Valhalla - AKSA 55

SamL · « **Reply #80 on:** 28 Aug 2003, 02:30 am »

Thanks Hugh for the timely review.
I am sure you will do the same for aksa100.

At the same time, I'll save the money and wait for the official Valhalla.

Sam

Malcolm Fear · « **Reply #81 on:** 28 Aug 2003, 04:03 am »

Hi Steve
I had the opportunity of having 2 AKSA 55 here. We modded one, and could then A/B them. E-Type Phil also popped over. The three of us heard a huge difference between the Nirvana and Black Gate. Riken Ohm mods.

ginger · « **Reply #82 on:** 28 Aug 2003, 04:38 am »

It has been my educated (I'm an Electronic Design Engineer) guess that C3 is reasonably important to good sound. The fact that it has only a few volts across it means its a great contender for an Organic Semiconductor (OSCON) Cap.

I'm in the process of building a 55W Nivarna - previous owner of a 100W.

Will be using an OSCON for C3 and will let you know results.

Where voltage rating is NOT a problem ie below about 35V OSCONS are reputed to leave even Blackgates for dead. My experience is that for Cathode Bypass Caps in my valve amp this is certainly TRUE.

I'm also of Hughs view that Blackgates are just too bloody expensive and am taking a bloody minded, moral stance against using them.

If you are designing for a commercial market then you can justify using them since being able to say it has blackgates has some marketing appeal.

Cheers,
Ginger

AKSA · « **Reply #83 on:** 28 Aug 2003, 07:15 am »

Interesting discussion

I am gratified with Ginger's post.....

Now, Malcolm, let us enjoin a little debate here

I would be willing to bet that most of your good sound is coming from the Rikenohms, particularly the base stoppers on the output devices. These resistors are GOOD, and I like them (although I'm starting a military campaign to Japan to launch an ambush on the headquarters of Riken Inc, please tell no-one).

Any passive component which stands in the way of the signal will have profound influence on the sonics. This applies also to the feedback resistor. Given the cost of the Rikens, you'd be better off spending the money there.

Ah, how I enjoy a little theology! Carols, anyone?

Cheers,

Hugh

Malcolm Fear · « **Reply #84 on:** 28 Aug 2003, 10:36 am »

Hi Hugh
I am starting to forget where I am. I guess you are talking about the AKSA 55.

We (Vic and I) only put Riken Ohms at R9 (signal path) and R1 (because we seemed to have a couple each of that value). The sound is sweeter with Riken Ohms.
Which resistors are the base stoppers?

cmscott6 · « **Reply #85 on:** 28 Aug 2003, 01:18 pm »

Um, I have to beg to differ with you folks about the Black Gate mods. When we subbed the caps, we only did one channel and made sure not to determine whether it was right or left. The difference in the modded channel in terms of depth of image and clarity was fairly obvious - especially on percussion. All of those listening chose the modded channel. I do agree with Hugh, though, that it is a subtle improvement on the Aksa "sound", and not a change in the sound as some have feared.

You folks really have me excited to try those Riken Ohms, now.

AKSA · « **Reply #86 on:** 28 Aug 2003, 10:55 pm »

Thanks Chris,

My considered judgment would be a BG for C3 only, and Rikenohms for the feedback and base stoppers. This is not too expensive, and will give very strong sonic benefit.

However, there may be more in it yet, so I continue to push the boundaries of the design. Ultimately, all this will appear in the next upgrade, which will probably be called (in keeping with modern marketing) Nirvana Plus......

Cheers,

Hugh

cmscott6 · « **Reply #87 on:** 29 Aug 2003, 12:44 am »

Can I show my ignorance and ask which are the feedback and base stopper resistors?

Thanks!

Chris

PSP · « **Reply #88 on:** 29 Aug 2003, 04:02 pm »

Hi Hugh,
I concur regarding BG at C3 is a big effect and is probably in some sense cost effective. But I have had a BG at C3 for several months now, and I heard a very nice improvement in the last few days after I substituted BGs for the other three 100uf electrolytic caps on the board. I wouldn't argue that this change is something everyone would be willing to pay for (that's the hurdle you face, Hugh) but I'm happy with the change and I'm willing to bear the cost.

What I heard was smoother highs and better imaging. The imaging judgement is based on listening to one recording only: I had seen a recomendation for a recording of Beethoven's Choral Symphony (it's at home and I'm writing from work... I can fill in the details if anyone is interested)... when I listened to it a few weeks ago, the image seemed disjointed, synthetic (i.e., like it was closely miked and heavily mixed), not pleasant at all. Two nights ago, after maybe 40 hours of burn-in on the BGs, the image was absolutely glorious... very coherent, broad, and stable. I could easily imagine the orchestra playing 30 feet in front of me.

I think I gotta get some Rikens...

Peter

ginger · « **Reply #89 on:** 1 Sep 2003, 06:17 am »

Whats all this about Riken Ohms etc.

Historically resistors were made from Carbon Film deposited on a ceramic base.
The sound of vintage (old) Carbon Film resistors is characterised as smooth and warm BUT their value tolerance, their temperature stability and their noise output are seriously crap. Never the less thet can be used to advantage in the right place. Eg the grid stopper resistors inthe GK1.(the right place is NOT in a low signal level preamp - none of these in the Phono Preamp PLEASE)

In the late 70's carbon film was progressively replaced by Metal Film. They have good value tolerance and temperature stability and low noise BUT their sound is often characterised as "Spikey and Cold". Despite this these are the best choice in low signal level areas like the phono preamp simply for their low noise characteristic.

There are some manufacturers of "high quality" metal films BUT these generally are bloody expensive.

There are also some "Metal Foil" resistors out there with a sound which is characterised as "80's High End" BUT once again are very expensive.

Next came Tantalum Resistors. Tantalum Capacitors seriously suck for audio use and so it is a complete mystery to me why tantalum resistors sound great. I'm fairly certain that production of these has ceased and so if you don't have them in stock your not likely to find any.

Last BUT cetainly not least there are the MODERN Carbon Film Composite Resistors like the Riken Ohms. Their sound approaches the warmth and smoothness of the "vintage" carbon films BUT without the tolerance, temperature stability or noise problems. They are also extremely fast (ie low capacitance and low inductance). These are the BEST choice for critical resistors in the audio path.

This is why they are suggested in above discussions for the main series feedback resistor (82K from memory - BTW this is the largest value commonly available) and the 100R driver transistor base resistors.

Hope this is of some benefit to those following this topic and that I haven't brushed off too much fairy dust for you.

Cheers,
Ginger

Malcolm Fear · « **Reply #90 on:** 1 Sep 2003, 09:21 am »

I agree. I use Vishay/Dale metal film resistors in the phono stage of the GK-1.

econ · « **Reply #91 on:** 4 Sep 2003, 01:05 pm »

Would like to second CMSCOTT66 's request: could someone translate for us what base stopper, feedback, signal path , low signal path,resistors and / or capacitors means ?

Ideally if they could be referred to by their circuit diagram designations
it would make a huge difference to those electronic airheads like me who seek enlightment.

JohnR · « **Reply #92 on:** 4 Sep 2003, 01:49 pm »

Base stopper is a resistor in series with the base connection of a transistor to prevent oscillation -- assuming this is the same idea as a grid stopper on a tube...; the feedback resistor connects from the output of an amp to the input, look at the circuit and you'll see a resistor that goes from the speaker output back to the first or second transistor from the input; low signal path... well there's a general belief that since many components alter the sound that fewer is better.

BTW I believe vintage resistors are carbon composition not carbon film - ?

AKSA · « **Reply #93 on:** 4 Sep 2003, 10:35 pm »

I've been avoiding this question to avoid misinformation for those who do not have the circuit, but yes, John, is exactly right.

Cheers,

Hugh

ginger · « **Reply #94 on:** 16 Sep 2003, 06:43 am »

In a moment of bordom (acute) I was doing some research on Transient Intermodulation Distortion and came across a paper which claims that any reactive component (that is Capacitors and Inductors) suffer a form of "shock" excitation giving rise to a "time displacement" distortions. The paper claimed that this effect can be cured by paralleling the reactive component with an energy dissipating resistor chosen to produce a current draw of 1 to 5 milli-amps.

IFF there is any merit to the claim then the bleeder resistors introduced across the power supply filter caps would not only be a safety thing to discharge the caps after turn off BUT would also offer sonic benefits.

Anyone care to offer an opinion from experience.

The same paper suggested a similar resistor across the power transformer secondaries ahead of the rectifier. I think I would want to be convinced that the Capacitor Bleeder Resistors offered sonic benefits before trying the transformer secondary shunt resistors. If you are going to try these be careful of the power rating of the resistors.

Anyone trying this - please post your results / opinions

Cheers,
Ginger

AKSA · « **Reply #95 on:** 16 Sep 2003, 07:11 am »

Ian,

I've seen this paper too, forget where. It seems to me to be credible, and has repercussions for power supply design. Could it be based on the damping of ringing of a simple parallel resonant circuit?

I've just sent you an email.......

Cheers,

Hugh

Jens · « **Reply #96 on:** 4 Oct 2003, 10:20 am »

Exactly which positions (R?) on the amp boards would benefit from the Riken Ohms?

Several people have asked for this information in this thread, but after re-reading everything I still haven't found the exact information.

Please, could someone identify the positions for those of us with feeble electronic knowledge?

Cheers,

EchiDna · « **Reply #97 on:** 4 Oct 2003, 11:58 am »

Quote from: Jens

Exactly which positions (R?) on the amp boards would benefit from the Riken Ohms?

Several people have asked for this information in this thread, but after re-reading everything I still haven't found the exact information.

Please, could someone identify the positions for those of us with feeble electronic knowledge?

Cheers,

I think it is not being stated to help preserve the IP of the AKSA Nirvana? anyway, it is probably only fair to Hugh if we don't publish half his circuit info here which could hurt his future sales. Just my $0.02 worth

Jens · « **Reply #98 on:** 4 Oct 2003, 03:57 pm »

Quote from: EchiDna

Quote from: Jens
Exactly which positions (R?) on the amp boards would benefit from the Riken Ohms?

Several people have asked for this information in this thread, but after re-reading everything I still haven't found the exact information.

Please, could someone identify the positions for those of us with feeble electronic knowledge?

Cheers,

I think it is not being stated to help preserve the IP of the AKSA Nirvana? anyway, it is probably only fair to Hugh if we don't publish half his circuit info here which could hurt his future sales. Just my $0.02 worth

Hi EchiDna,

Aren't you being a bit paranoid here?

Even I with my limited knowledge of electronics know that stating for example that the positions R3 and R7 are the ones that will give the biggest benefit when replaced with Riken Ohms will not compromise the IP of Hugh's grand design. If one does not already have the schematic such a statement would mean nothing!

Hugh, don't you agree?

Seeing that this thread has become very long and that it has become quite difficult to extract information, I am trying to prepare a sum-up of the tweaks that are most worthwhile and will post it here for the benefit of all. However, some precision is necessary if it is going to be worth anything. Again, there are lots of non-wizzes out there when it comes to electronics.

Cheers,

AKSA · « **Reply #99 on:** 4 Oct 2003, 10:26 pm »

HI Jens,

Interesting comments here! In truth Echnidna has a valid point, but clearly there is a balance between my sales and customer service. Finding that point is the tricky bit, but regardless of how you look at it, this information will improve the sonics at no profit whatever to me.

If you'd like to go replacing resistors on the 55W with Rikens, here's the list:

R1, R9, R13, R14. That's it. The others are not worth changing.

Of the caps, only C1, C3, C4, C2 and C7 are significant. The others make almost no difference, and that includes the rail caps.

Just replace with identical value parts in Riken and either BG (if you are feeling philanthropic!) or Nichicon Muse.

I'm confident, and I have tried all these mods (and I'm only 1 man with the usual subjective preferences) they take the present design to the limit. More is probably possible, and I'm thinking on this as we speak!

Take great care as you remove components. Use a solder sucker or braid, because lifted tracks on re-heat are a real possibility.

Hope this nails it!

Cheers,

Hugh