ผู้เขียน หัวข้อ: ECL86PP ตามแนวทาง Pro  (อ่าน 994 ครั้ง)

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ECL86PP ตามแนวทาง Pro
« เมื่อ: 19 เมษายน 2014, 05:47:51 PM »
 

              The design of the circuit shown in Fig. 1 is very similar to the well-known Mullard 'Five-Ten' monophonic amplifier. Only one channel and the common power supply are shown in Fig. 1 except for the loudspeaker phase reversal switch SC, the other channel is identical. The complete amplifier uses two EF86 and four ECL86; and a suitable rectifier is the GZ34.
Input Selector Switch

The input stages of both channels are connected to the 3-way input selector switch SA, which provides facilities for stereophonic reproduction from a crystal or ceramic pick-up head, and dual-channel monophonic reproduction from a monophonic pick-up head or fm tuner unit.
Input Stage

The input stage uses an EF86. The voltage gain of the stage is approximately 120 times. The stage is capacitively coupled to the phase splitter.
Phase Splitter

The phase splitter uses the triode sections of two ECL86 in a 'long-tailed' pair. Fixed bias to the grids is provided by a potential divider across the ht supply. The voltage gain is approximately 24 times per half.
Output Stage

The push-pull output stage uses the pentode sections of the two ECL86 opterating under class AB conditions with distributed loading (20% taps). With an anode-to-anode load of 9kΩ and an anode-to-cathode voltage of 300V, the distortion without feedback is less than 2% for outputs up to 10W.

The output transformer should be of the construction normally used in high-quality amplifiers. In particular, it should be free from any pronounced resonance up to about 50kHz The turns-ratio should be such that the anode-to-anode load is 9kΩ after allowing for winding resistances. The transformer used in the prototype has the following specifications:

    Total primary inductance 100H
    Primary resistance per half 265Ω
    Leakage inductance (whole primary, with secondary short-circuited 21mH, Secondary resistance at 15Ω terminals 0.9Ω

Negative Feedback

Overall negative feedback of approximately 20dB is applied from the secondary winding of the output transformer to the cathode circuit of the input stage. Coupling time constants which are considerably greater than the transformer time constant ensure low-frequency stability. A 'phase advance' network in the feedback path gives adequate high-frequency stability.

The amplifier design is such that more than 17dB of negative feedback is effective over a frequency range of 30Hz to 30Hz.
Tone-control Circuits

Passive tone-control circuits giving bass boost and cut and treble boost and cut are provided. The input impedance of the tone control circuits is about 500kΩ.
Balance Control

The balance control consists of a dual-ganged potentiometer, one track obeying a logarithmic law, and the other an anti-logarithmic law.
Power Supply

The power supply requirements for both channels of the amplifier are:

    Heaters 6.3V 3.2A for 4 x ECL86 plus 2 x EF86
    HT 320V No signal 138mA, 315V 10W sine wave l60mA per channel

PERFORMANCE
Sensitivity

The sensitivity of the basic amplifier for an output power of 10W is 2.3mV without feedback and 23mV with feedback. The sensitivity of the complete amplifier, including tone controls, is 210mV.
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ออนไลน์ CreÃte_Lek ♫

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Re: ECL86PP ตามแนวทาง Pro
« ตอบกลับ #1 เมื่อ: 19 เมษายน 2014, 05:53:29 PM »
Frequency Response and Phase Shift


Frequency response and phase shift characteristics of 10W amplifier

        The graph above shows the frequency response and phase shift characteristics of the basic amplifier (without tone controls). The response is flat to within 3dB from 3Hz to 60kHz at 50mW.

The power response (for 10W output) is also shown in the graph. This response is flat to within 3dB from 12Hz to 35kHz.

The loop-gain and loop phase-shift characteristics are given in the graph below.


Loop gain and loop phase shift characteristics of 10W amplifier


   Harmonic Distortion

 
Total harmonic distortion plotted against output power for 10W amplifier

The total harmonic distortion, measured with an input signal at 1kHz, is plotted against output power and shown in the image above. The total harmonic distortion at an output power of 10W is less than 0.2%, a typical value being 0.15%

Output Impedance

The output impedance of the amplifier measured at the 15Ω terminals is 1.4Ω for an output of 1W at 1kHz. This gives a damping factor of 10.7.

Tone-control Characteristics


Tone control characteristics of 10W amplifier

The response characteristics of the tone-control circuits are shown. The ranges of control with respect to the response level at 1kHz are approximately:

    Bass: +12dB to -12dB at 30Hz
    Treble: +12dB to -12dB at 15kHz


Hum and Noise

The level of hum and noise in the prototype amplifier, measured with a short-circuited input, is typically 75dB below 10W.

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