Tips on setting up bias for AKSA 100N?

Lost81 · « **on:** 5 Jul 2004, 04:28 am »

Hi guys/gals,

Anyone has tips on the final stages of the setting up of biasing for the AKSA 100 Nirvanas?

The Nirvana Upgrade Kit was completed before I completed my AKSA 100W, so I thought, "Why not install the Nirvana at one go?" (If that tells you how slow I have been with Hugh's babies, read on. It gets worse.

)

(1 year later...)

Well, it certainly is going to look like Hugh's 100 Nirvana Plus is going to be released before I set up the bias on these AKSA 100N babies (for the 1st time too!). Oh well...

Anyone has tips on setting up the bias?

I am thinking of leaving the transformer and filter cap PCB installed in the chassis, and run flying leads to the AKSA PCB boards for the testing stage. I think that will be safer.

I am either going to use an iPod as a music source, or an ancient Sony Walkman's FM Tuner.

FWIW, I will be setting up 1 channel at a time, as they are built in monoblock configuration.

I am most terrified of this stage. Terrified enough to consider air-freighting them to Hugh to get them biased (an expensive proposition considering that I'm in North California, and Hugh is in Australia...)

With sweaty palms,
-Lost81

AKSA · « **Reply #1 on:** 5 Jul 2004, 05:28 am »

Benny,

Take heart - brave heart - young man!!

Once the modules are fully assembled, turn the bias trimpot (blue, square, 100R, just near T3) fully CCW to reduce bias to the lowest setting possible within the range.

Now, REMOVE the rail fuses. That is, leave 'em out altogether......

With nothing switched on, connect the positive from the power supply to the left front tag, marked +50V, and the EARTH from star earth to the center front terminal, and the negative from the power supply to the RIGHT front tage, marked -50V.

Now, place a DMM probes across the fuse holders on the left side. Remember, there is a 100R resistor between the fuseholders, paralleling the fuse, specifically mounted for this initial test purpose.

With the power supply correctly wired up (and you should check this before you connect to the amp module, to be sure you have the correct +50V, 0V and -50V values), turn on the DMM, and prepare to switch on.

Stand back a little so your head is NOT directly above proceedings. This is only reasonable caution; there's a 100 volts here!!

Now, throw the switch on the mains supply, and read off the voltage on the DMM. It should be under about 3V. If it is 5V, it's a little high but OK, but anything over 10V, switch off immediately.

If all is well, with the supply still switched on, remove the DMM leads from the two fuse clips on the left side, and move them to the fuse clips on the right side. The voltage should be exactly the same. If it is not, there is a problem.

Anything below about five volts across the fuse clips can be sustained indefinitely, but if all is well, switch off, insert the fuses, switch on again, and set up the bias as per the instructions.

It's that simple...... I appreciate all the angst in this, but you must show real confidence and BITE THE BULLET!!

Cheers,

Hugh

AKSA · « **Reply #2 on:** 7 Jul 2004, 08:18 am »

Benny,

Have you biased up that amp, and how is it sounding?

There are people want to know!!

Cheers,

Hugh

ghamel · « **Reply #3 on:** 7 Jul 2004, 11:07 pm »

Benny,

I had the same issue, and finally just went with flying leads to calm my nerves.. Solder a pair of color-coded leads (red+/black-) onto each pair of test points, twist the two related leads around each other so you know which are a pair, and reassemble the amp with the two pairs run out to somewhere accessible.

You have to assemble/disassemble things a few times, but for me anyway this made it a whole lot easier to focus on the task at hand - no need to worry about juggling things around under power..

Good luck!

EchiDna · « **Reply #4 on:** 8 Jul 2004, 12:00 am »

hehe I remember this un-nerving step...

go for it Lost81!! you can do it

honestly, you are going to thank yourself

, yet curse yourself

for taking so blardy long over the process

PSP · « **Reply #5 on:** 8 Jul 2004, 05:06 pm »

Lost81,
In addition to the above advice, I would add the following:

- clean up your workbench... put "extra" screwdrivers and pliers away and clean up all those 3 inch lengths of hookup wire and all the miscellaneous crap. Once I dropped a screwdriver onto my junked-up bench and flipped a length of wire into my powered-up amp... lucky day because it landed harmlessly, but now you have been warned...

- be sure everything is fused.

- if your amp/heatsink module is not yet mounted to the chassis, cradle it in a dry towel (which covers the power supply PCB and power leads) to limit accidental contact.

- read the directions (and Hugh's advice above) one more time just to be sure

- power up... no smoke in the first few seconds is an excellent sign. One thing you could do to limit damage in the case of a really big problem is to follow John Curl's advice: http://db.audioasylum.com/cgi/m.mpl?forum=tweaks&n=29312&highlight=lightbulb+John+Curl&r=&session= I built this into a small metal project box and it has saved my butt from stupid mistakes several times... highly recommended.

- When it's time to hook up speakers for the first time I use a $30 pair just in case something really bad happens... but you know, the AKSA is so good that even these sound really good while completing the bias adjustments.

Now go in there and bias that amp!! Let us know how it sounds, yes?

Good luck,
Peter

Lost81 · « **Reply #6 on:** 8 Jul 2004, 07:09 pm »

Woah!

Thanks for the loads of advice, well-wishes and encouragement, Hugh, ghamel, EchiDna and PSP!

I haven't got to it yet as I have been busy with my studies.
But it will be very soon!

I hope to bear good news when I finally do it!

A thousand thank yous!

Cheers,
-Lost81

Lost81 · « **Reply #7 on:** 12 Jul 2004, 08:44 am »

Greetings, fellow AKSAphiles,

As of July 12th 2004 0100hrs, another of Hugh's creations roared to life.
I.e. I biased monoblock #4.
(I think.)

Quietsant voltage at start-up: 45.0mV
After 10 min idle / warm up: 54.8mV
After 20 minutes @ loud volume 56.0mV
10 minutes later: 55.0mV

Speaker output voltage offset: 36.7mV

I hope to complete biasing the remaining 3 modules sometime this week.

As for the sound?

I don't know how Hugh does it, but like all geniuses, they just do it like magic (step aside there, Gandalf!). I was playing through my iPod in mono channel (i.e. monoblock), and the music sounded more detailed, "lusher" and more full-bodied than my mildly-modified US$1100 VideoLogic Sirocco Pro secondary sound system. (The VideoLogic Sirocco Pro is no low-brow stuff. Do a search on it and read the reviews).

I can't wait until I get all 4 of these AKSA 100W N set up and mate it to the TLP Nirvana + Bolder smART DIO + CAL Delta Transport + Mission speakers.

Wish me luck for the remaining 3 monoblocks!

Cheers,
-Lost81

Lost81 · « **Reply #8 on:** 13 Jul 2004, 02:40 am »

Just curious here:

The manual said under +/- 50mV is acceptable for the output offset voltage between Speaker Output and Earth, while 15mV is typical. Does that mean that my final measurement of 36.7mV, with bias set at 55mV, is too high?

I don't want to end up damaging my speakers as parts for it are hard to find in USA (i.e. they are British speakers).

Also, anyone had to replace C4 before?

The stock set up instructions said:
"Measure the voltage between R5/R6 and earth. It should be approximately 30 volts. ... If the voltage comes up to 30 volts, replace capacitor C4 with a new component before proceeding."

The Nirvana set up instructions said:
"Switch on and measure the voltage at the junction of R5/R6 to earth. It should be between 28.5 and 30.5 volts. ... If the voltage comes up to 28.5 - 30.5 volts, replace capacitor C4 with a new component before proceeding."

My monoblock #4 100W Nirvana measured 29.8V.

So, should I replace C4?

If I have to, I probably will order some Elna Cerafines...

Thanks for any answers!

-Lost81

AKSA · « **Reply #9 on:** 13 Jul 2004, 03:27 am »

Benny,

Does it really say that? I must check; if so, it's WRONG.

If the voltage FAILS to come up to 28-30V, then C4 should be replaced IF offset falls within tolerance. Not otherwise.

Your C4 is just fine!

Cheers,

Hugh

Lost81 · « **Reply #10 on:** 13 Jul 2004, 04:15 am »

Quote from: AKSA

Benny,

Does it really say that? I must check; if so, it's WRONG.

If the voltage FAILS to come up to 28-30V, then C4 should be replaced IF offset falls within tolerance. Not otherwise.

Your C4 is just fine!

Cheers,

Hugh

Hi Hugh,

Yep, it says that.

The versions are V1.74 for both the stock AKSA 100W instructions and the Nirvana 100W instructions.

Cheers,
-Lost81

AKSA · « **Reply #11 on:** 13 Jul 2004, 04:34 am »

Hi Benny,

You had me worried, so I had a gander at the instructions again.

Quote

With the fuses NOT YET INSERTED, now measure the voltage between R5/R6 and earth. It should be approximately 24 volts. If it is less than 15V, remove C4, and re-measure. If the voltage rises to 24 volts, replace capacitor C4 with a new component before proceeding.

I've bolded the section which caused difficulty; note that if the voltage measures less than 15V, you should remove C4. NOW, if it comes up to 24V, then you should replace the original capacitor. I can see how the confusion arises; you need to have a lower voltage with C4 in place, then remove it, and IF IT RISES, only THEN do you replace C4.

I will revisit this wording because clearly it is confusing. Thank you for pointing it out.

Oh, and Benny, your amp is just fine.

Crank it up, let the listening begin.....

Cheers,

Hugh

Lost81 · « **Reply #12 on:** 14 Jul 2004, 07:02 am »

Ah, that makes it easier to understand now!

Whew!

I went to automotive shops today, looking for those female connectors to the spades.
I think I found some.
They do use a lot of tin-plated copper in their connectors.
Weird that some companies charge the earth for roughly similar parts?
Hmm...

Desperately looking for time to bias the remaining 3 monoblocks,
-Lost81