Copper Semi-octal Cornet2

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milosz

Copper Semi-octal Cornet2
« on: 8 May 2011, 09:56 pm »
I bought this from a Audio Circle member, I re-did some of his work to make it tidy.  For example, I made turret strips to mount all those Russian Teflon caps he put in, and I also fabricated a retaining bracket for the octal socket for the 6SN7 so that pulling the tube out doesn't take the octal socket with it.  Aside from that, I just made it look prettier.  The thing sounded great when I got it, and now it not only sounds great but looks pretty.









-before-










dangerbird

Re: Copper Semi-octal Cornet2
« Reply #1 on: 8 May 2011, 10:00 pm »
stunning--good on you.  :thumb:

poty

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Re: Copper Semi-octal Cornet2
« Reply #2 on: 9 May 2011, 10:35 am »
Nice job and marvelous look outside and inside. I'm always wonder how neat are the DIY things considering the tough work with metal!

milosz

Re: Copper Semi-octal Cornet2
« Reply #3 on: 9 May 2011, 03:39 pm »
The original builder used 5/64's copper sheet for the top plate and jack mounting plate. That's quite thick, and I think pretty expensive.


david62

Re: Copper Semi-octal Cornet2
« Reply #4 on: 9 May 2011, 08:33 pm »
What an improvement!Nice build quality now.How does it sound?
Dave

milosz

Re: Copper Semi-octal Cornet2
« Reply #5 on: 9 May 2011, 10:14 pm »
It sounded good when I first got it, and it sounds good now. I don'y my work did anything to improve sound, it was all just about build quality and appearance.   It  **MIGHT** be a little quieter now, hard to tell, but maybe a little less hum / buzz.  At any rate, it's a very quiet preamp.

Lots of detail, great clarity. Haven't done extensive listening yet, and have yet to do some close comparisons with some other good phono stages I have, but what I've heard so far, I like. 

In about a month I will post some comparisons with the other phono stages I have- Bottlehead Eros, Pass DIY Pearl, etc.

flocchini

Re: Copper Semi-octal Cornet2
« Reply #6 on: 12 May 2011, 02:52 am »
It looks absolutely beautiful !!!!

Bob

milosz

Re: Copper Semi-octal Cornet2
« Reply #7 on: 12 May 2011, 08:38 am »
Thanks for all the nice comments!   :D

The bubinga wood I used has pinkish colors in it that nicely compliment the polished copper. 




I learned a lot of craft stuff during this project, like for example I learned that in order to protect the copper from getting dull over time that you should use a special acrylic lacquer, not just regular clear lacquer.  The stuff to use on copper is called "Incrylac" which is used on trumpets and other brass instruments, and in museums.  You can order it online in a spray can.



analog97

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Re: Copper Semi-octal Cornet2
« Reply #8 on: 12 May 2011, 02:22 pm »
Every time I see one of these "super-built" Cornets, my jaw drops.  I have a stock + Auricap Cornet 2 and just love it.  Compared to my C2, this looks like an over-stuffed stromboli.  Those red caps look like sticks of TNT and all those huge Russian teflons......whoaa!!!   

Super beautiful work on that case!!  The copper work is truly awesome.  Wish you lived next door and we could swap for a week.  Only then would I know what the differences in sound are. 

Sound is the final arbiter.    :D

bean_counter

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Re: Copper Semi-octal Cornet2
« Reply #9 on: 12 May 2011, 06:40 pm »
thanks for the Incrylac tip

question - 5/64 is pretty thick, and as you said, expensive; do you think would 0.05 be sufficient?  It's roughly 2/3 as thick (0.05 vs 0.78)

0.05 is a lot cheaper!

milosz

Re: Copper Semi-octal Cornet2
« Reply #10 on: 12 May 2011, 06:44 pm »
I am guessing that the sonic improvements from the cap upgrades are pretty subtle, just likely to be a tiny little bit of extra smoothness in the highs.  Might not even be audible.  Even a properly setup pickup in a $$$$ topnotch arm on a multi-$1000 table has over 1% intermodulation distortion through the highs, mechanical transduction of a wavy vinyl groove is not a low distortion process. My guess is this nonlinear distortion would mask any subtle improvements brought about by capacitor upgrades and the like. But, the more linear the electronics are that follow the pickup transducer the less likely they are to EMPHASIZE the nonlinearity inherent in the mechanical process. So maybe... who knows.  The caps were part of the Cornet I bought, so I kept 'em.

One thing that MIGHT be audible is the RIAA equalization.  The Teflon caps used in the RIAA eq have a closer tolerance than the original caps, so channel-to-channel frequency response differences might be tighter, and this might be audible.

From my experience the sonic differences that arise from using the NOS Raytheon 6SN7 instead of the 12AU7 as the cathode follower, and from using RCA 7025's in the gain stages can be fairly audible, because it changes the harmonic "flavor" of the inevitable distortion added by the active stages.

Using all that copper, I doubt it makes ANY difference over an aluminum chassis.  Maybe if you were in a high RFI environment, like at a radio station in it's strong RF broadcast field, it might reduce RFI a dB or something. MAYBE.  It sure looks nice, though- and the original builder put it in there so I retained it, and polished it up.

milosz

Re: Copper Semi-octal Cornet2
« Reply #11 on: 12 May 2011, 07:10 pm »
COPPER

I don't think using copper is going to do anything for you, sonically.  Aluminum is perfectly fine.

If you want the look of the copper, which IS pretty, you want a metal sheet that is sufficiently stiff to act as a chassis.  I don't know what the minimum there would be.

You COULD just put a thin copper sheet over an aluminum chassis, using spray adhesive and a couple of small nuts/bolts. 

For the inside shielding I used .005 copper foil which is about 7 times as thick as household aluminum foil. This stuff was not expensive and easy to work with- it comes on a roll, you cut it with a utility knife.  See http://basiccopper.com/thicknessguide.html

flocchini

Re: Copper Semi-octal Cornet2
« Reply #12 on: 15 May 2011, 09:53 pm »
When I did the original scruffy version of this unit I thought that the Russian Teflons added sparkle to the highs. I am using Raven tweeters. That was in my system and to my ears.

If anybody wants to try the Teflons I still have some .1microF and .47microF. Let me know- I'm sure we can work something out.

Again Bill thanks for beautifying the original.

milosz

Re: Copper Semi-octal Cornet2
« Reply #13 on: 15 May 2011, 10:57 pm »
Bob,

Did you put all of the Teflon caps in there in one fell soldering swoop, or did you put them in section by section?

(I am tempted to call these "Teflonsky"  caps...)

flocchini

Re: Copper Semi-octal Cornet2
« Reply #14 on: 16 May 2011, 12:53 pm »
I bypassed the output caps first and then the others. Tubesforever had/has a nice thread discussing the Teflons followed by a group buy.

Best

Bob

milosz

Re: Copper Semi-octal Cornet2
« Reply #15 on: 16 May 2011, 07:35 pm »
Did you notice improvements at each step?  Or were some more noticeable than others?

flocchini

Re: Copper Semi-octal Cornet2
« Reply #16 on: 16 May 2011, 09:31 pm »
Most notable to my ears was bypassing the output caps. By passing the other caps was more subtle but I think still worth doing. I think so much depends on the rest of the system and the listener. One of the reasons I sold my tube gear was my obsessive need to tweak. It was time for me to just listen. I would do it all over again. Great learning experience !!!!

Best


milosz

Re: Copper Semi-octal Cornet2
« Reply #17 on: 16 May 2011, 10:32 pm »
Yeah I hear you there.  I don't have the tweaking bug so much as I have the "hmmmm -  XXX - I'd like to try that, "  where XXX is:

  • Pentode
  • Triode
  • Single-ended
  • Planar driver
  • Ribbon driver
  • electrostatic driver
  • Class A
  • Tube
  • MOSFET
  • Power JFET
  • Nelson Pass
  • DSP
  • ESS SABRE32 DAC
  • Analog
  • Moving Coil
  • Bottlehead
  • Hagerman
  • balanced
  • current-transmission (CAST)
  • stepped attenuator
  • etc....