What PRS amps do you own?

Discussion in 'Amplifiers' started by 11top, Aug 6, 2018.

  1. andy474x

    andy474x Knows the Drill

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    Let the record show, Les asked for it!

    I reduced the value of the coupling caps going into the phase inverter, to reduce the amount of just the very lowest frequencies on both channels. I also increased the value of the tone slope resistors on both channels, basically to shift more of the signal flow to the treble control, so I didn't have to run the knobs at extremes all the time (max treble, minimum bass), and it makes the amp less picky about "sweet spots" on the controls. That last part could be in my head though. It did definitely shift the EQ mildly, which was all I needed.

    The presence knob has a "pull deep" function on it, which is basically a negative feedback resonance control. Even in the normal/in position, there's still some effect to the tone - I would call it adding low, but I think what it's actually doing is removing some high which gives the illusion of adding low - anyways, I removed the capacitor that was doing that, so normal is now unaffected, and I can still do pull deep. The two barely had any contrast before, and now it's more noticeable, and more useful IMO in the "normal" position. With the deep cab, I really have hardly any need for the added depth setting, but more on that later.

    My last mod, as you can see from the photo, was to break the presence control knob off the pot shaft. Apparently I screwed the little hex set screw in too much and the thing cracked wide open on one side. That was surprising, as I wasn't torquing on it much when it happened. I have some superglue and have been meaning to glue it back together, it was a clean break so it should be fine. I haven't found a vendor that sells replacements, so if that doesn't work I'll call PRS.

    I also learned why the presence control itself is so touchy on this amp. It only changes the tone between about 8/10 and 10/10. I thought maybe I had a bad pot, or something had been wired incorrectly. What I discovered is that the pot is bridged with a second, fixed resistor in parallel with the pot. Many amps do this on their presence control as a "voltage divider," long story short it's usually done to reduce a scratchy pot sound on the presence control. The reason this amp has such sweet spot between 8 and 10 is because the pot itself is a 50K pot, bridged on the outer lugs with a 4.7K resistor. So, basically, that's a small fixed resistor in parallel with a large variable resistor. If you're familiar with how resistance combines in a parallel circuit, path of least resistance, etc., you can imagine how a 50K pot has to be turned to the point where it only has a resistance of 4.7K for there to start being a considerable overall effect on the resistance of the circuit. Which, if we were talking about a linear pot, would be in the last 10% of travel - whether this pot is linear or not, I'm not sure, but that 10% figure doesn't seem too far off when I fiddle with the knob. I'm considering tweaking that circuit to get a better sweep, but I haven't had time to do the math and see if I could just swap a resistor. I would assume that later revisions of the Custom amps have changed that, because the control is very hard to adjust with such a narrow sweep of useable settings.

    I should add that everything above is what I think I did to the amp. I'm fairly confident that I identified the correct parts to replace, and each change certainly had the desired effect. It's a heck of a lot easier finding the right component on an amp with hand wiring, rather than a PCB, but even so this is a complex amp just by the nature of the two channels. Fortunately the circuitry of each preamp channel as well as the depth/presence controls are heavily influenced by traditional M and F circuits, so they were easy to find relevant info on.

    And, going back to that thing about the deep tone of the big mouth cab, my LAST big mod I have coming up is going to be building a new 2x12! I've got the wood sitting in the garage at the moment, just trying to decide on a design. I've narrowed it down to either a Marshall 1936, or a modified Mesa design, either based on the horizontal or vertical slant 2x12 recto cabs, but not as deep front to back, to cut down on some low end. The big mouth PRS cab I have now is somewhere between a Mesa horizontal 2x12 and an Orange PPC 2x12, which are some of the largest on the market. The Marshall also has lots of internal volume, but every time I play through a Marshall cab it sounds more focused and less bassy. I've heard that it could be due to the method of baffle attachment. On the other hand, the Mesa cab would fit in my truck bed better due to the shorter vertical dimension. If you fellas have any recommendations, I'm all ears. When it's done, I've got a set of V30's sitting in a box, although the allure of Celestion Cream is a real thing too, if the cab comes out as nice as I would like, it might be worth the investment.
     
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  2. I own an Archon, and I absolutely enjoy using this amp.

    i.e.



     
  3. LSchefman

    LSchefman Hears Tones

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    Pretty impressive work there, seems to me. Just knowing what to think about doing takes a lot of electronics knowledge that I, for one, don’t have, but by some magic, I was able to follow your process. If you got where you wanted to go, that’s cool as cool.

    I have the PRS Big Mouth 2x12; it’s used with my HXDA. Like the Mesa Recto 2x12, it can project a lot of bass, but I control it with acoustics. Obviously, you’re going to build a cab, which is awesome, but in the meantime, I’d just get it off the floor and away from the wall a couple of feet.

    Putting the cab a few inches off the floor, plus the isolation, cuts a lot of the half-space bass reinforcement caused by reflections off the floor. Moving it away from side and rear walls also improves the half space reinforcement. Mine’s in a nook-like corner, but I tame that with a lightweight, portable bass trap.

    This is true in the studio as well as the stage: you’ll get the best response from a speaker if you get it off the floor. A chair works pretty well. If you bring it a couple of feet from the wall, you’ll also reduce reflections off the back wall (yes I know there’s no port on the back of the Big Mouth, but bass is omnidirectional).

    Another thing to try is to simply put the cab on its side and use it as a vertical 212. Getting one of the speakers away from the floor can reduce the floor reflections that reinforce bass.
     
  4. vchizzle

    vchizzle Birdman.

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    Archon 100 x 2
    4x12
    Deep back 2x12(big mouth?-same one Les has I think, that is no longer made).
     
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  5. HANGAR18

    HANGAR18 What Would Evel Knievel Do?

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    I'm impressed by your knowledge of the subject.

    As for cabinets, I have now replaced all but one of my cabinets (2x12's and larger, including my brand new Marshall 1936 cab) with Mesa vertical 2x12 slant cabinets. I'm keeping one Marshall 1960b cabinet for my JCM800 head, but aside from that, the vertical Mesa cabinets sound fantastic, make it easier to reach the amp head knobs, are rugged and easy to move. If I were to build my own cabinets, I would go with the Mesa specs on everything except for the speakers, favoring the Warehouse Guitars Speakers brand instead of the Celestion. (It's okay, PRS has used them in their cabs before.) imho, ymmv.
     
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  6. DreamTheaterRules

    DreamTheaterRules New and improved member

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    What Warehouse speakers have you tried and liked? I haven’t tried any yet.
     
  7. Boogie

    Boogie SuperD

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    Andy, here’s a rough sketch I drew years ago to help me visualize a potential project. It’s dimensionally accurate, so maybe it could be of some help?

    In all but my PRS cabs, I’ve swapped speakers a bazillion times. In the Boogie 2x12s, I stuck with 2 configs for live use, all C90s (the Mesa version of a Celestion Lead 90) and the other is a mix of Warehouse Veteran 30 and ET65. The WGS speakers are simply fantastic. I also have an ET65 in a little custom maker’s 1x12 that I’ve used with every amp I have with stellar results. It sounds sublime with the MkIII when I’ve dialed it to be a blues amp (long story) and did well in the MkIII’s open back combo cab. Not many speakers do well in closed and open back cab applications. But the pine 2x12 stays V30 because it defies what I perceived as typical V30 cabs.
     
  8. 11top

    11top Cousin Eddie's cousin

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    Me, too. I just plug stuff in. I have a hard enough time lining up the larger cord ground prong with the proper ac slot
    (And no, that is not a euphemism).
     
  9. LSchefman

    LSchefman Hears Tones

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    +1
     
  10. TroyBaer

    TroyBaer Really knows where his towel is.

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    I have an Archon 50 head and an SE 2x12 cab. Excellent combination.
     
  11. DreamTheaterRules

    DreamTheaterRules New and improved member

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    guess I never replied to the OT. I have an ARCHON BABY! And I've had a Custom 50 and a 2 Channel H.

    Still LOVE to try an HX/DA and MDT! Heck, a Sonzera as well.
     
  12. markie

    markie 11Top's personal Chauffeur

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    2 channel & Recording.....
     
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  13. 11top

    11top Cousin Eddie's cousin

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    And an original “Sewell?” (Which kinda counts, right?)
     
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  14. dmatthews

    dmatthews Dave's not here...

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    I don't think I recall you verbalizing that in this way before! Cool!
     
  15. AP515

    AP515 Mostly Normal

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    That's because I hadn't hooked it up to a 4x12 cab yet...:cool:
     
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  16. dmatthews

    dmatthews Dave's not here...

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    Well sir.. that is an eye opener.
     
  17. DreamTheaterRules

    DreamTheaterRules New and improved member

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    I thought the SE 50 was supposed to be like the Custom 50...

    That’s interesting because a friend of mine works in a store and they had an SE50 in stock several years ago and he fell in love with that amp. I’ve never heard one, or heard much about them at all, except my first sentence. Sounds like that was wrong.
     
  18. AP515

    AP515 Mostly Normal

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    I don't remember which came first, but the Custom 50 is 6L6 driven and the SE50 comes with EL34's. I have both and they do sound like sisters. I grew up (sonically speaking) on 6L6's so I'm a fan of that warm powerful sound. The SE 50 is just different enough to grab that harder overdriven magic. Well worth the $700 I have in it.
     
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  19. DreamTheaterRules

    DreamTheaterRules New and improved member

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    My buddy liked the one they had in the shop so well he was trying to sell his Budda Superdrive 18 to fund buying the SE. And the Budda is a very good amp! He didn't sell it in time though. Some guy he'd been bragging on the amp to came in the store and tried it and left with it. LOL
     
  20. Chester

    Chester New Member

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    Proud owner of this Custom 50 and 2x12 Bernie is playing through. Bought it from his tech earlier this year, and is a keeper



    Would love to own a DG or HX/DA head, but they are not sold in the UK. Sadly, we don't see too many PRS amps in Europe, although the Sonzera range is offered by many retailers thanks to their price point
     
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