Pultec filter section question

[CJ]

That looks good!
One of the prized points of the EQP is boosting and cutting bass at the same time, as you mentioned.
But if we brought the midrange freqs way down into the bass region, you would not need the bass cut.

 

[JPrisus]

Yeah that's what i'm thinkin CJ, if the lows can be covered between the HPF and low-mid cut, we can lose the original low cut. That way the cut/boost relationship can overlap or be seperated if desired. Personally I don't have much use for the HF cut either, but it's not such a big deal. Splitting off the mids into two bands seems better and better the more i think about it.

This is shaping into the most useful Pultec-inspired EQ I know of!

 

[CJ]

Good point on the high cut, heck a tube version Pultec with 3 transformers already chops off the highs by itself!

Here is a site where you can download the simulator that I use. Free of course, no 30 day trial bs or anything.
It's called SI Metrix:

http://www.catena.uk.com/ :guinness:

 

[JPrisus]

ah man, i'm on a Mac, figures! I'll start looking around for something similar.


anyone try different trafos for their Pultec copy other than the Lundhals? That's one other area for experimentation i'd be into.

 

[CJ]

Darn! We could have swapped files, making it easier/faster!

Oh well, if you find something for your mac that I can use also, let me know.

 

[JPrisus]

OK, got the girlfriend's laptop, gonna give this a shot!

 

[JPrisus]

Ok, been playing around with the simulator, getting the hang of the schematic drawing. Fun stuff! So what should I be looking for in the simulator tests?

 

[CJ]

Use the db probe in the ac/noise section and place it on the output to draw a graph.
use ac sweep test, 5 hz to 20 hz.
change the pots around to see how the controls vary the curves.
cj

 

[NewYorkDave]

Did ya consider using the MEQ mid-cut section verbatim before the EQP section?

I haven't done a careful analysis, but on the face of it, it seems it should work well.

 

[CJ]

will try now!
thanks dddd Dave!

 

[CJ]

hmmm, works, but only showing 1/2 db cut.
needs a voltage divider or something.
tried resistors on top and below the pot but got the same curves.

 

[NewYorkDave]

Did you use the series resistor before the mid cut selector?

That forms the upper half of the voltage divider.

Also, did you give your signal generator a realistic source impedance, or are you running zero source impedance?

 

[CJ]

Hey, I hooked it up to the output and got some good curves!

 

[Joechris]

The Helios Eq gives you a mid cut, by sending the signal in the mid (hi) boost section down to earth, with a two pole switch, insted of back into the circuit after the pot. If you make the 10K pot in the input of the pultek schem into two 20K in paralell, you could probebly have one for boost, and one for cut with lager cap/ inductor values to get you down into the nasty 237 Hz era that was wery unpopular in the 80ties :grin:
The Helios link is here somewhere...

jo

 

[JPrisus]

Great stuff guys... i'm still trying to get the hang of the simulator, so bear with me. Would this circuit be any easier of we elminated the low and hi cut for now? I'm assuming a 3-position HPF filter woudn't affect things too much if it were first in the circuit, and also, we talked about splitting the mids into two bands. I just want to make sure we're not dealing with things that could be easily eliminated.

Maybe we could get more interest and have some PCBs done up after the initial prototyping???

 

[CJ]

ok, i checked the curves both stock eqp-1a without the mid cut, and with the mid cut, and....

I see little difference, which means there is very little interaction/ill effects from adding on the mid cut on the output!
Maybe a little reduction in bass cut, but who cares.
If anything, you use the bass boost more often.
Plus, I am getting a lot more than 10 db midcut, more like 18 db!
So simulator wise, this looks very promising.
now to do some weird zany interaction curves!

here are the curves, each section by itself with all others turned off:

 

[JPrisus]

man i'm jealous... gotta figure out this program!


thanks CJ

 

[JPrisus]

another thought, what about setting the HF boost to shelf without variable Q?

 

[CJ]

yes, and use the pot slot for the mid cut.
I don't use the treble q much.

if you want i will link to the file .
also, i can call you toll free and walk you through this program from my screen.

 

[CJ]

file:

http://vacuumbrain.com/The_Lab/TA/Pultec/peq_meq_combo.sxsch