Care to explain?

[jwhmca]

So I built just the passive section of the G-Pultec. I didn't have a 600:600 input transformer for the input so I used a 600:3k in step-up configuration...

Then I was curious... I mean it's gotta be gain it from the step-up... so I hooked it into my desk and listened to some audio through it and it sounds fine... (I guess)

Okay, then... I find that the HF Boost works... lot's of gain at whatever feq I pick. The HF cut works... lots of cut.

LF Boost only adds a very little bit like maybe 3 db... I feel like I missing something basic here, so any thoughts would be appreciated.

I have checked for errors in the build, I am reasonable sure that there isn't any.

 

[lassoharp]

Try turning it around and terminating the low side with 600r resistor and see if you get the low boost back.

There's several threads here that address the need for passive EQs to be fed from a low source impedance in order to function properly.

As i recall they are spread out - I'll look around and see if I can dig one up.

If you have a copy of audio cyclopedia, this topic is covered in the section on EQs.


LINKS:  check NYDave's posts

http://www.groupdiy.com/index.php?topic=2238.msg27674#msg27674

http://www.groupdiy.com/index.php?topic=362.msg4510#msg4510

general

http://www.groupdiy.com/index.php?topic=2534.0

 

[jwhmca]

Thanks for the input. I'm reading those threads now... What do you mean "try turning it around/terminating with 600r"?

 

[jackies]

Use it in step-down configuration, put a 600 ohm resistor on the output (eq side)

 

[jwhmca]

Thats what I thought, trying it now.

 

[jwhmca]

I changed a lot of things back to what the schematic has...

I was using some random valued pots that I had laying around. I changed the in/out transformer to a Jensen JT-11P-1

Now the FEQ adjust is equal across all the boost/cuts...
Man! I have a lot to learn about EQ's!!!

 

[jensenmann]

This type of filter circuit is sensitive to loading condition at input and output. It wants to see a source with low source impedance and needs to see a defined output load of 10k (IIRC). The input is terminated, too, but that is between input tranny and circuit (IIRC 600 Ohm). Please correct me if Im wrong, longtime no see that circuit