Just finished a Phase 45 (w/ Univibe Mods), and I've obviously done something completely wrong.
I'm getting roughly 9v across both IC's :icon_eek:
Except 0.0v on both Pin 8's
I'm using a pair of matched 2n5952. Both read the same:
G - 3.3
S - 4.6
D - 8.8
I'm getting bypass signal, but effect engaged no sound. I spent the past few hours cleaning traces and eliminating bridges. Hard to photograph but in person I'm pretty sure there are no connections. (Some leads may appear to be touching but are just photographed on an angle)
Admittedly this is my most complicated build so there is a learning curve (excuse the mess!)
any guidance is much appreciated.
(https://i.postimg.cc/KKwt53Mb/1.jpg) (https://postimg.cc/KKwt53Mb)
(https://i.postimg.cc/Zvh3GkHD/2.jpg) (https://postimg.cc/Zvh3GkHD)
(https://i.postimg.cc/4nzFmsDy/3.jpg) (https://postimg.cc/4nzFmsDy)
Hi DJ,
Can you post a link to the build docs/schematic please? Did you use TL071s instead of TL072s? My bifocals can't resolve that lol. The schematics I have call the Phase 45 for dual, not single, opamps... :icon_eek:
You can remove the ICs and measure voltages at each socket point to see what's up, too....
Quote from: GibsonGM on October 10, 2021, 12:33:49 PM
Hi DJ,
Can you post a link to the build docs/schematic please? Did you use TL071s instead of TL072s? My bifocals can't resolve that lol. The schematics I have call the Phase 45 for dual, not single, opamps... :icon_eek:
You can remove the ICs and measure voltages at each socket point to see what's up, too....
My apologies, I used this layout.
http://tagboardeffects.blogspot.com/2012/07/mxr-phase-45.html
And oops there's my first problem I was using TL071 ::)
Ok, it's down to voltages now. The '71 has power applied to pin 7. TL072, power is on pin 8. What do you get on those sockets? If 0 on pin 4, 9V on pin 8, you have a chance of it working.
Just as simple builder error with the single opamps, we've all done it :) I gave you a like for your honesty lol
Ok updated numbers with the TL702 ;) (9V battery)
Both are pretty much identical:
1: .76v 8: .86v
2: 176mv 7: .76v
3: 176mv 6: 176mv
4: .9v 5: 176mv
Q1, Q2:
G: .4
S: .76
D: .76
I meant get the voltages with the ICs removed :o
Next issue: power on a TL072 is pin 8.....look closely at your pic, note where the locating dot is! I believe you have pin 4 on the same row as 9V, which means the chips are reversed. You have to do a 180 with the ICs...the dot will be 'upper left', and that's "pin 1". You can confirm that this is correct by doing the voltage measurement with nothing in the socket...pin 4 should be 0, pin 9 battery voltage...remembering to plug a guitar cord into the input jack to 'turn on' the circuit! ;)
See if this helps. Pin 4 VCC - (gnd) Pin 8, VCC+ (9V):
(https://s3images.coroflot.com/user_files/individual_files/613050_yztqbp55if4oxgfw2tqpfcgxb.png)
Ahh right once again. I was confusing those connection dots on the layout ;D
Gave the chips a 180, and I am now getting signal when switched on, but no effect.
Here are the socket voltages
"Top IC"
1: 3.6 8: 9.3
2: 3.6 7: 3.6
3: 3.6 6: 3.6
4: 0 5: 3.6
"Bottom IC"
1: 3.6 8: 9
2: 3.6 7: 118 mv
3: 3.6 6: .2 mv
4: 0 5: 59 mv
QuoteGave the chips a 180, and I am now getting signal when switched on, but no effect.
The bottom pin of the 150k to the right of the lower IC is going to the wrong place, currently in first PCB row but should be second row.
Quote from: Rob Strand on October 10, 2021, 07:38:32 PM
QuoteGave the chips a 180, and I am now getting signal when switched on, but no effect.
The bottom pin of the 150k to the right of the lower IC is going to the wrong place, currently in first PCB row but should be second row.
Rob good eye!
Fixed it, but still no effect when pedal engaged.
What are the voltages now?
"Top IC"
1: 3.6 8: 9.3
2: 3.6 7: 3.6
3: 3.6 6: 3.6
4: 0 5: 3.6
"Bottom IC"
1: 3.6 8: 0.9 v
2: 3.6 7: 1.4 v
3: 3.6 6: 1.4 v
4: 0 5: 0.9 v
Perhaps another bug in that bottom right area of the PCB: The 150k to the left of the top lead of the 7k5 resistor. Top lead of the 150k is off by one should align with the 7k5 top lead.
Maybe check over that whole corner.
Quote from: Rob Strand on October 10, 2021, 10:34:32 PM
Perhaps another bug in that bottom right area of the PCB: The 150k to the left of the top lead of the 7k5 resistor. Top lead of the 150k is off by one should align with the 7k5 top lead.
Maybe check over that whole corner.
Actually that one was fine, I did however completely miss a 150k next that 10n. Now I have effect! :D
Next issue is I'm only getting effect in one position of the trimpot, or at least a very tiny window of the turn.
I currently have a 500k in there instead of the 250k. I have a 250k on order.
the tiny window is to be expected. find the window, power off, and measure the resistance of the trimpot, one end to wiper. then you want to use a smaller value trimpot, maybe 50k, and add padding resistors to the total of 500k either side. then your window will be much wider, easier to trim.
Quote from: duck_arse on October 11, 2021, 10:00:26 AM
the tiny window is to be expected. find the window, power off, and measure the resistance of the trimpot, one end to wiper. then you want to use a smaller value trimpot, maybe 50k, and add padding resistors to the total of 500k either side. then your window will be much wider, easier to trim.
excellent thank you if I understand this right:
- measure the "sweet spot"
- replace with 50k trim? or did you mean 50k lower than resistance "sweet spot"?
- then add resistance to the amount of 500k?
And unrelated (sorry if this derails the thread) but can someone point out the 10k "intensity" resistor?
I.E. "intensity" pot via GGG mods: http://www.generalguitargadgets.com/effects-projects/phase-shifters/mxr-phase-45/
Is this the same as the "mix" pot shown here?
http://tagboardeffects.blogspot.com/2012/08/mxr-phase-45-modded.html
(https://i.postimg.cc/rKLGkBhj/INT.png)[/url (https://postimg.cc/rKLGkBhj)
(https://i.postimg.cc/vH989YmH/INT.png)
Thank you!
Is this the same as the Mix knob?
I plan on adding this "intensity" pot and replacing the 3M9 as a "width" pot
Before I hack this thing up, here's a sample of the pedal so far. It sounds pretty nice, although it does distort quite quickly. And maybe a little on the dark side. But has a nice watery swirl for sure.
Please excuse the unprofessionalism of my playing, It is bad! ;D
Using a tele into a blues jr, bridge PU - recorded on iPhone
https://soundcloud.com/user-809000973/psychic-vibe-test-1?si=6cc80f9323d34a09b06bdd6d209e8384
Quote from: DJPsychic on October 11, 2021, 10:56:21 AM
Quote from: duck_arse on October 11, 2021, 10:00:26 AM
the tiny window is to be expected. find the window, power off, and measure the resistance of the trimpot, one end to wiper. then you want to use a smaller value trimpot, maybe 50k, and add padding resistors to the total of 500k either side. then your window will be much wider, easier to trim.
excellent thank you if I understand this right:
- measure the "sweet spot"
- replace with 50k trim? or did you mean 50k lower than resistance "sweet spot"?
- then add resistance to the amount of 500k?
An example might help:
Say the best place with the 500K trim is measured as 345K.
So we replace the trim with a 50K trim. We ideally want the sweet spot to be right in the middle of the trimmer, so 25K either way.
That would give us 345-25=320K for the resistor at the bottom end of the trimmer.
The other end would be 345+25=370, which leaves 130K to get to 500K, so we stick 130K on the top end of the trimmer.
So we'd need 320K and 130K resistors.
In practice 330K and 120K are the nearest standard values (and, usefully, one went up by ten where the other went down by ten) so we'd use those and accept that our sweet spot might not be exactly in the middle. We should still have enough room for manoeuvre, even if the final position on the trimmer finishes up being 15/35 instead of 25/25.
HTH
Thank you for the rundown!
Concerning "depth"
If I replace the singular "R9" with a 10k pot, can I get more "depth" then the stock, or does this only act to reduce the wet signal?
Versus
JC Maillet "Mix", replacing both 10k's (R9 & R10)
QuoteConcerning "depth"
If I replace the singular "R9" with a 10k pot, can I get more "depth" then the stock, or does this only act to reduce the wet signal?
Versus
JC Maillet "Mix", replacing both 10k's (R9 & R10)
There's a difference between adjustable depth and more depth.
For more depth try reducing the 3M9 resistor to 3M3. That increases the sweep depth. Even when everything is working fine this value can need some tweaking as technically the right value depends on the JFETs. You might need to tweak the bias again.
The phase can lack depth if the bias is not set correctly, or, something is wrong.
Keep in mind the Phase 45 only has two all-pass filters so you can't expect too much. Listen to some youtube videos to get an idea where your unit stands. You can also compare against the Phase 90 to get an idea of the effect of adding more all-pass stages. (and keep in mind units vary and the later Phase 90s don't sound like the vintage ones so perhaps find a video with a vintage unit.)
FWIW,
Unfortunately I can't remember what the correct zener is for the Phase 45 and I don't have all my notes and original PCB pics.
The 1N5230 shown on the Phase 45 layout is a 4.7v zener which ends up at 3.6V (to 4.4V) or so due to the low operating current.
The Phase 90 uses a 1N5231 which is a 5.1V zener that ends up around 4.4V to 4.8V. A few schematics incorrectly had 1N5230.
The zener will affect the sound because it changes the way the sweep works.
The web isn't a good place to resolve this issue you really need original pics. There might be a post on the forum about it but most of the traffic is about the Phase 90.
EDIT:
What zener did you actually use? 500mW?, 1W? part number?
Perhaps even 3.6V is low, maybe that's for a 1W.
Thanks man. I realized after I asked the question how obvious the answer was lol
I ended up testing the "R9" 10k pot, and it might be a useful to clean up some of the tone but not really doing what I hoped. .
Would putting a 5m pot in place of the 3M9 be overkill?
- And one last issue I need to address is I'm barely getting much "headroom" before I get breakup. My signal wants to distort pretty quickly. It's usable if I'm playing quieter but muddy if hit a chord or play heavier.
Maybe try a different IC?
QuoteI ended up testing the "R9" 10k pot, and it might be a useful to clean up some of the tone but not really doing what I hoped. .
Would putting a 5m pot in place of the 3M9 be overkill?
It would work but a 5M pot is hard to get.
Another way is to put a 500k or 1M pot in series with the 1M resistor that goes to the bias trimpot wiper. 1M is easier to get.
The bias will probably need to be adjusted when you change that pot setting.
There's about 4 ways to mod the unit to add a depth trimpot. One of those ways will require less re-adjustment of the bias when the depth is changed.
Quote- And one last issue I need to address is I'm barely getting much "headroom" before I get breakup. My signal wants to distort pretty quickly. It's usable if I'm playing quieter but muddy if hit a chord or play heavier.
Maybe try a different IC?
The problem is the low (actual) zener voltage. Ideally you want the zener around 4.5V measured across the zener.
Typically that works out when you use a 5.1V 500mW zener.
If you use a 1W zener the actual zener voltage could be lower than 4.5V. If you can only get 1W zeners then it might be a good idea to get a 5.6V zener (as well as a 5.1V) then it will end up at 4.5V. This stuff is quite imprecise.
And who knows, perhaps after fixing the zener it could sound better.
At the moment you might have a 4.7V 1W and it's ending up way down at 3.3V to 3.6V.
Quote from: Rob Strand on October 12, 2021, 05:34:30 PM
QuoteI ended up testing the "R9" 10k pot, and it might be a useful to clean up some of the tone but not really doing what I hoped. .
Would putting a 5m pot in place of the 3M9 be overkill?
It would work but a 5M pot is hard to get.
Another way is to put a 500k or 1M pot in series with the 1M resistor that goes to the bias trimpot wiper. 1M is easier to get.
The bias will probably need to be adjusted when you change that pot setting.
There's about 4 ways to mod the unit to add a depth trimpot. One of those ways will require less re-adjustment of the bias when the depth is changed.
Quote- And one last issue I need to address is I'm barely getting much "headroom" before I get breakup. My signal wants to distort pretty quickly. It's usable if I'm playing quieter but muddy if hit a chord or play heavier.
Maybe try a different IC?
The problem is the low (actual) zener voltage. Ideally you want the zener around 4.5V measured across the zener.
Typically that works out when you use a 5.1V 500mW zener.
If you use a 1W zener the actual zener voltage could be lower than 4.5V. If you can only get 1W zeners then it might be a good idea to get a 5.6V zener (as well as a 5.1V) then it will end up at 4.5V. This stuff is quite imprecise.
And who knows, perhaps after fixing the zener it could sound better.
At the moment you might have a 4.7V 1W and it's ending up way down at 3.3V to 3.6V.
Thank you for the thorough breakdown!
I think I have a 5.1V zener on hand I'll give that a shot.
Ideally I'm going for a pot that acts as close to the "intensity" (depth) pot of a Uni-Vibe type clone.
QuoteIdeally I'm going for a pot that acts as close to the "intensity" (depth) pot of a Uni-Vibe type clone.
It's do able but the best way to do it would need some design time and also analysis of exactly what happens with the univibe.
The intensity on the univibe goes from full down to nothing. When intensity is on minimum the unit isn't "bypassed" as such, there is a notch. The notch is located at a particular frequency "somewhere" in the middle of the normal sweep range.
Upfront, the tweaks to the depth on the phase 45 so far aren't going mimic the univibe when the depth needs to work over a large range to nothing. Over a small range it's OK, mainly for tweaking but not for a user settable control.
The depth control "mod" as it is now, when you back depth off the moves the notch to a low frequency. It doesn't move the notch to "somewhere" in the middle like the univibe. By restricting the range of the depth control to a small range for tweaking that effect doesn't get out of hand. However having the depth control go to zero depth isn't going to work well at all and it won't be like the univibe.
The whole design effort for a univibe depth control would focus on getting the notches to be located at the correct frequencies over the range.
There are some depth mods for the Phase 90. They basically work over a narrow range. In fact I'm pretty sure they are just like the first mod I suggested, putting a pot in series with the 1M resistor to the bias trimpot wiper.
The biasing on these things is touchy so I'm reluctant to recommend untried "forum hacks" towards a univibe version.
Awesome info thank you again Rob.
I had a pack of these and tried one out. Seems to "clean" the signal up a tad, but feel I lost a a little "throb"
Do you or anyone recommend a better 5V zener for this application?
(https://i.postimg.cc/62H2zwKs/23550665-BE7-A-4251-80-B4-E863814861-DB.jpg) (https://postimg.cc/62H2zwKs)
QuoteI had a pack of these and tried one out. Seems to "clean" the signal up a tad, but feel I lost a a little "throb"
You might be able to tweak the LFO duty cycle by adding a large value resistor across the 10uF cap.
I'd say it would be possible to get what you want the problem is someone has to spend the time to do it. Lots of playing around tweaking the circuit. Adding stuff which isn't there now - that's probably the biggest stumbling block.
QuoteDo you or anyone recommend a better 5V zener for this application?
Any 5.1V 500mW zener will put you in the right zone. The original units averaged out at about 4.7V to 4.8V across the zener. You might see +/- 0.3V on that.
Some people can only get 1W zeners. The first thing to try would be a 5.6V 1W zener. And if the voltage is still too low you can drop the 10k resistor between the 9V rail and the zener to raise the zener voltage. Ideally you don't want to go below about 2.2k. If you can get 4.4V or above with 2k2 or above leave it. If it's still lower than 4.4V go for broke and put in a 1k.
Some 5.1V 1W zeners might work with the trick of lowering the 10k. No guarantees.
If you use a 4.7V 1W zener I doubt you will make 4.4V. If you have already bought one of these you might be able to add a 1N4148/1N914 silicon diode in series with the zener (pointing downward, the opposite direction to the zener). If that still doesn't make the voltage try dropping the 10k resistor. I suspect with a bit of stuffing around you can this to work - no problems.
A 4.7V 500mW zener might work by reducing the 10k.
A 5.6V 500mW zener will work but the voltage will be a little high. Better off not going there unless you are desperate.
The 5.1V 5W zeners you have are too large and the voltage will be low.
Perhaps try the series diode trick with the existing 4.7V 1W.
That pretty's much the DIY'es guide to zener tweaking!
Dude thank you for the master class! ;D
I ordered a set of 1/2w zeners last night. I'm def going to dig deeper in this circuit and shape it the best I can. May keep it as a one-knob, but I think having the some sort of depth may be valuable. I'll update with my findings. Thank you again Rob!
So I got a 5.1V .5W zener in there. Im reading 4.8v at the diode.
Still not a very "clean" signal. Kind of muddy and easily distorted. Usable with a fuzz but alone not a very clean phase.
QuoteSo I got a 5.1V .5W zener in there. Im reading 4.8v at the diode.
Still not a very "clean" signal. Kind of muddy and easily distorted. Usable with a fuzz but alone not a very clean phase.
That's a bit weird. Would you say it's cleaner than before? We could be dealing with multiple problems. The first is clipping due to the Vref being off. At 4.8V it's about as good as you will get. The second could be distortion from the JFETs themselves. Beyond that you could have a minor build error, or even a faulty opamp.
You do remember what VP values you got when you matched the JFETs? Having said that a few people have build phasers with surprisingly low VP values and didn't complain about it not being clean.
When you switch between effect and bypass you notice any boost in signal in effects mode? Any gain would point to too much gain on the first opamp.
Perhaps the next step is to listen to the clean path and the phased path separately. The circuit has two 10k's at the output of each signal path which mix the clean and phased paths. Lift the 10k from the phase path so you are listening only to clean signal. When you lift the 10k resistor the gain of the unit will double, just be aware of that. You should get a clean signal. If the clean signal isn't clean then stop there. Something is wrong. Remeasure the voltages on the output of each opamp.
Next is to restore the 10k on the phased signal and lift the 10k for the clean signal. That will give you a vibrato effect. The signal gain will be double normal like the previous test. Again the signal should be clean.
Perhaps going through those tests you will find something, or at least find something that narrows down where the problem is.
Thanks Rob for the response
I bought 2 sets of "quad matched" JFETS from "pedal parts and kits" to be used in P45/P90. I didn't check voltages before putting in the circuit. Probably should have!
As far testing the clean paths. I believe I tested this (circled) resistor using a 10k pot as sort of "mix". If I remember correctly I got a vibrato effect when pot was turned down and signal was clean.
Which is the 2nd 10k I should be testing?
(https://i.postimg.cc/hJrVKcZC/613-F840-F-62-F7-4-DE2-9-B2-A-A2406373-C630.png) (https://postimg.cc/hJrVKcZC)
Quotehanks Rob for the response
I bought 2 sets of "quad matched" JFETS from "pedal parts and kits" to be used in P45/P90. I didn't check voltages before putting in the circuit. Probably should have!
Not to worry. We should able to narrow things down anyway.
QuoteAs far testing the clean paths. I believe I tested this (circled) resistor using a 10k pot as sort of "mix". If I remember correctly I got a vibrato effect when pot was turned down and signal was clean.
Which is the 2nd 10k I should be testing?
That resistor was the correct one for vibrato. The key thing is not that you got vibrato but that you got a clean sounding vibrato. We are trying to find the source of the distorted sound.
The top lead of the 10k for the clean signal is three holes to left of the lower lead of the 10k you circled. It has long leads. The two 10ks connects to a track which is the whole width of the PCB and it goes to a 47n at the far left.
Quote
The top lead of the 10k for the clean signal is three holes to left of the lower lead of the 10k you circled. It has long leads. The two 10ks connects to a track which is the whole width of the PCB and it goes to a 47n at the far left.
Just to confirm:
(https://i.postimg.cc/f3X0C3w1/10K.png) (https://postimg.cc/f3X0C3w1)
That it.
Ok so I lifted the first "clean signal" 10k and everything sounds fine. More gain but clean.
Tested the 2nd "vibrato" resistor, it is clean but there is a slight "clipping" or breakup on part of the modulation cycle. It's only if you pick a note or play a chord hard that you get the "distortion". Useable but a bit muddy at certain points in the modulation.
Having trouble defining the "distortion" sorry, maybe wrong word. It's like when a chorus pedal or vibe distorts when you use a wah. It's hitting the ceiling or threshold of the effect. (I'm not an engineer obvi)
QuoteOk so I lifted the first "clean signal" 10k and everything sounds fine. More gain but clean.
Tested the 2nd "vibrato" resistor, it is clean but there is a slight "clipping" or breakup on part of the modulation cycle. It's only if you pick a note or play a chord hard that you get the "distortion". Useable but a bit muddy at certain points in the modulation.
Having trouble defining the "distortion" sorry, maybe wrong word. It's like when a chorus pedal or vibe distorts when you use a wah. It's hitting the ceiling or threshold of the effect. (I'm not an engineer obvi)
No problem. It's hard to convey finer points with words.
From you description, the clean path seems OK but the all-pass (phased) path is where the problem is. On face value that would imply the FETs are the cause. That doesn't necessarily mean the JFETs are faulty as that type of circuit does produce distortion. The difficulty is trying to work out if you circuit has an abnormal amount for that circuit. When the JFET VP values are low the distortion increases.
For sake of sanity it's probably a good idea to swap the positions of two opamps and redo the clean/phase check. If the opamps are OK then the distortion should remain. If one of the opamps is faulty the distorion will move to the clean path.
Assuming the opamps are OK. What you can do it mis-bias the JFETs. Lift the long leaded 10k so you are listening to phased path alone. Set the trimpot to one extreme and see if the distortion is gone or reduced. Set the trimpot to the other extreme and repeat. One end might sound cleaner than the other, that should be when the trimpot is set with the wiper connecting to ground.
Don't worry about losing the phase effect. The idea is to see if cutting off the JFETs electrically remove the distortion. That would be more evidence the issue lies with the JFETs.
While you at it, re-check the JFETs are in the correct way.
I'm thinking it's something with the jfets. I actually completely replaced the IC's yesterday and have the same issue.
Thanks for all the help, I'll perform the trim pot test next and report back.
QuoteI'm thinking it's something with the jfets. I actually completely replaced the IC's yesterday and have the same issue.
Thanks for all the help, I'll perform the trim pot test next and report back.
Ah OK, so yes, the JFETs are at the top of the list.
The weird thing is plenty of people have built Phase 90's with very low VP JFETs and they never complained about distortion issues. The Phase 90 doesn't even have the linearization nework that the Phase 45 has. The linearization networks are the 10k's and 10n caps around the JFETs, they reduce distortion when the signal level is high. The downside of the Phase 45 is it boosts the signal at the front end which will promote distortion. The Phase 90 doesn't do that as it actively mixes the clean and phased signals at the output. I have a old Ibanez 4-stage phaser and it boost the signal at the front-end and passively mixes at the output like the Phase 45 and I can't say I've noticed excessive distortion from that unit.
We don't really know if you JFETs have a low VP, maybe they don't. That would add more to the mystery.
This is why it would be good to check the JFET pinouts.
You might be able to make some small improvements by change the 2x10nF caps on the JFET gates to 50nF. However, it's probably best to pursue all other angles before doing unnecessary mods.
I forgot to mention JFET phasers are known for not being absolutely clean. To some that's the charm of them. In your case we need to know if it's beyond the normal amount.
Lifted long 10k and set trim pot to both extremes, clean on both sides.
Have another quad-matched set and (2) remaining from the quad I used for this pedal.
What is the best way to check V? What am I looking for?
could I use my tranny tester?
- as far as the amount of distortion, it may be normal. It's just not a very pretty sounding phase. When I play singular notes they get kind of muddied in the widest point of the modulation. (Maybe narrowest I don't know! Lol) just a certain point of the cycle it hits a thread hold. Again could be normal.
QuoteLifted long 10k and set trim pot to both extremes, clean on both sides.
So it's pretty clear now the objectionable distortion is due to the JFETs.
QuoteHave another quad-matched set and (2) remaining from the quad I used for this pedal.
What is the best way to check V? What am I looking for?
could I use my tranny tester?
You can measure the VP parameter for the JFET using a simple set-up like this. Don't worry too much about the
corrections on the side panel. It's really just documenting the small errors due to the test set-up.
(https://i.postimg.cc/c6X02rF2/JFET-VP-Measurement-Matcher-2021-10-20.png) (https://postimg.cc/c6X02rF2)
If the VP value is low there is generally more distortion. Typically you might get VP values around 1.5V to 2.5V for phasers but some of the ebay JFETs can have VP below 1V.
Quote- as far as the amount of distortion, it may be normal. It's just not a very pretty sounding phase. When I play singular notes they get kind of muddied in the widest point of the modulation. (Maybe narrowest I don't know! Lol) just a certain point of the cycle it hits a thread hold. Again could be normal.
The distortion is definitely not a black and white. It's always there to some extent.
For a given set of JFETs you can only go so far in reducing the distortion.
So what else can happen is if the JFETs have a low VPs, in relative terms the LFO circuit modulates the JFETs more. If this is the case, when the modulation changes direction you can get very jerky turn arounds. This can be fixed by changing a few resistor values. A few years back a forum member built a phase 90 with very low VP JFETs. With some tweaking the sweep was made to sound good. I might add despite the low VP's he didn't complain of a lot of distortion. Also, I don't remember a lot of distortion being present in the sound samples he posted.
Thanks rob. I'll try another set of JFETS when I get to my bench again.
The cycle is a bit jerky, hard to dial in nice "round" modulation. It can be done, but mostly "square" sounding
Quote from: DJPsychic on October 19, 2021, 08:22:38 PM
Thanks rob. I'll try another set of JFETS when I get to my bench again.
The cycle is a bit jerky, hard to dial in nice "round" modulation. It can be done, but mostly "square" sounding
OK, that might explain what's going on.
Checkout the mods on this post,
https://www.diystompboxes.com/smfforum/index.php?topic=122690.msg1159079#msg1159079
https://postlmg.cc/JshVHfzQ
The second circuit will work but third is likely to be better.
I don't recommend changing the resistor to 100k or adding the 150k. That might be going too far the VP's in that post were quite low and the small values only apply to that case. The large change from 1M to 100k meant we needed to change the 47nF (50nF) cap to 220nF. Smaller changes to the resistor won't need to go as high as 220nF.
You could just add 1M in place of the 150k shown in the third circuit. The 150k is an added component. A 1M pot might do to find the right value. If 1M outright is too low, ie. too much loss of sweep, then perhaps a 1M resistor in series with a 1M pot in the place of the 150k. Any change or adjustment to that resistor is likely to need a bias trimpot adjustment.
Measuring the VP helps guide the choice of the resistor a bit better but at the end of the day the thing that will fix it will be tweaking that resistor - which you can do with measuring the VP's. If you measure the VP's we know what we are dealing with.
Something worth mentioning is when you test JFETs with large source resistors, noise can can affect the reading quite a bit. The reading can seem stable but the value is wrong. Placing a 1 uF film cap across the source resistor/meter leads can stabilize the readings.
Quote from: Rob Strand on October 22, 2021, 05:59:02 PM
Something worth mentioning is when you test JFETs with large source resistors, noise can can affect the reading quite a bit. The reading can seem stable but the value is wrong. Placing a 1 uF film cap across the source resistor/meter leads can stabilize the readings.
Thanks Rob, good to know.
Waiting on a different set of JFETS from GGG.
I tested the ones I have and they all read 2.7-2.8
I may have been testing incorrectly though.
QuoteI tested the ones I have and they all read 2.7-2.8
I may have been testing incorrectly though.
If the 2.8V is the real value it's going to be hard to reduce the distortion. It's quite possible noise has stuffed-up the measurements.
If you doubt the measurements you can do a cross-check with different source resistors.
What you do is measure VGS in the test circuit with 10M (just the DMM), then add a 1M source to ground (ie. in parallel with the DMM), then repeat with 100k source to ground.
Next, apply the correction factors in the table (for say rd_on 300 ohm) to convert the VGS measurement to VP. 100k isn't in the table but for 100k + 10M DMM the correction is about 0.925.
In theory the VP measurements should all agree but in practice they don't quite match exactly. However what you will find is they are reasonably close.
If the VP values disagree then something might be wrong with the way you did the test.
It's not hard for the 10M test to be off if you are touching any of the wires but it can be off even if you aren't touching them. Sometimes powering the test circuit with a battery is more reliable than a DC power supply. I have a 1uF film cap in my junk box I use for testing high impedance circuits.
Using lower valued source resistors tends to make the reading more reliable/stable. The only down-side is the Vgs reading is a bit lower than the actual VP value (as can be seen from the small corrections in the table).
Received another matched set today, they measured 2.5 & 2.48v
Same issue.
I think I'm going to put this project on the back burner for the time being.
I've done all I'm willing to do for now.
Thanks Rob for all the great tips.
I can't see anything obvious. The VPs are nice and high and the problem is consistent with different JFETs. There's probably one silly thing not right. Maybe if you give it a break and come back with fresh eyes you will see it straight away.
Pardon me if this has already been addressed, I didn't read the thread, but your trimmer appears to be in a different location and/or orientation than the layout.
Quote from: fowl on October 25, 2021, 03:07:46 AM
Pardon me if this has already been addressed, I didn't read the thread, but your trimmer appears to be in a different location and/or orientation than the layout.
I think it's just the photo but the trim pot looks to be in the right location :)
I guess it's just a weird angle, but it just doesn't look right.
(https://i.postimg.cc/X73TV0dW/Untitled.jpg)
That trim was a big big but was in the right spot. I've since changed and appears to be correct as well.
(https://i.postimg.cc/sMVdrGP8/3-E772-AB0-7502-426-D-8-B73-724-EED125432.jpg) (https://postimg.cc/sMVdrGP8)
(https://i.postimg.cc/DWZ9WVMP/IMG-0292.jpg) (https://postimg.cc/DWZ9WVMP)
Right, sorry, I should have looked at your back side picture in your first post.
Carry on.
Quote from: fowl on October 25, 2021, 09:32:59 AM
Right, sorry, I should have looked at your back side picture in your first post.
Carry on.
All good, The more eyes on it the better. I was hoping you were right!
Early on in the thread you had 2N5952's, which matched the layout.
I'm not sure what the new devices you got were. For parts like the 2N5457's, the pinouts are flipped compared to the 2N5952's.
Yes sir, I checked the pinout. They are 2n5485.
The pic I just posted is a bit older. New set are reversed correct.
The only other mod I've done is I raised the 150k to 220k (I think) to match bypass unity volume.
But I was having the distortion issue before that so not the cause.
QuoteYes sir, I checked the pinout. They are 2n5485.
The pic I just posted is a bit older. New set are reversed correct.
Cool, I was just making sure.
Quote
The only other mod I've done is I raised the 150k to 220k (I think) to match bypass unity volume.
No problem there.
Quote
But I was having the distortion issue before that so not the cause.
Yes, it was a long shot. The thinking was it's possible a misconnected JFET can act like a diode. You can actually get diodes to work in a phaser. Normal they distort. I saw one professional design which used 20 diodes in series to keep the distortion down (!!!).