Post pics of your builds.... - Page 583

I rebuilt my Starving Student in an Hammond aluminum enclosure. After a paint job, it looks much better than the original.

I built Faraday cages around the tubes, but they still pick up WiFi interference. Does every tube amplifiers pickup EMI like this, or is it a design flaw of the MSSH?

I'm not sure about the rest of your question, but for a Faraday cage to be effective it needs to be fully enclosed.

Quote:

Originally Posted by KimLaroux 

 

I built Faraday cages around the tubes, but they still pick up WiFi interference. Does every tube amplifiers pickup EMI like this, or is it a design flaw of the MSSH?

are you sure it's your tubes that are picking up the interference?  Some areas I'd look at first:

-some of your wires in your case could be shorter

-do you have a star based ground set up

-are your pots and jacks isolated from the case

-are the audio wires near any power wires shielded or at least when they come near power lines doing so at right angles?

as for the faraday cage, is the cage itself designed for the frequencies you want to block, the higher the frequency the smaller the hole/mesh.  Also, as stated, a faraday cage must be fully enclosed.

This spurred me to do some further reading, the holes need to be less than one tenth the wavelength, so for wifi frequencies in the g or n spec, you're looking at 2.4GHz (rounding to 2.5GHz for convenience) you have a wave length of 12cm, so you would want holes smaller than 1.2cm.  For n and the ac bands it's 5GHz, wavelength = 6cm, mesh hole of <6mm.

I had it in my mind that the holes would be much smaller, my mistake.

I'm pretty sure the noise is picked by the tubes themselves: If I place my hands around the tubes, the noise stops. If I pick the amplifier up and lift it above my laptop, the noise stops.

I'm guessing the mesh I used is too thin and has too many holes in it to effectively shield 2.4Ghz. I tried adding caps to completely close the cages, it helps, but the RF still gets trough. From the little information I can find about RF shielding, it seems that the only efficient way to shield those high frequencies is to use a solid sheet metal. I think the best option, short of enclosing the tubes inside a metal box, will be to reposition the amplifier relative to my laptop. Right now they are less than a foot apart, with a direct, unobstructed space between the laptop's WiFi antennas and the tubes.

Laptops are notoriously noisy, may I recommend a high impedance air gap?  AKA  move your amp away from your laptop.  Cheap and easy.

...further thoughts...

Have you tried turning off your laptops wifi and see if you still have noise?  I would suspect that it's the power supply instead, as the frequencies they radiate are in the audible range where 2.5GHz is way past ultrasonic.  Not saying wifi couldn't cause trouble, but I find it unlikely.  If I'm proved wrong, I'd really like to do some reading on the matter.

I did, in fact, I just have to stop using the internet for it to stop. When I have a torrent client open, it's hell inside those tubes. It's not the 2.4Ghz that you hear, but the WiFi protocol. Strings of 0s and 1s round up to a "chick-click-clack" type of noise, a bit like a dial up modem does. Ever heard interference of a cellphone through powered speakers? It's this type of noise.

I tried moving the amplifier away, but it's not as efficient as just placing it above my laptop. This is explained like so: moving the source of the noise bellow the amplifier places the enclosure between the source and the tubes, which offers a better shield.

Fair enough, I've personally never run into this issue, but then again I don't screw around with tubes, so....

Anecdote:

A few years ago I was installing a large A/V plus video teleconference system for a software manufacture.  After a few months of install, we went to start turning on each room to test when we discovered some awful noise coming out of the ceiling speakers.  Time passes, heads are scratched, then it dawns upon me upon me to unplug the laptop that was installed in the rack, sure enough the power supply was dumping it's switching noise into the audio signal, even when it wasn't selected at the switcher as an audio source.  Awful nasty things.  

Thought I'd share this while we're on the topic.

The zone amp that I use for my desktop rig has a signal sensing trigger where it'll turn on when it detects an audio signal at the RCA input. You can adjust the input sensitivity with a pair of trimpots on the back of the chassis. Anyway, I figured out that whenever I turned on my lamp, the amp would trigger on as well. I guess the 120VAC in the lamp cord was enough to induce a voltage in the RCA cables that were running right beside it.
 

Well finally here we go I've been working on this one for a few months now. I finally got my case and decided to "wire" things up...

Wanted to use a smaller case but the power supply I ended up using forced a larger case. Then again it was a breath of fresh air working with a larger case -- my last few builds were Cavalli CTHs, which is as tight as it gets.

Mullet, how do you like the sounf of The Wire amplifier? I build myself one and like it very much!

At this point I've listened and built these amps in order: CMOY, Apheared 47, Cavalli CTH (2 variations), O2, The Wire. My next is going to be the EHHA Rev A -- someday. I know I can tell you I never liked the sound of the CMOY and A47. Maybe it was the opamps I was using -- maybe wrong headphone pairing. I love the CTH. I think I like it better than the O2 and Wire. Maybe it's the hybrid tube thing. I'm not sure. I have a hard time articulating the sound of an amp and the characteristics of what an amp sounds like, but I can tell you if I like something or not. I'm not sure what I prefer the O2 or Wire. I haven't had enough time with The Wire I guess. It sounds good though. My thoughts on this should be saved for another thread.

When using volume control -- I know you implemented some sort of digital control. How far up do you go before you get a volume you like and what gain if any did you choose? I used an 50k RK27 with a gain of 4 and I have to go up to around 2 to 3 o'clock before the volume is to my liking. Other amps I've used its around 12 o'clock. I've been told it's probably because they have higher gain to begin with.

I see you keeping yourself busy Mullet. Very nice. As for the digital PGA2320 volume control I use no gain at all, I think this chip is on unity gain settings by default or "1" so to say. The Wire i build is on default gain "1". With my 85 Ohm orthodynamics I feel good at about -4dB volume. At 0dB it gets loud enough for me. It can go higher up to about +20dB though. It is really good as many people with some engineering skills think that listening at reference level must be around 80-90% power of the amplifier for best quality and SNR. For your 2 to 3 o'clock on POT dial is good enough by these standards. Because you also have some headroom for harder to drive headphones. Just leave it like this. My plans for the future are somewhat difficult to build. Major part will take the FET transistors with possible minimal number of gain stages and likely balanced circlotron style.

 built to hold all my stuff :)

Quote:

Originally Posted by shaunybaby 

 built to hold all my stuff :)

Nice, I like my flexy myself!  

Question, what's the notch in the bottom shelf for????

Just finished a KGSSHV.  Here are some pics.  sounds really good!

Warning: camera phone pics:)