Household electrical problem

[slipperybidness]

The fuse is ceramic, white and opaque. I can't see inside if there is a broken filament. Believe it or not, I don't have simple volt-ohm meter to use as a continuity tester.
I use the rocker On/Off switch on front of the amp. There is no jack to hook up a remote trigger.

So, it is possible that the rocker switch has failed.

Possible that the switch has failed, but that seems unlikely.

 

[Swerd]

I thought I was in some form of audioholic recovery but all this talk of amps and then what really did it was the pictures. I knew I was on shaky ground when I found myself circling back to check out the fleabay listing. All I know is that the eventual owner of that amp can count his lucky stars I'm in no position to buy it myself ... 'cause I'm like that.

So you must be that other viewer who is stalking this amp .

I don't really consider myself lucky to be in the need of another amp. I regard audio amplifiers as a necessary utility, and only that. For good sound, speakers are where the rubber hits the road. A good amp must supply enough juice to the speakers so that the amp never ever clips. (I realize I'm preaching to the choir here.) And as TLS Guy has pointed out, a good amp must also be rugged and reliable, as bullet-proof as possible.

I thought I had that in the B&K amp. It is still possible that the fuse blew, or that something as simple to fix as the rocker switch failed. I have no idea what it might cost to locally repair such a switch or something else in the power supply section of the amp.

I hope I can find a local electronic repair shop today. If I can get a repair estimate, I can decide whether or not to jump on the fleabay Quad 909.

 

[Swerd]

ATI bought the assets and all documentation for B&K, so manuals are available.

I got a pdf copy of a manual from B&K when I first bought the amp in 2008. It is actually the very same document that KEW linked.

 

[Johnny2Bad]

Dead wrong. Law of conservation of energy says so. A watt is a watt, one joule per second, actually. Amplifiers have an efficiency factor, and it is absolutely impossible to have an efficiency factor greater than 100%, which is what you're proposing. The most efficient amplifiers available, so-called Class D types, are advertised to be about 90% efficient, while Class A amps are often in the 25-30% efficiency range. Put in 1000W from the wall outlet and get ~250W at the output terminals. Most Class AB amps are usually about 65% efficient.

Apply ohm's law and the numbers work out. I am not proposing an efficiency of more than 100
%. Far from it.

If you read the consumption @ 120V AC in watts, and expect to see that same wattage rating into 8 ohms ... lets not forget every single amplifier works from a rectified DC supply, which will produce 1.414x the AC voltage of the transformer tap ..., you will be way off the mark.

EG (selected at random)
Accuphase E-202
Power Consumption 375w AC
Power Output (Class AB w/Linear Supply):
100 wpc RMS 20_20,000 Hz @ less than 0.1% THD into 8 ohms

An amplifier of that size and construction would run typically from a +/- 65~70V DC supply (per channel), from an AC transformer tap of 46~50V.

You sometimes see naieve sellers on eBay who read the power consumption label on the back panel and then advertise an amp such as the Accuphase as a "375 watt amplifier". Not true.

 

[highfigh]

I got a pdf copy of a manual I got from B&K when I first bought the amp in 2008. It is actually the very same document that KEW linked.

I think it's great that they're making these docs available, but they did buy the company with thoughts of keeping it going, not to kill it. Too bad they bought it when they did- maybe a year earlier could have made the difference.

 

[Johnny2Bad]

I think it's great that they're making these docs available, but they did buy the company with thoughts of keeping it going, not to kill it. Too bad they bought it when they did- maybe a year earlier could have made the difference.

If you have documentation for any components, check with hifiengine dotcom and if they don't have it, upload a scan or pdf. They like good photos of units, literature, brochures, etc. as well. By the same token, it's a great source of documentation if you need.

There is a sister site for turntables and cartridges, vinylengine dotcom.

 

[KEW]

Apply ohm's law and the numbers work out. I am not proposing an efficiency of more than 100
%. Far from it.

If you read the consumption @ 120V AC in watts, and expect to see that same wattage rating into 8 ohms ... lets not forget every single amplifier works from a rectified DC supply, which will produce 1.414x the AC voltage of the transformer tap ..., you will be way off the mark.

EG (selected at random)
Accuphase E-202
Power Consumption 375w AC
Power Output (Class AB w/Linear Supply):
100 wpc RMS 20_20,000 Hz @ less than 0.1% THD into 8 ohms

An amplifier of that size and construction would run typically from a +/- 65~70V DC supply (per channel), from an AC transformer tap of 46~50V.

You sometimes see naieve sellers on eBay who read the power consumption label on the back panel and then advertise an amp such as the Accuphase as a "375 watt amplifier". Not true.

So was your earlier assertion that output wattage should exceed input wattage a mistake?

I ask because your example reinforces my point!
I just want to be clear on this because my EE theory is weak and if I have a mistaken concept, I would like to be corrected and learn!

 

[TLS Guy]

So you must be that other viewer who is stalking this amp .

I don't really consider myself lucky to be in the need of another amp. I regard audio amplifiers as a necessary utility, and only that. For good sound, speakers are where the rubber hits the road. A good amp must supply enough juice to the speakers so that the amp never ever clips. (I realize I'm preaching to the choir here.) And as TLS Guy has pointed out, a good amp must also be rugged and reliable, as bullet-proof as possible.

I thought I had that in the B&K amp. It is still possible that the fuse blew, or that something as simple to fix as the rocker switch failed. I have no idea what it might cost to locally repair such a switch or something else in the power supply section of the amp.

I hope I can find a local electronic repair shop today. If I can get a repair estimate, I can decide whether or not to jump on the fleabay Quad 909.

I think you have an over simplistic view of power amps. They do not all sound the same into a given speaker by a long shot.

The B & K is a 1985 design typical of the period. It is over fussy, with a complex predriver stage. The output stage is 5 pairs of matched MOSFETS. The biggest concern is that speaker protection is only a 7.5 amp fast blow fuse in the speaker leads. This is a big problem. Fuses cause significant thermal dynamic compression. Worse the speaker usually protects the fuse, if a high DC off set situation occurs. It takes only one of those old and aging MOSFETS to blow and far more likely than not one of your nice new speakers will be seriously damaged.

I think for almost certain you will notice a large and significant increase in sound quality driving those speakers from a 909. I would press the buy now button on that Quad pronto.

That B & K would have no place in any of my systems, not for an instant.

 

[Swerd]

I think you have an over simplistic view of power amps.

Perhaps

That B & K would have no place in any of my systems, not for an instant.

No doubt

This morning I took the amp to a local repair shop http://www.esc-website.net/. I was surprised to find a shop that specialized in repair of audio products. The owner does all his repairs in his shop. He recognized the B&K, said he'd examine it, and noted that most parts, especially those in the power supply section, were made using standard available parts. He said he would get back to me in 5 days. For a $45 bench test fee I'll take a chance that it might be repairable – before I rush to spend $1K on anything from Ebay.

 

[Alex2507]

most parts, especially those in the power supply section, were made using standard available parts

That's a help. I had some Carvers needing unavailable parts. The shop had the amps for over a year. Then I met Kurt ... and started tri-amping.

 

[Irvrobinson]

Apply ohm's law and the numbers work out. I am not proposing an efficiency of more than 100
%. Far from it.

If you read the consumption @ 120V AC in watts, and expect to see that same wattage rating into 8 ohms ... lets not forget every single amplifier works from a rectified DC supply, which will produce 1.414x the AC voltage of the transformer tap ..., you will be way off the mark.

EG (selected at random)
Accuphase E-202
Power Consumption 375w AC
Power Output (Class AB w/Linear Supply):
100 wpc RMS 20_20,000 Hz @ less than 0.1% THD into 8 ohms

An amplifier of that size and construction would run typically from a +/- 65~70V DC supply (per channel), from an AC transformer tap of 46~50V.

You sometimes see naieve sellers on eBay who read the power consumption label on the back panel and then advertise an amp such as the Accuphase as a "375 watt amplifier". Not true.

Let's see... 375 watts x 65% = 243 watts = 121 watts per channel... how about that! The amp is rated at 100w/ch into 8 ohms and 140w/ch into 4 ohms, which is about right on the money of the efficiency factor expected (65%) for a Class AB amplifier. I don't know what you're talking about WRT to Ohm's Law in this case, but I highly recommend going to a public library and checking out a high school physics book.

 

[PENG]

https://www.manualslib.com/manual/14276/BAndk-Two-Channel-Amplifier-Ex4420.html

I agree that it looks like a good solid amp, but there is a contradiction somewhere between the Input Watts and Output Watts specification.

@PENG any ideas?

It depends a lot on how they define max power consumption. Even if it is average (so called rms), the output numbers are still believable as long as they are not literally "continuous", that is, "continuous" is defined as 1 (or even 30 seconds) or up to a few minutes. Linear power supply based on transformers and capacitors do have excellent overload capability. So if the 650W maximum power consumption is rated on truly continuous basis, it could in fact deliver twice that for a short duration; and depending on the design and build, that short duration could easily exceed a few minutes, and that would satisfy the requirements by certain standards as "continuous".

For reference, below is link to a good read:

http://www.sengpielaudio.com/Mathew-AudioPrecisionSpecifications.pdf

For definitions related to power, go straight to page 13. It says:

"rated power The rated power is the figure the manufacturer has chosen to claim as a minimum performance specification. RMS power RMS power is a misnomer, but one used in good faith. It means the same thing as “sine output power,” defined below. Although the output voltage is measured in rms volts, the result does not have the “rms” term in it. The result is simply “watts.” sine output power One of several common terms for the accepted means of measuring and reporting output power, used in EIA/CEA- 490-A, IEC60268-3 and the FTC Amplifier Rule. Also called continuous power, continuous average power and (wrongly) rms power. The stimulus signal is a sine wave. The true rms voltage is measured across a load resistor and the power is calculated by the formula V2 /R. The amplifier should be capable of delivering this power continuously for at least 30 seconds (IEC) or five minutes (CEA-490). Visit the standards documents for detail."

 

[Swerd]

That's a help. I had some Carvers needing unavailable parts. The shop had the amps for over a year. Then I met Kurt ... and started tri-amping.

That was no guarantee – only a reassuring comment that it was his experience that brands from smaller companies, such as B&K, used standard available parts whenever possible. Those parts were standard at the time of manufacture, not necessarily now.

I'll know more after he has a look inside.

 

[Swerd]

It depends a lot on how they define max power consumption…

Peng

Thanks for your comments. Please note that I originally thought this amp (an old B&K EX4420) had 650 watts maximum AC power consumption based on a manual. I later saw the tag on the back of the amp, which said 900 W 64U (what does 64U mean?) by the AC inlet and fuse.

With a 900 W maximum power consumption, does a power rating of 200 wpc at 8 ohms, 350 w at 4 ohms for a stereo amp with class A/AB design seem reasonable? The manual never specified what type of rating it was, FTC, EIA, etc., but it did say power was measured at 1 KHz, not 20 Hz to 20 KHz.

 

[Alex2507]

Let's see... 375 watts x 65% = 243 watts = 121 watts per channel... how about that! The amp is rated at 100w/ch into 8 ohms and 140w/ch into 4 ohms, which is about right on the money of the efficiency factor expected (65%) for a Class AB amplifier. I don't know what you're talking about WRT to Ohm's Law in this case, but I highly recommend going to a public library and checking out a high school physics book.

Mine goes to eleven.

 

[Irvrobinson]

Peng

Thanks for your comments. Please note that I originally thought this amp (an old B&K EX4420) had 650 watts maximum AC power consumption based on a manual. I later saw the tag on the back of the amp, which said 900 W 64U (what does 64U mean?) by the AC inlet and fuse.

With a 900 W maximum power consumption, does a power rating of 200 wpc at 8 ohms, 350 w at 4 ohms for a stereo amp with class A/AB design seem reasonable? The manual never specified what type of rating it was, FTC, EIA, etc., but it did say power was measured at 1 KHz, not 20 Hz to 20 KHz.

350w/ch is awfully tight for 900w of mains power.

 

[Irvrobinson]

Mine goes to eleven.

Mine has a 20amp power cord.

 

[PENG]

Peng

Thanks for your comments. Please note that I originally thought this amp (an old B&K EX4420) had 650 watts maximum AC power consumption based on a manual. I later saw the tag on the back of the amp, which said 900 W 64U (what does 64U mean?) by the AC inlet and fuse.

With a 900 W maximum power consumption, does a power rating of 200 wpc at 8 ohms, 350 w at 4 ohms for a stereo amp with class A/AB design seem reasonable? The manual never specified what type of rating it was, FTC, EIA, etc., but it did say power was measured at 1 KHz, not 20 Hz to 20 KHz.

I don't think 64U is directly related to any power or energy units. It may just be some code that B&K used to supplement the serial number, such as date and/or place of manufacture, revision etc., I am obviously guessing though, but again, that is not an energy, or power unit.

You can still download some of the old B&K unit manuals such as the reference 4420, as well as pictures of the back panels of the EX or Ref 4420 and I have seen 600 and 650 W but not 900 W. So again I am guessing depending on their date of manufacture, they might have used different standards.

If the so called 650 W is specified as maximum average power consumption on continuous basis, then the peaK power would be 2X that because for sine wave peak=2X average, would be 1300 W. In that case it is reasonable to assume the amp can be rated 350 W into 4 ohms for a short duration that is long enough for it to be rated as "continuous". In fact that would be in line with how Adcom, Anthem, Marantz, Parasound and even some higher end amps rate some of their amps. I know so because I do own a few amps.

Please also note that as KEW alluded to, the rated power did not specify both channels driven and no THD, freq bandwidth specs cited either. That means the 350 W into 4 ohms could be for one channel driven. In that case, if rated for both channel driven, and at 1% or higher THD, it could have been rated less, such as 300 WX2, still pretty good for a 40 lb amp.

There are no shortage of amps, some Krell, Passlab, Bouder models would be safe assumptions, that are rated continuous in truly and literally sense, but I am sure that B&K is not one of those based on the information provided in their manual and pictures of their innards that are googleable.

 

[PENG]

350w/ch is awfully tight for 900w of mains power.

I agree, but it would be fine, and even considered conservative if one channel driven. If for both channel driven, then they would have to base such figures on the short term definition of "continuous" (FTC, EIA blablabla). ATI does provide those figures with a little more info, including both EIA, 1kHz and FTC full bandwidth ratings for the output figures. If you look at their power consumption figure, e.g. for the 7ch ATI1800, that was rated 375W (EIA), or 300W (FTC) with power consumption of 1800W, that's quite comparable to that of the B&K.

The bottom line is, when it comes to the relationship between class AB power amp's power supply transformer kVA rating, rated output power, power consumption, or power requirement figures provided by various manufacturers, it is a guessing game that left any electrical engineers guessing when trying to compare apple to apple, except the ones who actually work for the said manufacturers.

 

[Johnny2Bad]

Let's see... 375 watts x 65% = 243 watts = 121 watts per channel... how about that! The amp is rated at 100w/ch into 8 ohms and 140w/ch into 4 ohms, which is about right on the money of the efficiency factor expected (65%) for a Class AB amplifier. I don't know what you're talking about WRT to Ohm's Law in this case, but I highly recommend going to a public library and checking out a high school physics book.

Yeah, you are only out by 20%. Probably good to go in the schools you went to. Not mine.

(AC x 1.414 = DC) x supply/amplifier efficiency. There is no need to guess at the combined efficiency, you can get it from the values provided. It's not 65%.