Hi
I copied this circuit for the DI output section for another Fender amp.
The DI transformer is on the top right corner of the page of page 6.
My question is how do I determine the right capacitor value on the input prim of the transformer. In the attached schematic they used a 0,1uF.
When I connect the cap with my chosen transformer, an OEP A262A3E, I get a slight boost of the higher frequencies.
I copied this circuit for the DI output section for another Fender amp.
The DI transformer is on the top right corner of the page of page 6.
My question is how do I determine the right capacitor value on the input prim of the transformer. In the attached schematic they used a 0,1uF.
When I connect the cap with my chosen transformer, an OEP A262A3E, I get a slight boost of the higher frequencies.
The 100n is across the primary and will reduce the HF. A bit of an odd transformer as the primary is 150R with a 12.5k split secondary, so no use as balanced line output.
If that really is a 150:12K transformer, you are a long long way away from the specified 600:600CT.
Fender/Boogie used a 938 Ohm network to drive a 600r winding, which is fine.
Putting 150r winding on 938r source is likely to soften the bass.
As Jon says, 12.5K is a very odd/poor choice for driving a line.
Also consider that you have a HIGH level output (20V), padded with 15K:1K, and transformer loading, then transformer ratio. Fender's plan puts 1.2V out. Your 1:9 ratio part wants to put out a LOT more level, but highly dependent on what you put on the 12K side. With a 12K load it does come to 1.8V, a fine value; if you find a hi-Z load it could be 11V(!), with 600r (rare but not unknown) it would really suck.
I would turn the transformer around. Change the 15K and 1K to 10K and 10K. Feed the 12K side. You get around 1.5V on the 150r winding, and steady for any audio line or load.
Fender/Boogie used a 938 Ohm network to drive a 600r winding, which is fine.
Putting 150r winding on 938r source is likely to soften the bass.
As Jon says, 12.5K is a very odd/poor choice for driving a line.
Also consider that you have a HIGH level output (20V), padded with 15K:1K, and transformer loading, then transformer ratio. Fender's plan puts 1.2V out. Your 1:9 ratio part wants to put out a LOT more level, but highly dependent on what you put on the 12K side. With a 12K load it does come to 1.8V, a fine value; if you find a hi-Z load it could be 11V(!), with 600r (rare but not unknown) it would really suck.
I would turn the transformer around. Change the 15K and 1K to 10K and 10K. Feed the 12K side. You get around 1.5V on the 150r winding, and steady for any audio line or load.
- Status
- Not open for further replies.