 12ax7, but sometimes you just have to have the extra gain. The parallel input solves that -- more 12ay7.

    The new tube set & a 5u4 came today. I had to increase the bias resistor to cool it off, but this thing just turned into Superfly TNT with the 5u4. Trying it now really opens my eyes to how much of the difference in Tweed/Blackface tone involves the rectifier. I'm using JJ's across the board, but the 5u4 really gives it a Blackface/6L6 tone. The huge, firm bass sounds like a piano now. It's unworldly loud though. I actually thought I heard a crackle or two with my Veteran 10, so I'm afraid to run it through there now and it's a 20 watt speaker. Currently looking at 410v at the plate and 60% bias level.


    Man, I'm a liberal arts major -- I didn't have a schematic when I started! That layout in the other thread is what I've worked from. Luckily, I scanned it for the post because I either lost it or accidentally threw it away, but I still have it saved on my computer. I'm going to have to sit down and look at everything on the board and double check what I've got where at this point. I'm just glad I punched all the eyelets that I needed before I got it hooked up. I've punched my own boards for a few others by now, but this is my first "design build", so I'm pretty stoked. May have to celebrate a little tonight...:D
     
  16. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I'm loving this thing. I tried it with my Blues Driver today with both rectifiers, and a the 12ay7 is definitely a sweeter sound with the OD pedal. Just a fat, smooth, chewy overdrive. It actually has a bit of a Tube Screamer sound to it with the fat midrange. I didn't get a chance to record it today, but will when I get the chance.

    Youtube link to the last Soundcloud clip above.
     
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  17. reckless toboggan

    reckless toboggan Tele-Holic

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    That sounds absolutely delicious. Fat, saturated, and a bit crunchy. Great work.
     
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  18. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Can anyone tell me if this is guitar, amp, or electrical ground related? Every guitar does it, I've tried different guitar cables, speaker cables, outlets, rooms. It's mostly quiet with no guitar plugged in. Let go of the strings and it's bad. This is with the amp on 3-4 range.

     
  19. Snfoilhat

    Snfoilhat Tele-Afflicted

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    I hope my poorly-evidenced speculation doesn't crowd out someone with a good answer, because I'd like to know too.

    Is this some kind of radiated noise picked up by the guitar and/or cable that finds ground through the player easier than it finds ground down at the end of the cable shield at the input jack sleeve? And so not really an amp issue?

    It makes me think of a post I saw in a recent thread about shielded leads inside an amp, and this poster went against the more common wisdom of shielding only one side, to say it's really more nuanced and it depends on the frequencies you want to protect the inner lead from. Maybe the player touching the grounded parts of the guitar are like going from a shield with only one side grounded (the input jack sleeve) to both sides grounded.
     
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  20. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Well, I reflowed a lot of connections; put in new leads from the jacks to the board and twisted them together, and did the same from the board to V1. It seemed to help some with the noise. Les Paul & Tele do it, but is pretty quiet when I'm touching the strings or metal; also, an iPod plugged in is dead quiet with no buzz or noise, so I assume it's guitar related. WiFi, refrigerators, LED/CFL bulbs, computer....who knows what's shooting through the airwaves.

    I have a feeling that the extra gain stage that I'm not used to dealing with on these amps is adding to it as well.

    I've been looking at line filter/conditioners for a while, or even an isolation transformer. I feel like the possible time saved trying to track down noise issues that may be completely out of my control would be worth the cost.
     
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