Poor Man's Pultec EQP1-A Build Support Thread

[chrispbass]

Nice job Holger, have you fitted a bypass on each channel?
Cheers
Chris

 

[Holger]

Nice job Holger, have you fitted a bypass on each channel?
Cheers
Chris

Yes, utilising the Dingo relay bypass.

 

[chrispbass]

Thanks Holger, wasn't familiar with the dingo Io kit...just had a look on the jlm site.

 

[e.oelberg]

How much makup gain do you need for that EQ ?

thanks, Nicholas

 

[ruffrecords]

How much makup gain do you need for that EQ ?

thanks, Nicholas

It needs a little over 20dB and less than 26dB so a gain make up amplifier with 26dB of gain and a preset pot in front of it is normally used.

Cheers

Ian

 

[mus1k_freak]

if anyones interested here's a link to my mouser cart for this build, i had to use 5k, 50k and 500k pots instead of the 4.7k 47k and 470k, otherwise i kept everything else the same just to keep it simple. nothing in the cart for the tube make up stage just the eq with bypass switch http://www.mouser.com:80/ProjectManager/ProjectDetail.aspx?AccessID=cbfa3d750d

 

[ruffrecords]

if anyones interested here's a link to my mouser cart for this build, i had to use 5k, 50k and 500k pots instead of the 4.7k 47k and 470k, otherwise i kept everything else the same just to keep it simple. nothing in the cart for the tube make up stage just the eq with bypass switch http://www.mouser.com:80/ProjectManager/ProjectDetail.aspx?AccessID=cbfa3d750d

I just had a look at this and unless I am mistaken it looks like you have ordered a 1 pole 12 way switch (CK2372) instead of the 2 pole 6 way (CK2373you need for the hi/lo EQ.

Cheers

Ian

 

[erikb1971]

Hi Ian

Iam sourting for the gain make up stage now, and what are:
preset pot VR2 1K Lin
preset pot VR1 470K Lin

 

[ruffrecords]

Hi Ian

Iam sourting for the gain make up stage now, and what are:
preset pot VR2 1K Lin
preset pot VR1 470K Lin

VR2 is the adjustment for the pad and VR1 is the adjustment to set the overall gain to unity. The system attached system diagram shows how they are connected:

http://www.ianbell.ukfsn.org/pics/EQSystem.png

Cheers

Ian

 

[erikb1971]

so that could be something like this, even though it does not state lineair?

http://www.reichelt.de/Miniaturtrimmer/75H-1-0K/index.html?;ACTION=3;LA=2;ARTICLE=3475;GROUPID=3131;artnr=75H+1%2C0K;SID=12Twg8738AAAIAAFK8aRgffe5c225175f44e6d02d3f5e3cb32f64

and for these:
fixed 100nF 100nF 400V Polyester
fixed 2.2uF 2.2uF 400V Polyester
fixed 2.2uF 2.2uF 400V Polyester
Am I looking for ac or dc? I am a bit spooked with all the stories about danger with tubes....

edit: I am guessing DC, since AC is stated seperately elsewhere on the xls file.

 

[bernbrue]

Am I looking for ac or dc? I am a bit spooked with all the stories about danger with tubes....

Hi Erik,
tubes are lovely things. They even glow to show you that they are giving their best. They are just a little bit hungry in terms of current. Don´t be scared.
regards
Bernd

 

[erikb1971]

hmmm ok.. going from scared to very careful then!

 

[ruffrecords]

so that could be something like this, even though it does not state lineair?

http://www.reichelt.de/Miniaturtrimmer/75H-1-0K/index.html?;ACTION=3;LA=2;ARTICLE=3475;GROUPID=3131;artnr=75H+1%2C0K;SID=12Twg8738AAAIAAFK8aRgffe5c225175f44e6d02d3f5e3cb32f64

That looks OK. You just need to check it will physically fit onto the PCB. The spacing I used fits a range of standard preset pots.

and for these:
fixed 100nF 100nF 400V Polyester
fixed 2.2uF 2.2uF 400V Polyester
fixed 2.2uF 2.2uF 400V Polyester
Am I looking for ac or dc? I am a bit spooked with all the stories about danger with tubes....

edit: I am guessing DC, since AC is stated seperately elsewhere on the xls file.

Yes, 400V dc is what you need.

You do need to be careful where you put your fingers with tubes. There are very high voltages involved which can give you a nasty electrical shock. Just take extra care.

Cheers

Ian

 

[erikb1971]

Hi All

I have decided to go with stepped pots for all boost / cut pots. So I am trying to calculate the appropriate R values. I have a few questions on them:

1. could someone verify what I have so far?
2. What are the values for the posh mid boost/cut pots? And are those 1 pole or two pole swithes?

Cheers

Erik


Ok, Iam going to read more on this and then come up with my actual question...

 

[rmaier]

I've prepared stepped pots using the R values posted on page 1, post 3.

 

[erikb1971]

Is there a difference between a "normal" log pot and the 40db one mentioned in post #3? I have received an excel sheet from SilentArts, and that gives me different values...

And btw, does anyone know the values of the boost/cut pots for the posh mid sections? Or (oh men I am getting confused now, forgive me) do I need two deck 12 pos switches to have different values for the resistors for boost and cut? (makes sense I think... my poor brain)

 

[ruffrecords]

A normal linear pot obviously has 50% of the total resistance between wiper and top and 50% between wiper and bottom connection when the pot is at the mid way position giving a nominal
6dB attenuation at the mid point. For a normal log pot, at the mid way position there is 90% of the total resistance between the wiper and the top and 10% between the wiper and the bottom giving a nominal 20dB attenuation at the mid point. So for a log switch to look like a log pot you need to aim for 20dB at the mid point. So if you have an 11 way switch this would be at position 6 with 4dB attenuation per step:

1 0dB
2 4dB
3 8dB
4 12dB
5 16dB
6 20dB  middle
7 24dB
8 28dB
9 32dB
10 36dB
11 40dB or infinity

Normal you want your pot to give infinite attenuation when turned fully anti clockwise so you usually make the last switch position do this.

Notice that in principal there is now reason why you have to have 20dB at the mid point - this is just normal practice. With a switch pot you could make it 30dB and have 6dB steps.

For EQ designs, you often do not want a potential divider but a variable resistance and you choose a log or lin pot depending on which gives a more or less equal change of boost/cut as the pot is rotated. In general though, neither a lin or a log law is exactly right for this and you generally choose depending on which give closest to half the boost/cut at the mid point of the pot. If you then decide to use a switch pot instead you could calculate the exact values to give exactly the same dB  boost/cut for each step. I have not done this for the poor man's EQP.

Cheers

Ian

 

[erikb1971]

clear, thank you!

And what about the properties / values of the boost / cut pots in the poshmen's? (the two different mid ranges with one boost / cut pot per band with on off on switch)

 

[erikb1971]

I am for a few days in Poland and surviving the cold by finally working on the pm eqp1. Of course running in problems right away... Can't read all my docs here... So who knows the relation between the r1-r5 on the power board and the values in the parts list excell file? And what precautions should I take with the 1n4007s? Electrostatic precautions the sticker says... But not how!

Cheers from -18!

Erik

 

[ruffrecords]

clear, thank you!

And what about the properties / values of the boost / cut pots in the poshmen's? (the two different mid ranges with one boost / cut pot per band with on off on switch)

Exactly the same as the poor man's.

Cheers

Ian