I wasn't able to get the static sound again, so I was starting to think that I had the levels set too high on my audio interface or in Logic, but looking at the scope I'm wondering if I am getting HF oscillations. I'm attaching 2 images.
The first is what the outputs of the input op amp (the top left chip, right?) look like. Are those ripples in the saw tooth wave HF oscs?
The second photo is from one of the 18K resistors between the input op amp and the APF ladder (signal taken from the lead on the op amp side not the ladder side). It's not at the op amp, so I'm not sure about HF oscillations effecting the signal at the resistor like this, but it kind of looks like what you were describing above - this shot is at a time base of 10-20us and is a sine wave but not one centered around ground.
Also, again, not exactly sure what the expect at the Aux output versus Main output, but to clarify when I said earlier that the vibrato volume didn't drop on the Aux output, what's keeping the volume up there is that I'm still getting dry signal mixed with the APF signal in vibrato mode. Is that right? Also when I play around with the Pitch and Osc Level controls a bit, even on the Main output, I can get the level difference between phaser and vibrato a little smaller. However, looking at the outputs of the OPA2134, U2, with the scope, the signal there is much much lower than what I'm seeing at the input op amp, U1.
IMG_2660.JPG
Description:
Filesize:
1.44 MB
Viewed:
484 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.
IMG_2662.JPG
Description:
Filesize:
1.11 MB
Viewed:
461 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.
Also, again, not exactly sure what the expect at the Aux output versus Main output, but to clarify when I said earlier that the vibrato volume didn't drop on the Aux output
JH. _________________ "I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
How did the scope images look to you? From what I describe where those signals were taken do you see any signs of HF oscillation?
The upper picture might have HF on the lower part (where there is a band instead of a line). But I cannot tell this from the picture - it might be something else.
As I tried to say, it's extremely difficult to make a remote analysis on a circuit. Do you have someone living nearby who is skilled with that kind of stuff, and can detect HF oscillation with a scope? (I tried to describe it above, with short time base and all, but it's *really* hard to explain this from afar. At least for me.)
JH. _________________ "I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
From what I describe where those signals were taken do you see any signs of HF oscillation?
You should try to zoom in a bit using your scope controls to the interesting bit in the wave form, that is make the timebase run faster and use a higher input sensitivity, the interesting bit would be the bit in the image attached, try to make that full screen or maybe zoom in even more. In the current image it could just be motion blur, hard to tell.
scope-2.jpg
Description:
Filesize:
23.05 KB
Viewed:
18030 Time(s)
_________________ Jan
also .. could someone please turn down the thermostat a bit.
Ok, I couldn't get a non-blurry photo, so here's a short video instead. Now I think I see what you mean by a "band" though and I'm not seeing that here nor am I seeing it on any of the other audio op amp outputs, so it would seem I'm free of HF oscillations, yes?
I poked around a little more, though, and now I'm not so sure the signal coming out of the APF is lower than the dry signal going into the stereo matrix. Juergen, correct me if I'm wrong, but the output from pin 1 of U3 is all APF, right? That signal is strong. I'm able to trace it to R35, where it's still strong and looks equal to the signal coming out of the mode switch into R34, which is the dry signal, right? On the other side of each of these resistors, though, where they junction with U4A, I lose the signal on the scope. I assume this is normal because the output coming out of pin 1, the Main out, is strong until switched to Vibrato mode, then it drops considerably as you've heard. Since the signal is pretty consistent between modes on the Aux channel, it seems like something is going on around around the Main out components. They all check for continuity and are the right parts in the right places. Switched out the op amp IC too but same problem. Also no more static or intermittent connection sounds when I poke the components. I'm really stumped and frustrated.
Ok, I couldn't get a non-blurry photo, so here's a short video instead. Now I think I see what you mean by a "band" though and I'm not seeing that here nor am I seeing it on any of the other audio op amp outputs, so it would seem I'm free of HF oscillations, yes?
No HF, as far as I can tell.
Quote:
I poked around a little more, though, and now I'm not so sure the signal coming out of the APF is lower than the dry signal going into the stereo matrix. Juergen, correct me if I'm wrong, but the output from pin 1 of U3 is all APF, right?
Right.
Quote:
That signal is strong. I'm able to trace it to R35, where it's still strong and looks equal to the signal coming out of the mode switch into R34, which is the dry signal, right? On the other side of each of these resistors, though, where they junction with U4A, I lose the signal on the scope.
... which is to be expected. It's a virtual GND summing node ...
Quote:
I assume this is normal because the output coming out of pin 1, the Main out, is strong until switched to Vibrato mode, then it drops considerably as you've heard. Since the signal is pretty consistent between modes on the Aux channel, it seems like something is going on around around the Main out components. They all check for continuity and are the right parts in the right places. Switched out the op amp IC too but same problem. Also no more static or intermittent connection sounds when I poke the components. I'm really stumped and frustrated.
All of what you describe sounds reasonable, and like it should be.
Except your output level.
And that static noise that came (and went).
JH. _________________ "I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
In the mono sample (actually the stereo sample as well) I posted earlier, does the mix of APF and dry signal coming out of main sound right for the phaser mode - does the phasing sound good/right to you for the Main channel, basically (besides obviously the static sound on the stereo sample)? That's the main thing I'm concerned about - that the APF is too low in the phaser mix as well. If that sounds right I will poke around a little more and worst case just won't use in vibrato mode.
Well, I finally got setup for stereo. Here's the twin Tau phasers, fed with 3 MOTM 310 VCOs (tuned to unison and a fifth). Resonance on both Taus just below self-oscillation, slow LFO rates with about 1/3 depth. Nothing else - just VCOs and one Tau in each ear - but in Stereo this time.
The "Boop" you hear (just over halfway through) is the switching of the colour switches.
By the way, I'm pretty sure I figured out my problem. I have the switch wired incorrectly. I have R42 connecting to R34 and R41 connecting to R39 when in Phaser mode. Not sure offhand why that would cause the volume issue, but that is clearly incorrect and mixing the outputs incorrectly in Phaser mode. Will report back once I've rewired the switch.
EDIT - Just rewired and while I *think* the phasing might sound better the volume drop on the Main output between modes is still noticeable
100k log (or "audio taper") is what I recommend.
100k lin will work also, of course, but the variation of LFO rate with rotation of the potentiometer knob will be different. See what behaviour you like better - that's the one you choose. Electrically there is no difference.
JH. _________________ "I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
I'm getting noise from my Tau. Not the intermittent static like in the audio sample earlier but a consistent white noise. I can hear it with an input and without - especially if the input audio is mostly low end, there's a higher pitched swooshing of the noise mixed with it. I see you suggest shielding the input cable and the switch cable if either is long. These are both as short as they can be. Plus, not sure if this means anything, but I turn the input attenuator all the way down and the noise level stays the same (in other words, not sure if that rules out needing to the shield the input or not). Does this sound like a shielding issue? I can upload a sample if it would help but it is a faint but clear higher frequency white noise (rather than a lower frequency hum).
Also I followed your "basic" wiring for the outputs (except for the level pots) so I did not include the 10uf bip caps and 100K pull down resistors on the outputs - could this be the problem?
I'm getting noise from my Tau. Not the intermittent static like in the audio sample earlier but a consistent white noise. I can hear it with an input and without - especially if the input audio is mostly low end, there's a higher pitched swooshing of the noise mixed with it. I see you suggest shielding the input cable and the switch cable if either is long. These are both as short as they can be. Plus, not sure if this means anything, but I turn the input attenuator all the way down and the noise level stays the same (in other words, not sure if that rules out needing to the shield the input or not). Does this sound like a shielding issue? I can upload a sample if it would help but it is a faint but clear higher frequency white noise (rather than a lower frequency hum).
Also I followed your "basic" wiring for the outputs (except for the level pots) so I did not include the 10uf bip caps and 100K pull down resistors on the outputs - could this be the problem?
Thanks.
You will always have some noise. Nothing wrong about that, especially with signals in the mV range passing thru 40 PN junctions.
Output cap blocks DC, not noise.
JH. _________________ "I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
Would it be of any use to reduce the number of stages ?...
it's a simple mod, does it worth trying a more subtul 12 stages effect ?
In theory, it's a simple modification; just select a stage more "upstream" in with a 2pole switch. But that part of the circuit is very sensitive (high impedance, low level), so I can imagine very good shielding of the cables to and from the switch would be required.
JH. _________________ "I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
JH. _________________ "I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
Joined: Jan 21, 2007 Posts: 583 Location: France
Audio files: 3
Posted: Sun Mar 22, 2009 1:05 pm Post subject:
Hi,
i'm real sorry but i can't find any note about GAIN trimming.
My TAU is almost finished, new panel, and it has its proper psu now, so i'd like to trim it once.
(can't remember what i've done with that gain trimmer eight months ago )
PS : I've just realized that cv input can act as a lfo output due to the "crossfade style modulation", range pot acting like a strange attenuator
Hi,
i'm real sorry but i can't find any note about GAIN trimming.
There isn't much to say about gain trimming.
Just set it by ear - it won't make much difference anyway.
Background:
In most Phasers, precise wet/dry level trimming is important, because of Notch Depth. In the Tau, there are so many notches that it doesn't make much difference which one is deepest. (It's impossible to max them all, anyway.)
JH. _________________ "I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
Joined: Jan 21, 2007 Posts: 583 Location: France
Audio files: 3
Posted: Sun Mar 22, 2009 4:46 pm Post subject:
Cool !
All is perfectly tuned now. honey-sounding.
I've understood that GAIN trimmer prevents your gear from auto-oscillation (input pot fully ccw, keyboard into 1v/o), according to your Manual Shift setting and Pitch trimming.
Or maybe I have something wrong while it's sounding pleasant
Maybe I'll try to tap 12stages to see what happens, as now, with definite panel/wiring, there is no more LED clicks on audio outputs.
You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum You cannot attach files in this forum You can download files in this forum
Forum index » DIY Hardware and Software » Jürgen Haible designs
FAQ
Calendar
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
Chat Room
