Thursday 10 October 2013

DOD Studio Bifet Preamp / 410

Without the pseudo-balanced output and adapted to work as a stompbox. Not really sure if this is worth a build as it is supposed to be not that loud. Simple design with low parts count, so it might be nice thing to experiment on... The pot tapers are not mentioned on the schematic i found, but i suspect that linear should work well enough for both.



Posted by at 20:20
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34 comments:

  1. Unknown10 October 2013 at 21:30

    Hi Mirosol, This looks very interesting to me however Id like to have seen how the (Pseudo) balanced out would have worked in the circuit. I can think of loads of reasons. I may have to try it but id want to know how to reconnect that balanced out that you've ommited. Also what did you mean by "pseudo balanced output" ? Is it not really a balanced out ?

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    1. mirosol10 October 2013 at 21:55

      Schematic didn't have the output, so i'm not 100 percent sure how it's done. And no. According to forum posts, it is not really balanced.
      +m

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    2. Unknown10 October 2013 at 23:11

      Ok, Ive started the build anyway however Ive noticed the top right 4.7uF cap is sitting a trace cut ?

      Delete
    3. mirosol11 October 2013 at 06:29

      Damn. That cut should not be there. My bad. I can't fix it until monday..
      +m

      Delete
  2. Jishnu Dasgupta13 October 2013 at 10:27

    Mirosol, speaking of balanced wiring, could you try your hand at an active D.I schematic sometime? Would be interesting to have one of those put up.
    Thanks,
    J.

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  3. Unknown13 October 2013 at 15:31

    Theres one of these on sale on ebay right now with some really good photo's in good detail especially of the balanced out, I dont know if some of you folks on here might be able to pick out the detail of how the balanced out is connected up ?

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  4. Unknown14 October 2013 at 15:39

    OK Im giving up with this one. voltages at the ic were pin 2 - 4.69, pin3 - 3.31 and pin 6 4.69. No sound at all. I tried a tl071 amongst other single op amps while waiting on the 081.

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    1. mirosol14 October 2013 at 16:54

      Those voltages don't look too bad.. Have you tried probing it?
      +m

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    2. Unknown14 October 2013 at 20:45

      Unforntunately I dont have any thing I think that will do that, you mean like an audio probe/ oscilloscope ?. Just got a digimeter (DT9202).

      Delete
    3. mirosol15 October 2013 at 06:31

      http://www.diystompboxes.com/pedals/debug.html
      +m

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    4. Unknown15 October 2013 at 11:43

      ok feel embarrassed now, thats a great tool thanks Mirosol, wired it up and checked the circuit. There is sound at the chip and it is amplified at the other end.
      There is no signal beyond the 3.9M resistor at the bottom end.
      There is no signal on pin 2 of the volume but there is at pin 3.
      If you set the probe at pin 6 of the chip and adjust the tone, you get volume change.

      Delete
    5. mirosol15 October 2013 at 12:47

      No worries mate.

      You should have the output at the pin 6 and the "tone" seems to work also as intended. If you have the double link placed correctly, your signal should reach the output cap and go through it to the volume pot.
      +m

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    6. Unknown15 October 2013 at 15:15

      Yeap all good except Im starting to think there is a problem with the grounding in this, Ive tried various set ups but nothing seems to be letting the signal through to the output jack.

      Delete
    7. Unknown15 October 2013 at 15:33

      What I mean is with the probe the signal gets through the volume pot without the ground connected, as soon as you connect ground from anywhere you get no signal at pin2 of the pot.

      Delete
    8. mirosol15 October 2013 at 21:10

      You mean without ground connected to lug 1 of the volume pot? Is that pot ok? As it seems to work ok without that pot. You can measure the pot without signal or power. Turn it all the way clockwise and measure resistance between lugs 1 and 3 (that should be 100K), then between lugs 2 and 3 (that should be zero ohms). If that is ok, i'm guessing you're getting your signal grounded after the volume pot.

      Debugging may not seem like a fun thing right now, but you'll learn a lot by doing it. :)
      +m

      Delete
  5. Unknown16 October 2013 at 22:32

    You are right about the debugging thing - having the probe tool is great.
    Yeap I mean a signal on lug 2 with no ground on lug 1 - with the probe ground to the common ground, however when you connect the common ground to lug 1 then nothing, Ive checked this with 3 100k pots a 22k, 49k and 10k all do the same thing.

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    1. mirosol17 October 2013 at 06:24

      That sounds pretty strange. The pot is wired as a standard output level control, so i'm surprised there is any issue with that.. From where do you take your ground for lug 1?
      +m

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    2. Unknown17 October 2013 at 08:59

      At the moment its wired up ground from the power socket to the board then the board to input ground the input ground to output ground then to lug 1 volume pot.

      Delete
    3. mirosol17 October 2013 at 09:14

      This may be a stupid question, but you are using the sleeve of the input jack? Tip connecting to pot lug 1 could explain everything.

      Try taking two wires to board ground - one from power jack and other to pot lug 1.
      +m

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    4. Unknown17 October 2013 at 20:57

      I think in this case there are no stupid questions !. I swaped the ground and hot wires around and tried it, then wired the ground as you've said and still no luck.

      I think Im going to try to build a new one from scratch over the next few days and compare.

      Delete
    5. multipraktik26 October 2013 at 21:32

      Working with ua741, sound is great.
      Thanks

      Delete
    6. mirosol27 October 2013 at 00:14

      I'm tagging this as verified. Thanks multipraktik.
      +m

      Delete
  6. Unknown11 November 2013 at 15:14

    got it working, dunno what was up but the switch seems to have done the trick.

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  7. Unknown14 January 2014 at 22:10

    Anybody USED the TL071 in this? I tried a NE5534 since I had them and it's no go. Tayda doesn't carry TL081 but they do handle TL071. Don't see much difference. Mike.

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  8. dexxyy14 January 2014 at 22:37

    Ne5534 is not a replacement for tl081, tl071 is ok .

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  9. Unknown15 January 2014 at 16:26

    Yeah, after looking closer, the 5534 won't work. Ordered some TL071's. Mike

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  10. Unknown26 January 2014 at 23:33

    Works fine with TL071's. Ordered some 061's too just because the order was going in. Just have to box it.

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  11. Carpe DM28 April 2015 at 05:56

    Has anyone compared this build against the original?

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  12. Carpe DM28 April 2015 at 05:57

    This comment has been removed by the author.

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  13. Unknown18 January 2016 at 13:32

    Would Anyone know how to connect the XLR Lo-Z output ? I would greatly appreciate the help, I am drawing a blank..
    Awesome job mirosol

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  14. Christian26 November 2016 at 11:04

    I seem to have come across a mistake on this layout:

    The 22k resistor connected to pin 3 of the op-amp, i.e. the non-inverting input, needs to be moved one hole upwards, so that it connects to the inverting input. This makes the tonestack work much, much better. It is also consistent with the various schematics of the original that I managed to dig up.

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    Replies
    1. RareDevil27 December 2016 at 09:36

      Hello Christian, there is no 22K resistor connected to Pn3 in this layout. There is a cut under the 3.9M resistor.

      Delete
    2. Christian7 January 2017 at 14:37

      Well, that's a bit embarassing, isn' it!?

      Delete
    3. Christian7 January 2017 at 14:39

      In that case, I guess I can say if one forgets to make that particular cut, then moving the 22K resistor up a bit also makes the tonestack work. Ahem... I'll just show myself out.

      Delete

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