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Summary of Contents for Musical Concepts PA-5
- Page 1 Musical Concepts PA-5 ALL MODELS INCLUDING VER 2 Modification for Hafler amplifiers...
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Page 2: Circuit Description
This modification is designed for the Hafler DH-200/220/500 and XL-280/600 power amplifiers. Dedicated constructors with consider- able experience can use the PA-5 to drive a MOSFET output stage using from 2 to 12 lateral power MOSFETS in complementary source follower mode. Such projects should be undertaken only by the most self sufficient types, since Musical Concepts cannot offer assistance for custom installations. - Page 3 These transformers can be rectified into a single or even a pair of PS-200 boards or the new, designed for DH-500, PS-500 power supply. The rail fuses are mounted directly on the PA-5, which makes any other proposed dual-mono conversion much easier.
- Page 4 The shoulder washer must fit inside of the hole to be electrically isolated. These will be wired to eyelets E1 and E2 of the PA-5 in a later step. Once the RCAs are installed and tightened, twist the wires about 2 turns per inch awaiting installation into the PA-5 boards.
- Page 5 Clip this wire at the RCA jacks, even if you keep the originals. Now remove both original RCA jacks if you choose. Install the two new jacks as shown in step 7, but the twisted wires from the RCA jacks to the PA-5 boards have different lengths in different amplifiers(DH-500/XL-600 = 2 - 11"...
- Page 6 21.( ) Select the PA-5 boards. Make sure that the DC OFFSET pot is set to center and BIAS pot is turned about 20 degrees CW. 22.( ) Select the value for R18. Those who have installed the VER 1 of the PA-5 will recall this step, but it is not required for the VER2.
- Page 7 Look to Fig. A, B and C and this table to connect your PA-5 boards. Final version of XL-280 varies - look to Fig. A, B and C Purpose of connections to PA-5 compared to original Hafler circuit boards PA-5...
- Page 8 Reconnect it according to your notes and with reference to the table, plus Fig. A, B and C. Connect the input jack wiring to the PA-5 . Remember eyelet E1 on PA-5 is for the hot wire of the input signal, i.e. connect to the center pin of the RCA jack, while eyelet E2 is for the ground part of the input jack.
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Page 9: Performance Options
We like parts without character. EXTRA GAIN: It is possible to increase the gain of the PA-5 by 3 or 6 DB. This is done by changing only one feedback resistor per channel. Extra gain can be useful if you are using a passive control center or a CD player without preamp. The original value of R13 is 90.9 ohms - using 68.1 ohms gives about 3db increase - changing to 47.5 ohms yields approximately 6db gain increase. - Page 10 Figure A. PA-5 'hot' input connection ground connection from input pair, i.e. to from input pair, i.e. to center pin of RCA jack ground tab of RCA jack Set DC offset voltage using this potentiometer. Set it to center at start. Set to 0V at + speaker terminal com- pared to ground.
- Page 13 PA-5 voltage pictorial This pictorial may be useful for verification of operating points and/or repairs. It is provided as a tool in the event of malfunction so that a local competent technician might assist you with repair services. The voltages shown are typical of a properly functioning amplifier.
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