Created on 03.06.2008 20:54.
Updated 05.03.2015 19:50.
Author: V. CHERKASOV.
I would like to share with the readers one of the ways to improve the sound quality of the acoustic system, which are supplied with the “Comet 235C”, “Nota 225C” tape recorders and their modifications. It consists in replacing the long-obsolete 5GDV-1 high-frequency head with a more modern 6GDV-4.
Refinement of the speaker system does not require any special alteration of the case. You only need to make two cuts for the petal leads of the new head. To do this, it is necessary to remove the rear wall of the speaker cabinet, unscrew the screws holding the decorative panel and remove it. Then, after removing the old head and making cuts in the front panel of the speaker (Fig. 1), install the 6GDV-4 head on it. The holes of the tubular rivets should be covered with plasticine.
Further, to match the newly installed head, you need to redo the crossover filter. For this purpose, the resistor R1 is excluded from the old filter, the capacitance of the capacitor C1 is increased to 2, and C2 is increased to 4 μF. The number of turns of the U coil will have to be halved, i.e. unwind 75 turns. The schematic of the redesigned filter is shown in Figure 2. After such a refinement, the sound quality of the acoustic system becomes more pure and transparent.
If the radio amateur does not have a 6GDV-4 head, the 4GDV-1 can be used. But since its dimensions are much less than 5GDV-1, a new mounting flange will need to be made for it. It can be made of any suitable material (plywood, textolite, plexiglass, etc.) with a thickness of 6 mm. In order not to complicate the work of marking the flange, you can attach the 5GDV-1 head with a diffuser to the workpiece and circle it around the contour, marking the centers of the holes; After that, connect the centers of opposite holes, the point of their intersection will be the center of the flange, from which further marking can be carried out. On the front side of the flange, bore a hole for the 4GDV-1 head for a cone in the form of a horn (Fig. 3). The MZ screws, which fasten the head to the flange, must be countersunk.
They are inserted into the countersunk holes and fastened “tightly”, and putty on the front side. The flange itself is painted black. Next, the head is installed on the flange, and it is placed in the loudspeaker case. The separating filter is modified in the same way as in the case of the 6GDV-4 head installation.