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Laurie
Double Platinum Member
Canada
4854 Posts |
 Posted - 03/06/2008 : 20:10:50
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When I was repairing my old OC-2 (1987) it was necessary to replace the TL022 opamps with something else (I was unable to obtain TL022s). I landed on RC4558 opamps as an equivalent (although they are higher current draw).
Now I'm in the process of doing some maintenance on my not-so-old BF-2 (1998) and I noticed the circuit has two RC4558s and one TL022. Clearly, Boss does not consider these opamps to be equivalent. I can't for the life of me see anything to recommend one over the other (from a specification viewpoint) for low-signal audio applications other than the current draw.
Any comments or discussion about this would be most welcome!
Regards,
Laurie |
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Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 03/07/2008 : 10:50:44
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Hi lauries2
Do you need the datasheets?
Or where you just thinking-typing out loud?
I have access to ChipDocs.com online at work.
If you give a bit of notice, I can download most datasheets.
Regards Dr. Bob |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 03/07/2008 : 16:45:43
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Thanks Dr. Bob! I have the data sheets. Still can't see how thay could be different in these low level ausio circuits?
Laurie. |
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Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 03/07/2008 : 17:09:15
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Hi lauries2 & guys
I havn't studied the specs. for the TL022
But perhaps they have a faster-Higher Slew rate V/uS.
I see them used mainly on the Oscillator-Clock circuits of Boss pedals.
Same, with some of the Ibanez series 10 & 5 delay pedals have repaired.
I think they were use in some of the early GE-7,Graphic EQ's as well.
When I PM-ed you, did I send you that text clipping, where the guy claims, that have a higher input impedance?
perhaps the outputs are capable of swinging closer to the rails.
Do you have the actual Texas Instruments datasheet for the TL022's?
They may have gone into more detail than a general datasheet.
Regards Dr. Bob |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 03/08/2008 : 00:46:41
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I went through the manufacturer's (TI) spec sheets and have drawn up a comparison table. I've copied the "typical" values where available.
The major differences are:
- #11 large scale signal amplification. The RC4558 has 4 times the amplification.
- #16 equivalent noise. The TL022 is 6 times noisier.
- #17/#18 supply current and power dissipation. But we knew about that...
- #19/#21 rise time a slew rate. The RC4558 is around three times "faster" than the TL022.
So, the TL022 is noisy and slow but very low power consumption. And the RC4558 is fast with more amplification but higher power consumption.
Maybe the TL022 is more "musical"?
Maybe the faster response of the RC4558 is what cleaned up the tracking in my OC-2?
Perhaps the only reason Boss used both in the BF-2 is that, at the time, TL022s were cheaper and so they used one where they could "get away with it".
Still seems to me that if you are Ok with the power consumption, the RC4558 is a viable alternative (and 10-15% of the price of TL022 - if you can get them).
Laurie.
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Edited by - Laurie on 03/08/2008 00:49:05 |
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I don't get it!! TL022 vs RC4558 opamps
