What does the project present?
This DIY electronic kit contains all the components needed to build a 15W audio frequency amplifier. Its performance, the relatively affordable price of the components, the ease of execution, make it accessible to any electronics enthusiast passionate about the audio field.
How does the project work?
The assembly contains the following floors:
- Pilot floor - made with transistor T1 and the related circuit elements; has the role of maintaining the symmetry of the exit floor.
- Attack floor (driver) made with transistor T2 and related circuit elements; has the role of controlling the exit floor.
- Exit floor - made with transistors T3, T4, T5, T6 and the related circuit elements; it is made after a quasi-complementary symmetry and has the role of transferring to the load a certain amount of power, depending on the level of the signal applied at the input.
The assembly benefits from some specific circuits audio frequency amplifiers:
- Group R6, C2 - ensures an additional decoupling for the polarization circuit of the base of the transistor T1, thus maintaining a high level of the signal / noise ratio. Rin R6 also achieves the symmetry of the exit floor.
- Group R1, C1 - ensures the coupling of the assembly with other stages within an audio frequency chain and a constant phase shift in the whole frequency band reproduced by the amplifier.
- Group R5, R7, C4, C5 - ensures the negative reaction both in direct current and in alternating current.
- Group R9, D1 - ensures an initial polarization of the output floor, thus reducing distortions.
- Group C7, R15 - ensures the stable operation of the assembly by canceling any tendency of self-oscillation.
Technical characteristics of the assembly
- Rated power: 15W
- Voltage gain: 20 dB
- Frequency band: 40… 20000 Hz
- Sensitivity: 0.7 Vf
- Input impedance: 150 KOhm
- Signal to noise ratio: min. 65 dB
- Supply voltage: 30V
- Maximum current absorbed: 1A
List of required components (with recent equivalents):
- T1 - transistor BC 251 or BC 557
- T2 - transistor BC 171 or BC 547
- T3 - transistor BD 135 or BD 137 / BD 139
- T4 - transistor BD 136 or BD 138 / BD 140
- T5 - transistor 2N3055 or 2N3773 / BD 243 / BD x53 / TYPE 41 / MJE 3055
- T6 - transistor 2N3055 or 2N3773 / BD 243 / BD x53 / TYPE 41 / MJE 3055
- D1 - diode DRD 3 or 1N4007
- R1 - resistor - 1.2..18 KOhm (min 0.4W)
- R4 - resistor - 1.2..18 KOhm (min 0.4W)
- R2 - resistor - 150..160 KOhm (min 0.4W)
- R3 - resistor - 150..160 KOhm (min 0.4W)
- R5 - resistor - 4.7 KOhm (min 0.4W)
- R6 - resistor - 68 KOhm (min 0.4W)
- R7 - resistor - 470..560 Ohm (min 0.4W)
- R8 - resistor - 33 Ohm (min 0.4W)
- R9 - resistor - 220..330 Ohm (min 0.4W)
- R10 - resistor - 2.7 KOhm (min 0.4W)
- R11 - resistor - 680 Ohm (min 0.4W)
- R12 - resistor - 82..120 Ohm (min 0.4W)
- R13 - resistor - 82..120 Ohm (min 0.4W)
- R14 - resistor - 47..68 Ohm (min 0.4W)
- R15 - resistor - 47..68 Ohm (min 0.4W)
- R16 - resistor - 0.47 Ohm / 3W
- R17 - resistor - 0.47 Ohm / 3W
- R18 - resistor - 10..22 Ohm (min 0.4W)
- C1 - capacitor - 2.2uF / 63V
- C2 - capacitor - 10uF / 40V
- C3 - capacitor - 22uF / 25V
- C4 - capacitor - 100uF / 25V
- C5 - capacitor - 100pF
- C6 - capacitor - 222pF
- C7 - capacitor - 0.1uF
- C8 - capacitor - 1000 uF / 25V
- Recommended acoustic enclosure: 4 Ohm / 20W
- Two radiators for T5 and T6; the transistors are mounted on a aluminum radiator with a minimum surface of 200 cm2.
- Printed wiring or breadboard test board
- Tin or connecting threads
At commissioning it is recommended to go through the following steps:
- carefully checking the installation;
- checking the connection of the final transistors;
- charging impedance connection;
- the correct connection of the supply voltage, after which the assembly is supplied and an audio signal of maximum 0.7 Vef is applied to the input.
Download the original IPRS Baneasa SME-8310 leaflet
For a better understanding of the operation of the circuit we will need electronic scheme presented below:
I have also attached below a view of the location of the components:
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 the packaged product (new) and the contents of the envelope. Thank you Mr. Marius Balauta for providing pictures!
4,780 total hits, 1 hits today
It would be interesting to see if anyone has a clear picture of the wiring for a reproduction attempt.
In the article I also attached the image of the wiring. The picture is pretty clear.
I saw it now, being on the phone I didn't orient myself too well there.
The best amplifier for amateurs in the '90s!
I had a bad hand, neither the 10W nor the 2x15W ones I assembled with the utmost care did. I never found out the cause, I gave them to more advanced colleagues to fix them and that was it.
I had a similar problem with the amplifiers. Whenever I powered them, they didn't work at first .. but .. after two, three days of troubleshooting .. they worked .. 🙂 I found components that were defective and of course incorrectly positioned / placed ..
Daaaa… great… 20 years ago, I still modify them with colleagues, at work, I "upgrade" them…
I'm doing very well. With small modifications you can get 30-40W. They were in vogue among the amateurs of the '80s. Recently, together with my son, out of nostalgia I made an amplifier with two such amplifiers. I had many kits bought for the parts.
There was also a 12V powered converter that lit a 20W neon lamp with 2n3055. She was gorgeous!
With changes in components, power supply, etc. could increase power to 80W…
I heard / saw such an amplifier on Romanian 15-inch speakers I think. Sounds very nice!
Powered at 45 vdc. Prefinals BD237 / BD238 on radiator. KD 507 two pieces in parallel and electrolytic on 63 vdc. A friend's father was generous after explaining to us how things are with the scraps from those packages. After the modifications, they got along perfectly with two "Nova" of 45 W. It was fierce competition! The prize went to the one who managed to sell the amplifier. I was the winner and I received a defective AS 2050. I only resurrected him in '92. How proud I was of Nea Tase! AS 2050 reached a collector in 2000.
I found a modified 1987W amplifier diagram from 10. The scheme was given to me by a colleague and I did not put it into practice.
It is powered by 2x30V, has a small change and of course capacitors on higher voltage. I remember the amplifier, it sounds good.