anatech said:
Well geez, what do you think you've got a wife for? 😀
Might make nice feet though.
I dunno, my foot fetish doesn't extend quite that far. 😀
se
Why not make a case out of this stuff http://en.wikipedia.org/wiki/Lead_glass it'ss a conductor so rf shielding is no probleme, and you would have the aded bonus of seeing the insides of the amp.
PMA:
Please support my latest brainstorm and list it here along with a link:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=104824
Each forum now has a "Best Of" thread for this purpose.
Variac
Please support my latest brainstorm and list it here along with a link:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=104824
Each forum now has a "Best Of" thread for this purpose.
Variac
Hi Mark, Pavel,
I posted it. I made this thread "sticky" for now at Pavel's request.
-Chris 😉
I posted it. I made this thread "sticky" for now at Pavel's request.
-Chris 😉
The lead-glass thing is interesting; you could coat the inner surfaces with ITO to increase the shielding while retaining the transparency. And it would be esthetically pleasing to shape things into an acoustically dead box (lots of mass and strength to work with).
Of course, the whole preamp goes to a pile of expensive powder if it gets hit with anything or is dropped...
Of course, the whole preamp goes to a pile of expensive powder if it gets hit with anything or is dropped...
Magnetic vs Electrostatic Shielding
Electric and magnetic fields behave differently and require different types of shielding. A good conductor like copper or aluminum is sufficient to shield against electric fields. It can easily be shown by the application of Gauss's law that the E-field within a closed conducting volume, with no internal charge sources, is zero.
By contrast, magnetic shielding is a function of the ratio of uo (permeability of free space) to u of the shielding material. As an earlier post pointed out, magnetic fields can't be completely shielded, at least at room temperatures, since doing so would require an infinite permeability material. Various high u materials (such as mu metal) are available and can significantly attenuate stray magnetic fields. For example, I have used mu metal foil to shield magnetically actuated meter movements to prevent errors in an aircraft magnetic compass.
If you really want infinite magnetic shielding, be prepared to cool the material below its superconducting point, about 4-10 degrees K for many metals. At these temperatures, u becomes infinite, due to the so called Meissner effect. Explanation of this phenomenon requires use of quantum mechanics applied to electron pairs, and I won't bore anyone here with those details.
Electric and magnetic fields behave differently and require different types of shielding. A good conductor like copper or aluminum is sufficient to shield against electric fields. It can easily be shown by the application of Gauss's law that the E-field within a closed conducting volume, with no internal charge sources, is zero.
By contrast, magnetic shielding is a function of the ratio of uo (permeability of free space) to u of the shielding material. As an earlier post pointed out, magnetic fields can't be completely shielded, at least at room temperatures, since doing so would require an infinite permeability material. Various high u materials (such as mu metal) are available and can significantly attenuate stray magnetic fields. For example, I have used mu metal foil to shield magnetically actuated meter movements to prevent errors in an aircraft magnetic compass.
If you really want infinite magnetic shielding, be prepared to cool the material below its superconducting point, about 4-10 degrees K for many metals. At these temperatures, u becomes infinite, due to the so called Meissner effect. Explanation of this phenomenon requires use of quantum mechanics applied to electron pairs, and I won't bore anyone here with those details.
Regarding shielding - I design measurement instruments for high power/high voltage testing laboratories and I am quite familiar with this issue. These instruments are influenced by both LF high B and very fast HF EM fields.
Al or Cu are great for shielding HF fields, and also for LF fields (magnetic fields!) in case they are thick enough.
Skin depth for Al:
50Hz ... 11.6mm, 1kHz .... 2.62mm, 10kHz .... 0.82mm
Skin depth for Cu:
50Hz ... 9.3mm, 1kHz ... 2.1mm, 10kHz ... 0.66mm
There is one great advantage of non-magnetic (eddy currents) shielding - no saturation. Iron saturates, depending on permeability. Mumetal or Giron are great for shielding of low intensity LF magnetic fields. But they saturate early (0.7T, 2T) and as soon you get into saturation you loose all advantages.
I have great experience with thick alluminium. I may show photos of casework parts milled from thick alluminium later.
Al or Cu are great for shielding HF fields, and also for LF fields (magnetic fields!) in case they are thick enough.
Skin depth for Al:
50Hz ... 11.6mm, 1kHz .... 2.62mm, 10kHz .... 0.82mm
Skin depth for Cu:
50Hz ... 9.3mm, 1kHz ... 2.1mm, 10kHz ... 0.66mm
There is one great advantage of non-magnetic (eddy currents) shielding - no saturation. Iron saturates, depending on permeability. Mumetal or Giron are great for shielding of low intensity LF magnetic fields. But they saturate early (0.7T, 2T) and as soon you get into saturation you loose all advantages.
I have great experience with thick alluminium. I may show photos of casework parts milled from thick alluminium later.
Hi PMA. I don't grasp what skin depth means in this context. What do your figures imply for attenuation, for example, of 11.6 mm Al at 50 Hz? (Not that anything below 60 Hz matters. 😉)
Hi rdf,
50Hz is a frequency used in Europe, 60Hz in US, Japan etc.
Skin depth is a depth of material for flux density attenuation to 37%. Skin depth depends on permeability, resistivity and frequency according to well known formula.
50Hz is a frequency used in Europe, 60Hz in US, Japan etc.
Skin depth is a depth of material for flux density attenuation to 37%. Skin depth depends on permeability, resistivity and frequency according to well known formula.
THE PROOF IS IN THE LISTENING
Recently a Tokyo audiophile who is lucky enough to own TWO CTC Blowtorches lent them to me to have a listen.
One is a silver colored line stage only which was imported by the official Japan importer and sold through a retailer in Japan (i.e. it passed through two markups after the manufacturer). Since CTC sold direct in the USA, the retail price in Japan was roughly twice the US price (more then US$40,000). The other is a black unit with both phono and line stages that was bought used from a US dealer.
I have been interested in the CTC Blowtorch over the years, but never had a chance to listen. I knew Bob Crump and met him at many CES shows (I was connected with Crosby Audio Works and Demian Martin who had a relationship with Bob), and I have also had the pleasure to meet John Curl.
Now that I have had the chance to listen to the venerable CTC Blowtorch, I must say I am in full agreement with all of the positive reports I have seen. This is a very special unit indeed, and it is a pity it had to be discontinued. One can only hope that the new JC-2 from Parasound will retain some (or most?) of the magic. Only a chance to listen to it will tell.
As far as my impression goes; this unit has power, dynamics, and energy, but at the same time it has delicacy, finesse, and warmth. In many ways it is like combining the best of tube preamps and the best of transistor amps fused into a single preamp. (Have your cake and eat it too.)
Kudos to the CTC team, posthumous to dear Bob Crump whom I hope is listening with a grin on his angel face...
Whether I ever will own one will depend on my luck finding one on the second hand market. On the other hand, I have a hard time understanding why anyone would ever part with one (except maybe after that final travel). 🙂
Recently a Tokyo audiophile who is lucky enough to own TWO CTC Blowtorches lent them to me to have a listen.
One is a silver colored line stage only which was imported by the official Japan importer and sold through a retailer in Japan (i.e. it passed through two markups after the manufacturer). Since CTC sold direct in the USA, the retail price in Japan was roughly twice the US price (more then US$40,000). The other is a black unit with both phono and line stages that was bought used from a US dealer.
I have been interested in the CTC Blowtorch over the years, but never had a chance to listen. I knew Bob Crump and met him at many CES shows (I was connected with Crosby Audio Works and Demian Martin who had a relationship with Bob), and I have also had the pleasure to meet John Curl.
Now that I have had the chance to listen to the venerable CTC Blowtorch, I must say I am in full agreement with all of the positive reports I have seen. This is a very special unit indeed, and it is a pity it had to be discontinued. One can only hope that the new JC-2 from Parasound will retain some (or most?) of the magic. Only a chance to listen to it will tell.
As far as my impression goes; this unit has power, dynamics, and energy, but at the same time it has delicacy, finesse, and warmth. In many ways it is like combining the best of tube preamps and the best of transistor amps fused into a single preamp. (Have your cake and eat it too.)
Kudos to the CTC team, posthumous to dear Bob Crump whom I hope is listening with a grin on his angel face...
Whether I ever will own one will depend on my luck finding one on the second hand market. On the other hand, I have a hard time understanding why anyone would ever part with one (except maybe after that final travel). 🙂
Any thoughts on using this general topology for IV conversion ?
I.e Driving the sources of the input jfets instead of the gates.
A complimentary pair of sk170/Sj74 running 10mA each would present the dac with about 12ohms half that if two pairs where ran in parallel.
I.e Driving the sources of the input jfets instead of the gates.
A complimentary pair of sk170/Sj74 running 10mA each would present the dac with about 12ohms half that if two pairs where ran in parallel.
Hi John,
I'm honestly hoping you can continue building the same circuit to the same levels of performance. I am curious as to your preference in case styles. I gather these will strongly affect the finished cost of the preamplifier.
Comments?
-Chris
I'm honestly hoping you can continue building the same circuit to the same levels of performance. I am curious as to your preference in case styles. I gather these will strongly affect the finished cost of the preamplifier.
Comments?
-Chris
Hi, all,
As an evidence, Anatech, PRIVATE Forum rules are not made for me...
And I won't argue with you any longer about that. You have your orders from Chief-moderators, about rules to be enforced, and you just make your job, eh?
Perhaps that some Forumers will go and see what "Anastasie" was...
About the VR3, John, almost all housing will be OK, IMO, because the very hard grounding/EMI/RFI work ever did... Doesn't allow too much variations around. People are just much more expecting performance from the Killer engine that is inside, and as it will stick with classical LP players, an hot-rod look with large tires and flames won't be the best. Just stay classical looking with a light touch of modernity (blue front led, or your engraved "signature" on...).
All the best,
Jbaudiophile
As an evidence, Anatech, PRIVATE Forum rules are not made for me...
And I won't argue with you any longer about that. You have your orders from Chief-moderators, about rules to be enforced, and you just make your job, eh?
Perhaps that some Forumers will go and see what "Anastasie" was...
About the VR3, John, almost all housing will be OK, IMO, because the very hard grounding/EMI/RFI work ever did... Doesn't allow too much variations around. People are just much more expecting performance from the Killer engine that is inside, and as it will stick with classical LP players, an hot-rod look with large tires and flames won't be the best. Just stay classical looking with a light touch of modernity (blue front led, or your engraved "signature" on...).
All the best,
Jbaudiophile
Hi Jbaudiophile,
If you'd rather, simply PM me if you think there is a problem here. I can't quite understand what you mean so together we can work it out.
If you send me an email in French, my daughter can translate it for me. She is officially bilingual. In this way I will understand your message properly.
-Chris
I'm sorry. I don't understand what you are getting at. I passed your post, so nothing to hide here.
We work as a team. So I can't take the out that I am a zombie.
If you'd rather, simply PM me if you think there is a problem here. I can't quite understand what you mean so together we can work it out.
If you send me an email in French, my daughter can translate it for me. She is officially bilingual. In this way I will understand your message properly.
-Chris
Hi John,
Understanding is on the path to friendship. I have the feeling JB is unhappy about something. Unfortunately I don't know what it is.
Have you any idea of styling? I know I'm nagging you severely, but I am curious. If you have plans (or not) and would rather not say, that's fine. Just say the word. I would be sad to hear a fine preamplifier would no longer be made.
-Chris
Understanding is on the path to friendship. I have the feeling JB is unhappy about something. Unfortunately I don't know what it is.
Have you any idea of styling? I know I'm nagging you severely, but I am curious. If you have plans (or not) and would rather not say, that's fine. Just say the word. I would be sad to hear a fine preamplifier would no longer be made.
-Chris
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