Aksa 100W-N Complete!

MattCassidy · « **on:** 20 Jul 2004, 12:23 am »

Hi All, Just a quick one to say I am now an official DIY'er having just completed an Aksa 100 with Nirvana upgrade.

My sincere thanks to Hugh for his help and patience with a newbie like myself, it is always nice to deal with a gentleman! Also my thanks fo tot he members of this circle who have patiently answered many of my questions without succumbing to the temptation of making fun of me!

As for the Amp it is sounding good although i am only powering music from my laptop at present as i have no preamp so far. GK-1 here i come.

I will post some pics of the finished product soon.

kind regards
Matt

Malcolm Fear · « **Reply #1 on:** 20 Jul 2004, 07:12 am »

Congrats on the AKSA.
You could go buy a 20k logarithmic pot from Dick Smith (Radio Shack), shove it in a metal box, add input and output leads. A $10 passive pre amp.

MattCassidy · « **Reply #2 on:** 20 Jul 2004, 07:14 am »

That sounds like a fine idea malcolm, think I will. It will probably take a while to get the GK-1 sorted.

Matt

Malcolm Fear · « **Reply #3 on:** 20 Jul 2004, 07:34 am »

While your at it, set the pot up as a fake shunt, by using a 30K resistor.

MattCassidy · « **Reply #4 on:** 20 Jul 2004, 07:57 am »

Huh? you know not the depths of my ignorance! I get the resistor bit where do I put it so it becomes a shunt?

MattCassidy · « **Reply #5 on:** 20 Jul 2004, 10:15 am »

hello again, I gave the Aksa 100N a bit of a floggin this arvo. Geez Louise it sounded really good now that it has about 12 hours or so of running up! Some righteous base compared to my old amp! and lots of details.

but

At one stage though the right speaker sputtered out.....not completely but mostly, only a couple of feeble sounds. I stopped the music, changed the track and no more problem..It was only when I played it fairly loud, and i could not get it to repeat this, i thought perhaps a short to the chassis of one of the binding posts, so with the speakers detached I checked and there was an open circuite between the binding post and the chassis..any other suggestions?

AKSA · « **Reply #6 on:** 20 Jul 2004, 10:35 am »

Matt,

Check that the binding posts NEVER touch the chassis, especially if the star earth is connected to the mains/chassis earth.

However, don't be concerned, because if it recovered no problem it's most unlikely you have damaged anything.

Cheers,

Hugh

MattCassidy · « **Reply #7 on:** 20 Jul 2004, 09:42 pm »

Thanks hugh, I am not sure if this was the problem but was curious.. I am pulling it apart to check things out, I did make sure there was an open circuit with the DMM when I stuck the case together. Is there anything else I should look for?

My star earth is currently no connected to the case and I have heard no evidence of Hummm so far. I have to do the final final bias test today then hoepfully all shoudl be sweet.

Cheers
Matt

Malcolm Fear · « **Reply #8 on:** 20 Jul 2004, 09:55 pm »

>>Shunt volume.
Normally on a pot, the signal goes to pin 1, the output comes from pin 2 and the earth is pin 3.
With a shunt, the input goes through a 30K resistor, then to pin 3, then to output.
Pins 1 and 2 are joined together and go to earth.

Greg Erskine · « **Reply #9 on:** 21 Jul 2004, 12:43 am »

Hi Malcolm,

I just started reading about stepped attenuators and am curious about the "shunt" setup. I was wondering what effect the variable impendence has on the AKSA amp. With a 30K resistor and a 20K pot the impendence varies from 30K to 50K. Am I right? I imagine this is OK matched to 47K input impedence of the AKSA?

Thanks
Greg

AKSA · « **Reply #10 on:** 21 Jul 2004, 02:21 am »

Greg,

My calcs tell me it's no problem at all. Mal, can you confirm that the low volume settings are reasonably progressive, not too tetchy?

Cheers,

Hugh

Malcolm Fear · « **Reply #11 on:** 21 Jul 2004, 04:42 am »

Hi Greg
I don't know about the maths. It sounds fine to me. Plus you can vary the value of the resistor to get a usable volume range. Plus you can then start switching in different brands of resistors rather cheaply.

Aren't you in the process of making a ladder attenuator. You won't need the shunt mode -- would you?

Greg Erskine · « **Reply #12 on:** 21 Jul 2004, 07:28 am »

Malcolm,

You're right, I'm looking at a ladder, but from what I can work out the only difference is with a ladder, you effectively have 23 shunt resistors and therefore you can adjust the impendence for each setting. This of course means 23 x Rikens and that means $$$$. I imagine, I could wire up a ladder to share one one resistor and therefore be a shunt. I don't really know yet? I could be missing something?

Hugh,

I really don't understand the implications of putting a 50K impedence in front of the 47k impedence of the of the AKSA. I guess it means at low volumes you have approx. 50K||47K overall impedence. At mid pot setting you have 25K||47K. Is this why you stick a pre-amp in between to give you a constant impedence?

Greg

bluesky · « **Reply #13 on:** 21 Jul 2004, 07:33 am »

Hi Everyone

I can highly recommend Chris Taylor's site for a volume pot. For $20 you get an Alp's that has a heap of resistors in it and it sounds great!

I had to get another one after destroying the one Hugh supplies in the TLP kit.

Cheers

Ian

AKSA · « **Reply #14 on:** 21 Jul 2004, 08:04 am »

Greg,

A 50K works fine, but a 20K gives a more constant impedance. You have to go to other configurations, such as a T pad, to get constant impedance regardless of volume setting, but in practice all this is a bit academic.

If you reduce the pot to around one tenth of the target impedance, that is a 4K7 pot, then the variation in impedance going into an AKSA is very small. However, driving a 4K7 load is pretty hard going, and certainly many tube preamps would have trouble with this. The average opamp output stage on a CD/DVD player has a source impedance around 100R, so this is a walk in the part, nevertheless the jury is out on whether one can hear differences between a 5K load and a 50K load.

There are other issues too. A 50K load will be far more susceptible to hum intrusion, by a factor of ten times over a 5K load. If shielding is good, however, this is usually not a consideration, though noise issues do intrude if the output is sub-10mV, like a Moving Magnet phono.

You have chanced upon a morass of compromises!

Cheers,

Hugh

Lost81 · « **Reply #15 on:** 21 Jul 2004, 08:11 am »

Quote from: AKSA

Greg,

A 50K works fine, but a 20K gives a more constant impedance.

Would 5K more (over 20K) result in noticeable / significant sonic penalties?

TDK make some 25K attenuators (US$225)....

Although, at that price, I will reserve that level of upgrade for the GK-1

Cheers,
-Lost81

AKSA · « **Reply #16 on:** 21 Jul 2004, 08:44 am »

Benny,

No, that would be fine at 25K, no problem at all.

But OUCH!!! That's serious money for a volume control!

Cheers,

Hugh

Lost81 · « **Reply #17 on:** 21 Jul 2004, 09:26 am »

Quote from: AKSA

Benny,

No, that would be fine at 25K, no problem at all.

But OUCH!!! That's serious money for a volume control!

Hi Hugh,

Yes, that's some serious money for a volume control.

Here's the dig on the unit:

TKD Stepped Attenuator:
The best off the shelf assembled attenuator that you can buy. Discrete resistive elements are used for each position in a series configuration assuring very precise tracking between channels. Mounting is accomplished by three standoffs and screws on the front of the control so only a hole large enough for the 6mm shaft is required in your faceplate. Each stereo control requires a footprint 2.125" H x 1.75" W and 2.0" deep behind your front panel. The shaft extends one inch beyond the back of the panel to which ithe control is mounted. 40 steps (1dB steps to -24dB, 1.5dB steps to -31.5dB, -33.5, -37.5, -39.5, -42, -45, -48.5, -53, -58, -65dB)
Specify 10K, 25K, 50K, 100K or 250K impedance. Éach stereo attenuator $249.

I guess they increased their prices to US$249 now.

I believe it is the same unit on Darren K's GK-1 in Melbourne.

Cheers,
-Lost81

AKSA · « **Reply #18 on:** 21 Jul 2004, 12:47 pm »

Absolutely the same, Benny,

In fact, I fitted it to Darren's GK1...........

It is exquisitely made, the sort of construction you normally see in physics laboratories

Cheers,

Hugh

MattCassidy · « **Reply #19 on:** 22 Jul 2004, 10:14 am »

Well I hate to drag this topic back to it's origins but I took my amp up to my mates place last night, he has a pretty serious setup and
i am happy to say the Aksa 100-N performed like an absolute champion! Without getting to caught up with terminology and analysis (I am not the man for this job) suffice to say the base resolution was fantastic and the detail in the mids and highs was really amazing. I was hearing never before heard sounds in tracks I amvery familiar with. All this after around 12 hrs of running.

On a slightly different note, earlier in the day I went to do the final check on the bias after 20 mins of loudish music. The heatsinks were appreciably warm, however when I went to measure the bias, rahter than being around 48mV as suggested in the Gospel according to Hugh, it was up around 65 on the left and 67/68 on the right, hmmm.. I left it for the recommended 10 minutes idling and the values were still quite high. I re-adjusted the bias to 55, left it for a few more minutes, confirmed it was still 55 and put it all back together and headed over for the test. Sounded great!

I suspect that when i set the initial bias the amp was not warm enough (it was a cold night) as I remember the heatsinks were not very warm at all.

Would this be a likely explanation?? as to why the bias was a bit high?

Do I now need to do the 20 minute thingo again?

TIA
MAtt