[sdiy] Resistor in feedback loop - interesting point on theTL07x

[Harry Bissell]

And especially necessary for the TL07x / 08x series. They will oscillate easily
with standard audio cables on the output, usually 10 - 100 ohms is enough to decoiuple the capacitive load.

This is SERIOUS SH!T, ultrasonic oscillation can easily damage tweeters and power amps before you notice...

H^) harry


----- Original Message -----
From: Juergen Haible <jhaible at jhaible.de>
To: KATAYAMA <pata at ieee.org>, Synth-DIY DIY <Synth-diy at dropmix.xs4all.nl>
Sent: Fri, 08 Jul 2011 00:55:13 -0400 (EDT)
Subject: Re: [sdiy] Resistor in feedback loop - interesting point on theTL07x

These resistors keep capacitive loads away from the opamp outputs, and 
prevent oscilation.

JH.


----- Original Message ----- 
From: "KATAYAMA" <pata at ieee.org>
To: "Synth-DIY DIY" <Synth-diy at dropmix.xs4all.nl>
Sent: Friday, July 08, 2011 3:01 AM
Subject: Re: [sdiy] Resistor in feedback loop - interesting point on 
theTL07x


> Hi Tom and Lists!
>
> I think almost synth circuits nssds NO external series resistor after 
> OPamp outputs.
> Maybe output series resistor is good for short circuit with AC power 
> lines, telephone lines(DC48V), or surge voltage of static discharges or 
> lightnings.
>
> 07x/08x family types, as Tom says, output stage has series resistor 
> inside, and these resistors are simple current limiter.
> But it is to protect short circuit to GND and OPamp power rails, no other 
> short circuit is NOT protected.
> So, in output terminal in modular systems or that of all-in-one set, it is 
> useful to use protection resistor in series to OPamp output terminal.
>
> Taku
>
> (2011/07/08 8:58), Tom Bugs wrote:
>> Well, a couple of days ago I happened to look at the TL074 datasheet
>> and, in particular, the internal diagram of the chip. Interesting - I
>> saw that there's a 200r resistor already in series before the output.
>
>> So, is it really necessary to add further resistance here?
>> (I should check some other opamp internals to compare too)
>>
>> Cheers, Tom
>> _______________________________________________
> -- 
> =/========================================
> K/ATAYAMA, Takuya
> Muse Music Synthesizer Laboratory, Japan
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
> 

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-- 
Harry Bissell & Nora Abdullah 4eva