Phase 90 Build

[ny_racer_xxx]

I think I posted this in the wrong area???

OK, so I bought some NOS MXR Block Phase 90 boards off fleabay, read all the mods and does and don'ts, built it and it works, sorta...

My first mistake was taking anything for granted.  I went to BYOC because they had "matched" 2N5952 Jfets, true bypass switch, and power jack.  Well, "Matched" turn out to be a pretty good stretch!!!!  They meant, they're pretty good from the factory, they don't need to be matched...  The leads were never touched, perfectly straight, and not a single mark from where they contacted a socket for testing...

The issue I have, is that I'm only getting a slight effect, not anywhere near what the box is suppose to sound like.  If I jump one of the 150k mixing resistors with another 150k, I can get a little bit more of the wet signal, and I can tune the bias so it's pretty even, but still not very swooshie....  I did a few mods, and tested before and after, like I pulled R28, C11 and C12.  The caps really darken up the signal, it's really transparent without them....

So I built a Jfet tester last night, after a few foul words and tossing the crappy rat shack board across the room, I did a point to point sloppy mess, but it works!!!!  It's the simple layout with no IC and a toggle switch for measuring Idss and Vp.  This is what I got from the non installed Jfets:
#1 .472/1.810
#2 .721/2.473
#3 .497/1.840
#4 .461/1.763

As you can see #2 is off the charts, and #4 is pretty far off also, pretty not matched to me.....  I have to desolder the ones on the board and test them tonight, but I'm expecting similar results....

On the good side, BYOC customer service is pretty good, they are sending me more Jfets without sending the old ones back, but I don't expect the new sets to be matched either...  I kinda feel like it's a scam, it's about $0.15 each for the Jfets, and they get $5.00 for a "matched" quad.  I was happy to pay that for the service to save me the time and trouble, but I'm going through that time and trouble, so what was the point of being over charged?

Anyway, just a heads up for anybody out there planing on building one, if you want it done right, do it yourself!!!!

CR

[ny_racer_xxx]

 So I went and de-soldered the original 4 Jfets and tested them:

#1 1.680/.418
#2 1.787/.461
#3 1.722/.422
#4 1.888/.496

So #1 and #4 look like the stinkers.....

From what I had on hand:

1.888 paired with 1.840
1.810 paired with 1.787

It's still 0.1v from low to high, more than I like, but that's as close I can get with what I have and it's already 100x better....  The original was about 11%, now is about 5.5%, I think 2.5%, should be doable.  BYOC is sending me another 2 sets of quads, so I'll see how close I can get with those.  Worse case, I order a bundle and weed through them....

CR

[SmoothAction]

The phase 90 should be pretty swooshy and BYOC has excellent customer service. Also, I don't mind spending 5 buck on a quad matched pair of jfets. Have you ever matched your own? It can be quite a pain in the ass, as in sometimes buying 20 jfets you get 3 that match. BYOC kits are of high quality, it's cool they are sending you a matched set. I would double, triple, and quadruple check your own work before laying blame on a highly reputable kit dealer. If youre absolutely certain you've built it well, try new jfets because they are finicky little bastards. Good luck, this phaser is highly dependent on proper matches so don't give up.

[ny_racer_xxx]

I agree with you about matching them is a PIA, and paying five bucks would have been worth it, if the actually did try to match them.  That was my thought and why I purchased from them.

I was avoiding building a Jfet test rig, but I ended up building one last night and the voltages are above.  I also pulled the jfets from the board and tested them, and they are all over the place.  I matched them as best as I could with what they gave me, and installed them.  It does work a lot better, but the matching is still pretty far off.

Bottom line, with the exception of maybe 2 of them, the rest are waaaaay off, they never matched them.  Whether it was an oversight, or their common practice, I would like to believe it was an oversight, but I was told that they are pretty close from the factory and they don't need to be, so I tend to lean toward common practice.  And that's cool, but don't advertise "Matched" when they are not.  I guess if the next set they send me is pretty close, then maybe it was an oversight.

I'm not trying to bash them, although I was pretty pissed when I tested them, but just a heads up for anybody buying "matched" Jfets to check them, because most likely they ain't...

CR

[tubegeek]

Have you ever matched your own?

I think, from reading the two posts you just responded to, that yes, he has.

WTF?

[SmoothAction]

It wasn't meant as it came out, of course OP knows how to do it and I apologize if I came off sounding too literal. Dude obviously knows his stuff. 

It's a shame byoc sent you a bunk matched quad. My byoc phaser had a nicely matched set, I must've gotten lucky. Getting a 4 pack of untouched "in package" trannies suggests they haven't matched them. The premium you payed should ensure they have done so. Bummer for sure.

Again, good luck and let us know!

[ny_racer_xxx]

 No P Smoothie....

What I can imagine, and I can't prove it, is that they probably match the Jfets for their own kits, and the leftovers to who ever buys them without the kits....  I think that looks pretty obvious from the 2.473 that was in there....

And again, that would be OK if they didn't state "Matched".

It is what it is, I'm sure they don't keep the lights on with the profits they make from selling Jfets, like I said, just a heads up....

On another note.....  I was reading through to see how close a good set is, and I was seeing like around 0.020v or better?

CR

[duck_arse]

much as I hate to say it, have you got any j201's you can throw in?

[ny_racer_xxx]

much as I hate to say it, have you got any j201's you can throw in?

LOL, naaah....  I'll wait it out....  I bought 3 of these old stock boards, I might do something different with another.  How do they sound with the 201's?

CR

[duck_arse]

well, they work. the voltage spec is so low to start with, any 4 parts "in spec" will still be much closer matched than the best set you've got at the moment.

[ny_racer_xxx]

 Thanks, I'm waiting for the new bundle, hopefully they will be better, or I'll buy a crap load of 5952's, and go from there like most people do...

CR

[ny_racer_xxx]

USPS Tracking says tomorrow, so maybe I'll time to mess with it this weekend....

CR

[ny_racer_xxx]

USPS dropped them off today thankfully, I thought I might have to wait till Monday.....

Nick hooked me up with 10 Jfets, a few were pretty close....

1. 1.881/.465
2. 1.869/.458
3. 1.765/.420
4. 2.213/.642
5. 1.880/.442
6. 1.824/.425
7. 2.172/.555
8. 2.408/.644
9. 1.757/.407
10. 1.933/.483

So, 1.881, 1.869, 1.880 look like the closest, and if I take 1.888 from the other batch, I should be pretty good....
I think I can squeeze out a second set also, 1.765, 1.757, 1.763, 1.787.

CR

[ny_racer_xxx]

 Well, that didn't help.....  I did some "research" as my wife would say, and listened to some Phase 45's on youtube, that's kinda what it sounds like not a full sweep.  It could be something with the circuit I guess, but from what I also researched, is that they need to be matched to at least two decimals places, and I'm still not there yet....

How close do they need to be?

CR

[Seljer]

I built mine with jfets that were about 50mV apart and it sounds fine :shrug: (are MXR's original ones even matched at all?)

Whats the reference voltage on the cathode end zener diode in the circuit? What range of voltages do you get on the gates if you probe it with a voltmeter (with the LFO at it's slowest...unless you can look at it on a oscilloscope).

If you have everything socketed you could also try running removing the first two or last two jfets and comparing the sound to see if a specific section of the circuit is acting p (without the fet installed the opamp will just function and as fixed non-moving phase shift stage)

[ny_racer_xxx]

 Thank you for the reply....  I was thinking about each opamp section today when I was fooling with it....  It can't be a bad opamp, because they cascade, if one was dead, there wouldn't be any wet sound...  I haven't checked voltages, but I will tomorrow and post back...  Also I used TL072's for the opamps, I see something about 3558's also for the LFO...

I was thinking of getting one of the duel trace USB PC based scopes...  What's a good freq for a signal generator for testing guitar circuits?

CR

[tubegeek]

1K Hz typical, 80 Hz min, 10K pretty much max.

[duck_arse]

a spread of 20mV should be good enough.

those who know suggest you put something distorting in front of a phaser when testing. it shows the complexities at work much better.

[Seljer]

a spread of 20mV should be good enough.

those who know suggest you put something distorting in front of a phaser when testing. it shows the complexities at work much better.

Also fun is to hook up a distortion pedal with everything at 100% as a makeshift white noise source, then hook up to output of your phaser to your computer and run some FFT software (or even into your smartphone, plenty of apps for those these days). You can see the notches moving up and down

[ny_racer_xxx]

 Seljer, thanks for the inspiration...  Not sure how useful but I came across some sound card based scope software....

This one shows how to build DIY Probes..

http://homediyelectronics.com/projects/howtomakeafreesoundcardpcoscilloscope/?p=1

This one also has a signal generator...

http://www.sillanumsoft.org/prod01.htm

CR