Tube Amps / Music Electronics
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|8/6/2004 8:57 PM|
||NE 5534 compensation cap|
I've used 5534's for all sorts of things in the past but now I'm having oscillation problems with one and wonder what value cap to use on the freq comp pin...and where it goes to?
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|8/7/2004 3:57 AM|
I guess between 5 and 8. Check out the link. It's the same info (for the compensation cct. given in my old op amp manual). Think it shows 10pF on one of the diagrams. How about adding a small resistance directly to the output also. I think that was supposed to help reduce oscillations too. Something I read in an article on opamp upgrades--something recommended to try to stabilize when the new one gives problems.
|8/7/2004 7:49 AM|
Hey Thanks Dai,That was just what I wanted.And it was from Jaycar too,my No1 shop for modern stuff.
|8/9/2004 2:59 PM|
ON data sheet suggests 22 pfd to 47 pfd across pins 5 and 8.
|8/12/2004 9:19 AM|
DECOUPLING & STABILITY.
5532 and 5534 type opamps require careful supply-decoupling if they are to remain stable; otherwise they appear to be subject to some sort of internal oscillation that degrades linearity without being visible on a normal oscilloscope.
The essential requirement is that the +ve and -ve rails should be decoupled with a 100nF capacitor between them, at a distance of not more than 2 inches. It is NOT necessary, and often not desirable to have two capacitors going to ground; every capacitor between a supply rail and ground carries the risk of injecting rail noise into the ground. The main rail decouple electrolytics can be used to do the job for several 5532/4 packages nearby, and this cost saving is an important layout point. Likewise, it is not normally necessary to decouple each package individually. One capacitor every few inches is sufficient if the power tracks are of reasonable thickness. (ie 50 thou)
Not me, mr Douglas Self.
Kindest regards, Bernt.
|8/12/2004 4:30 PM|
The question relating to compensation and the concept of supply rail decoupling address two separate technical issues.
With all due respect to Mr. Self, on the supply decoupling matter, all IC manufacturers and most if not all circuit designers recommend that the supply rail(s) be decoupled by a 4.7-100uFd electrolytic in parallel with a small film cap. This is particularly applicable to audio (and higher) applications since the high frequency characteristics of electrolytic caps is suspect. Tube equipment PSUs don't often include such features since tubes generally have much better supply noise rejection characteristics. How close to the IC you put the decoupling component is very much related to the frequency of operation and noise. Digital decoupling caps are usually configured such that the supply rail has the larger electrolytic where the rail enters the circuit - perhaps board edge, while the small, high frequency caps are placed as close to the IC as possible. This approach can get backed off as the frequency goes down. In audio work it would be overkill to have more than one decoupling arrangement per IC and even this could be relaxed if IC's were very close together.
Let common sense prevail. Decoupling is important but ANY decoupling in an audio stomp box circuit is probably enough.
|8/15/2004 9:27 AM|
Guys,I made a mixer,a while back,with about 18-20 odd op amps,5534's tlo71,2,4's and had a 100nf right below the IC,between rails,and then each rail had a 2.2uf tantalum and a 100pf cap to ground.This may have been overkill but the thing works absolutely fine.Recently I made something and didn't do any decoupling between a small power amp and the pre and got oscillation,real slow ones,at about 2-5 hertz,I suppose something like a slow DC pulse.I'll go back in sometime soon and put a bunch of caps around it as well as a regular resistor and cap to ground between pre and power rails.I just got lazy I suppose.
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