Saturday, 4 February 2012

Skreddy Screwdriver Deluxe

Get your big boxes out for this 5 knobber! :o)



Although having said that it is only 21 columns wide and so will fit into a 1590B if you're feeling adventurous (and you're more precise with your measurements than I am)

28 comments:

  1. just tried it. no luck yet. might have a troubleshoot this arvo.

    ReplyDelete
    Replies
    1. I'm pretty sure someone on the BYOC forum built this one successfully so I think it should be verified. Send me a front and back pic if you want and we can see if the extra set of eye can pick something up.

      Delete
  2. trying to do a 4-knob one without the brilliance. what should i be wiring to just leave it maxed at 0k instead of 2k?

    ReplyDelete
    Replies
    1. The Brilliance pot is basically a lowpass filter in conjunction with the 3.3n cap. If you want to omit it that's no problem, just take the wire connection for Brilliance 1 & 2 directly to Volume 3. The existing Brilliance 3 / Volume 3 wire can be removed completely, as can the 3.3n cap if you can be bothered desoldering. There's no problem leaving the cap in-situ if you want though because it won't be making any electrical connection to anything anymore (other than ground).

      Delete
    2. Ooh, just noticed you said 2K, the Brilliance pot is 100K. Do you mean Pre-Gain?

      Delete
  3. Just built this and it works perfectly, cheers for another great layout Mark.

    I've built one before using a schem from freestompboxes that's since disappeared, so this one came in handy.

    Last time I used an AC176 for the germanium transistor, and my two builds sound exactly the same, so that's a good sub if you can find one.

    ReplyDelete
    Replies
    1. That's great, glad you're finding the layouts useful, and thanks for the transistor info

      Delete
  4. so this is a Positive ground circuit right? just use a battery?
    I have some russian gt402 germanium's that are supposed to be kinda like ac127's. (anyone know if that's true at all?) Is there a gain range recommended for any or all the transistors on the board?

    ReplyDelete
    Replies
    1. No it's negative ground. The AC127's are NPN so you'd want some GT404B's rather than GT402B's. The GT404B's that I have had have been very hit and miss though in terms of leakage, so I'd suggest looking at the MP38's instead. They're lower gain but very low leakage.

      Delete
  5. Hmm. Seems like missing "Verified" tag on this one :)
    +m

    ReplyDelete
  6. I've used an AC187. Sounds great! Thanks for the layout!

    ReplyDelete
  7. i see all these recommendations for transistor model numbers, but no recommendations for hfe... anyone?

    ReplyDelete
    Replies
    1. Google is your friend: http://www.diystompboxes.com/smfforum/index.php?action=printpage;topic=76199.0
      +m

      Delete
  8. Just built this one and it sound fabulous. The only issue is the master volume. I have to have it cranked for unity. Any ideas on how to increase the volume?

    ReplyDelete
    Replies
    1. Assuming you've checked for the usual dodgy solder joints and unwanted bridges, have you socketed the transistors? And if so have you tried swapping another germanium? With the exception of a few Russian ones, the vast majority of NPN germanium transistors that I've bought have been a crap shoot. What voltages are you getting at the transistor pins just to see if anything stands out.

      Delete
    2. Hi IvIark.

      Double checked all the joints and no bridges.

      Q1
      D: 6.65
      G: 4.02
      S 1.969

      Q2
      C: .579
      B: .547
      E: 0

      Q3
      C: .878 and continually increases
      B: .575
      E: .497

      I used an AC127 from Pedal Parts Plus ($4!). Its HFE measures 92.

      Again, it sounds exactly like it should -- I own a real Screwdriver. The only issue is the overall volume.

      I'm guessing it might be Q3 but I don't have any others lying around right now. I think I may get a few AC187s, OC140s and CV7112s and try them out.

      At the end of the day it's not a deal breaker since I usually play at unity volume. It would be nice to be able to turn it up past that though.

      Delete
    3. Yes something doesn't sound right with Q3. If it's increasing it suggests a problem with the resistors supplying it (2K7, 8K2 or maybe the 100n from that junction), or more likely the transistor itself. Do you have a silicon transistor that you can try in that spot? It may not sound right because it won't be properly biased, but if that gives you a volume boost then you know the transistor is responsible.

      And if you want some NPN germanium transistors I can highly recommend the Russian MP38A. It's the only NPN germanium transistor that has ever had any consistency for me. Out of a batch of 50 the gain ranged from 54 to 90, and all were very low leakage. NOS Newmarket transistors, particularly NPN ones have been very expensive gambles for me in the past, and the chances are you're more likely to get a duff one than one with perfect gain and leakage. Unless they've been measured beforehand and are guaranteed to meet that spec, I just stay away from them now.

      Delete
    4. Yep -- it was Q3. I put a 2N5088 in it just to see what would happen and it almost blew my head off! :D

      Think I'll go with an OC140.

      Thanks for the help!

      Delete
    5. Yep -- it was Q3. I put a 2N5088 in it just to see what would happen and it almost blew my head off! :D

      Think I'll go with an OC140.

      Thanks for the help!

      Delete
  9. Do you reckon you could use a very low gain silicon transistor in Q3? All my npn germaniums are either around 10 hfe, low leakage or 150 hfe with high leakage. Just a thought......
    I did order some new ones from russia but they never made it to Oz. Must have had a stopover at Germania (ok, that was BAD!!), hehheh.
    Cheers for any help at all.

    ReplyDelete
  10. This comment has been removed by the author.

    ReplyDelete
  11. I just put one together, but at the moment the output is below unity gain. If anyone were able to post voltages from a working board, I would be grateful. I've been over the board several times. All the joints are good, no bridges, etc... I'm guessing it might be an issue with one of the transistors.

    ReplyDelete
    Replies
    1. I have it sorted at this point. Thanks.

      Delete
    2. What was causing the problem with your pedal? I am facing the same thing now. Volume is below unity. I have tried 4 ac127 but there is no difference. Thanks

      Delete
  12. Is the brilliance knob known to cause a volume change across its sweep? My pedal's volume is very low at the lowest brilliance setting and increases significantly as I turn it to max brilliance. I leave it at max now but its not very useful at other positions.

    ReplyDelete
  13. How would I sub the germanium for a silcon NPN transitor. Or do you have a layout of a great cranked tweed style od that is nice and saggy but it can't use a jfet. I don't have any j201 or equivalents right now. Tons of mosfets and npn transistors

    ReplyDelete
  14. AC127 (the germanium transistor) is NPN so you could just pop in a NPN silicon transistor. Just check the pinout of your transistor and follow the CBE labels on the layout.

    You might shoot for a relatively low hfe to approximate the performance of the AC127

    It's definitely worth buying some JFETs and germanium transistors in the future

    ReplyDelete
  15. Hi , Apart from the Cry Baby is there a pedal circuit that can be made to reproduce the Orca/seagull sounds in PINK FLOUYD ECHOS Album. I would really love to make a pedal that can produce this sound . Any ideas.

    ReplyDelete