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What is my amps ACTUAL wattage?

Postby seriousnewbie » Sat Dec 26, 2020 12:07 am

Merry Christmas everybody, I hope you are having and will have a great day!

I have the TC Electronic BQ500 bass amp . I need a cab for it, Although it does say it has 500 watts in the advertising, at the back it says 80 watts, I have attached a picture so you can see what I am talking about. So I need to know what the wattage is on the amp so I can choose the right speaker cab. Thank you for reading!

edit: Sorry, I don't know how to add an image to my post so I can't show the image. On the back near the power input it says 80 watts, if more info is needed just lemme know!
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Re: What is my amps ACTUAL wattage?

Postby zenguitar » Sat Dec 26, 2020 12:36 am

We don't host images the site. So the secrets to use a 3rd party host site like Imgr of Flikr to save your pics. Then you can use the inks those sites provide to post here. You can copy the image URL and is the Img tags to post here, or some sites offer links that include the full phpBB code already.

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Re: What is my amps ACTUAL wattage?

Postby seriousnewbie » Sat Dec 26, 2020 1:28 am

zenguitar wrote:We don't host images the site. So the secrets to use a 3rd party host site like Imgr of Flikr to save your pics. Then you can use the inks those sites provide to post here. You can copy the image URL and is the Img tags to post here, or some sites offer links that include the full phpBB code already.

Andy :beamup:

Thank you for the info for future reference, but looking back on it doesn't really matter that much because realistically the only thing I needed to show you was the letters "80 watts" which doesn't need a picture..
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Re: What is my amps ACTUAL wattage?

Postby MOF » Sat Dec 26, 2020 2:29 am

On the back near the power input it says 80 watts, if more info is needed just lemme know!

That’s very confusing because that’s input power of 80watts and yet supposedly an output power of 500watts. Even if it had massive capacitors to store energy, eventually it would run out of reserves.
My knowledge of modern switch mode power supplies is non existent, maybe they can account for the discrepancy.
If it is 500 watts rms output I suggest a speaker capable of half as much again. If it’s 500watts peak then the same value of speaker (also at rated at 4 ohms) should be fine. Don’t run the amp flat out just to be certain.
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Re: What is my amps ACTUAL wattage?

Postby zenguitar » Sat Dec 26, 2020 2:53 am

Just had a look at the product page on the TC Electronic site.

80W is the power consumption, how much it draws from the mains.

500W is the power that the amp can deliver to a 4 Ohm load. It doesn't specify that is peak power, RMS, or something different again. The power amp is Class D, so it is capable of delivering a lot of power efficiently. But the only way to be certain is to seek clarification from the manufacturers.

TC are part of the Music Tribe group. You have to register an account to get access to tech support. The site isn't great, I'm registered but gave up trying to register my gear.

The speaker output uses a Speakon connector, so when you choose your cab you need to be aware of which connector it uses and source a suitable cable.

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Re: What is my amps ACTUAL wattage?

Postby Music Wolf » Sat Dec 26, 2020 8:35 am

The spec quotes 500w as being peak power. The 80w is, as Andy says, power consumption. It is quite normal for there to be such a big difference.

By way of comparison I just pulled up the spec of a Yamaha DXR12 PA cab (since I'm sitting right next to one) which has a 'dynamic' power of 1100w, a 'continuous' power of 800w but consumption of only 110w.

When choosing a cab look at the output power rating of the amp. The amp will be capable of producing large peaks even though the average power (used to calculate consumption) will be much less.
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Re: What is my amps ACTUAL wattage?

Postby ef37a » Sat Dec 26, 2020 8:53 am

This guy, https://www.talkbass.com/threads/tc-bq5 ... w.1404259/ seems to know his onions. The amplifier looks to be capable of a bit over 300 watts into 4 Ohms. He reckons 225 -250W into 8 Ohms but class D amplifiers fall off in power faster than linear amps into higher than nominal loads so my guess would be 150 watts in 8R?

Those are 'continuous sine wave" BTW as per VxV/R NOT the daft 'rms watts' (tho' I admit that is almost a lost cause!)

Suitable speaker? Don't know who speaks the truth apart from Celestion but if a 4 Ohm cab go for 500W minimum . 8 Ohms would IMHO be safe if rated at 250-300W.

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Re: What is my amps ACTUAL wattage?

Postby Sam Spoons » Sat Dec 26, 2020 12:16 pm

Just to reenforce the above, the 'power consumption' marked next to the IEC socket is the power needed to play music through the amp. Music is not continuous and the amp can supply brief bursts of much higher audio output than that power consumption figure suggests. Some manufacturers quote ⅛th power as the typical consumption of a full range speaker and those with a SMPSU are very efficient so losses are remarkable small.

I measured a few amps and speakers several years ago when I was speccing a generator for an off grid gig and my little 18 watt (class A) valve guitar combo drew, IIRC, 0.35A or around 80 watts, my bass players 500 watt Ashdown Superfly head drew 1.3A (299W). The '1000 watt' QSC K12 PA speakers OTOH claim to draw 110W which subsequent experience suggests (not surprisingly) is probably correct.
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Re: What is my amps ACTUAL wattage?

Postby wireman » Sat Dec 26, 2020 3:50 pm

Sam Spoons wrote:Music is not continuous and the amp can supply brief bursts of much higher audio output than that power consumption figure suggests.

I'm not sure many people have a clue on how much power gets into the air given how inefficient speakers are, a few watts goes a long way. If the 'music power' had any relation to reality then we would be in the regime of the noise level you get from an aeroplane. ( I realise that music power will likely relate to the electrical power (amp/speaker).
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Re: What is my amps ACTUAL wattage?

Postby MOF » Sat Dec 26, 2020 3:51 pm

Music is not continuous and the amp can supply brief bursts of much higher audio output than that power consumption figure suggests

If the bassist is playing a muted down beat note at the beginning of every bar then this might work, but what if the bassist is playing four or more notes per bar, eventually the power reserves will be used up?
Here’s hoping Hugh, or someone else well versed in electronics, will explain how this amplifier gets more power out than its input.
Even the RMS figure of a 500watt peak doesn’t work for me.
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Re: What is my amps ACTUAL wattage?

Postby Sam Spoons » Sat Dec 26, 2020 6:12 pm

My understanding is that it's related to the average power consumption, the power supply caps store energy which can be released for brief bursts of loud output so the peak output from the amp can exceed the average power consumption. The figure of ⅛ is bandied about as the average consumption of a power amp playing music, my measurements suggested this is about right. I'd guess some bass heavy genres might exceed that though.
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Re: What is my amps ACTUAL wattage?

Postby ef37a » Sat Dec 26, 2020 6:13 pm

MOF wrote:
Music is not continuous and the amp can supply brief bursts of much higher audio output than that power consumption figure suggests

If the bassist is playing a muted down beat note at the beginning of every bar then this might work, but what if the bassist is playing four or more notes per bar, eventually the power reserves will be used up?
Here’s hoping Hugh, or someone else well versed in electronics, will explain how this amplifier gets more power out than its input.
Even the RMS figure of a 500watt peak doesn’t work for me.

Well. guess Hugh is Having a well earned rest and maybe just a tincture with his family so I will have a go if you like?

The "80 watts" I will assume refers to the no signal power draw or, when driving a 4 Ohm load, just under clipping with some unspecified 'music like' waveform* . Or, it might be an 'average' mains current pull for the purposes of a legal rating plate? My back o fagpacket calculation gives the pull of a 500W (con't sine) class B amp would be around 20W but then I don't know how much extra 'stuff' that amplifier is running?

Class D amps are often feted for their high efficiency but in fact a well designed class B amp gives them a good run for their money and class 'G' does even better.
No, it is the switch mode power supply where the real energy savings are to be had (ever noticed how hot mains traffs get? Even when doing buggeall)

The downside to regulated supplies however is that you don't get the 'dynamic boost' as with simple supplies.

*In his book "Power Amplifiers" D Self shows how difficult it is in reality to measure efficency and chose a suitable drive waveform.

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Re: What is my amps ACTUAL wattage?

Postby wireman » Sat Dec 26, 2020 9:04 pm

Sam Spoons wrote:My understanding is that it's related to the average power consumption, the power supply caps store energy which can be released for brief bursts of loud output so the peak output from the amp can exceed the average power consumption. .

I think so, and of course there is always a peak that exceeds the average for a music signal and on many scales. If the amplifier can deliver a given peak current then the power supply just has to be designed to support this for as long as needed, and of course there may be no issue if the amplifier is never driven hard.

You can get an idea of the power supply design process from this article.
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Re: What is my amps ACTUAL wattage?

Postby resistorman » Sun Dec 27, 2020 1:36 am

Bassically, you plug a decent bass cab into an amp and start playing. If you smell the coils burning you turn it down. If the speaker flutters limply you plug in an amp with more power.
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Re: What is my amps ACTUAL wattage?

Postby ef37a » Sun Dec 27, 2020 10:41 am

wireman wrote:
Sam Spoons wrote:My understanding is that it's related to the average power consumption, the power supply caps store energy which can be released for brief bursts of loud output so the peak output from the amp can exceed the average power consumption. .

I think so, and of course there is always a peak that exceeds the average for a music signal and on many scales. If the amplifier can deliver a given peak current then the power supply just has to be designed to support this for as long as needed, and of course there may be no issue if the amplifier is never driven hard.

You can get an idea of the power supply design process from this article.

Given how complex a good class D amplifier needs to be and that it needs to be partnered with a nearly as complex regulated* and protected PSU it is a wonder to me that they are a popular as they are? Their distortion performance is unlikely to equal a really good class B design and certainly not better it. Then there is all that high power RF flying about.

Apart from the marginal efficiency gain their only other advantage it seems to me is lighter weight? Especially when you exceed 100W or so. But even there you can have SMPSUs in a linear amplifier.

*MUST be regulated because class D has no inherent PS ripple rejection.

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