Hi all,
Hope this is the proper forum for this topic - mods please move it if it's in the wrong spot.
OK, first off I'm not one of "those" people who claim to be able to hear differences in various alloys of speaker wire or differences in capacitor brands, etc...
Now, to the point: I've got a little Class D audio amplifier with Sony SSCS5 speakers for playing PC sound output. The amplifier has two 8 pin DIP sockets so that the pre-amp op-amps can be "upgraded". The amp came with generic NE5532 parts... sounded fine.
Although I don't believe in "audiophile" things like "premium speaker wire" or $150.00 "speaker fuses" or "magic infused capacitors", etc, I thought I would try a few different op-amps and see how they "sounded". I tried TL072, TL082, 4558, LM358 and OPA2134. To compare them, I left a 5532 in one channel and put the test op-amp in the other channel. I connected a signal to one side, then the other so that if there were any difference, I should hear it.
As I expected, they all sounded the same. After all, it's just an op-amp. Signal in, signal out.
Then, I read about the OPA1656 and thought "why not?". Well, OMG how to describe it? The resulting audio seemed a lot "better". More bass, and it sounded "tighter" (like the difference between a cheap ported speaker and a sealed one). The high end was, for lack of a better word, "brilliant". Even the midrange was a lot "cleaner". (by the way, all the chips I tested came from Digi-Key, not cheap Chinese knockoffs).
OK, so now I am totally confused. It's just an op-amp. Signal in, signal out. HOW ON EARTH can the OPA1656 sound SO much better? Is the 1656 "better", or is it "right" and the other parts "insufficient"?
Another observation: I built a little stereo signal summer which is a pair of simple unity gain inverting amplifiers (+/- 9 volt power, 47k feedback and 47k input, non-inverting input grounded, dc coupled, 3 inputs per channel). It works fine and with this circuit, ALL op-amps sound the same. There is no difference between the NE5532 or the OPA1656 or any other one.
So now I'm more confused. Why the big difference in my amplifier and NO difference in the summing circuit?I
The audio amp, by the way, is a AIYAMA A04 which had a TPA3251 power stage, one NE5532 preamp per channel, and it's running on 32 volts. I also have a AIYIMA A07 which is basically the same as the -04, but it uses a TPA3255 power stage instead of the 3251. This one also works dramatically better with the OPA1656 preamp.
Any explanations for this strange (to me) behavior?
Thanks!
Hope this is the proper forum for this topic - mods please move it if it's in the wrong spot.
OK, first off I'm not one of "those" people who claim to be able to hear differences in various alloys of speaker wire or differences in capacitor brands, etc...
Now, to the point: I've got a little Class D audio amplifier with Sony SSCS5 speakers for playing PC sound output. The amplifier has two 8 pin DIP sockets so that the pre-amp op-amps can be "upgraded". The amp came with generic NE5532 parts... sounded fine.
Although I don't believe in "audiophile" things like "premium speaker wire" or $150.00 "speaker fuses" or "magic infused capacitors", etc, I thought I would try a few different op-amps and see how they "sounded". I tried TL072, TL082, 4558, LM358 and OPA2134. To compare them, I left a 5532 in one channel and put the test op-amp in the other channel. I connected a signal to one side, then the other so that if there were any difference, I should hear it.
As I expected, they all sounded the same. After all, it's just an op-amp. Signal in, signal out.
Then, I read about the OPA1656 and thought "why not?". Well, OMG how to describe it? The resulting audio seemed a lot "better". More bass, and it sounded "tighter" (like the difference between a cheap ported speaker and a sealed one). The high end was, for lack of a better word, "brilliant". Even the midrange was a lot "cleaner". (by the way, all the chips I tested came from Digi-Key, not cheap Chinese knockoffs).
OK, so now I am totally confused. It's just an op-amp. Signal in, signal out. HOW ON EARTH can the OPA1656 sound SO much better? Is the 1656 "better", or is it "right" and the other parts "insufficient"?
Another observation: I built a little stereo signal summer which is a pair of simple unity gain inverting amplifiers (+/- 9 volt power, 47k feedback and 47k input, non-inverting input grounded, dc coupled, 3 inputs per channel). It works fine and with this circuit, ALL op-amps sound the same. There is no difference between the NE5532 or the OPA1656 or any other one.
So now I'm more confused. Why the big difference in my amplifier and NO difference in the summing circuit?I
The audio amp, by the way, is a AIYAMA A04 which had a TPA3251 power stage, one NE5532 preamp per channel, and it's running on 32 volts. I also have a AIYIMA A07 which is basically the same as the -04, but it uses a TPA3255 power stage instead of the 3251. This one also works dramatically better with the OPA1656 preamp.
Any explanations for this strange (to me) behavior?
Thanks!
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Maybe you should post here :
OPA1656: High-Performance CMOS Audio Op Amp
It's the OPA1656 fanboy thread . 😉
How do you test a quad opamp like TL084 in a dual socket ?
Personally , I admit to buying expensive opamps hoping they are better than the rest BUT in a preAmp with OPA627's I used OPA132 for the treble and bass and couldn't hear any difference with bass and treble in neutral or bypassing them.
I haven't tried OPA1656 yet.
OPA1656: High-Performance CMOS Audio Op Amp
It's the OPA1656 fanboy thread . 😉
How do you test a quad opamp like TL084 in a dual socket ?
Personally , I admit to buying expensive opamps hoping they are better than the rest BUT in a preAmp with OPA627's I used OPA132 for the treble and bass and couldn't hear any difference with bass and treble in neutral or bypassing them.
I haven't tried OPA1656 yet.
I don't understand what that has to do with sound quality, but I'll check and let you know.
Simple: you observed a huge difference between NE5532 and OPA1656 in the class D amp, but no difference in your circuit. So where does this come from?
It could be that the class D amp has bad layout around the opamps so a fast 50MHz opamp like OPA1656 is unstable, which can sound... interesting. But looking at a picture of the amp, there are lots of caps around the opamps, so I assume some of them are on supply decoupling duty, the feedback resistors are very close, there is a ground plane, so I don't see why the opamp would get unstable. So, hypothesis "layout" dismissed.
I presume your test summer circuit has a clean power supply and no HF noise source nearby. The class D amp will make lots of HF noise, so the quality of the opamps' power supply is unknown until it is actually probed.
That could be an explanation, considering OPA1656 has much better supply rejection than 5532. So you can check the amount of noise (audio frequency, but also HF) on the supplies. If the supplies are clean, then hypothesis "different power supply rejection explains it" is dismissed. If you find lots of noise, then, maybe it's a clue.
You could make plenty of hypotheses, maybe it's the FET input if there is a high impedance feeding it, or the better CMRR, input stage nonlinearity vs common mode, etc. For example your summer circuit is wired in inverting mode so it doesn't care about the CMRR of the opamp or any common mode dependent nonlinearity in the input stage, since the common mode is constant 0V.
It could be that the class D amp has bad layout around the opamps so a fast 50MHz opamp like OPA1656 is unstable, which can sound... interesting. But looking at a picture of the amp, there are lots of caps around the opamps, so I assume some of them are on supply decoupling duty, the feedback resistors are very close, there is a ground plane, so I don't see why the opamp would get unstable. So, hypothesis "layout" dismissed.
I presume your test summer circuit has a clean power supply and no HF noise source nearby. The class D amp will make lots of HF noise, so the quality of the opamps' power supply is unknown until it is actually probed.
That could be an explanation, considering OPA1656 has much better supply rejection than 5532. So you can check the amount of noise (audio frequency, but also HF) on the supplies. If the supplies are clean, then hypothesis "different power supply rejection explains it" is dismissed. If you find lots of noise, then, maybe it's a clue.
You could make plenty of hypotheses, maybe it's the FET input if there is a high impedance feeding it, or the better CMRR, input stage nonlinearity vs common mode, etc. For example your summer circuit is wired in inverting mode so it doesn't care about the CMRR of the opamp or any common mode dependent nonlinearity in the input stage, since the common mode is constant 0V.
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Also the drive capacity? While 5532 is no slouch, still it's simply not comparable to the 1656's output current capacity. It all depends on what kind of load (with maybe dynamic changes) the class d input scheme presents.
And ten years ago I said:
All here:
Swapping Op-Amps... you have checked to see it's stable haven't you ?