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Burson BANG (inside pics, technical stuff etc.)

trl

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#1
Hello,

Got a BANG amplifier over one month ago from Melbourne, Burson Audio. For some reason they like when I dismantle their stuff and try to find bugs inside. :)

BANG_01.jpg

Burson BANG's PCB

It's 2 x 29W/8Ohms or 2x40W/4Ohms speakers amplifier based on LM3886TF, so yes...another gainclone, but one that fits inside a desktop computer case and done with really good parts: ELNA caps, WIMA caps, Panasonic relays, ALPS potentiometer, Vishay metallic resistors.

BANG_02.jpg

The two LM3886TF chips (see the surrounding decoupling capacitors; there're also 2 decoupling caps on the backside as well)

Initially I got a pre-production PCB and there was a bit of roll-off on trebles...like almost -1.5dB @20KHz, but seems that I got a wrong PCB. Next day they sent me another one from the normal selling batch. The later has a flat response, even @20Hz, which is great.

BANG_07.png

24-bit/192KHz RMAA frequency response

It has the size of a 5.25” internal computer bay size (CD/DVD-ROM/old 5.25"floppy) and using a very well positive ventilated case this amp is colder when inside the case then on the desk. However, a good low-noise PSU is recommended for this, otherwise just stick to the power brick provided by BURSON which is really low-noise and powerful enough (well, for 4 Ohms operation the included 120W power brick is on the edge, but still OK for a regular computer user or gamer).

BANG_10.jpg

The main SMPS (power brick) has an output of 12V/10A and is indeed low-noise. When overcharging it, the internal chopper becomes a bit noisy, but under normal conditions you can't really overcharge it (I was able to make both LM3886TF to oscillate to overcharge the PSU and actually hear chopper's noise).

The 2 output chips are powered through 4 x SMPS power regulators, 2 x XLSEMI 6019E1 and 2 xXLSEMI 4015E1, each regulator being able to sustain a load of 5 Amps, so quite beefy. I was able to measure +/-24.5V on each dual PSU without any visible spikes or high frequency artefacts on my scope, so pretty clean rails for a switching power supply.

BANG_03.jpg

The 4 power regulators

BANG_05.jpg

Power regulators close-up

There's also an input buffer stage created by a dual op-amp. Choosing the best op-amp here will matter a lot in regard with amplifier's DC-voltage output. I find MUSES8920 having a 1-2mV of DC, way better than NE5532 (15-20mV of DC). This input op-amp gets power from 2 linear regulators ST7812/7912. From this stage we can setup the gain as well from the built-in small switches: 0.75X vs. 1.5X.

BANG_04.jpg

Linear regulators for the input op-amp


Manufacturer specifications:

Input impedance: 100 KOhms
Frequency response: ± 1 dB 0 – 20Khz
THD: <0.03%
Output impedance: 1.5 Ohm @ 1 kHz
Signal-to-Noise Ratio: 92.5dB

Inputs: 2 X RCA (2V RMS line level)
Outputs: 2 X Speaker Outputs

Power/Impedance, Signal To Noise Ratio, Separation between the two channels:
- 40W/4Ohm, 91db, 99%
- 29W/8Ohm, 91db, 99%
- 15.2W/16Ohm, 91db, 99%

Power Supply 100-240V AC (12V 10A)
Weight: app. 2.5Kg
Dimensions: 210mm x 145mm x 45mm
 

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trl

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#2
I was able to get the BANG inside a well ventilated computer case and realised that temps are even lowered than standing on my desk @25-26C. With moderate listening levels I got >40C on top of BANG when standing on my desk and <30C when inside the computer case from below:

BANG_08.jpg BANG_09.jpg BANG_10.jpg

PSU used was a very powerful one (1700 Watts), so no issues when doing full-load tests. Also, the water-cooled and lot of huge fans helped a lot in getting rid of BANG's dissipated heat. Inside a regular PC case BANG will most likely overheat, but with a good positive airflow things seems pretty good.

Power tests I did with a dummy resistor of 4.9 Ohms show quite a decent powerful amplifier here of 2 x 40W. However, for 4 Ohms speakers BANG's external power adapter of only 120W may not fit TI's output power requirements of almost 55W/channel. Instead, for 8 Ohms BANG is within TI's power specs of 29W/channel:

BANG_output-power.png
Who wants more power out of BANG may get a more beefy external power adapter (perhaps a linear one) or use a computer PSU of at least 180W. Although, I'm not sure BANG's case, that acts as a heatsink, will be able to dissipate quickly the heat generated by 2 x 55W. I personally find a good match between BANG amplifier and it's default external PSU, at least for a regular small office, a bedroom or a 20 to 25 m2 living room.

I haven't tested BANG on 2 Ohms, it's just not recommended to do that and I don't want to push it. :)


BANG_11.png

13.55 V RMS @4.9 Ohms 37.5 W RMS (no visible distortions)


BANG_12.png

14.5 V RMS @4.9 Ohms 42.9 W RMS (the bottom starts showing few distortions)


We all know that some gainclone amplifiers are prone to oscillations when the PCB is not well designed or the schematic is too simplistic (not enough decoupling caps, low quality components used, lack of Zobel network etc.), but for BANG I was having really hard times to make it oscillate. Actually, I couldn't...even when adding 0.33uF on its outputs:

BANG_13.png

BANG driving 0.33uF capacitive load (>20V RMS of 1KHz square-wave; red line is the input source, blue is BANG's output). No ringing, no phase shift, no oscillations!


BANG_14.jpg

Output coils/inductors and powerful resistors installed to prevent unwanted oscillations


BANG_15.png

The green resistors & the WIMA red capacitors make a R-C filter, parallel with the outputs (part of the Zobel network) to combat any possible oscillations)


P.S.: LM3886TF gain is 20X made with 21 KOhms feedback resistor and another 1.1 KOhms resistor to the GND. I was changing the 21K resistor with a 10K one and now I was able to make it oscillate a bit, but only with 0.33uF capacitance on outputs and >10KHz square-waves; with normal sinewaves, the 10X gain "modded" amplifier was still rock stable. However, adding such a high capacitance on amplifier's outputs it's just silly and not recommended; I only did that for fun and to see if I can make it oscillate. Also, swapping SMD resistors from the PCB will definitely void the 5-years warranty!
 
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FrantzM

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#3
HI

The 1 KHz square wave output is most impressive. How much do they retail for? URL?
Thanks in advance
 

Wombat

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#4
H

The 1 KHz square wave output is most impressive. How much do they retail for? URL?
Thanks in advance
Too impressive??

Is 0.33uF a typical load?
 

trl

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#6
Same square output up to 50KHz I’ve tested, so it measures quite decent. However, the 47uF caps from the RCA inputs are shown on the 10-20Hz squares; I’ll try bigger “audiophile” caps next week. However, 10-20Hz sines are OK.

I’ve tested BANG with NE5532, MUSES8920 and SS V6. Perhaps with SS V6 soundstage is bigger and there’s a bit more musical sound, but the DC-output is on pair with NE5532 (15-20mV), so I’ll stick to FET-input opamps like 8920 (1-2mV).

0.33uF is a “typical” 1-2km long speakers cable. :) Usually these stability tests are done with hundreds of pF or couple dozens of nF at most.
 
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trl

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#7
There's also a delaying relay to protect speakers from power-on noise. I've attached the almost non-existent noise when powering on BANG (few mV only for few milliseconds).

BANG_jack_adapter_power_ON_1_01.png


BANG_jack_adapter_power_ON_1_02.png


BANG_jack_adapter_power_ON_1_03.png


After few ms the horizontal line gets flat.
 

restorer-john

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#9
Great photos BTW. :)

a few points:

The FR plot shows about -0.5dB at 20KHz and you haven't stated the test conditions for that plot- is it loaded, unloaded and at what output?

Your 13.55v top picoscope trace is showing mild flattening in the sine peaks.

And what's with power output testing at 4.9 ohms load??

I also don't believe they are genuine Elna capacitors. Can you take a closeup of one for me?
 
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trl

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Unloaded, and it's -0.18dB if I remember correctly (will double check that soon). Loaded test was about the same, but I can run more tests in about a week from now. Output was RMAA standard...I guess pretty close to 2V RMS; I know, I need to get a resistive divider there to test it loaded @10W and @25W...will do that for sure, just that I'm out of town for the moment. Thank you!

I simply couldn't make a 4 Ohms powerful resistor, so I did a ******-looking one that works well with my tests (attached pic).
IMG_1419.jpg

Hmmm...I really think they're ELNA, kinda difficult to believe something else, but I'll do a close up within a week or so. Meanwhile, I got some crops done from existing pics, attaching here now. Focus is not on the caps, but perhaps pics are helpful somehow.
ELNA_01.png ELNA_02.png ELNA_03.png ELNA_04.png

Also FUN is probably using the same caps: https://audiosciencereview.com/foru...aked-pics-some-technical-thoughts-a-s-o.3958/
 

trl

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Forgot to say: output impedance is 0.00... Ohms. I setup the output voltage to 7.000 V RMS @1KHz unloaded and I got 6.998 V RMS loaded with 4.9 Ohms. Only 2mV difference makes it impossible for me to calculate the output impedance @1KHz sinewave, so pretty close to zero and damping factor a bit less than..."infinite". :)
 

restorer-john

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#12
Hmmm...I really think they're ELNA, kinda difficult to believe something else
Based on the pics, the screen printing and the vent stamping is too rough for Elna. Their sleeve printing is much finer IME.

The Chinese have been faking all the major cap brands for a long time now and they are getting harder and harder to spot. That said, most of the quality cap makers have moved production to Thailand and China so it gets even more difficult to be sure.

Didn't you post an image the other week where we discussed the fake Sanyos in another Burson item?
 

amirm

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#13
@trl those are some nice pictures, technical data and measurements. Well done!

They do have pretty PCBs with nice solder mask color, via stitching, etc.
 

trl

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trl

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#15
I was able to measure the above FUN @5V RMS (dummy resistor at around 600 Ohms).
2nd harmonic is somewhere around -95dB, pretty good actually. The 3rd harmonic is at around -103dB.

FUN_1KHz_spectrum.png




Dynamic is 108dB and there is no adjustable gain, just the output ALPS pot for volume adjust. However, with my 16 Ohms/103dB sensitivity IEM's connected, background noise becomes audible only if the volume pot gets over 2-3 o'clock, otherwise is dead silent.

RMAA_5V_RMS_FUN.png


P.S.: Input source was having 1V RMS and FUN's gain is almost 5X, hence max. output fundamental is -1.1dB because of that.
 
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#16
Well my Bang has now gone bang......it has lost one channel *after* becoming very noisy on the *OTHER* channel.
A weird mode of failure to my simple mind. Could it be due to a fault in the buffer section? I read somewhere that there were issues with the amp locking out at high volumes. Anyway, here is what happened:

First the right channel became very noisy, sounded like it was clipping at low volume level and the sound broke up on certain frequencies, lots of distortion. So I tured it "off" to check connections and it was still as bad when powered back up.

Then I leave it for a few hours and my son turns it back on to listen to TV off the DAC.
Everything is fine now. Until about an hour later when I lose the left channel completely.

The only sound that comes from the left channel is now a series of clicks or squeaks when the unit is turned on. The right channel does the usual pop as you turn on, I always turn the power amp on at the end after powering up the DAC, the pre-amp (fun) and source. Only ever used the headphone output from the Fun pre-amp to check that this wasn't a problem with the pre-amp or higher up the chain, which it wasn't - never disconnected headphones when it was all powered up.

Switching speakers and inputs to other channel confirms the Bang is at fault.

The other thing I noticed was a strong smell that reminded me of my father's workshop when he was repairing electrical appliances (mainly TVs and VCRs) in the 70s/80s. Haven't opened the case to check and wonder if there is anything I should be thinking of before contacting Burson to discuss the options?? Am I likely to find a popped capacitor if I open the case?

I was using the stock PSU and there is no obvious sign of a problem with it.
 

Sal1950

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The other thing I noticed was a strong smell that reminded me of my father's workshop when he was repairing electrical appliances (mainly TVs and VCRs) in the 70s/80s. Haven't opened the case to check and wonder if there is anything I should be thinking of before contacting Burson to discuss the options??
Yea I'd just give them a call to see what they say.
Good luck!
 

trl

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#18
@lardyl if the chips got overheating I assume you would notice that, right?
What speakers were you driving, please (impedance across audio range is probably more important here)?
Was the speakers cables very long (trying to understand if the output chips were oscillating)?
It would be very interesting to see what got fried inside, maybe it's about the power regulators...who knows...just open up the case and post some shots here.

BTS, @Thomas savage could yo uplease move the last 3 posts (related to BANG) to https://www.audiosciencereview.com/...on-bang-inside-pics-technical-stuff-etc.4302/? Thank you!
 
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