OTHER SCHEMATICS

Misc. Audio Projects

Here are the schematics for some gadgets I built just for fun.

Tube Mic/Line Preamp ( Schematic )

• This is a simple tube preamp based on the Altec 1566A, an industrial / commercial preamp from the 1960s. Has low and high impedance inputs and outputs for compatibility with a wide variety of musical and studio equipment.

Treble Booster Pedal ( Schematic + Layout )

• This is a simple effect box for electric guitar, using one germanium transistor. Based on a 1960s vintage effect called the ''Rangemaster'' which was sold by Dallas-Arbiter. It shifts the frequency response curve toward the high end and significantly boosts the signal level from the guitar, which makes it ideal for overdriving tube amps.

Simple Attenuator and Dummy Load ( Schematic )

• Useful for testing amps at full power without damaging your hearing and pissing off your neighbors. This version will handle amps up to 40 Watts.

High Voltage Flash Trigger ( Schematic + Layout )

• This has nothing to do with amps, but I found it useful for photography. It's a simple circuit that safely interfaces vintage high-voltage flash units to modern cameras that can't handle the high voltage. Most modern digital SLR cameras can only handle a few volts on the sync circuit. For example, most of Canon's EOS digital cameras are only rated for 6 volts on the sync circuit. Unfortunately, many of the large flash units available on the used market put much higher voltages on the sync circuit, reportedly even as much as 400 volts on a few makes/models.

Other Amp Schematics

Here are a few schematics of other manufacturer's amps that I needed to repair but couldn't find schematics elsewhere for, so I ended up having to trace the wires and draw the schematics myself. I'm putting these up here in case any other amp techs need to work on similar amps. The amps I worked on could have been previously modded or hacked before I received them, so these schems might not match the original amps exactly. Use at your own risk.

In case it's not obvious, I'm not affiliated with the companies that made these amps, so I can't really answer questions about them.

Electromuse Model 8A ( Schematic )

• A typical house-branded Valco/National amp from the lap steel era. A small vinyl-covered box with the amp chassis facing rearward on a shelf above the 8-inch speaker.

Gregory Mark 1 ( Schematic )

• An el-cheapo practice amp from the 1960s.

Kay Model 750 ( Schematic )

• The K-750 was only made in 1967 (right before Kay went bust), so nobody ever seems to know anything about this particular model. It's electrically identical to the 'C' version of the Kay 703 amplifier, but looks completely different on the outside.

Kent Models 1475, 2188, 2198 ( Schematic )

• This schematic applies to some of the USA-made Kent amplifier models from the early 1960s. The Kent name was also used on Japanese import amps in the late 1960s and 1970s, but the construction of the Japanese units was similar to the prior US units (i.e. very cheap). Kent amps seem to always fail from bad tube sockets. Try replacing the sockets before fixing anything else.

London Electric Model 8 ( Schematic )

• A practice amp from the 1960s with a built-in tremolo effect. ...and groovy paisley pattern grill cloth.

Supro Valkyrie ( Schematic )

• This Supro is unusual because it has 7355 output tubes. It's otherwise very similar to several other Supro/Valco models. This model was probably not manufactured in very large quantities before the 1967 merger of Valco and Kay.

If you were looking for schematics of Rick-Tone amps, go here.

If the schematic you need isn't here, there are loads of other guitar amp schematics over at Larry's SchematicHeaven.com. Check it out.

Guitar Schematics

Danelectro 59 DC Re-Issues ( Schematic ) ( Upgrade Photos )

• When I was working on some Danelectro guitars, I had trouble finding schematics for any of the two-pickup versions so I ended up drawing them myself. The drawing shown here includes two schematics. The first is for the 2007 Danelectro 59 (made in China re-issue) with two knobs (one volume, one tone). The second is for the 1999 Danelectro 59 DC and DC PRO (made in Korea re-issue) with two pairs of stacked concentric knobs (two volumes, two tones). Also see the photos of a 2007 re-issue I upgraded to the vintage style concentric controls.

OTHER USEFUL INFORMATION

Table of primary impedance values for common 70v/25v audio line transformers.

• PDF