Hey Guys.
I've recently purchased a headphone amp from aliexpress (based on beyrdynamic a1) and I'm not too happy from the sound quality (esp the bass). I was thinking of replacing the opamps, but got into a bit of a snag! So basically, it has two NE5532P's which appear to be fake, according to this post:
https://www.diyaudio.com/forums/parts/362781-fake-op-amp-tester-op-amps-genuine-fake-2.html
They have 19YLDZM markings on em. Now, here's the tricky part, I've used my multimeter and measured 24.38V (VCC - and +) which I presume to be the voltage they're running on. I've also looked at the official TI datasheet, and 22V is the max:
https://www.ti.com/lit/gpn/NE5532
Is there something I misunderstood in the datasheet? Anything wrong with the way I've measured the voltage? Does this mean I'd have to get replacement opamps that are capable of withstanding 24V? And if so, any suggestions? Thanks.
I've recently purchased a headphone amp from aliexpress (based on beyrdynamic a1) and I'm not too happy from the sound quality (esp the bass). I was thinking of replacing the opamps, but got into a bit of a snag! So basically, it has two NE5532P's which appear to be fake, according to this post:
https://www.diyaudio.com/forums/parts/362781-fake-op-amp-tester-op-amps-genuine-fake-2.html
They have 19YLDZM markings on em. Now, here's the tricky part, I've used my multimeter and measured 24.38V (VCC - and +) which I presume to be the voltage they're running on. I've also looked at the official TI datasheet, and 22V is the max:
https://www.ti.com/lit/gpn/NE5532
Is there something I misunderstood in the datasheet? Anything wrong with the way I've measured the voltage? Does this mean I'd have to get replacement opamps that are capable of withstanding 24V? And if so, any suggestions? Thanks.
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The absolute max voltage rating is 44 volts and this is the voltage between pins 4 and 8.
So if you are seeing +24 on pin 8 and -24 on pin 4 then yes, the device is being used outside its absolute max rating.
How that 44v is made up doesn't matter, you can have +15 and -29 or +40 and -4 and so on.
So if you are seeing +24 on pin 8 and -24 on pin 4 then yes, the device is being used outside its absolute max rating.
How that 44v is made up doesn't matter, you can have +15 and -29 or +40 and -4 and so on.
I appreciate the fast response Mooly! But that sounds a bit confusing. To re-iterate, my multimeter was autoranging on DCV, negative (black) probe was put onto pin 4, and the positive (red) probe was put onto pin 8, and the reading was 24.38 on both opamps. Not sure how you've reached 44. And where does it say on the NE5532P's datasheet that it's 44 btw? I've only saw 22 as the max. I need to get this voltage thing figured out before I could look for compatible replacements.
If you measure from pin 4 to pin 8 and see 24.4 V, you're fine. That's a bit more than half of the specified 44 V supply voltage (±22 V -> 44 V total).
If you suspect the opamps are fake, why not try a genuine pair? You can get them from Mouser: Mouser Electronics
Something like the LM4562 or OPA1656 would work well also. Note that the OPA1656 is only available in a surface mount package. If your opamps are socketed, you'll need an adaptor if you want to use the OPA1656.
Tom
If you suspect the opamps are fake, why not try a genuine pair? You can get them from Mouser: Mouser Electronics
Something like the LM4562 or OPA1656 would work well also. Note that the OPA1656 is only available in a surface mount package. If your opamps are socketed, you'll need an adaptor if you want to use the OPA1656.
Tom
Thanks for your assistance Tom! I think I'm starting to get it. So, the voltage specified in the datasheet is per each VCC pin (- and +) individually? And when measuring the voltage using a multimeter between pins 4 and 8, the end result is in fact a combination of both? I.E 24V means each pin receives 12V?
And for the record, mine are DIP8 and are non-soldered (removable, sitting in sockets). And after reading various opamp opinions, I'm leaning more towards trying OPA2228/OPA2107/OPA2134,
How can you be so sure? What would affect bass response then?
Well, I can't be 100% sure, lets say it's a gut feeling! It's not my headphones (as they have good enough bass with other sources) and it's not like the bass on this headphone amp is non-existant, its just under-emphasized. Also, I've seen various opamp threads (where people did state that they've noticed bass differences with different opamps). Apart from the opamps though, it also has 2x BD139 & 2X BD140 transsitors (which I was thinking of replacing with 2SC5171 & 2SA1930 as I've read it provides some degree of improvment) and it also has 2X BC546 & 2X BC556, which I was thinking of leaving as-is. And no. I don't have the gear (osciliscope I'd imagine) to measure the frequency response I'm afraid.everything else! how can you be sure it is the opamp?
Fake opamps that still work are re-stamped LM358, the cheapest crap on the market. They are noisy and low end, but bass response is not affected. period.
btw, did you measure frequency response to backup your claim?
That's entirely possible.And I have a quite strong feeling you are barking at the wrong tree.
Afraid I couldn't find one, but if it helps, I've added pics of the PCB. the small caps are hard to read without a close inspection, but the yellow ones are samyoung nxh (25v 470uf), the 4 bigger ones are nichicon VZ & VR (3x VZ) all rated for 25v 3300uf. I'd say the nichicon's prob do the low freq filtering (although, I could be wrong) Also, keep in mind those are standard caps and not audio grade, could this be the issue?
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
The large Nichicon power supply capacitors will not impact on low frequency output. The capacitors that can are input or interstage coupling capacitors in series with the signal, which are sized to set the low frequency high pass cutoff, and bypass capacitors in the feedback circuit which reduce the gain of the amplifiers below a designed cutoff frequency.
Audio grade capacitors have a more linear behaviour across all audio frequencies especially higher frequencies so do not expect any change in apparent bass level from changing them.
It isn't clear without a schematic whether the yellow and/or black & gold capacitors are used for coupling or feedback circuits. The chances are that the four black and gold capacitors near the transistors are coupling and/or feedback bypass capacitors. You could try doubling or quadrupling their values at the same voltage rating, which will halve or quarter the low frequency cutoff frequency respectively.
These are ones you should choose Elna Tonerex or Nichicon Fine Gold or similar audio grade. The yellow ones are likely local supply bypass capacitors, and not directly implicated but that is only a guess!
Audio grade capacitors have a more linear behaviour across all audio frequencies especially higher frequencies so do not expect any change in apparent bass level from changing them.
It isn't clear without a schematic whether the yellow and/or black & gold capacitors are used for coupling or feedback circuits. The chances are that the four black and gold capacitors near the transistors are coupling and/or feedback bypass capacitors. You could try doubling or quadrupling their values at the same voltage rating, which will halve or quarter the low frequency cutoff frequency respectively.
These are ones you should choose Elna Tonerex or Nichicon Fine Gold or similar audio grade. The yellow ones are likely local supply bypass capacitors, and not directly implicated but that is only a guess!
Actually I do not think there is anything wrong with your amp, in fact the bass region will be reproduced perfectly linear, whereas you compare it wjth the boosted result of a different amp because of the series output resistor being high like 47 to 68 ohms.
When you have low ohm phones like the T1 with 32R this resistor creates a boost around the resonant frequency (80-100Hz) by more than 6dB.
In your amp (I guess the 4.7 ohm is the series resistor) it is so low only a very tiny boost results.
Probably you got used to the boosted sound and now bass seems to be lacking. I would suggest to listen to as much music as possible to burn-in your ears so to say
ciao Bansuri
When you have low ohm phones like the T1 with 32R this resistor creates a boost around the resonant frequency (80-100Hz) by more than 6dB.
In your amp (I guess the 4.7 ohm is the series resistor) it is so low only a very tiny boost results.
Probably you got used to the boosted sound and now bass seems to be lacking. I would suggest to listen to as much music as possible to burn-in your ears so to say
ciao Bansuri
First, connect the output to an amplifier and see the response, or try another headphone.
Second, if not satisfied, check the voltages.
Third, while changing op amps, bear in mind that the input and output impedances will need changing to match.
And just see if they are JRC, or others, the JRC seem to perform better.
And then put real JRC, or JRC/TI 072 in place.
Use contact spray to prevent corrosion in the contacts in the socket...long term insurance.
Second, if not satisfied, check the voltages.
Third, while changing op amps, bear in mind that the input and output impedances will need changing to match.
And just see if they are JRC, or others, the JRC seem to perform better.
And then put real JRC, or JRC/TI 072 in place.
Use contact spray to prevent corrosion in the contacts in the socket...long term insurance.
All the opamp cares about is the voltage from the V- pin to the V+ pin. That's commonly specified as 44 V (±22 V). The ±22 V is added for convenience or perhaps to prevent a divide-by-two error. Most audio circuits (and many other opamp circuits) operate with a bipolar (i.e. both positive and negative) supply and reference the signal to ground.
Have you ever measured the voltage of a 9 V battery? If you connect the + probe of your voltmeter to battery + and the - probe to battery -, your meter will show +9 V. But if you swap the leads, it'll show -9 V.
Now imagine what would happen if you connected two 9 V batteries in series. If you connect the - probe of your meter to the centre point between the two batteries and then touch the + probe to the + pole of the 'top' battery you'll see +9 V. If you then touch the + probe of your meter to the - pole of the 'bottom' battery, you'll measure -9 V. But measure from the bottom of the stack to the top and you get +18 V.
Tom
I have noticed with some opamps their bass sounds subjectively 'weak'. Its nothing to do with the frequency response, that will be flat enough. My hypothesis is that its to do with noise - the best sounding opamp to my ears (in an optimized circuit) is LT1028 and that has very low noise right down below sub-sonic frequencies. So it could well be your fake 5532s have rising LF noise and this translates into de-emphasized bass. Or my hypothesis could be quite wrong.
Thanks for all the support guys!
Ended up swapping the opamps with NE5532P & OPA2134 taken from my other amp, and there's been a definite improvement in the bass section! The reason why I've gotten this new one is because the sound on my original amp was overly condensed and didn't had enough spacing. Surprisingly, my a1 replica with the same opamps doesn't have that problem. Anyways, bass issue is resolved, not entirely satisfied from other elements of the sound, but I've got multiple opamps on the way, some audio grade caps, and 2SC5171 & 2SA1930 to replace the BD139/BD140s, so hopefully I'll get a resoltuion on that part later. Also, turns out I did measure the voltage of the opamps incorectly (as I wasn't familiar with the fact that they get two separate voltages) I've gotten 12.30V from the GND point to pin 8, so I guess that's the real voltage they're getting. Anyways, I guess it's a wrap for this one. Thanks again guys.
Ended up swapping the opamps with NE5532P & OPA2134 taken from my other amp, and there's been a definite improvement in the bass section! The reason why I've gotten this new one is because the sound on my original amp was overly condensed and didn't had enough spacing. Surprisingly, my a1 replica with the same opamps doesn't have that problem. Anyways, bass issue is resolved, not entirely satisfied from other elements of the sound, but I've got multiple opamps on the way, some audio grade caps, and 2SC5171 & 2SA1930 to replace the BD139/BD140s, so hopefully I'll get a resoltuion on that part later. Also, turns out I did measure the voltage of the opamps incorectly (as I wasn't familiar with the fact that they get two separate voltages) I've gotten 12.30V from the GND point to pin 8, so I guess that's the real voltage they're getting. Anyways, I guess it's a wrap for this one. Thanks again guys.