Oscillation - Page 4

davidallancole · 18th February 2006, 11:06 PM

This amp sounds pretty good. The treble is not to **** hot, a cymbal doesn't sound like a cymbal, but the rest is all good.

You will all laugh your butts off when you read here what I used for parts:

Op-amp: LM741
Transistors: TIP 120

Thats all I could get at work. I think I will look for better parts from Digikey and try building it again. Then I will try to build a voltage stage with transistors and the like.

anatech · 19th February 2006, 02:37 AM

Hi David,
A 741 will take the realism out of a cymbal for sure. Two suggestions for you. An LM318 (old part), watch out. They are fast. An NE5534, nothing wrong with this old guy either. You may already have these lying around. RS might even carry one.

-Chris

clem_o · 19th February 2006, 08:43 AM

I'm also sure it will sound a bit better when the FB capacitor is reduced! :-)

Furthering Chris' suggestions, how about an LF356? Tame enough, fast, cheap. Or a TL071...

Cheers!

Clem

ps: one other thing - if you do switch to a faster op-amp (uh, what opamp isn't faster than a 741 these days...), don't forget putting bypass capacitors (0.1uF) from each supply rail to ground - near the op-amp.

davidallancole · 19th February 2006, 02:35 PM

I agree, I think it will sound better when the fb cap is reduced. I will have to see if we have any smaller ones at work tomorrow. I think there was a low noise instrument op amp of some sort in stores, so I will have to try that op amp as well.

anatech · 19th February 2006, 03:38 PM

Hi Clem,
I was thinking of output drive capability too.

Your suggestions may do it as well. The NE5534A does have a good sound.

And yeah. Almost anything is faster than a 741 type at 0.6 V/uS. I'm trying to figure out how bad things are to get a 741 to oscillate. The feedback cap should have been much smaller as you have pointed out.

-Chris

clem_o · 20th February 2006, 01:01 AM

Hi Chris,

Good point!

Things would have to be pretty bad for a 741 to complain - something like heavy capacitance at the output, or unstable power supply, or bad grouding... - Eva's suggestion of putting in series resistors would be a good idea to decouple the op-amp a bit?

Cheers!

davidallancole,

Maybe it's time to have a good look at your grounding as well!

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18th February 2006, 11:06 PM	#31
davidallancole diyAudio Member Join Date: Nov 2005	This amp sounds pretty good. The treble is not to **** hot, a cymbal doesn't sound like a cymbal, but the rest is all good. You will all laugh your butts off when you read here what I used for parts: Op-amp: LM741 Transistors: TIP 120 Thats all I could get at work. I think I will look for better parts from Digikey and try building it again. Then I will try to build a voltage stage with transistors and the like.

19th February 2006, 02:37 AM	#32
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi David, A 741 will take the realism out of a cymbal for sure. Two suggestions for you. An LM318 (old part), watch out. They are fast. An NE5534, nothing wrong with this old guy either. You may already have these lying around. RS might even carry one. -Chris

19th February 2006, 08:43 AM	#33
clem_o diyAudio Member Join Date: Jun 2005 Location: Manila	I'm also sure it will sound a bit better when the FB capacitor is reduced! :-) Furthering Chris' suggestions, how about an LF356? Tame enough, fast, cheap. Or a TL071... Cheers! Clem ps: one other thing - if you do switch to a faster op-amp (uh, what opamp isn't faster than a 741 these days...), don't forget putting bypass capacitors (0.1uF) from each supply rail to ground - near the op-amp.

19th February 2006, 02:35 PM	#34
davidallancole diyAudio Member Join Date: Nov 2005	I agree, I think it will sound better when the fb cap is reduced. I will have to see if we have any smaller ones at work tomorrow. I think there was a low noise instrument op amp of some sort in stores, so I will have to try that op amp as well.

19th February 2006, 03:38 PM	#35
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Clem, I was thinking of output drive capability too. Your suggestions may do it as well. The NE5534A does have a good sound. And yeah. Almost anything is faster than a 741 type at 0.6 V/uS. I'm trying to figure out how bad things are to get a 741 to oscillate. The feedback cap should have been much smaller as you have pointed out. -Chris

20th February 2006, 01:01 AM	#36
clem_o diyAudio Member Join Date: Jun 2005 Location: Manila	Hi Chris, Good point! Things would have to be pretty bad for a 741 to complain - something like heavy capacitance at the output, or unstable power supply, or bad grouding... - Eva's suggestion of putting in series resistors would be a good idea to decouple the op-amp a bit? Cheers! davidallancole, Maybe it's time to have a good look at your grounding as well!

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