Frank's Pultec Support

[audiophreak]

Hi All,

  Got a Question .... if I used a separate lorlin switch connected to the LF Cut frequencies and LF Cut pot, would that give me independent LF boost and cut ? 
     

 

[audiophreak]

  sorry for Newbee stuff  - also  - I have axial lead inductors,  can / should I tie all leads on one side to the 0mH pad , then spider web out to appropriate value pads ?

  Thanks  ;D

 

[mitsos]

1. yes, you can separate out the LF boost and cut frequency switches.  It has been done before and works fine.  I think the latest one I saw was Kingston's spiffy EQ.

2. I assume the inductor values are equivalent to the values at each individual tap of the normally used multi-tap inductors? If so, I think that should work fine.

also, if you are using the V1.4 boards from gustav, you'll need to do the modifications posted by briomusic for your EQ to work properly.

 

[audiophreak]

Thanks so much ! 

            I thought I could split off the Low Cut, just wasn't sure.

            Yes, the inductor values are the same as the individual taps except for two, I need to put two inductors in series for the 78mH and the 155mH - ( I hope it works that way )

    Yes, i do have the v1.4 boards and plan on doing briomusic's modifications.

  Thanks Again  .. man I love this stuff  ;D

 

[mitsos]

no prob... good luck and please post back with results!

 

[audiophreak]

  Thanks !  Will Do 

 

[mylesgm]

Hi All,

  Got a Question .... if I used a separate lorlin switch connected to the LF Cut frequencies and LF Cut pot, would that give me independent LF boost and cut ? 
     

That sounds neat, on PCB v1.4 which traces would you cut to achieve this?

 

[audiophreak]

 Hi,

     Using briomusic's modification illustration, instead of connecting the lead to the "C" pole of the two pole switch, I would connect it to the pole of another switch set to 5 positions and connect LF cut pads C7,8,9,10,11 to the corrisponding position on that switch for that pole, there for being able to say cut 30hz AND Boost say 90hz at the same time instead of just being able to Boost OR cut the selected LF. ( just an example ) but I think that may give one more adjustability.  

 just my 2 cents , not sure if its worth it, but I think I'm gonna try it anyway, its just another switch  ;D


EDIT :  No trace cut nessesary 

 

[mylesgm]

got it!  thats pretty simple and seems like more should be known about that.  I'll certainly be trying it...

 

[audiophreak]

1. yes, you can separate out the LF boost and cut frequency switches.  It has been done before and works fine.  I think the latest one I saw was Kingston's spiffy EQ.

2. I assume the inductor values are equivalent to the values at each individual tap of the normally used multi-tap inductors? If so, I think that should work fine.

also, if you are using the V1.4 boards from gustav, you'll need to do the modifications posted by briomusic for your EQ to work properly.

    I found that post from Kingston  - http://www.groupdiy.com/index.php?topic=39842.0

  What a beautiful piece of gear, and some good info on passive EQs.

Thanks again mitsos 

 

[mitsos]

yeah, that's a nice EQ, huh?  I don't remember now but I think it has a even more freqs than this version.  Did you finish yours already? I love mine, but now I know I need more!

 

[audiophreak]

 No ... gonna be a few weeks, just finishing up on the filter boards, was  gonna perfboard Gyrafs SRPP gain stage cuz I love the way my Dual G-Pultec sounds, but after reading Kingstons post , I might try a little more experimentation   ;D

 

[audiophreak]

Helloooo  .....  got a question  :  In briomusic's illustration , the right hand lead coming off the PCB to the HF BW 2k5 pot, does that connect in some way to the 10k resistor thats on the PCB ?  and if it does , is that end of the resistor " lifted " or does this lead " pass through "  ( going from board to resistor then on the pot ) ?

Thanks as always 

 

[briomusic]

hi audiofreak,
the bandwith pot is not connected to either the 10k or the ground pane, sorry it is a bit unclear in the diagram.
cheers briomusic

 

[audiophreak]

Thanks briomusic 
  just want to get it right ... and thanks for figuring out the mod ... and posting it !!

 

[seavote]

i have some basic questions that i cant find answered in either "franks" threads.  should the lorlin switches be shorting switches?
i'll be using franks solid state gain stage. what are the voltage requirements?thanks for any help.
8) 8) 8) 8) 8) 8) 8) 8) 8) 8) 8) 8) 8)

one more!!???  what pots are members using that fit the pcb and work with the faceplate that is available on line?

 

[audiophreak]

Hi Seavote,
              I used MBB ( Shorting ) Lorlins on my Dual G-Pultec with no problems and AML carries the 20mm pots all in 1/4  inch shafts however I dont know if they fit the on line faceplate.

 ... although I just noticed that Franks Enhanced High Q is 2k5, and the G-Pultec High Q is 2k2 ... would that make much of a difference ?

EDIT :  sorry ... the AML pots are PCB mount but don't know yet if they fit / work with these PCBs , I used them on the G-Pultec, but wired off board  ;D

 

[Andreas Pfeiffer]

Do you use Frank´s gainstage with the modifications show in the pic? I also have a 6dB boost in bypass mode,
while using Frank`s gainstage not Gyraf`s :-\

Brio,

Brilliant work. Following your modifications made mine work perfectly!!

Thanks for sharing that diagram.

hi mitsos,
yes i did get frank's filterboards to work with the gyraf tube amp stage.
it needs quite a few modifications but they can all be done with offboard wiring and without cutting any traces. the following is my corrected wiring scheme. I have no idea how the filterboard interfaces with frank's op amp stage, but with the tube amp it works like this and not as described in the original documentation - at least for me.

cheers briomusic

 

[benlindell]

Do you use Frank´s gainstage with the modifications show in the pic? I also have a 6dB boost in bypass mode,
while using Frank`s gainstage not Gyraf`s :-\

Yes I did, as I remember I didn't have a 6db boost. Are you sure it's a boost of gain or is the filter attenuating 6db when switched in?  That'll make it easy to see where the problem lies.

 

[Andreas Pfeiffer]

After some fiddling I have this results:
Eq switched in: -6db loss, high boost and high cut working normal
If i feed a sine of 90Hz: low boost is only around 9dB max, low cut around -26dB...