[Carlman]

Before I go too far, I think I know what the problem is but, I want to be sure before I go buying more fuses.  I think I have fuses that are too weak.  I'm using a fused IEC power inlet.  It uses a 20mm fuse.  Up to now, I've used 10 and 6.2 Amp slow blow fuses (250V).  I think Hugh suggested 20 or 30 amp... can't remember.  I ran out of the larger values and now all I have is 4-amp.  When I switch on the amp, the LED's come on for a split second and go out... because the fuse is blown.

The amp has been built and operational (with 6.2 fuses) for about a month.  I had to turn the power on and off a lot and blew a 6.2 fuse.  However, I didn't have a problem again until recently when I had to turn off the amp when a storm was coming.  When I powered it on this morning, I blew the fuse and tripped the breaker.     I opened the amp and took a look under the hood.  I found a small, single strand of wire lying across the power supply circuit board.  There were no burn marks and it probably happened when I moved the amp.  However, I vacuumed the whole thing anyway.  I still blew my little 4-amp fuses, though.

I'd appreciate any thoughts.  I'm really hoping it's just that the fuses are too small.

Thanks,
Carl

P.S. No, this isn't a dirty joke full of puns... not intentionally, anyway

[PSP]

Hi Carlman,
Hugh will weigh in on this, but if you want to get started before it's morning in Oz, you might search the arcives on Harmonic Discord.
http://www.harmonicdiscord.com/forums/viewforum.php?f=42&sid=8ffef212c20d9723a914f1b33b2d5f5b

I think the thread(s) you are looking for occurred fairly early in the lifetime of Aspen on HD.  

I use 15 amp breakers on my AKSA 55s.  My theory is that the 5amp fuses on the board will protect the amp and if there is a serious problem in the power supply a 15amp breaker will blow before a fire starts.... otherwise, I don't want the music to stop...  

BTW, I shake my chassis hard, and use a can of compressed air to dislodge little metal bits, then shake it again... I have been so close to having my AKSA fried by little pieces of metal crud....


Good luck,
Peter

[Carlman]

I tried a little experiment,
I disconnected everything and took it to my test bench.  I connected the power and no problem.  I figured it must have been one of my DIY power cables.  I hooked it all back up with a new power cord and the fuse blew.  Unfortunately, I was over confident and hooked up speaker wires and IC's.  I did check to be sure the speaker cables were connected well and not shorting anywhere.  I figure now it's either my DIY power strip, or that my current is higher because it's a dedicated outlet with all really top notch outlets and cabling.... which blows the little fuse with the higher inrush.  Maybe?

I searched on HD and found a few comments about fuses in certain applications.  I was just wondering if 4A was enough to power it on.  I couldn't find anything specific to that question.  But, people were using 5A fuses with success.  I have no idea what happened since the amp hasn't been moved in a long time.

I'm using an Arco switch that is a 3-way switch.  Middle is 'Off' and up or down inverts phase one way or another.  There's a slight sound difference between the 2.  But, nothing has changed with anything so, I'm probably looking too deeply into this.

-Carl

[PSP]

Hi Carlman,
Some thoughts...

First, until you track down this problem, simplify your plumbing.  Use a vanilla power cord plugged into a vanilla outlet.... something you know for sure works.  It is very unlikely that your DIY power strip could be so excellent that you now have a big inrush (did you make it from 2 guage superconductor???)...

If you are still blowing fuses, disconnect the power supply leads from the AKSA amps.... do the fuses in the IEC blow under this condition?  Are the DC voltages on the + and - terminals of your power supply correct?  

Then look hard at your AKSA amps... once I caused a short... digging around on the PCB trying to fix problem #1 I pushed some components together that Hugh (and God) meant to be separate... so then I blew fuses until I found the error of my ways.  Make sure that there aren't more metal chunks on your board, and that everything is standing tall and free away from other components.

When all is well with the power cords and power supply, attach the power supply leads to the AKSA amps (one amp at a time?).  This amp made good music just a little while ago... the problem can't be burried too deeply!

Finally, when working on problems like this, I can't recommend strongly enough use of a current-limiting box as suggested by John Curl on AA:  http://www.audioasylum.com/audio/tweaks/messages/29312.html


Good luck,
Peter

[Carlman]

Peter,
Thanks a LOT for taking the time to wade through this with me.  I blew my last fuse on that last experiment so, it'll be a while before I get some new ones.  I bought some pricey ($2 each) ceramic filled 10 and 15 amp slow blow's from across the country so, I'll have plenty of time to investigate what's happening while I wait for their arrival.  
I am using a Volex power cord now, as vanilla as I've got.  I checked the voltage at the IEC end of the cable and it is equal to the other outlet and IEC output.  So, from what I can gather, it only blows while connected to speakers and IC's.   I triple-checked the wires at the speakers.  Everything is fine.  The only odd thing is that I have the speakers out of phase from the amp but, that's because my preamp inverts phase.  And, it's always been connected this way.

I've looked and looked at the internals of the amp.  I vacuumed it, fiddled with wires, etc...  I'm wondering if this has been a slow process of something breaking or dying over time.  I don't know but I can't wait to figure out.  Sunday without tunes blows.

Thanks again,
Carl

[PSP]

Hi Carl,
I'm at a loss to think of a reason for blowing fuses ONLY when you have ICs and speaker wires attached.  

Take your voltmeter out and test the resistance across the speaker leads.  Measure at the amp end with the speakers attached.. should be something like 4-8 ohms, NOT zero (or 0.1 ohm) and not OPEN CIRCUIT either.  If you had a short in your speaker or the cables, that would blow the output devices (I think) and maybe put enough stress on things to blow the marginally too small fuses in your IEC...

Is there any way that your speaker cables are shorting to the amp chassis?  Can you confirm that all is well here by measuring resistances?  Since speaker negative goes to power supply SPG (single point ground) that lead could be grounded to the chassis (if you have a wire linking power supply SPG to the chassis) or it could float free (if you did not put a wire between SPG and chassis... this is the configuration, BTW that is shown in my manual, at least).  In any case, the resistance between the positive speaker cable and SPG (and/or the chassis) should be equal to the resistance across your speakers (or a bit higher, due to the small resistance of your speaker cables).  It should NOT be lower than the resistance across your speakers, and 0.1 ohm is a sure sign of trouble.

Regarding connection of ICs, I'm totally baffled.  Can you make up a pair of shorting plugs from some cheap spare RCAs (put a 1K to 5K resistor from the pin to the outer connector), and put those into the amp RCA inputs... and compare that situation with inserting your ICs instead?  If your IC's cause the fuse to blow, I'd suspect a major (and unsafe?)grounding problem somewhere in your system.

You said that this problem ocurred when you unplugged your system as bad weather approached.  Any chance that one of your components (or the speakers) got damaged in a lightning strike?

This is my last post for the day... got a big paper to write before morning.

good luck, and be careful, OK?
Peter

[Carlman]

I checked the resistance of the speaker posts and got 7 ohms with cable connected, 3 ohms disconnected, both channels.  I had to go out this afternoon and happened to stop by a Radio Snack.  I bought some 5A fuses to do some more testing.  I figured, why not?...  

Without doing anything, the amp powered right up and is delivering great sounding music as I type.  I can't believe it would be that 1A difference.  Could it be that I have found the threshold of my particular AC/IEC/Power Switch system?

The system is sounding great again.  So, I can't complain.  New 10A and 15A ceramic fuses are on their way... but, the 5A is working at the moment.  I think turning it on and off must be wearing away at the fuse.

Thanks again, Peter, for your help on a Sunday morning.  My wife thanks you as well because it was giving me fits.  I knew what to check so we didn't do any real damage.

Oh, here's a mini-review of Volex vs. Belden 83802:
Not much, if any difference noticed on my amp.  Buy Volex, $8, already made.

Thanks again,
Carl

[PSP]

Hi Carl,
report written, on my way home to listen to some sweet music...

glad you got your AKSA back.... once you get used to that level of performance it can be real painful to live without it, especially if you think you might have killed it!!!

I use Volex cords... with IEC for my TLP/N (and GK-1 someday); I cut off the IEC end and hard-solder them for the AKSA amps.

happy tunes!

Peter

[AKSA]

Carl,

On 120V with the 100W AKSA, you might try up to 7.5A fast blow.

This should solve your problems.  Inrush is certainly an issue with toroidal transformers, and inrush surge protectors are available which are inserted into the line to limit inrush.

However, the cheapest way around it is to merely increase the value of the fuse, or use a slow blow and you've already figured.

Hope this helps,

Hugh

[ginger]

I built a Nivarna Kitted 100W AKSA which I have since foolishly sold to pay for parts for my new 120W Valve Amp - while I wasn't using it for my system I wish now that I had kept it for a Reference Amp.

I had some rhopoint components SG39 'Surge Guard' Inrush Current Limiters in my components bin (4 Amp Continuous Rating) which were a bit high for a 240V Powered Unit so I put one in each of the Active and Neutral Lines before the fuses (I always fuse both Active and Neutral) - This worked extremely well in suppressing the Toroidal Transformer Inrush Current. For 120V AC just one of these in the Active should be OK. For a SINGLE device in the Active ONLY for 250V AC unit use SG240.

Farnell can supply these:
2A Continuous (SG240) - Farnell 606-741 $5.10 Australian
4A Continuous (SG39) - Farnell 606-777 $6.31 Australian  

Cheers,
Ginger

[karthikn]

I had some rhopoint components SG39 'Surge Guard' Inrush Current Limiters in my components bin (4 Amp Continuous Rating) which were a bit high for a 240V Powered Unit so I put one in each of the Active and Neutral Lines before the fuses

Hi, would these current limiters have any downside as far as sonics go ? If they are always active, I guessing they will put a damper on the bass side of things, right ?

Karthi

[AKSA]

Hi Karthi,

This is a moot point;  I can't actually tell you.  I believe it's possible, but only a slim likelihood.

If the series impedance is say ten times more than a fuse, say 100 millliohms or so, then maybe.  So take a good DMM capable of milliohm measurements and check these circuit breakers out before purchase.

Hope this helps,

Hugh

[ginger]

Inrush Current Limiters are a Negative Temperature Coefficient (NTC)Thermistors.

If you choose the right one then it only has influence at switch on when it has maximum resistance.

For example the SG240 has a Cold Resistance (25 Degrees C) of 40 Ohms and an operating resistance at a nominal 2 Amps continuous of 0.6 Ohms. This means that it limits the inrush current at switch on to 6 Amps. This also provides protection to the rectifier bridge and the power supply filter capacitors by limiting the initial charge current through the diodes and into the capacitor at startup. It will certainly improve their life.

At operating current the 0.6 Ohms reflects across the transformer acording to the square of the turns ratio.

For a 240V to 35-0-35 V transformer such as for the AKSA this means that fitting the SG240 on the primnary side is equivalent to fitting a 0.013 Ohm Resistor on the secondary side. This will be swapped by the resistance of the secondary winding.

Summary:
Effect is ONLY at initial Power ON
There will be NO Sonic Effects
There WILL be improved Electrolytic Capacitor Life

For further info see Application Note:
www.rhopoint.co.uk/components/ICLSG/pdfs/2app.pdf

[Lost81]

Carl,

On 120V with the 100W AKSA, you might try up to 7.5A fast blow.

This should solve your problems.  Inrush is certainly an issue with toroidal transformers, and inrush surge protectors are available which are inserted into the line to limit inrush.

However, the cheapest way around it is to merely increase the value of the fuse, or use a slow blow and you've already figured.

Hope this helps,

Hugh

Hi Hugh,

I am about to order the Potter & Brumfield Thermal Circuit Breakers, Type W28:

I am assuming the figure you gave for the above are for dual mono operation (i.e. 7.5A). What is the correct figure for a monoblock 100W AKSA?

According to the catalog, they come in the following values (amps):

0.25, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 20.

While waiting for them to arrive, I have some 5A slow-blow fuses at hand. Are these too high a value to protect a single-channel AKSA 100W (i.e. monoblock)?

Many thanks!


Cheers,
-Lost81

[AKSA]

Hi Benny,

Use the 7.5A P&B breakers.

The 5A slow blow should be OK, but might blow with heavy drive into four ohm loads.

Protection will be fine.

Cheers,

Hugh

[SamL]

Guess I must be lucky. I am using 2.5A slow blow for my AKSA100n while it was still under testing and bias adjusting. So far I'd blow the fuse 3x but that is 1 out of 20 times I turn it on. Maybe it got to do with the Antrim transformer from Harbunch Electronics in Sydney.


Sam

[Lost81]

Hi Benny,

Use the 7.5A P&B breakers.

The 5A slow blow should be OK, but might blow with heavy drive into four ohm loads.

Protection will be fine.

Cheers,

Hugh

Darnit!
The P&B breakers don't fit into my rear panel.
And I am not going to attempt dremeling the 12 gauge steel panel.
Maybe at some point I will widen the hole in the panel to fit these breakers but the tool of choice sure ain't gonna be a dremel

Right now, I am using 5A slow-blow fuses.
The speakers are 6 ohm impedence.

One of my AKSA modules sometimes put out a crackling distortion (sounds like breaking up) when music material containing high frequency (e.g. violins) is played at medium-loud or loud volume. Hmm...


-Lost81

[AKSA]

Benny,

The AKSA amps are all true dual mono.  That is, electrically, they are built as monoblocs but mounted together, usually, in one box.

So your monoblocs won't need anything more or less than stock.

That is, 7.5A fast blow on the rail fuse of each module is fine, and for the mains fuse, I'd suggest 10A for 120V grids.

Hope this helps,

Cheers,

Hugh

[fos]

Regarding the inrush current suppressors, I am considering using one on the supply to my GK1.

RS have a 2A device that drops from 25R to 0.55R after 55 seconds at full current [RS 210-689]. Since my GK1 uses less than 1 amp, I assume the running resistance of the device would be greater than the 0.55R quoted.

My GK1 has no power switch fitted atm, its left powered up unless we are going to be away for more than a couple days. This I gather eats into the life of the tubes?

Since the transformers in the GK1 are small when compared with the torroidal units fitted to the power amps, is inrush protection a worthwhile addition?

[kyrill]

. . .

My GK1 has no power switch fitted atm, its left powered up unless we are going to be away for more than a couple days. This I gather eats into the life of the tubes?

Since the transformers in ...

Yes Hugh
that is an interesting q. And if you power it off once a day waht is the lifetime of the tubes?
Kyrill