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Problems recording with an Aguilar DB 359

Discussion in 'Amps and Cabs [BG]' started by 44me, Jun 26, 2002.


  1. 44me

    44me

    Jun 17, 2002
    Bedford, NH USA
    Does anyone have any experience using Aguilar’s DB 359 for recording? I purchased this amp about a month ago, and it has absolutely killer tone. I can’t say enough about how good it sounds - BUT, it seems to generate too much hum for recording. This is particularly disappointing, since one of the main reasons I bought this thing is that I thought it would be great for recording. I contacted Aguilar when I first got it, because it seemed to buzz more than any other amp I’ve owned. They were very responsive, but I really didn’t get a satisfactory answer.

    I tried to recorded with it for the first time yesterday. I already new that the buzz was going to be too much to mic the cabinet, so I just ran the line-out directly to the board. The tone was fantastic, but there was still too much buzz. Thinking it might be my bass, I unplugged the instrument cord from the amp, but the buzz was virtually the same. In fact, even with the volume turned all the way down (the output volume was always down) the buzz was still there. The ground lift switch had no effect. Taking the amp out of standby made the buzz a little worse (apparently standby just shuts down the power amp, as the preamp still worked). I unplugged the line going to the board, and the buzz stopped. I plugged the line into a couple of direct boxes and an Eden amp and there was no buzz. I ended up using the Eden.
     
  2. bassmonkeee

    bassmonkeee Supporting Member

    Sep 13, 2000
    Decatur, GA
    It sounds to me like there is a ground, or interference issue. Have you tried other amps in the same outlet that you have the Aguilar? My DB750 has a little hiss when I have it through amps, but the preamp is dead quiet into the board, so I am lead to believe there is definitely something amiss, and it isn't just inherent to the head.

    If you can't alleviate the issue, I would recommend taking it to a repairman. He might be able to identify the problem.
     
  3. 44me

    44me

    Jun 17, 2002
    Bedford, NH USA
    The Eden I used for the day was plugged into the same outlet, and it was dead quiet. I checked the ground with a meter to make sure the line cord and outlet were OK. Also, I’ve had the same problem at home in my practice room. I was just hoping that the line-out would be quite. Your kind of response is what I’m looking for, as I’m trying to figure out if something is wrong with this particular amplifier, or if it’s just an inherent characteristic of the design. I sure hope something just needs to be fixed, as I otherwise love this amp.
     
  4. bassmonkeee

    bassmonkeee Supporting Member

    Sep 13, 2000
    Decatur, GA
    Yeah, I find it hard to believe that a company that made it's name on a studio preamp would knowingly release an all tube head that was inherently buzzy.

    Have you checked the tubes? Maybe they need to be biased, or you have a tube that has gone microphonic. I think that could be a source of noise. Perhaps Chuck M will stick his head in this thread. He knows a heckuva lot more about tubes than I do. Actually, my tube knowledge has been pretty limited, as far as problems go--I've been fairly lucky, so far.
     
  5. lneal

    lneal

    Apr 12, 2002
    Lee County, Alabama
    Did you buy it new? If so, the company should give you more than just a few suggestions. If its still under warranty insist that they take a look at it. Don't know how they handle service, but it definitely needs attention. You may have a tube problem. If its out of warranty, you can go through it one stage at a time using known good tubes and see if you can stop it. I'm guessing its probably in the preamp section. If you can't fix it that way, do as bassmonkee said and take it to a tech.
     
  6. 44me

    44me

    Jun 17, 2002
    Bedford, NH USA
    I bought it used, and therefore have no warranty protection. At this point I wish I would have spent the extra money for a new one. Aguilar's orginal owner warranty is 10 years. Supposedly it's just a few months old, but that's not to say it can't have a defective tube, or something else for that matter. I'm just trying to figure out if this behavior is normal for this amp before I have someone look at it. It sure doesn't seem like it should be.
     
  7. lneal

    lneal

    Apr 12, 2002
    Lee County, Alabama
    Don't know much about Aggies either, but they wouldn't have built their stellar reputation by building noisy amps. Try the tube swapping thing and then if that don't help, find a good tech.
     
  8. Describe the buzzing. Is it a constant hum or does it fluctuate? A microphonic tube wouldn't cause a buzz. Check to see if there's a hum balance pot on there. My SVT buzzes badly if the hum balance is off.. If there was a blown tube it might buzz, but the amp wouldn't sound right..... IF it isn't the hum balance, it sounds like a grounding problem to me. I wouldn't imagine it's an inherent problem with the amp. All the Aguilar stuff I've ever used has been very quiet. Take it to a very good tube amp tech to get it checked out.It might be as simple as one loose ground trace or a funky capacitor. Unless you are comfortable working on tube amps and really know what you're doing don't take it apart yourself, there can be enough energy stored in the filter caps to kill you, even if it isn't plugged in.
     
  9. 44ME,
    I've recorded with the Aguilar DB680 and had the same type of noise problems. I can almost assure you that there is nothing wrong with your amp. I received the same response from Aguilar, and they never told me the best way to eliminate hum other than really obvious sources. At the studio we even turned off all of the video monitors, tried ground lifts, tried plugging into different circuits, and more with no real solution. When recording at home I had less noise than at the commercial studio, but sometimes it would still get noisy. Did you try using a very high grade line conditioner (not just a glorified power strip)? I suspect a possible source of the noise is from other electrical devices such as fans in the HVAC system etc. as I observed some intermittent noise problems when recording the other day.
    Let me know if you find a solution to this problem.
     
  10. I'll also add that tubes are inherently more noisy than transistors, so with ~10 tubes in a preamp there is going to be significantly more noise than solid state gear. I believe the Aguilars S/N is 80db, which is considerably more (>10X) noise than the typical 92+ db of solid state gear.

    G
     
  11. I've recorded with the DB680 and while it's a bit noisier than SS preamps (hiss mostly) it's certainly not noisy enough that it couldn't be used for recording. I never noticed any buzzing. The power in the studio I engineer in from time to time is transformer isolated, though, which probably helps.
     
  12. jokerjkny

    jokerjkny

    Jan 19, 2002
    NY / NJ / PA
    ...and the spacegoat strikes again... ;)
     
  13. 44me

    44me

    Jun 17, 2002
    Bedford, NH USA
    Tubes are certainly noisier than transistors as The General points out, so when I see comments about hearing some hiss, I think that’s perfectly understandable. Everything we’ve got plugged into the board contributes some amount of hiss. The buzz, or hum, is more of an interference or susceptibility problem, depending on whether you want to blame the thing creating the undesirable signal or the circuit picking it up.

    I have not tried using a good quality line conditioner. That seems like an excellent idea. Swapping preamp tubes also seems like a pretty easy thing to try although this doesn’t seem like a failing tube problem (as I’ve said, the tone is excellent). I also could try running the amp through an isolation transformer, but that would be just to prove a point. I should also point out that we are using lots of other tube equipment (mic preamps and guitar amps), and none exhibit this level of hum. I’m sure its there, but it’s so low that it’s obscured by the hiss. On the other hand, I don’t even hear the hiss from the amp, as it’s obscured by the hum. If this were an old piece of vintage gear, I would just blow this off as part of the price of admission, but the DB 359 is a modern design, it’s extremely well constructed, and it’s made by one of the more respected companies in the business.


    By the way, thanks for all the great feedback! I’m new to this site. I just discovered it a few weeks ago. It’s great to be able to talk to so many other bass players!

    - John
     
  14. lneal

    lneal

    Apr 12, 2002
    Lee County, Alabama
    I have to say:
    Tubes by themselves are not inherently noisier than transistors. Tubes operate at much, much higher impedances than transistors and therefore are more susceptible to picking up noise, especially the man-made type. Also, when you have several hundred volts present, as you do with tubes, it magnifies the problem. That is why they are percieved as noisier. I have heard a couple of high end all tube home stereo systems that were dead quiet.
    In fact, if you could get rid of all outside electrical interference, you would still have a low level of hiss. Why? Because electrons make noise when they rub against each other, much like people in a crowded hallway. That's right!
    And, think about this: in transistors, electrons pass through a solid matter, and in tubes they pass through empty space, a vacuum. Think about that!
     
  15. 44me

    44me

    Jun 17, 2002
    Bedford, NH USA
    Ineal, that’s a good point. Noise and unwanted signal pickup are often simply called noise, but this oversimplification is really only a reasonable term for the end result. As you’ve pointed out, the causes are much different. The problem with this amplifier is that it is either generating too much of an unwanted signal (60Hz and harmonics from the power supply) for the preamp to adequately reject, or the preamp is overly sensitive to this unwanted signal for the intended purpose (recording in this case). What I want to know is, is this a shortcoming of the design, or this particular unit (bad part, connection, etc.).

    The General’s response from Aguilar tech support, as well as my own, is leading me to believe that this is a characteristic of the amplifier design. A higher end approach, with a completely separate preamplifier and power amplifier, makes it a lot easier to get good isolation between the circuits generating unwanted signals, and those most susceptible to them. For my recording situation, I wouldn’t even have the power amp turned on.
     
  16. lneal

    lneal

    Apr 12, 2002
    Lee County, Alabama
    I tend to get a little technical sometimes, but I do realize the need for generalizations. Forgive me. And noise is one of those broad terms that must be generalized. Anyhoo, I am not familiar with Aggies and their design philosophy, so I can't really offer any specific help on it, just, well, general suggestions that apply to tubes. I have played through a couple of Aggies here and there and I have always dug their sound. It just seems strange that a quality piece would be too noisy to record with unless there was something wrong. And watch out rubbing up against those electrons!
     
  17. Chuck M

    Chuck M Supporting Member

    May 2, 2000
    San Antonio, Texas
    I played through a DB 359 when they first came out and it did not hum. There may have been some hiss present but my high frequency hearing is damaged so I might not have heard it if it were present.

    I'm puzzled by the response you got from the factory. Aguilar equipment is aimed at the Pro market and many pros use them for recording. You'd think the factory would be eager to solve problems like this.

    Tube circuits can be noisy, however, they can also be very quiet. Check out an older Demeter VTBP-201 in good shape. They sound great and are dead quiet.

    The first thing I would try is changing out the preamp tubes. I'm not sure what the tube compliment is in the 359, however, it probably has 12AX7/7025's and maybe a 12AU7 or two. If it has only 12AX7's just get one good 12AX7 and try it in each slot to see if the hum goes away. Do the same thing with the 12AU7 if it is used in the preamp.

    If that does not help, sounds like a tech may be your best bet. I'd be tempted to try to convince the factory that it would be cool for them to help you out. This kind of thread can cause a lot of potential buyers to look elsewhere and the folks at Aguilar surely know it. I've heard good things about the guys at Aguilar so I'd sure ask them for some help if the preamp tube swap does not help.

    Good luck to you and feel free to email me if you have other questions.

    moses@compuvision.net

    Chuck
     
  18. I said it probably isn't a tube problem....:D
     
  19. lneal

    lneal

    Apr 12, 2002
    Lee County, Alabama
    Yea. We are all mindless Groove Tube drones. I wouldn't put one of those sh***y tubes in YOUR amp! We were just trying to help the man out with a little friendly advice. I'm an electronic tech with more than just a pedestrian knowledge of tubes and tube circuitry, not some mindless Pittman drone! And if you don't know that a bad tube can cause hum....

    I believe I told him to take it to a tech, didn't I?
    I also said I wasn't familiar with aguilar circuitry, too.
     
  20. bassmonkeee

    bassmonkeee Supporting Member

    Sep 13, 2000
    Decatur, GA
    You said that better than I could. I just wish I had it all figured out like Psycho Bass Guy. He's my hero. He knows everything about everything. :rolleyes: