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The Dude

MC33079 Op amp upgrade to TL084 or better

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I have been looking at doing some mods or trying the mods that Mdeneen have done to a Crown D45, as this post here.

https://community.klipsch.com/index.php?/topic/150389-difference-between-crown-d45d60d75/

One of the questions that have came up is, is there a better replacement for the original mod or Op amp that was replaced. The original is a MC33079, the update per the mod was a Texas Instrument TL084. Here is some data on the 2.

http://www.onsemi.com/pub_link/Collateral/MC33078-D.PDF

http://www.ti.com/lit/ds/symlink/tl084m.pdf

I believe they are both quad amp op amps, or what ever that means. There are some recommended replacements for the TL 084 which one is a TL 074, but I think someone advised against it. Anywho I was talking to Dr. Who and he himself are looking over the schematic to see exactly was it going on. But wanted to go to the threads as well to see what other ideas pop up. Here is the schematic for the D45

D45-75A J0650-2 Rev B (1).pdf

For the record I am not trying to achieve much, just trying to have some fun hotrodding a little.

Thanks

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I find this topic interesting too and hopefully there will be some good feedback. I've got the parts to do an OP Amp mod to a Creek OBH-11 headphone amp and plan to use the National Semiconductor LME49720 Dual op amp replacing a very good NE5532 op amp.

I believe they are both quad amp op amps, or what ever that means.

My understanding that "quad" means four channels. Dual is two channels, etc.

I have been looking at doing some mods or trying the mods that Mdeneen have done to a Crown D45, as this post here.

https://community.klipsch.com/index.php?/topic/150389-difference-between-crown-d45d60d75/

One of the questions that have came up is, is there a better replacement for the original mod or Op amp that was replaced. The original is a MC33079, the update per the mod was a Texas Instrument TL084. Here is some data on the 2.

http://www.onsemi.com/pub_link/Collateral/MC33078-D.PDF

http://www.ti.com/lit/ds/symlink/tl084m.pdf

I believe they are both quad amp op amps, or what ever that means. There are some recommended replacements for the TL 084 which one is a TL 074, but I think someone advised against it. Anywho I was talking to Dr. Who and he himself are looking over the schematic to see exactly was it going on. But wanted to go to the threads as well to see what other ideas pop up. Here is the schematic for the D45

attachicon.gifD45-75A J0650-2 Rev B (1).pdf

For the record I am not trying to achieve much, just trying to have some fun hotrodding a little.

Thanks

I'm curious if the good doctor has any experience with the LME49740 (I don't with this op amp), which is the quad version of the LME49720 op amp I'm using in the Creek.

http://www.ti.com/product/lme49740

Edited by Fjd

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I don't see why you would need/want a JFET input amp in this application which the TL074/84 are. The bipolar 33079 shoud be just as good if not better. All of these devices are old designs(30+ years) "Quad" opamp just refers to 4 individual amplifiers in the same package sharing common power supply pins and MAYBE some biasing circuits. There are newer designs out there. Maybe the Linear Technology LT1359. If you are going to install a socket try several different types, have fun.

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If you are going to install a socket try several different types, have fun

That is one of my goals, but what are the important keys to look at. As far as ratings so nothing gets damaged.

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The schematic you posted shows + and - 10 volt power supply rails for the opamp. So any device rated to work up to the usual + and - 15 volt rails will work and not cause damage. Devices made especially for single supply operation will not work. I suggested the LT1359 because it is fast and relatively low noise. The LME49720 that Fjd suggested is supposed to be an excellent device for audio but I have no experience with it. Again have fun.

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I believe that these links are somewhat informative when rolling op amps.

Swapping Op-Amps... you have checked to see it's stable haven't you ?

http://www.diyaudio.com/forums/analog-line-level/191389-swapping-op-amps-you-have-checked-see-its-stable-havent-you.html

Op-Amps in Audio Circuits - A quick 10 point check list

http://hifisonix.com/wordpress/wp-content/uploads/2010/10/Opamp-in-Audio-10-Point-Guide.pdf

I believe that when the Music Fidelity V-DAC came out, it may have used the MC33079 and there were guys rolling the LME49740 or the OP467 into the unit and reporting good results. The V-DAC also used the NE5532 dual op amp and guys replaced it with the LME49720 similar to what I'm doing with the Creek.

Here are links for two quad op amps that would seem to work.

LME49740 [audio]

http://www.digikey.com/product-detail/en/LME49740NA%2FNOPB/LME49740NA%2FNOPB-ND/1576986

OP467 [general purpose]

http://www.digikey.com/product-detail/en/OP467GPZ/OP467GPZ-ND/820359

Edited by Fjd

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babadono, thanks for the info, there's some good stuff here folks.

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FJD, I haven't read the threads you posted. But I seem to be getting a lot of hate for the TL084, which a couple of folks seem to like it in this amp. I guess that would be the plus of having a dip socket to " roll ". I will take into consideration that these mods where done 7 years ago, so after some long testing things might have changed.

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FJD, I haven't read the threads you posted. But I seem to be getting a lot of hate for the TL084, which a couple of folks seem to like it in this amp. I guess that would be the plus of having a dip socket to " roll ". I will take into consideration that these mods where done 7 years ago, so after some long testing things might have changed.

The more recent links about swapping op amps and op amps in audio circuits are more from the perspective of understanding stability issues regarding op amps rather than more choices.

At least from the standpoint of the D45 there seems to be at least four people that have heard it (and anyone that was present for an audition) and the TL084 didn’t appear to impact them in a negative way and you already know from Mark's work that it can be made stable in the circuit. It looks like moray james indicated in the other thread that he can offer some insight into pulling it down into Class A too.

I've read the negative opinions too (some are even warranted given the circuits they were using as there are now better choices); however, keep in mind that the TL0xx op amps were a mainstream “audio favorite” several years ago and used in lots of audio gear. From a speed perspective, I believe that they have a slew rate of 15 V/uS (the LME49740 is considered an elite audio chip today and has 20 V/us for a 25% increase over the TL0xx models), which doesn’t seem bad for the Crown circuit.

The main negatives that I have read that could be of importance are that, in comparison to the op amp selections today, the TL0xx series have limited output current, have higher distortion, and are relatively noisy. Of course, that is all 'relative' to today and depending upon the circuit, may only have a negligible impact, if any on sound. I don’t believe the D45 circuit has been updated significantly where the issues of the TL0xx series would be much of a concern, or at least not more of a concern when it was selected and used in the original Duke.

Given the above, of course there have been huge advances over the last several years. Keep in mind that the big semiconductor companies spend large sums of money on R&D as they tend to ‘compete’ against each other with designs that will ‘out-perform’ the rest. These companies are designing the chips down to the very intricate details of the properties of each transisitor and each chip contains many types of internal components that are not even available as discrete parts. In addition, these same companies have labs full of very expensive advanced equipment for design and testing.

For an individual project, such as the D45 modifications, you could buy the TL084, LME49740, OP467 and LT1359 then try them all over a period of time. The LME49740 prices at only $4.28 each for small quantities, although the OP467 is getting pricy at $14.49 each.

Edited by Fjd

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TL084 stinks (compared to modern opamps), imparts a 'thin' character to the sound, will latch to the rail on severe overdrive and sound very, very bad.

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I've never had a TL074 latch to the rail. Perhaps I've never overdriven one hard enough?

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"Perhaps I've never overdriven one hard enough?"

Probably.

The lower ±10V rail voltage will make the problem worse.

If you look at the output on a scope you will see it clip on the negative rail and then shoot all the way to the positive rail.

In 1997 I did a commercial design for a couple of different amplifiers and used the (customer requested ) TL072 part. It sounded OK until you slammed it hard, then made horrible disgusting sounds. The engineer asked what that was and I replied "TL072 latch-up". He asked what could be done and I plugged in a NE5532. Problem solved, and it sounded better at any volume level.

The new $5 version from TI does not have this problem.

Another suggestion would be to use Brown Dog dip to surface mount adaptors ($6) and use surface mount duals (more variety available).

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I was looking at the Brown Dog adapters thinking it would be cool if one of the duals could do the left channel and the other the right. But alas with the adapter and the Crown amp design the pinouts would not work. But still with the adapter you could do both channels at once and make up different adapters with different SMT ICs. It would be fairly easy to roll amps then.

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Another suggestion would be to use Brown Dog dip to surface mount adaptors ($6) and use surface mount duals (more variety available).

I was looking at the Brown Dog adapters thinking it would be cool if one of the duals could do the left channel and the other the right. But alas with the adapter and the Crown amp design the pinouts would not work. But still with the adapter you could do both channels at once and make up different adapters with different SMT ICs. It would be fairly easy to roll amps then.

When I look at the schematic in the first link below for the Brown Dog 'Two-Dual-to-Quad' Op-Amp adapter, this schematic seems to have the same standard quad pinout that I found in duder's link to the datasheet above for the MC33078 and MC33079 quad case 646/751A originally used in the D45.

http://cimarrontechnology.com/%5Cpdf%5C070401sch.pdf

http://cimarrontechnology.com/2xdual-to-quadop-ampadapter.aspx

Other than the inherent possible lack of space given how the components are crammed into the D45 with those two 'sandwiched on top of each other' PCBs, what am I missing in looking at these pinout schematics acknowledging that I have not yet followed the D45 schematic all the way through and I'm not really clear on what other adapter would be needed?

Using a pair of dual op-amps sure would open up the possibilities.

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Wow this is really taking off, I love it. I have and will remain busy between work and home for the next week or 2. But once I am done, I would like to really get something down. Hopefully with the help of you folks and your wonderful knowledge, in the mean time I will try and keep up on the readings. Thanks alot you guys.

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Gosh this is going to hard to explain. The Brown Dog adapter will work as long as you use two of the same duals on the same adapter. If you use 2 different devices on the same adapter half of one will be in the left channel along with half of the other. Same for the right channel. (Technically this would still work but what a hodge-podge). I was just saying how it would be nice if you could use 2 different devices on the same adapter and have one doing the right channel and the other the left. I think that would make it easier to compare devices.

From the Crown schematic determine what pins of the quad package do the left channel and which do the right. Now take that info and transpose it onto the Brown Dog adapter schematic. I think you will see what I am trying to explain.

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From the Crown schematic determine what pins of the quad package do the left channel and which do the right. Now take that info and transpose it onto the Brown Dog adapter schematic. I think you will see what I am trying to explain.

Thanks. I guess I should have looked at the schematic first as that was easy enough to follow through.

I was just saying how it would be nice if you could use 2 different devices on the same adapter and have one doing the right channel and the other the left. I think that would make it easier to compare devices.

This is interesting since it sure would provide a better opportunity to compare and identify differences.

It would probably be somewhat cumbersome and unwieldy and I guess the schematic should be checked; however, it seems that if someone was really adventurous they could drop a couple of 'single-to-dual' OP-amp adaptors with the DIP sockets attached onto the 'two-dual-to-quad' Op-amp adaptor and try comparing two matching single Op-amps agains two different matching single Op-amps for each channel.

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"Lock up? Never saw it on any instrument, and never heard it in the Duke. No one ever reported it to me."

You have lead a sheltered life then.

"One quirk of some op-amp models is that of output latch-up, usually caused by the common-mode input voltage exceeding allowable limits. If the common-mode voltage falls outside of the manufacturer's specified limits, the output may suddenly "latch" in the high mode (saturate at full output voltage). In JFET-input operational amplifiers, latch-up may occur if the common-mode input voltage approaches too closely to the negative power supply rail voltage. On the TL082 op-amp, for example, this occurs when the common-mode input voltage comes within about 0.7 volts of the negative power supply rail voltage. Such a situation may easily occur in a single-supply circuit, where the negative power supply rail is ground (0 volts), and the input signal is free to swing to 0 volts."

"Phase reversal

In some integrated op-amps, when the published common mode voltage is violated (e.g. by one of the inputs being driven to one of the supply voltages), the output may slew to the opposite polarity from what is expected in normal operation.[7][8] Under such conditions, negative feedback becomes positive, likely causing the circuit to "lock up" in that state."

In the Crown this will happen when driven hard into clipping and the large cap in the feedback loop drives the signal at the inverting input below the negative power supply rail.

Edited by djk

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Protection Schemes for

National Semiconductor

Application Note 447

Wanda Garrett

July 1987

BI-FET™ Amplifiers and

Switches

To use integrated circuits in real applications

taking the non-inverting input below the inverting input

causes the output to slew toward the negative supply rail.

If the voltage at the non-inverting input is more negative than

the negative common-mode limit, the input stage ceases to

function properly and the output swings to its positive limit.

This apparent “phase-reversal” is temporary; bringing the

non-inverting input back within the legal input common-mode

range restores the part’s normal operation.

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