Tl074 upgrade

[dai h.]

how about the power supply caps? Since it's apparently a few decades old, the caps may be degraded and be contributing to noise (ripple and maybe from the digital portions) I would guess.

As I understand some of (what are sometimes perceived as cheap low quality) op amps are actually capable of good performance if implemented well (not an expert here, but I guess things like having a clean power supply, good layout, grounding, well chosen values). I have a joemeek VC3Q which has a lot of (perhaps even lesser?) TL064s, and I don't find it to be particularly noticably noisy.

[cbass]

it also pays to look at the circuit and see where they used the TL074 and where the duals. Not every op amp is in a high gain stage and is not probably contributing much to any hiss.

Peavey is suposed to be sending me a schematic. I was just curious because apparently there was a mod a while back that changed out the recommended peavey upgrades and the only info I could get about the other opamp was its almost twice the size of the other ones. I assumed that it has to be the tl074 . these mods I speak of are from like 15years ago . I think you could get the opa4134 in a dip package back then

[Enzo]

I don't have that model on my computer, and in the paper files - located elsewhere - I think I only have the original Profex. But will be interesting to see what the TL074 does in there. I mean it might be driving LEDs and then what does it matter how noisy it might be?

If you mean physical size, the TL074 is a 14 pin while all the duals are 8.

[cbass]

how about the power supply caps? Since it's apparently a few decades old, the caps may be degraded and be contributing to noise (ripple and maybe from the digital portions) I would guess.

As I understand some of (what are sometimes perceived as cheap low quality) op amps are actually capable of good performance if implemented well (not an expert here, but I guess things like having a clean power supply, good layout, grounding, well chosen values). I have a joemeek VC3Q which has a lot of (perhaps even lesser?) TL064s, and I don't find it to be particularly noticably noisy.

Probably wouldn't hurt to change out the electro's but I don't think the noise is power supply related . it's really not that bad but Im pretty picky about my amps being very quite.
I read that the profex was originally designed for opa2604's and 4558's were used as a cost cutting measure

[cbass]

I don't have that model on my computer, and in the paper files - located elsewhere - I think I only have the original Profex. But will be interesting to see what the TL074 does in there. I mean it might be driving LEDs and then what does it matter how noisy it might be?

If you mean physical size, the TL074 is a 14 pin while all the duals are 8.

Right yes the tl074 is 14 pin . I'm pretty sure it's in the audio circuit just by where it's placed in the layout but who knows until I get as schematic

[Chuck H]

FWIW you might also look at any voltage dividers in the signal path that could operate with lower resistance (keeping the same ratio of course) where it won't affect amplifier operation. Just thinking out loud since I can't comment on chip choice.

[Enzo]

Life will be so much better when we can see a schematic.

I'll see if I can download it from my dealer site too.

[cbass]

Still ain't heard from em. Did you have any luck?

[MarkusBass]

Maybe you should have mentioned that this is a programmable MIDI multi-effects preamp and not amplifier like some of us think. Something like this:





It seems that TL074 is not used in the audio chain.

Mark

[Enzo]

Beg to differ, I see only one TL074 in it, U402, and three sections are used, all in the signal path. Page 4. They are the analog out from the DAC on the way to the circuits feeding the out jacks.

Schematic attached:

[cbass]

Thanks Enzo.