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Old 28th March 2005, 01:30 AM   #1
Htguy is offline Htguy  United States
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Default carver av 505 opamp upgrade for TL072?

Hi,

I have been looking into upgrading the opamps in my carver av505 5 channel amp. It uses TL072cp opamps. They are j-fet type with a max of 30v in an 8pin dip package. What would be a good upgrade of these opamps?

Thanks for your help.


God bless...


mark
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Old 28th March 2005, 02:23 AM   #2
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the best new opamps are generally surface mount -- so you can use an SMT to DIP adapter. Use the parametric search engines at Analog Devices, Texas Instruments, Linear Technology.

the TL072 isn't a bad opamp at all. you might find, however, that improving the power supply regulation with lower noise, faster response discrete circuitry (i.e. use the Jung Super-Regulators as done in AudioXpress modification of the Adcom preamp) would be a best first step. if you can, get a service manual for the device.

oh, one other thing -- an EMI/RFI filter on the power input is a really good idea -- all of the switching power supplies used in your house contribute to a hostile environment for audio. You can get a small unit from Jameco or Digikey which replaces the male power receptacle on the chasis with an incorporated bifilar choke and polypropylene capacitors for a couple bucks.
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Old 28th March 2005, 02:40 AM   #3
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"oh, one other thing -- an EMI/RFI filter on the power input is a really good idea -- all of the switching power supplies used in your house contribute to a hostile environment for audio. You can get a small unit from Jameco or Digikey which replaces the male power receptacle on the chasis with an incorporated bifilar choke and polypropylene capacitors for a couple bucks."

Or,if you have a well stocked "junk room",You can scrounge a couple from old monitors,and PC PSU's. I've found 5-6 of them so far.
They usually only cost about $5,less at most surplus places.
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Old 4th December 2012, 11:19 PM   #4
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If I were going to replace TLO72 opamps, I'd go with the OPA2134's. I heard a very good quality recording of the Portland Chamber Orchestra through the Linkwitz Orion speakers, which are tri-amp'd with an active EQ and crossover that uses all 2134's, and they sounded spectacular. Maybe the best I've ever heard. I've been using the 2134's in recent years and am very happy with them. They also have the Fet inputs, and are capable of driving 600ohm loads with ridiculously low distortions. To be honest, I doubt if I would hear any difference, but the 2134 is well proven to be top notch, and they're only about $2.40 each at Mouser.
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Old 5th December 2012, 01:36 PM   #5
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Bob Richards beat me to it.

OPA2134 is a VERY good OP-amp.
Faster, quieter, less distortion than the 072.
Then there always types as the NE5534
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Old 5th December 2012, 07:39 PM   #6
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Quote:
Originally Posted by TANDBERGEREN View Post
Then there always types as the NE5534
The 5534 is a good single opamp (so not pin compatible with the TLO72), but not unity gain stable, and because of the bipolar input transistors it will load circuits a bit, which could be an issue in some cases. The input current due to the bipolars can also cause significant output offset voltage (DC) when the inputs see different DC resistance to Gnd.

If a unit is properly designed, the engineer has checked the stability/phase margin and/or squarewave overshoot of the final circuit. When you go in and change the opamp with what is supposed to be a better one, you run the risk of ending up with a slimmer phase margin. Phase margin and crossover distortion (when one output transistor turns off and the other turns on in a push-pull output topology) are the two main things I worry about with opamps (and any high open loop gain, high feedback amp circuits in general). I would at least compare 10kHZ squarewave overshoot before and after the change on an oscilloscope, and if the ringing got worse with the new opamp, I'd definitely go back to the original one. If different opamps actually sound different, it's quite possibly because of the change in phase margin (unless you're looking at really bad opamps). You don't need to have continuous or even noticeable sporadic oscillations to have phase margin distortion issues.

Last edited by Bob Richards; 5th December 2012 at 07:50 PM.
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