Do Fender Prosonics REALLY get THAT hot??

Discussion in 'Amps and Cabs' started by StompBoxBlues, Sep 20, 2005.


  1. StompBoxBlues

    StompBoxBlues Member

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    Hey folks!

    I recently got a Fender Prosonic head. Tried it out for the first time at "volume" at a jam with some people.

    Sounded great. The only thing, and I have owned almost exclusively tube amps (Ampeg VT-22, Carvin MTS3212,
    Carvin Vintage 33, Peavey Classic, Gibson Starfire..) but unless I just forgot about my old Ampeg, I don't recall evert having an amp that was this physically hot on the metal on the back of the amp.

    There are two metal toggle switches, power and standby, on the back and I swear you can barely touch the standby on and off, with out feeling like you are going to burn your finger.

    Any other owners out there? Is this normal for this amp?
    I had it cranked, and had it set to Class A. Don't know if maybe that contributed.

    If anyone has one here also, one other question, I read on HC that the effect loop on Prosonics run really "hot" (NOW we are talking signal amplitude, NOT physcial hear) signal out to any pedals you might hook up. I seem to recall one reviewer even saying he thought it may have damaged a pedal (I have a hard time believing THAT though...but) some mentioned that it would tend to overdrive the pedal effects on the input. Overdrive that is not wanted for example on a chorus, or delay.

    So, anyone here have any advice/experience on specifically the Prosonic effects loop? I haven't tried it myself yet, would like to hear other folks experiences with it if possible.
     
  2. Rock Fella

    Rock Fella Member

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    yeah they run hot allright, when i had the combo, sorry i sold it actually, look at the transformer on the left hand side, there is a copper strip running down it, mine had quite a bit of it burnt clean off.

    you get the channel switch pop sorted on yours ?
     
  3. StompBoxBlues

    StompBoxBlues Member

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    It's minimal on mine. I bought mine new, just now. I think maybe I'm lucky and the tubes are minmizing it. It cannot be what people are mentioning with this amp cause it isn't that bad.

    We'll see if it develops into being a problem with time though.
    I got ahold of the mods anyway, just in case.

    Did you notice if you ran through tubes much quicker with this amp? Did you play it mostly in Class A, or notice if it ran any cooler in AB?

    Thanks for the reply!
     
  4. Eric Pykala

    Eric Pykala Member

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    I think one of the reasons the Prosonic did not fare well on the market was the +4 line level loop. It was just too hot for a lot of pedals, but perfect for rack gear.
    Yes, they get hot, particularily in Class A.
    Somewhere on I believe this forum, there was a reply by Bruce Zinky, designer of the amp, with some mods to fix the channel-switch pop and to further smooth-out the distortion. Try a search, or try finding Bruce yourself.
    I always felt that this was one of the best amps Fender ever made; it just had a few quirks that soured it in the marketplace.-Eric
     
  5. StompBoxBlues

    StompBoxBlues Member

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    It's minimal on mine. I bought mine new, just now. I think maybe I'm lucky and the tubes are minmizing it. It cannot be what people are mentioning with this amp cause it isn't that bad.

    We'll see if it develops into being a problem with time though.
    I got ahold of the mods anyway, just in case.

    Did you notice if you ran through tubes much quicker with this amp? Did you play it mostly in Class A, or notice if it ran any cooler in AB?

    Thanks for the reply!
     
  6. StompBoxBlues

    StompBoxBlues Member

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    Do you know of any mod for the effects loop?

    What are the consequences of that effects loop, and was this ever changed by Fender? Because it says nothing about it other than "you can use the loop to pedals, will be between preamp and output amp" (paraphrased) basically.

    Can a +4 signal actually do damage to stomp boxes? (mass produced or botique?) I think they can't and that you mean only that it would peg the input, causing distortion (not the good kind) right?
     
  7. Rock Fella

    Rock Fella Member

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    ther is a dvd called peter green splinter group and he and the other player are both using prosonics, tones from the gods, i urge you to check it out, those amps sound incredible on this dvd.
     
  8. hipfan

    hipfan Member

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    The +4 loop just works better with rack gear and other stuff designed to take a full line-level signal (H&K Rotosphere and Boss DD20 delay, for instance). It shouldn't hurt your instrument level stompboxes, but they may get overloaded by the strength of the signal. I would think that a mod to get the amp's loop to play better with instrument level boxes would be pretty extensive and probably not worth it...

    As far as the hot amp issue, I used to have a Prosonic head, and I remember it being biased extremely hot from the factory - both in "Class A" (cathode bias, I think) and "Class A/B" (fixed, variable bias I think) rectifier operation. There's a trim pot on the circuit board to adjust the fixed bias, and you can change a resistor to adjust the cathode bias. I don't remember the location of that resistor, but there's a lot of info on the Fender Forum from other amp owners regarding that.
     
  9. bluessyndicate

    bluessyndicate Supporting Member

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    Mine ran very hot...I never used the loop. I ran in class A alot...

    I maxed the channel volumes and controled volume with the EQ's..it gave up one of the best power tube distortion tones I've ever heard....
     
  10. Teleplayer

    Teleplayer Silver Supporting Member

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    I used to own both a Prosonic head and 2x10 combo. Loved the tones in both "Class A" and "Class A/B" modes. The combo ran so hot though, that the pcb fried in mine. Had to take it into an authorized Fender repair shop. The repair was done for no charge, but took about eight weeks (I think they needed a part from Fender).

    I actually wound up with the head that Gary Hoey used for a Fender demo at a local shop. I ran it through a Marshall 4x10 cabinet, and it sounded really, really good.

    In the end, if Fender would have resolved the heat issue and popping issue when switching channels, it would have been a killer amp. However, I think it wound up in the "sleeper" category instead, because of those problems.
     
  11. Jeff Flowerday

    Jeff Flowerday Member

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    Get the amp biased up a little cooler.

    There is a bias pot for the AB-Rectifier and AB-SS modes. Find a happy medium between the two.

    The Class A(actually Cathode Biased mode) will need a resister change. I think it's a 220 ohm, try a 240 - 270 ohm.

    Any tech will be able to do this for you.


    There are alot of great mods for the Prosonic, search the Fender Forum for the Prosonic thread, I've posted most of them on there.




    Jeff
     
  12. StompBoxBlues

    StompBoxBlues Member

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    You know...it definitely sometimes feels like there is a cosmic jokester, or gremlins...

    Last night, trying out the effects loop for myself the first time, sounded, not as good as the effects loop on my Carvin MTS.
    But not really badly overloaded either. I went a little back and forth, using a Deja Mini vibe, and a Visual Sound H20 (both handmade pedals...so I was a little concerned if the +4 could do any damage. I don't know or have specs handy...but I think that a guitar signal is generally seen as like -20db or so, that "line level" was about 0 db, that the difference is guitar ~200mv pk-pk, and line ~1 V pk-pk....but then what is +4? Anyone know or can confirm my recollection?...it's like 5 times the voltage expected, but can it actually do damage is my big question)
    They worked. I'm not decided yet on if it is worth it.
    I know I could put a potentiometer in the send circuit and try to match the guitar level input impedance to the pedals, but you have to make it up again on the other side I think...

    Leads me to another question. I have found schematics for the prosonic on the net, but they are for the combo, so there is a I stereo cable footswitch cable, and reverb circuitry. My question is if this is otherwise the same amp on the schematics, or if anyone has a link to the head-only schematic?


    Anyway, after trying out the Prosonic, I went over to my MTS3212.
    (I was trying to decide which amp to take to practice tomorrow night) and I plugged in my same pedals to the MTS effects loop. Last week I finally finished repairing (my first repair and mod job on any amp) the MTS. I already played a 4 hour jam at normal playing volume and it held up so I was pleased.

    Played it a little, sounded okay. Soon after I plugged in to the effect loop...HUGE hum...farty-really-low-level guitar sound in there...oops. Chut it down immidiately. Tried again, same thing. Thinking "damn, damn, damn...did the Prosonic loop ruin my pedals? DAMN..." calmed down (important step that...) tried once again after rechecking every setting, (guitar too, pedals, power, footswitch, evertyhing) and trying to clean up the jacks in case the snd-ret jackes were getting flaky after my repair... I had touched up a lot of solder joints, some were bad, but not the jacks for SND RET...then I took the whole shebang over to my Peavey Classic 30. Same thing...

    To shorten this a little....ended up the damn effects cable (I had bought a Hosa double mono cable for convenience, and redid one end with right angle jacks. Had always worked fine) suddenly had an open on the pin-pin side. It wasn't where I changed out the right angle either. I will clip the molded plastic end and see if it helps and repair it.

    Scared the bejesus out of me...two fairly expensive pedals...but I think all is well.

    Main thing, just to be really sure, the +4 level (is this known by the way that is IS definitely +4?) really cannot hurt even butique pedals?

    Thanks!
     
  13. son7091Jason Jones1

    son7091Jason Jones1 Member

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    My prosonic, when not using the effects loop, makes a high pitch, feedback like sound with tuner,wah, overdrive and leslie pedals run straight through the front of amp. Any thoughts anyone?
     
  14. Tele Jr.

    Tele Jr. Member

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    Sounds like you have an issue with your effects loop jacks. It is common for them to eventually need replacement in Prosonics. I had them replaced in both of mine under the warranty period. The footswitch jack in my head also went bad.
     

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