Novel concept for a HiFi power amplifier

Dipl.-Ing. MICHAEL WIEDERHOLD

In this post, an interesting, not yet
for high quality performance amplifiers presented.
The functional connections and calculation options
are for different performance classes spelled out in detail.


There are already a large number in the literature by Scholtungen,
who the bou of NF power amplifiers higher
Enable quality and different output performance.
The concept described in the following, based on [1]
declines has the following advantages.

- DC-free output
- Possibility of using unpaired power tranistors
- A circuit design for a wide range of services
- Eliminate any adjustment work
- Availability as a DC power amplifier.

1. Circuit description

The block diagram is shown in the picture.
An operational amplifier designed electrometer amplifier
a power amplifier is connected downstream.

The feedback takes place from the rise the inverting input.
With the resistors R1 and R2 let adjust the gain.


The detailed circuit shows picture 2.
The amplified gets through the operational amplifier OV1 (A709).

Input signal via D0, T0, R5 to the emitter of T1,
T0 works with R5 as a voltage follower for relief
of the operational amplifier OV1.

This increases the level of modulation
of the perational amplifier up to close to the operating voltage.

D0 protects the base-emitter path of T0 against too high reverse voltages.

The transistor T1 is used for potential shift and causes with R5 a slight disturbance.
The base of T1 is at ground potential, D1 R6 and T2,
R10 and D2, R7, T3 and R1 form respectively a constant current source,
R8 and R9 protect the transistors T2, T3 in front of 24 large Bosis reverse currents
and suppress wild ones vibrations.

The push-pull output stage is before the darlington working transistors T4, T5
and Complementary pair stage T6, T7 formed.

The emitter resistors R16 and R17 are current feedback resistors.
With them and the three diodes D3, the quietescent current can be constant.
To the loss of performance in to keep the emitter resistances small, are bridged with diodes.

The diodes take over the load current from the resistors
when voltage drop at the emitter resistors exceeds the voltage of the diodes.
The takeover wrestling remain negligibly small.

D8 and D9 are fast switch diodes to limit surge voltages.

R14 and R15 limit the load current.
By interconnecting constant current source, D4 and R15 contribute to R14 and T5
Reaching the maximum load current like a constant current source.
The output is so reliably protected against insufficient load resistance and short circuit.

Table 1: Technical data of the 25 W. amplifier

Output power at 4 ohms
Sinus 25 W
Music 40 W.

Nominal load resistance
THD <0.1%
Frequency gong (at 25W) 3Hz..45 kHz

2.25 W amplifier (40 W music power)

In the following, a 25 W amplifier (sine power) is to be calculated (Figure 2).
The calculation method applies analogously to all of the performance classes presented.

2.1. Power, voltage, current

The amplifier should deliver a sinusoidal power of P = 25W on RL = 4Ohm.
Then the RMS and peak values ​​of
Output current and output voltage
assume the following values:
 U = 10.0V, I = 2.5A
 U = 14.15 V, I = 3.54A
  

2.2. Operating voltage

There are two operating voltages of the same size
Ur with opposite sign
necessary. To be the operating voltage
the minimum voltage drop must be correct
on D6 T5, T4, T2 and R10 can be determined.
For the forward voltage drop on
D6 T3, T4 is 2.5V on.

The collector-emitter voltage of T2 should be at 1 V,
do not fall below.
At R10 about 1.2V drop.

for the idle operating voltage U8:
Ub = 15.15V + 2.5V + 1V + 1.2V + 6V = 25V


 

 



https://www.amazon.com/Halbleiter-Schaltungstechnik-German-Ulrich-Tietze/dp/3540428496
https://www.amazon.com/Electronic-Circuits-Handbook-Design-Application/dp/3540004297