forced but will strip the threads). To avoid marring the panel when tightening the screws, use nylon washers under the screw
heads.
For best results, the input cables plugged into the HA-6A should be shielded. Balanced connections should use shielded,
twisted-pair cable. Headphone cables and speaker cables do not need to be shielded, though no harm is done if shielded
cables (such as microphone cables) are used.
Circuit Description
CAUTION! This section is intended to assist the professional user with considerable experience in electronics to achieve a
better understanding of the operation of the HA-6A. Under no circumstances should persons without electronics troubleshooting
experience and training undertake repairs on their own. There are no user serviceable parts inside the HA-6A. All problems
should be referred to the factory or to other qualified service personnel.
The inputs to the HA-6A proceeds from the input connectors to op-amp buffers wired as differential (balanced) amplifiers.
The input connectors are stereo 1/ 4" phone jacks. In the HA-6AB, these will be paralleled by XLR connectors. If a mono plug is
inserted, the ring connection will be grounded through the body of the plug, converting the differential amp to a noninverting
amp. After the buffers, the left and right signals proceed to the two decks of the stereo Input Level control.
The HA-6A's power amplification is derived from a pair of LM1875 integrated circuits, which have internal short-circuit and
thermal overload protection. They are set for a voltage gain of 26 dB. The LM1875's drive the speaker outputs directly. The
headphone outputs first pass through special high-power pots wired as volume controls.
The
HA-6A's power supply pr/-
24 volts unregulated to the LM1875 stages, which may drop to
+/-
20 volts under full
load. A network of dropping resistors and zener diodes provides ±15 volts to the rest of the circuit.
Both the Overload LED's and the Signal Present LED's monitor signal levels at the output (before the volume controls).
Limited Warranty
The Furman HA-6A is warranted against failures due to defective parts or faulty workmanship for a period of one year after
delivery to the original owner. During this period, Furman will make any necessary repairs without charge for parts or labor.
Shipping charges to the factory or repair station must be prepaid by the owner; return shipping charges (via UPS Ground) will
be paid by Furman.
This warranty applies only to the original owner and is not transferable. Also, it does not apply to repairs done other than by
the Furman factory or Authorized Repair Stations.
