Smothie not phasing

[midwayfair]

Did you probe it yet?

If the LFO just isn't functioning and all your values are correct and there are no soldering mistakes, you may have to desolder IC2 and replace it.

[aballen]

Not sure what you mean by probe. 

I don't have an oscilloscope, if that's what you mean.  That's unfortunately a bit out of my reach.

De-solder and replace IC2 then?

[jkokura]

Audio probe. It's a helpful debugging tool.

I would agree, IC2 may be a problem. Whenever Phasers are phasing for me, it usually has something to do with the pot, the trannies, or the ICs.

Jacob

[gtr2]

Not sure what you mean by probe. 

I don't have an oscilloscope, if that's what you mean.  That's unfortunately a bit out of my reach.

De-solder and replace IC2 then?

I always link this when someone asks about an audio probe.  (Not my site)

http://diy-fever.com/misc/audio-probe/

Josh

[aballen]

gotcha, an audio probe.  I'll make one and see if it helps.  Will this help with my scenario?  Where I am in fact getting sound... just no effect?

[Scruffie]

It might help but they are better for tracing lost signal... however it may be you are just receiving the dry signal and not the wet so no harm. Although to test this you could also lift the 10k mixing resistor (the pair of 10ks that meet right before the output on here - http://www.freeinfosociety.com/electronics/schematics/audio/pictures/mxrphase45.gif the one coming from IC1a pin 1 is the dry signal resistor) and see if you still get signal which would imply the signal is going through the 'wet' phase stages.

Not much use for the LFO really either other than hearing it tick but you should see the voltage moving on one of the TL072 pins.

Personally i'd just try reflowing the board at this point to be sure if I thought everything else was right.

The voltages from the other pins of the ICs may help in uncovering something.

[aballen]

I'll try reflowing tonight... and I'll make a probe, honestly hering the LFO tick would be good... cause maybe its not ticking.

[madbean]

Like Scruff said---gotta get that LFO working or there is no phase sweep. Monitor pin7 of IC2 with your DMM to confirm the voltage there is sweeping up and down a bit. If not, that's the source of the problem.

[aballen]

Thank you beans!  I checked pin 7 on IC2, and it is actually sweeping.  drops down to the 1s and sweeps back up to the 8s.  I'm seeing a few values in between as well... I think that is just the sampling rate of my DMM.

so this means the LFO is working right?  If I'm getting a clean signal already is the mixing suspect... or should I still be looking at the wet signal somewhere before it gets mixed?

and what components should I check next?

I'm going to try to reflow the whole board tonight, just to be safe, but I'm pretty sure all my joints are good.

really appreciate the assistance here guys... I feel like we are getting closer to my problem

[aballen]

Hey guys I'm really hoping someone can help me with next steps here.  I tried looking at the pcb to trace where the signal from IC7 goes... but I cant really figure out what to test next.  Some diagnosis is done though, and I think I'm getting close to the problem.

To summarize: 

• I'm getting sound. Clean out(just a little change to the tone)
• The LFO is sweeping
• Just not sure where to look next

I'm thinking the problem could be where the wet gets mixed in?  Or, the mix is fine, but the wet is just not being affected properly by the sweep in pin7?

I'm not sure if I can read in to the tone change, that may just be the clean buffer, or the wet is in there, just not filtered as it should be.

I've got an audio probe, and a DMM... please just point me at what to check next.

[aballen]

Ok I just re-flowed the entire board.

And I pulled voltages from from the ICs.

IC1
P1: 3.64
P2: 3.64
P3: 2.45
P4: 0
P5: 3.57
P6: 3.64
P7: 3.64
P8: 9.18 (this matches my power supply voltage)

IC2
P1: 3.65
P2: 3.64
P3: 3.57
P4: 0
P5: 3.33 then jumps to 5.61( I noticed the speed changes if I change the pot setting)
P6: seems to be sweeping when pot is centered, but when I move the pot to either extreme... it hovers around 4.7
P7:  lowest pot setting sweeps from around 1 to 9v, highest hovers around 4.7, tiny fluctuation
P8: 9.18

Q1 G S D
.36-.5     3.57    3.64

.37-.5     3.57    3.64


The pot
center pin all the way down gets the biggest fluctuation 1.3 to 8.4
all the way up, sweep changes only 4.32 to 4.7

suggestions guys?

[aballen]

Ok,  I've verified every component, and I've breadaboarded a matcher.

I tested and matched some 5457s of my own... mine measure a cutoff of ~ 0.4V  (0.33 - 0.57)

the ones from small bear are 1.33, I tested them, and I got the same measurements, so I think the matcher is breadboarded properly, but the cutoff voltage is soooo much higher then my jfets.  Is there a proper cutoff voltage for the phase 45?

At this point it has to be one of the TL072s right?  Which one?  I also noticed that mine are TLO72CN  is it possible the CN is the problem?

[midwayfair]

I'm sorry you're having so many issues with this build.

The CN on the chip won't be a problem -- the handling characteristics won't come into play in a stompbox. I also don't really think that your chips are malfunctioning if you're getting amplified signal on all the output pins.

Your cutoff voltages look much closer to what I got with my matches. Did you try them in there yet?

[aballen]

yeah I actually tried a perfect match set at 0.45 cutoff voltage to no avail.  I think small bear gave me a really good set with those high cutoff voltages... but I'm stumped why none are working.

I'm pretty bummed, This is my first phaser, and I've  never had this much trouble with a build before.

I have an audio probe built, I'm just not sure how to follow the signal, or where to test.

Heading out for the weekend, but if anyone has any suggestions, I will be able to do some more testing Sunday night when I get back.  Please be specific if you can, like check pinX or probe the left side of Rx... unfortunately I don't understand the circuit well enough to troubleshoot myself, but I have the tools to do it, and at this point Ill try just about anything.

[aballen]

Ok guys I've been making some progress on this, I think it may be the trimmer pot.  Can you point me to a good 250k trimmer pot, one that is small enough to fit on these 1590a builds.  I had to bend the leads on mine to make it fit I think its binding, but this was the smallest one I could find in a 250k value. 

I swear I had smaller ones in the past, I just cant find them in this value.