Source of "no name" inductors?

ernperkins

Member
2009-11-24 8:39 pm
Anyone know the source of these "no name" inductors? I'd like to upgrade them, but need the pad footprint dimensions. These are from a 3116 based TinySine TSA7800B amplifier (LINK). They're dual coil inductors and have approximate dimensions of 10 mm X 9 mm. It's hard to get an accurate measurement due to the nearby components. Any information appreciared.

Inductor.jpg
 

bucks bunny

Member
2020-01-19 12:40 pm
I was going to say, what makes you think replacing them is any advantage? Because they are small? They are just wire.
Now, there may be better choices in larger coils, different value or physical size as in other amps. Without a schematic to do a Spice simulation, you are on tenuous ground. Kind of what you get in a inexpensive amp as output integrators are expensive and that is half the battle. There is a reason a Hypex or Purify costs more.
 

bucks bunny

Member
2020-01-19 12:40 pm
I was going to say, what makes you think replacing them is any advantage? Because they are small? They are just wire.
Now, there may be better choices in larger coils, different value or physical size as in other amps. Without a schematic to do a Spice simulation, you are on tenuous ground. Kind of what you get in a inexpensive amp as output integrators are expensive and that is half the battle. There is a reason a Hypex or Purify costs more.
I do not get your point - why do you ask for a source of these inductors if not trying to replace them?
Believe me or not, but I have tested enough inductors around these TPA-amps to say without further technical information of your amp that inductors of same size and shape from different brands do make tiny differences in THD contribution and the bigger cores normally behave better than the smaller:
And no, they are not just wire. There is ferrite around them with limited linearity.
Whether hunting for smallest THD will improve the sound - is another question
 

ernperkins

Member
2009-11-24 8:39 pm
Could also be Murata. But what do you want to upgrade?

When testing this amp I noticed the 3116 goes into fault mode when driving all channels at >25 W per channel using 4 ohm loads. After doing more testing and some reading it seems that the inductors going into saturation is a likely cause. I was hoping to find some information on the inductor's specs to see if that made sense. I highly doubt if I will change the inductors though: First, I don't like to drive a 3116 beyond 25 W per channel due to increasing distortion. Second, it would be a real challenge for me to remove the inductors without damaging the board. I'll concentrate on the "low hanging fruit": replacing the SMD output caps with MKS poly caps. I'm capable of that. :)
 

bucks bunny

Member
2020-01-19 12:40 pm
With a saturation current about 5 amps these inductors are working at the bleeding edge with 4 Ohms load - for 8 Ohms they would be suitable imho.
Smallish inductors and MLCC-filter-caps - oh well - you get what you paid for.
But wait - you wrote that you drove all channels >25W. You should test one single channel with max load - and in case this works w/o fault mode, inductor saturation is probably not your problem.
 
When testing this amp I noticed the 3116 goes into fault mode when driving all channels at >25 W per channel using 4 ohm loads. After doing more testing and some reading it seems that the inductors going into saturation is a likely cause. I was hoping to find some information on the inductor's specs to see if that made sense. I highly doubt if I will change the inductors though: First, I don't like to drive a 3116 beyond 25 W per channel due to increasing distortion. Second, it would be a real challenge for me to remove the inductors without damaging the board. I'll concentrate on the "low hanging fruit": replacing the SMD output caps with MKS poly caps. I'm capable of that. :)
I not shure, if these fruits are very sweet :) . The MKS poly caps have lower series resonant frequencies than the 1206 X7R capacitors (if I have identified them correctly in the picture). Are you shure, that the inductances areg oing into saturation? If so, their effective inductance would be lowered and their filter function would be partially lost. How does the amp detect inductance saturation to show you a fault?
 

ernperkins

Member
2009-11-24 8:39 pm
Smallish inductors and MLCC-filter-caps - oh well - you get what you paid for.
But wait - you wrote that you drove all channels >25W. You should test one single channel with max load - and in case this works w/o fault mode, inductor saturation is probably not your problem.

I did a couple of permutations: only two channels (both using the same 3116 chip) and just a single channel. In the 2 channel case the fault still occurred, but in the single channel case I could go up to the full 50 watts. I initially thought this ruled out saturation too. But the 3116 datasheet lists these possible fault conditions: over current, over temp, too high DC offset and over/under voltage on PVCC. I'm using a Meanwell LRS-350-24 power supply so I don't think it's the over/under voltage case. To test the temp fault condition I used the signal generator in REW. Using a 400 Hz signal set to create a 30 W output I can cause the fault to occur in second or two with a "cold" amp. You can watch the output try to climb to the 30W voltage, reset (Fault) and try again (FAULTZ is tied to SDZ which resets the fault). It seems to me that only a second or two to cause an over temp fault is awfully fast (FWIW). The amp inputs are AC coupled so the DC offset fault doesn't seem to be it either. Which leaves saturation.

I should mention that the amp has an ADAU1701 DSP. I replaced the vendor's program with this "straight thru" program to remove any DSP signal shaping.

TinySine Straight Thru.png
 

bucks bunny

Member
2020-01-19 12:40 pm
TPA 3116/18 features RDSon = 120mR @25C, rising with junction temperature.
Load current always passes two devices. And so a simple math teills us:
considering a load of 4R the RDSon-loss is 0,24R/4R = 6% of output power.
Assuming 30W/4R this gives 1.8W/channel or 3.6W in 2.0 configuration.
As the chip will not stay cold, RDSon increases and dissipation rises further - maybe twice!
And will at least double once more when driving 2*2 Ohms.
This is a lot on such a tiny chip and in case of improper heatsink I would expect a rapid shutdown.
That is why I prefer Monoblocks with paralleled outputs thus halving the internal power dissipation.
 

bucks bunny

Member
2020-01-19 12:40 pm
Please, read about magnetism. Larger cores have larger looses as looses are volumetric and magnetic flux flows in all the core volume. So as loose density is constant, looses are proportional to core size. "Yes sense".
Thank you for your nice recomandation - sadly it comes some decades too late. Your are right that magnetic losses are volumetric. And you are wrong in the conclusion that a bigger core - under the same condition - would increase losses. This simplified generalisation obviously derives from the wrong assumption, that flux densisity stays the same no matter how big the core you choose.
Please, read about magnetism