JLM AUDIO

I never use the pad on my BA's but i could certainly use a hi pass 70hz filter at times.

is there a way of doing this? converting the pad switch even?

chrisp wrote:http://jlmaudio.com/user/viewtopic.php?t=50

ok I've responded there...

Hi!

I built a BA several years ago and have had some really good recordings made with it.

Now, I would like to exchange either the phase shift or the pad for a 70-75 Hz high pass filter. Unfortunately, the link above has expired. Is there a way to access this answer?

Best,
Jon

jonte-72 wrote:Hi!

I built a BA several years ago and have had some really good recordings made with it.

Now, I would like to exchange either the phase shift or the pad for a 70-75 Hz high pass filter. Unfortunately, the link above has expired. Is there a way to access this answer?

Best,
Jon

To work out the best way to do the HPF
Need to know what input transformer you have fitted?
And do you have variable impedance fitted?

Excuse me for jumping in on this old post. but I would like to pick up where it left off.
I have a sowter API input transformer jumpered for 150 ohm input. No variable impedance. wired on a BA. I tried a adding a high pass 3 db cut at 70 Hz by putting a capacitor in series at the input transformer, but the 70 Hz was boosted instead of attenuated.

sb1 wrote:Excuse me for jumping in on this old post. but I would like to pick up where it left off.
I have a sowter API input transformer jumpered for 150 ohm input. No variable impedance. wired on a BA. I tried a adding a high pass 3 db cut at 70 Hz by putting a capacitor in series at the input transformer, but the 70 Hz was boosted instead of attenuated.

If the transformer has bad transfer characteristics or not loaded well like API input is setup you can get a roll off followed by a bump. This can be fixed usually by making the cap smaller so the roll off is higher but need to graphed with something like RMAA to work out the best value.

Ideally cutting the track between transformer secondary to the +in of the opamp before any resistor from +in to 0v (or half rail in BA BAD) and adding capacitor across the cut track can work very well as a HPF.