I just finished up the Tractor Beam phaser and all controls work, but distorts at all settings. I know that getting rid of the feedback resistor helps the Phase 90 clean up, but turning the feedback knob all the way down doesn't help the Tractor Beam. Anybody else experiencing this?
One common cause of distortion can be incorrect VB rail voltages. I'd start by comparing the build voltages in the docs. If those look good the next step would be audio probing to see where the distortion is introduced.
Thanks for the reply, Madbean.
My voltages look to be alright. I tried the audio probe, but I can't quite follow the schematic. Signal going into OPA2134 is clear and strong, so it must be a problem at the phase stages? Pin 7 of TLE2074 sounded good, but pins 2 and 3 sounded thin and raspy. I don't know, I might take the board out of enclosure and double check my soldering next.
A question: Could I have screwed up the orientation of the resistor arrays?
Thanks for the help!
The resistor arrays don't need to be oriented in a specific way according to the build doc, so you're good there!
Correct, resistor array orientation in this build doesn't matter. How about your 2N5952? Are they a matched set?
Maybe a clear pic of the top of your build.
The 2n5952's are matched in the 1.49-1.50 range. Solder side "looks" to be okay, but I will reflow to make sure. I did use a 1/2 watt 4.3 volt zener I had on hand, not a 1 watt rated one and I used 1.5k resistors instead of 1.43k. I don't have a phone or camera (hard to believe, I know) but will post a pic as soon as possible somehow.
No worries, I'll get it sorted.
None of those changes/differences should cause a problem. I'll wait for the pic and see if I can spot something.
Thanks, Brian. Still no pics, but maybe a clue: I pulled all 4 jfets out and the sound was crystal clear. I'll keep at it... it's gotta be a problem around the phase stages.
Caught my neighbor at the fence and he took some shots for me :).
Removed jfets for the pics. Also, one of the 10k resistor's pads got fudged when I removed previous resistor so I had to wrap around board to solder to other side.
I checked resistors with meter, so they should be all correct values. Caps are tight between resistor array and chip, so can't see values.
Solder side:
Your OPA2134 looks funny. You sure it's legit?
Quote from: Aentons on January 23, 2018, 06:00:37 PM
Your OPA2134 looks funny. You sure it's legit?
Thanks for taking a look. I got the OPA2134 several (probably more) years ago directly from the Texas Instruments sample program. I can swap it out with a different chip to see if it helps.
AAARGH! Still no luck!
I think I'm gonna build up a phase 90 "Script" circuit with my matched jfets and see if they are the culprit.
How do you even get it in the case with the wire and cap hanging off the edge of the board?
I thought I might've put in wrong resistor value there, but when I attempted to remove it and replace it, I broke off one of the leads inside the pcb and couldn't get it out. I just temporarily did what I could to see if that was the problem. Didn't have some of the caps in compact size, so I laid them down to fit in enclosure.
I have more success debugging etched boards.... a lot easier to unsolder components and add holes if needed.
You have a lot of excess solder on those joints, but I don't think that has much to do with your issue. Your work-around on the 10k resistor seems fine. Getting clean signal through when you pull the FETs is good - it means that the problem is either those FETs or the LFO. If you are getting oscillating voltages on the LM358 then by process of elimination it is most likely the FETs. If yo uhave any other FETs it might be helpful to pop them in there...even if they are not matched just to see what happens.
Thanks, Brian. A lot of extra solder due to me trying to reflow in hopes of correcting a possible cold joint. I'm getting the right voltages on the LM358, so it is more than likely the jfets. I'll try to rustle up some others to try and will report back.... hate to give up!
A tip: don't need to add solder to reflow. Just work the existing joint. However, if you are reflowing a lot of joints at once it's a good idea to remove ICs temporarily to prevent the part from overheating.
No luck :(. Even tried using 2n5457's (flipped around) and changed out all the chips. I'm going to put it aside for another day and go on to a phase 90. If the jfets work cleanly in it, I'll try to mod it to do some of the Tractor Beam stuff. 8)