Tl074 upgrade

[cbass]

I have Peavey Profex II .Dont laugh it has very good reverb and delay. And very powerful EQs.However it can be a bit noisey.I was reading about upgrading the opamps to reduce noise . Aperantly a lotCof Steel players used this unit and peavey even had a factory upgrade that swaps the 4558 ICs with opa2604..
Im plannng on swapping the 4558s with opa2134.
I read about a feller named Lemay that offered a chip upgrade package . Years ago.the only info I could find about is that it included ICs to replace the 4558s and one that was about twice the size of the others.
Im assuming the one that was twice the size is the tl074 . Any ideas for upgrades?

[cbass]

Perhaps an OPA4134

[g1]

That's what I thought may be a sub for the quad chip. Hopefully the lower noise chips will make a difference. Sometimes you are limited (as far as noise reduction) by other components in the circuit.
By the way, it's been a long time since you've been here, welcome back!

[Mick Bailey]

I would follow the Peavey upgrade bulletin and replace the ICs listed by them. The OPA2134 should be a better choice, but how much difference you'd hear compared with the OPA2604 is debatable. A lot of noise comes down to gain settings and even with the replacement ICs there can still be a fair bit of unwanted noise from the rest of the circuit.

There's an interesting section in the Stompox Cookbook regarding op-amp noise - well worth a read.

[g1]

Can anyone post the Peavey upgrade bulletin here for the archives?

[cbass]

That's what I thought may be a sub for the quad chip. Hopefully the lower noise chips will make a difference. Sometimes you are limited (as far as noise reduction) by other components in the circuit.
By the way, it's been a long time since you've been here, welcome back!

Thanks for the welcome. I like it here There are a lot of very smart people that aare very geenerous with their knowlodge.
I read a lot of threads on the steel forum about replacing chips.It seems that almost everyone agreed it lowered the noise level noticably and quite a few claimed it improved the sound whatever that means?

[cbass]

I would follow the Peavey upgrade bulletin and replace the ICs listed by them. The OPA2134 should be a better choice, but how much difference you'd hear compared with the OPA2604 is debatable. A lot of noise comes down to gain settings and even with the replacement ICs there can still be a fair bit of unwanted noise from the rest of the circuit.

There's an interesting section in the Stompox Cookbook regarding op-amp noise - well worth a read.

Besides The recomended upgrades by PV Im planing on replacing the Opamps in the the FX loop. Im not real happy with it seems to muffle the sound and a its noisy
Thanks for the tip I'll look that up

[pdf64]

Thanks for the tip.
I found a working download here Libro de Cocina del Stompbox-Nicolas Boscorelli after going down a couple of dead ends.

[Mick Bailey]

Here's the official mod;

profexiimod.pdf

[MarkusBass]

The problem with TL074 replacement is that in many cases you want to replace opamp in DIP-14 package but modern replacement opamps exist only in SMD version. To solve this problem I have DIP-14 to 2xSOIC8 adapter and I solder 2xOPA2604 to the adapter (see the attachment).

Mark

[cbass]

hmm sounds like more trouble than i want to go through .I probably just swap out the 4558s

[Enzo]

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.

[Mick Bailey]

I would have thought that if the TL074 was a problem then Peavey would have identified this in their upgrade bulletin.

[Enzo]

That is a reasonable assumption, but is there a ready substitute for the TL074? "Better" dual op amps abound in DIP8, but in DIP14?

[Mick Bailey]

Maybe the OP470 (5nV/Hz) or LT1125 (2.7nV/Hz) compared with 15nV/Hz for the TL074. Both now obsolete in DIP packages. Sometimes though swapping an opamp can cause instability.

As you say, it comes down to gain and location. I've had customers request opamp swaps in all kinds of equipment and my conclusion is that in the main it makes little or no difference unless the opamp really is the main source of noise.