Making A Monoblock out of a VK-55

From the BAT website.

Sensible Upgrade Path
The VK-55 is available as either a 55 watt per channel stereo amplifier or a 110 watt per channel monoblock power amplifier. Start with a single stereo VK-55 and if you ever change speakers or simply want more power, you can buy a second amplifier and have your stereo unit easily updated to monoblock status.

Call BAT and they will tell you what to do. Great customer service. They always take time to help you out. I have a VK-75 that needs 2 sets of jumpers in place to make a mono.

Tim

Here's how its done, some as what you can do with our amps:

put a Y adaptor on the inputs so the both have the same signal. Put a wire from the right +output to the left +output and then another wire from the right -output to the left -output. The only nuance is that whatever tap you are using at the output is the one where the +outputs are tied together. The tap that you used before monostrapping may not be the one you prefer when monostrapped.

That's all there is to it- the result will be double the output power, and you will loose a slight amount of delicacy.

Hi Ralph,

I'm wondering how or if doing that would double output power, into a given load such as 8 ohms.

As I see it, what you are doing by paralleling the channels is doubling the amount of current that is potentially available, and also halving the output impedance of the amp. The reduced output impedance would produce some increase in the voltage swing that could be applied across the 8 ohm or whatever load, thereby providing some increase in the current and power delivered, but not nearly by as much as a factor of 2.

Also, I think it's worth noting for others who may read this that this would not be safe to do with most or all solid state amps, and is not the same as what is done when solid state amps are mono-strapped. In that case, the two channels process signals that are inverted relative to one another, and the speaker is connected between the two red terminals.

That can be thought of as placing the output stages of the two amp channels in series, doubling the voltage swing capability and increasing the available power by an amount that may approach a factor of 4, if current capability and thermal constraints allow. While at the same time having the downside of causing each channel of the amp to have to drive a load that it sees as equal to the speaker impedance divided by 2, which would not be the case with the paralleled channel approach.

Best regards,
-- Al

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.