cheep koreans amps no good -FI

[CleanSierra]

I believe what that are saying Wicks, is that the tinsel leads are a conductive material and the resonant frequency is in microwave range. The noise comes on, which is microwave, and cooks(literally) the leads right off.

[TeamHT]

^^^^

[Chris Hammer]

If they put the statements out there then they should, and are expected, to have some real evidence and tests backing the claim...if that's the case throw the tests, pics, videos and whatever else out there for all to see. Who gives a shit if it calls a few select brands out on their amps, or looks bad for nendo,skar etc that have been mentioned. People need something a little more concrete then he said so, and a picture of 10words about 30%more heat that looks like 4th grader notes.

[iwannabeloud]

The information is out there,

http://www.analog.com/library/analogdialogue/archives/40-06/class_d.pdf

Taming EMI

The high-frequency components of Class D amplifier outputs

merit serious consideration. If not properly understood and

managed, these components can generate large amounts of EMI

and disrupt operation of other equipment.

Two kinds of EMI are of concern: signals that are radiated into

space and those that are conducted via speaker- and power-

supply wires. The Class D modulation scheme determines a

baseline

spectrum of the components of conducted and radiated

EMI. However, some board-level design techniques can be used

to reduce the EMI emitted by a Class D amplifier, despite its

baseline spectrum.

A useful principle is to minimize the area of loops that carry

high-frequency currents, since strength of associated EMI is

related to loop area and the proximity of loops to other circuits.

For example, the entire LC filter (including the speaker wiring)

should be laid out as compactly as possible, and kept close to the

amplifier. Traces for current drive and return paths should be

kept together to minimize loop areas (using twisted pairs for the

speaker wires is helpful). Another place to focus is on the large

charge transients that occur while switching the gate capacitance

of the output-stage transistors. Generally this charge comes

from a

reservoir

capacitance, forming a current loop containing

both capacitances. The EMI impact of transients in this loop

can be diminished by minimizing the loop area, which means

placing the reservoir capacitance as closely as possible to the

transistor(s) it charges.

It is sometimes helpful to insert RF chokes in series with the

power supplies for the amplifier. Properly placed, they can confine

high-frequency transient currents to local loops near the amplifier,

instead of being conducted for long distances down the power

supply wires.

If gate-drive nonoverlap time is very long, inductive currents

from the speaker or LC filter can forward-bias parasitic diodes

at the terminals of the output-stage transistors. When the

nonoverlap time ends, the bias on the diode is changed from

forward to reverse. Large reverse-recovery current spikes can

flow before the diode fully turns off, creating a troublesome

source of EMI. This problem can be minimized by keeping the

nonoverlap time very short (also recommended to minimize

distortion of the audio). If the reverse-recovery behavior is

still unacceptable, Schottky diodes can be paralleled with the

transistor’s parasitic diodes, in order to divert the currents and

prevent the parasitic diode from ever turning on. This helps

because the metal-semiconductor junctions of Schottky diodes

are intrinsically immune to reverse-recovery effects.

LC filters with toroidal inductor cores can minimize stray field

lines resulting from amplifier currents. The radiation from

the cheaper

drum

cores can be reduced by shielding, a good

compromise between cost and EMI performance—if care is taken

to ensure that the shielding doesn’t unacceptably degrade inductor

linearity and sound quality at the speaker

LC Filter Design

To save on cost and board space, most LC filters for Class D

amplifiers are second-order, low-pass designs. Figure 3 depicts the

differential version of a second-order LC filter. The speaker serves

to damp the circuit’s inherent resonance. Although the speaker

impedance is sometimes approximated as a simple resistance, the

actual impedance is more complex and may include significant

reactive components. For best results in filter design, one should

always seek to use an accurate speaker model.

To address these concerns, the LC filter is sometimes eliminated

entirely, to create a

filterless

amplifier. This saves cost and space,

though losing the benefit of low-pass filtering. Without the

filter, EMI and high-frequency power dissipation can increase

unacceptably—unless the speaker is inductive and kept very close

to the amplifier, current-loop areas are minimal, and power levels

are kept low. Though often possible in portable applications like

cell phones, it is not feasible for higher-power systems such as

home stereos.

Another approach is to minimize the number of LC filter

component s requ i red per aud io c h a n nel. T h is c a n be

accomplished by usi ng si ngle - ended half-br idge out put

stages, which require half the number of Ls and Cs needed for

differential, full-bridge circuits. But if the half-bridge requires

bipolar power supplies, the expense associated with generating

the negative supply may be prohibitive, unless a negative supply

is already present for some other purpose—or the amplifier has

enough audio channels, to amortize the cost of the negative

supply. Alternatively, the half-bridge could be powered from a

single supply, but this reduces

output power and often requires

a large dc blocking capacitor

[iwannabeloud]

http://www.eetimes.com/document.asp?doc_id=1274877&page_number=4

http://www.ti.com/lit/an/sloa119a/sloa119a.pdf

https://www.coldamp.com/store/media/pdf/Class_D_audio_amplifiers_White_Paper_en.pdf

[Karkov]

Is this why Steve uses RF amps, lol

[iwannabeloud]

From nick

My the crickets sure do make a lot of noise in this corner of the internet these days..

The test bed has been brand X 3500 watt amps and brand Y 9000 watt amps, both from the same build house in Korea. One running on 12 volts, one running on 16 volts. These amplifiers BOTH have the same problems with the high frequency noise on the positive swing of the amp (Verified by O-scope, they're switching at 120kHz, and 160kHz respectively). They are the same amps that everybody and their cousin sells for 15 different prices and they all argue who's mosfets are upgraded more..the result is still the same. They do not ALL do it, it's literally the luck of the draw as overseas "Manufacturing" is questionable at best. One day Mr. C might cut a good deal with his friend Mr. K on some sweet mosfets that failed QC for his medical devices that he is making, in turn you get mosfets in your amp that have crap silica and suffer shoot through amongst other issues. Two days after that they may very well be in another good batch of parts that function properly. I've gotten failed QC capacitors printed with a major manufacturer's logo right on them inside of an amplifier as the people who were making them considered them to be "equivalent parts". How are you supposed to sell an amplifier under a given brand name with KICKER capacitors inside of it? Also note this there is one competitor in particular ran that exact same 9000 watt amplifier from a different batch and never had an issue burning a lead up. EVER.

The wave form looks as below on these amps, note the notch on the positive 30% (outward) push on the amplifier, excuse the accuracy of the drawing as I didn't reference "0" as a cross point and drew it in a few seconds during dinner. This is high frequency noise in the top 30% of this wave form that becomes notched as the coil starts to move towards the peak of the excursion level.

Now, once it gets to that point on the positive swing where you see the 'fuzzy' noise coming out of the output stage of the amp everything suddenly becomes super heated. The coil is at Xmax (30% of it left in the gap) and it burns the bottom 30% of the coil, along with the positive tinsel lead. The negative tinsel lead is NOT fatigued, or heated at all.

On both of these amplifier setups in two completely different vehicles if you swap the positive and negative on the amplifier respectively and wire the sub "out of phase" (Treating the positive, as the negative), the negative lead magically starts burning up and the positive lead is no longer fatigued.

So wait a second. If heat energy is based on "Watts" and you have the same amount of "Watt energy" going through the leads into the coil in the forward direction, as the rear-word direction. Why is the positive lead burning when it is hooked up in phase and the negative isn't being effected at all?

It's the high frequency noise that the amplifier is not being filtered out of the output stage on the amp. If you wire it one way and it burns the positive lead up and the negative isnt effected (with the same amount of heat, or watts, present) then you have something else going on.

It's the high frequency noise as shown above. That's what it looks like on an O-scope. We didn't have this problem 10 years ago when amplifiers weren't switched as high, or as hard. 1500 watts hasn't changed in 10 years, it's still 1500 watts. How they are getting that 1500 watts has however changed and they're doing it by using less parts, ran much harder, and it causes issues as seen in the picture above.

We've confirmed it with various other EE's that actually design amplifiers for a living for major manufacturers and spend a lot of time trying to make sure that no high frequency noise gets out of the output stage of the amp.

When all else fails, FOAD.

The magnet/steel acts as a buffer for the 'negative' wave form and soaks up enough of it to not be an issue. You don't have a magnet or steel on the outward stroke of the coil so the coil goes into free space and there is only the height of the top plate to buffer it out and soak the high frequency energy up so it crashes at whatever is considered the positive tinsel lead at that point. The only steel that you have around is the material that is comprised of the top plate which is where the high frequency noise seeks out causing a super-heated area on the coil (turning it black on that bottom 1/3 of the coil).

Big rack mount amps do not have this problem because they use A/B designs that do not switch anywhere near as hard (or not at all in class A's case) as these half bridge and/or "ultra efficient" class D amps. If I did "design" an amp (not pick out from a catalog) I'd make damn sure that there was not any HF noise coming out of the thing anywhere near the operating frequency of the mosfets. But, there isn't any money in it, because nobody is willing to pay for what a properly designed amplifier is worth that doesn't have these problems.

When the wire on the coil gets hit with the high frequency noise if it is at the peak of the excursion level it sits there and bakes like so:

Induction Heating - Quick Demonstration - YouTube

Note that the metal does not glow north or south where it is being induced with the high frequency noise (induction heating). It ONLY gets hot when the high frequency noise is induced, with which on this amplifier it only induces the high frequency noise when 2/3 of the coil is out of the gap. It sucks all of that heat energy into the very edge of the top of the top plate where the coil is resting sitting there getting hammered with 120-160kHz and 3000++ watts of power present.

I've got coils at the shop that the bottom 1/3 of the coil is black, the top 2/3 of the coil is completely normal for one that was wired "in phase".

The coil that was wired "out of phase", the top 1/3 of the coil is burned black, the negative tinsel lead is burned up on both sides, and the bottom 2/3 of the coil is completely fine.

Same amplifier, same install, same everything, just flipped the polarity respectively to change what lead the high frequency noise is going to.

[n8ball2013]

I think what isn't being mentioned is that Scott does a ton of r and d IN HOUSE. He sees things other companies may not be seeing because he has access to every step in the manufacturing process. As one of the few if not only company who does everything going IN HOUSE he may be seeing things and have per perceive into things that others don't. While it's not a knock on any company that imports parts they may just not do the same things or see the same things. While I completely agree that names need to be named and hard evidence needs to be shown I've known Scott and Nick long enough to know they aren't going to say something if they don't have proof

[Kyblack76]

I think what isn't being mentioned is that Scott does a ton of r and d IN HOUSE. He sees things other companies may not be seeing because he has access to every step in the manufacturing process. As one of the few if not only company who does everything going IN HOUSE he may be seeing things and have per perceive into things that others don't. While it's not a knock on any company that imports parts they may just not do the same things or see the same things. While I completely agree that names need to be named and hard evidence needs to be shown I've known Scott and Nick long enough to know they aren't going to say something if they don't have proof

Agree.

I respect Nick to the fullest. If he says this or that...... he isnt just throwing wind around.

Also, people on here think it happens to all Fi subs/4" coils. Far from the truth.

Their failure rate is LOWER than any company i know. THEY are just going a lil deeper than "others".

[iwannabeloud]

Id rather look at this thread logically...

We know that this "upgrade" has been implemented on team fi/sp4 subs

Now, simple, answer these questions so we can understand

Why only sp4/team series

Why doesn't the issue occur in similar power range subs from other brands

If those questions can not be answered, the idea is moot to me since logic and reasoning for you to design the idea of FOAD should be able to answer those questions

1) 4" coils and the 6 spoke basket,will not work with a 12 spoke basket as the geometry is not correct.

2) Subs fall apart before you get to that power range and suffer mechanical failure. After they figure out how to keep a surround down or a spider landing down ( screws and mounting brackets :shakes head: ) they then will get to the point where we are which is ok, now it stays together, it's just burning up now..why is it burning up...it didn't burn up 10 years ago with that same amount of power, why is it doing it now?

We started out with 1 tinsel lead loose with 8x3 spiders 13 years ago with RE. The SE was a 1000 watt single spider sub. Back then 1000 watt amps didn't burn the tinsel leads up..and they were still 1000 watts. At that point the cooling technology hadn't been figured out yet and coils burned up. That was the weak point and the failure mode, the leads would take 1000 watts of a/b power but the coil would not because the heat would not wick away.

Now, a "SSD" which is equivalent to an "HC" (1200 watt two spider sub 13 years ago) is now a 1000 watt 5 (equivalent) spider sub, with 4 times as many tinsel leads if integrated, and double the amount of tinsel leads if in 7x3" spider loose lead form with strain relief on the leads around the terminal block.

Coils don't burn up anymore as the cooling technology was figured out, soft parts don't rip any more as the strain relief was figured out as was different changes in materials. The end of the road is the fatigue of the tinsel lead.

1000 watts 13 years ago was a TON of money but it is still 1000 watts now, the difference is now that it is made horribly cheap, QC is questionable at best, and any 17 year old kid can afford a 3500 watt amplifier for the low price of 300 bucks on alibaba.com

But, now, to get a speaker to stay together with 1000 watts of power you have to build it like a 3000 watt speaker would have been 13 years ago.

The industry has been infected with those who are insanely abusive and buy amps that have very little control over the moving assembly of the speaker at all (damping factor).

Thank you, and good night.