Shaker Amplifier

[Toby Paddock]

Warning, this got real long again. 
Feel free to bail out if you start dozing off.

Earlier I wrote: 
>Wait a minute....  If all the transistors are 
>the same, how can you have + and - drive?

All the drive transistors are NPNs (PP4058, 
I think they are discontinued. Does that 
make it *vintage*?)  After looking at the 
simplified schem I nearly understand how this works.

There are 2 pretty much identical power amp sections, 
LEFT and RIGHT, filling a rack bay.  Somewhere in the 
preamp the input signal gets inverted for one section.  
The output is 2 conductors, the LEFT and RIGHT 
output buses. The RIGHT output bus is connected to 
the emitters of the LEFT bank of transistors (0.5 ohm 
series with each emitter for load sharing). The collectors 
are tied to the LEFT heat sink which is connected to the 
(+) of the LEFT 85V power supply.  The (-) of the LEFT 
power supply is tied to the LEFT output bus.  And the 
same thing for the other side, except flip RIGHT and LEFT.

Then there is another amp bay, same as above, with the 
output connected in series with the first.  I guess you can 
just add on amp bays in series till you get enough.  
The interconnections are copper pipes, one inside another 
(with an insulator) to reduce inductance. The AC drive coil 
of the shaker is connected by ten 12-conductor #10 cables.  
In each cable half the conductors go to each of the 2 drive 
buses so the currents are opposite, mag fields cancel, and 
inductance is reduced. (Wow, what an awful description.)

So for each amp bay, instead of a bipolar supply, it's 2 single 
supplies each referenced to the other output bus.  
Or something like that.  Only one side is active at a time. 
This might be a standard power amp config, but it's new to me.  
In each bay: 500 output transistors, 46 base drive transistors, 
12 diodes (all water cooled), one 480v 3-phase transformer 
about 1 foot x 1.5 foot x 1.5 foot, 46 19,000uF caps, preamp 
(don't know what's inside), and assorted do-dads.

Magnus Danielson wrote:
>I guess that the stroke-length used for maximum sinusoidal 
>responce may not be 1 inch all the way up to 2k, right?

Yes absolutely. For sine, g is a function of displacement and freq^2. 
g pk= 0.0511f^2D, where D is displacement pk-pk. 
1 inch pk-pk at about 4 Hz is 1g pk.  
0.001 inch pk-pk at about 2000 Hz is 200g pk.  
The system is rated for 20,000 force-pounds and minimum 
moving weight is 100 pounds (the armature) so the max 
acceleration is 20,000/100= 200 g pk.  
If you add 300 pounds load then it's 50 g pk. 
In theory. Some frequencies is more, some it's less.  
Low frequencies hit the displacement limit. 
High f hits current limit. 
For mid frequencies the armature velocity is high and the 
amp runs out of voltage due to the shaker's back emf.  

Some pictures I took today:

One of the 2 amp bays, lower left is the transformer 
for that bay, lower right are 4 water cooled blocks for the 
12 diodes, above that are 2 base drive groups, above that 
the output stuff is visible.
http://www.seanet.com/~tpaddock/images/P001664.jpg

Closer view of transformer, diodes, and base drive.
http://www.seanet.com/~tpaddock/images/P001665.jpg

Front of output buses.
http://www.seanet.com/~tpaddock/images/P001666.jpg

Left are output buses, center is 1 row of 19,000uF caps, 
right are output transistors in square water cooled copper 
pipes, each transistor has a small circuit board on it.
http://www.seanet.com/~tpaddock/images/P001667.jpg

Back of amp bay.
http://www.seanet.com/~tpaddock/images/P001669.jpg

Closer view back of amp. From center out: 30 
amp fuses, 0.5 ohm load sharing resistors, 
more output transistors.
http://www.seanet.com/~tpaddock/images/P001668.jpg

480V power input at top, shaker connectors at left.
http://www.seanet.com/~tpaddock/images/P001671.jpg

Output buses of one amp section, note the coaxial pipes
at the top.
http://www.seanet.com/~tpaddock/images/P001674.jpg

Connecting the 2 amp bays together. There is a 
copper pipe inside the visible pipes tying the 2 bays together. 
The cables go to the shaker connectors.
http://www.seanet.com/~tpaddock/images/P001672.jpg

 - -- -  Toby Paddock
http://www.seanet.com/~tpaddock