Audiophiles - This is what your Mega Dollar Cables Connect to inside your amps

[dannyf]

There is an oscillator, a low-pass filter, a comparator, a dc-dc converter, a feedback loop, etc.

The amplifier is a variable output power supply.

[IanB]

In thermodynamics, there is a direct relation between power, surface area and surface temperature (with some assumptions to be made)
Who is fluent in this? I would have to search for the formulas...

With that numbers, the surface temperature must be high enough to cook an egg on it.

Actually, that would not come under thermodynamics, it would come under heat transfer. But thermodynamics does tell us that the continuous average power output must be less than or equal to the continuous average power input from the mains.

[M4trix]

The topic should be --> Audiophoolers - This is what your Mega Dollar Cables Connect to inside your amps

 

[Red Squirrel]

Maybe it's audio grade solder. 

Ok I was joking, but apparently this actually exists:

http://rankoaudio.com/AudioGradeSolder/241.htm 

[xrunner]

So two half wave rectifiers going to the different capacitors to cheaply get split power from mains, what's so wrong with that?

PS. how is the isolated input amplifier coupled into the non isolated power amplifier though? I don't see a second transformer, linear optocoupler?

Redrawn attached showing the bridge converted to two diodes and yes you can see two half wave circuits. Also some things require various taps of lower AC voltages ...

[cosmicray]

Right, this was bought back in 1997 or so. Remember, it's operating as intended designed. I'm only trying to stop the hum when it's in standby (it never goes off).

Any chance the caps (at ~18 years) have reached their retirement age ?

[wraper]

I just wonder about the inrush current of this thing. 2x of 1500uF capacitors and no current limiting at all (like NTC or power resistor + relay). Doesn't it trip circuit breakers by the chance   .

[xrunner]

I just wonder about the inrush current of this thing. 2x of 1500uF capacitors and no current limiting at all (like NTC or power resistor + relay). Doesn't it trip circuit breakers by the chance   .

It does make a large "thump" when plugged in, and the plug at the wall sparks a bit LOL. 

One of the large caps retains 165V for days, and it's dangerous to be in there until it's discharged. I discharge it with a large resistor, I think I just grabbed a 1.47k power resistor.

Any chance the caps (at ~18 years) have reached their retirement age ?

I don't think so cosmicray. I checked both large caps and they were perfectly fine. I checked some others at random and found no problems.

This thing is a Bob Carver Sunfire MKII "true" (whatever that means) subwoofer. It has known humming problems if you research it. There are various solutions out there, and my brother wanted me to check out the capacitor issues, but like I said, it has no issues with caps. The other known issue is the notorious ground loop issue. This is what I think it is.

At his house he claimed it hummed badly, but at my house it's not nearly so bad. The ground loops are different. I ordered an el cheapo ground loop isolator and we'll see what that does for it. It connects to the audio input and stops an ohmic path around the ground loop (whatever weird path it takes in your particular house and equipment) 

[amyk]

That is exactly like the voltage-doubler circuit used in half-bridge PC PSUs, giving a +/-170V supply. The transformer is there to power the lower-voltage circuits.

Not surprised that it will hum, when the reservoir caps get old and lose capacitance.  They're driving the speaker directly from mains voltage.

[dannyf]

Carver is the guy who thumped the golden ear types before thumping the golden ear types was cool.

He showed that tube amps and solid state amps, when in their respective performance envelops, are indistinguishable, audio-wise.

[xrunner]

Might as well post this. It's the massive magnet inside the thing. I'm not even kidding, this thing weighs a TON. It hurts my back to move it into the living room.

[Galenbo]

Actually, that would not come under thermodynamics, it would come under heat transfer. But ...

In our school all this was treated in the course "thermodynamics", things like Turbines, Black body, convection, Isochoric process, heat exchanger rendement, cavity, turbulency,...

[xrunner]

Funny discovery. I had brought the woofer back into the living room and hooked it up to my system. It was there all morning and it wasn't humming. I went in to microwave lunch and then by chance checked the woofer - it was humming a lot louder than it ever had. Didn't think too much about it but all of a sudden it stopped humming ... just as the microwave stopped. I started the microwave again and sure enough it started humming, and it quit when the oven stopped.

Was it a ground loop or RF? I started the oven and while the woofer was humming, I pulled the audio input - it stopped humming even though the oven was still running.

It's a ground loop issue.

[SeanB]

Ground lop is easy to fix cheaply as you are not actually using the capacitors to transfer a high fidelity ( foley sub noise only) signal, so just isolate the 2 input sockets ( I assume you feed it from a dedicated sub output) from the alloy chassis with some sleeving and plastic washers, and then couple the input and input ground using some 47uF 400v capacitors on the 4 leads. That should get rid of the hum.

[Marco]

It's a ground loop issue.

You might need an active ground loop isolator by the way, or you're going to lose some low end.

[free_electron]

It looks like it's a switched mode power supply. There should be a high frequency ferrite transformer but it's not visible on the photos.

The resistor, near where the yellow/white twisted pair is connected to the board, has overheated.

nope. they rectify incoming 110 volt and store it on two 200 volt caps.. that is the main supply for the amp....

[Zero999]

It looks like it's a switched mode power supply. There should be a high frequency ferrite transformer but it's not visible on the photos.

The resistor, near where the yellow/white twisted pair is connected to the board, has overheated.

nope. they rectify incoming 110 volt and store it on two 200 volt caps.. that is the main supply for the amp....

I get that now but how are the inputs isolated from the PSU? The signal connections need to be isolated from the mains, otherwise bad things can happen.

[SeanB]

Probably they use optoisolators run in linear mode, at the frequency range a sub handles 10% or more distortion, and a bandwidth of 3Hz to 60Hz will be easy for even the poorest opto to handle.

[thm_w]

I'm really confused by the image of the RCA inputs.

They are using a single earth wire from the mains lead, connected only to one RCA jack (saved some pennies there).
I'll assume that the insulated RCA jacks are not actually insulated and make contact with the black anodized plate. Otherwise if you plugged in the wrong jack it would have no ground reference.

Wouldn't this lead to a huge ground loop?

[xrunner]

They are using a single earth wire from the mains lead, connected only to one RCA jack (saved some pennies there).
I'll assume that the insulated RCA jacks are not actually insulated and make contact with the black anodized plate. Otherwise if you plugged in the wrong jack it would have no ground reference.

Wouldn't this lead to a huge ground loop?

They are all grounded together, I just checked it because of your post.

When you touch the black anodized finish with the probe leads (but not hard enough to scratch it) it will not even read into the megohms range - it's an open circuit as far as my DMM is concerned. But if you dig in a bit with the probe lead, it will go into the nearly zero ohms range. So since the RCA jacks are tightened pretty good, they have penetrated the anodizing well enough to make a good ground.

[NiHaoMike]

How is the input board grounded to the chassis? Maybe try adding a direct connection with copper wire as aluminum is infamous for making bad connections. Also try shorting the inputs to ground at the connectors themselves to see if it might be a floating input picking up noise.

[Someone]

Funny discovery. I had brought the woofer back into the living room and hooked it up to my system. It was there all morning and it wasn't humming. I went in to microwave lunch and then by chance checked the woofer - it was humming a lot louder than it ever had. Didn't think too much about it but all of a sudden it stopped humming ... just as the microwave stopped. I started the microwave again and sure enough it started humming, and it quit when the oven stopped.

Was it a ground loop or RF? I started the oven and while the woofer was humming, I pulled the audio input - it stopped humming even though the oven was still running.

It's a ground loop issue.

Is the neutral isolated from the earth somewhere in the subwoofer? If it isn't it's created the mother of all earth loops. Neutral will flap around as other loads are turned on/off, such as the microwave. If it is isolated then the rejection of the isolating is poor and you'll need to look at how to increase the common mode rejection of the isolation.

[xrunner]

Is the neutral isolated from the earth somewhere in the subwoofer? If it isn't it's created the mother of all earth loops. Neutral will flap around as other loads are turned on/off, such as the microwave. If it is isolated then the rejection of the isolating is poor and you'll need to look at how to increase the common mode rejection of the isolation.

I dunno. Look at the schematic I drew up in an earlier post. Neutral goes off to the circuit board after that I don't know. Also, one terminal of the speaker is connected directly to neutral.

[xrunner]

Ha - I just thought of a new business opportunity. Just advertise to audiophools to install Mega De-oxygenated wire (or whatever catch-word turns them on) on the inside of the amp from the terminals to the circuitry. Just show them pics like I took, where their Mega cables transfer to little cheap wires, and they'll freak out. 


Oh crap - the shipping costs would be a little on the high side though.

[wagon]

Ha - I just thought of a new business opportunity. Just advertise to audiophools to install Mega De-oxygenated wire (or whatever catch-word turns them on) on the inside of the amp from the terminals to the circuitry. Just show them pics like I took, where their Mega cables transfer to little cheap wires, and they'll freak out. 


Oh crap - the shipping costs would be a little on the high side though.

Can't see them caring about the shipping cost when they're paying thousands for their space-heating amplifiers.