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SE-5a Reading your schematic




Click on the picture above to open a window showing the SE-5a's full-size schematic. This is the same circuit as the block diagram shown in Part 2, but with all of the component values added and with numbered lugs for all off-board components (see Solder lug numbering, right). All components are numbered on the schematic (R1, C3, D2, etc), so that you can relate this schematic to the Kit contents and Turret board layout pages..
      It's the specific values in the circuit that combine to make the amplifier work and sound the way that it does. For example, capacitor C2 does two jobs. The first is to block the high DC voltage (supplied to the first stage of the preamp via resistor R2 and R14) from feeding into the input of the second amplification stage; any value of capacitor would work for this task. The second job that the capacitor does is to control the amount of lower frequencies in the amplified guitar signal that are passed from the first amplification stage to the second - higher values allow more bass through, lower values allow less.

Build now, tweak later

It's the ease with which you can alter individual components in an amp circuit that makes hand-wired amps so appealing. For example, you can swap in components with the same ratings but different values to change the response of part of the circuit. This is the real beauty of building your own amp - you can fine-tune it to the tone you like.
      It's best to get your amp up and running first, by sticking to the components specified on the schematic and supplied with your kit. There are many ways to tweak the SE-5a circuit, and you can decide if you want to try that when the amplifier is working properly as standard. While it may be tempting to leap ahead and increase the bass frequencies by using other capacitor values, for example, doing this in the wrong part of amp circuit may inadvertently cause your amp's distortion tone to become 'muddy'.

Solder lug numbering
Look closely at your schematic and you'll see numbering for the solder lugs of some of the components. For example, control pot and mains input socket each have 3 solder lugs. To avoid any confusion, your schematic includes numbers next to each connection for these components, and at the bottom left of the schematic there's also an annotated photo reference for each.


      There are nine solder lugs on the underside of each valve socket. These are numbered clockwise, starting at the gap.


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