Op Amp question

[nacho459]

I have been in the market for a new console for a while to replace my P.O.S. TOA I picked up a while back. After returning back from AES I have realized that no one makes the console I could really use, at least not in my price range so I have decided to rebuild my TOA part by part.

I have decided to start with the mic pre's.

The console is a TOA RX-7 with 32 IMP-7 channel strips. I have had an impossible time finding schematics, so I attempted to reverse engineer one. Here's what I have for the mic pre. http://www.459audio.com/1010.jpg I don't have my multi meter on me so I just labeled the unlabeled ceramic discs as "CD".

I am thinking of starting off by switching out the Cheapo Xfmr and Op Amp with something killer like a Jensen input xfmr and a JH990c. I have no Idea what a 1010 op amp is but it looks like it is the exact same size & pinout as the API/ Melcore / JH990 op amps. So I am assuming that I can just swap them out as long as the voltages are the same.

I have been looking at the simple John Hardy pre amp in his 990 paper, http://www.johnhardyco.com/pdf/990.pdf fig 1 on Page 4. The TOA circuit has a bunch more crap in it that it probably doesn't need and I could simplify it down to something like the JH schematic no problem. I am just wondering what the whole "RL1" box with the inductor is all about.

So Here are my real questions...

1. Do you think I could simply swap out the 1010 op amp with a 990c op amp with no problems? Or, should I convert my PCB to use John Hardy's schematic?

1a. What is the "RL1" thing about?

2. What about an API 2520 or Melcore op amp? I want to make some clean and clear and some fat and nasty.

3. What is a 1010?

4. What Lundahl transformer(s) would work instead of the Jensen? for a fatter more British sound.

5. Who makes those 2520 clones?

Thanks

 

[PRR]

> my P.O.S. TOA

What is actually wrong with it? You don't want to spend a lot of time fixing the wrong problem.

I'd leave the 1010 module alone for now. And those little japanese transformers are sometimes fine. But the 4458 beg for replacement.

 

[nacho459]

It just doesn't really sound that great. I have a Presonus MP20 that kills these mic pre's. What would you suggest to replace the 4458's?

 

[PRR]

> It just doesn't really sound that great.

Tells me nothing. Don't have a clue where to start on that.

My gut still says the transformer, 1010, and associated parts don't suck bad, and 4458 at high levels might. What does it sound like if you listen at the INS jack, using just the tranny/1010 stage and bypassing the rest of the board? Does that suck?

 

[NewYorkDave]

Nacho, do you mean 4558?

Perhaps a 4458 op-amp exists, but I've never seen one.

If it's the 4558 you're talking about, that's a jellybean bipolar dual opamp. The NE5532 might be a good substitute depending on the circuit...

 

[nacho459]

[quote author="StDomingo"]2 - do you know where you can get API2520s?[/quote]

eBay, etc.

[quote author="PRR"] My gut still says the transformer, 1010, and associated parts don't suck bad, and 4458 at high levels might. What does it sound like if you listen at the INS jack, using just the tranny/1010 stage and bypassing the rest of the board? Does that suck?[/quote]

I usually track through just the pre.
Xfmr> 1010 OpAmp> Insert send> Tape machine> Insert return> EQ> FB> Mixbus...

I don't think the pre's sound downright bad, just dull. Sometimes they sound a little harsh on vocals there's a harmonic thing that dosen't groove right. I have several external mic pre's (Altec 1567a, PreSonus MP20, MCI JH416) that all sound better IMHO than my TOA's pre's. The Atlec sounds chunky and gritty, the MCI sounds really "brown" the Presonus is clear and smooth. the TOA pres just sound bland.

My ideal would be to get some to sound kinda Neve or API like, (thick, chunky, rock and roll) and some to have a clean, pure sound. Right now they just sound, well, Japanese. Not bad just boring.

[quote author="NewYorkDave"]Nacho, do you mean 4558?[/quote]

There are several little 8 pin 4458 IC's all over the channel PCB. You can see a couple of them in the picture near and under the gray wires.

 

[nacho459]

ok, I'm thinking of trying the little John Hardy preamp circuit w/ a 990c. Then I'll try messing around with some Lundahl transformers to get a phater sound. Who knows maybe these transformers rock, I'm gonna try to swap things out and figure out what sounds I like. I guess experimenting with different components is the way to go.

If John is around please chime in :wink:

 

[SSLtech]

The 4558 is used all over the Studer A827 audio cards, along with a near-relative the 4560, if I recall correctly.

Looks like a Tamura input tx, often these were quite passable, they make things for everyone from cheap to expensive, I believe.

I usually frown on ceramic disc caps in audio paths, ...I kinda might be tempted to try swapping those out, but most of the time when people get into chip-swapping frenzies in a bid to improve the sound, I advise against it unless you really have a specific, identifiable problem. Otherwise the only really sound advise is try it and see.

4558s are all over Otari tape machine audio cards as well... there's not much wrong with them per se, though they don't have the output grunt of a 5532 into low impedances. -I've used 5532s and 072s to replace them in dire emergencies... later on, -when I've had the right part to replace the temporary substitute with- I've gone back and listened for a difference, and never really heard anything.

My personal experience is that unless a particular type of IC is used outside of its operating 'comfort zone', there's little or nothing to be gained, but don't let that stop you trying... However, if you really don't experience any benefits to chip-swapping, please post and help balance out the almost pervading belief that some cheap consoles can be sonically transformed by simply popping different chips in there... -as if (in modern consoles at least) the thought never occured to the designer!

Keith

 

[nacho459]

Yeah, but these TOA modules doesn't have 4558s it only has 4458s. Are they the same thing, I mean are they interchangeable? Is it something like where the 4558 was discontinued and replaced by the 4458?

edit: I'm an dyslexic idiot The IC's are 4558's.

 

[CJ]

Here is John laying down the law at the AES show. Very friendly and easy to talk to, plus he knows the nuts and volts of these servo's like nobody's bussiness. That's a Valley People discrete on the desk. John used to use clear resisn to pot things, but thermal expansion was ripping the leads off the diodes, so he switched to kind of a silicone compound. But it looks cool, being able to see inside the opamp!

Here are a few pics of some preamps.
I want to try one of those Jensen inputs. He describes them as one of the best input transfomers in the world. His data sheets have all the schematics and info in them, he is obviously confident that nobody can duplicate his fine work. I like people like that!
Interesting story on the output transformer. He said Deane Jensen wanted to do it on a nickel core for low distortion. It started out as a quad-fillar but I think it's now either litz or bi-fillar due to the increased difficulty of winding four wires side by side.

x

x