Monday, 24 December 2012

DOD 280 Compressor

Here we go with another classic optical compressor. Original unit uses VTL5C2, so could get away with using any LDR with 1M dark resistance. So the LDR resistor would be  resistor leads of VTL5C2 and that green LED acts as LED leads of the vactrol. Positive/anode to strip four and negative/cathode to strip one. Haven't built it myself yet..




26 comments:

  1. A nice addition thanks !
    And merry christmas

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  2. I can get the VT5C2 fairly easy for $5.24/ea. However, i have never used this component and it looks to have multiple leads (2 on one side and 2-3 on the other)! Thee layout shows 2 hookup points. Soo, how do we hook this up?? Thanks in advance and Merry Christmas!

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    1. VTL5C2 has four leaads - 2 for the LED and two for the resistor. The five leaded one is dual resistor one - and that is not VTL5C2. If i recall correctly it is VTL5C2/3 and those are used with one particular red box envelope filter.

      So basically you wouldn't hookup VTL5C2/3 for this one...
      +m

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    2. mirosol, in theory, a VTL5C3/2 (not VTL5C2/3) with the five leads, can be used to replace the VTL5C2. Comparing them side by side, you just have to ignore number 4 on the VTL5C3/2, and use 3 and 5 right? I'm thinking that this would be better than making an optocoupler.

      here is a comparison http://img692.imageshack.us/img692/769/h34a.png

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    3. This comment has been removed by the author.

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    4. Works like a dream ignoring the middle pin on a VTL5C3/2 :D

      Great compressor

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  3. any particular diode at the 9V input to the IC?

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    1. Knew i forgot something. That's for polarity protection, so 1N5817 or 1N4001 would be perfect.
      +m

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    2. thanks! figured it wasn't any sort of specialty model

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  4. Right, I've decided that I've got enough dirt pedals and random noise generators for this week so I'm going to start on this as I've not got a compressor and I've never tried the LED/LDR trick. Quick question; is the LED used going to make much of a difference? I've got a bunch of red 5mm, green 3mm and a handful of various ultra bright 3mm; having never tried an optical pedal build I've got nothing to base this on, I can socket the board but since I'll be using heatshrink wrap to cover the LED/LDR I'd really like to try and get this right first time. Any suggestions anyone?

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    1. I read somewhere that green non-clears work the best. Whether this is correct, I have no idea.

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    2. Brigthness of the LED affects the LDR quite a bit. Only way to know for sure is to use sockets and try it out. What are your LDRs rated at?
      +m

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    3. I picked up a few to try different values, I think they're all 1M or higher after 1 second dark. Cheers for the help guys. Sockets it is I guess.

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    4. Ok this one's good for tagging. To be honest I've never really been a compressor pedal user, the last time I used one was about 10 years ago, so I may not be the best judge of the quality but it's definitely doing what I understand a compressor to do: makes things louder, warms things up a bit, works as a clean boost.

      I'll experiment with the different LDR/LED combos but I used a green 3mm and it worked first time, all the LDR's I had were unmarked so it's anybody's guess what value it was. Cheers for the advice before guys.

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    5. That's just super. Thank. You!

      I think that the LED/LDR combo will affect the depth, or squishiness. Next time i place order, i'll get some VTL5C2s and build it myself.

      I'll tag it. You rule!
      +m

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  5. Haha, I've had a few days off work because my girlfriend's been ill, a combination of no work and a girlfriend in bed equals plenty of time to indulge the hobby! I just need to squeeze out a delay and a decent tremolo and I might need a breather for a few days

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  6. Hi,

    is D2 the LED part of the LDR/LED? if so, which way round does it need to go? If not, what is it? (do you have the schematic for this too? it doesn't quite match the other DOD280 I found online)

    Cheers!

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    1. Yes, it's a part of the vactrol. The ldr goes in either way and if you look closely, the little cut on the led denoting a cathode is facing up. So that's cathode on row one and anode on row four.

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    2. LDR/Led pins are noted in the post.
      Schematic is at http://www.tonepad.com/project.asp?id=21
      +m

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  7. I finally got around to building one of these. Although I'm happy with my Really Cheap Bass Compressor, the attack time isn't exactly right for fast fingerstyle playing (it's absolutely perfect for slap, however). I changed quite a few values to let more bass in (470n input cap, 100n caps in the peak detector, and 4.7uf on the output). The most important mod I made was changing the 47uf hold cap to 10uf. This one's most likely going to get boxed, but it absolutely needs a 500K rev log pot for the compression control (plus the only 500K pot I have on hand is dodgy)

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  8. Nice, I had to sub in some other resistor values but it came up good. Had to make one after I saw the Australian guy doing a pedal demo.

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  9. Hi good people! I've built this a few times by now with a home rolled optocoupler, and one with an original Vactrol...but I prefer my optocoupler better heh! Works pretty good, I like it, simple, and useful! Here are some links, you also have a sample under the photos:

    http://hgecontraptions.blogspot.ro/2016/02/dod-280-optical-compressor-third-one.html

    http://hgecontraptions.blogspot.ro/2014/09/dod-280-optical-compressor-aother-one.html

    http://hgecontraptions.blogspot.ro/2014/09/dod-280-optical-compressor-my-favorite.html

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  10. built this for my 2nd build ever.
    success!! and sounds great!! good sustain

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    1. Nice! I've built two of these, one for me and one for a friend. It sounds great on bass and guitar.

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  11. This is a great compressor IMO. I've never been a fan of compressor pedals as they tend to be too squishy, but i built one for a freind and, after playing around with some of the values, found you can make this really versatile.

    I took the advice somebody had mentioned in the comments about changing the hold cap from 47uf to 10uf and this really speeds up the release time. However, in some cases it was too fast so ended up putting the 10uf cap and a 100uf cap on a DPDT switch to be able to go between 'fast' and 'slow' settings. I also increased the input and output caps to 220nf so it would play nicer with beefy humbuckers and acoustic guitar. Finally I found that blue non-clear LED's worked best for my tastes.

    Word of (possible) warning; I built two of these using the same IC, transistors, and LDR's and they worked great. I then bulk bought 10 of each from a different supplier. The third one I build acted VERY differently; on the original two, with the 'comp' pot at zero you would only get compression if you really laid into the guitar. With the third one, with the 'comp' pot at zero, there was a lot of gain reduction being applied. After a lot of troubleshooting, I found that it needed 100k resistors instead of the 220k resistors that had worked fine the first two times. I'm *guessing* the transistors had a higher gain than the original four I'd bought but haven't measured then yet. Anyway, that's just an FYI if you experience the same thing when building more than one

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