jnb said:
Actually yes - but not with the bolt collar. Most of those things cannot stand much over 300V, and the field is aggravated by the sharp bolt threads.
I have regulator power transistors sitting at 650V w.r.t. the heatsink (earthed) with only a mica wafer. That can stand well over 1000V if not too thin or cracked. But one must watch the rest of the hardware. I clamp the transistor(s) with a separate aluminium U-shaped section across the top, securing that with screws between the transistors and some 5mm away (screws and nuts, not self-tap - no sharp edges). Also minimum lead distances from any ground plane must be observed, as well as keeping collection of dirt away. In that sense, no grease oozing out! It becomes quite an exercise in neat mechanics in the end, but quite feasible. I have tested my arrangement up to 1100V, with the necessary equipment (through a high resistance, etc.)
And of course, conforming to safety statements required here: You touch something thereabouts, friend .......... LESS THAN THAT CAN BE LETHAL (there are probably storage capacitors somewhere in the circuit - discharge etc.) It is like handling a loaded gun.
I'm really sorry , but manufacturers say they "don't like the sound of aluminum" What theheck? Things have gotten out of controll in the high end world. The chassis does not add to or take away from the sound if everything is done right to avoid mechanical vibrations and edy currents-which are not a big deal if you know where to place the transformers. Like the other day I saw a pair of speaker wires that cost $23,000 each.. 
Sheesh
Aluminum is much easier to work with if you just have simple drill press/chassis punches. Its downfalls are that it is easier to scratch bend or ding. However it is light ( making your HEAVY tube amp a lot lighter) wont rust, polishes to look like chrome if you are on a budget and cant afford plating, is easy to drill through and cut.
Dissimilar metal corrosion isn't a factor if you use rubber isolation gromets on everything, Ideally a chassis would not be grounded anyways and would have a star ground at the input of the amplifier, floating from the chassis. This eliminates any RF noise caused by that big ol' metal antenna called a chassis.
SheeshAluminum is much easier to work with if you just have simple drill press/chassis punches. Its downfalls are that it is easier to scratch bend or ding. However it is light ( making your HEAVY tube amp a lot lighter) wont rust, polishes to look like chrome if you are on a budget and cant afford plating, is easy to drill through and cut.
Dissimilar metal corrosion isn't a factor if you use rubber isolation gromets on everything, Ideally a chassis would not be grounded anyways and would have a star ground at the input of the amplifier, floating from the chassis. This eliminates any RF noise caused by that big ol' metal antenna called a chassis.
jnb said:
More like a ring or ping from chassis microphonics.
As for a test, hook it up and tap with a screwdriver handle to find the ringy points. Add a brace or another screw.
There are easier ways, including mounting the sockets via ordinary rubber grommets or using tube dampeners (sometimes they are called for
) and spiked feet.Such simple measures can even avoid mechanical feedback from an amp sitting ontop of a 4x10 cab with a demon on the guitar trying to break it. To go anymore for a listening room HiFi setup would seem IMO, silly, since the noise pickup from cables will mask any minute mechanical rustles.
Cheers!
microphonics = soundstage
What I have found is sound stage and other nuances of reproduced music are a result of fine detail first being extracted from the CD then then being amplified and played back.
Any loss of that detail or phase changes or phase shifting of the information reduces sound stage and "realness" of the sound. Micro phonics occurs when parts (e.g transformers, capacitors, chassis etc) resonant with the sound they are playing.
At all levels of this resonance should be controlled. You can never stop it but you can control it. Some easy ways are using high quality transformers and rubber mounting them on a 2 mm thick steel chassis sitting on on brass isolation cones.
What I have found is sound stage and other nuances of reproduced music are a result of fine detail first being extracted from the CD then then being amplified and played back.
Any loss of that detail or phase changes or phase shifting of the information reduces sound stage and "realness" of the sound. Micro phonics occurs when parts (e.g transformers, capacitors, chassis etc) resonant with the sound they are playing.
At all levels of this resonance should be controlled. You can never stop it but you can control it. Some easy ways are using high quality transformers and rubber mounting them on a 2 mm thick steel chassis sitting on on brass isolation cones.
Three of them for me ! Al is useful for large amps like OTLs : easy to work on, and good dissipating factor . Cu is nice when i find for cheap a thick (5 mm) plate , but for small amps (DHT projects) : best antimicrophonic results. And last : stainless steel (for foods) : nice looking for small 9 and 7 pins tubed projects .
Without quoting the lot, I would again support ThSpeakerDude88 (post #44).
I don't want to spoil my own evening thus far, but with folks one can be excused for thinking they know something (like manufacturers), then coming up with such drivel as the sound of aluminium .... That is a major factor of what is wrong with high-end hi-fi. There is hardly an advertisement I read or I want to reach for antacid. Not because I am so good but because they ... let me refrain lest I get stuck with a libel suite.
I would plead that we regard this business of microphonics soberly. With respect for what Mhouston says qualitively (post #46), the detrimental end result of any vibration lies in what is converted to electricity of the signal kind. (That is the definition of microphonics.) While it is true as Mhouston said, that a good stereo image (or not) is dependent on fine effects, I find it rather difficult to see that any such practical effect could materialise from transformers, capacitors or whatever "vibrating" - unless the construction resembles more of a suspension bridge that any half-decent electronic build-up.
One can tap a part of a chassis and perhaps get an audible "ring" - but then is that part of the chassis suspect, or is the impulse merely propagated to a microphonic tube? (... and a tap injects an impulse into the metal orders of magnitude higher than an outside acoustical wave). One must keep in mind that tube geometry is directly related to signal current variation, thus acoustic waves impinging on a suspect tube could cause problems; not so vibration in components which are supposed to be solid.
With that I am not saying one should neglect solid mechanical construction, but I personally never found rubber mounting of transformers, tube sockets and the like of any consequence. Also damping rings on tubes ... not to step on toes, but how exactly has that ever been shown to improve matters? (And isolated hearing testimony by this or that famous individual does not constitute proof, I fear.) One way to go about showing this would be to blast a chassis with unbearable sound (from a different source) and look on a scope - but I cannot recall ever reading about such a test. Should be simple to perform, however .....
I don't want to spoil my own evening thus far, but with folks one can be excused for thinking they know something (like manufacturers), then coming up with such drivel as the sound of aluminium .... That is a major factor of what is wrong with high-end hi-fi. There is hardly an advertisement I read or I want to reach for antacid. Not because I am so good but because they ... let me refrain lest I get stuck with a libel suite.
I would plead that we regard this business of microphonics soberly. With respect for what Mhouston says qualitively (post #46), the detrimental end result of any vibration lies in what is converted to electricity of the signal kind. (That is the definition of microphonics.) While it is true as Mhouston said, that a good stereo image (or not) is dependent on fine effects, I find it rather difficult to see that any such practical effect could materialise from transformers, capacitors or whatever "vibrating" - unless the construction resembles more of a suspension bridge that any half-decent electronic build-up.
One can tap a part of a chassis and perhaps get an audible "ring" - but then is that part of the chassis suspect, or is the impulse merely propagated to a microphonic tube? (... and a tap injects an impulse into the metal orders of magnitude higher than an outside acoustical wave). One must keep in mind that tube geometry is directly related to signal current variation, thus acoustic waves impinging on a suspect tube could cause problems; not so vibration in components which are supposed to be solid.
With that I am not saying one should neglect solid mechanical construction, but I personally never found rubber mounting of transformers, tube sockets and the like of any consequence. Also damping rings on tubes ... not to step on toes, but how exactly has that ever been shown to improve matters? (And isolated hearing testimony by this or that famous individual does not constitute proof, I fear.) One way to go about showing this would be to blast a chassis with unbearable sound (from a different source) and look on a scope - but I cannot recall ever reading about such a test. Should be simple to perform, however .....
There's a simpler way, which I use. Mount a piece of piezo film near the tube (tube connected as a common cathode amp), then hit it with an impulse. That shock-excites the tube, and it's pretty easy to look at the microphonic signature. The piezo could, in theory, interfere with the measurement by radiating the impulse, but the time response is so quick that it's easy to separate out that sort of interference and just examine what happens after the first few microseconds.
SY,
OK, not disparaging that. But I was trying to get closer to the actual practical situation. What are we using as a norm? Every tube will be microphonic per se; the innards are not made of concrete. But what exactly does the loud hi-fi outside do? Acoustic waves cannot directly impinge on the construction, it is in a vacuum. Influence can only come through the socket/pins, or perhaps resonance when everything outside is vibrating and the electrodes have sufficient mass/resonance.
Tapping on a tube/chassis is to me a little remote from this. But a salesman will demonstarte the effect by impulsing a tube, and out comes our money for the newest damping ring or fancy feet or Kalahari desert pebbles. OK, I tap too. But one judges comparatively. Over the years the brain has been programmed to subjectively feel "this is bad" - not very scientific, but at least valid as a first approximation.
Not to belabour, but my fear is that this thing is pretty overrated .... unless someone out there can broaden my horisons and point out some real tests (and once again, I say respectfully, some well-known critic's hearing does not constitute proof for me).
OK, not disparaging that. But I was trying to get closer to the actual practical situation. What are we using as a norm? Every tube will be microphonic per se; the innards are not made of concrete. But what exactly does the loud hi-fi outside do? Acoustic waves cannot directly impinge on the construction, it is in a vacuum. Influence can only come through the socket/pins, or perhaps resonance when everything outside is vibrating and the electrodes have sufficient mass/resonance.
Tapping on a tube/chassis is to me a little remote from this. But a salesman will demonstarte the effect by impulsing a tube, and out comes our money for the newest damping ring or fancy feet or Kalahari desert pebbles. OK, I tap too. But one judges comparatively. Over the years the brain has been programmed to subjectively feel "this is bad" - not very scientific, but at least valid as a first approximation.
Not to belabour, but my fear is that this thing is pretty overrated .... unless someone out there can broaden my horisons and point out some real tests (and once again, I say respectfully, some well-known critic's hearing does not constitute proof for me).
Man, you're right, that is a strange statement. Almost all of the high-end tube equipment I've ever seen has an aluminum or steel chassis with a thick aluminum faceplate.
I think for the average diy'er aluminum is by far the easiest to use and 1/8" or 3/16" is readily available at any scrap merchant.
If you want sophisticated vibration isolation in your chassis, cast ZM11, COSMAL, or ZA27H1/H2 zinc alloys are the most economical. Ordinary ZA27 or ZAMAK alloys probably have no better damping properties than plain aluminum. I use 3/16" unalloyed aluminum myself because it has some damping ability and, most of all, it is the easiest metal to work.
John
As mentioned in an earlier post I am building my first power amplifier from scratch. I have decided upon the Dynaco St70 (availability of parts, relitive simplicty of construction + wanted to build a stero unit) but I am setting up my own layout and design. So far I have built a cardboard mock-up and I am about to take it to a sheet metal worker.
This was his first post.... Has anyone answered it?
I say go with whatever YOU want, neither are going to make a big enough difference in sound to matter at all.
Aluminum is cheap, won't rust, and is easy to work with. However if you are having someone else cut it for you, steel is stronger, and if properly primed and painted won't rust either.
This was his first post.... Has anyone answered it?
I say go with whatever YOU want, neither are going to make a big enough difference in sound to matter at all.
Aluminum is cheap, won't rust, and is easy to work with. However if you are having someone else cut it for you, steel is stronger, and if properly primed and painted won't rust either.
Rob11966 said:
I would go Alu.
kevinkr said:
I like copper even better, but it's too expensive, really hard to work because of it's softness, (Clogs drill bits, end mills, punches, etc), greater thickness is required for a given load on the top plate, needs to be well protected from oxidization, and is prone to bending and scratching. However nothing looks better than clear coated copper IMHO..
It sounds better too. I went that route with my preamp, and although a PITA, I am happy that I did.
Attachments
The biggest stimulator of microphonics, save for Motorhead's road crew, appears obvious to me: the power transformer. A piece of audio gear which doesn't reward an ear to the chassis with loud buzzing is rare. If some day I stop playing with circuits long enough to complete another amp the tube sockets will mount on a rubber isolated, mechanically floating metal platform inside the chassis.
Hi Folks,
I didn't realise that the topic had come around to the original question again. Following the initial posts I decided to go with aluminium, 3mm for the top and 1.6mm for the sides and base (they are turned over along the top for strength).
That's no longer the problem...long sigh....the metal work shop is now the weak link in the chain. These guys have promised a finished chassis everyday for the last 3 weeks. Definitely arriving today (hmm, it is now 10pm so I guess I am unlikely to get a call now!). They have however managed to convince me that it is almost complete and they are holding my cardboard mock-up hostage so I have not gone anywhere else yet.
Otherwise I have accumulated all the parts and am ready to get building. I will post an update and picture when/if the chassis arrives.
Cheers,
Rob
I didn't realise that the topic had come around to the original question again. Following the initial posts I decided to go with aluminium, 3mm for the top and 1.6mm for the sides and base (they are turned over along the top for strength).
That's no longer the problem...long sigh....the metal work shop is now the weak link in the chain. These guys have promised a finished chassis everyday for the last 3 weeks. Definitely arriving today (hmm, it is now 10pm so I guess I am unlikely to get a call now!). They have however managed to convince me that it is almost complete and they are holding my cardboard mock-up hostage so I have not gone anywhere else yet.
Otherwise I have accumulated all the parts and am ready to get building. I will post an update and picture when/if the chassis arrives.
Cheers,
Rob
I generally use the Hammond aluminum chassis types. But speaking of chassis punches, I swear by the old Greenlee brand.
I did get a set of punches from Harbor Freight Tools, made in China, that are supposed to punch even steel, and as a matter of fact, it seems like some folks on Ebay are (or were) trying to sell these $10 sets for quite a markup bogusly. I only used them on aluminum, but after about 4 holes one of these punches actually stripped its own threads during the procedure. Quite crappy in the long run. Will try to get more Greenlee sizes from now on, to be sure.
I did get a set of punches from Harbor Freight Tools, made in China, that are supposed to punch even steel, and as a matter of fact, it seems like some folks on Ebay are (or were) trying to sell these $10 sets for quite a markup bogusly. I only used them on aluminum, but after about 4 holes one of these punches actually stripped its own threads during the procedure. Quite crappy in the long run. Will try to get more Greenlee sizes from now on, to be sure.
Just my amen to the above (Frank 754).
If you are going to use punches with any regularity (like a few times/annum), invest the little extra; Greenlee, but there may be other proven brands these days. There are few things that make one use foul language like a blunt or b.....ed up punch in the middle of serious work.
If you are going to use punches with any regularity (like a few times/annum), invest the little extra; Greenlee, but there may be other proven brands these days. There are few things that make one use foul language like a blunt or b.....ed up punch in the middle of serious work.
Good metalworking tools seem less prevalent than they used to be but they can still be had. In my neck of the woods you need to move away from the chain shops to get them.
Even something as simple as a drill bit or a socket. You can get a cheapie or a good one at your local hardware shop, with a wear rate corresponding to the price, but If you go to an engineering shop with professional tools you'll see a whole new range of quality.
Man, I despise tools that break during their first use
Even something as simple as a drill bit or a socket. You can get a cheapie or a good one at your local hardware shop, with a wear rate corresponding to the price, but If you go to an engineering shop with professional tools you'll see a whole new range of quality.
Man, I despise tools that break during their first use
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