Quad Opamp Replacement

[Scott S.]

I just picked up a Rane PE-15 Parametric EQ for cheap and I am going to mod it for better performance. I like the topology they used but the opamps and passives can be improved.

The schematic is available on the Rane website (thank you Rane), and I can see that it uses several NJM2059 quad opamps.

These are a quad version of the 4558 more or less.

So any recommendations for filter opamps?

The TL074 would be an upgrade over the 2059, and TI makes a OPA4134 that looks good, any others to consider?

I have all gear required to verify stability after the swap, so that is not an issue.

[edanderson]

you will be hard pressed to find the opa4134 or opa4132 in DIP package any more. you can get the surface mount version and a converter, but it will add to your cost. maybe look for a two dual to quad adaptor if you are going to go that route anyway.

jakob recommended the mc33079 to me at one point as a good quad chip, and it is pretty easy to get and quite inexpensive.

ed

[ulysses]

Has anybody tried the Burr-Brown OPA404? I've been looking at the spec sheet and it looks VERY good. It's basically a quad OPA604 but it actually specs even better. And Digi-Key has them IN STOCK in DIP packages! They're expensive ($11 apiece from Digikey) but it sounds like the holy grail.

[bauman]

OPA404 looks good! I'll try'EM on my Urei545 and let you know.

[img]graemlins/beerchug.gif[/img]

[BjornZetterlund]

If the OPA404 really is a quad 604 I'm gonna be well pissed off! I spent ages modding a TC 2240 dual parametric by replacing each TLO74 by two OPA2604's (the dual 8 pin version of the 604), and that was seriously time consuming. Haven't looked at the data sheet yet, but is this a new addition? Has the 604/2604 data sheet now been expanded to include the 404?

Think the MC33079 in its different versions is as used in the Amek Rupert Neve desk.

Bjorn

[cuelist]

Originally posted by Bjorn Zetterlund:
I spent ages modding a TC 2240 dual parametric by replacing each TLO74 by two OPA2604's...

And what is your opinion of the result? Less noise? Clearer sound?

Would be interesting to know!


Mats

[Shalimar]

I've modded a TC2240. But that didn't do no good, I just don't like the sound of the basic eq.

I replaced the in/out, the FETs (actually, took 'em out) and the wimpy PSU.

Didn't replace the opamps, instead I made a new pcb for single opamps. Never got it stuffed though. The initial testing/sound, still left a lot to be desired.

Well, it was many moons ago and a fun project. 2240s is something you encounter in pretty much any studio and venue in my country so they're dirt cheap secondhand (like 200Euros).

A HQ quad is definitely something I've been waiting for though!

[PRR]

> These are a quad version of the 4558 more or less.

Which is a dual 741, which is a compensated 101.

But the 101 is not a bad topology, only limited by 1970 silicon. NJM has been tweeking the masks and process for decades to optimize audio performance. The specs may not be WOW! but some of the NJM chips are very smooth and sweet. Not all, but I'm sure Rane ordered a sampler pack (from several makers) and picked the 2059 after bench and ear tests.

Yes, it is also one of the cheapest quads in the world. That doesn't prove it is bad.

> The TL074 would be an upgrade over the 2059

Except for bias current (which is probably not important for a para-EQ), I would not say the TL0 is better than an audio-optimized 741. The TL074 actually has rather poor load specs compared to 741 or 2059, which could be critical if Rane designed some low impedances in the filters. Unless filter impedances are super-high, the TL074 tends to have higher noise than a bipolar input. A BiFET's distortion may be a wee bit sweeter, or may not be if they've sweetened the 2059's input pair. It will probably sound "different" with BiFETs, but "better" may be a matter of taste and mood. And a lot of people sneer at TL074s.

I happen to like LM837, but my ears are no good. The 837 does have ample output drive and nice low noise, with an audio slant.

[Scott S.]

OK, I have the quad options fleshed out.

I also plan on shortening the signal path which may improve more than the parts sub.

There is a balanced to unbalanced input stage, which I dont need (running unbalanced), then the subsonic filter (don't need this either), and then a variable gain stage (I will control level elsewhere).

The variable gain stage opamp section will become a buffer, and I will jumper around the other 2 opamp stages. The layout and conveniently placed series resistors will make this both easy and reversible.

[BjornZetterlund]

My 2240 mod is currently on hold, but nearly complete. I need to replace all the pots as well, as even though I cleaned them with contact spray, some are still noisy. Just haven't put in the order yet. I have two 2240's, and one is left unmodded, so I'll let you know what it sounds like when I can do a proper AB.

Bjorn