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Naksa vs others, again

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Hi Andyr,

Please don't start a war on this, that's absolutely not my intention. Like I wrote, it must be that something went wrong becuase I cannot believe it myself. I'm on to it and I'm the first to put the blame on myself if it was caused by something I did. Why did I write this, just because I strongly believe something was wrong and has to be fixed. I'm not golden eared, absolutely not and I'm not saying everybody is incapable of listening. I work as a sound engeneer and I work with live instruments on a daily basis and I know what they sound like, that's my reference, nothing more, nothing less and I do immediatly recognize if something comes close to the real thing or sounds artificial. (No, I'm not saying here that the NAKSA sounds artificial, so pleas don't read it that way) Sometimes there is a thin line between reality and artificial like with the UCD amps. On the other hand, I have never ever heard any difference between mains cables wich some people believe make all the difference in the world. So, golden eared, no I don't think so, not in the audophile sense of the word, noipe. Please, read and do not start a war here and lets just stop this discussion till I have sorted thing out. I'm not bashing anyone, I'm writing my observations, my disbelieve and my doubt that's it, there's nothing more to it, really
 
Well,
I have a Soraya and a Lifeforce here and the Naksa is a later generation than both so it should be an evolution of the house sound and I am truly surprised to read that it sounds worse than all the amps you have listed...

Of course you are being very honest and I truly respect that, not questioning your motivation, especially the way you describe why you chose to audition them in the first place, resonates quite well with me. What I would do is I would try it in another system, sometimes we tailor our equipment so much to the room or the source or something else that a component like the AKSA might be out of place.

The Soraya belongs to a friend and it was auditioned in a system where it sounded distorted and cracks were constantly heard, later we were told that the speakers had a custom series filter with no caps. Not sure if that was the reason but the Soraya was definitely not a good combination with them, sounds fabulous with a Swans F2.3B though, you would say this is a kW amp, such is the control over them.
 
hi Hugh,

...
Anyways, I understand you are not waiting on a negative review and like I said, things go slowly here nowadays and I guess there must be something wrong because I cannot believe that they can't sound any better then this. I will figure it out. Offcoarse you are making progress in amplifier design but this design had such a high claims of it's quality, these claims if true should easily survive 5 years in audio. Why on earth would it otherwise be possible that it gets beaten by a 30 year old design (The Hiraga). Again, something must be wrong in my case and I'm on to. The amps where on the shelf for quite some time due to the illness of my girlfriend but now I have time again

I don't want to get in the way of you buiseness so if you want I'll just delete my posts, no problem whatsoever. It's not my intention to diss ASPEN, I only post my findings. And I just want to figure out what the hell went wrong, did you really think I wanted to write a negative review, no absolutely not. If i would to sell the NAKSA's again people will google them and will find this review. So it's in my own interest to get this figured out.

Just asked the moderator to delete my last two messages, don't want to get in the way of your business. Will report new review in other forum when things are sorted out

Hello

I've read your post before it was deleted, your NAKSA70 may have oscillations or others problems, I have myself a Naksa and it don't sound like you describe in your post and really not like a typical class AB sound.

Can you find a guy who have a oscilloscope and a 10 khz squarewave signal generator, to test potential oscillations of the NAKSA70 ?

All ground are ok ?

Bye
 
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Yes, I think it might be something like that. First thing I'm going to do is finally finish the second one, it's been on the shelf for way too long and see how this one sounds.

I'm allready looking for a new oscilloscope, my old one has been accidantly parked next to a woofer with an 8 inch magnet on it for a long time, cathode ray tubes don't like that. I've got some time this week to get it sorted out.
 
Sjef,

Could I ask a few questions about your N70?

Did you buy the entire transformer and case from Jens, or just the modules, then added your transformer?

This might mean that your rail voltage is not the correct 42V at DC. Much depends on the rail voltage, and particularly the output stage bias.

Thank you Gaetan, great ideas,

Hugh
 
Finally finished the second amp today (after almost a year, shame on me) and guess what. this one sounds much better right from the start. No midrange hardness and much much better treble resolution and because of that bass is better defined as well. This is getting somewhere. Measured both amps. Offset voltage varies from almost zero to about 30mV wich is fine. Bias current settles at around 65 to 70mA on the first one and around 85 mA on the second one. First thing I'm going to do is to raise the bias on the first amp to 85mA. Another strange thing is that the transformer of the fist one is getting pretty warm after a couple of hours, the transformer of the second amp stays totally cool. The first amp also has some very low level 50hz hum the other one is totally silent., both are build exactly the same way. There is absolutely something wrong. Maybe the transformer is saturating or there is a almost short circuit in a winding. I'll try and swap transformers and see what happens. I will also build a mains dc blocker and see if that fixes it.

Anyways, I'll stop posting about it over here , just wanted to let you know, that's all
 
Hi Sjef,

This is much better news! Thank you for telling us the story.

I generally send the bias a bit higher than 85mA, around 100mA for the N70, and it does have an influence.

You raise the transformer heat. This might indicate one of the two transformers is a bit higher flux; please check the voltage on the rails are at +/-42, and both identical. A difference in the two rails might be indicating there is an unbalance in the transformer secondaries, and I know this affects any audio amp.........

Cheers,

Hugh
 
Hi Sjef,

This is much better news! Thank you for telling us the story.

I generally send the bias a bit higher than 85mA, around 100mA for the N70, and it does have an influence.

You raise the transformer heat. This might indicate one of the two transformers is a bit higher flux; please check the voltage on the rails are at +/-42, and both identical. A difference in the two rails might be indicating there is an unbalance in the transformer secondaries, and I know this affects any audio amp.........

Cheers,

Hugh

Um, dumb but all too common - check the transformer secondaries are correctly connected. Transformer working flat out doing nothing.......
 
Yes maybe you are right and could it be helpfull to others if they ever face the same problem.

Hi Hugh,

I have read in the instructions that the N70 is supposed to have 85mA +/- 10mA of bias current. Are the later production versions set at 100mA or was this a setting for personal use ? Does this have an influence on long term stability (I guess not) I also thought that the bias was self limiting at 150mA, is that right ? The reason that I haven't set the bias allready is becuase it seems to be varying continue. At the moment that I think it's stable for minutes or even 20 minutes it start varying again. The variations are getting smaller after some time but I let the amp running idle with a voltmeter attached for two hours and it still varies after this time. That makes it hard to adjust the bias, what to measure ? The peak bias ? this hardly ever exceed 75mA on this one. Left and right channel are not varying in the same manner so it's not a matter of temperature only. This is an amp that could benefit from being on power 24/7

I might try to raise it to 100mA. This way the amp will be operating in class A most of the time. Since I only intend to use them in an active setup for mids and tweets with medium high sensitivity.
 
Hi Sjef,

Thank you for coming back to me!

Yes, 100mA seems to be better than 85mA, and yes, it's a preference! The bias is not self-limited at 150mA; as long as the amp is cooled well there is no problem with this.

Bias control on all AB amplifiers is problematic, and I improved this on the N80, which has rock solid quiescent in all situations. The N70 has a tendency to move to higher quiescent in 4R loads and in high temperatures with insufficient cooling. Cooling is important of course in all amp. The variations of quiescent tend to minimise in operation but you'd be hard pressed to find a difference in the sound. It's a small 200R trimpot, blue, near the four 4148 glass diodes. Turning it CCW increases the quiescent. I'd suggest that 75mA is a bit low; 100mA is better....... and I would not bother leaving it on all the time, BUT, it takes 20 minutes to give the best sound.

You might try, as the previous poster suggested, reverse ONE of the secondary transformer windings on ONE of the rails, that is, either top side of the pcb, or the bottom side. Just remove the two spades, reverse them and refit.

Cheers,

Hugh
 
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