Are you sure? I've never seen them mentioned on any datasheet, and I have seen them damaged by static on inputs when used as multiplexers.
The DG408/9/etc have this issue too... Maxim make the MAX309 which seems to be pin compatible and has ESD protection built in - i'm going to give it a test and see if it's worse than the ADG409's i have.
i've actually got a rackmount EQ here someplace which is designed for professional use. I'll have to take a look in it again and find out what opamps are used, but I know it does have SOME 4558's in it!
Ok, my EQ is discrete using 2SC1845 transistors. There are opamps though, 2 of them, and these are NJM4558. Probably used as input and output buffers, while the filtering is done by the transistor stages.
Ok guys, i have a full circuit diagram. I will make a scan of it and will post it here so we can take a better look at it.
About the op-amps, after some discusions here about them, can you please tell me what`s the best option voor now, let the 4558 inside, or replace hem with opa2134 or ne5532??
Thanks for all help.
Regards Rick...
About the op-amps, after some discusions here about them, can you please tell me what`s the best option voor now, let the 4558 inside, or replace hem with opa2134 or ne5532??
Thanks for all help.
Regards Rick...
Hi,
You say that you have this unit for 20 years - has it always been noisy? Eva keeps mentioning the faders for a reason - it's not as glamorous as "rolling" opamps but it might be the actual root of the problem.
I have a similar one but like jaycee's it mainly discrete. I did some monkeying around with it and did some measurements in this thread.
I keep it around because it looks cool and the chicks dig it, but I don't use it anymore.
You say that you have this unit for 20 years - has it always been noisy? Eva keeps mentioning the faders for a reason - it's not as glamorous as "rolling" opamps but it might be the actual root of the problem.
I have a similar one but like jaycee's it mainly discrete. I did some monkeying around with it and did some measurements in this thread.
I keep it around because it looks cool and the chicks dig it, but I don't use it anymore.
HI MJL21193, Yes it has always been noisy, but the last year there is more noise. The most noice is when i use the IMX expander function on it.
The imx function is the little board at the left with the 2 op-amps. Equalizer stage use trannies like ksc945c and a lot of caps.
The imx function is the little board at the left with the 2 op-amps. Equalizer stage use trannies like ksc945c and a lot of caps.
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Solution: Don't turn that on. 🙂
What type of noise is it producing? Are you sure it's the unit that is making the noise?
Mine is dead silent when switched on and it shows in the measurements that I made.
How is that possible, when It has a few of those nasty, evil 4558's in there too?
😱
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Hi, i have make a record from the noise, so you can hear there is noise and hum. The volume on my amp denon pma1560 stay`s on 40%. When i use the bypass function there is also noise, so even when the imx expander is off, so the signal is not totally bypassed. When i turn the equalizer off, everything is silent and you hear nothing, so even when volume is 100%. So i hope my record give`s you any idea what i mean.
http://www.megaupload.com/?d=ZYEOISA2
Regards Rick...
http://www.megaupload.com/?d=ZYEOISA2
Regards Rick...
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OK, so the multiplexers are just part of the spectrum analyzer.
The regulators are zener based. The capacitors across the zeners could be stuffed and this means an increased supply noise. I'd be inclined to wire some 7815/7915's in there myself.
The muting circuit could be suspect. Bad capacitors there could be making those FETs turn off.
The regulators are zener based. The capacitors across the zeners could be stuffed and this means an increased supply noise. I'd be inclined to wire some 7815/7915's in there myself.
The muting circuit could be suspect. Bad capacitors there could be making those FETs turn off.
That is mains hum:
That is the frequency spectrum of your sound file - see the peaks at 25, 50, 100, 200Hz.
Looking at the schematic, the unit has a regulated power supply and there shouldn't be that much hum. It is possible something is bad there.
Also, what is the source? Unplug the input to the unit and see if this reduces the hum. You need to do some basic things to eliminate possible causes.
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Oh, and replacing the opamps won't make much difference - the main equalizer circuitry is all discrete.
I'd say replace the capacitors in the power supply, at least to begin with. See if this brings the noise down. Also do C502-C504 as these are in the mute circuit.
Guys thank you so mutch for all help. I really appreciate it.
Ok, I will begin with the power supply. Is it better to take a higher cap like 1000uf instead off 470uf??
The noise and hum are also with no any source connected.
There is a third 4558 and this one is not on the expander board. IC 301.
MJL21193, what kind of frequency Analysis tool do you use, can i found that somewhere on the internet?
Ok, I will begin with the power supply. Is it better to take a higher cap like 1000uf instead off 470uf??
The noise and hum are also with no any source connected.
There is a third 4558 and this one is not on the expander board. IC 301.
MJL21193, what kind of frequency Analysis tool do you use, can i found that somewhere on the internet?
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Nice to see you have already found a copy of the circuit diagram, i'll cease my own searching for it!
Looks like you are getting some decent advice as per usual, best of luck with the rebuild & modification 😉
Looks like you are getting some decent advice as per usual, best of luck with the rebuild & modification 😉
Wahab is quite right about this, theres a night and difference between those two opamps, 4558 is terrible, ne 5532 is a much better drop in.
as far as i can see, the equalizer array using transistors is itself inserted
in the feedback loop of a discrete operationnal amplifier, q103/105/107
for a channel and q104/106/108 for the other one..
they have simple resistance from differentials emitters to negative rail,
thus supply rejection is very bad, making the thing sensitive to a badly
regulated power supply...
in the feedback loop of a discrete operationnal amplifier, q103/105/107
for a channel and q104/106/108 for the other one..
they have simple resistance from differentials emitters to negative rail,
thus supply rejection is very bad, making the thing sensitive to a badly
regulated power supply...