Eric Clapton Mid-Boost Problem

Discussion in 'Tech-Talk' started by tanner0614, Jul 21, 2012.

  1. tanner0614

    tanner0614 Strat-Talk Member

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    I just had my Strat routed out to fit the mid boost by a local luthier and he said that he could do all the electronics himself but he wasn't familiar with the mid-boost so I assumed he would be fine and he could manage. I have a few problems though. When the boost knob is all the way down to 0 or 1, I get no signal at all even with my volume all the way up. Then when i have my volume all the way down and the boost up i can still hear it through the amp although it's not loud at all. It's not that much of a problem but i just didn't think something was right. I just had a lesson today though and my teacher plugged it in and said something isn't right since the fender blues deluxe was at 10 and it just wasn't loud, especially when he plugged in his Strat to compare so he's having his friend look at it who's good with electronics. Can anyone tell me what's wrong with it possibly? A wiring problem or something? I don't know anything about electronics so any help is welcome. The pickups are also Vintage Noiseless like Clapton has so it's the whole set up if that matters at all.
     
  2. blackstrat

    blackstrat Senior Stratmaster

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    The mid boost kit comes with a full installation diagram so it shouldn't have been very hard to get it working right. Just in case, here is Fender's EC strat schematic: http://support.fender.com/service_diagrams/stratocaster/011-7602A_SISD.pdf

    If you are handy with a soldering iron, you could pop up the pickguard and compare the wiring to the schematic above in order to locate (and fix) the fault. Alternatively, print the diagram and take it along with the guitar to your tech and he should be able to fix it without any extra charge (it is his fault after all).
     
  3. guitargeekaz

    guitargeekaz Senior Stratmaster

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    I would do like blackstrat said. Print the diagram and take it back. I'm far from a luthier, but I've wired up a clapton mid boost myself.
     
  4. tanner0614

    tanner0614 Strat-Talk Member

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    Yeah he still has the diagram cause he wanted to keep it in case a customer comes in with a strat that has one so he can refer back to it but I've never soldered anything in my life and so I'm planning on having someone work on it. Have y'all had any problem similar to this?
     
  5. Electgumbo

    Electgumbo Not Of This Earth

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    I have a kit in one of my guitars. I seem to recall a problem with the diagram. It had something left out. But I got mine to work just fine. Sorry I don't remember what the issue with the diagram was.
     
  6. Carlsoti

    Carlsoti Senior Stratmaster

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    If the guy has lutes, violins, harps, etc in his shop, don't be too surprised if he doesn't know electronics. This is where a "tech" would come in handy. I have yet to meet a guy that can build an amp but can't wire up a guitar.
     
  7. tanner0614

    tanner0614 Strat-Talk Member

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    He said he noticed that and he had to call Fender but they were being asses cause he's not a "certified fender repairman" or something stupid like that so they weren't really a help at all but he said he figured it out but he may have done it wrong anyways
     
  8. tanner0614

    tanner0614 Strat-Talk Member

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    It's like you know what the inside of his shop looks like haha but yeah my instructor's friend is a tech so hopefully he can find the problem but i'm kinda mad that i spent $200 on the luthier to do the work and it seems pointless to take it back even though he'll do it for free but if he didn't get it right the first time how would he get it the second time around.
     
  9. blackstrat

    blackstrat Senior Stratmaster

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    I would still advise you to do a comparison between your actual wiring the diagram supplied in my previous post. This this is the master production drawing for the guitar (which also contains the same pickups) and it might actually be different than the one supplied with the kit. It won't take you more than 10 minutes to take the strings and pickguard off and make the comparison and it might save you from a lot of trouble.
     
  10. tanner0614

    tanner0614 Strat-Talk Member

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    I would but I left it at my instructor's place but if the problem is still there after everything is checked then I'll make sure that I look it over. I have the site you posted bookmarked on my tablet so it won't be going anywhere
     
  11. tanner0614

    tanner0614 Strat-Talk Member

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    I just got a call from my instructor saying that he got it fixed for $50 but apparently it wasn't wired correctly at all
     
  12. Electgumbo

    Electgumbo Not Of This Earth

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    So how do you like it now??
     
  13. tanner0614

    tanner0614 Strat-Talk Member

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    it's absolutely amazing. unfortunately i don't have a nice fender tube amp to play with at home but when i go over to my instructor's and play through his blues deluxe it sounds great.
     
  14. Electgumbo

    Electgumbo Not Of This Earth

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    Yeah it's pretty cool!!!
     
  15. franblanc

    franblanc Strat-Talk Member

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    Guitar Pre Amp – Fender Mid Tone Boost Kit Problems

    The featured Fender Mid Tone Boost Kit was installed in 2008 inside a 1992 Fender Stratocaster American Standard. However the result was lot of unpleasant distortion and noise. This is a common complaint with the pre amplifier which is marketed as a Fender product. It was purchased off of ebay from a reputable Electric Guitar Parts dealer who is still trading. Recently it was decided to examine the preamp to see if it could be improved.

    The preamp has a circuit board which is usually branded with “Fender” however this board does not have any markings. The second thing I noticed is that the AC bi polar (+ -) capacitors marked with yellow arrows are not audio caps. They are 10uf 25volt capacitors made by “United” which might be Chemi-Con. I decided to replace these with Nichicon UFW Audio Caps because these capacitors receive the Alternating Current signal directly from the pickups.

    There were also three NPN transistors marked MPS A18 701 in the positions marked with red arrows. These transistors have the job of boosting the gain of the guitar signal in three stages. On the layout diagram for this circuit board they are represented as 2N6429 TO-92 transistors but on the circuit board the components were MPS A18 701, both types are NPN. I replaced them with new transistors (MPS A18). The new transistors had a hFE (gain) value of 470 – 500, which is expected from this type of transistor. Whereas the old ones that I removed had a hFE of 150 to 170. This is alarming because it is possible that one transistor drifted over the years but it is unlikely that all three drifted to the same extent. It is possible the pre amp was made with a bad batch of transistors but it is equally possible that it was a counterfeit Fender product not subjected to the same testing or quality control. Because of this it was decided to replace the PNP transistor 2N5087 marked at the top of the image. The old one measured 400 hFE and its replacement measured 500 hFE so the old transistor was actually alright. I tested all the resistors and they appeared good. Four of them were lifted to test them out of circuit to make sure. Lastly I tested the yellow polyester DC caps with a multimeter and they too appeared to be well.

    The guitar was reassembled and tested and the sound was much improved. The gain is audible but the noise is gone and the clarity of the tone is much better. It should be noted that most of the grounding connections inside the guitar were re-soldered and the red power lead from the 9v battery was reattached more firmly. The battery itself was insulated and the entire preamp was placed inside a small anti static bag for safety. Lastly the guitar cavities were shielded with copper foil to eliminate hum. One conclusion is that there may be bad circuit boards on the market which might possibly be fixed by replacing the transistors and electrolytic capacitors. If you have a Mid Tone Boost kit and the sound is poor, then this might be the reason. I have included the only image I could find of the layout and component list for the Mid Tone Boost Kit as a guide. There are a number of compatible equivalent transistors for the 2N6429 (MPSA18) and the 2N5087. The only stipulation is that the former must be NPN and the latter PNP (Positive Negative Positive). Fender_Pre_Amp.jpg
    eclayout.jpg
     
  16. tinkertoy

    tinkertoy Strat-O-Master

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    Glad you got it worked out.

    I was told the clapton circuit boards are somewhat fragile.

    Mine was purchased/wired from 920d (I was lazy, and couldn't find my soldering iron) I had midboost pot issues as well.

    Mine was intermittent in function. I traced the wiring to no avail. I ended up replacing the pot with a 250k audio pot, which works fine.

    Why is it so hard to find 250k linear pots? Gfs has them.
     
  17. Lonn

    Lonn Mod Admin Staff Member

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    Admin Post
    Replying to an EIGHT year old thread?
     
  18. franblanc

    franblanc Strat-Talk Member

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    Will I start a new thread with this post? What do you recommend? I think it is informative....