Just making sure, the correct wiring of OEP A262A2E as 1:4

Hi,

I can't seem to get my head around this. Could someone help? I'm using this OEP transformer 1+1:2+2 as 1:4 and wanted to make sure the correct wiring.

Here's the data sheet: http://www.canford.co.uk/commerce/resources/catdetails/2739.pdf

I'm in fact trying to use it as a 10k:600 tube amp step-down trafo, but I'm not entirely sure if it's at all suited for that task. Any help appreciated.

Mike

You could use one primary, and wire the secondaries in series to get 1:4 I think.

you could use both primaries parallel, me thinks. the secondaries in serie, like rod said.

but those are exactly the bits that confuse me. I'm not familiar what the S1,S2,F1,F2 on both the primary and the secondary mean, and hence I can't be sure *how* to wire as parallel and series.

AFAIK the primary connected as series is 'S1 connected to S2, and F1 connected to F2', but I have a tight knot in my brain and I'm not sure about the secondary parallel wiring, and where the ground and preamp output goes in that.

aargh. I'm not even sure I got that one right :shock:

This should be right:

Thanks,

seems like a had it right all along. The reason wanted to make sure is because when I use this in the preamp at high gain (the last 1/4 of the gain knob) I seem to get some high frequency loss (not distortion at all though). Now that I've ruled out incorrect trafo wiring, I'm not too sure why that happens. Could possibly be high frequency oscillation eating up the trafo head room, or maybe I should just use a higher output rated trafo instead of this small one. Beats me. The preamp has no high frequency loss when running without the output trafo, unbalanced.

whats the circuit? nyd´s one bottle?
the transformer should be capable of doing this. you didnt connect it in a wrong way?
it should be 4:1 , so secondary = input and primary = output.

[quote author="ioaudio"]whats the circuit? nyd´s one bottle?
the transformer should be capable of doing this. you didnt connect it in a wrong way?
it should be 4:1 , so secondary = input and primary = output.[/quote]

It's the two-bottle, and yes it's connected just right. That's what I wanted to check here. The gain loss of this configuration is about 13dB or so compared to the unbalanced version. I don't know wether that's normal or not.

The high freq loss is a bit of an oddity to be honest. It shouldn't be there at high gains, as the trafo isn't even saturating when it happens.

[quote author="Kingston"] The gain loss of this configuration is about 13dB or so compared to the unbalanced version. I don't know wether that's normal or not.[/quote]

yes of course, thats normal. its a 4:1 step down , so you loose some gain.

[quote author="ioaudio"][quote author="Kingston"] The gain loss of this configuration is about 13dB or so compared to the unbalanced version. I don't know wether that's normal or not.[/quote]

yes of course, thats normal. its a 4:1 step down , so you loose some gain.[/quote]

yeah I seem to recall reading the exact figures in some threads here, and it seemed about right.

The really weird thing is, the high frequency loss does not occur if I run the trafo as 2:1 step down (AFAIK I win some gain, loose some balancing, no biggie). The frequency loss at high gain only happens as 4:1. I'm going to leave this as 2:1 as it seems to work just fine.

Thanks guys.

hmm, wired indeed. what plate-transformer cap do you use?
do you terminate the output of the transformer?
whatever happens, if you dont plan to use the pre out on inputs lower than 2.4k, you can just leave it 2:1.

[quote author="ioaudio"]hmm, wired indeed. what plate-transformer cap do you use?
do you terminate the output of the transformer?
whatever happens, if you dont plan to use the pre out on inputs lower than 2.4k, you can just leave it 2:1.[/quote]

there's a 2.2uF plate cap, and surely it could be a bit bigger, but AFAIK that would only extend the extreme low end (it's already good enough). I'm not sure what you mean by terminated output, I guess this one isn't. I'm not using a 220k tiedown resistor between the plate cap and ground, since the pre sounds better without it. It's only necessary with unbalanced output anyway.

I was worried about going 2:1 since I'm using a 600-ohm output attenuator, but even that seems to work as intended now.

[quote author="Kingston"] I'm not sure what you mean by terminated output[/quote]


look at gyrafs g9 schematic - can you see the 10k on the output?

I see it yeah. What is its purpose? I can't see much relevance even if it isn't there.

found it, right from the gyraf site of course>

The output of the transformer is taken to SW4, the phase reverse switch, that has 10K resistors across it to control transformer load when switching. And then to the output XLR.....

Doesn't seem like I would need it, but correct me if I'm wrong.