Svart
Well-known member
So I bought a handful of MC33079 from Newark a few weeks ago. They had/have a promotional price on the MC33079 from ST micro, something like .50$ a piece, non-returnable of course.
I had previously purchased ONsemi MC33079 and old Motorola MC33079 which both work great and sound great.
This time I thought I was getting a deal.
So I populated a couple console channels with the new ST parts since the whole reason for purchasing them was because I ran out of the other ones.
I immediately noticed a faint, fuzzy sound but discounted it to the fact that I had the channel sitting out in the open, not shielded like it would normally be.
I still didn't notice for a few days until I switched my meters over to OUT instead of IN and noticed that certain channels registered a signal although I couldn't hear it. The rest of the channels were fine.
I pushed up the faders and noticed that I could hear a very high frequency whine. Yup, those puppies were oscillating like crazy. I initially thought that I had maybe done something wrong while modding the channels but I couldn't have done the same wrong thing to 8 channels..
Since the console connects 8 channels to an elco I/O I unplugged the elco and all other I/O to the channel thinking that maybe it was coming from the recorder or something. NOPE. Still oscillating. I went as far as to probe with my finger and find that the Elco input was very sensitive to touch meaning that parasitic capacitance could fix the problem.. Yet another clue that these things were oscillating.
So being the dense one I am, it finally dawned on me that THESE NEW opamps were oscillating!
I changed them out with both OPA404 and TLo84s which both worked FINE. I also moved some of the ONsemi MC33079's from another channel over to one with the ST parts and then moved the ST parts to the one where I got the ONsemi parts.
The oscillation moved with the opamps and the channel that now has the ONsemi parts works great.
I suppose there is a moral to this story..
If the deal is too good, then it's going to cause to to drink heavily and cuss a lot while listening to The White Rose Movement.
At least that's what I'm doing.
But really, I suppose this really shows that one part may not be the same as another.
I see that the promotional price has now extended to the ONsemi MC33079 but I'm sorta wondering if there isn't a reason that these parts are half the price they usually are...
I had previously purchased ONsemi MC33079 and old Motorola MC33079 which both work great and sound great.
This time I thought I was getting a deal.
So I populated a couple console channels with the new ST parts since the whole reason for purchasing them was because I ran out of the other ones.
I immediately noticed a faint, fuzzy sound but discounted it to the fact that I had the channel sitting out in the open, not shielded like it would normally be.
I still didn't notice for a few days until I switched my meters over to OUT instead of IN and noticed that certain channels registered a signal although I couldn't hear it. The rest of the channels were fine.
I pushed up the faders and noticed that I could hear a very high frequency whine. Yup, those puppies were oscillating like crazy. I initially thought that I had maybe done something wrong while modding the channels but I couldn't have done the same wrong thing to 8 channels..
Since the console connects 8 channels to an elco I/O I unplugged the elco and all other I/O to the channel thinking that maybe it was coming from the recorder or something. NOPE. Still oscillating. I went as far as to probe with my finger and find that the Elco input was very sensitive to touch meaning that parasitic capacitance could fix the problem.. Yet another clue that these things were oscillating.
So being the dense one I am, it finally dawned on me that THESE NEW opamps were oscillating!
I changed them out with both OPA404 and TLo84s which both worked FINE. I also moved some of the ONsemi MC33079's from another channel over to one with the ST parts and then moved the ST parts to the one where I got the ONsemi parts.
The oscillation moved with the opamps and the channel that now has the ONsemi parts works great.
I suppose there is a moral to this story..
If the deal is too good, then it's going to cause to to drink heavily and cuss a lot while listening to The White Rose Movement.
At least that's what I'm doing.
But really, I suppose this really shows that one part may not be the same as another.
I see that the promotional price has now extended to the ONsemi MC33079 but I'm sorta wondering if there isn't a reason that these parts are half the price they usually are...
