Reamp with OEP A262A7E

[Lasselakken]

Hello
I am trying to build a reamp based on the Jensen as092 diagram, but using an OEP A262A7E. I can't figure out how to connect the transformer right, though. Can anyone help me?
I will include a part of the data sheet for the transformer in the next post.

 

[Lasselakken]

Here's the pinout from the data sheet.

 

[lolo-m]

Even if it's not the best transfo for the task in term of impedances , it will work if you connect it that way:
- Primary: connect A3 to A4 (this is your hot XLR Point) and connect A1 to A2 (cold XLR Point)
- Secondary : connect B2 to B3, ground is B4 and signal is B1

Have fun

 

[Lasselakken]

Thanks a lot for the reply!
I have been looking for some time for a suitable and cheap transformer here in the EU. You mention that this is not perfect in terms of impedances. What kind of impedance should I be aiming for in order to match better?

/Lasse

 

[lolo-m]

The best transformer should be 600/10K but as a transformer is reflecting impedances any transformer with a ratio of 1:4 should work.

 

[Lasselakken]

The best transformer should be 600/10K but as a transformer is reflecting impedances any transformer with a ratio of 1:4 should work.

I am by no means an expert here, but are you sure that you are right about this? The transformer in the original Jensen diagram has (as far as I can see) a turns ratio 1:1 http://www.jensen-transformers.com/datashts/11p1.pdf
That's why I thought the OEP would fit since it is 600:600. But maybe I am missing something?

 

[lolo-m]

Yes and no :
Paralell connected primary is 600 ohm
serie connected secondary is 2K4 ohm
The ratio is about 1:2

The OEP A262A2E would do a ratio of 1:4 connected the same way
The OEP A262A3E would have a ratio of 1:6.45 with both windings connected in serie. If you use this last one it would be better to have the value of the volume pot changed to 22k (or better 25k) not to have a reflected load on the input of 600 ohm...

I hope it's clearer now  ;D.

 

[Meathands]

AFAIK, most reamp schematics use a 1:1 transformer with a pad/volume control after the output. I used a step down transformer in order to skip the pad.

The one thing you probably don't want to to is step up the voltage/impedance. You may not get a high enough input impedance reflected from some loads, and you'll definitely have too much signal.

 

[Lasselakken]

Oh, does that mean that if I want to use the OEP A262A7E in 1:1 in the Jensen diagram I will have to wire the secondary in parallel too?

I guess that would be B4 and B3 connected as ground and B2 and B1 connected as signal?

 

[lolo-m]

Connect it as I told you. The worst that can happen is that you'll have to turn the volume down. Mine uses a 1:5 Lundahl transfo and it works perfectly. I mostly use it with the volume at mid position so I bet yours will work safely like this.

 

[Lasselakken]

Reviving an old thread here, sorry.
After some detours, I finally finished my reamp with OEP trafo as described above. It works really nice, distorts on the last part of the volume pot, but thats no problem.
I have a 20k pot in the signal path as impedance control, but after trying four different amps I haven't been able to spot any difference in the sound when turning that control. Can anybody tell if I am doing anything wrong, or it just happens to not affect the inputs of my amps?

 

[Meathands]

I wouldn't expect to hear a difference between 0-20k Ohms when going into a guitar amp. Some circuits, like the Fuzz Face, have a capacitive input impedance that interacts with the output impedance of the guitar, but in most cases until you hit 100-500k there will be no change in sound.