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Old 18th January 2013, 04:53 PM   #21
jcx is online now jcx  United States
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I think Steve claims Cinemag can be cheaper at same quality

somewhere int here: diyAudio - Search Results


coax vs shielded twisted pair, shield termination options really depend on "threat environment"
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Old 18th January 2013, 05:30 PM   #22
Loren42 is offline Loren42  United States
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Originally Posted by Eli Duttman View Post
Loren42,

I've done some thinking about your long cable issue. Blue Jeans, IIRC, uses a simple coaxial construction, which is not suited to the task at hand. Shielded "twinax" in a differential, if not true balanced, configuration seems correct. That length of shield, when carrying signal, can all too easily pick up noise. The shield should not carry signal and only be connected to the upstream end chassis, not signal, ground.

You previously mentioned wall plates. 2X Neutrik 203Ms will do the job for you. Online Components carries the Neutrik plates.

No ifs, buts, or maybes, you will have to buffer the PAS preamp. I'm giving the buffer some thought. More about that to to follow soon. However, this much is clear. You will need trafos to break ground loops up. Jensen can be pricey. CineMag offers competetive products, at lower cost. CineMag's CMOB-2L looks like a candidate for your situation. A DC blocking cap. is needed between the buffering voltage follower and the trafo. Contact CineMag for assistance in sizing that part.
Called CineMag and left a message.
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Old 18th January 2013, 07:04 PM   #23
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Got for X-Mas a Sony Cordless [FM Infrared] Stereo Headphone System. Useful range to 26 feet and has a frequency response of 10 Hz-20 KHz. No mention of THD. Maybe a solution?
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Old 18th January 2013, 07:24 PM   #24
Pano is offline Pano  United States
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Cinemag are great but can take a long time to get if they are not in stock.
I'm in the "Use high quality shielded cable (Belden, Mogami, Canare) and break the loop" camp.
That's what I do and it works well for me over about the same distance.
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Old 18th January 2013, 07:28 PM   #25
Loren42 is offline Loren42  United States
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Eli,

Ordered two CMLI-15/15B transformers after having a long talk with Dave at CineMag. Thank you for the recommendation!

Now we just need to address the changes to the PAS 3 to make this work
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Old 18th January 2013, 07:29 PM   #26
Loren42 is offline Loren42  United States
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Cinemag are great but can take a long time to get if they are not in stock.
I'm in the "Use high quality shielded cable (Belden, Mogami, Canare) and break the loop" camp.
That's what I do and it works well for me over about the same distance.
Fortunately, they had what I needed in stock and they should ship today! I am a happy camper. These will mount nicely inside my amp.
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Old 18th January 2013, 07:30 PM   #27
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Long term I would like to roll my own preamp, but in the interim, does it make sense to upgrade the PAS 3 with one of those Tubes4HiFi PC boards?
I would not spend much on the PAS, if you are going to build soon. The buffer you build for the PAS will serve you well in combination with the new, DIY, preamp. The awkward cabling situation will not disappear and you will already have the circuitry needed to cope with it. Given the presence of a competent buffer, a nice sounding 12B4 based line stage could work out very well.

BTW, asking the 'X7 triode to drive both the power amp and tone control circuitry, as was done in the old Dyna PAS preamps, is problematic. AVA offers PAS rebuild kits that eliminate the troublesome tone controls. I can tell you from 1st hand experience that the AVA stuff is good. My son uses a rebuilt PAS of mine hand me down. I've uploaded a schematic for a single channel that shows just how complicated good tone controls are. Also, it is a fact that few recordings benefit from tone controls. Therefore, tone controls, if present, should be capable of being totally switched out of the signal path.
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File Type: jpg Tone_Control.jpg (27.8 KB, 97 views)
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Last edited by Eli Duttman; 18th January 2013 at 07:33 PM. Reason: typos
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Old 18th January 2013, 07:57 PM   #28
Loren42 is offline Loren42  United States
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Eli,

Yes, I want to add a defeat switch for the tone controls.

The circuit presented is a little hard to read (too small when expanded), but it looks like the output impedance is going to impact the tone circuit. Is that true?

The next step would be drilling down to a good recommended circuit that I could not only use for my next amp, but could also transplant into my PAS.

Having an active tone network would be the cat's meow versus the circuit used now in the PAS.
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Old 18th January 2013, 08:56 PM   #29
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Other than the commercially available upgrades, leave the PAS alone, if no reason other than severe PSU limitations.

PM me with your EMail address and I'll send you the high resolution, .bmp, version of that Max Robinson designed tone control setup. 4X 12AX7s for 2 channels of tone controls is (IMO) OTT. It doesn't take much effort to replace the cap. coupled cathode followers with DC coupled ZVN0545A source followers and reduce the bottle count to 1/channel.

As Max's design is "unity" gain, my inclination is to switch the tone control circuitry in/out of the signal path right at the line stage's I/Ps.

FWIW, the PSU I have in mind for the cable driver buffer will easily support a 12B4 line stage, along with the buffer. Perhaps a combined line stage/buffer effort is in order, as you will avoid some duplicated work. Ignore the PSU in the uploaded 12B4 line stage schematic. FWIW, the 12B4 line stage can drive a 10 KOhm I/P impedance amp, IF the interconnect cabling is reasonably low capacitance. Your situation is anything but reasonable.
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Old 19th January 2013, 09:53 AM   #30
Pano is offline Pano  United States
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Fortunately, they had what I needed in stock and they should ship today! I am a happy camper.
Hurray! I'm sure you'll like them.
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