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Peachtree Decco opamp rolling (previously: Will I destroy my amp?)

post #1 of 17
1/9/10 at 2:23pm
Thread Starter 

Hey all, I am planning on rolling opamps in my Peachtree Decco, something that it seems that I'm the first to do, besides the owner of the Bolder Cable Company who mentioned it in another forum. Since there isn't any documentation on the amplifier in the Decco, I want to be sure that rolling opamps cant cause any harm. I plan on rolling in the LM4562NA in place of the TL082CN, but I bought backup TL082CN if the 4562 doesn't work.

But rolling in the standard "audio application" opamps (those that get mentioned in popular opamp rolling threads) shouldn't cause any harm, right? At worst, just not work?

 

EDIT: Update on page 2. Peachtree has fitted my Decco with sockets and I am now waiting for it and my opamps. 

 

I was advised not to try and work on the Decco circuit board, but since it was out for repairs, and a new cabinet, I figured I'd ask them about the opamps. And Bret, the service manager at Peachtree, was more than happy to do the work for me. Very good experience overall- I'm glad that they're still supporting their older products.


Edited by LingLing1337 - 7/27/11 at 6:49pm
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post #2 of 17
1/9/10 at 4:49pm

worst case you can destroy more than just the rolled op amp

it is better to replace fet input op amps with other fet input types rather than a bipolar like the LM4562 - circuits designed with fet inputs often have higer feedabck impedance and will have greater offset V and noise when BJT input op amps are substituted

another potential problem is replacing with op amps of differing "speed" - Gain Bandwidth Product on the datasheet - much faster op amps are more likely to oscillate, potentially overheating output stages and sometimes destroying them - the LM4562 is >10x faster and thus dangerous for someone without an oscilloscope to verify that its stable in place of a TL082

you also need to pay attention to Vsupply limits - some otherwise attractive modern op amps can only take lower supply V than was considered standard decades ago when the TL082 was released
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post #3 of 17
1/10/10 at 1:00am
Thread Starter 
Is a jfet input type OK?
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post #4 of 17
1/10/10 at 1:36am
Yes, you can fry an output stage of the amp, and your headphones by using "wrong" opamps.
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post #5 of 17
1/10/10 at 2:08am
Thread Starter 
FallenAngel, any recommendations on a replacement for the TL082CN?
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post #6 of 17
1/10/10 at 3:00am
Any dual fet input opamp really. LME47920 ("official" name for LM4562) is nice, I'm also a great fan of AD825 (you would need 2 on an adapter).
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post #7 of 17
1/10/10 at 2:19pm
Thread Starter 
JCX above you just said that the LM4562 is a bipolar input...

But I did order the LME49720NA.
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post #8 of 17
1/10/10 at 3:22pm
opa2132/4 are dual fet input that are only ~ 2x faster than the TL084 - quieter inputs, lower distortion with load - should work as substitutes in most circuits
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post #9 of 17
1/10/10 at 5:35pm
Thread Starter 
Cool, I'll check those out. Thanks.
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post #10 of 17
1/10/10 at 5:39pm
it is questionaable that the op amp is even serving a audio frequency function - as a "designer DAC" it would be really strange to find a TL082 directly handling audio so its possible that it functions as offset servo or regulator
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post #11 of 17
1/10/10 at 9:16pm
Thread Starter 
I believe that Signal Path themselves (I think it was David) mentioned that the opamps ARE in the signal path... And as I mentioned before, the rep from Bolder Cable Co. mentioned that swapping opamps offered an improvement in sound.
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post #12 of 17
1/10/10 at 9:36pm
LM4562 is bipolar but the input bias current is so low that you can use it in most circuits
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post #13 of 17
1/10/10 at 9:52pm
Thread Starter 
Very cool! Is the NA version the same?

EDIT: Also, is there any procedure I should follow to make sure I don't blow up my amp when I try the LME49720NA?
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post #14 of 17
1/10/10 at 10:23pm
NA is the package - DIP8
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post #15 of 17
1/10/10 at 10:25pm
Thread Starter 
Cool, thanks for all your help.
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