EH Memory Man needs repair...any techs in Canada? | Page 2 | The Canadian Guitar Forum

EH Memory Man needs repair...any techs in Canada?

Discussion in 'Effects Pedals, Strings and more' started by 335Bob, Dec 15, 2009.

  1. 335Bob

    335Bob

    Joined:
    Feb 26, 2006
    Location:
    Buckhorn, Ontario
    Opened it up, nothing looks amiss. I tried taking some pics, they come out too fuzzy for diagnosis of anything. Definitely this one has the MN3005 chips. The board looks clean, no damage or loose wires. I didn't think I'd see anything. This pedal has been in the center of my board and pretty much shielded by the other pedals on the outer perimeter. So it still looks new.

    I appreciate your offer to look at it. I won't be able to come by during the holidays. Just too crazy around here, leaving very little time. The only way I could get it to you is by mail with return postage included. If you think you can fix it, I'd be more than happy to cover your time/parts. I understand if you don't have the time. I hardly have time to do any of my own projects. Again, I appreciate everyone's offer to help out with this.


    Thanks,
    Bob
     
  2. mhammer

    mhammer

    Joined:
    Nov 30, 2007
    Location:
    Ottawa, Ontario
    So 2 MN3005 chips?

    I'll dig around for a schematic and try and make some productive suggestions for what to look for as preliminary troubleshooting.
     
  3. 335Bob

    335Bob

    Joined:
    Feb 26, 2006
    Location:
    Buckhorn, Ontario
  4. Rwinder

    Rwinder

    Joined:
    Oct 19, 2008
    Location:
    Calgary, AB
    hey just a little heads up

    If your thinking of replacing your DMM there is one in spaceman music ottawa for $189 which is a smoking deal, it looks mint. didn't play it though...
     
  5. mhammer

    mhammer

    Joined:
    Nov 30, 2007
    Location:
    Ottawa, Ontario
    Well that's one of them, at least.

    Does the chip complement appear to be the same as yours? If so, then you will see there are three trimpots visible in the bottom part of that schematic. The one on the far left (100k) sets the bias voltage to the BBD. The bias voltage needs to be set right. A little on the high or low side, and the chip will pass signal but in a distorted fashion. If higher or lower than that, the chip stops passing signal. It isn't fried, necessarily, just not working right under those conditions. frequently, complaints about broken or disappointing delay pedals, flangers, and chorus pedals come down to that adjustment. happily, it can be tweaked all over the place wiothout destroying anything. The worst that will happen is you'll lose track of the sweet spot and have to find it again. Pros will look for the sweet spot with a scope and signal generator, but you can do it by ear and have 98% the precision of a scope job. Note that there is a 100k bias trimpot for each MN3005. (check to the far left of the schematic)

    The MN3005 has essentially two pathways internally, one driven by the "tic" from the clock generator, and the other driven by the "toc". Put them together and they make a complete picture of the signal. They need to be in proper proportions to do so, though. Some manufacturers achieve that balance through equal-value fixed resistors, and some through trimpots. EHX uses trimpots here (the 5k unit). When the balance is not spot on, the clock signal can become more audible (whine). Like the bias trimpot, you can tweak them all over theplace without damaging anything, you just lose the sweet spot.

    Finally, most BBD chips will introduce some difference in output signal level, relative to input. EHX tries to maintain level balance by sticking in an op-amp stage between and after the delay chips to bring the signal up to unity gain level. That would be the other 100k trimpot (shown lower right). Like the other two, it can be tweaked to your heart's content, and all you stand to lose is the sweet spot.

    As for the malfunctioning of the Blend control. That may be as simple as just replacing the pot with another 10k unit.
     
    Last edited: Dec 18, 2009
    1 person likes this.
  6. Voxguy76

    Voxguy76

    Joined:
    Aug 23, 2006
    Location:
    Halton Hills, ON
    Bob,

    The least of your worries i'm sure but Customs should have only charged you on the price of repair job and even thats iffy. If you decide to send it back to the states for repair, before you send it back go to your local customs office and bring the pedal with you. Ask them for a Y38 for a temporary exportation for repair. They will probably affix a small serial number sticker on the pedal and stamp the green card. Its just proof that you owned the item prior to it re-entering Canada again. No Officer in his right mind will charge you again upon its reimportation..
     
    2 people like this.
  7. hollowbody

    hollowbody

    Joined:
    Jan 14, 2008
    Location:
    Toronto, ON
    Hey thanks for the info! I got dinged with customs for a Sparkledrive that was being repaired for me, and I did some yelling but got nowhere with it. I'll definitely remember this next time!
     
  8. Rwinder

    Rwinder

    Joined:
    Oct 19, 2008
    Location:
    Calgary, AB
    Great info, i was thinking about this but wasn't sure how to get it done.

    thanks
     
  9. gtone

    gtone

    Joined:
    Nov 1, 2009
    Location:
    Moose Jaw, SK
    It was those fargen bastage Canada Customs dudes playing your DMM that messed it up! 9kkhhd
     
  10. Ringwraith

    Ringwraith

    Joined:
    Nov 17, 2007
    Location:
    GTA Ontario
    Hey guys
    I know this is an old thread but I was wondering how ya made out with your DMM??
    I'm wondering if mine needs tweaking. It's working ok but the delay seems pretty hissy.
    Maybe that's part of the mojo but I wonder if it can be cleaned up at all.

    Cheers
    Sean
     
  11. mhammer

    mhammer

    Joined:
    Nov 30, 2007
    Location:
    Ottawa, Ontario
    1st and 2nd generation delay pedals were generally hissy. There are ways to deal with the hiss, but they tend to deviate from the original design. To some extent, it would also depend on the circumstances under which it becomes hissy. For instance, a typical DMM of that era would be more noticeably hissy at the longest delay time and most feedback/regeneration. One of the issues made without a compander chip would also be noticeably hissier than an issue with one. There are also issues that have small gain trimpots inside that bring the level up to an optimum for the next delay chip, in order to maintain maximum S/N ratio. So, the hiss may not be a permanent aspect of the design but simply the result of some drift in the fine-tuning over the years that can be easily remedied with a small screwdriver.

    Do you experience objectionable hiss ALL the time with it?
     
  12. Ringwraith

    Ringwraith

    Joined:
    Nov 17, 2007
    Location:
    GTA Ontario
    Heya MHammer, thanks for your reply!

    My DMM PCB says EC2002_Rev_D
    There are 7 trim pots, it's an adapter powered pedal.
    It has the 4 MN3008 & 4 CO4558N chips.
    It also has 2 other chips...
    Philips SA571N / J81874 / Jnr0209 Q
    HCF 4047BE / W99180352 Malaysia (under pot)

    [​IMG]


    I recorded some sound files to demonstrate the noise.
    The unit works pretty good besides the hiss I'm wondering about.
    The files are recorded going into my Chandler TG2 direct inputs.
    Left is the echo out only & right is the direct out.
    There is quite a bit of hiss on the echo out even when not playing/delaying.

    While the hiss is more noticeable at longer delays (460ms)
    I also hear it on shorter ones & when not playing.
    I recorded a few examples so hopefully you'll be able to hear if it's normal
    or it could use a tweak. I couldn't find a schematic that has my chip layout
    so I'm not sure which trim pot does what & don't want to fiddle until I'm sure.
    I have no problem changing out parts if needed, I've built a few pedals/tube amps
    & recording gear so if there are other mods that may help let me know. I read that
    changing the 4558's may help clean it up. What do you think?

    Thanks again
    Sean

    DMMNoise01.mp3
    DMMNoise02.mp3
    DMMNoise03.mp3
    DMMNoise04.mp3
     
  13. mhammer

    mhammer

    Joined:
    Nov 30, 2007
    Location:
    Ottawa, Ontario
    I'm unfamiliar with that particular issue, but a few things are immediately apparent from the sound files. One is that the hiss is pretty much 95% from the delay path. On that last sample you can almost hear the hiss pulsing with each repeat. It would appear to be an issue from the "turn of the century", when the world's supply of MN3005s had pretty much dried up, but MN3008s were still around in reasonable supply, and Coolaudio hadn't started producing MN3205 clones yet.

    As to what the individual trimpots are for, there is a lot to mull over. Typically, there will be one trimpot for adjusting the bias voltage at the input to the BBD. When there is more than one BBD (and this one has 4 MN3008s, for a total of 8192 stages), sometimes the designer assigns one per BBD, and sometimes they use only one and share the bias voltage with all the chips. It is also a common practice to fine-tune the balance of the two complementary outputs from each BBD to optimize the cancellation of the clock signal (a major source of hiss), though some designers decline to do so, preferring instead to simply use two same-value resistors on the BBD output. It was also the case that EHX elected to insert an op-amp gain stage between BBD chips in series, to compensate for the fact that BBDs can lose a bit of signal, and included a trimpot to set the gain of that recovery stage. Finally, it is also common practice to include a) a master clock adjustment trimpot to set the maximum delay appropriately, and b) a feedback trimpot to bring the maximum feedback setting just up to the point where you get lots of repeats but not easy or unstable oscillation.

    So, with so many possibilities, and so many trimpots, it is difficult, in the absence of a schematic and parts layout, to say what each of them does. The picture I'm including here, that was part of a thread where I answered questions on this very pedal about a year ago, shows two ways in which this was done. The top is for the 4xMN3008 issue and the bottom is for the 2xMN3005 issue that preceded it. I can't vouch for its accuracy, but what we see here is 7 trimpots. Starting from the left, there is a 100k bias trimpot feeding the input pin of the MN3008, but a pair of 2k4 resistors are used to balance the outputs. Then we have an op-amp feeding the 3rd MN3008, with a 100k gain-setting trimpot and another 100k bias trimpot. That 3rd MN3008 also uses a pair of 2k4 resistors tobalance the outputs, but the fourth MN3008 has, you guessed it, a 100k bias trimpot and a 5k pot to fine-balance the outputs, in stead of a pair of 2k4 resistors. Why they have been content to do the fine balancing for one chip but not the others is beyond me, since they are contribute clock noise that needs to be "nulled" out. But like I say, I can't vouch for the accuracy of the schem provided, although I suspect it probably is accurate. The 7th trimpot shown brings the level of the delay signal back up again.

    The diagram shows the pins that each trimpot connects to, and their value (remember that 100k = 104 markings on the trimpot), so you can confirm for yourself if the diagram corresponds to your unit. If it does match what you have, then it may well be that the 5k balancing trimpot is your prime target. Never having used one of these pedals close-up, I have no idea if the noise level can actually be imporved upon, or if yours is noisier than the majority.

    As for the 4558 chips, yes there are better chips on the market, and they might conceivably reduce some hiss, but I suspect the hiss you hear is largely from the clock and from a mis-adjustment of the balance trimpot/s.
    [​IMG]
     
  14. Ringwraith

    Ringwraith

    Joined:
    Nov 17, 2007
    Location:
    GTA Ontario
    Ok (wow lots of info thanks!!)

    Looking at the end of that top schematic, it corresponds to my layout.
    The R,C,U numbers aren't totally accurate but the values & connections are.

    So I can turn the 5K pot without messing things up?? What about that last 100k pot?

    Cheers
    Sean
     
  15. Ringwraith

    Ringwraith

    Joined:
    Nov 17, 2007
    Location:
    GTA Ontario
    Ok the suspense was killing me so I went ahead & played with the 5K & 100K trims... :)

    The 5k was set in the middle, going either way didn't realy affect the hiss but introduced
    a faint high pitched frequency. So I guess it's set at the optimal level in the middle. The 100k
    after that 5k brought up the overall volume but the S/N ratio sounded the same I believe. It did
    drive the feedback a lot harder so raising this pot made me lower the feedback level in order to
    control it. The 100k pot was set "just" past it's lowest setting & I've put it back pretty much there.
    It seems to me the noise is coming before this stage.
    Any suggestions? ;-)

    Sean
     

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