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Active Monitor Pops after Op Amp Swap
Old 1 week ago
  #31
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Brian M. Boykin's Avatar
Quote:
Originally Posted by enginefire View Post
I’ve never tried to use any soic.. I hear they are making better op amps in the surface mount packaging, I just very been great at soldering that small, nor have I tried to find a good and affordable adaptor board. Last time I looked, a few years back, the adaptor board were like $5 a piece!
If your doing an entire console then yes, it gets pricy, however, when your doing a compressors input and output stage it’s not so bad. I have one Ashly SC55 left to do and they’re a lot of work. They require the 4136 adapter. The VCA’s are made up of one dual, three singles, and a transistor supermatched pair. Totally worth it though. They do their job so well. I use them on stereo guitars to level them out. I have 4 total including the older globe model which I think turned out the best of the bunch.
Old 1 week ago
  #32
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TobyToby's Avatar
 

Quote:
Originally Posted by Brian M. Boykin View Post
I used dale/Vishay in my console also. Going from carbons to metal film made a difference sonically, better, who knows? I’ve often wondered about changing caps in the feedback loop. I used WIMA’s in the EQ section. Same values. The console was internally Star grounded also. Pics speak a thousand words and just looking at those I got some questions answers. I’ve also noticed ceramics in the audio path and thought they could be changed out also. Capacitance is capacitance, but my ears can hear the difference in the different types. I’ll try some poly’s on a module. I have 8 spares I’m gonna experiment with. I added 23pf to the op amps that didn’t have them. Soldered them right to the pins on the foil side. I’ve read putting them across the resistor works also. Any input is welcome. I’m always learning.
Wima's are a nice & solid choice. Unfortunately certain values from their FKP series [which I prefer over the MKP series] are hard/unable to find in a small package. I also like polystyrene caps in the high/treble section of the EQ [if they have a a hint of audible distortion than I like the sound of it]
Old 1 week ago
  #33
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Styroflex caps are hard to fake, eBay had been great for them. Lots of 100 for like $10 creep up all the time. Great in eq, and in the feedback for op amps.
Wima caps are great too.
Old 1 week ago
  #34
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Brian M. Boykin's Avatar
So polystyrene and silver mica to replace ceramics in the audio path? Seems like the mic parts kits I’ve built use silver mica on the PCB and polystyrene for the capsule buffer cap. So I should try both and my ears decide? Could knock out a module in 30min I’d think.
Old 1 week ago
  #35
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Film caps are also good, even metalized film caps are ok in places, esp higher cap value and where size is a limitation. No hard and fast rules, I usually just use what I have around, plus there are laws of diminishing returns and maybe there are other quality choke points that would hide any potential benefit etc. Like at a certain point, where do you draw the line? Some caps cost $50 a pop and only really sound good if you use esoteric silver moon solder delivered from nasa in 1950. How’s your flux capacitor ?
Old 1 week ago
  #36
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Brian M. Boykin's Avatar
Diminishing returns is a very real issue. I count 8 ceramics in the audio path per input module including the ones I added in feedback loops. I usually do value for value unless someone gives me trusted intel from mods they did and measured. It’s a crap shoot otherwise unless your extending octaves. I bypass electro’s in the audio path with .01 WIMA’s. I’ll try some of this on the 8 stick modules I have.
Old 1 week ago
  #37
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Quote:
Originally Posted by samwinston123
TL072 is JFET input so input bias current is quite low at 65pA, vs 10nA for the bipolar input LME.
This.

The offset monkey-motion at startup is simply the consequent of one main reasons that bipolar-input opamps like the LME49720 simply cannot be considered as universal replacements for JFET-input opamps like the TL072. You can either ignore it, identify the point in the chain causing the problem and engineer a solution (i.e. lower DC impedance or add a startup muting circuit), or swap in some JFET-input opamps with a low input offset current.
Old 1 week ago
  #38
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Brian M. Boykin's Avatar
Quote:
Originally Posted by kirkus View Post
This.

The offset monkey-motion at startup is simply the consequent of one main reasons that bipolar-input opamps like the LME49720 simply cannot be considered as universal replacements for JFET-input opamps like the TL072. You can either ignore it, identify the point in the chain causing the problem and engineer a solution (i.e. lower DC impedance or add a startup muting circuit), or swap in some JFET-input opamps with a low input offset current.
Ignoring is not an option. Swapping in a JFET with a low input offset current would be the most practical for vs engineering it out. I’m not there yet. Thanks for the input. You have any suggestions?
Old 1 week ago
  #39
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Brian M. Boykin's Avatar
The opa1642 on a browndog adapter seems to fit the bill and is recommended as a drop in for the tl072 by several people I trust. Low bias, low current, and lower noise and distortion than the opa2134. I’ve wondered about these. I’ll give them a shot. It’ll be a little over a $100 for both monitors. I’ll pull the monitor back apart in the morning and get serious about recapping them also.
Old 1 week ago
  #40
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Those are both at the top of the list for low-noise FET-input audio opamps. Personally, I don't think that the extra cost and (especially) time warrants going the route of putting SOICs on adapters . . . the difference in numbers is academic, and the Johnson noise from the likely associated circuit impedances will vastly swamp the opamp noise (otherwise they wouldn't be using FET-input opamps to begin with). But you certainly can't go wrong with either.
Old 1 week ago
  #41
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Brian M. Boykin's Avatar
Quote:
Originally Posted by kirkus View Post
Those are both at the top of the list for low-noise FET-input audio opamps. Personally, I don't think that the extra cost and (especially) time warrants going the route of putting SOICs on adapters . . . the difference in numbers is academic, and the Johnson noise from the likely associated circuit impedances will vastly swamp the opamp noise (otherwise they wouldn't be using FET-input opamps to begin with). But you certainly can't go wrong with either.
I have a slew of 2134’s in my parts bin. I’ll try some before I get crazy with the 1642’s. I just feel the 2134’s are not as neutral/invisible as others I’ve tried. I like them in input stages and compressors because I feel they impart depth and have a fuller sound, not what I want in a monitor. However, I’ve done listening tests against tl072’s, 5532’s, and what I now believe to be bunk 49720’s. So who knows. I need to start over with the 4562’s I have coming in and retrain my ears.
Old 1 week ago
  #42
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Brian M. Boykin's Avatar
Here’s the update. Got off shift this morning and got straight to work. I just yanked the lme’s and dropped in the 2134’s I have and bam, no more pop. The JFET/Bipolar scenario made the most sense to me. The drivers ever so slightly move but nothing like before and the pop is gone. Thanks everyone. The 1642 is still of interest because it’s lower noise, lower distortion, and draws close to the same current as a tl072. $110 is a small price to pay compared to new monitors. Recap coming soon.
Old 1 week ago
  #43
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Quote:
Originally Posted by Brian M. Boykin View Post
Here’s the update. Got off shift this morning and got straight to work. I just yanked the lme’s and dropped in the 2134’s I have and bam, no more pop. The JFET/Bipolar scenario made the most sense to me. The drivers ever so slightly move but nothing like before and the pop is gone. Thanks everyone. The 1642 is still of interest because it’s lower noise, lower distortion, and draws close to the same current as a tl072. $110 is a small price to pay compared to new monitors. Recap coming soon.
Nice! Good job. Damn those phoney eBay op amps. Damn them all to hell.
Old 1 week ago
  #44
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Brian M. Boykin's Avatar
I get the 4562’s in today. I’ll swap them in and see what happens. I stopped buying electronic parts off EBay a while back. Had the same issue with some MAT03’s and some 2sa1084’s I bought. Who would of thought the NOS obsolete parts market would be an area to scam buyers?
Old 1 week ago
  #45
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JohnRoberts's Avatar
 

Quote:
Originally Posted by Brian M. Boykin View Post
Here’s the update. Got off shift this morning and got straight to work. I just yanked the lme’s and dropped in the 2134’s I have and bam, no more pop. The JFET/Bipolar scenario made the most sense to me. The drivers ever so slightly move but nothing like before and the pop is gone. Thanks everyone. The 1642 is still of interest because it’s lower noise, lower distortion, and draws close to the same current as a tl072. $110 is a small price to pay compared to new monitors. Recap coming soon.
Still curious to know if you hear a noise floor difference between new improved op amps and old school TL07x?

But don't do any experiments just for me... If it works and sounds OK, button it up and move on...

JR
Old 1 week ago
  #46
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Brian M. Boykin's Avatar
Quote:
Originally Posted by JohnRoberts View Post
Still curious to know if you hear a noise floor difference between new improved op amps and old school TL07x?

But don't do any experiments just for me... If it works and sounds OK, button it up and move on...

JR
My ears cannot hear a difference. I’m doing a/b listening tests and sonically I do not hear a difference. I’ll flash the room later today and see if the frequency response has changed compared to the unmodded monitor. I just finished setting up my measurement mic and setting the spl of the tweeters and woofers the same for each speaker using a 100hz tone for the woofer and a 10,000hz tone for the tweeter. Then setting the total outputs the same using a 1k tone. REW will tell me how close I got with this technique. They were within 1db total output pre modding the one and the frequency response graphs plotted right over each other. Same peaks and nulls. I will say, changing passive components makes for a more significant sonic change than changing op amps in my experience. Changes I can actually hear with my ears.

5 op amps - $20

The educational experience - Priceless

And thanks John for responding. I’ve been reading Geekslutz since 2005 and you’ve been a huge influence I’m my progression. I didn’t even know what an op amp was in 2004.
Old 1 week ago
  #47
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Brian M. Boykin's Avatar
Here ya go guys. This really isn’t apples to apples because the speakers were set up left/right. To really get a solid comparison I’d have to flash them from the same location. I used a MOTU 828es. Mic is a Dayton Audio EMM-6. Software is REW. A calibration file was made for the 828es. The calibration file for the EMM-6 was downloaded into REW. Preamp is a Jim Williams modded Symetrix SX202. Levels were set per REW and and REW SPL meter was calibrated to an external SPL meter app on my phone. Mic was measured equal distance as close as possible. Smoothing set to 1/12th. Blue line is opa2134. Orange is tl072. Green is both. Be my guest to pick this apart. There are obvious flaws in the process I’m sure.
Attached Thumbnails
Active Monitor Pops after Op Amp Swap-736c3b44-dc5f-4e5f-b28a-34f8ed692225.jpg  
Old 1 week ago
  #48
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Brian M. Boykin's Avatar
Here’s two more. I pulled the unmodded speaker. It got the same treatment. I tried the 4562’s that came in today and while it didn’t pop on start up and popped powering down. Not nearly as bad however. I still don’t like the popping so it got 2134’s. The first graph is the tl072 in orange and the 2134 in brown. Same speaker. Same location. I left REW up with settings and mic in the same position. You can see changes in the frequency response. The second graph is mixed 2134/072 in green and 2134/2134 in turquoise. Again, changes in response. Some better, some worse. It will be interesting to see what happens as I add more acoustical treatments.
Attached Thumbnails
Active Monitor Pops after Op Amp Swap-06098a61-edfe-498f-beb1-67381850ee02.jpg   Active Monitor Pops after Op Amp Swap-ef1f349c-2aad-45fd-80d3-0297c23cec37.jpg  
Old 5 days ago
  #49
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audiospecific's Avatar
 

Quote:
Originally Posted by Brian M. Boykin View Post
Short of the long is I was replacing a broken trim pot on my Active Event 20/20’s and noticed it’s packed full of tl072’s. So I got the “while I’m in here bug” and soldered in sockets, decoupled the power rails, and dropped in lme49720’s. Now when I power the monitor on it pops and the drivers cycle through their full range of motion. It never did this before and the other one does not which I haven’t been in. I’m figuring it’s DC and the offsets are off. Any other explanation? Is it time for a PSU filter cap change? They’re probably 15 y/o at this point. I do follow protocol and power them on last and down first.
It sounds like the op-amps you installed are behaving like they are latching up. This is a condition where an op amp with an internal constant current source has the non inverting input signal goes negative beyond the negative dc supply voltage (only takes a few millivolts on theses), which causes the internal ccs to unload and the output to slam to the positive rail voltage.

Not everything is 100% interchangeable just because its an op amp. In this case the tl072 is the better part to use because it has an anti-latch circuit built in.

The differences you are observing with the 2134 is from the small impedance change in the negative feedback, that effects the damping effect of the XC in that path.
Old 5 days ago
  #50
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Brian M. Boykin's Avatar
Thanks. This makes sense. In the past I’ve only swapped what I’ve known to be proven replacements for a specific circuit. Basically following a known mod or copying someone else’s work. I’m trying to branch out a little. Normally when I drop in 2134’s I put a 22pF cap in the feedback loop if a resistor is present. I did not do that this time. I’m not that concerned with the changes in frequency response at this point. At 1/12th smoothing there are differences but at 1/3rd smoothing it’s almost indistinguishable. There will be differences at 1/12th flashing the room 5 times in a row with the same exact set up. I was just looking for major changes. I soldered in sockets so tl072’s can easily be dropped back in. I think they’ll benefit from a recap more than an op amp swap. I’m gonna see if I can find the schematics.
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