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SSE Schematic Question

cbutterworth

Member
2006-10-03 11:02 pm
Funny, I've never noticed that line! My Edcor OPT's came with clearly identifiable wires.

AND, if you look at the connections guide that George has, it'll is pretty clear about which color wire in the OPT goes in which connector. At least, that is what I have assumed. Mind-you, I am using a fairly standard OPT.

I hope this helps.

Charlie
 
The referenced table went obsolete when Edcor changed their color scheme and Hammond changed the hookup of their OPT secondaries. (6 or 8 years ago) It was too old to accurately reflect the OPT's currently available, so it was deleted.

My Edcor's have two blue wires, a black, a red, and a white/blue wire. They are painted a bright metallic blue. They changed the exterior, and wire colors a long time ago.

The older Hammonds had two secondaries that had to be interconnected in different ways to obtain the desired impedance ratio. That has changed to a single tapped secondary.

The Transcendars that I have are no longer made, I don't know if his newer OPT's are the same or not.

The only way to know if the phasing is correct, is for the transformer to be labeled by the vendor, which doesn't happen often, or to hook it up and test it. It is impossible for me to test all the current OPT's in the market.

If nobody here has the proper connections for your particular OPT, hook it up and try it. The OPT is connected properly if the gain goes down when the CFB is turned on. If the amp gets louder when CFB is turned on, then swap the secondary connections.
 
Does it matter if you don't use cathode feedback?

For most people no. If CFB is not used, the OPT secondary has no connection back into the amp. One side should be grounded for safety....a shorted OPT could put B+ on your speaker leads. It is very rare for this to happen, but I have seen one primary to secondary short in an OPT where the amp otherwise worked....with 400 volts on the speaker wires.

There are some who want to preserve "absolute phase" through the entire system. This means that pushing inward on the microphone diaphragm during recording causes an outward motion of the loudspeaker cone during playback. Obviously there are many variables in this entire chain, some of which we don't control, or even know, but polarity of the OPT is one. Again, unless phasing dots are drawn on the hookup diagram by the manufacturer, you can only determine the phasing by testing.

You can try reversing the polarity of BOTH loudspeakers to see if you can hear a difference. In uncontrolled testing with high school band kids we liked the sound of the kick drum better if the speaker cone was moving outward when the drum was hit. The mic was placed in front of the drum. Nobody noticed a difference on any other instruments, but most of the kids were in the drum line.
 
The OPT is connected properly if the gain goes down when the CFB is turned on. If the amp gets louder when CFB is turned on, then swap the secondary connections.

OK, I'm confused...kind of. I'm using the Edcor CSXE (5K primary, 8 Ohm secondary). The output wires are labeled as Yellow - 8 Ohms and White - Common. When I activate feedback (enabled), my signal gets louder. Obviously, that is an issue. Previously, I had the polarity reversed and I barely had any signal output, but the signal would be reduced when the feedback switch was enabled.

When looking at the wiring diagrams from the Tubelab pages, it looks like the polarity of the xformer output reverses when it is wired for feedback (follow the green and black output wires).

This is like beating a dead horse, but I either get very, very low signal out with signal reducing when feedback is enabled or decent signal output and signal increasing.

I drew my wiring many times and it matches the wiring diagrams. Just not sure why feedback is not correct.
 

sgtnoah

Member
2015-03-04 11:47 am
This is not the greatest pic, if you need further details, let me know. The feedback switch is on the top left.

-- Pete
 

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sgtnoah

Member
2015-03-04 11:47 am
My OPT only has a ground and an 8 ohm tap - the yellow is the 8 ohm tap. I can take some better pictures tomorrow if needed. I wired it exactly as it is shown in the left channel schematic (the one wire is clipped off the top of the right channel)... The secondary reference to system ground is on the 8 ohm terminal - this caused me to pause and think. Those more experienced than me can tell you why it is not grounded at the black speaker terminal.

Either way, I wired it exactly as per the diagram, and it works well.

-- Pete
 
Pete, if not too much trouble...one more photo showing your red and black wires meeting your yellow and white on your banana jacks.

I understand what you are saying about your system reference ground. NOt sure why I am having an issue. I have the Edcors with the white and yellow output wires as well.

Thanks
 

sgtnoah

Member
2015-03-04 11:47 am
Hopefully this clears it up. Are you sure that you don't have it correct as is? When you send the 0 tap (white wire) to C22, it should get louder. When the 8 ohm tap goes to C22, it should get quieter (feedback engaged).
 

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Update:

Amp is finished. My problem ended up being an issue with polarity. When connected for feedback, polarity reverses. I did not swap my test cables going to my load / oscilloscope. The oscilloscope ground was shorting the output signal. Inverting my test leads (for polarity correction) and everything was good.

Thanks for the photos again to keep my sanity!