Kleos - Dipole Line Array

[Johnloudb]

Man, no sparks? That's no fun... there's a reason I call electronics wires and sparks, you know... gotta have both!

Haha, I know, I was disappointed!

[Johnloudb]

I had it all working well, and then got it all wired up and now I've got distortion at the output of the high frequency filter. I think the input of the JFET opamp got damaged, not sure how but suspect the loose cap at the opamp input that is not soldered. It had an intermittent connection. Just going to solder that in there. I can always parallel another cap if I need to increase the value, will start with a low value.

the waveform looks fine at the output of all the JFETs buffers, except the last one which has very slight distortion which could be due to the opamp input being damaged and perhaps pulling too much current? if not I'll replace that JFET pair too.

Anyway, got more opamps on the way. could be here Friday. But it works!

[Johnloudb]

I am at a complete loss!!! The new op amp came yesterday and I replaced it, and even the JFET buffer before the op amp and still get the exact same distortion at the output on the High Pass filter, and the slight distortion at the output of the buffer.

What could be doing this???? It's just on the positive half cycle, what the hell!!!???

I should mention that I hooked up the output of my function generator to the output of my crossover with both turned on by accident. That's what I thought may have damaged the op amp the first time. Okay, so made exact same mistake just before measure this time too!

But there is a 422 ohm resistor at the output!!! so it shouldn't damage anything!!! To make sure I just connect the output of my function generator to the output of the lowpass filter ... it still works perfectly!!!

I don't know, I mean both op amp sections share the same power supply and filter caps. So, not going to bother with them. I will check resistor values and maybe replace the wima cap in series with the op amp input.

Any thoughts??? This is just too weird and it work at one time, then I wired up the inputs and output to the chassis and then i got this problem ... ?????

?????????????????????

[JonMarsh]

We've got the wedding couple as guests this weekend, so I'm short on time- I'll have to go back in this thread train and find the schematic- or you could re-link it for me!

Sometimes FET input op amps can be a bit touchy, but that's a pretty gross distortion product for anything coming out of an op amp- modern ones are usually down in the dot triple zero range, and you're in the not visible to the eye point by the time you get down to about 1% THD or so. Even more than that. Refresh my memory- which op amp are you using? Are you sure you don't have an asymmetric load on the output of that chip, loading it down? And what's the frequency of the test signal?

[Johnloudb]

We've got the wedding couple as guests this weekend, so I'm short on time- I'll have to go back in this thread train and find the schematic- or you could re-link it for me!

Sometimes FET input op amps can be a bit touchy, but that's a pretty gross distortion product for anything coming out of an op amp- modern ones are usually down in the dot triple zero range, and you're in the not visible to the eye point by the time you get down to about 1% THD or so. Even more than that. Refresh my memory- which op amp are you using? Are you sure you don't have an asymmetric load on the output of that chip, loading it down? And what's the frequency of the test signal?

I'm using the LME49880 op amp. Just a 100kohm resistor at the output. The waveform there is 1-2khz.

I notice that at higher frequencies above 5khz. the distortion gets let's less or changes to look more like clipping. I'll check resistor values and perhaps there is a load problem at the output like you suggest.

I'll repost the schematic too. Thanks!

[Johnloudb]

The feedback path is actually the biggest load. a few values are slightly different on the schematic. I'll go measure.

[Johnloudb]

The feedback path measured at 4.9k which is right on given that I used 10k for R33 and 1k for R35, and they are in parallel. so things look okay there.

Perhaps the feedback cap is damaged.

You enjoy your friends Jon! I have other stuff to do today too. But appreciate any input you have when you get a chance. Will get to the bottom of this in time, I'm sure.

[Johnloudb]

Oh, I'm now suspecting that the 221 ohm resistor before the op amp input is too low. I think it makes sense given the wierd waveform changes and that it seems a somewhat intermittent problem, and it has some affect on the JFET buffer output. Well, we'll see, I'll try changing that perhaps 800 or ever 1k should work. On the low pass there is significant resistance between the JFET ouput and op amp input.

[Johnloudb]

still having problems even with a 1.2k ohm resistor (R32) in series with the op amp input. I also get distortion from the JFET buffer output at lower frequencies like 400hz - 1khz.

I'm going to clean the flux off the board again and try to get this figure out. Maybe C18 is damaged and leaking at low frequencies. I did test the cap and it measured the correct capacitance, but maybe a lower frequencies it leaks? I don't know ...

I'll keep working at it.

The first pic is 1khz at the output and the second on is 10khz. shows different distortion waveforms.

[Hank]

Hang in there, John. When you first cleaned the flux, could you have saturated that cap? don't know what you cleaned with or if that particular cap is well sealed. Do clean again and yank the cap and measure it.

[Johnloudb]

Hank in there, John. When you first cleaned the flux, could you have saturated that cap? don't know what you cleaned with or if that particular cap is well sealed. Do clean again and yank the cap and measure it.

Thanks Hank, The flux remover was sprayed on the underside of the board and didn't come in contact with any parts. It's supposed to be safe with most plastics. I did clean the flux off and it may have made a difference. That bad distortion at 1khz is still there, but it looks like the opamp is working okay cause I'm now getting that same kind of distortion at the output of the JFET buffer as the opamp. May be a cap in the crossover causing that distortion and makes sense since it happens near the crossover frequency. I think I'll take some distortion measurements next anx perhaps that will clear up some things.

[Johnloudb]

Just a quick update. I'm going to do some more investigating tonight and tomorrow, probably reflow some solder joints and take more measurements of my crossover. See if I can pinpoint the problem and make some sense of all this. Things have been kind of complicated lately with other activities and stuff ... School starts Monday but I can't study all the time and will keep at this.

[Johnloudb]

Well, I've working on this a bit, red lowing some solder joints in the circuit that looked suspect. Also, hard trying to chatch up with math and electromagnetics I took over 17 years ago! This is for my lasers class, but it's coming along.

This problems or problems with my crossover are really puzzling. It seems to be some kind of phase based distortion only on the positive half cycle, and changes with frequency. The distortion originates at the input of the opamp. I think the input just may be damaged, don't think a bad cap would do this.

May change op amp to the LME 49722 after some more investigating.

[cjd]

This has me wary of going active! I'd be completely stuck where you keep testing. Is it the specifics of how youchoseto implement, or the nature of the beast? I'd end up with boring SK opamp setups, but still...

I sure hope you get this sorted.

C

[JonMarsh]

John, if I had some more spare time, I'd get some detailed macro models for the op amps you're using and simulate your circuit first. If you haven't got this sorted by late fall, I'll take a look at it- could have more free time then, if work goes right.

[Johnloudb]

This has me wary of going active! I'd be completely stuck where you keep testing. Is it the specifics of how youchoseto implement, or the nature of the beast? I'd end up with boring SK opamp setups, but still...

I sure hope you get this sorted.

C

I'll get it sorted out ... The prototype worked well, but I have changed some resistor and cap values since then, but don't see how those slight changes could cause this ... But not positive.

I think you'd be fine going active if you start with a proven design, and modify it to accomplish what you want. Maybe start with one of Marchand Electronics boards and then work from there.

[Johnloudb]

John, if I had some more spare time, I'd get some detailed macro models for the op amps you're using and simulate your circuit first. If you haven't got this sorted by late fall, I'll take a look at it- could have more free time then, if work goes right.

Thanks Jon! Any help would be welcome. I had another look at it and it yesterday and it looks like two problems, not just the op amp. The problems are at low frequencies near the crossover frequency and below, for the crossover filters. At 2kHz all looks good though. At 1khz the opamp input causes the pic I showed awhile back, but the crossover buffers are fine at that frequency though.

I'll take some pics later today and post them. Just been trying to get ready for school and have my first actual lasers class tomorrow, as the professor was away last week. But things will settle down once I get into it I'm sure, kind nervous, it's been awhile!

[Johnloudb]

Well, I haven't done anything yet, but I suspect that the second JFET buffer and and that opamp input are damaged. The only reasonable explanation I can think of, but will check it out this weekend. The opamp does not work at all right now for the high pass filter I'm having problems with. So may have damaged it further when reflowing a solder connection, but will check it out this weekend.

[Hank]

Motivation: Jon and I are ready to look for a white van to rent...
Just sayin'

[Johnloudb]

Motivation: Jon and I are ready to look for a white van to rent...
Just sayin'

Oh, I forgot, the white van ... Something about you two kidnapping my speakers ... I hear ya! Anyway, we'll see what I can accomplish this weekend.

[Johnloudb]

Okay, here are the measurements I promised. Note that the waveform after the input buffer looks fine! Then everything goes to hell! So got this massive distortion, at 600 hz and below, it does change phase with lower frequencies, but here is what's happening at 400Hz.

Here is after the first buffer:


Here is after the first LP filter/buffer:



Here is after the second LP filter/buffer:



Here is at the opamp input:



The wave gets attenuated after each stage cause of attenuation of the filter below the crossover frequency.

I noticed that the distortion is a copy of the distortion after the first LP filter, so I'm guessing that a damage JFET causing this ... it only happens on the positive have cycle of the wave. But open to other ideas of course. A question I have though, is does this occur only at low frequencies below the crossover frequency? Just seems weird ... and it changes with freuquency like it is flattening the signwave at different places.

[Johnloudb]

Hey, the semester is done and got through Lasers well! Just couldn't focus on audio during that period ... but got the holiday break now so will be posting updates and be done before Spring semester starts. Fingers crossed!

Jon! I owe you a music album, disc or digital. I honor my bets, and hey it's the holidays! Edit: PM sent

[wkhanna]

Congrats on the academic accomplishments!
Investing in a good education now will likely help pay for audio extravagance in the future!:T

[Johnloudb]

Congrats on the academic accomplishments!
Investing in a good education now will likely help pay for audio extravagance in the future!:T

Thanks Bill! Yes, I certainly hope so! Next semester I'm taking Analog Integrated Circuit Design and something else. Fun!!! Just about 34 hours between me and my degree!

[JonMarsh]

Hey, the semester is done and got through Lasers well! Just couldn't focus on audio during that period ... but got the holiday break now so will be posting updates and be done before Spring semester starts. Fingers crossed!

Jon! I owe you a music album, disc or digital. I honor my bets, and hey it's the holidays! Edit: PM sent

I really appreciate you getting back to me about that, but what I'd like you to do is buy yourself a copy of Cafe Blue (CD or HD Tracks download) to listen to when you get these puppies running.

Speaking of important milestones like your school, it looks like we'll be wrapping up this project in Cupertino around mid January, and I can get a more normal life back. If you're still struggling with the crossover, we should hook up and see if I can help you more directly in trouble shooting your issues.

[wkhanna]

Now that is an offer not to be refused!


Image not available

[Johnloudb]

I really appreciate you getting back to me about that, but what I'd like you to do is buy yourself a copy of Cafe Blue (CD or HD Tracks download) to listen to when you get these puppies running.

Speaking of important milestones like your school, it looks like we'll be wrapping up this project in Cupertino around mid January, and I can get a more normal life back. If you're still struggling with the crossover, we should hook up and see if I can help you more directly in trouble shooting your issues.

Congrats with the project, glad you'll be less busy for awhile!

Okay, if that's your wish, I'll get the Cafe Blue download, since I have a Pono Player arriving soon. Will be nice to hear it.

Yeah, I really need to spend some time with that crossover, hopefully the next couple days. If replacing those JFETs in the first LP filter doesn't help, not sure where to turn. I'll post once I find out if it changes things. Thanks!

[Johnloudb]

I am now presently looking at my crossover and preparing to put the new FETs in, after removing the pair in the first section of HP filter.

I needed time to decompress after school and enjoy the holidays. I should have plenty of time to get this thing going. Been cleaning a table off earlier today, in my room (messy!), so I have a place to work.

Getting after it now. More to come ...

[Johnloudb]

JFETs installed and burning 13.5mA of current ... As they should. Will look at them on the scope tomorrow. I have no good expectations after all that's happened.

[Johnloudb]

No audio measurements for time being. Power is out and it is 8 degrees outside, 60+ MPH winds and snowdrifts outside... Brrrrr

[wkhanna]

Yikes!

Light a fire?

[Johnloudb]

Yikes!

Light a fire?

We have gas fireplace insert, but not working, remote got lost, and I'm not sure it works without electricity.

My dad turned on the gas burners on kitchen stove. I got upset ... Does anyone else care about CO poisoning?

Anyway, the power is back and all is well.

[wkhanna]

Well that good!

Now get back to work on those speakers! :W

[Johnloudb]

Well that good!

Now get back to work on those speakers! :W

Absolutely! I did hook it up to a scope this morning and still have the same distortion but slightly different less noticeable, also on the positive half cycle of the waveform. It only noticeable when you get near of below the crossover point.

Here's my idea, and I think it is the JFET input capacitance interacting with high pass series capacitors in the high pass filter. I used caps twice the size of the ones in my prototype filter, to lower impedance at the JFET gate ... I think this backfired. The crossover frequency was the same as I altered the resistor values to compensate. I don't get the same problem on the low pass filter. So, I think putting a larger gate stopper between the caps and the transistor should solve the problem.

I thinking 1k ohm should do it. Does that sound okay to everyone? Any thoughts? I'm so tired of chasing ghosts, but that's my next planed move.

[Johnloudb]

Happy New Year Friends!!!!

On a side note I bought books for my Analog Integrated Circuit Design class a couple days ago ... Only FIVE text books for that class! One required, two recommended, and two optional. I got away with buying just two for now, since that's all the bookstore had ordered, $275.00 used! $400 in books so far for Spring Semester, just two classes. Geezz, school is just so unaffordable nowadays!

[wkhanna]

Happy New year, John!

Don't be too concerned about the $400.
You will probably get $0.10 on the dollar when you go to sell them at the end of the semester. 8O :roll: :M

[JonMarsh]

Happy New Year John!

Regarding your idea, after I have some coffee I'll think about it- need to go back and find the schematic. The cheater way would be to setup a simulation of this. Since you're studying Analog IC design, I'd suggest you might want to do that, too. Have you heard of TINA, TI's free SPICE simulator? OR LTSPICE? They would fit your budget... should work OK with standard models for the type of parts your using. If it's the kind of interaction your positing, it should show up there, too, and be analyzable by FFT.

[Johnloudb]

Happy New year, John!

Don't be too concerned about the $400.
You will probably get $0.10 on the dollar when you go to sell them at the end of the semester. 8O :roll: :M

Yep, one reason I keep all my books. Other reason is I like to have them for reference.

[Johnloudb]

Happy New Year John!

Regarding your idea, after I have some coffee I'll think about it- need to go back and find the schematic. The cheater way would be to setup a simulation of this. Since you're studying Analog IC design, I'd suggest you might want to do that, too. Have you heard of TINA, TI's free SPICE simulator? OR LTSPICE? They would fit your budget... should work OK with standard models for the type of parts your using. If it's the kind of interaction your positing, it should show up there, too, and be analyzable by FFT.

Well this is a puzzle. I do use SPICE, B^2 SPICE 5, and simulated the circuit before I built anything. I just ran some sims and they don't up anything bad.

[Johnloudb]

Jon, sorry, the sine waves are hard to see. They are of 1kHz and 500Hz. Well, I don't know what the problem is in my circuit. I'll post the most recent schematic next.

[Johnloudb]

Here is the schematic ... I know it is hard to read, but hopefully good enough.

[Johnloudb]

Alright, I just took some pics of the measure waveforms again, at 400Hz. So this first one is after the first HP buffer. And the second one is after the Second HP buffer. Well, I'm going to try increasing the gate capacitance of the first buffer, and see if it clears up that distortion on the positive half cycle. Then if does, I'll try it on the second one. The distortion only appears at and below the crossover point of 600 - 700Hz. So I the filter before the JFET buffer has something to do with this. The distortion region also changed with frequency in past measurements, so I'm thinking there is some instability at a certain region operation for the buffer. So, will try larger gate stoppers, and see what happens.

[Hank]

Hi John - happy new year to you! I was thinking you'd get some more testing done during the holidays. Are you going to try one of the sim programs that Jon recommended?

[Johnloudb]

Hi John - happy new year to you! I was thinking you'd get some more testing done during the holidays. Are you going to try one of the sim programs that Jon recommended?

Thanks Hank! Same to you! The sim software I use B^2 SPICE is a good one and I'm familiar with it. The ones Jon mentioned are good too, but I'd have to learn how to use those.

Oh, I noticed a big Oops in my last post, I'm not increasing the gate capacitance, as if I had any control over it. I'm just increasing the gate stoppers to 1.3 Kohm. I did run a sim of that and it had no affect on the simulated distortion ... That's good. But will it get rid of the real world distortion in my circuit, going to find out. I did find finally some good resistors in my parts mess for the job. Hopefully after I get some shopping done, I'll put those later today and report back.

I was pleasant surprised whdn talking to my school buddy Andrew that school doesn't start till the 12th!

He's says, "my classes don't start till next week" and I'm like "well, mine probably don't either"

I hate the way the school website is organized. I couldn't find the date classes start, then I scrolled down the page past the "important" dates calendar for Spring semester, and there it says classes start Jan 12th. Oh, I guess that's not an important date!??? Stupid! Well I should have scrolled down but I didn't know anything was down there.

Anyway, extra time for speakers!

[Johnloudb]

Well, replaced the gate stopper resistor on the first HP filter. No difference!

Okay, so let this be a lesson to me! Don't change component values when you have a working prototype with low distortion.

I was able to completely remove the old resistor this time, and put in the new one. But caps are harder to replace. I should have put in those 3M sockets so I could change components easier. But they raise the components off the board quite a bit and I was worried about that causing problems.

Not sure what to do now. I guess I could put smaller caps in, say .0047uF like I had in before, and changing to two filter resistors accordingly. Hmmm ...

Any thoughts on what to check out???