Home › Forums › Help/Technical Questions › Convert old Deluxe Memory Man from AC to DC power

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  • March 15, 2009 at 6:05 pm #77898
    riversitter
    Member

    Hello all-

    I have an old Deluxe Memory Man. I think it’s an early 80s model. Anyway I would like to convert it from using AC power to DC for 2 reasons: (1) It’s noisy in a ground loop kind of way. (2) I would love to power it from my Voodoo Labs Pedal Power II.

    I have done a lot of mods on guitars, amps, and pedals before but I’m really more of a “following instructions” guy than a tech myself. So when I have to figure out technical things out for myself I’m afraid I’m usually not very good at it.

    Here is how I understand the power supply of my old DMM. Please correct me if I am wrong.

    1. 110 VAC is supplied to the internal transformer
    2. Transformer steps this down to 24VAC
    3. Bridge Rectifier (CSC B20S) converts 24VAC to DC. However, I’m not clear about the voltage coming out of the BR. I am terrible at understanding schematics but it looks like the circuit should be using 15VDC. Is this regulated by the 2N6111, the BR or something else? I’m lost at this point.

    Here is what I am proposing to do to convert to DC power.

    1. Disconnect the internal transformer
    2. Attach a DC power jack to the chassis
    3. [ERROR] Run the green wire from the PCB (which I am assuming is ground) to the sleeve of the DC power jack.
    4. [ERROR] Run the brown wire from the pin of the DC power jack through the slide switch and attach it to one of the bridge rectifier’s output legs. This would supply 24VDC to the circuit so I think there will need to be something regulating this down to 15VDC. I can’t find any info about this point.
    5. Use a 24VDC external transformer with a positive pin/negative sleeve.

    Below is a crude diagram of the old AC power supply and my proposed new DC power supply.

    DMM_DC_convert_mod.png

    Here are a couple of pics of the relevant section of my PCB:

    DMM_bottom.jpg

    DMM_top.jpg

    Am I missing something here or do you techs around here think this makes sense?

    I found a couple of interesting and related topic here but nothing that really lays it out for an amateur like me…

    http://forums.vintageamps.com/viewtopic.php?f=6&t=78012&start=0
    http://archive.ampage.org/threads/0/fxgen/000460/Re_EH_Memory_Man__Electric_Mistress_voltage_supply-1.html
    http://archive.ampage.org/threads/6/fxgd/321081/different_EH_Memory_Man_schem-1.html

    Any help would be appreciated. If I am way off let me know. I won’t be surprised.

    Thanks.

    EDIT: Edited to notate errors.

    March 15, 2009 at 6:56 pm #94544
    The EH Man
    Moderator

    The vintage 5-knob Deluxe Memory Man uses a positive ground power supply. You’ll need to reverse the red and green wires coming off the jack. The red wire goes to the LED and the green wire to the rectifier pin.

    March 15, 2009 at 8:20 pm #94545
    riversitter
    Member
    Quote:
    The vintage 5-knob Deluxe Memory Man uses a positive ground power supply. You’ll need to reverse the red and green wires coming off the jack. The red wire does to the LED and the green wire to the rectifier pin.

    Thanks for the reply EH Man. So I guess I’m not completely off-base in the way I am approaching this. I think I understand “positive ground” now after a little research. I have updated my drawing to reverse the positive and negative coming from the DC power supply.

    DMM_DC_convert_mod_02.png

    I think my primary question now is what regulates the power to -15V which is what appears in the schematic? Is it the 2N6111?

    Thanks again.

    March 15, 2009 at 8:42 pm #94549
    The EH Man
    Moderator
    Quote:
    I think my primary question now is what regulates the power to -15V which is what appears in the schematic? Is it the 2N6111?

    Thanks again.

    Drawing looks fine now. The 2N6111 is used for regulation, but it’s not an actual regulator. The combination of parts connected to it forms what’s called a “series regulator” circuit. Let us know how it turns out.

    March 15, 2009 at 8:49 pm #94550
    riversitter
    Member
    Quote:
    Drawing looks fine now. The 2N6111 is used for regulation, but it’s not an actual regulator. The combination of parts connected to it forms what’s called a “series regulator” circuit. Let us know how it turns out.

    Thanks again EH Man. I’m going to do this mod as soon as I get a power jack. I’ll come back and let you know how it sounds after the mod. I am crossing my fingers that some of the hum goes away since I really love the tone of this pedal.

    March 22, 2009 at 10:04 pm #94795
    riversitter
    Member

    Update:

    Well, unfortunately wiring up things as shown in my last diagram did not work for me.

    I bought an Electro-Harmonix 24VDC 100mA (positive tip) wall wart and tried it after making the mods but no joy. No power LED and no working effect from the pedal. Bummer.

    I also noticed the Electro-Harmonix wall wart is putting out 32VDC instead of 24VDC.

    As an alternative I am considering using a 24VAC wall wart and hooking up the AC output before the bridge rectifier as was the case with the internal transformer.

    I’m researching to try to diagnose the issue but I suck at troubleshooting. But I have been learning a lot. :facepalm:

    July 26, 2009 at 8:19 pm #99998
    Primus
    Member

    This was a really nice thread… What happened?

    I am looking at this thread myself and trying to understand whether the problem was in the plan or the execution. Did he apply +24V where he should have applied -24V? I’d like to do this myself and make it into a photo essay. Could someone take a second look at this and make sure the logic is correct?

    J

    July 26, 2009 at 8:45 pm #99999
    riversitter
    Member
    Quote:
    This was a really nice thread… What happened?

    I am looking at this thread myself and trying to understand whether the problem was in the plan or the execution. Did he apply +24V where he should have applied -24V? I’d like to do this myself and make it into a photo essay. Could someone take a second look at this and make sure the logic is correct?

    J

    Hello J-

    I have not given up on this. My intention was to share more detailed instructions about this mod if I was successful. I do not think the issue is my execution. I am almost positive that somehow my logic is not correct. However, I do think the polarity in my updated post is correct. I think the issue may have something to do with the original power supply being dual supply voltage which I do not completely understand. I am thinking about trying the DC power before the rectifier rather than after to see what happens. I have been researching this but I just haven’t had a chance to pull out the soldering iron yet. If anyone has thoughts about this I’d be glad to hear them. Otherwise I’ll update this topic when I have anything new to report.

    July 26, 2009 at 8:58 pm #100000
    Primus
    Member

    Your documentation is great, so I’m sure you will get it working eventually. Looking at a schematic I found online, your approach makes sense. The way you are connecting the power to the LED, does it also provide +24V to the base of the 2N6111? I’m going to take a whack at this later, perhaps.

    J

    September 15, 2009 at 11:01 pm #101508
    riversitter
    Member

    One last update for closure.

    I reverted my mods back to use the original internal transformer and everything still works fine. So the good news is apparently I didn’t fry anything. The bad news is the pedal is still noisy whether on or off. So for now I’ll be using a true-bypass looper and when I get some time I’ll pursue this idea again or maybe send it to a pro for some kind of noise reduction solution. Or maybe I’ll just spring for a Memory Boy and save some pedalboard space…

    December 9, 2009 at 12:44 am #105027
    petejt
    Member

    I need to get this done for my Deluxe Electric Mistress, as I want to eliminate using my step-down transformer.

    This thread will come in handy, thank you!

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