While the M.NATS 1176 Revision J board is very similar to the Gyraf Revision 7 board in most respects, there are a few important differences. Two differences that directly affect the wiring of the board are the output transistor (Q8, Q9) pinouts and the audio output pads. The rev J board is designed for either the originally specified BD517/518 or the replacement BD135/136 or BD139/140 output transistor pair. If using the original BD517/618 transistors, the alternate EBC/CBE placement must be used and two small wire jumpers must be added. If using the replacement BD135/136 or BD139/140 output transistor pair, the normal BCE/ECB placement applies and no wire jumpers are needed near the transistors. Refer to the checkplot (overlay) to identify the transistor footprint that applies.

Also, looking at the rev J board, the audio output pads are wired + 0 - as opposed to the Gyraf rev 7 board that are wired - 0 + (note: the input pads are wired identically to the Gyraf rev 7). These are the only two differences that would make the boards incompatible if swapped without changes. Wire the output leads differently and replace the output transistors and you will have a 100% compatible board.

Component identifications (C1, R8 etc) are silkscreened onto the boards rather than component values (1uF, 10k). While this might seem more difficult and complicated for the beginner, component IDs allows you to clearly identify specific components from the schematic. The advantages of this will become clearer if you ever want to modify the circuit or have to troubleshoot the board. During construction simply refer to the Bill of Materials table to identify which component value gets installed in each footprint.

A good example of the efficacy of component IDs is the frequently asked question - "which components can I eliminate if I want to use the transformer input on my 1176?" Answer: IC 2; R1-A, B, C, D, E; R3; R4; C*4 (C35); C30; C31; C32; C33; C34; C100; C101.

The M.NATS 1176 Revision J board adds the following features to the Gyraf Rev. 7 as well:

  • Options for either OEP or Lundahl input AND output transformers
  • Lundahl output transformer is installed 'reversed' to increase gain to the equivalent of the original UREI 1176. OEP is installed natively (its ratio is 1+1:2+2 primary to secondary) for the same result
  • Star grounding scheme isolating the various sections of the circuit and bringing them separately to the star point beneath the output transformer for elimination of hum
  • Additional pad for stereo interconnect between two units
  • Three styles of trim pots can be installed on the one board and in any combination

    In addition, the rev J adds these features over the earlier revisions:

  • Better component 'footprints' for easier component insertion and less chance of damage to delicate parts such as glass diodes
  • Better pad designs for increased 'grab' on crucial components, off-board hookup wires and in/out cables
  • More room for power supply capacitors - no more crowding!
  • Additional ground pad for hum-free off-board wiring
  • Thorough labelling of various pads that connect to other parts of the circuit

    Suggested component values are on the BOM. Optional components are marked with an asterisk. R* and R*1 are 10k resistors and are used only with the optional Lundahl transformer input. Refer to the PDF file on Jakob's site for component values of the other optional parts.

    Please direct any questions about the Rev H to J board to The Lab after doing a search. General questions about the DIY 1176 can also be asked at The Lab, of course, but please do a search first as your question may very well have been answered previously.

    Gyraf Audio DIY 1176 site: http://www.gyraf.dk/gy_pd/1176/1176.htm

    The Lab: http://http://www.groupdiy.com/index.php?board=2.0

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