Ultrasimple SIT PP amp from BAF , or SIT Beast with a Thousand PSUs - Page 3 - diyAudio
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Old 8th October 2013, 06:06 PM   #21
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally Posted by analog_sa View Post
What if the balanced source has already nasty output caps?
separate issue , isn't it ;

however , just to spoil part of Buzz's happiness :

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Old 8th October 2013, 06:09 PM   #22
PKI is offline PKI  United States
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A bit random, but.. ZM, I was always wondering if there is a point of having this kind of symmetrical-balanced amp if all your sources are not balanced?
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Old 8th October 2013, 06:10 PM   #23
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Quote:
Originally Posted by Zen Mod View Post
separate issue , isn't it ;

however , just to spoil part of Buzz's happiness :

As if 4 power supplies wasn't enough, you get closer and closer to the amp in the title
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Old 8th October 2013, 06:13 PM   #24
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Originally Posted by PKI View Post
He also used them coz he had them left from F6 amps ;-). What if you have an external buffer like B1, still need one in the front?
What is the output impedance of your buffer?
If it is less than 200 Ohms then should be no problem.
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Old 8th October 2013, 06:20 PM   #25
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Quote:
Originally Posted by PKI View Post
A bit random, but.. ZM, I was always wondering if there is a point of having this kind of symmetrical-balanced amp if all your sources are not balanced?
Definitely best to run a balanced source.
Main benefit I see of running balanced circuit with single ended source is power supply is not modulated with signal while in Class A, and you are able to create 4 x the power at the output working with low voltage parts eg sk70/sj74 ie no need for cascode

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Old 8th October 2013, 06:34 PM   #26
Zen Mod is offline Zen Mod  Serbia
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me tellin' that gnd is just state of mind ;

take that primary arrangement (ref gnd) just as arbitrary ; connect your + and - from XLR wherever you want ..... even across primary , while stickin' gnd wire to potato
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Old 8th October 2013, 08:00 PM   #27
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Default Concept bias PSUs

Quote:
Originally Posted by OllBoll View Post
As if 4 power supplies wasn't enough, you get closer and closer to the amp in the title

The schematic and pictures of the amp suggest the following for the biasing circuit:
  • PSUs ride atop and are referenced to the power rails; but not to ground.
  • May need to read and especially confirm the presence of the bias voltage on each SIT; which must be rock stable.
  • Expect different bias voltages for the 4 SITs. This may require up to 4 PSUs [stereo] ; but one may get away with only two; one for each 23 V power rails.
An approach to the bias PSUs are wall-mounted/energized AC/DC PSUs [~15 VDC output];switching ; like for ACA or linear. Overkill for the biasing power demand; but available and cheap. The intrinsic voltage of the PSU is stepped down with an adjustable voltage regualtor; e.g. LM317T and LM337T[ or Belleson's]. The voltage regulators may best sit close to each other on the same heat sink so as to get a stable no output DC offset. A digital voltmeter module is then used to monitor each bias voltages. Bias voltage to each SIT is best left on/energized all the time to protect them.

A detailed schematic of this concept bias psu will follow.
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Old 8th October 2013, 08:50 PM   #28
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Jensen transformer datasheet:
http://www.jensen-transformers.com/datashts/112lcf.pdf
JT-112-L 2SJ28/2SK82=E=mc2
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Old 8th October 2013, 08:52 PM   #29
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it's best to situate each of these 4 wall mounted PSUs in different room ;
that way , sound will be more diffused and spatial

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Old 8th October 2013, 08:56 PM   #30
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Default Concept Bias PSU

Please find attached. If SITs need differing Vgs then one will need one wall AC/DC PSU and two independent LM317Ts. Ditto for the negative 23V power rail; but with 2 LM337T instead.

Forthcoming is another concept bias PSU.
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