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In Reply to: Re: Bypassing Opamp??? Do not understand posted by Glenn2 on June 10, 2002 at 11:12:29:
Glen.
I have not received the schematic yet but there seems to be an electrolic cap (1uf)going to ground next to each of the ICs. Would just adding a film cap under the board be sufficient?Thanks for the Help
Mike
Hmmm... 1uf seems very small for this role, although probably OK for the RF/IF stages. These 1uf caps could be doing practically anything so I would wait for the schematic before meddling.
I assume there is only one output stage op-amp. This is where most attention is needed (and maybe the stereo decoder).
Glen:
Ireceived the schematic when I got home and after a quick look it looks like the opamp are driven of of a +12V and -12V lines. I do not see any additional caps except for what is on the output of these voltage regulators. These are 10uf, 50volts. I will upgrade these values a little (don't want to blow out the regulator) and would you suggest adding additional caps right on the ICs? Should I do that on all of the ICs or just the opamps? Thanks for all the help.Mike
I don't think you would blow out the regs by beefing them up a little. Go for 470uf or if you would like to be safe then 100uf. If the op-amp is physically close the regs and their caps (an inch or two) then you may not need any more big caps. The key thing is to provide the op-amp with a low-impedance supply and by storing charge near it in the form of capacitors that is what you are doing.
You can tack 0.1uf films on the underside of the electrolytics if they are near the op-amp and that will probably do.
If you think you need the extra big caps at the opamp it can be tricky because you don't have a space for them on the board. You can probably squeeze a couple of 47uf/16v caps on the underside of the op-amp between each of the supply pins and the nearest ground point (the op-amp doesn't have one). Putting films across these may be tricky though! You could just try the unfussy OPA2604 and then see how it sounds.Look for the stereo decoder (the last stage before the op-amp) and you will probably find a big cap on its supply anyway 47uf-220uf. If it's less than 100uf you could try a bigger one (say 220uf). I wouldn't worry about any of the other chips.
Good luck!
Glenn.
I have ordered some caps from Digikey and will do some upgrading this weekend. I appreciate all the information about the opamps and the caps. Thanks a lot.Mike
It looks like the +-12v supply would be perfect for the ad8610. Would need browndog adaptors.
What is a Browndog Adaptor?Thanks
Mike
They allow the mounting of single SOIC's to a dual DIP.
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