A year or so ago I published the evolution of building my full range Melquiades amplifier:

http://www.goodsoundclub.com/Forums/ShowPost.aspx?PostID=2502

Now, I am staring a thread where I will cover the progress of building Dima’s “Zarathustra II” amplifier. I will besloew but it will be built eventually. The “Zarathustra II” is up to 200W in pure class A1. The amplifier is hybrid with Melquiades’ input stage in SRPP, high current (upto 60A, 90A peaks and 5A constan bias) bipolar output stage, input choke filtered supplies, the Dima’s proprietary “Newton Bias” (it is fixed bias with no cheap tricks for class A operation, still it has some “kinkiness” atop of it). The “Zarathustra II” will have some interesting “activities” with it and I am interested to see what it will do sonically...

http://www.goodsoundclub.com/Forums/ShowPost.aspx?PostID=4023

The project stared proximally a year ago and Dima had alredy built for me the amplifier section itself. It is 3.5 layers assembly with SS layer at the bottom; with bias, control and automatics layer at the second level (large an convoluted circuitry) and with the tube stage at the top floor. Now it is my part of the game to package everything and build the power supplies for the thing...

I have a well defined design how the amp should look like and how everything might be packaged electrically and magnetically and today I was for a first time tried to implement that layout with the largest parts of the amp. I spent a few hours today but was not able to do what I need dispute the relative simplicity of the task. It looks like it will be a painful journey to package the amp in design I want it to be…

In the end, completely loosing, I did not fine anything better to do as send to Dima the picture of the real-estate that I am fighting with… I made a shot of the pre-dissected Zarathustra.., and then I asked myself: why do not bump it on my site? Here were go…. the Zarathustra in semi-infantry. The parts themself and what my Koshka thinks about it….

hagtech wrote:

Yes, steel chassis can be both good and bad.  It likes to conduct magnetic fields, so you have to treat things appropriately.  A little spacing under a choke can go a long way.  Otherise you have a 120Hz motor.  I have another trick that helps with the far field.  The stray magnetic spray from the Hammond chokes is pretty big.  Helps to measure it to see which directions it has maxima and minima.  Then you mount the coil with the proper aim.  Usually away from the input tubes.  My trick is to use two chokes instead of one.  Wire them up in parallel or series, then mount them side-by-side and magnetically out of phase.  You get quite a bit of far field cancellation.  I did this in the Trumpet.

Jim, and perhaps others. I have question.

Packaging how the “Zarathustra II” chassis I have a chose for selection of the materials for my power supply’s firewall (the wall on which the chokes will be sitting). Sure, for the sake of magnetic shielding the steel wall would go fine but I afraid that 2 input chokes with 5A in each will ignite steel very enthusiastically. (I have this problem in my Super Milq). Jim, I what you did in your Trumpet with side-by-side and magnetically out of phase chaos was great and I wonder if I doing it at those currents would be enough. As you see at the image of the Zarathustra PS my chooks are in the oppose wings and one of them care plus and another minus. Still, would it be better to go for some kind of other material wall that would not be vulnerable for “singing” under the stay fields but at the same time do the magnetic shielding. I was thinking perhaps to use an aluminum wall with multiple layers of Magnetic Shielding Coating of to use behind an think aluminum wall a layer of GIRON Shielding Film of NETIC and CO-NETIC Alloys. Did anyone tried it and then actually measured with gaussesmeter the effectiveness of got it?

I am sure that for the folks who do audio design professionally it should be a routine task to make those decisions and in my case, since I do juts one unit I am not restricted by any financial considerations.

How about some sort of composite?  You need the strength of steel, these parts weigh a lot.  But maybe a different approach.  Maybe something like plywood glued to a sheet of aluminum?  That would give you the solidity and conductivity.  I think it might also work as mechanical damping.  You could put the wood on the topside, which means the metalwork does not have to be too clean in appearance.  Copper would work even better.

Or maybe something like corian instead of plywood?

The hum-bucking windings help mainly in the far field.  That keeps interference from the amplifier stages at a minimum, but does not change the "motor" characteristics in its own mount.  Another trick I recently used is to remove the bells and flip the core, so that it effectively mounts the tranny upside-down.  Don't think that will help you here, though.

I worry about the use of too much mu-metal and the like.  It opens the possibility of too much distortion and influence on the magnetics to the point of audibility.  In this case, less is more.  Try not to force good behaviour, but rather encourage it.  Keep the chokes and trannys out of prison and let them breathe.  I think all they might need is a little space, or rather distance.  A clever arrangement with symmetry may end up providing all the cancellation you need.

jh

After consulting with a few peoples I decided to use the brutal force method: use a regular steel wall, but to make it the wall of the high thinness (~3/8”) and weld it to the chassis. The presumption is that if the wall will be rigid and not “trembleable” then it might vibrate but will not produce any noise. To assemble this thing with the weld walls would require to have fingers of a damn octopus… but it will be juts one amp. Once again… here is my permanent pain: why I do not have somebody to recruit and to pay off in order do not do it myself? Then I will be able to do what I do the best – to bitch what about other’s mistakes.

It is Dima’s and my strong conviction that the most beautiful in this world comes to our lives for free as a gift. Some people gave to us a gift of thier experiences. We in our turn would like to in-reach public (no mater now moron the public might be in it’s majority) sharing the Melquiades.

I bucked up and bought a Lightspeed Attenuator from George. I've played music through it for a handful of hours, so I have but a preliminary perspective on its sonics. I think George has a winner on his hands. First impressions are: the unit is quiet as the night is dark, it excels in coherence and resolution, and high frequencies are to die for---holy cow, no grate or edge, and what delicacy. The HFs alone are worth the price of admission. Comparison preamps are an Emm Labs active pre stuffed to the gills with teflon bypass capacitors, a DIY Paradiso TVC and an Audio Consulting Silver Rock TVC. The latter is my reference; it beat out a Placette I once owned, and comes close to the LA, but mucks up the HFs in comparison. Thanks for a great product, George. More listening will tell, but the LA seems an appreciable step forward.

Wow, what a preamp! Shockingly good! I can find no fault with its sonics. That, I suppose, should be expected because it so elegantly solves so many problems associated with preamp design. I've had several, mostly involuntary thoughts listening to it, like, "geezus, that actually sounded like a cymbal." I won't belabour the others because they all practically come to the same point. Best pre I've heard by a considerable margin. George deserves a fricken award.

Another day of listening and I have yet to hear anything I dislike about this unit. Everything is three notches more realistic through it. Why does the Lightspeed perform so well? I'm familiar with the difference changing a cheapo resistor for a Vishay makes. That difference is considerably smaller than changing my previous reference pre, the AC TVC, for the Lightspeed, and the AC beat out a Placette. Personally, I'd place my money on George's contact theory.

I tried to explain this contact phenomena before about 200 posts ago in this thread, I’ll try this time to explain what I found a bit more clearly. First it had nothing to do with corrosion of the contacts in potentiometers and switches, it was the fact that all had a very small pin point size contact area between the surfaces. In potentiometers it is even worse because the pressure is so light as not to wear out the carbon or plastic resistance track, Switch resistors are almost as bad especially if the rotary switch is of the single leaf variety, dual leaf is better one each side of the common, but still I saw a problem even with these. The way the problem was found, I managed to borrow for a day a very trick digital 10 gigahertz for memory storage oscilloscope from the CSIRO a massive research company here in Australia, god knows what it was worth 50k or so it made my high end Tektronix look like a toy. With this scope I was able to store and magnify the corner’s of a cd level 1 to 2 volt 1k square wave, and what I saw was an extremely high oscillation embedded in the original this oscillation disappeared once I put extra pressure on the wipers of the pots and switches with a non conductive toothpick, all I can say is that the rise time is 100’s of volts per micro second and it causes the contacts to become poorly conductive at these levels and creates a diode effect and tries to rectify the AC music signal into DC, I’ve for want of a better word called it contact bounce, you guys call it what you will but the proof was there and disappeared once more pressure was applied, in the case of RCA connectors the area is 10 to 20 times larger and the pressure much higher, so the phenomena does not seam to happen, but I think maybe it does, ever wonder why your system sounds cleaner after you’ve done a clean up of your RCA’s. And please all you non believers, don't say anything till you've seen it for yourself, on a scope like I had the good fortune of borrowing. Not on a toy 400mhz Tektronix like mine, you won't see it. Cheers George