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Old 15th January 2007, 11:01 AM   #1
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Default Small power amplifier + Phono MMHa

For whom need a small power amplifier with good performance and not excessive part count, here is a project of my own which has well operated for 5-6 years before it's substitution with a "vintage" (and cheap!) amplifier which is just more esthetically compliant to the taste of my relatives.

BE AWARE - It's not a work for untrained people. Building it is not too difficolt but neither easy.

Here is also included a MM phono cheap phono stage which, with CD, was my ever preferred source and was build contextually with the proposed amplifier.
Adding a rotary input selector and a two pots volume and balance control and you obtain just an essential small power integrated amplifier. Ah, you must add a power supply too, obviously... ;-).

Driver must be mounted on a *different* heathsink from that used for output devices (which are TIP2955/3055 but may be any complementary pair of at least 60 Vce and 8 Amp Ic, with a minimum Hfe of 30-40 at 4 A of Ic - Dissipation capabilities must be *at least* that provided from TIP2955/3055).

The Vbe multiplier BD137 must be mounted on the same heathsink where are mounted output devices. Overall dissipation capabilities to be provided for each channel must be *at least* of 25 Watt, especially when lowest impedance speakers are used.

BD537-538 must be provided of their own heathsink in order to provide a dissipation capabilities of 3-4 Watt if mounted paired together, or 2 Watt if each driver is mounted on their own single heathsink.

Quiescent current must be set in reading between the emitters of ouput devices (and with 0.47 Ohm ballast resistors as laid down un schematic) about 90 mV.

Power supply must be filtered by 15mF+15mF if common for two channels or by 10mF+10mF per channel if any amplifier is supplied by it's own rectifier (the main transformer may be common for the two channel; it must be just able to supply the required current for the complete amplifier - I used a 150 VA toroidal transformer but minimum is just 100 VA or so).

The Phono MM require just the regulated supply of a pair of 7812/7912 voltage stabilizers wich, in turn, may be feed by the main PSU of the amplifier or, if you will, by a dedicated third rectifier, filtering section).

Even I have a draft of PCB layout, this is a bit outdated and, however, i suggest to build it on a breadboard PCB in order to best fit your mounting exigences.

Have fun! :-)
Piercarlo
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