nOhr ACA Owners manual

Audio Control Amplifier (ACA)

Congratulations

If you are reading this for the first time, you are probably not yet aware what a wise pur­chase you have made buying the nOrh Audio Control Amplifier (ACA). While the ACA is
one of the least ex p ensive pream plifi ers on the market, it is also o n e of the best. Best?
You might wonder how we can claim that this preamplifier is one of the best.

The function of an audio control amplifier is to provide switching, provide preamplifica­tion and amplitude ad j ustment. In performin g these tasks, it is essential that the a ud io
control amplifier not introduce any noise or change the character of the signal what-so­ever.

The nOrh ACA was designed by Werner Hartinger, presi dent o f Audioform. Werner
believes in the philosophy of creating the shortest possible signal paths and keeping the
design as clean as possible.

The bottom of the preamplifier contains the transformer. The transformer is oversized by
any standards. It is larger than many receivers and integrated amplifiers use. The con­nection between the transformer section and the preamp section is made via a stainless
steel wave tunnel to isolate the RF interference from the preamplifier section.

The volume control is one of the world's best volume controls made by DACT. This volume
control is better than the volume control found in preamplifiers costing many times that of
the ACA.

All of the switc hing is done via sealed gold plated relays. Only the signal path requir ed is
in the circuit at one time. This elimin ate s noise . T h e volume contr ol and the relay switch -

ing will eliminate the big ge st sour ce of fa ilures for prea mplif i ers.

The AD 797 is the best audio op amplifier in the world. They are expensive and they are
hard to source. The AD 797 has a 9 parts per million THD figure and will sync or source
with an input of 50 milli-amps. While some preamplifiers use the AD 797 to drive the
amplifier, nOrh uses the BUF 634 from Burr Brown to increase the output of the AD 797
by a factor of 5x. The output from the ACA is enough to easily drive headphones. In fact,
the output is enough to drive a small pair of external speakers.

The BUF 634 acts like a line conditione r. T his allows you to run longer wires between the
amplifier and preamplifier. It also makes the selection of wire between the amp and
preamp less critical. If you are using the Multiamp in active mode, it is therefore better to
place the amplifier closer to the speakers and let the ACA drive the cables to the Multi­amp. This will also allow you to save money on speaker wire.

Operation

Now that we have to ld yo u how good the ACA is, it is time to learn about its feat ur es and
how to use the ACA.

Headphone

A switch is provided to power a pair of headphones. The jack is in the back of the ACA. If
you are listening to headphones, push the switch up. An LED will remind you that the
headphone c irc uit is activa te d. Usi ng th is arrang eme n ts allows you to leave the head­phones plugged in even when not listening to headphones. If you haven't enjoyed listen­ing to headphones in the past, chances are you have never had a good amplifier driving
the headphon e s. The ACA is on e of the best hea dphone amplifiers on the market .