I have a Yamaha preamp channel that I liked so i pulled out a channel And rack mounted it. However it is a little noisy on the EQ stages cause it still has jrc4458d op amps in that stage. Would it be beneficial to switch them discrete op amps? How big a difference would something like a seventhcircleaudio discrete opamps vs burr brown opamp have?
It is running at +-15v currently and I am installing sockets to play around with components in the EQ section, but I can't help but think that discrete op amps play a role in the magic that big name companies like API use.
The preamp sounds great, the EQ just gets too much hiss when boosting high midrange and highs, but I am working on it for fun.
It is running at +-15v currently and I am installing sockets to play around with components in the EQ section, but I can't help but think that discrete op amps play a role in the magic that big name companies like API use.
The preamp sounds great, the EQ just gets too much hiss when boosting high midrange and highs, but I am working on it for fun.
I replaced JRC4558 (not 4458) Op amps with ST33078 op amps. There was a considerable reduction in hiss. I had to put .1 ceramic bypass caps on the power supplies within 2" of the socket, and a 22 pf cap around the feedback resistor, to eliminate the resulting oscillation. I don't know your circuit, but it is a cheap experiment. The Amp dip sockets were $.56 and the op amps were $.38 each. The shipping was $6. The capacitors were junk from a dead PCAT switcher power supply. I had to change the rail voltage dropping resistors (330 ohm) the designers were using to suppress hum, since the 33078 uses more power. They were running it off +-3.5 v with no filter caps after the resistors; I'm using +-8v off 1n5344 zener diodes as regulators, and electrolytic caps before and after the zener diodes.
If I want to do further experiments with $6 apiece op amps or something, the sockets are in there. Matter of taking the cover off. I have other equipment much more broken, however.
If I want to do further experiments with $6 apiece op amps or something, the sockets are in there. Matter of taking the cover off. I have other equipment much more broken, however.
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Despite of all beliefs and fashions 4558 when biased by 6k8-7k5 resistors to the + rail sound obviously better than 5532. I experimented with different channel strips in TOA console when wanted to upgrade it, so could check and compare immediately. As the result, left all 4558 there, biased them, but replaced in summing amps only, by OPA1612.
One more "obsolete" opamp that I never replace is 5534. It is still better than the majority of modern opamps.
If you hear "hiss" boosting highs that does not mean that the EQ itself hisses. It may boost hiss of what is before.
One more "obsolete" opamp that I never replace is 5534. It is still better than the majority of modern opamps.
If you hear "hiss" boosting highs that does not mean that the EQ itself hisses. It may boost hiss of what is before.
Yes. Also it increases a bit base current of output emitter follower and collector current of the driver stage on some linear value, making it a bit more linear and faster, except class A benefits.
Some persons that design best in the world equipment know better what to measure than the majority that does not have a clue what and how to measure.
Hi,
Still one persons opinion obfuscating the basic facts.
The 5532 is faster, has lower noise, lower distortion and
better drive capability, and is dirt cheap to try compared
to buying discrete op-amps, and compare to the 4558.
I've no idea if "class A" bias improves it or not. I do know
when I've used it to replace dual op-amps in cases I've had
problems (I don't change op-amps for fun, if it works, fine)
the 5332 has fixed the apparent problem, mainly inputs.
Suck the 5332 and see is my opinion, you will get less noise.
rgds, sreten.
I see.
But honestly, I don't see how replacing opamps in the EQ can decrease hiss, since both original opamps, and suggested as replacements, have better noise figures than required for "no hiss" on line levels. If to go for improvement of sound quality, as I suggested, biasing in class A gives more real improvement than replacing of opamps. Yes, THD+N figures of 5532 in datasheets look better, but it is not THD+N that matters in this particular case. It is what is below that "N", dynamically occurring, matters, that is hard to measure, and according some beliefs don't matter if below that "N", while it is against the nature of human perception of signals of levels below of noise levels. It is not in the human nature to prefer widening spectum of decaying sounds, like decay of strings, or reverberation. And it matters much more than what is easier to measure ignoring what is "below accepted threshold".
What else can be suggested for EQs? Most probably the EQ uses set of gyrators. On resonant frequencies in gyrators most probably opamps are loaded on very low impedances. That means, opamps with better drive capability may give better improvement than opamps with better noise figures, again in terms of audible distortions.
If I'm not mistaken, in (Burr Brown) opamp's pdf documentation there is a chart showing the source impedance where a (very) low noise opamps start to be better than high slew rate opamps. I think the impedance starts at around 15K for low noise opamps to be better. This is a relatively low number for most applications, so low noise opamps rule in term of "distortion".
To take benefit of that characteristic of very low noise opamps, I started to work with amplifiers where transistor's bandwith/slew rate/transconductance is not critical. It can be an opamp driving a phase splitter (like JLH69), but I'm recently working with opamp driving CFP output (where stability is more easily achieved with slower parts).
Slow but very low noise instrumentation opamps do have some good characters. I think with such topology the audible benefit will be more. Hopefully.
Sure they do! But more often their explanations are in terms of precise perceptions translated into some (mis)understanding of technical terms. But if you try you can find scientific explanations that not necessary correspond to the technical language that they use. It is always more profitable to learn foreign languages instead of complaining that experts in other fields do not speak fluently yours.
Well, I proposed an experiment, after all. Put in a socket, try something else. I find in my 50x gain mag phono circuit, ST33078 is less hissy than NJM4558. Your results may very- particularly as the tone control circuits under discussion have low impedance sources (other amp stages). I've got the socket, have RC4560, TL082, and LM4562 in the parts box for other experiments some rainy day. I already tried the experiment of NJM4558, NJM4560, ST33078 in the input stage of a CS800s amp, driven by a low impedance 2k ohm output stage (33078) of a Herald RA88a mixer. Results, the latter two op amps are indistinguishable, the 4558 is hissy.
The only thing scientific about my experiments is my calibrator. I have a Steinway console piano in the same room as the hifi. I have always been of the opinion that recorded piano music sounded artificial, from the days of the Bozo the Clown record player with the paper cone "amplifier", forwards. With the SP2-XT speakers, the equipment is getting pretty close, now. On the premium brand LPs the records weren't the worst part of the distortion chain after the old ribbon microphones went out of fashion for classical recordings, my ears tell me.
Interesting about the class A use of the 4558. There are places that might be useful- like this 50x mag phono circuit. Having 300 ohms between part and both supply rails, and no cap afterwards, surely did something to supress the hum in this circuit before I modified it for more powerful op amps.
The only thing scientific about my experiments is my calibrator. I have a Steinway console piano in the same room as the hifi. I have always been of the opinion that recorded piano music sounded artificial, from the days of the Bozo the Clown record player with the paper cone "amplifier", forwards. With the SP2-XT speakers, the equipment is getting pretty close, now. On the premium brand LPs the records weren't the worst part of the distortion chain after the old ribbon microphones went out of fashion for classical recordings, my ears tell me.
Interesting about the class A use of the 4558. There are places that might be useful- like this 50x mag phono circuit. Having 300 ohms between part and both supply rails, and no cap afterwards, surely did something to supress the hum in this circuit before I modified it for more powerful op amps.
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