Chameleon Labs 7681 User manual

Chameleon Labs
Model 7681
Discrete Class AB Microphone Preamplifier
Module
Owner’s Manual
704 228th Avenue NE, # 826
Sammamish, WA 98074
206-264-7602
www.chameleonlabs.com
Revision A May, 2010

Your Model 7681 microphone preamplifier card has a transformer
balanced input with a gain range of +25dB to +80dB.
The Model 7681 has been carefully constructed and individually
tested for quality. It utilizes class ‘AB’ circuitry. This unit is
made with 100% discrete components and was fabricated to
precisely match vintage counterparts manufactured in the early
70’s.
The Chameleon Labs Model 7681 is based on high audio
performance design techniques. By employing classic circuit
design, polystyrene capacitors, hand selected components and
custom wound transformers, Chameleon Labs ensures that the
Model 7681 will exhibit classic audio sound. It is also designed to
comply with any 500 series powered chassis approved by the
API®VPR Alliance.
Your Model 7681 represents a dramatic breakthrough in
delivering vintage audio performance at an affordable price.

Features of the Model 7681:
•Fully balanced transformer mic input which can be
upgraded to a vintage Carnhill® unit;
•Transformer balanced output;
•300 Ohms or 1.2K Ohms mic input impedance selectable on
the front panel;
•48VDC phantom power selector on the front panel;
•12 position Grayhill® gold contact rotary gain switch for
Mic gain section;
•LED illuminated push buttons for visual confirmation
•Output level control functions as a fader when going straight
to D.A.W. or tape;
•API® 500 series compliant card;
•One-year warranty

Front Panel Controls:
General rule: When the button is pressed in, the feature is selected and the
LED illuminates.
48V Button-
This button supplies +48V (Phantom Power) to the microphone
circuit.
1.2K/300 Ω-
This button selects the microphone input impedance to either
300Ωor 1,200Ω.
Ø Button-
This button shifts the phase of the unit 180°.
DI Button-
This button connects the DI jack to the gain stage of the unit.
Gain-
This selector switch controls the gain of the preamplifier circuit.
The microphone section provides 25 to 80dB of gain in 5dB steps.
Output-
This control acts as a master fader. This allows for trimming of the
output signal, as well as allowing the input to be intentionally
overdriven. The normal position for this control is wide open.
Four position LED array-
This array provides the user with the following information:
Peak - Indicates the presence of a peak amplitude signal.
+4dB - Indicates the presence of a +4 dB signal.
Signal - Indicates the presence of signal.
Power - Indicates that the unit has power turned on.

Installing the Preamplifier Card
The Chameleon Labs Model 7681 has been designed to be
powered by an API® compliant powered chassis. Consult the
chassis’ product manual for further information.
The card can also be powered by the Chameleon Labs CPS-
501 powered chassis.

First time users
Set up of the Model 7681
1- Select 40 dB on the Gain control. Turn the Output control
fully counter clockwise. Make certain that the DI, 48V and
Phase buttons are all out.
2- If the microphone requires Phantom Power, press in the 48V
button. The normal position for the 1.2K/300Ωbutton is 1.2K,
this matches most professional microphones used today. If you
have microphones that require a lower impedance you may
select 300Ω. You can change between the values without
damage to the microphone in order to determine which
impedance performs best for your application.
3- Use the Gain control to adjust to amount of amplification
that your card will produce. The standard gain is 50dB, with
some ribbon microphones requiring as much as 70dB gain.
4- Turn the Output control clockwise until you can see level on
the input of your recording device. Increase until the desired
level is achieved.
(Vintage Hint: Adjusting the Gain control along with the Output
control can provide a variety of different sounds by overdriving
the amplifier circuits while lowering the final output level in
order to not overdrive the recorder.)
5- When an electronic instrument such as an electric guitar is
used, it may be plugged directly into the ¼” DI plug located on
the front of the card. Press the DI Button to select this input
device.
6- If phase reversal is needed, press the Øbutton.

Technical Specifications
Microphone Input Impedance: 300Ωor 1,200Ω
Microphone Amplifier Gain: +25 dB to +80 dB in 5 dB steps.
Output Impedance: 100Ω
Noise: -115.5 dB
Maximum Output: +26 dB into 600Ω
Frequency Response: 20Hz – 20 kHz +/- 1 dB.
Dimensions and Weight
Weight: 2 pound 8 ounces
Dimensions: Width – 1.5”, Height – 5.25”
Depth to Rear of Mounting Surface: 5.938” =/- 0.02”
Power Requirements: +/- 16 V @ ≤130 ma, +48 V @ 5 ma

Warranty and Liability
Your Chameleon Labs product is warranted to the original owner for
a period of one year. Chameleon Labs guarantees this product to be
free from electrical and mechanical defects and will repair or replace
defective components, or replace the unit at Chameleon Lab's option.
Should service be required for your Chameleon Labs product, please
contact the manufacturer. Service is provided for products beyond
the warranty period. Seller warrants that the goods are described in
this agreement, but no other express warranty is made in respect to
the goods. The entire risk as to the quality and performance of the
good is with the buyer. Seller disclaims all warranties either
expressed or implied, including any implied warranty of
merchantability or fitness for a particular purpose, and seller neither
assumes nor authorizes any other person to assume for it any liability
in connection with the sale of said goods.
MODEL NUMBER __________________________
SERIAL NUMBER __________________________
DATE OF PURCHASE __________________________
PURCHASED FROM __________________________
Please visit www.chameleonlabs.com for the latest updates and technical information.