Audiophile fuses...

oscroft

Member
HP 6632B precision power supply + Keysight 33465A, in case you're interested.

I'd be interested to see the circuit diagram for the PSU, and the location of the fuse.

A simple, 'classic' linear supply has an absolutely horrible V-I characteristic on the AC side. The current is zero most of the time, but as soon as the peak of the mains waveform exceeds the voltage on the reservoir cap + diode drop, the rectifier diodes turn on resulting in a huge dI/dt. A large current then flows into the caps until the mains waveform reaches its peak and starts to reduce, at which point the rectifiers turn off and current drops to zero again.

The resulting current waveform is a series of spikes at 100 Hz intervals, producing electrical and magnetic interference with a Fourier spectrum of harmonics that extends throughout the entire audio band. (Think about that the next time someone suggests that linear supplies are "quiet" in a hi-fi context).

The argument for the effect of the fuse could go either way. You could argue that, by having resistance, it's slightly reducing the magnitude of the current peak each time the reservoir caps are topped up, resulting in less interference in the audio band. In this case, more would be better, and you might expect the amp's power supply to include a series resistor for this reason.

Or, you could argue that the voltage drop across the fuse is modulated by the current being drawn by the amp, which in turn follows the audio signal, and that this is 'bad' for some reason that almost certainly depends on the specifics of the amp's design. In that case, lower resistance would be better.
Very interesting, and educational, thanks (and nice test gear, beyond my means). I hadn't thought at all about harmonics from the rectifier switching (and I don't think I've ever come across it in anything I've read).

PSU schematic attached, plus block diagram showing fuse F1 at bottom left. Only difference is that the 10,000uF caps have been replaced with 15,000uF ones as part of the recap. There's also a pair of 4.7uF (bypass, I presume) caps on the +44V and -44V lines at the output transistors.

P11.jpgP17.jpg
 
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AndyC_772

Active Member
Very interesting, and educational, thanks (and nice test gear, beyond my means). I hadn't thought at all about harmonics from the rectifier switching (and I don't think I've ever come across it in anything I've read).
Tools of the trade - I'm an electronic design consultant.

To anyone interested in learning about electronics, I normally advise people to learn from anywhere except:

a) Sources that deliberately try to go against established scientific thinking (eg. those that promote conspiracy theories, that misuse the word "energy" to mean anything intangible that they don't understand, or that use language like "the truth about..." or "what THEY don't want you to know about..." - and

b) hi-fi forums. Though they're almost always well intentioned, the good science is lost amongst plausible sounding anecdotes that don't stand up to analysis, or 'explanations' that are just science-y sounding words strung together that simply don't mean anything at all.

Start with a copy of Horowitz & Hill "The Art of Electronics", 3rd edition, and go from there.

I'll take a look at the schematic later on. Real (paying!) work beckons.
 

oscroft

Member
a) Sources that deliberately try to go against established scientific thinking (eg. those that promote conspiracy theories, that misuse the word "energy" to mean anything intangible that they don't understand, or that use language like "the truth about..." or "what THEY don't want you to know about..." - and

b) hi-fi forums. Though they're almost always well intentioned, the good science is lost amongst plausible sounding anecdotes that don't stand up to analysis, or 'explanations' that are just science-y sounding words strung together that simply don't mean anything at all.
Couldn't agree more. And even some of the more electronics based forums can host some ludicrous arguments sometimes. My own knowledge is relatively basic, but I started at school electronics and radio club where I first learned how to burn myself with a soldering iron (a skill I retain to this day).
 
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Baobr

Active Member
I'm not suggesting anyone on this thread believes quantum crystal alignment of their hi-fi interconnects is anything other than snake oil, but there will be other areas where the marketers successfully push your buttons to get you to buy their product over a competitors.

I'd be grateful for all opinions - if there's any forum where this subject can be discussed in a friendly manner, surely this is it. (Though I have to say, I did hesitate before deciding to post my findings... :))
I've been listening to music and therefore had an interest in hi fi for 40 odd years,and joined this forum to listen to other interested parties,who are far more technically minded than I'll ever,or wish to be!.. Thanks @oscroft for this post and pointing the forum to the youtube posts of Ethan Viner et al. With plenty of time unfortunately on my hands I have watched good few of these now. What a chuckle you have given me (not through your experience with you're new fuse) but the posts on youtube.....Jars of pebbles placed in corner of rooms, alligator clips on interconnect,rubber microthin discs and on and on,all selling for ludicrously amounts.. weird......but probably not as strange as the people buying this stuff.... looking forward to more..... Thanks
 

Khazul

Well-known Member
I read somewhere that the fuse is there to protect the wiring in your house, and not the wiring in your amplifier. If the amplifier was to fail short, you would be relying on the higher rated fuse or RCD in your consumer unit to cut the supply and protect this wiring...

Fuse/breaker in the thing it is protecting (house wiring/cable/appliance for each of their respective breakers/fuses) and RCD to protect you.
 

dogfonos

Well-known Member
Can't resist the urge to add actual scientific data to a debate...

I've just measured the V-I characteristic for a couple of different fuses, one rated 0.5A and the other 2A.

The 0.5A fuse has a resistance of 208 mOhm @ 100mA, rising to 223 mOhm @ 500mA. Beyond this, the resistance starts to rise significantly with current and also with time, as the wire heats up. At 1A it's 300 mOhm. Failure occurred within a couple of seconds at 1.7A.

The 2.0A fuse starts at 69 mOhm, rising to 77 mOhm @ 2A. Above its rated current, like the smaller fuse, the resistance starts to rise with current and over time, so although it didn't fail straight away at 5A (the upper limit of the PSU I was using), it almost certainly would have done eventually.

The question is, therefore, how significant can ~70mOhm in series with the mains supply be, and is it possible to make a fuse that has the correct rupture current but lower resistance than a standard type when used below this rating?

I wonder how a MCB (~3A) would measure? Do mains plugs with in-built MCB's exist? Or maybe a power strip with in-built MCBs? Or are MCBs just for mains consumer units? A suitably rated MCB could then be used in place of the equipment's original AC fuse - and the original fuse bypassed a la ocroft. Maybe?
 

oscroft

Member
I wonder how a MCB (~3A) would measure? Do mains plugs with in-built MCB's exist? Or maybe a power strip with in-built MCBs? Or are MCBs just for mains consumer units? A suitably rated MCB could then be used in place of the equipment's original AC fuse - and the original fuse bypassed a la ocroft. Maybe?
I've only ever heard of them used in consumer units.

But looking round, I did find this - "a reliable compact Circuit Breaker designed to protect audio speaker systems, amplifiers and power supplies from internal over-current."
 

AndyC_772

Active Member
I like the 1.6A version; internal resistance "<0" mOhms!

Comedy typos aside, I don't see any approval markings on these, and the max interrupt current is very low. Don't use on the mains.
 

AndyC_772

Active Member
wonder how a MCB (~3A) would measure?
I think I have a spare 10A one in my spares box. Will take a look if I get bored over the weekend.

It's a little off topic, but this might be interesting viewing for anyone with an interest in mains protection, or the lack thereof. Happy Friday, enjoy!

 

Khankat

Well-known Member
My introduction to electricity was as follows: fascinated by the light emanating from a bedside lamp, I decided to investigate. First, I turned off the lamp, waited for the bulb to cool, then discovered how to remove the bulb- it was a bayonet fitting and the lamp switch was one of the horizontal, sliding two position types; on or off. After carefully placing the bulb where it wouldn't come to harm, I then inserted the middle finger of my left hand into the place the bulb had been and then threw the switch.

Whump! It hurt, I think. But I decided there and then, that I did not like electricity and vowed to have as little as possible to do with it from that point on. I was about five years old at the time.
 

phil t

Well-known Member
My introduction to electricity was as follows: fascinated by the light emanating from a bedside lamp, I decided to investigate. First, I turned off the lamp, waited for the bulb to cool, then discovered how to remove the bulb- it was a bayonet fitting and the lamp switch was one of the horizontal, sliding two position types; on or off. After carefully placing the bulb where it wouldn't come to harm, I then inserted the middle finger of my left hand into the place the bulb had been and then threw the switch.

Whump! It hurt, I think. But I decided there and then, that I did not like electricity and vowed to have as little as possible to do with it from that point on. I was about five years old at the time.
Eek.

I'd have been about 8, had a torch with a 1.5v bulb ( lamp). I wondered how much brighter it would glow if put in my bed side lamp plugged into 240v.

Lucky for me I was touching the glass bit of the bulb, so didn't get any shock.

That put me off for a number of years.
 

Hixs

Distinguished Member
And the Darwin award goes to.....
 

oscroft

Member
@oscroft Any updates on your audiophile fuse experiment?
Not yet. I have a selection of ordinary fuses (including ceramic) plus one "audiophile" fuse to test, but I need to think about the best way to compare them. And I need a reasonable amount of undisturbed spare time, which I haven't had.

As an aside for anyone who assumes ceramic fuses are always filled with sand for quenching - I broke open a 2A ceramic fuse to check, and no sand.
 

musicphil

Active Member
oscroft,
I look forward to your findings on these fuses- as I will get myself some that you recommend to try in my system.

This can be really a cheap upgrade!!!!
I am always interested in anything that can make an improvement. 👍
 

Baobr

Active Member
oscroft,
I look forward to your findings on these fuses- as I will get myself some that you recommend to try in my system.

This can be really a cheap upgrade!!!!
I am always interested in anything that can make an improvement. 👍
I doubt we can take too much from it but watched Paul McGowan's post on this subject.....at least he says he was very sceptical it would have an effect.....but was genuinely impressed by the result.....which he couldn't fathom
 

oscroft

Member
OK folks, here's my latest take...

Cautions first... No blind testing, just me, and I knew which fuse was which all along. I'm still working on the possibility of blind testing, but for now this is all I have. What I have to do is unplug the mains cord from my Audiolab 8000A amp (otherwise you can't get the fuse out - it's a safety thing). Then open the fuse drawer (fiddly, but with a dental pick it's easy enough). Swap fuses, plug in again, and resume playing music. There's a delay between samples, of probably around 30 seconds.

My test album is Open Sky, by guitarist Stephanie Jones - Stephanie Jones - Store. I'm using a FLAC rip, played on my dedicated Mac Mini, via M-DAC, into Audiolab 8000A (with upgrades). My speakers started life as Mission 780s, but I've upgraded the bass/mid drivers and the crossovers and improved the damping. I usually play with a subwoofer, but I left it out for these tests as it's something more to switch on an off again (and there isn't any deep bass in this music anyway).

0) I've had my shorted not-a-fuse (ie copper wire) in place of the fuse in my amp since I posted my findings, so I'm used to the sound of that.

1) I switched back to an original 2A glass fuse, and there was a definite degradation in top-end detail (to my ears), same as I reported last week.

2) Next up, a 2A ceramic fuse, and it sounded exactly the same as the 2A glass fuse to me.

3) Then a 5A glass ceramic fuse, and I was back up close to the improved copper wire sound.

4) Back to original 2A glass fuse again, and back to the poorer sound.

5) Then... drum roll... an "audiophile" 2A fuse. It's an "AMR Audiophile Gold HiFi Fuse" and cost me £15 (and didn't come with any BS about quantum effects or whatever). The sound was back up there again.

6) And once again back to the 2A glass fuse, and a step back down in sound again.

So in this test, fully sighted, plenty of room for psychological misdirection, the audiophile fuse (and I'm finally going to drop the scare quotes), the copper non-fuse and the 5A ceramic fuse all sounded the same to me. And the sound with the two 2A fuses was inferior.

That's my ears, my head, my delusion possibly, my 90s-design amp (which might have power supply weaknesses)... and how it sounded to me. You gotta make up your own minds ;)
 
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Ugg10

Distinguished Member
Many thanks for your efforts, interesting.

Any chance you can measure the resistance of each fuse, looks like there is a switching point around that 2amp capacity wire, the “audiophile” fuse may have a slightly lower resistance than the “normal” fuse partially confirmed by the difference with a “normal” 5amp fuse. Maybe the “audiophile“ fuse has a lower resistance for the same blowing capacity????

No idea if there is anything I this but just a thought.
 

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