[Larry]

I have eventually put GK-1 into a case. At the last minute, I decided to go seperate for preamp as well -- I will put a source selector into a seperate case.

I don't think this layout is the one I like best. What I don't like is the horizontal PCB orientation so that the signal wires are longer. As I have no hum at all, I can live with it.

One thing I need to address is the vibration. Even though the transformers and PCB are mounted on seperate bars, I can feel slightly the vibration on the PCB caused by transformers. If a screw driver is used with one end against the ear and the other on the PCB to hear it, I would say the vibration is loud, which I believe will cause microphonic effects on the tubes.

Any suggestions to isolate the transformer vibrations?

[Raj]

Hi,

I don't know how much heat is around the area in question, but perhaps the rubber you find on mouse mats would be ok to isolate the bars for your trannies from the chassis? I've heard you can take a mouse mat and peel the  decorative sheet off it leaving you with just the foam like rubber, this should be ok to soak up the hum.

Thanks
Raj

[andrewbee]

I have eventually put GK-1 into a case. At the last minute, I decided to go seperate for preamp as well -- I will put a source selector into a seperate case.

I don't think this layout is the one I like best. What I don't like is the horizontal PCB orientation so that the signal wires are longer. As I have no hum at all, I can live with it.

One thing I need to address is the vibration. Even though the transformers and PCB are mounted on seperate bars, I can feel slightly the vibration on the PCB caused by transformers. If a screw driver is used with one end against the ear and the other on the PCB to hear it, I would say the vibration is loud, which I believe will cause microphonic effects on the tubes.

Any suggestions to isolate the transformer vibrations?

Try this, First place rubber gromets through all the transformer mounting holes in the chassis.
Get a bolt then place a flat washer and then a rubber washer. Place this through the transformer mounting tab, then add another rubber washer and then mount the transformer. Then add another rubber washer and another flat washer and then put on the nut and tighten gently.
BE SURE TO SOLDER A GROUND WIRE ONTO THE TRANSFORMER FRAME TO ENSURE SAFETY. THE MOUNTING TAB IS A GOOD PLACE FOR IT.

Andrew

[andyr]

Nice looking job, Andrew.

Can I offer an alternative suggestion - isolate the GK-1 PCB, not the trannies.  The best stuff to use for this is Sorbothane - you can buy sheets of it from various places ... try a place which manufactures "special shoes/prosthetic devices" as a last resort.

The GK-1 PCB looks rather tightly packed (so there may be a lack of available space) but the simplest thing to do would be to make up, say, four "pillars" of Sorbothane to support the corners of the PCB ... with a dab of glue.  Of course, if you are gonna keep removing the board for tweaking purposes, then this won't do!

Or - and I've just thought of this while I'm typing - why not suspend the PCB from wires attached to the top sides of your case?  IE. drill a hole in each corner and run some piano wire from here to the sides?


On an entirely different matter ... Hugh, can you comment on the advisability of enclosing the transformers in metal housings like Andrew has done?

Regards,

Andy

[Malcolm Fear]

Another isolation approach, is to suspend the circuit board from rubber bands.

[andyr]

Another isolation approach, is to suspend the circuit board from rubber bands.

Much better idea, Malcolm ... I'll do it this way when I build my GK-1 (I'm waiting for Hugh to release Stage 3!).  Or you could use the elastic from an old pair of underdaks, eh?

Regards,

Andy

[SamL]

Hi Larry or anyone.

A few questions about the two isolation box used for the transformers.
I plan to do the same for my AKSA100 transformer and wonder if the transformer will generate any heat. Is aluminum better then steel?

TIA,
Sam

[EchiDna]

Hi Larry or anyone.

A few questions about the two isolation box used for the transformers.
I plan to do the same for my AKSA100 transformer and wonder if the transformer will generate any heat. Is aluminum better then steel?

TIA,
Sam

If you are using Torroids for the AKSA, there should be no reason for sheilding. I even went as far as buying some MU metal and found that it was not needed. the transformers were not the problem, it was wire routing that was far more critical in hum removal. With a bit of tweaking, my AKSA became totally silent with respect to hum and noise intrusion. FYI my torroids are only about an inch from the corner of the circuit boards (check the pics in my gallery - link in signature).

[SamL]

Thanks Glen,

Yes I will be using torroids and not needing to isolate them will make my life a bit easier. The wire routing that you mention. It is the main power from IEC to the torroids or it also include the power wire between the power pcb & AKSA pcb?


Sam

[AKSA]

You know, there are many things in audio which defy full and complete comprehension.      Let me explain......

I suggest mu metal shields, Glen proves it ain't necessary, and rather it is wire routing which is important.  I suggest mounting the modules at the rear of the case so input leads can be short, and countless builders, all protesting a hum free zone, prove such precautions are unnecessary.

Then I suggest Star Earth of the amps should be connected to chassis and mains earth.  Someone does it, voila!!  HUM!!!  So we disconnect Star Earth, and on some amps hum intrudes and on others goes away.  

I think this demonstrates that building an amp is a bit like a recipe;  add to taste!  An informed tinkerer can always eliminate the hum;  but it is a common problem and always the last frontier.

Now, another can of worms.  Damping.  

I have had one hour telephone calls from people extolling the virtues of wrapping the pcb in plastic bags full of sand, mounting it on pitch, using various composites of rubber and neoprene and balsa to support the various structures.  My eyes have at times rolled completely out of sight....

There is no doubt that many electronic components are microphonic.  The obvious ones are tubes (though NEVER in my designs!), but also caps, and arguably, semiconductors, particularly the small ones which weigh little and stand on their leads.  Furthermore, there is not yet any storage medium which does not move;  so here, microphonics could reasonably be expected to have profound influence.  The obvious example is a turntable, but CD players are highly susceptible to vibration transmission, with the laser assembly in particular very tetchy.

That said, there are countless examples of materials which 'improve' the sound when added to audiophile components.  Let's explore the electronic side of this observation.

Vibration is primarily dependent on two things;  stiffness, and mass.  If the excitation comes from the music, which is music, replete with a wide range of different frequencies, it's reasonable to assume it will affect small, light parts, which are a little 'floppy', not overly 'stiff'.  

On the AKSA amplifiers, the parts most likely to be affected are the electros, the diff pair, and the voltage amp to a lesser extent.  The outputs and drivers are securely attached, and pretty heavy, so they may not vibrate much, although their excitation currents are high to compensate.  Nonetheless you get the point;  any vibrations will affect the electrical characteristics to a small extent, and may even be manifest in the sonics.

On the GK-1, however, we have a very light assembly, with a long, floppy pcb, and a tube.  There is definitely an issue with attachment here;  we might well mount it on some sort of elastic, compressive medium which will prevent vibrations from persisting.

So, in general, I support mounting on damping materials.  There is not sufficient known about this phenomenon to dismiss it out of hand.  Correspondingly, there is not much literature on this vexed topic, so, we must keep an open mind and admit there might be some sense to it.  We need to understand that complex systems are very difficult to analyse;  music, and the long chain of electronic amplification in all our stereos, is a complex system, and this defies mathematical modelling.  Hence the dearth of information on the topic;  but that's not to say it should ever be dismissed.  It's fair to say that the human ear is extraordinarily sensitive - far more than test instruments - and if 10 people in a group of 15 hear something, it's probable that there's something in it.

Cheers,

Hugh

[SamL]

Hi Larry,

Sorry, don't mean to hijeck you post but your insulated transformer is what I have in mind.
Anyway, as for your question about isolating the GK1 PCB. Well what you can do is secure the GK1 PCB on a heavy material, like corian and then sit the corian (with GK1 on top) on isolation pad or feet.


Sam

[andyr]

Hugh,

A very well explained response, Hugh, and you were covering a number of points which "vexatious builders" have espoused!

However, I would have thought that Malcolm's suggestion to suspend the "floppy" GK-1 PCB from, say, 4 elastic bands at the corners would be a much better solution to prevent vibrations from persisting than my suggestion of mounting it on Sorbothane or some other damping material.  Ya can't get a more springy - yet isolating - solution than elastic bands!

Regards,

Andy

PS: Hugh, I'm sorry, I must take issue with something you said - viz "CD players are highly susceptible to vibration transmission, with the laser assembly in particular very tetchy."

You musta forgotten - in 1980 or thereabouts, when the CD was introduced, the marketing hype was ... "perfect sound forever".  Now we all know that a) marketing people don't lie and b) they know everything!

They knew that LP replay suffered from all sorts of problems to do with vibration etc. and the CD was the solution to all of this ... so you must be mistaken!!

[Larry]

A few questions about the two isolation box used for the transformers.

The transformer boxes are used not for viration isolation. It is used to shield electrical fields. There are two types of fields around transformers: electrical field and magnetic frield. (In fact around any electronic devices but they are strong enough to do harms around transformers.) The interference of these fields to the signals are in two forms: hum and parasitic modulations. Hum is easy to understand and eliminated as it can be heard. However, the parasitic modulations occur when the music is being played, which distort the music waveforms. Their sonic signatures are difficult to be pinpointed but these distortions are measuarable.

The electromagnetic interferences, or parasitic capacitive and inductive couplings, are complex phenomena. Basically, they are the interactions between changing magnetic/electrical fields and conductors (wires/tubes/components) and between signal currents and magnetic/electrical fields, or moving (vibrating) conductors in magnetic/electrical fields. Except hums, most of them occur when the music is being played (there are currents in power parts and signal parts.) So, hum is the first thing to look at but no hum does not mean no interference.

Now how to eliminate the interferences? The electrical fields can be effectively shielded with an earthed metal box, like the one I used for transformers and the attenuator. However, the magnetic fields are difficult to tackle, in particular at home as DIY projects. To shield the magnetic fields, besides using magnetic conducting materials, one has to figure out the direction of magnetism in question, which is related to mounting orientation of the magnetic sources like transformers and inductors, and design a proper structure of magnetic shield to short magnetic fluxes. The box like that I used in the picture will not effectively shield the magnetic fields. Simply housing a transformer in a box will not do much for the magnetic shielding. But better than nothing. Fingers crossed.

So it is always a good idea to shield strong electromagnetic sources. The transformers coming with GK-1 already have  some shielding measures in place. But multiple shileds with air in between are often necessary for best shielding constant and low frequence magnetic fields.

If you look at some high end designs, you will find a lot more shielding measures you don't usually find in common electronics. In particular, power supplies are either accommodated in a seperate chamber or seperate case, or the small signal section is totally shielded. Even for some Class A power amps it is adviced to put power supply in a seperate case and place at least 50cm away from the PCB for minimal distortions. (Electromagnetic fields extend to infinite but their power decays exponentially.)

Having said that much, the issue in this thread is vibration. (I have no hums at all.)  Microphonic effects occur when there is mechanical vibration on tubes, which is nothing to do with circuit design; it's a construction issue. Microphonic effects occur when there are currents flowing or electrons flying, in a vibrating tube; that is when the music is being played. So you can not hear it without playing; microphonic effect does not cause hum. (When I said I heard it loud, I was saying that I heard the audible mechanical vibrations on PCB, not the microphonic effect or hum from speakers.) The vibration on the tubes will modulate the music currents flowing through tubes therefore will distort the music. So, it's critical to ensure tubes are free of vibrations. That's why people find good results by mechanically isolating tubed amps.

Thank you all for your suggestions. I think I will try those ideas, starting with Malcolm's rubber bands.

I think putting the PCB at the back is a good idea. As I had some problems with the shaft extention, I put the PCB close to the attenuator in a rush to complete the case. The shorter signal wire itself is not an issue, comparing to the length of interconnect outside of the case. The issue is the interference in the case; longer wires have more exposure to electromagnetic interferences - we are returning to the issue of shielding.

I plan to do the same for my AKSA100 transformer and wonder if the transformer will generate any heat. Is aluminum better then steel?

I housed the transformers of AKSA100 in a box with some small venting holes. But AKSA100 transformers, and GK-1's, run pretty cool so the heat would not be an issue, I think.

For shielding purpose, steel is better than aluminum.

The case I use is basically a steel case.

[PSP]

Hi Guys...
I don't want to be a "rubber band nay-sayer", but I should point out that rubber is susceptible to attack by oxygen, especially when stretched.  Have you ever wrapped up some papers with rubber bands and come back six months later to find the rubber all brittle and crumbly?  

So, when you stretch a rubber band, the rate of oxidation increases (we could have a lot of fun speculating on mechanism... stretching leads to more exposed surface area, and the mechanical stress probably increases the rate of chemical reactions that would relieve the stress, like oxidation)... blah, blah, blah.  The problem for us is that the mechanical properties of the rubber band almost certainly change with time over a time-scale of weeks and months... so if you get a good isolation design when you begin, your isolation will change (for better or worse) with time.  

Maybe if the design included a lot of rubber bands so that none of them were appreciably stretched.... after all, unstretched rubber bands sit in a desk drawer for years and do just fine, it's only when you stretch them that they go to hell.

Peter

[Malcolm Fear]

Rubber bands

I mentioned rubber bands as a method of isolation.  If you are worried about longevity then you could delve further, if serious and try other stretchy things:

Those rubber "O" rings that are used to suspend the expensive SME turntables?

Strips of innertube. They should last longer.

Surgical rubber. I have used this in catapults. I think this is used in spearguns. It does fall apart after a while (several years).

[Larry]

I have tackled the vibrations.  

I first tried to suspend the PCB with rubber bands. When I undid the last mounting screw, I was very careful to avoid the PCB falling down. In fact, it did not fall at all. What happened was that I could not simply move the PCB. There are 30 wires holding it firmly in the air! I thought now the vibration might be gone. I picked up my screw driver and touched it to the PCB.    The vibration was there unchanged! The 30 wires were transmiting the vibrations. So in this case, there was no way to suspend the PCB at all.

It appeared that isolating transformers is the only way to go. I got some rubber top caps from Bunnings warehouse, which is used in toilet flush, and sat the transformers on top of them (two for each) with slightly tighted bolts with rubber washers. All the weights are on the two rubber top caps, which are very elastic. I picked up my screw driver again and touched it to the PCB. Deadly quiet!

Thank you all for your inspirations!  

[andyr]

I got some rubber top caps from Bunnings warehouse, which is used in toilet flush, and sat the transformers on top of them (two for each) with slightly tighted bolts with rubber washers. All the weights are on the two rubber top caps, which are very elastic. I picked up my screw driver again and touched it to the PCB. Deadly quiet! ...

Hi Larry,

I am just starting my GK-1 and want to use your transformer isolation method ... the rubber washers.

Can you pleeze identify a bit more exactly what those rubber washers were - both the ones under the transformer and the ones under the mounting lugs, which the bolts go through.

Then I can go to good ol' Bunnings and get the same stuff.

Probably better to email me directly: andy.redwood@telstra.com

Thanks,

Andy