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Raven Labs PHA-1 schematic?

Discussion in 'Amps and Cabs [BG]' started by metron, Feb 26, 2013.


  1. metron

    metron Supporting Member

    Sep 12, 2003
    Denver
    So I plugged the power supply into the wrong jack on the back on my Raven Labs PHA-1 headphone amp. Now there is no right output. :rolleyes: I think one or more of the op amps is toast but the surface has been scratched off all 4 in the unit so I can't identify the devices. I think there are 2 dual and 2 singles but I don't really want to guess.

    I searched high and low on the web for a schematic but came up with nothing. Anyone have a copy? :)
     
  2. metron

    metron Supporting Member

    Sep 12, 2003
    Denver
    Anyone? I called/emailed the place that supposedly handled the service for raven labs when they stopped production but i dont think they are around anymore either.
     
  3. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    I might be able to help if you take careful close-up pics of the top and bottom of the board. The reason is that singles and duals have different power supply pinouts. Singles are 7+ and 4-, while duals are 8+ and 4-. You might even be able to beep this out with an ohmmeter. Next, you can probably replace the op amps with any decent modern JFET type. If you install sockets, then you get more than one try. ;) Sockets also let you power up the board without the chips to verify that the supply voltages are up and running, before you commit the chips.
     
  4. metron

    metron Supporting Member

    Sep 12, 2003
    Denver
    Hey thanks for taking the time to post! Good news is all the op amps are socketed. I did test the supply pins which is how I figured there are dual and singles in there. The power supply appears to be in working order. I found some old parts I've had sitting around forever and I actually found a few burr brown op amps, one dual one single. Not sure if they are good or not though. I might have a chance to take it completely apart and snap pics tonight.
     
  5. gregbackstrom

    gregbackstrom Supporting Member

    Feb 3, 2005
    Tacoma, Washington
    I'm glad to hear that some other folks have these, and that repairing them may be an option. I'll have to unbox my non-working PHA-1 and remind myself why I stopped using it. I believe that the Aux input--or output-- stopped working. IIRC, the other functions worked fine.
     
  6. daveman50

    daveman50 Supporting Member

    Feb 24, 2007
    Westchester County NY
    I love my PHA-1. Too bad Steve retired.
     
    Jeff Scott likes this.
  7. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Burr-Brown (now TI) OPA134 (single) and OPA2134 (dual) would be a good choice. Mouser has them in plastic DIP, with quite a few in stock, suggesting that they are a widely used part. You should poke around the socket for the single, because they might be using pins 1, 5, and 8 for compensation. If you're unsure, you could lift those pins on the replacement chip when you insert it.

    @greg, the OP's problems notwithstanding, most gear problems are mechanical at the root cause level. Maybe the solder joints broke between the jacks and the circuit board. This could just require re-melting the solder. It's worth inspecting the entire board with a magnifying glass and bright flashlight for cracks or other damage.

    I am guessing that the circuit is a straightforward design, not exotic, but just good solid engineering and a high quality build.
     
  8. chucko58

    chucko58

    Jan 17, 2002
    Silicon Valley, CA, USA
    I paid for all my gear myself. Well, me and MasterCard.
    Francis's post gave me an idea: If all the chips are socketed, maybe the socket contacts have gotten dirty. At the very least, see what happens when you remove and re-insert each chip. That may be all it needs.
     
  9. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Worth a try. That's how most repairs went when I worked at a place that serviced Apple computers in the 80s.
     
  10. gregbackstrom

    gregbackstrom Supporting Member

    Feb 3, 2005
    Tacoma, Washington
    Thanks Francis! I'm still digging my HPF-3, BTW. It has become my favorite "instant lousy room rumble-remover"!
     
  11. metron

    metron Supporting Member

    Sep 12, 2003
    Denver
    Rise zombie thread! :eek:

    [​IMG]

    So I forgot about my broken PHA-1 headphone amp for a few years. Ok half a decade. I got it out of storage about a month ago and decided to give another shot at a fix. I tried a few op amps when I started this thread and concluded that one side of a dual op amp failed. One of them brought back the right output, but it was distorted. I couldn't remember which one I tried. Might have been a Burr Brown something or other.

    I dug through my stash of parts and tried a TI TL082CP dual JFET. BAM!! That did the trick. :woot: Beautiful pristine stereo output just like I remember when it was new. I feel sort of stupid that this thing collected dust for 5 years before I put effort into fixing it :meh: but I am ecstatic it's working again. I'm using it everyday for late night practice. :cool:

    IMG_3255.JPG
     
    Last edited: Oct 28, 2018
    wave rider, Jeff Scott and revroy like this.
  12. Jeff Scott

    Jeff Scott Rickenbacker guru.......... Supporting Member

    Apr 11, 2006
    I am using mine, right now. :thumbsup:
     
    metron and daveman50 like this.
  13. Sometimes our imaginations run riot over our common sense and we think something is massively wrong with our precious toy. :)

    Glad you got it sorted. :bassist:
     
    metron likes this.
  14. Leo Smith

    Leo Smith

    Oct 21, 2009
    Brooklyn, NY
    @metron thanks for starting and reviving this thread to share your experience. Is there any chance you can share an "under the hood" photo to show which opamp is the single and which is the double?

    I use my every day with much joy. I'm starting to notice a problem with the MIX L and R knobs. Starting from zero, one of them increases the volume smoothly and steadily, as it should be. The other one goes to nearly full volume as soon as it's cracked open from zero. Any thoughts or insight from anyone would be appreciated. I've tried cleaning the pot. Next I suppose I could try pulling and reseating the opamps?
     
    metron likes this.
  15. metron

    metron Supporting Member

    Sep 12, 2003
    Denver
    Thanks bassminpaul! :)
     
  16. metron

    metron Supporting Member

    Sep 12, 2003
    Denver
    Hi Leo,

    I will certainly pop it open this evening and post a pic of the insides. There are about 5 op amps inside, all unlabeled, and at least two of them are duals. My first instinct is that reseating them won't result in any change. You could try that but be careful because you can bend the pins in an instant, and they only bend back into place once or twice before breaking off. I wouldn't recommend that just yet.

    Based on your symptom, it sounds like that pot may have failed. That should be easily verifiable by measuring the resistance with a VM/DMM between terminals as the dial is turned. I would expect it to go from max resistance with the dial at zero to zero resistance at the point where you find the volume is maxed. Probably a cheap part and not hard to find, but might take a little effort to replace since it will it will require soldering the terminals to the pcb.
     
  17. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Likely a cracked (broken) pot element. Leave the opamps alone. Proper troubleshooting prevents new unrelated problems from being created.

    It's also possible that the pot got damaged from improper cleaning and the connection between one of the pots terminals and the resistive element's silver conductive ink got damaged.

    Generally, replacing the pot is necessary, but if that's a dual pot, it may have a custom taper.
     
    metron likes this.
  18. metron

    metron Supporting Member

    Sep 12, 2003
    Denver
    Well this is a good day. My technical advice is consistent with that of a real design engineer. :laugh: Thanks for chiming in Andy :)
     
    agedhorse and wave rider like this.
  19. Leo Smith

    Leo Smith

    Oct 21, 2009
    Brooklyn, NY
    @metron and @agedhorse thanks both for your input! It's been a small malfunction I can live with for now. I'm not in a hurry to fix it, but I'd rather have a solid tech do the work instead of doing it myself. However, I will check the pots with a meter. That's easy enough to do.
     
    metron and agedhorse like this.
  20. metron

    metron Supporting Member

    Sep 12, 2003
    Denver
    Here is a shot of the inside with the mix pots too, from the left are Mix R and Mix L. Marking on the pot says B50k. The rest is either 0135 or 0205, probably batch codes. This might be a suitable replacement

    Digikey B50k panel mount

    IMG_3257.JPG
     
    Last edited: Oct 30, 2018

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