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Old 05-31-2011, 08:43 AM   #1
Ace of Bass
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Red face Changing Dip-8 Dual Op Amps--is there an audible difference?

Seems to be a common upgrade in audio circles, just swapping out the stock op amps for another one.

It would be an extremely simple mod (assuming there's a socket), and most op amps cost less than one dollar, many under 50 cents.
Some articles on the web seem sensible, with comments like "They're all slightly different, play around and see if you find one that sounds better", while other people seem to imply changing the single op-amp chip can make a Boss DS-1 sound like a Mesa Recifier.

And then, of course, there's the audiophile crowd. Here's a guy who swapped a 30 cent LF535 with an over $100 chip and thinks it's worthwhile.
http://www.rock-grotto.co.uk/opamp.htm

Anyone done this? Opinions? Is it really worth trying on on some pedals or preamps?
I'm not exactly the kind of person who believes that extending the frequency response from from 10MHz to 100MHz really improves my basses treble tone. But I could see some benefit to a $3 chip instead of a $0.30 chip in my preamp. So where would I start? Just order a bunch of compatible chips in my price range from mouser? There are hundreds of these DIP-8 op amps, all interchangable... what specs indicate one might sound good? Mosfet, Jfet, etc?
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Old 05-31-2011, 09:03 AM   #2
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I'm not exactly the kind of person who believes that extending the frequency response from from 10MHz to 100MHz really improves my basses treble tone. But I could see some benefit to a $3 chip instead of a $0.30 chip in my preamp. So where would I start? Just order a bunch of compatible chips in my price range from mouser? There are hundreds of these DIP-8 op amps, all interchangable... what specs indicate one might sound good? Mosfet, Jfet, etc?
There is a lot more to it than an extended frequency response. Two big specs you want to look at for in audio applications are 'slew rate' and 'common mode rejection ratio' (CMRR).

My suggestion would be to read up on those (and other specs you feel are important), find out what's in your current pedal(s), and then start buying op-amps based on what you've found and what you think you would like to try to change.

Just make sure that all of the pin-outs and power requirements are compatible. Not all 8-pin op-amps are swappable like that.
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Old 05-31-2011, 09:04 AM   #3
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Most times you can get better ops, but the tone difference is negligible. I can get the same effect by adjusting my tone stack, or changing speaker placement, or changing input impedence.

I really despise audiophiles. Those fuckers just take it too far.
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Old 05-31-2011, 09:14 AM   #4
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Most times you can get better ops, but the tone difference is negligible. I can get the same effect by adjusting my tone stack, or changing speaker placement, or changing input impedence.

I really despise audiophiles. Those fuckers just take it too far.
I tend to agree with you in general. But I disagree in this case.

I'm not necessarily one for swapping out op-amps. But that is the heart-and-soul of the pedal's pre-amp.

Changing all your 1/4" pedal jumper cables to Lava cables is going too far. But for < $1.00, swapping out an op-amp has a far greater potential, dollar-for-dollar, than most anything else the DIY consumer can do to improve the sound.
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Old 05-31-2011, 09:28 AM   #5
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I tend to agree with you in general. But I disagree in this case.

I'm not necessarily one for swapping out op-amps. But that is the heart-and-soul of the pedal's pre-amp.

Changing all your 1/4" pedal jumper cables to Lava cables is going too far. But for < $1.00, swapping out an op-amp has a far greater potential, dollar-for-dollar, than most anything else the DIY consumer can do to improve the sound.
I dig it. I've swapped a few, but the components I bought were so close in spec to the original that the difference was barely audible. I guess if you had a really shit original op, then a swap could be beneficial. I mean we're not talking about a Behringer pedal, are we?
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Old 05-31-2011, 09:49 AM   #6
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Changing all your 1/4" pedal jumper cables to Lava cables is going too far.
Totally depends on if the copper is wrapped clockwise or counter-clockwise with respect to the rotation of the earth.
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Old 05-31-2011, 10:27 AM   #7
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I dig it. I've swapped a few, but the components I bought were so close in spec to the original that the difference was barely audible. I guess if you had a really shit original op, then a swap could be beneficial. I mean we're not talking about a Behringer pedal, are we?
Yeah. As I was typing one of my previous responses I kept thinking, "what pedal manufacturer would use such a low-quality op-amp that it would make that big of a difference?"

But... then I thought... it's cheap, and could be more of a learning experience than anything else.

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Totally depends on if the copper is wrapped clockwise or counter-clockwise with respect to the rotation of the earth.
But isn't that also dependent on which hemisphere you're in?
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Old 06-01-2011, 07:08 AM   #8
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You'd be surprised at the crappy op-amps pedal and/or amp manufacturers use. Swapping op-amps with better ones can improve sonic performance but more often than not, it doesn't. However, you can't just swap op-amps willy-nilly. If you put a modern high bandwidth op-amp in a circuit designed for a low-bandwidth one without paying attention to power supply bypassing it might turn your preamp circuit into a really good HF oscillator. Seriously, I've seen situations where high end op-amps swapped in for crappy ones have gone ballistically unstable.
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Old 06-02-2011, 03:23 AM   #9
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Well, out of curiosity, I just checked my beloathed and despised DOD Supra Distortion, and it uses two 4560D JRC op-amps, currently going for 39 cents a piece at Mouser.

It also uses a Motorola MC14007UBCP (CD4007) 14-pin chip. This seems to be primarily a logic chip, a "Dual Complementary Pair Plus Inverter", though it does say on the data sheet that it can be used as an extremely high impedance amplifier: The MC14007UB multi–purpose device consists of three N–channel and three P–channel enhancement mode devices
I thought this was a rather odd thing to use in a pedal, so I checked the schematic to see what exactly it does, and how the audio might be improved with a replacement...

...This chip is responsible for engaging the LED light when you step on the pedal's switch. Rather overkill I'd think, but whatever.

Anyway, I'm rather curious to know what kind of a different sound could be made by changing the op-amps to something a bit more classy...
But I'm not interested enough to do it, because it's a DOD FX55. I'd have better luck with the sound by just rubbing this along all the componants:
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Old 06-02-2011, 03:35 AM   #10
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I think my favorite op-amp review was were a guy sent out his amp to have the op-amps changed to boutique ones (like $10/each) in a tube headphone amp. At the same time he also had his electrolytic capacitors swapped. Since the caps needed to "form" properly, he left the amp on for a week before using it. He swears the op-amps sound much better than old ones--apparently based on how he remembered them sounding 2 weeks beforehand. Not exactly a back-to-back test...
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Old 06-02-2011, 05:20 AM   #11
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...This chip is responsible for engaging the LED light when you step on the pedal's switch. Rather overkill I'd think, but whatever.
Are you sure it's not part of the buffering circuit as well?
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Old 06-02-2011, 06:09 AM   #12
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Old 06-02-2011, 08:03 AM   #13
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Are you sure it's not part of the buffering circuit as well?
It's a pretty simple schematic--there's only one wire as the output from that chip, and it just goes straight to three transistors. The first is a normal PNP transistor that turns on the LED. The second is a depletion JFET that bridges the input to the output, while the third is another depletion JFET that bridges the distorted signal to ground. So LED on = bridges open, LED off = Bridges open, bypassing the distortion. Very simple--the same thing could be done with a wire connected to the V+ through a resistor. I have no idea why they used that chip.

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Old 06-02-2011, 08:09 AM   #14
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Hah!
That's kind of a big difference.
I just noticed that schematic uses the MC1458 op amp (slew rate: 0.5v/us)
My pedal (newer model) uses the 4560D (Slew rate: 4.0v.us)
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