Simple Hybrid Audio Amplifier
Author: Circuit ProjectsCategory: amplifier circuits
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The controversy still continues regarding that are better, valves or transistors. We don’t plan to get involved with that argument here. But when you can’t make your choice, you should attempt out this straightforward amplifier. This amplifier utilizes a valve like a pre-amplifier along with a MOSFET within the output stage. The strong negative feedback helps make the frequency response as flat like a pancake. Within the prototype from the amplifier we’ve also tried several alternative components.
For instance, the BUZ11 could be replaced by an IRFZ34N as well as an ECC83 may be used rather than the ECC88. If so the anode voltage ought to be reduced slightly to 155 V. The ECC83 (or its US equivalent the 12AX7) requires 2 x 6.3 V for that filament supply and there's no screen between your two triodes, normally attached to pin 9. This pin has become attached to the common of these two filaments.
The filaments are attached to ground via R5. If you’re keeping track of the standard, you need to a minimum of use MKT types for coupling capacitors C1, C4 and C7. Better yet are MKP capacitors. For C8 you ought to have a glance at Panasonic’s selection of audio grade electrolytics. P1 can be used to create the quantity of negative feedback. The greater the negative feedback is, the flatter the regularity response is going to be, however the smaller the general gain becomes.
With P2 you are able to set the quiescent current through T2. We've chosen a reasonably high current of just one.3 A, making the output stage operate in Class A mode. This may produce a relatively great deal of heat, which means you should make use of a large heatsink for T2 having a thermal coefficient of just one K/W or better. For L1 we connected two secondary windings in series from the 2x18V/225 VA toroidal transformer.
The resulting inductance of 150 mH was a great deal a lot more than the recommended 50 mH. However, by having an output power of just one W the amplifier struggled reproducing signals below 160 Hz. The distortion rose up to 9% for any signal of 20 Hz at 100 mW. To correctly reproduce low-frequency signals the amplifier requires a bigger coil by having an iron core as well as an air gap. Jetski from the core from saturating whenever a large DC current flows with the coil.
