Mix Buss Opamp upgrade advice...

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donnie7

Member
Joined
Jan 17, 2005
Messages
10
Gyraf and PPF members,

What would be the best pin compatible opamp upgrade for an Output Master Section/Module that uses TL072's? Heard that OP275, OPA2604, OPA2134 are often used. Seems Gyraf likes the MC33078. But it's slew rate seems a bit slow compared to today's parts. How would the MC hold up in today's advancing tech marketplace? The bus rails are + and - 17.5 volts. This upgrade is for an Amek TAC Scorpion-II mixer. Requesting your expert advice. Looking for the best bass, mid and treble response possible. All electrolytic caps have been upgraded to Nichicon Muse. And Signal path coupling cap values were increased from 100uf to 220uf. Thank you all!
 
> slew rate seems a bit slow compared to today's parts. How would the MC hold up in today's advancing tech marketplace?

Has the music changed in 30 years?? Not that much. A Fender is a fender, a cymbal is a cymbal, and we have the same voices that Adam and Eve had.

The venerable 5532 is still a killer part, more stable than some of those hot-rods you mention, and in mix-bus duty will give much lower noise than a TL07x.
 
I read today that API 2520 has a slew rate of only 3v/uS. Can't say that I have ever thought of API stuff sounding "Slow" . . . Hmmmm . . . . Still use mine every day, and I am making all kinds of "modern" and "stylish " music.

- All the Hepcats are groovin' on my Sounds, Daddio! I'm Hep to the Beat, and no mistake!!!

Andy P
 
2520 has really gotten me thinking about slew distortion. Ive often thought of the 2520 as slow, it has this thickening that is nice, BUT its not SMEARY. Its not fast, but it doesnt sound slow if that makes any sense. Ive always equated smeary sounding opamps with slew distortion and speed but maybe thats not accurate. This is probably the stuff of another thread but thought Id comment.
 
[quote author="donnie7"] What would be the best pin compatible opamp upgrade for an Output Master Section/Module that uses TL072's? Heard that OP275, OPA2604, OPA2134 are often used. [/quote]

Is the input capacitatively coupled, or direct-coupled? If direct-coupled, as you trace backwards through the circuit, is there a pot anytime before a capacitor intervenes?

What I'm getting at is that you might replace the TL072s with an NE5532 *if* the opamp has coupling caps on the input, or otherwise has no DC path to a pot's slider. The NE5532 has significant input bias current, which can cause pots to get noisy. I found out the hard way.

Even if there's a coupling capacitor, if the resistance from input pin to ground is high you might wind up with serious offset on the output of the opamp, as the bias current flows through that resistance.

If your noise figure is reasonable with the TL072s in place, and you feel like doing replacements, I'd go for the OPA2604. If you're getting way too much noise, then try a 5532 (provided the conditions above are met), but when it's been installed measure the DC voltage on each output. You may see a nasty surprise.

Peace,
Paul
 
[quote author="pstamler"][quote author="donnie7"] What would be the best pin compatible opamp upgrade for an Output Master Section/Module that uses TL072's? Heard that OP275, OPA2604, OPA2134 are often used. [/quote]

Is the input capacitatively coupled, or direct-coupled? If direct-coupled, as you trace backwards through the circuit, is there a pot anytime before a capacitor intervenes?

What I'm getting at is that you might replace the TL072s with an NE5532 *if* the opamp has coupling caps on the input, or otherwise has no DC path to a pot's slider. The NE5532 has significant input bias current, which can cause pots to get noisy. I found out the hard way.

Even if there's a coupling capacitor, if the resistance from input pin to ground is high you might wind up with serious offset on the output of the opamp, as the bias current flows through that resistance.

If your noise figure is reasonable with the TL072s in place, and you feel like doing replacements, I'd go for the OPA2604. If you're getting way too much noise, then try a 5532 (provided the conditions above are met), but when it's been installed measure the DC voltage on each output. You may see a nasty surprise.

Peace,
Paul[/quote]

wow... Good info. As a newbie, I don't know exactly what everything in that statement means, but I can see that things aren't as easy as just popping in new opamps.. Glad I didn't start ripping mine apart.

I was thinking of re-capping the master section of my soundtracs console, and maybe opamp upgrade also. Would you expert members on here be able to tell me what I can change just from me snapping a pic? or should I try to post up schemos also, ( I think they are in the manual).




-Learn a little each day @ groupdiy!!!
 
it seems that a good rule of thumb is that a FET opamp can usually replace a BJT opamp but not the other way around without modifications.


Wiz1der, post the pics, we may be able to see what we need to upgrade, but a schemo will really be the best choice.
 
Paul Stamler.

Thanks for your awesome info. I could send a schematic for you to see or add it here. Is there a way of posting a jpeg file? See you all over the net. Newsgroups, Recording Mag and such. Keep up the great work and we do appreciate your kind advice. With Maximum Respect. PEACE!
 
[quote author="Svart"]

Wiz1der, post the pics, we may be able to see what we need to upgrade, but a schemo will really be the best choice.[/quote]



thanks Svart, here ya go!!

http://www.groupdiy.com/index.php?topic=64567#64567
 
Having looked at the schematics, there's no question in my mind that if you replace the TL07x's with different opamps, they must be FET-input units. They have direct-coupled fader sliders or high-value resistors on the inputs, and you'll make pots noisy or generate offset voltages if you use a bipolar-input amp.

Unfortunately, they're quad packages, so you can't use OPA2604s unless you wire up some header/socket combinations.

Peace,
Paul
 
[quote author="pstamler"]Having looked at the schematics, there's no question in my mind that if you replace the TL07x's with different opamps, they must be FET-input units. They have direct-coupled fader sliders or high-value resistors on the inputs, and you'll make pots noisy or generate offset voltages if you use a bipolar-input amp.

Unfortunately, they're quad packages, so you can't use OPA2604s unless you wire up some header/socket combinations.

Peace,
Paul[/quote]

Thanks for your input. Would you happen to know off hand of any quad fet input replacements? Everything i look at mc33079 and others all seem to be bipolar.
 
[quote author="wiz1der"][quote author="pstamler"]Having looked at the schematics, there's no question in my mind that if you replace the TL07x's with different opamps, they must be FET-input units. They have direct-coupled fader sliders or high-value resistors on the inputs, and you'll make pots noisy or generate offset voltages if you use a bipolar-input amp.

Unfortunately, they're quad packages, so you can't use OPA2604s unless you wire up some header/socket combinations.

Peace,
Paul[/quote]

Thanks for your input. Would you happen to know off hand of any quad fet input replacements? Everything i look at mc33079 and others all seem to be bipolar.[/quote]

Maybe take a look into AD-713's? The LF347 will probably perform about the same as the TL074.

Peace,
Paul
 
Why you cannot solder one 2604 from top and one from bottom of pcb?
Just pull some pins to side.
 
Pstamler:

are you saying that if you have replaced bipolar opamps that have coupling caps before their inputs with FET input devices, you could likely remove the coupling caps? interesting. I have a few channels that I experimented with that had 5532's and t072s. I attempted to remove caps in certain areas but encountered offset and bias broblems. I reinstalled the caps but later replaced the opamps to opa2604's(BIG UPGRADE, very happy with it!) but didn't think of trying to remove the caps again. If i can, this would surely cut down the number of caps in my audiochain to almost nothing..

what do you think before i give it a go?
 
[quote author="Svart"]Pstamler:

are you saying that if you have replaced bipolar opamps that have coupling caps before their inputs with FET input devices, you could likely remove the coupling caps? interesting. I have a few channels that I experimented with that had 5532's and t072s. I attempted to remove caps in certain areas but encountered offset and bias broblems. I reinstalled the caps but later replaced the opamps to opa2604's(BIG UPGRADE, very happy with it!) but didn't think of trying to remove the caps again. If i can, this would surely cut down the number of caps in my audiochain to almost nothing..

what do you think before i give it a go?[/quote]

I think it's at least possible, and certainly worth trying. (Sorry it took a few days to reply; I've been busy with cooking projects for Valentine's Day.)

Peace,
Paul
 

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