To locate the feedback resistors, you probe the op amp with meter on pins 7,6 then 1,2. 0 ohms to both ends of a nearby resistor locates it. You can confirm by reading value 7 to 6 etc then reading the color code on the resistor nearby. Reading on meter should be lower than feedback resistor because of leakage into the op amp.
Pin 1 on op amps has a dot, or the end has a cut and pin 1 is on the left on top. You count around a DIP package counter-clockwise from the top from 1 to 8.
I buy REAL parts from farnell (newark in US) digikey or mouser. RS in UK has a reputation but I haven't used them.
Before debit cards I had to buy parts from TV repair shops, and their capacitors & resistors were often "bargains". Got 8 year life out of electrolytic caps from such a source. Life is too short to replace e-caps in an amp 4 times. The tantalum caps had popcorn noise. Secret to big distributors, the box costs $9 to ship, fill it up with parts for stock if you really need a $.22 item. They charge a "handling fee" if your total charge is too small.
First line suppliers of ceramic disk caps are AVX, Kemet, Epcos. Farnell has a house brand multicomp which has always been okay in metal film resistors, anyway.
When I bend legs apart on anything, I hold lead close to body with needle nose pliers, to hold it straight. Then I bend. Most things fall apart if bend is too close to body. The pliers at dollar stores tend to have tips about 2.5 mm around. You can get really fine nose pliers, 1 mm tips, from distributors. That could be a $10 item to fill up your box and avoid handling fee. Good tiny diagonal cutters are worth $10 too.
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So now try with just one cable connected, I guess the whistle is gone now too? Almost found it!
Don't connect that signal plane to the enclosure, at least not directly. Try to connect it with a cap, say 10nF, so you ground it for HF but you don't create a ground loop for mains.
Jan
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No with just one cable the noise is the same...
actually the whistle is not consitunous, it comes and goes, what's continuous is a hash / noise higher than it should and that goes away with no input cable
that high noise sometimes modulates to that horrible whistle that pierces the ears, but it's not continuous
Would a cable shielded with a foil be more effective than a simple braid-shielded cable?
It is not a matter of shielding. It's not an external whistle you need to keep out. The whistle is generated by the particular arrangement in your system.
In fact, using a tightly twisted pair may be better than a screened cable.
Jan
I don't understand...
Where does the whistle come from? Why no whistle when no input cable? where does it radiate through? Must come from outside right?
Sorry just trying to understand... I thought I DID understand and now I'm all lost again... haha
Does the whistle you hear persist with the inputs grounded?
If not, it may be external or it may be an issue with the input circuitry.
If so, it is definitely internal.
At one point you said you had it stopped by adding bypass caps on the chip's power pins... did you undo that? Why?
By "inputs grounded" do you mean connecting the outer part of the RCA connector to the enclosure via a small ceramic capacitors? They aren't. At the moment they are isolated.
I didn't remove the bypass caps; I just thought the whistle was gone after installing them, but in fact, it came back, it is not constant, it seems to be influenced by something external, it comes and goes. So I THOUGHT I solved the problem, didn't, but left the caps in because they have to be there anyways.
I do not think what I hear is oscillations. I hear it with ALL the op-amps I've tried: OPA2132, the Chinese discretes, and the original NE5532 (that are in there at the moment). Only the LEVEL of the whistle seems to be slightly different from opamp to opamp; but I'm not even sure about that.
At the moment I'm using professional microphone cable because my "expensive" cable has been terminated in XLR when I was using my other crossover; maybe I should terminate them back to RCA because they are VanDenHul Integration Hybrid and I believe they are very well shielded but the shield isn't attached on one end. Could help, maybe?
One radical test to make sure it doesn't come from your environment: take the whole shebang to a friend, or your mum's, and see if it whistles there. ...
Analogy: it's better to spend some time to close in on your enemy and take him out with a shot between the eyes, than it is to continue to lob some ammo in the general direction where you think he might be ...
Jan
Analogy: it's better to spend some time to close in on your enemy and take him out with a shot between the eyes, than it is to continue to lob some ammo in the general direction where you think he might be ...
Jan
A proper RCA cable has it's shield attached to ground at both ends. And, to be honest... that could well be your problem.
No kidding... try these ... From Amazon
I don't even want to guess how many times I've gone into "high end" setups having all kinds of silly problems... one even had the local CBer coming out of his speakers... and pulled out all nature of expensive BS cables, replacing them with standard $10.00 RCA cables that fixed the problem. For all the money these guys spend "tuning" they systems with ridiculous cables, they could have had a better pair of speakers.
From your descriptions you are quite near a rather busy transmitter. It may only be a few milliwatts but with incorrectly shielded cables, it doesn't take very much at all to give you all kinds of crap to deal with.
If you turn off the router... does the noise stop?
If you disconnect the crossover from the amps does the noise stop?
If you short your crossover's inputs to ground (momentarily with a metal tool) does the noise stop?
Are there any parts you touch that either stop the noise or make it worse?
Without access to an oscilloscope, it's a process of elimination.
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No but the cables I have been using with THIS crossover has the shield attached at both ends. I was talking about some other cables I have.
I’ve put some 39pF ceramic caps across the input RCA this morning and I haven’t heard the whistle today. But it may well be that whatever is emitting interferences was not active today because it’s Sunday... if tomorrow is whistle free maybe it’s solved. Fingers crossed...
You may find this article interesting. It's a few years old, but it chronicles a problem that is far more common than most people seem to realize.
RFI From Computer Networks - Linksys Router RFI!
Hmmmm...
so there was no whistle sound Sunday... and no whistle sound yesterday.
I don't dare to call it a victory yet (I've been fooled before) but still - I think if today if another whistle-free day it means the small caps worked. because it was every day, many times a day, ever since I bought that x-over two (three?) weeks ago...
so there was no whistle sound Sunday... and no whistle sound yesterday.
I don't dare to call it a victory yet (I've been fooled before) but still - I think if today if another whistle-free day it means the small caps worked. because it was every day, many times a day, ever since I bought that x-over two (three?) weeks ago...
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Thank you everybody for your help, I learned a lot - precious informations on a quite complicated matter!
I've seen a very nice filtered power strip in the local ads, sold for very cheap; I'm gonna buy it and give it a try - not to "solve" anything but because this whole issue made me read a lot about noise and I'm eager to see if such a device actually brings some benefits. I will only connect my sources and my x-over on it, maybe the preamp, but not the amps.
I've seen a very nice filtered power strip in the local ads, sold for very cheap; I'm gonna buy it and give it a try - not to "solve" anything but because this whole issue made me read a lot about noise and I'm eager to see if such a device actually brings some benefits. I will only connect my sources and my x-over on it, maybe the preamp, but not the amps.
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If all is quiet then I would suggest you take my tack ... Check it frequently for a week, less frequently the next week and so on. It usually takes me about 2 or 3 weeks to trust a fix.
You would be surprised at the amount of audio gear that hits the market with no RF filtering whatsoever. Even the so called "High End" gear is seldom adequately filtered. It's like a forgotten science.
All well and good until you get "CQ CQ Rusty Bedsprings calling CQ CQ" at full volume out of your speakers at 3:00 am.
I generally set up RF bypasses to take everything above about 500khz to ground.