Preamplifier with IPRS Baneasa tone corrector - Prospect 8201

Reading time: 4 minute

What does the project present?

This mounting complements the "10W Amplifier" 8109 set and is followed by the third mounting set "Audio Mixer" 8203. All these 3 vintage DIY electronic kits together form an audio frequency amplification chain, having absolutely all the elements necessary for a classic amplifier.

The preamplifier with tone corrector is made with 6 silicon transistors, distributed on several floors.

How does the assembly work?

First floor, made with T1 and T2, amplifies the signal provided by the dose, microphone or mixer and compensates the disc recording characteristic, in case of using a magnetic or ceramic dose.

Second floor is a passive network, consisting of RC elements, which makes the response curve of the preamplifier coincide with that of the ear, at low levels of listening. Thus, in the maximum position of the R13 resistance, the medium frequencies are strongly attenuated compared to the low and high frequencies. From R16 the maximum output voltage is regulated, and from P1, the signal level in the amplification chain.

Third floor, equipped with transistors T3 and T4, is a linear amplifier that compensates for the attenuation introduced by the physiological volume adjustment in the previous stage.

The top floor, the fourth, made with transistors T5 and T6, is a tone corrector, Baxandall type, which acts in the field of low and high frequencies.

Mounting output it is done by means of a repeater on the transmitter - made with the transistor T6 - in order to easily adapt the preamplifier with tone corrector to any power amplifier.

Details on the practical realization:

Particular attention must be paid to the implantation of electrolytic capacitors, with the addition in the indicated direction, as well as to transistors, whose terminals are identified following the drawing.

For establishing the optimal operating regime of transistors T1, T2, T3, T4, T5 and T6, the resistors marked on the diagram with "*" will be chosen by probing, so as to obtain the voltages indicated in table 1.

Also, the connections from the board to the potentiometers and to the plug will be made with shielded wire, if the length of the wire exceeds 5-7 cm.

List of required components (with recent equivalents):

• T1 - transistor BC 413 (BC 109) or BC 550
• T2, T3, T4, T5, T6 - transistors BC 173 (BC 109, BC 108, BC 107, BC 171) or BC 549
• R4, R12 - resistors 150 Ohm / min. 0.25W
• R1, R23, R27 - resistors 1 KOhm / min. 0.25W
• R24, R26 - resistors 1.5 Kohm / min. 0.25W
• R20 - resistor 1.8 KOhm / min. 0.25W
• R36 - resistor 2 KOhm / min. 0.25W
• R17 - resistor 2.2 KOhm / min. 0.25W
• R22, R31, R33 - resistors 2.7 KOhm / min. 0.25W
• R8 - resistor 3.9 KOhm / min. 0.25W
• R10, R37 - resistors 4.7 KOhm / min. 0.25W or 2.2K / min. 0.25W
• R11, R15, R25 - resistors 10 KOhm / min. 0.25W
• R7 - resistor 12 KOhm / min. 0.25W
• R3 - resistor 33 KOhm / min. 0.25W
• R6 - resistor 39 KOhm / min. 0.25W
• R9, R29, R35 - resistors 56 KOhm / min. 0.25W
• R2 - resistor 680 KOhm or 1 MOhm or 2.2 MOhm / min. 0.25W
• R5 - resistor 100 KOhm or 820 KOhm or 470 KOhm / min. 0.25W
• R19, ​​R30 - resistor 68 KOhm or 150 KOhm or 470 KOhm / min. 0.25W
• R34 - resistor 1 MOhm / min. 0.25W
• R14 - resistor - 82 KOhm / min. 0.25W
• R18, R28 - resistors 120 KOhm / min. 0.25W
• R21, R32 - resistors 220 Ohm / min. 0.25W
• C2 - ceramic capacitor 10 pF / min. 50V
• C18 - ceramic capacitor 3.3 nF / min. 50V
• C6 - ceramic capacitor 22 nF / min. 50V
• C12 - ceramic capacitor - 47 nF / min. 50V
• C11 - styroflex capacitor - 220 pF / min. 50V (or ceramic)
• C9 - styroflex capacitor - 680 pF / min. 50V (or ceramic)
• C16, C17 - polyester capacitors 0.68 uF / min. 50V
• C10 - polyester capacitor 1 uF / min. 50V or 0.68 uF / min. 50V
• C1, C5, C19 - electrolytic capacitors 4.7 uF / 40V or 6.8 uF / min. 40V
• C3, C4, C8, C13, C14, C15, C20 - electrolytic capacitors 22 uF / 25V
• C7 - ceramic capacitor 68 nF / min. 50V
• C21 - electrolytic capacitor 100 uF / 6.3 V or 150V / 10V
• R13 - semi-adjustable resistor - 50 KOhm / 0.5W
• R16 - semi-adjustable resistor - 10 KOhm / 0.5W
• P2, P3 - linear potentiometers - 10 KOhm / 0.5W (can also be rotary)
• P1 - logarithmic potentiometer - 10 KOhm / 0.5W
• Input plug with 5 contacts
• buttons
• Printed wiring or breadboard test board
• Tin or connecting threads

Download the original IPRS leaflet Baneasa 8201

For a better understanding of the operation of the circuit we will also need electronic scheme presented below:

In order to carry out this project in our own laboratory, we will also need printed wiring PCB layout From lower:

Many of you are probably wondering how this DIY electronic kit was packaged or distributed. Below I have attached some pictures with packaged product (new) and the contents of the envelope. Thank you Mr. Marius Balauta for providing pictures.