2-Channel "H" head -- amp hum and no FX loop signal

Discussion in 'Amplifiers' started by mb1685, Nov 16, 2015.

  1. mb1685

    mb1685 New Member

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    Hello everyone,

    Recently I bought a used 2-Channel H head after reading great things about them. The amp is in excellent condition and the owner still had the original packaging and stated he had never gigged with the amp. He also had recently done a complete retube on the amp, so I don't think the problem is related to tubes.

    One thing that's offputting is that the amp has a very noticeable hiss/hum on both channels, even with no guitar plugged in. The noise is present even with the master volumes turned all the way down, and it seems to relate to the levels of the FX send and FX return knobs on the rear of the amp. Even with them set low, the noise is what I would consider excessive. I did some searching and saw that the user henryjurstin13 had recorded two quick videos of the noise and they are definitely a good representation of what I am hearing:

    http://s76.photobucket.com/user/hen...B-47D1-A9BD-F3C964582F59_zpskuchr919.mp4.html

    http://s76.photobucket.com/user/hen...5-429F-B950-025C91418FCB_zps3ugoptas.mp4.html

    Another strange thing that I think may be related is that I don't seem to be able to get a usable signal from the FX send. I enjoy recording preamp signals into my audio interface by utilizing FX send or line out jacks and then utilizing cab simulation in my DAW, but the only way I can get ANY signal at all to my audio interface is to crank the FX send level knob all the way up and crank the audio interface's preamp gain all the way up (+45 dB), and then the signal is still extremely faint and the signal to noise ratio is atrocious.

    Does anyone have any ideas about what the issue could be? I've e-mailed PRS support but haven't heard back yet. If the fix is simple and inexpensive, I'd love to take it to a local tech, but am not opposed to sending it to PRS (although it would be nice to not have to pay for shipping charges both ways).
     
  2. andy474x

    andy474x Knows the Drill

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    Have you tried replacing the tube for the effects loop? I know the last owner replaced the tubes, but for the symptoms you're having, it really sounds like it could be a tube.
     
  3. mb1685

    mb1685 New Member

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    I definitely wouldn't mind giving that a try. Do you happen to know which preamp tube is for the FX loop? The diagram in the manual says which tube types go where but doesn't seem to specify which one is for the FX loop.
     
  4. LSchefman

    LSchefman Hears Tones

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    My PRS amps are dead freaking quiet. No noise, ever, unless a tube goes bad.

    Tubes go bad all the time, especially ones of recent manufacture, and there's no warning. They just go, and can certainly be damaged in shipment. The first thing I'd do is look for a noisy tube, and the way to do it is to get a known good, quiet tube, and go methodically through the process of plugging that tube, one socket at a time, into each preamp tube socket until you find the bad tube.

    Based on what you're describing, noise that's there all the time even with the master turned down, I'd also check the power tubes in addition to preamp tubes, since master volume comes before the output tubes in any amp. If you turn down the master and still get noise, the power tubes must be checked.
     
  5. mb1685

    mb1685 New Member

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    I'm wondering if maybe the previous owner didn't look at the tube types in the manual and just threw all 12AX7s (or something else) in every preamp slot and maybe that's the problem. I'll check when I get home. I was reading about the 12DW7 (which looks like it's closest to the FX loop) and saw that each side has drastically different gain factors and was thinking maybe the wrong tube type in there could make things awry.
     
  6. rocguitar

    rocguitar New Member

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    Regarding the first problem that you have noted, I had the exact same problem with my brand new 2 Channel H Head, right out of the factory-sealed box, a couple years ago.

    Initially, PRS sent me a new FX Loop tube to try, but the problem with the hiss/hum was not affected at all.

    So, I sent the head back to the factory. The amp guys replaced the FX Loop Return Pot, and the noise problem was totally eliminated. Since this fix, the amp has been nice and quiet, and it still sounds great!

    Regarding the other "strange thing" that you're also experiencing, it too may be connected to the first issue. However, I can't say for sure because this never happened in my case.

    The guys at the PRS factory will able to troubleshoot the problem, but they'll likely need to put it on their bench for the best diagnosis!

    I hope this helps!
     
  7. Rider1260

    Rider1260 New Member

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    100 percent on sending PTC a line !!!!
    They totally got my H going 100%
     
  8. mb1685

    mb1685 New Member

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    Thanks for the replies!

    Rocguitar, I actually quoted your post when I contacted PRS Support since it sounds like possibly the same issue I'm having (although maybe the FX send pot is busted too rather than just the FX return pot). I hope they respond soon.

    I opened up the amp and saw that an ECC832 (same as 12DW7) is indeed in the FX loop spot, which is correct. I'll go ahead and order another tube though in case that particular tube is just bad. The previous owner also put 12AT7s in some of the slots that the manual says should be 12AX7/ECC83s, but based on my understanding those are interchangeable and just result in slightly lower gain, so that shouldn't be the culprit.
     
    #8 mb1685, Nov 17, 2015
    Last edited: Nov 17, 2015
  9. Boogie

    Boogie Zombie Two, DFZ

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    Changing the tube type (12ax7/12at7, etc) generally has little to do with the noise floor. The integrity of the tube can, however. But a bad FX loop pot certainly makes sense, too. Try rotating both pots quickly (back and forth numerous times) to clean the wiper and/or remove any impurities from the trace and take another listen. This isn't as affective as it used to be before printed carbon traces, but it's worth a try. A noticeable change in volume or signal clarity might point you in a particular direction for a fix.

    Otherwise, wait for an answer from PRS and they'll get you situated.
     
  10. mb1685

    mb1685 New Member

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    Haven't tried a new preamp tube yet, but I did try cleaning the FX loop tube socket (by spraying the pins of the tube with contact cleaner and plugging it in to the socket and removing it a few times) and the FX loop jacks (same thing but with a cable). No change, but I think I've actually discovered that the amp actually is working properly and I'm just a bit ignorant.

    I realized that the times I've recorded preamp signals through FX sends before, it was with amps that have a preamp volume control AND a preamp gain control (like Mesa Rectifiers, for instance). In those cases, I could have the master very low (or even at 0) and still get whatever preamp signal level I wanted with the channel volume control. Given that the 2-Channel H's preamp "volume" controls are more like gain controls, it occurred to me that maybe the preamp volume is directly tied to the master volume. I tried recording from the FX send again while slowly turning up the master volume, and sure enough, the input level increased as the master volume increased. Unfortunately, it seems that I would have to crank the master up to a pretty loud point to get a signal with a decent signal to noise ratio into my interface (since I would have to have the input gain on the interface cranked otherwise), so it looks like the amp isn't ideal for recording the FX send that way. I know that I could get an attenuator with a line out (and get the power amp's influence on the tone too) or a load box to disconnect the amp from the cab, but I'd prefer not to spend the extra money since I really have been quite content with recording other amps with preamp signals + cab and power amp emulation in the past (and I enjoy having the cab providing a little bit of volume in the room too).

    With regards to the noise/hum issue, I think I'm just not used to using an amp that has the FX loop always in the circuit. I found that lowering the return level increased noise and increasing the send level increased noise, and vice versa. I found that setting the return all the way up and the send anywhere from about 9 o'clock to noon reduced the hum/hiss to a level I'd consider normal. I guess the "2 o'clock is the sweet spot" talk just confused me because there was quite a bit of noise in that setting (like in henryjurstin13's videos that I posted in the original post).

    Could any other 2-Channel H users report in and tell me if what I've written matches their amps? In short, preamp volume (and thus FX send) is connected to master volume and the FX send knob is more a trim control for that signal, and increasing FX return level and decreasing FX send level results in less noise and vice versa? If so, then it sounds like the amp is fine and I'm just a newbie. My main concern is just that the amp isn't malfunctioning in some way.

    EDIT: One other thing I noticed is that the FX loop controls also seemed to influence the amount of bleed from the lead channel. I'll have to play with it more to figure out the exact correlation, but I recall that noisier FX loop settings would also result in a very faint bleed of the lead channel (unless the channel's "volume" control was down, of course) when playing the clean channel. The bleed behaved like the noise I spoke of, and would stay at the same low level even if the master volume was increased. With the "low noise" settings I mentioned earlier (return all the way up, send at 9 o'clock to noon or so), the bleed was pretty much gone, but the "both at 2 o'clock" settings would result in the bleed being a little apparent when playing the amp at very low volume.
     
    #10 mb1685, Nov 18, 2015
    Last edited: Nov 18, 2015
  11. LSchefman

    LSchefman Hears Tones

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    As a guy who makes his living in the studio, I'm going to make a suggestion: using the FX loop to create a preamp send to a DAW really isn't a very good way achieve good tone with a speaker impulse response, because you're missing the sound of the output transformer and output tubes, and they have a lot to do with the tone of an amp.

    If you like the sound of the speaker in the room anyway, just mic up the speaker with a 57 or mic of your choice. If you really feel the need to go direct, the way to do it is with a load box like the Mesa or Suhr. With the Mesa load box, if you keep the speaker hooked up to the box, you get a reactive load instead of a passive one, and it's very close to the sound of a speaker cab, Without a speaker, the Mesa becomes a passive load, and you get a little less "speaker sound," however with the impulse model of the speaker you're a lot closer anyway.

    With the Suhr load box, you start with a reactive load and don't need a speaker to achieve it. Then the impulse response is as above with the Mesa or similar box.

    To worry over the tone you get employing the least effective method to achieve what you're trying to accomplish, doesn't make a ton of sense to me, especially when you can pick up something like a 57 on eBay for under fifty bucks.
     
    #11 LSchefman, Nov 18, 2015
    Last edited: Nov 18, 2015
  12. Rider1260

    Rider1260 New Member

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    In your post below you mentioned the issue I had " Bleed " from the gain channel into the clean channel, ( at very low levels )
    I sent it back to PTC all better now ( didn't really say what they did except replace a reverb tube )
    My H is now very quiet and the loop works great as an active level control.
    IE: I can set my amp to my favorite level and tone and then use the loop to control the volume of the amp.
    I can run mine down to 1/3rd ( 9 o'clock ) for bedroom level and up to 3 o'clock to let it sing ( noon -1 o'clock works best for me )

    EDIT: One other thing I noticed is that the FX loop controls also seemed to influence the amount of bleed from the lead channel. I'll have to play with it more to figure out the exact correlation, but I recall that noisier FX loop settings would also result in a very faint bleed of the lead channel (unless the channel's "volume" control was down, of course) when playing the clean channel. The bleed behaved like the noise I spoke of, and would stay at the same low level even if the master volume was increased. With the "low noise" settings I mentioned earlier (return all the way up, send at 9 o'clock to noon or so), the bleed was pretty much gone, but the "both at 2 o'clock" settings would result in the bleed being a little apparent when playing the amp at very low volume.
     
    #12 Rider1260, Nov 18, 2015
    Last edited: Nov 18, 2015
  13. mb1685

    mb1685 New Member

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    I use power amp sims too and have been very happy with the results with other amps. I've been into direct recording for quite a few years and I'm very satisfied with the results I can get. I've owned a Rivera RockCrusher reactive load before too and used it with another amp I used to own, and I honestly was just as satisfied (if not more) by using that amp's FX send with power amp simulations. I'm definitely not a recording novice and have been recording guitars for quite a long time now. After a lot of experimentation, an analog preamp signal combined with a digital power amp and cab simulation has proved to be a great combination for me and the kind of tones I go for. I considered just buying a rack preamp (my first experimentation with this many years ago was with an ADA MP-1 and a Marshall JMP-1) for the task, but I also enjoy the bit of guitar-speaker interaction I get from using a cab (even at low volumes), and it's a lot easier to find good deals on heads than it is to find good deals and preamps and power amps. I've done lots of miked recordings too, but I find that analog preamps (with master volume amps) into digital cab/power amp emulation strike a fantastic balance between volume control, great tone, and flexibility.

    Anyway, my concern right now is really just whether or not the amp is functioning properly, regardless of what I'm using the amp for. I wouldn't want to sell someone an amp that doesn't work properly.
     
    #13 mb1685, Nov 18, 2015
    Last edited: Nov 18, 2015
  14. mb1685

    mb1685 New Member

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    Interesting, I guess that means the bleed means there is indeed some type of malfunction. Could any other 2-Channel H users let me know if they get faint lead channel bleed (or hiss/hum) in this situation (clean channel selected, master volume very low, FX return volume below half and FX send volume above half)?
     
  15. mb1685

    mb1685 New Member

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    Bump. Could any 2 Channel H users chime in and tell me if their amps behave similarly? The main thing I'm curious about is if they hear a little bit of noise increase when the FX return level is lowered and the FX send level is increased, and less noise vice versa. I'm in contact with PRS but haven't heard from them in a while so I figured I'd get some input from other owners.
     
  16. BlueSky

    BlueSky New Member

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  17. AP515

    AP515 Mostly Normal

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    My "H" is very quiet. I haven't tried changing the settings of the FX loop. I'll play with it when I get back home but that is more than a week from now.
     

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