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*

Tuesday, March 29, 2011

Measured current draw of some op-amps

As I was going to use my cMoyBB on a regular basis, I was curious as to which op-amp to use for maximum battery life.

Of course I can search the datasheets, but what's the fun in that. Also, I want to try to find clues that can tell me whether my OPA627BP's are fake.

LM4562 10.1mA
OPA-Earth 49.1mA
OPA627 14.0mA for two
LM6172 >60mA (error)
OPA2604 10.0mA
OPA2227 7.3mA
JRC4580 5.1mA
OPA2132 8.8mA

Yup, the numbers are as the datasheets say, mostly. LM6172's is over 60mA and increasing, and it was getting warm fast. It still has a very high DC-offset (>100mV!) despite the unity-gain mod - LM4562 dropped from 20 to 2.3, JRC4580 from 40+ to 10+, and OPA2227 from... I forgot from how high/low, but now it is 0.1 and 0.3mV.

OPA627 taking 7mA each as according to the datasheet, low DC-offset of... 0.0 and 0.0mV which was expected when reading the datasheet too. Things are looking better for these unknown-authenticity chips, some THD and load tests (to test the 45mA output current) later will wrap things up.

Subjective listening yielded good results too - particularly the bass, which is powerful yet clean, as though all the other op-amps I've tried so far have difficulty driving the 32-ohm MS1 (I haven't tried high-current ones like AD8397. And the background instruments come out more too. The main instruments are also more forward and wider but less deep soundstage which is not to my liking.

I wasn't specifically listening for anything nor having any expectations so it pleasantly surprised me. But hey, I've demonstrated to myself that I can hear tweaks even before doing them, so take these results with a pinch of salt. I've also failed a recent "Name that op-amp in the dark" test, although I have more confidence of identifying this OPA627 but these are not possible to do that test with.

Well, these chips are looking to look like the real stuff, pity I sold off two pairs cheaply at SGD25 per pair because I wasn't sure if they were real.

Sunday, March 27, 2011

Random thought: Amplifier output power ratings, 4Ω vs 8Ω

Typing the Ω symbol reminded me that I have a lab report to complete. It's week 9 yet I feel like zero hour.

Many if not most amplifiers specify max output power ratings at 4Ω or 6Ω for those that cannot handle the high current, rarely 8Ω. Amplifiers and limited by both the voltage their power supplies provide and the current their output stage can put out. However, in marketing speak amplifiers are always be able to source or sink 1000A of current for a nanosecond. Hence current is not a problem and output power is limited by voltage instead. Since V²/R, the smaller the R, the bigger the power.

Hence the Tripath TP2050 power stage chip is a peculiarity. It is highly current-limited such that it is rated at 8Ω in the datasheet (although it is also mentioned that the minimum it can go is 6Ω).

However, there is something interesting about this chip - in stereo mode, it is a pair of bridged amplifiers. Change some resistors and switch it to mono mode, the two bridged outputs combine together to form a 100W into 4Ω amp that is capable of twice the current. Hooray for FET output stage. These numbers also suggest that the max power into 8Ω in this mode is still 50W, but hey extra headroom is always nice.

Now, this thing has my interest because some completed product amp manufacturers misuse those numbers, dunno if it is by their marketing department, or a careless designer. 100W and 50W output powers were quoted with different combinations of number of amp chips and load impedance. You can see that some combinations don't work.

Official specs for this chip is 50W into 8Ω in stereo mode and 100Ω into 4Ω in mono mode. But nothing was mentioned about power into 4Ω in stereo mode.

So a few calculations using Ohm's Law later,

Current limited = fixed current = power proportional to resistance = half of power into 8Ω = 25W

Well, that is veryyyyyyyy small compared to 50W.

For a few seconds it didn't make sense, until I remember the other form of the formula P = I²R. In paralleled mode it has twice the current capacity. Hence four times the power.

Well, the amount of thinking that was carried out would take just a few seconds, but this reminded me that a good amplifier should never be current-limited. And amplifier power ratings are screwed up.

Thursday, March 24, 2011

Tuesday, March 22, 2011

What's the difference between a programmer and a manga artist?

The manga artist chose to torture himself for fun and pride.

Thursday, March 17, 2011

JDS Labs cMoyBB v2.03 Review: Measurements Section

Update: The measurement results for OPA2604 have been deemed invalid. Update on this here.

E-MU 0404 PCI - Detailed RMAA Results

The card I used to measure - E-MU 0404 PCI

Note that the first measurement is taken a long while back while the other two are taken on the day the cMoyBB is being measured and with the same setup, minus the cMoyBB of course. Also those voltage values are RMS voltages out from the E-MU 0404 line-out and into the E-MU 0404 line-in, which are the voltages at which the cMoyBB will be outputting for this review. The small things to be done that avoids false bad measurements of the thing to be measured.
For the above measurements the E-MU's output voltage is lowered by software, but counter-checking measurements show no appreciable decrease in performance figures. When feeding the cMoyBB, the E-MU is at max output.

Also note the strangely bad crosstalk numbers. This is because I only measured one channel (the left) and the right channel was duplicated from that one. Ignore those numbers for now. (Although you can also use it to find, not absolute numbers, the relative performance between the different things.) Or, you can look at the stereo graph versions.

The test

The cMoyBB will be tested in four conditions:

1) 1V into no load
2) 1V into 33ohm resistor
3) 0.2V into no load
4) 0.2V into 33ohm resistor

The voltages (in RMS) are chosen as such because 1V is the standard 0dBV line voltage, while 0.2V into 33ohm gives V^2/R = about 1mW of power into the load, and most ear/headphones' sensitivities are rated @ 1mW.
0.2V into no load acts as a control, to see how much of the distortion is caused by the 33ohm load.

Lower impedances require higher current draw, so 33ohm was chosen, and 1V into no load tests for scenarios where high voltage swings but low currents are needed for high-impedance headphones. Even for a 600ohm headphone, 1V into it yields 16.7mW, so unless its sensitivity is in the 80dB's and you have bad hearing, that is more than sufficient.

1V into 33ohm is a scenario you will never see in real life unless you want to destroy your earphones and/or your ear. But I'm including it anyway just to see how the amp handles such a scenario and how much headroom it has. But in the event of a fight-to-the-death between your earphones and your ear, my money goes to the earphones.

cMoyBB v2.03 - Default OPA2227

cMoyBB v2.03 OPA2227 - Detailed RMAA Results
cMoyBB v2.03 OPA2227 - Detailed RMAA Results - 0.2V into 33ohm

Starting off we have the cMoyBB v2.03 with its default op-amp OPA2227. Well, since this review is about the cMoyBB.

No load 1V and 0.2V give the same numbers as E-MU 0404 PCI, which means the performance of this amp is most likely better than what E-MU 0404 PCI can measure.

1V into 33ohm proved too much for the amp to handle with rocketing distortion numbers and huge signs of clipping, but even so it is below the 10% THD that many amp manufacturers like to rate their products at. Not that you should stand for that, but just saying.

0.2V/1mW into 33ohm, now we see much better numbers. However, compared to 0.2V without any load, we still can see some harmonic distortions that get significant from 10kHz and up. By significant, I mean there are more spikes that are still less than -100dB each in the audible frequency. Maybe you can hear a little bit more "detail", maybe not.

Notes on op-amp rolling

What's the use of the DIP socket if you're not going to roll op-amps?

So far I tried LM4562, LM6172, JRC4580, OPA2132, and OPA2604. LM6172 and JRC4580 have too high DC offset when used in this circuit, while LM4562 have around 20mV, which is high but still usable with care.

If in doubt, use FET-input op-amps.


LM4562 - Detailed RMAA Results
LM4562 - Detailed RMAA Results - 0.2V into 33ohm

There seems to be some problem when measuring LM4562, which resulted in abnormal and fluctuating noise levels, which affected the distortions results to some extent. But you can always see the detailed results.

Unlike the OPA2227, the LM4562 had almost no problem driving the 33ohm load at 0.2V, with numbers close to the E-MU 0404's limits. Well, almost, because as you can see below, there is still some extra spiking at above 20kHz, and between 10 and 20kHz the spikes are taller than the EMU's, albeit by a few slightly audible dB's.

Known for its accuracy and price, the LM4562 would have been an ideal drop-in replacement in the cMoyBB if not for its DC offset, and some noise issues and frequency spikes that might have been caused by the noise. Needs to be retested when possible. Granted, it was not in a proper circuit for it anyway. But still, overall performance, minus the DC offset, is excellent.


OPA2132 - Detailed RMAA Results
OPA2132 - Detailed RMAA Results - 0.2V into 33ohm

Burr-Brown's "audio op-amp" pays a visit. "Audio grade" means bad performance on the whole, so there was not much expectation for it. On the other hand, OPA2227 is said to suck too, so there is hope for OPA2132 after all.

The distortion pattern from 10kHz onwards look similar to the OPA2227's, only smaller in magnitude. However between 1kHz to 10kHz there is much more lower-order harmonic distortion. Some may like the sound, some not, but in terms of accuracy, OPA2227 would come out ahead of the two.


Update: The measurement results for OPA2604 have been deemed invalid. Update on this here.

OPA2604 - Detailed RMAA Results
OPA2604 - Detailed RMAA Results - 0.2V into 33ohm

At SGD$6, this isn't much more expensive then the rest of the contenders. However, it's minimum rated supply voltage of ±4.5V is right on the voltage that a 9V alkaline battery can provide. I was slightly worried about this, but my worries proved unfounded.

The higher current output capability over LM4562 (35 vs 26mA) proved to be useful -no sign of clipping anywhere. Even though it was working at its lowest voltage limit. Well, I did read somewhere that the absolute lowest required is a bit lower. So it was not the TLE2426 that was bottlenecking. (It shouldn't, by right, because 0.2V / 33ohm = 6.1mA) But that also means all the other chips have a bit of current issues in this particular circuit, specifically, CMoys that are powered by a 9V battery pushing 0.2V into a 33ohm load. Further experimentation is required.
But then again, most of the shitz is above the audible range, so should it be cared?

Not only that, OPA2604 also gives a very nice hill of harmonics, highest at the better-sounding lower-orders, and decreasing as the order increase. OPA2132 did have something like that, but the gradient was less steep so there was more of the nasty higher-order. Also, OPA2604's hill is there even without any load, evident from the no load 1V test. It's as if OPA2604 synergized with this circuit to give a warm sound. Measured THD numbers are bad of course, but it may sound much better than what the numbers say.

A summary of the performance numbers (OPA2132 omitted):

Conclusion - cMoyBB

There are amps that measure bad, amps that are expensive, and amps that are both. With no-load @ 1V performance better than what the E-MU 0404 can measure, 33ohm @ 1mW just slightly worse, real-life usage can only result in even better numbers. At these numbers, the bottleneck is likely to be your whatever player if not headphones. Or, pop a suitable op-amp like OPA2604 in to change the sound while still retaining great performance. This thing definitely comes out great in the measurement grading, and the only reason I'm not giving it excellent is because it didn't get below E-MU 0404 performance while driving 33ohm @ 1mW. Though, with signs that it is the chip that is being the bottleneck, I doubt other similar designs using the same chip would do better. Or you can slap an AD8397 onto this amp, but do you really need that much output current while sacrificing the ability to roll op-amps to suite your taste in sound?

But you know, I'm an anal guy. So great, no excellent. And I blame it on bad initial op-amp choice. Wakakaka.

As for the price grading, I know of...... no portable amp that gives this type of performance for SGD$80. Those that probably do don't have measurements. Only many bad ones that cost less or around this price. Even if you go higher, there are some decent measurements of some amps but the measurements do not mention voltage and load, so it is difficult to judge.

Engineering is the art of compromise, and this amp did it right. Don't want output capacitors because they audibly and measurably add distortion, check. A TLE2426 instead of a bad resistor divider in order to avoid output capacitors, check. No need for extra current capability via ground buffer and certain op-amps (you can't do it without either), saving costs, check. The numbers don't lie, and this thing is perfect for most sane situations as a portable headphone amplifier. Sure, you can get better performance by paying more, and worse performance while paying less. But you don't really need higher performance, and you shouldn't stand for worse performance since it is easier to design an amp that performs better than a DAC (that includes portable players and soundcards - anything doing digital-to-analog conversion), so the amp should never be the bottleneck. And this thing smacks right at that point. Getting the job done right at the lowest price. Okay, maybe not really, I would've wanted slightly more current. But then again, that's the op-amp's fault.

So unless I find an amp that either 1) achieves the same performance for less money, or 2) achieves better for the same money, this thing will be at the top for value. And with measurements of other amps hard to come by, there is a lack of evidence to bring this guy down.

Conclusion - op-amp rolling

Being able to use only FET-input op-amps reduces op-amp choices, but there are many high-performance op-amps with FET-input.

LM4562 is the sure choice if you want clean and accurate, and if you can live with the DC offset. Changing some resistor values will solve that problem, I will need to look into that.
OPA2604 also works pretty nicely too if you want that kind of sound.
The default OPA2227 with its super low DC offset isn't bad either, with somewhat decent performance. But there might be better alternatives out there.
AD8397 (untested) might be a good choice, if you really need that current. You most likely won't, but hey.

Thursday, March 10, 2011

Boston Acoustics HPS 10HO subwoofer repair - Day 1

Note to self: a 15.7kg white cube is very hard to carry by hand

Fuse intact.

Power on, nothing exploded. Nothing happened at all either. Fuses intact.

Took it apart.

Transformer secondary continuity check pass.

Transformer primary continuity check pass.

Ok, now this is strange.

Power cable continuity check fail. And at neutral somemore.


Changed cable. Power on. Voltages on secondary side okay. At this moment the transformer is not connected to the power supply cum amp board.

Connected transformer to PSU board. Power on. Hum for a few seconds, fuse break.

So the good news is - transformer is okay. And the bad news is - the power supply/amp board isn't. Well, something has to be broken somewhere.

But the worse news is - there isn't any sign of damage on the power supply board.

Well, an amp board with built-in power supply is easy to get.

But the even worse news is - the stupid preamp stage board is fking hot-melt-glued to the metal plate like a motherf*cker. That means to keep things clean I'd better reuse the preamp board. But the even worse news - I can't even tell how that shit is connected to the power supply/amp board via a 7-pin connector, and what voltage it uses. And if it's working.

Well, that's enough for day 1. Diagnosis will continue after I get more fuses.

Tuesday, March 8, 2011

Random thought/quote:

The size of the audio system owner's penis is proportional to the size of the low-frequency driver.

Saturday, March 5, 2011

Almost completed - Linear post regulator

I needed a 15V power supply to replace a dead one. And something at least 2.5A.

But there are two issues:

- 15V power supplies of >2.5A are significantly more expensive than the more common 19V (at the time of my searching)
- Always expect worst-case scenario when not proven otherwise - the DC quality of these power supplies are crap. And when I say crap, it is more crap than a typical desktop computer power supply. Much more crap.

Hence the idea of using a linear regulator + filter to clean up the circuit and drop the voltage at the same time came up.

Thanks to a group of helpful and knowledgeable enthusiasts over at diyAudio forums a good design was created very quickly. I implemented one of the earlier designs but the topic has progressed even further.

I will not post the design I used out of respect for the community by keeping the internet free of bad circuits when superior ones exist, but basically the idea I used was capacitor multiplier with one RC stage at the base of the darlington, fed to a LM338 linear regulator.

I so need a camera. PC Show coming soon.

Missing input connector and output strain relief. Grommet I got was too small.

P2p build, active devices bolted to the tin case which doubles as a heatsink.

I'm getting 38°C with no load and 46°C with load for the LM338, and 34°C no load 38°C load for the transistor, taken directly from metal part of the TO-220 packaging. Same 29°C air temperature. Compare it with the 47/54 heatsink temp with the Zhaolu power supply.

I don't know if this or having the cover closed, and the surface with the components bolted-on flipped over to face the top would provide better cooling, but for certain, at these temperatures and power draw, it would not matter.

Thursday, March 3, 2011

Fun with power

Since my regulator is coming soon, I had to check how much heat will be coming out of it. So I had to see how much the amp draws and calculate from that.

0.24A. No change whether playing music or not.

Lets make it a quarter of an ampere for easy calculation. The regulator drops 4V. 4V @ 0.25A = ...1W.

That's pretty easy to dissipate with a mints tin. Heck, even 2W would be possible.

Just that the full power dissipation of 12W would be really impossible. Lets hope I'll never come to that. Can that amp draw 3A anyway?

Since the Zhaolu is now open I might as well take a few temperature readings... I've always known its power supply to be inefficient, lets take more evidence of it.

Power draw should have a somewhat linear relationship with temperature rise. In practice, the relationship between rate of heat transfer and temperature may not be linear, but the error is reduced by having the heatsink in the open with the fan blowing onto it - this minimizes the issue of different surround air temperature screwing the calculation.

Power supply power off - air temperature

Power supply on, amp off

Power supply on, amp on

18 vs 25 degree rise.

Output voltage = 15V, input voltage = 14V x √2 = 19.8V, voltage drop = ~5V, current draw = 0.25A, additional power dissipated = 1.25W, additional temperature rise = 7 degrees, thermal resistance = ~5.6ºC/W

Sounds logical. It is actually way lower than what it should be, but I had a fan blowing at it.

Using that thermal resistance, power used by regulator doing nothing = ~3.2W

Sounds logical.

I did remember this bugger to use 7 to 8W idling. 3.2W is for one LM317 at 20V in/15V out. There is also the negative -15V guy and a +5V guy too, so roughly would add up to around there alright, assuming power draw by the DAC + headphone amp circuit to be negligible, which it should be.