Paralleling Audio Transformers

Web Police · Feb 26, 2014

Sounds good. Carry on. :rabbit:

Gepetto · Feb 26, 2014

Call your doctor if it lasts for more than 4 hours Lee. As a matter of fact, call everybody if it lasts for more than 4 hours

laatsch55 · Feb 26, 2014

Take out an ad in the local paper..

laatsch55 · Feb 27, 2014

Ok, I have some toroids that are around 800VA apiece. 169 volt center tapped secondaries should give 118 volt DC rails. Steve wants a 4 ohm driving monster. So I'm gonna parallel 2 of the toroids PER CHANNEL, with 4- 120 volt/35,000uf caps per power supply. I'm going to take 1 700B chassis and make 1 channel out of it by tying the Backplane boards together, that is if Joe says we can do this. That will give each channel 22 output devices, that should drive any 4 ohm load into the ground......so Senor Joe......am I nuts?

laatsch55 · Feb 27, 2014

Joe I'm basig that 800va on the fact that the dual primary 115 vilt windings have #18 wire and the secondaries have #14..

Gepetto · Feb 27, 2014

laatsch55 said:

Ok, I have some toroids that are around 800VA apiece. 169 volt center tapped secondaries should give 118 volt DC rails. Steve wants a 4 ohm driving monster. So I'm gonna parallel 2 of the toroids PER CHANNEL, with 4- 120 volt/35,000uf caps per power supply. I'm going to take 1 700B chassis and make 1 channel out of it by tying the Backplane boards together, that is if Joe says we can do this. That will give each channel 22 output devices, that should drive any 4 ohm load into the ground......so Senor Joe......am I nuts?

Lets give er a go Lee...

laatsch55 · Feb 27, 2014

Unrectified secondarios measure 82.5 , rectified should be around 115 actual.... At what place on the board will I have to start swapping out the 100 volt caps...

laatsch55 · Feb 27, 2014

These also have a 24 volt center tapped winding and an 18 volt winding, perfect for 24volt DC off the 18. What's the 24 volt Dc for??? We'll figger somethin out to do with it...

Joe will my 2,000 watt load be enough to saturate one of these. Looks like a 15 amp secondary winding at 165 volts DC so that's 2400 watts, or is DC figured that way?

Gepetto · Feb 27, 2014

laatsch55 said:

C1, 2, 4, 5, 6, 8, 9, 11, 14, 15, 16, 17 = low voltage

C3, 23 = 20V on it
C7, C10 are already 500V on boards I build.

Bulk caps would be your issue Lee.

laatsch55 · Feb 27, 2014

Bulk caps are 120 volt, 35,000uf....

laatsch55 · Feb 27, 2014

Gepetto said:

So nothing to change on the board?? That's VERY cool. How do I tie the boards to cascade??

laatsch55 · Feb 27, 2014

On the backplanes I'll have to beef up the caps there.....

laatsch55 · Feb 27, 2014

Nope, they're 250 and 160, nevermind...

premiumplus · Feb 28, 2014

Wouldn't it be a good idea to put a current sharing resistor in series with the outputs of the power supplies prior to paralleling them? I built a hefty dc power supply back in college, and being poor, I used two smaller primary transformers together to get the needed amperage. I seem to remember using a 0.3 to 0.5 ohm 20 watt resistor in series with one of the transformers. Don't remember if I did it on the ac side or the dc side of the rectifiers though. I don't think it would be critical, really. I'd probably try it right at the secondary output of the transformers, before the bridge. That would absorb any voltage difference in the secondaries, similar to the small resistance, high wattage resistors we use on shared output transistor banks.

laatsch55 · Feb 28, 2014

Joe and I discussed this very same thing when I was using 2-35 amp BRs with a large toroid and 4-35,000uf caps. Joe was concerned with the current sharing between the BR's. Not so with this configuration. He said the BR's will absorb any difference in the transformers, beins they measure almost identical. Not as critical on the DC side where these will be paralleled.

laatsch55 · Feb 28, 2014

Stephen wanted a VERY stiff power supply on one of these fully comp 700's and it has morphed into 2 separate mono blocs with twice the power supply on each channel beyond the factory setup along with 14 times the original resevoir caps. There will be 2 separate chassis with 22 output devices per channel. The faceplates will be an anodized black aluinum with one meter right in the middle, absolutely NO AC in the chassis, all ouboard power conversion. Rail voltage between 115-118, should drive a 4 ohm load all day cotinuously for as long as he wants at a rate of near 1,000 watts at 4 ohms, about 600-625 into 8 ohms, simply a F*&*&^% BEAST!!

premiumplus · Feb 28, 2014

That's gonna be flat out impressive...wish I could hear it. Oh, wait...I'll just open my windows. Michigan's not THAT far from Gillette!

laatsch55 · Feb 28, 2014

No Dave it really isn't..

laatsch55 · Feb 28, 2014

Joe, to drive the other side of the board what besides the B+/- do I need to run.?? Jump the bias over, and no other control wires from there?

Gepetto · Feb 28, 2014

laatsch55 said:

This is what I wrote up for the PL400 boards Lee. Most of it should be applicable but I have not read it through carefully in your context.

Cascading Backplane Boards for higher power amp applications
If you are going to cascade 2 of the Backplane Boards here are a couple of recommendations. The first board in the cascade set is referred to as the upstream board, the second board is referred to as the downstream board.
Use the test point locations to wire from board to board ONLY for:
TP1 to TP1 (BIAS+)
TP3 to TP3 (BIAS-)
Load R36 and R37 on the upstream board with one 150 ohm, Â½ W resistor.
Load R38 and R39 on BOTH boards with 20 ohm, Â½ W resistors instead of one 10 ohm, Â½ W resistor.
Use the FUSED_B+_IN and FUSED_B+_OUT to cascade the positive rail voltage or run 2 separate power runs, one to each board from your power supply. DO NOT use the test points to cascade the power rails, the traces are not sized for this on the board.
Use the FUSED_B-_IN and FUSED_B-_OUT to cascade the negative rail voltage or run 2 separate power runs, one to each board from your power supply. DO NOT use the test points to cascade the power rails, the traces are not sized for this on the board.
Use the OUT1 and OUT2 to cascade the OUTPUTs or run 2 separate power runs, one from each board to your output speaker connection point. DO NOT use the test points to cascade the OUTPUTs, the traces are not sized for this on the board.
Populate only one of the Zoebel networks on the downstream board OR populate each board with 20 ohm resistors instead of the normal 10 ohm resistors in locations R47and R48. The C5 caps remain the same at 0.1uF.
The PRE-drivers on the downstream Backplane board are NOT populated (the Q11/Q12 locations).
The Control board ONLY wires using the 11 (pin 3 to pin 12 plus PNPR) interconnect wires to the upstream or first board in the cascade set.
On the Control Board, populate and wire to the R (right) channel. The +/-20V power regulators are supplied from the connections to the Right channel. That way you will be able to keep the left channel totally unpopulated.

Paralleling Audio Transformers

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