MXR Phase 45 build problem - Need advice

[evhfan]

Hello everybody,

I just finished building the mxr phase 45 from the schematic on this site and i'm having an issue with it phasing. The board is basically acting like a bypass or lineboost should i say.. The guitar's sound is going through it but it's not producing any effect.. I have triple checked the board which i did pin to pin and it all checks out fine. Is there some trick to getting these to work or is there somethin that maybe i should look for?

I used sockets on the board for the op amps instead of soldering them direct to the board so what i did to troubleshoot was swap spots with the op amp to see if that was the problem but it still acted the same telling me the op amps are fine. I don't know what else to do at this point, it's kind of exhausted my brain after 3 days..

If anybody has built one and has some advice it would be greatly appreciated!!!!

[oldrocker]

I assume you matched the two JFETS. Which FETs did you use? Did you socket these too? Also the trim pot is touchy. I used a 1M so I could dial in the phase somewhere around 10 O'clock. I also mounted that on the outside of the enclosure so I could tweek it easier. Did you use the GEO JFET matcher circuit to find the closest match?
This is a subtle phase but I like it that way. There are also univibe mods for this which I later added to mine and also makes the vibrato available via a toggle switch.

[evhfan]

Hello there oldrocker,

I didnt match the jfets, i just bought 2 of the same part, does it really matter if they're matched or not, will that cause it not to phase shift at all ?

Yes i did use sockets instead of soldering the op-amps direct to the board.

The Jfets i used are the NTE312 , they are supposedly the EXACT replacement for the ones that came in the mxr. The Op-Amps i used were TLO72.


thanks for your reply..

[oldrocker]

Yes from what I understand Jfet matching can make all the difference in weather it will phase and how much. I'm assuming you didn't socket the Jfets. The dual opamps you used should be fine. I avoided the build for some time until I finally broke down and bought 15 jfets of the same type and found the closest match. You can match by ear also but it's a little more difficult do it that way. And don't forget adjusting that trim pot while testing to find the sweet spot. If that trim pot is not adjusted correctly it will not phase at all. Good luck.

[evhfan]

oldrocker, I honestly didn't know that if the jfets werent matched it would cause it not to phase at all I also didnt know that the trimpot would cause it not to phase at all, i figured the trimpot would just vary the amount of phase or frequency of the effect.. I'll have to try it again and slowly turn the trimpot while the guitar is ringing..

By the way yes I did socket the jfets LOL i know they are sensitive to heat, only problem is when i bought them there was only 2 of them left in stock at the supplier's warehouse so i couldnt grab anymore. I'll go out today or tomorrow and try to find a bunch of the same jfets, then i can try and match them like you said.

Thanks again for your replies, i'll keep you posted on what happens with this thing.

[oldrocker]

Yes there is a sweet spot on the trim pot and there is only one spot that will give you phase.