low cut filter ?

Hi guys



i recently looked at my low cut on my pultec eq ting  , and it is not behaving as it should do.

i tried the waves plugin version and it is cutting in the right places but my hardware version seems to be dippin instead of cutting.

What would cause this?.


for analysis i what to bread the low cut part of the pultec filter , will this circuit work .

As it is, it is a cut-only LF shelf EQ, with 6dB max cut.
Decreasing the load resistor would make it more efficient (and alter the turnover frequency).
For example, a 10k load would yield 17dB cut at 20Hz, instead of 3.
But that would also modify the response of the other filters. IIRC, the nominal load is 40k. Then max cut is 7dB at 20 Hz.

so would the load resistor be at the input or the out of the circuit?

is the (100k) the load resistor


skal1

skal1 said:

so would the load resistor be at the input or the out of the circuit?

is the (100k) the load resistor


skal1

Click to expand...

Yes, the load is the 100K resistor between the pot and ground..

The 100K pot and the load resistor form a potential divider. With the load at 100K the maximum attenuation is 6dB as has already been mentioned. In the real Pultec the load varies depending on the setting of the lo boost control but it is in the region of 10K.

Cheers

Ian

so i am a bit confused  i have an  enhanced pultec eq board ver 3 from tat 2008 and the low cut part of the eq seems to be dipping out the middle all other controls work.., what is causing the low to do this .



I through the mke up amp was causing this affect, so i have taken the make up amp from the filter board and  yet it still exhibits the same behaviour 

whats wrong.


skal1

Is your low boost working/wired properly? Do you get flat response 20-20K with everything at 0? If your low boost is not wired properly (as in it's always boosting a bit) it would interfere with the low cut and could cause a mid dip somewhere above the frequency you are cutting.

I don't know the V3 boards, but the V1.4 or 1.5 enhanced pultec boards do not work properly without some modifications. Do your boards have the 10K and 1K resistors on it? If not, check out the "Frank's pultec help" thread and look at the mods Briomusic posted for the V1.4 boards that gustav sold.  Also check your PCBs against the V1 boards which are known working.

mitsos said:

Is your low boost working/wired properly?.

Click to expand...

Seems to be

mitsos said:

Do your boards have the 10K and 1K resistors on it? 

Click to expand...

yes 10k coming from pin 1 of the 1k hi cut pot  and the 1k rs is coming of the 10k rs to pin 1 of the Q pot  and the 75 ohm rs  going to the wiper of  the hi cut rotary pot  from the 1k hi cut, is this making sense.

cheers

skal1

Sort of, but it doesn't sound right. The Q pot should not be connected to either of those resistors.  The Q is in the HF boost circuit, which goes HFboost->Qpot->cap->inductor , or in maybe some other order. I don't have the V1.3 files, so check your board against the V1 one attached, it is known working.
HTH!

Thanks mitsos just checked my ver3 against the 1 you post , for a start i have not got that extra 1ok Rs  underneath the hi boast/ q pots that might be the problem


You r a star

skal1