Making A Monoblock out of a VK-55

Right, Al, you can't use this technique with transistors!! They have to be bridged.

Dynaco describes this monostrapping technique in the manual for their old Stereo 70. You do indeed get 2X the power. Since the output impedance is reduced (as seen by the fact that the current **potential** is doubled), the output voltage is slightly increased, by about 9V RMS. That doubles the power. Try it :)

Thanks, Ralph. Here is a link to the ST70 manual, in which the relevant paragraph is on page 12:

http://www.curcioaudio.com/st7_mnl.pdf

However, I think that what is being said is that to realize the 2x power increase, a 4 ohm speaker would have to be connected to paralleled 8 ohm taps, and an 8 ohm speaker would have to be connected to paralleled 16 ohm taps (assuming they are present).

If an 8 ohm speaker were connected to paralleled 8 ohm taps, the manual appears to say that a considerably smaller increase in power would occur, although distortion would be improved. That makes sense to me, and can be seen by considering the example of power delivery into 8 ohms, assuming constant source voltage but assuming in one case an amp output impedance of say 4 ohms, and in the other case an amp output impedance of 2 ohms (corresponding to paralleling the channels but without changing taps). That results in a 44% power increase. Amps with lower output impedances would realize smaller power increases.

I do see, though, that paralleling channels AND moving to a tap rated for twice the load impedance would result in twice the power capability, since the higher impedance tap presumably puts out a voltage that is higher by a factor of the square root of 2, and the paralleling of channels provides the current capability to support that higher output voltage.

So I believe that the bottom line is that for a nominally 4 ohm speaker the power can be doubled by using paralleled 8 ohm taps, but it can only be doubled for a nominally 8 ohm speaker if 16 ohm taps are available.

At least, I THINK so :)

Best regards,
-- Al

I always like it when atmasphere and almarg join in. Thanks for the info guys, its always enlightning when reply. I think more of what I was getting at is that isn't it better to have an amp that is designed as a monoblock than one that is paralleled to present one channel? Does parralleling an amp affect it's sound for better or worse? And what does this sound like on the VK-55?

Ikonetic, I refer you to my earlier post- you will loose some delicacy.