Golden Age Project PRE-73 MKIII Manual

Golden Age Project Modtager PRE-73 MKIII

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W W W . G O L D E N A G E P R O J E C T . C O M I

Vintage Style Pre Amplifier

PRE-73 MKIII

INTRODUCTION

Congratulations on choosing the Golden Age Project PRE-73 MKIII microphone preampliﬁer!

The PRE-73 MKIII is a one-channel vintage style microphone-, line- and instrument preampliﬁer. The signal

path uses only discrete components like resistors, capacitors and transistors. The in- and output is trans-

former balanced, using two different transformers, each one optimized for its purpose. This is the way audio

components were built before integrated circuits became available.

Integrated circuits are small and cheap and they are widely used in most modern designs. It is clear though

that audio components built with modern technology doesn´t always provide the best perceived sound quality

or the type of character that the modern user desires.

On the contrary, the subjective sound quality delivered by vintage equipment is often prefered over the one

delivered by modern units, a situation that is even more obvious now when music is recorded with clean-

sounding digital audio equipment.

This is the reason why so many vintage audio components are cloned and produced again and also why the

vintage originals are often very expensive on the second hand market.

The circuit used in the PRE-73 MKIII is similar to the preamp section in the classical 1073 module with a

corresponding sound character that is warm, punchy, sweet and musical. These classic characteristics have

been heard on countless recordings through the years and it is a versatile sound that works very well on

most sound sources and in most genres.

The essence of this sound is now available at a surprisingly low cost, making it available to nearly everyone.

FEATURES

- Vintage Style electronics. No intergrated circuits in the signal path.

- Maximum gain in MIC mode is 80 dB, enough to handle passive ribbon mics with quiet sound sources.

- GAIN switch range 20 - 80 dB. GAIN/LINE mode switch, gain is reduced by 30 dB in LINE mode.

- Selectable two position high frequency AIR boost eq, 3 or 6 dB @ 30 kHz.

- Selectable 6 dB/octave two frequency high pass ﬁlter at around 40 (HP1) and 170 Hz (HP2).

- Tantalum capacitors in the signal path.

- Switchable impedance in MIC mode, 1200 or 300 Ohms, will change the tone of most mics. The input impedance in LINE mode is 10 kohm.

- Switchable phantom power and absolute phase.

- A high-impedance instrument input for any sound module, electric guitar or bass.

- A simple but effective 4-step LED output level meter.

- The output level control makes it possible to make ﬁne gain adjustments and also to overload the main gain stage(s) for more character and then

lower the signal to a suitable level before the output stage.

- Combo XLR/TRS input jack and separate output XLR and TRS jacks for ﬂexible connections.

- Insert jack for inserting EQ´s and other units.

- Selectable 600 ohm output termination.

- The pcb is prepared for the Carnhill input transformer.

- External power supply to avoid interaction with the audio circuits and transformers.

- A solid build quality that will last many years of normal use.

W W W . G O L D E N A G E P R O J E C T . C O M II

CIRCUIT DESCRIPTION

The signal ﬁrst enters the input trans-

former. The primary of the transformer

has two windings that are either con-

nected in series or in parallell which

results in an input impedance of either

1200 Ohms or 300 Ohms in MIC mode. A

resistive balanced -30dB pad is inserted

before the transformer in LINE mode.

The transformer is followed by two input gain stages. For gains up

to 50dB, only one of them is being used. For gains above 50dB, the

second gain stage is inserted in the signal path. Both gain stages

uses only three transistors each.

The signal then goes to the insert jack and from there to the

output level potentiometer and then to the output stage. This stage

again only uses three transistors, the last one in the chain is a

hefty 2N3055 power transistor run in class-A mode, driving the

output transformer.

So, all in all, the complete signal chain only contains a maximum

of nine active elements. Compare that to the big number of tran-

sistors that are usually used in one single integrated circuit!

MODERN VERSUS OLD

It is true that there are some great IC´s available today that

achieves very low levels of static and dynamic distortion.The

simple circuits that the PRE-73 MKIII uses, and even more so the

transformers, cannot match the low distortion speciﬁcations of

modern IC´s.

It is the distortion components that imparts a sound character

to the audio signal and, if the distortion components are of the

right type, this is a good thing since it makes the recorded voice

or instrument sound “better”, more musical, more pleasing to

the ear. This is one reason why vintage style units are so popular

today.

This is not to suggest that modern, transparent sounding audio

circuits is a bad thing, sometimes they are prefered over colored

ones. It´s all about taste and it depends on the genre. For most

modern music styles, color and character is deﬁnitely a good

thing.

And doesn´t it feel good to use audio components built according

to the old, minimalistic approach where one can follow the signal

from one discrete component to another?

USING THE PRE-73 MKIII

Using a preampliﬁer is not rocket science. Here are some points

though to help you getting the maximum out of the PRE-73 MKIII:

- Connect the cable from the power supply to the AC 24V connec-

tor at the back of the PRE-73 MKIII. Power on the unit with the

POWER switch on the front panel.

- Connect your Mic or Line input source to the input XLR/TRS

combo jack on the back panel.

- Select MIC or LINE mode by the MIC/LINE switch.

- Engage one of the positions of the High Pass ﬁlter if you want

to roll off the lower frequency range. Set the switch in the center

position to remove the high pass ﬁlter from the signal path.

- Engage one of the two positions of the AIR eq boost if you want

to add some level in the upper frequency range. The center of the

boost is at around 30 kHz. The switch center position = OFF.

- If you want the smallest amount of coloration, always set the

OUTPUT level potentiometer at or close to maximum and adjust

the output level with the stepped GAIN switch.

- If you want more character, turn the OUTPUT level potentio-

meter counterclock-wise and increase the gain with the GAIN

switch. This will drive the input gain stage(s) harder and provoke

more character from them.

- You can also overdrive the output stage and the output trans-

former for even more character, but you will then usually need a

level control after the PRE-73 MKIII in order to reduce the level to

the appropiate one. This level control can be a passive damping

device (like the Shure A15AS XLR switchable pad) or an input level

control in the unit following the PRE-73 MkIII. The Shure A15AS

is also useful for reducing the ouput level if the PRE-73 MKIII is

connected to a unit that has a standard operating level of -10 dBu.

The standard operating level of the PRE-73 MKIII is +4 dBu, the

output level into a 600 ohm load will be about 1,23V when the “0”

VU LED is lit.

- Instruments can be connected to the TRS input at the front which

has an input impedance of about 100 kohm. Press the DI switch to

engage this input. A source at the back can remain connected.

- Engage the +48V phantom power for any mic that needs it. It is a

good procedure to always disengage the phantom power and wait

for about 10 seconds before unplugging the mic.

- When the LOW-Z switch is engaged, the input impedance of the

input in MIC mode drops from 1200 Ohms to 300 Ohms. This will

change the tone of most mics and will give you one more sound-

shaping option. It also increases the level, which is normal.

- The phase switch simply reverses the phase by reversing the

wires from the secondary winding of the output transformer.

Reversing the phase of the signal is useful on a number of occa-

sions, one example is phase reversing the the lower mic of a

snare drum to make it sum in phase with the upper mic.

- There is an unbalanced Insert jack located at the back panel

where you can insert Equalizers and other external effect units

that has an operating level of about -10 dbu to -18dBu.

Send is on “tip” and return on “ring”.

- The output transformer used in the PRE-73 MKIII is made for

having an ideal load of about 600 ohm. The input impedance of

most modern units is 10 kohm or more. The PRE-73 MKIII there-

fore has a 600 ohm output termination resistor that is engaged

by the jumper (JP1) located just behind the XLR output jack. The

termination reistor will lower the ouput level slightly and make

the frequency response ﬂatter in the upper range, it will also roll

off the upper frequency range earlier, Remove the jumper if the

PRE-73 MKIII feed a unit with a 600 ohm imput impedance of if you

want to add som level in the upper range,

WARRANTY

The PRE-73 MKIII is built to last. But as in any electronic device,

components can break down.

There is a 1,0A, slow blow fuse located inside the unit. If the unit

dies, please check this fues. If it has blown, replace it with a new

one. You can also try with another 24V AC adaptor if you have one

available.

If this doesn´t help, or if the unit has another problem, it will need

repair and you should then contact the reseller where you bought

the unit.

The warranty period is decided by the Distributor for your country.

The Distributor will support Golden Age Project resellers and end

users with repairs and spare parts.

REGISTRATION

You are welcome to register your unit at our website:

www.goldenageproject.com

---------------------------

I would like to thank you for chosing the PRE-73 MKIII!

I hope it will serve you well and that it will help you in

making many great sounding recordings.

Yours,

Bo Medin

Vintage character for modern ideas!

Produkt Specifikationer

Mærke:	Golden Age Project
Kategori:	Modtager
Model:	PRE-73 MKIII

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