erikb1971

Re: any ideas for adding a sweepable mid to the Poor Man's Pultec EQP1-A ?
« Reply #80 on: November 23, 2011, 04:22:41 PM »
Oh I am sorry you did not get my sarcasm on my own sloppy design... they were not meant to be double boost, nor off-off switches. It was a matter of thoughtless copy pasting and no checking... it has been corrected!
We are getting way past relatively easy


baadc0de

Re: any ideas for adding a sweepable mid to the Poor Man's Pultec EQP1-A ?
« Reply #81 on: November 23, 2011, 04:55:59 PM »
Yeah, Ian is right, the FPD file is a gift to this wonderful forum of wonderful people :)

also, the dials are created with the jskala application linked above, though for more complex designs, I turn to the scale designer in FrontDesigner 3.0. It's not really a nice app, but the dial designer is great, has a good preview, etc..

I'll attach here another FPD file of another intricate design that uses dials created in FrontDesigner 3.0. The symbols were made in corel draw .. badly haha

EDIT: again you will have to rename the PDF to FPD ;)

ej_whyte

Re: any ideas for adding a sweepable mid to the Poor Man's Pultec EQP1-A ?
« Reply #82 on: November 23, 2011, 05:36:19 PM »
first sketch of stereo 2U posh men's eq... love the way you can switch the mid sections off or off and how there is a double boost mid, but no cut..... sloppy work, better later!:-)

I am not sure about the double boost you have there. The idea was you could have a single frequency control that could be switched to either boost or cut OR you could have two frequency controls, one assigned to cut and the other to boost. Although you could have two mid boosts you would have to be very careful how you used it. If you set the boosts to the same frequency you would not get double the dB boost. The boosts are quite wide so you might well get two separate boosts where the frequencies are an octave apart for example but much closer and they will start to interact. I am not saying don't do but just be careful if you do. An interesting alternative might be to look at a pair of mid boost/cuts with no-overlapping frequencies using two different inductors. That way the lower end could be extended to the region of 150Hz and include frequencies like 150Hz and 180Hz which are useful for removing hum. So one control could cover from 150Hz to 1.5Khz and the second from 1.6KHz to 16KHz for example.

Cheers

Ian

I was planning on having 2 mid bands, both boost/cut switchable, haven't decided whether they will have identical overlapping freqs. or split bands yet. Is this still feasible as long as I dont put both bands in boost at close frequencies as described?

Cheers

ruffrecords

Re: any ideas for adding a sweepable mid to the Poor Man's Pultec EQP1-A ?
« Reply #83 on: November 23, 2011, 05:37:54 PM »

I was planning on having 2 mid bands, both boost/cut switchable, haven't decided whether they will have identical overlapping freqs. or split bands yet. Is this still feasible as long as I dont put both bands in boost at close frequencies as described?

Cheers

Yes, and the same applies for cut as well.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

baadc0de


ruffrecords

Re: any ideas for adding a sweepable mid to the Poor Man's Pultec EQP1-A ?
« Reply #85 on: December 30, 2011, 11:39:50 AM »
Is this design feasible then?

Large picture:
http://dl.dropbox.com/u/12679166/PoshMan4U.png

FPD file:
http://dl.dropbox.com/u/12679166/PoshMan4U.fpd

Yes, that's pretty much what I had in mind for the four band semi-parametric.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

mikeyB

Hi Ian - just been reading your notes regarding an eq with 2 non-overlapping bands. Do the 2 bands connect to the same places in the network (effectively in parallel) each with a 1k and 4k7 back into the network?

Thanks in advance
making better music!

ruffrecords

Hi Ian - just been reading your notes regarding an eq with 2 non-overlapping bands. Do the 2 bands connect to the same places in the network (effectively in parallel) each with a 1k and 4k7 back into the network?

Thanks in advance

Yes, they do. It is because they are in parallel that the frequency bands should not overlap.

Cheers

ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

mikeyB

Great stuff - gotta give this a go!
making better music!

mikeyB

Hi Ian - you mentioned somewhere in the notes about scaling the capacitors down by a factor of 4 if you scale the pots up by a factor of 4.
Is this the case for the mid boost band as well regarding the inductor. I notice the carnhill has a max of 1H whereas a standard pultec inductor has a max typically 267mH (roughly a quarter).

Can you use this general rule of thumb?
I have quite a few pots in magnitudes of 22 (ie 2k2/22k/220k) and was thinking of trying these out. I would then be talking of a network with input imp of 2k5? Cap values would be halved from an original network of 600R.

Thanks as usual for such a great project.
making better music!


ruffrecords

Hi Ian - you mentioned somewhere in the notes about scaling the capacitors down by a factor of 4 if you scale the pots up by a factor of 4.
Is this the case for the mid boost band as well regarding the inductor. I notice the carnhill has a max of 1H whereas a standard pultec inductor has a max typically 267mH (roughly a quarter).

Can you use this general rule of thumb?
I have quite a few pots in magnitudes of 22 (ie 2k2/22k/220k) and was thinking of trying these out. I would then be talking of a network with input imp of 2k5? Cap values would be halved from an original network of 600R.

Thanks as usual for such a great project.

Broadly speaking yes. The RC parts of the EQ all scale this way and the mid inductor must scale the same to keep the Q as the original. The only components that go contrary to this are the caps in the mid boost/cut which need to go in the opposite direction to its inductor for the resonant frequency to be the same.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

gemini86

I have a few questions. To preface; I'm planning to build a 4 band unit, non overlapping centers.

1) am I correct to assume the each mid band is connected the same?
2) according to my simulations, the bandwidth of the boost frequency is much wider than cut. This can be changed by lowering the 4k7 resistor. Does doing this cause any problems with impedances or anything?
3) There's nothing stopping me from using individual inductors vs a multi tap inductor, correct?

Thanks!
- Rodney

"...you better call Kenny Loggins, 'cause you're in the danger zone."

ruffrecords

I have a few questions. To preface; I'm planning to build a 4 band unit, non overlapping centers.

1) am I correct to assume the each mid band is connected the same?
2) according to my simulations, the bandwidth of the boost frequency is much wider than cut. This can be changed by lowering the 4k7 resistor. Does doing this cause any problems with impedances or anything?
3) There's nothing stopping me from using individual inductors vs a multi tap inductor, correct?

Thanks!

1. Yes (see reply #87)
2. The bandwidth of the cut is much narrower than the boost. This is one of the limitations of a simple circuit like this. It is designed for a boost Q of between 1 and 3 which gives a cut Q several times the boost Q. In most cases this is not a problem as gentle boost and sharpish cut are what is normally required. Lowering the 4K7 resistor will sharpen the boost. However it does lower the minimum impedance the EQ presents to the transformer and to the driving source. I was attempting to ensure this never fell below 4K7 for a 10K:10K tranformer (and another reason why bands shold not overlap). If your sources can drive 600 ohms then you could reduce the  4K7 resistors and use a 600:600 transformer at the input, or, if you are going the semiconductor route your op amp unbalancing input circuit will handle this with no problem.
3. You can use individual inductors. Another way to solve the Q problem is to use different inductor values for boost and cut and switch them with the boost/cut switch but that's not really a poor man's EQ ( but that's what I did on the REDD EQ).

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

gemini86

Thanks Ian. Last question, is the cut supposed to be limited to about 6dB?
- Rodney

"...you better call Kenny Loggins, 'cause you're in the danger zone."

ruffrecords

Thanks Ian. Last question, is the cut supposed to be limited to about 6dB?

No, It depends on the total resistance of the RLC circuit when the pot is fully off. This is the sum of the pot's off resistance, the inductor resistance and the 470 ohm resistor. The 47K lin hi boost pot and the 4K7 lin hi cut pot form a basic pot divicer with a loss od just over 20dB. You get mid boost by partially shorting out the 47K pot and you get gcut by partially shorting out the 4K7 pot and specific frequencies determined by the LC values. If you short out the 4K7 with a 470 ohm resistor you get another 20dB of attenuation which is the theoretical maximum cut. Unless your inductor resistance is very high you should be able to get more than 6dB cut.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

gemini86

Thanks, Ian. Reading through your posts has taught me a ton about passive eq and how it all works. You're a scholar and a gentleman.
- Rodney

"...you better call Kenny Loggins, 'cause you're in the danger zone."

mikeyB

Re: any ideas for adding a sweepable mid to the Poor Man's Pultec EQP1-A ?
« Reply #96 on: August 09, 2013, 09:29:39 PM »
Hi Ian,
I ain't too great on spreadsheets but have just spent the last couple of days getting my head around the capcalc.xls
Do you have a cap/inductor calc spreadsheet for the mid sections?
You may recall, i want to try some different Z networks as i have orders of pots in the 2.2 magnitudes.
I've tried to create a spreadsheet for this, but alas, a working spreadsheet evades me!!
Any help would be much appreciated!!

Thanks - Mike
making better music!


 

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