W A R N I N G !

W A R N I N G !

This page is full of non-facts and bullsh!t, (just like the internet and especially forums and other blogs), please do not believe entirely without exercising your intellect. Any resemblance to real things in reality is purely coincidental. You are free to interpret/misinterpret the content however you like, most likely for entertainment, but in no case is the text written on this blog the absolute truth. The blog owner and Blogger are not responsible for any misunderstanding of ASCII characters as facts. *cough* As I was saying, you are free to interpret however you like. *cough*

Saturday, April 30, 2011

List of the amplifier chips used in some studio monitor speakers

Got this from here, now to make a copy before it disappears

Alesis M1Active / M1Active 620 - LM3886 x2 - National Semiconductor
Behringer B2030A / B2031A - LM3886 x2
Dynaudio Acoustic BM5A / BM5A Compact - LM3886 x2
Fostex NF1A - LM3886 x2
Event - PS、TRシリーズ LM3886 x2 / ASP6 ASP8 (LM3886 x2) x2
ESI nEar05 eXperience - TDA2052 + ?? - STMicro
Genelec 1029A - LM3886 x2
Genelec 1030A - STK4036V x2 - Sanyo
Genelec 1031A - STK4241V - Sanyo
Genelec 8030A - LM4780 - National Semiconductor
Genelec 8050A - STK442-130 - Sanyo
KRK V4 V6 V8 Series2 / VXT6 - LM3886 + ??
KRK Rokit Powered RP5 RP6 RP8 - TDA7294(LF) + TDA2052(HF) - STMicro
M-Audio EX66 - TDA8927 (Class-D) - NXP
Roland DS-5 - LM3886 + ??
Tannoy Reveal 5A 6D - LM3886 x2
Yamaha HS50M HS80M - LM3886 x2
Yamaha MSP7 Studio - STK415-130A - Sanyo

Go gainclones.

Saturday, April 23, 2011

Energy conservation

As I read this topic, cost savings and ROI keep coming up.

Use less electricity = lower electricity bill.

And if the whole world uses less electricity, demand goes down, price per unit goes down also, because it is cheaper to generate.


My ass.

Cost-based pricing is never used in the real world.

And if OPEC realizes they are selling less oil, they will simply increase the price instead so they earn the same amount of money.

And locally we have good examples too.

When oil prices increase, electricity and transport prices go up.

When oil prices drop back, electricity and transport prices go up, citing "other costs".

That's why you can't trust the system.

Friday, April 22, 2011

I just discovered I can tell the difference of 3cm of head positioning

I've been feeling that my left speaker's a bit louder than the right. Thinking it could be either due to room acoustic, supported by the fact that the perceived bass is stronger on the left even though the subwoofer is on the right, I ignored it.

Today I was thinking that the left/right volume can be altered by the positioning of the head, so I decided to shift my head towards the right to get the perfect balance. When I got the balance I want, I looked at my head's position...

...to find it right in the middle of the two satellites.

You see, due to some strange situation of my table, my monitor is placed 6cm closer to the left satellite than the right. And I always make sure my head is at the middle of the screen. Which resulted in my head being 3cm off the sweet spot.

But what's a concept without testing.

Test methodology

Music is played through the speakers. Subwoofer volume turned to zero to prevent it from influencing the balance. The room lighting and computer screen are turned off (it's night btw). Eyes remained closed throughout each test until each measurement is taken.

1. Stand up from the chair, pulling it a short distance away from the original position.
2. Walk a metre or two away and back, pulling back the chair and sitting down at a random position. The direction to face is decided by the chest feeling against the table edge (my table is fairly large enough to do this).
3. The positioning of the head is shifted left right forward backward while facing the same direction as much as possible as the center position is attempted to be found.
4. After deciding position of head, a torchlight, one end placed against the chin and the other end pointing at and close to the table is switched on. There is a piece of paper fixed onto the table and where the torchlight is pointing at (the brightest part at the center) is marked.
5. Repeat from step 1 for next measurement.

A total of 6 readings were taken with the speakers at the original positions untouched. Then the left speaker is shifted 6cm to the left such that the distance between each satellite and the screen is both approximately 9.5±0.5cm. (Originally the left speaker is approximately 3.5cm away) This results in the sweet spot shifting left by 3cm. Another set of 7 readings was taken.

The screen is 53cm wide, so the original distance between the speakers is 66cm while the new distance is 72cm - an increase of 9.1%. The speakers are approximately 65cm from the edge of the table. The resulting change in distance between speaker and "sweet spot" - taken to be the edge of the table, equidistance from each speaker, is 1.9%, and resulting increase in angle is 7.7%.


The first set of readings are those directly above the horizontal line while that of the second set are indicated by a circle.

It is not a lot of readings and variance is fairly huge. However, two important observations - the average distance (from the left side of the paper) of each set of readings differed by approximately 3cm, while the differences between both maximums and both minimums are both 3.5cm. The difference between max and min values of each set is 4cm, resulting in a 0.5cm overlap.

Which means that it is fairly possible for the human ear(s) to detect changes in sound due to the sweet spot shifting by 3cm. 5cm would be a safe estimate.

Note that this little test does not reveal which position is the more accurate one, since there are other factors that affect balance of both channels - channel imbalance of equipment, room acoustics, hearing loss etc, but the main objective is to see if audible differences in perceived sound can result from small shifts in the positioning of the head relative to the speakers.

Granted, I used some sort of averaging technique to increase my precision - I shifted my head left and right to find the positions at which one channel is a certain degree louder than the other, and took the center. Like the way you tune the TV and focus the camera. But my head only moved by a few cm in the process (although it feels like a lot). This adds more weight to the idea that our hearing is precise to a few cm.

I'm not really surprised by the result - animals are able to pinpoint the location of predators and preys that are far away by just hearing, and some are even able to use them to navigate and eat prey. This would require even better precision. Way, way better. If I go and search I believe I would find better technical articles on the precision of human hearing.

This has implications on speaker positioning and how subjective listening tests are being carried out. I already know that some instruments in a particular song sound relatively louder and softer depending on the position and angle of my head, but having numbers puts things in perspective. We would need to be accurate to a few cm and a few degrees when positioning our speakers, and in subjective listening tests you may be hearing differences that are not actually there due to the head not being in the same position. And how many people actually make sure their heads are in the same position throughout the test? It also questions the credibility of auditions carried out simultaneously by a group of people, for no two heads can be in the same position at the same time, although subjective bias caused by the first guy to open his big mouth is more likely to cause everybody to "hear the same thing".

Looks like we may need, as it is jokingly mentioned on some forums, a vice clamp for our heads.

Friday, April 15, 2011

[Update] JDS Labs cMoyBB v2.03 OPA2604 measurements

I noticed some peculiarity with the OPA2604's distortion graph. This is a chip that is used in some high-end designs achieving lower than -100dB THD+N, so the graph I had wasn't reflective of its true performance. And I was checking this blog's stats on a hunch, and found many traffic sources from Google image search, with the search term OPA2604.

People may get the wrong idea reading that graph, so to reduce the amount of rubbish on the internet, I decided to do a retest with a 12V power adapter this time.

Results are shocking.

The EMU wasn't cooperative that day, and I was in a rush, so I didn't bother getting 0.001% THD. But this is good enough to show the previous measured performance of the OPA2604, which was shocking bad as >0.01%.

The first thing to notice is the numbers for THD dropped by an order of magnitude.

Now it measures okay. Most of the spikes are EMU's "noise floor" (for the lack of a better term that I know).

And yup, this is with 9V battery. So the issue wasn't insufficient voltage. This is an example of why control measurements are important, for if I had measured only 12V scenario, I would had gotten a different and wrong conclusion.

The main difference is the greatly-reduced even harmonics.

My guess for the cause? Is not going to be something groundbreaking - probably a bad contact.

Other graphs are similar, 12V and/or 33Ω load, so I won't go into that. Into 33Ω for both cases THD is 0.005+% but how much of it would be due the the EMU? Even-order harmonics did increase with current draw as with the case of OPA2132. Speaking of which, now I wonder how accurate are the measurements for OPA2132, particularly the 0.015% reading.

So here I declare the previous OPA2604 measurements invalid. Some others might also be questionable.

Thursday, April 14, 2011

Boston Acoustics HPS 10HO subwoofer repair - Day 2

Day 2 start - got my fuses, lets go.

The symptoms on day 1 got me feeling that it is the power amp section that is spoilt. So I have to disconnect just the power amp section. A good way is via removing the rectifier. But before I do that, lets look at a strange thing I saw on day 1:

Yes, one leg of the rectifier is missing. In replacement a wire is soldered on half that leg and the solder pad on the underside of the board. Why would anyone do that is out of my comprehension.

This does hint of something wrong with this portion of the circuit, or maybe the rectifier. Unfortunately the rectifier measures fine out of circuit and unpowered, plus the humming when turned on (after the capacitors get their power before the fuse blew) indicates something wrong further downstream. There is also a previously unnoticed burn mark on one of the connector pins for the wire from the transformer, which further hints that the power amp section is the problematic part.

The 20W of my Goot iron really shows its inadequacy here, I am unable to desolder the bridge. Thick leads and traces conducted heat away too fast. I had to cut the legs off to remove the rectifier then desolder the remaining sections of the legs.

The right side of the board, the blue capacitors and the parts below it, is the power supply for the pre section. This tested working fine, and nothing blew up with the pre board connected either. Now I just need a way to tap the pre-out to ensure it is working, then I'll stuff an amp inside and finish it up. But this is enough for the day.

Bugger has 50VAC x 2, wooorr. But that is also a problem because I don't remember any chipamp that can handle ±70VDC. (Erm yes those big capacitors are 6800uF 80V)

God I want one

For some reason this lab also has many Audio Precision - the early 2700 series units. Many faulty ones - burning smell when power on - all lined up on the shelf.

Also has Neutrik audio analyzers. Just what does this lab do?


One day I heard lots of mynah chirping (as in a lot of the chirping, not mynahs). I looked to the source thinking it was another mynah fight. But no, all I saw was four mynahs standing close to each other. Two of them were slightly smaller than the other pair. Upon close look I realized they were juveniles.

They can already fly and are walking around pecking at things, but following close to their parent and chirping incessantly. Probably learning how to hunt.

On first look they can be easily mistaken for adult mynahs, since they can already fly and such. But they are not adult yet and probably still stay in the same nest as their parents. Isn't it the same for humans; some of us appear to have reached adulthood, but are missing one critical step to really becoming one. That includes NSFs, uni students, businessmen, investors, inventors and entrepreneurs - those who stay with their parents and throw their savings away via their businesses because they can't do real jobs.

Tuesday, April 12, 2011

"Wouldn't the cheap ring terminal bottleneck the performance of the faceplate?"

I was chuckling hard when I typed that.

On a serious note, hire a licensed electrician for in-wall mains wiring, or check with your local authorities on required permit and inspection. Also, make sure the connections are rated for mains and safety earth, though that isn't an issue if a licensed guy carried out the job. You wouldn't want to void your insurance.

Sunday, April 10, 2011

[Rant] Pokemon - Infernape

How the hell does a monkey know stealth rock?

Wednesday, April 6, 2011

Non-fiction fail or win?

They are real!

Monday, April 4, 2011

Tweens 250mAh 9V (8.4V) rechargeable battery - first charge/discharge cycle (almost) complete

Just to prove that not all China batteries are crap.

Tweens 250mAh 9V (actual 8.4V) 250mAh battery, why did I get the cheapest battery that is 250mAh instead of paying a few tens of cents more for 280mAh?

One reason is it has the highest number sold among the sub-USD$3 batteries.

Second reason is that you wouldn't believe that these batteries have over 200mAh anyway. And the same manufacturer probably made them and put them in different packagings.

And the charge rate is a giveaway (ya the manufacturers are nice enough to print the charge rate on the sticker) - 15 hours at 20mA. Usually the formula for charge rate and time is 1.5 x 10 hours x 0.1C. 10 hours @ 0.1C gives full charge but some extra is needed to make up for losses and give it a bit of overcharge. That 20mA pretty much tells us the actual capacity.

Well, there are batteries on eBay stating 300mAh and 30mA charge rate. Maybe I'll try that out when I need another 9V battery. But by then Chinese LSD 9Vs would most likely be out.

Ok, enough talking, the most important part of this post:

Is not the graph. But the note that I only charged it at a rate of 14-15mA on average for 700 minutes, and the charge rate slowed down towards the end before I terminated the charging. There are reasons for this but I'm not going to waste bandwidth. That gives us roughly 160-170mAh of charge, after losses I'm inclined to think the former.

Without further ado, here is the graph for the first discharge after the first recharge (or the second discharge if you count the discharge I did right out of the box):

Discharge rate is 10.1mA, which is the current the LM4562 draws. That gives us about 150mAh.

Pardon the lack of readings at the start which makes the graph too linear at the start. I didn't have the opportunity to check it. I'm guessing it should be linear up till 8.8-8.9V before it shoots upwards (counting from the back).

If you take into consideration that full capacity could be higher, not bad for $3 SGD. At least it is not crap. Now that I know, I can do a 200mAh test, if I decide to do one.

Sunday, April 3, 2011