Fender TGA-3 User Manual

15730 Stagg Street | Van Nuys, CA 91406 | 818-994-7658 | http://www.demeteramps.com/

TGA-3 100 Watt Guitar Amplifier User’s Guide

INTRODUCTION

Congratulations! You’ve just purchased one of the finest, best-sounding and most versatile amps on this planet!
Please be patient and read this manual before you power-up, and you will be richly rewarded.

OVERVIEW

The Demeter TGA-3 was designed by James Demeter as literally three amps in one. Therefore, a basic explanation
of the front panel controls and rear panel jacks is necessary to enable you to unlock the great potential of this
professional tool.

Looking at the front control panel, there are four colors of knobs: yellow, green, red, and blue. The blue knobs
are controls which are common to all channels: stereo effect returns and the presence control. We’ll talk more
about these later on.

The yellow knobs control the “clean” channel, reminiscent of a vintage Fender Deluxe or Bassman. This channel is
capable of delivering plenty of squeaky-clean volume for country or traditional Jazz styles. It also has a great
blues “bite” to it when you turn up the gain, similar to a Tweed Fender Deluxe with everything on “10.”

The green and red overdrive channels give you every possible combination of distortion, feedback and sustain.
From smooth to hard, from Vintage British Crunch to “ modded” super distortion, this amp has it all and more.

Rear Panel

Before you turn on the amp, let’s take a look at the rear panel, where you will make the proper connections to
your system.

Speakers

No tube amp should be powered up without making sure that the speakers are connected. If you have a TGA-3­100 combo amp the speaker will come connected, but it is always a good idea to check anyway. A tube amp can
burn up its output transformer (an expensive repair) if operated without being connected to a speaker.

Impedance

Always obser ve proper impedance matching. The Demeter TGA-3-100 has 3 speaker output jacks: for 4, 8 and
16 ohm cabinets. If you don’t know what the impedance of your speaker cabinet is, you should find out! If your
cabine t or speaker is not marked (most are), you can try the following:

Connect an ohmmeter bet ween the terminals or to the input jack of the cabinet, and se t the meter’s range for
at le ast 20 ohms full-scale. The reading will usually be a bit less than the actual impedance (6 or 7 ohms for an
8- ohm speaker, 3 or 3.5 ohms for a 4- ohm speaker, 13 to 15 ohms for a 16 ohm speaker). Impedance matching
is necessary to get optimum volume and tone, and to avoid undue stress on your amp.

Note: most Marshall-type cabinets will have an impedance of 16 ohms, but some may be wired for 4 ohms.

15730 Stagg Street | Van Nuys, CA 91406 | 818-994-7658 | http://www.demeteramps.com/

TGA-3 100 Watt Guitar Amplifier User’s Guide

Speaker Combining

A word about speaker combining: as mentioned earlier, there are 3 speaker outputs on the rear panel, labeled
4, 8, and 16 (ohms). When connecting one speaker cabinet to the amp, you can choose one of the three jacks
for proper impedance matching. When connecting a “full stack”, or multiple cabs, you should first determine the
impedance of e ach cab, then calculate the total impedance of the stack. This is very simple to do when using two
identical cabs with the same impedances. Simply divide the cab’s ohms by 2, and use the next smaller valued jack
for the second cab, or plug one cab into another (if you can) and go into the 4 ohm jack only.
Example: If you have 2 Marshall-t ype 4X12’s at 16 ohms each, plug one into the 16 ohm jack and one into the
8 ohm jack. If you’re running two Fender-type 2X15 or 2X12 cabs, or equivalent, at 8 ohms each, use the 8 ohm
and 4 ohm jacks, or plug one into the other and use 4 ohm.

Impedance Formula

With differing impedances, or more than two cabs (not recommended), it is a bit more complex. The formula for
calculating parallel resistances works in this situation, and is as follows:

RT = ____1_______________

__1__ + __1__ + __1__ + . . . .

R1 R2 R3
or,

____1____ = __1__ + __1__ + __1__ + . . . .

RT R1 R2 R3

Or you can take my word for it, this means if you combine more than t wo speakers with low impedance, the
figure becomes too low to use with this amp. Examples: 4 8-ohm speakers, when chained together have a total
impedance of 2 ohms, and 2 ohms is too low. Conversely, a 16- ohm Marshall cab combined with one wired for
4 ohms equals about 8 ohms. Wire cabs together and plug into 8 ohms, or plug one into 16 ohm and one into 4
ohm. Two twin-12 or t win-15 Fender cabs, usually 8 ohms e ach, equal 4 ohms. Plug one cab into the 8 ohm jack
and one into 4 ohm, or chain together and go into 4 ohm.

Loading

Note: this amp should always be connected to a load, even if you are using it as a “preamp.” You can come out of
the slave amp output jack (on the rear panel), but only if this amp is connected to a speaker, or what is known
as a “dummy” load. This is a large resistor, 8 or 16 ohms, mounted in an insulated box with a heat sink, which
has a wattage rating of 100 wat ts or better. A “power soak” (speaker emulator) or “power attenuator ” is not
always a dummy load. Although not recommended, this scheme will work. Remember, power attenuators, which
work with the amp fully “cranked”, will shorten the life of your tubes.