[Lost81]

Hi fellow AKSAphiles,

I have this weird problem with one of my monoblocks.
Can you help me with it?

Let me try my best to describe it:

Turn on CAL Delta CD Transport.
Turn on modified ART DIO.
Turn on TLP Nirvana (modified beyond Nirvana with BlackGate for C2, C2' and tantalum resistors).
Wait 5 minutes.
Turn on right bass monoblock.
Turn on left bass monoblock.
*Unbelievably loud 60 Hz buzz/humm from Hell. Lights on same circuit dim and brown out*

It is so bad that I have learnt to be really really fast with turning off the right bass monoblock again when it happens.

---

Here's the really strange thing.

The 1st time it happened: I shifted the power cables of the source components away from the input cable of the right channel bass monoblock. I also put cheater plugs on the transport and the DAC.
(TLP already uses cheater plugs).

Turned on the switch again. Everything is fine.

I thought that was that, and that it was fixed: the amps played for 10 hours straight and idled for 20 hours after that.

---

Today, after being off for 24 hours, and I turn on the amps, it happened again. Except that high frequency noise also came in together with the buzz from hell.

(And this time it is my beloved Mission 754 Freedom 5 speakers. *sob!*)
I hope it didn't damage anything.

---

I did the same thing again.
Shifted power cables even further from the input cable of the amp.
Made sure that the ground tabs of the cheater plugs are not touching the metal power strip.

Took a deep breath, and flicked on the switch of the right channel bass monoblock. Everything is ok.

What gives?

---

Notes:

that this has NEVER happened with my modified Harman Kardon CD player serving as both the transport and DAC. This previous set-up played for 40 hours without a problem. I also turned on and off the entire system multiple times within 5 minutes with no problem.

this problem only began when I started using the CAL Delta as a transport, and the modified ART DIO as the DAC.

Bias and output voltage offset of the affected amplifier are within range: 45mV cold-start; 55mV after 15 minutes idle; -28.6mV Output Offset Voltage.

When it happens, and if I were to turn the everything off, and then turn on the amplifier ONLY, the amplifier does NOT buzz if there is no input cable connected to it.
Immediately repeating this with the input cable reconnected yields the same buzz from Hell.
However, if I wait 5 minutes, and then turn everything back on again, in the same sequence, everything is all right.

Anyone can tell me what is going on?
 
I feel like a man about to perform a bungee jump everytime I turn on my amplifiers now.

Thanks!


-Lost81

[AKSA]

Benny,

Start at the beginning.

Disconnect all but the power cord and speakers from each monobloc.

Now switch on.  Is the noise there?

If not, now connect the TLP, again, with no source connected to the TLP this time.  Is the noise there?

Once we know the answer to this, we isolate the problem - this is a large system, and any of four or five components might be causing it.

Cheers,

Hugh

[AKSA]

Benny,

My mistake;  I reread your post, and realized you'd already done this.

It seems the amp doesn't do it alone.  The problem is earthing.

Run a single wire from your source component chassis to the chassis on the monobloc.  This might scotch an earth loop.

If not, try running this same wire to the star earth on the monobloc.

Cheers,

Hugh

[Lost81]

Hi Hugh,

Wow!
Thanks for the quick reply!  

The weird thing is that it is ONLY the right bass monoblock that is doing this.
The right mid-range / treble monoblock, which shares the same input (in parallel) is unaffected.

Following your suggestion would mean that I connect the chassis of the CAL Delta chassis to the right bass monoblock's chassis?
(They are already disconnected via a cheating plug now).

How about I disconnect ground from the chassis of the CAL Delta and the outboard Power Supply of the ART DIO?

My apartment's circuit doesn't have ground anyways.

I ran my own ground to the cold water pipe last week, but my housemate warned me about a floating ground situation that will blow up other things, so I disconnected it.

I hate hate hate earth-loops!  

I hope I don't have to resort to installing this:
Loudspeaker protection
It sounds like there is a sonic penalty for it.


Cheers,
-Lost81

[AKSA]

Benny,

Check R2 on the right monobloc is good, and connects.  It is 10R.

Yes, from the chassis of each component to the chassis on the AKSA.

If that doesn't work, try running the same wire from the power earth on the source to the star earth on the AKSA.

It rather sounds like something has come adrift.  Have a good look inside;  look for bad connections, even dry solder joints.

Cheers,

Hugh

[Lost81]

Thanks, Hugh!

I will do that later today!


*fingers crossed*
-Lost81

[Lost81]

OK, so after re-soldering some of the legs of the NPN and PNP transistors, as well as re-soldering R2 and R3, and re-testing and rebiasing Monoblock #4, "the hum from Hell" is still there. All the other 3 monoblocks are fine.

And so, after reading Sean's post on Audiogon.com about an audiophile who replaced 1/2 his system over a length of time (and lots of cash) and then finding out that it was due to a single defective cable, got me thinking.

And so, I swapped out that single interconnect cable...

Problem solved.

Turns out that there was intermitten connection for the ground side of that particular interconnect cable.

Well, what can I say?
Next time I will check everything before thinking it is the AKSA's fault...


(But really, who would have thought it is due to the wire? )

Remind me never to consider a career as a bomb disposal specialist...
"Blue wire or red wire?"
I can see it now



-Lost81

[kyrill]

Hi
Still congratulation with yr idea to check the wires.
what a relief you must have felt after finding the cause.

[Lost81]

Thanks, kyrill.

Yes, I'm extremely relieved

I have been playing my AKSAs almost non-stop since


They keep sounding better and better.
I believe the electrolytic capacitors are still breaking in.
That, along with the 2 blackgates in my TLP Nirvana too


For the 1st time today, I heard the whistling of an AM radio in the background of "Wish You Were Here"...
That little piece of detail added an immeasurable poignancy to an already poignant song...

Thanks, Hugh!


-Lost81