Theory
OVERVIEW
It should be noted that over time Crown makes im- provements and changes to their products for various reasons. This manual is up to date as of the time of writing. For additional information regarding these amplifiers, refer to the applicable Technical Notes provided by Crown for this product.
This section of the manual explains the general opera- tion of a typical Crown power amplifier. Topics cov- ered include Front End, Grounded Bridge, and ODEP. Due to variations in design from vintage to vintage (and similarities with other Crown products) the theory of operation remains simplified.
FEATURES
Micro Tech amplifiers utilize numerous Crown innova- tions including grounded bridge and ODEP technolo- gies. Cooling techniques make use of the what is essentially air conditioner technology. Air flows bot- tom to top, and front to side. Air flows a short distance across a wide heatsink. This type of air flow provides significantly better cooling than the “wind tunnel” technology used by many other manufacturers. Out- put transistors are of the metal can type rather than plastic case. This allows for a significantly higher thermal margin for the given voltage and current ratings. All devices used are tested and graded to ensure maximum reliability. Another electronic tech- nique used is negative feedback. Almost all power amplifiers utilize negative feedback to control gain and provide stability, but Crown uses multiple nested feedback loops for maximum stability and greatly improved damping. Most Crown amplifiers have damp- ing in excess of 1000 in the bass frequency range. This feedback, along with our compensation and
Features specific to the Micro Tech Series’ include two seperate power transformers (one for each channel), a full time full speed fan which also serves as the low voltage transformer, slew rate limiting, and audio muting for delay or protective action. This amplifier can operate in either a Bridged or Parallel Mono mode as well as dual (stereo). A sensitivity switch allows selection of input voltage required for rated output. Level controls are mounted on the rear panel and are of the rotary type. Front panel indicators let the user know the status of the low voltage power supply (enable), and an ODEP indicator for each channel which shows the reserve energy status. In general, the
packaging of this model is designed for maximum watt/price/weight/size value with user friendly fea- tures.
For additional details refer to the specification section, or to the applicable Owner’s Manual.
FRONT END OPERATION
The front end is comprised of three stages: Balanced Gain Stage (BGS), Variable Gain Stage (VGS), and the Error Amp. Figure 1 shows a simplified diagram of a typical front end with voltage amplification stages.
Balanced Gain Stage (BGS)
Input to the amplifier is balanced. The shield may be isolated from chassis ground by an RC network to interrupt ground loops via the Ground Lift Switch. The
Variable Gain Stage (VGS)
From the output of the BGS, the signal goes to the VGS where gain is determined by the position of the Sen- sitivity Switch, and level is determined by the level control. VGS is an inverting stage with the input being fed to its
Error Amp
The inverted output from the VGS is fed to the non- inverting input of the Error Amp
8
