Output transformer wiring
« on: November 18, 2019, 08:43:54 AM »
hey guys

could you please confirm where this transformer primary leads are attached to? I only see pin 7 here for the primary, or is this pin 7 and 8 to ground are the primary connections? i am confused...

many thanks!


Re: Output transformer wiring New
« Reply #1 on: November 18, 2019, 09:41:56 AM »
Show some more of the schematic...at least the output stages.   

If the output amplifier is a monitor or cue amp, you need a low impedance to line output transformer....try a UTC A21 or something equivalent...the primary should be pin 7 on the octal plug hot,  pin 8 ground (common); secondary pin 4 hot, pin 6 cold...this should correspond to XLR pins 2 (hot), 3 (cold).   Connect a 47 ohm resistor across the primary of the transformer to load it.   Ground the shield of the transformer.

As far as I can tell, the amplifier output is capacitor coupled so there should be no dc voltage present across the transformer primary connection (pins 7 and 8 of the octal socket)..

 If the output of that amp is high impedance, then try a UTC A24 or something equivalent with the same wiring.  Do not terminate the output with a resistor.

These transformers are expensive but you could test this with something cheaper.
« Last Edit: November 19, 2019, 01:05:03 PM by rmburrow »

Re: Output transformer wiring
« Reply #2 on: November 18, 2019, 09:45:22 AM »
Show some more of the schematic...at least the output stages

Unfortunately, that is the only snapshot I received from a person connected to this old Bozak people in the US. The mixer is a Bozak CMA10-1 but without the output transformer. All information I did receive is that this output should be a 600 Ohm line transformer.

I wish I had the full schema but for that particular gear, I could not find that on line anywhere. :(

and the issue with this mixer amplifier output is that the level is very low as no transformer is connected to the output. I am thinking  to add an octal Altec 15356A , very similar in the pinout configuration. Just odd that only one pin 7 is connected to the primary.. unless the pin 8 ground is the other primary to ground?
« Last Edit: November 18, 2019, 09:53:58 AM by Studiogearlover »

mjrippe

Re: Output transformer wiring
« Reply #3 on: November 18, 2019, 02:42:19 PM »
and the issue with this mixer amplifier output is that the level is very low as no transformer is connected to the output. I am thinking  to add an octal Altec 15356A , very similar in the pinout configuration. Just odd that only one pin 7 is connected to the primary.. unless the pin 8 ground is the other primary to ground?

Unless the output transformer is a step up type, it will not increase the output level.  It is very likely that pin 8 is the low side of the transformer primary though.

Re: Output transformer wiring
« Reply #4 on: November 19, 2019, 02:40:19 AM »
Thanks for your help !

I have opened up this mixer to see how the output is connected to the octal socket. Basically the pin 7 has 2 leads soldered together. ( Red and Blue/white) and this goes trough pin 6  to the XLR plg pin 3 ( this will be the signal I assume) .

I have the black leads which goes to chassis and interesting that the pin 2 XLR is soldered to the octal socket pin 4 but that pin does not doing anything. Again, I assume that this was done for the original output transformer CMA-558 and only Buzzy has these transformers now days.

Am I seeing this right that now I have the red and blue/white as primary so this can go to the Altec 15356A primaries.

What I am unsure of what signal I am getting to that output from the mixer/preamp cards-transformers.

I only can guess that the mic input transformers are 150 to 600 Ohms?

mjrippe

Re: Output transformer wiring
« Reply #5 on: November 19, 2019, 09:57:43 AM »
If there is no output transformer installed, there should be jumpers in the octal socket to pass signal to the XLR.  Or is there another output such as 1/4" or screw terminals?

Re: Output transformer wiring
« Reply #6 on: November 19, 2019, 10:00:41 AM »
If there is no output transformer installed, there should be jumpers in the octal socket to pass signal to the XLR.  Or is there another output such as 1/4" or screw terminals?

yes, there is a jumper wire. I did re soldered and installed the Altec transformer carefully following the schematic of the Altec.

It did not worked at all. Hum and buzz.

The primaries are still unclear. Maybe it is not a good idea playing around with this rather expensive gear.


scott2000

Re: Output transformer wiring
« Reply #7 on: November 19, 2019, 12:10:49 PM »


 

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