Friday, 6 June 2014

MXR Phase 90 - 4 / 8 Stage

I was going to just add this to the bottom of the Phase 90 post, but on reflection thought it better to start a new one to keep discussion about this build in one place.

A few people have requested a layout for the Phase 100 and I thought this could be a happy medium until I start on the circuits that are currently a low priority due to my preference for PCBs when it comes to larger circuits to keep the box dimensions down.

I was happy with the size of the Phase 90 layout and so I thought it would make sense to make this modular rather than using a large single board as it will then allow you to add more daughterboards if you want to, maybe two to make a 12 stage phaser if you like, or three for 16 stages.

The standard Phase 90 layout was used as an example in this layout, but you could do exactly the same thing with the modded version with the depth pot if you prefer.  This inserts the new stages in between stages 2 and 3 of the main Phase 90 board which means that all other components of the Phase 90 can remain exactly the same, making it easy to add this to an existing build if you want to.  All you need to do is add a cut and make the switch connections shown at the top of the Phase 90 layout and the daughterboard, daisy chain the supply and ground and link the sources and gates as shown.  Voila, you have a Phase 90 with 4 or 8 stages selected by the Stage Switch.

I haven't done this from a verified schematic and so it's all just theory at this stage, so it's definitely one for the experimenters out there.  And of course the people who don't mind matching at least 8 JFETs :o)




14 comments:

  1. Would it be possible/useful to add fixed stages?

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    1. What do you mean fixed?

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    2. I'm not sure exactly how to explain it. Mark Hammer talks about it in this thread :http://music-electronics-forum.com/t27649/

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    3. MH also suggest taking one or two of the swept phase shift stages and making them fixed in a build I was having trouble with here: http://www.diystompboxes.com/smfforum/index.php?topic=107019.0
      I ended up not needing to as the problem was just a bad solder joint but that informed me of the possibility of fixed phase shift stages.

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    4. From the suggestions he gives in my troubleshooting thread I could probably mod your layout pretty easily for a fixed stage though from what I ready I think you would only want two fixed stages. I might just have to give it a try.

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    5. Just had a read through and it may be something worth trying, but I want to see how this works out before thinking about other methods. The feedback loop caps will be easy enough to add if necessary, gain could be set with trimmers if that precision is needed, so I'd like to see the real world results using stages rather than trying to fix something that isn't broken yet.

      Bear in mind it's R28 that is feeding signal back, and the script mod removes that from circuit. A lot of people find it much more pleasant without R28 in the stock 4 stage version, and I don't doubt the same will be the case with this version. So we don't need to feed the signal back in that way any way.

      So we'll see how it goes I suppose.

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    6. ^^
      Give it a try and see what you think. If it works well I'll add an extra layout based on your suggestion.

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    7. I'll plan on it. I think I need to build a P90 from your layout to make it easier to add in extra stages. Hopefully I can get this built and tested this weekend.

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  2. So all 8 must be matched together? I have 2 sets of 4matched fets.... =/

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    1. The sources and gates are all connected so all 8 will need to be matched. 2 sets of 4 may still work, especially if they are close enough anyway, but 8 matched would almost certainly give the best results. It won't take you long because you build these things in about 5 minutes anyway, so just use sockets and give it a try :o)

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  3. I built this with 8 matching fets the main board works but the daughter board is silent until a string is plucked then it becomes a siren, a very loud distorted siren. The voltages seem to check out as far as I can tell. 9v on 8 0 on 4 and half supply on the rest.

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  4. Hi,

    can you help me? Signal come trough the effect but there is no phase. Wiring is ok (I checked it thrice). Could it be in LCs? They are soldered direct in board with normal pen solder (some say that isnt right). Could it be in FETs? How can I find out orientation of FETs? They are from ebay and I dont know they have same orientation like another 2N5952.

    Thanks a lot.

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  5. This is a great 'little' phaser but it ticks in unison to the rate control. The trimmer has no effect on the tick. Any ideas about what could be wrong....before I rebuild it.

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