Poor Man's Pultec EQP1-A Build Support Thread

[mike76]

Okay, thanks for your patience. I appreciate this.

 

[buschfsu]

hello all,

i'd like to make my two channel unit for mastering purposes.  i'd stick with dual mono but think that using stepped attenuators would be wise for the boost and cuts.  can someone show me how to figure out the resistor values to give 1db per step?  Last question is about the Q.  i remember ian mentioning dropping from 1 to 0.6 i think.  is it a huge effort to broaden the Q a bit more?

thanks

 

[ruffrecords]

hello all,

i'd like to make my two channel unit for mastering purposes.  i'd stick with dual mono but think that using stepped attenuators would be wise for the boost and cuts.  can someone show me how to figure out the resistor values to give 1db per step?  Last question is about the Q.  i remember ian mentioning dropping from 1 to 0.6 i think.  is it a huge effort to broaden the Q a bit more?

thanks

The poor man's EQP1A has no inductors in it so there is no Q to set. The add on mid boost/cut board does use an inductor so you can adjust the Q. The mid boost/cut circuit is something of a compromise because it alters boost/cut amount and Q together.

I have never plotted the pot positions versus boost or cut so I do not have figures for stepping in 1dB steps. The circuit is fairly easy to simulate if you want to do it yourself. You just manually adjust pot values in the circuit until you get the boost/cut you want and then repeat for the next 1dB increment/decrement. Tedious but it works.

Cheers

Ian

 

[buschfsu]

Thanks ian.

Sounds like we are already at a Q of .3 based on the drawing board thread so thats where i want to be. I will jump the inductor and be set.

Never done a circuit sim so this will be fun and should learn something. (All my time is spent in eagle pcb!)

 

[ruffrecords]

Thanks ian.

Sounds like we are already at a Q of .3 based on the drawing board thread so thats where i want to be. I will jump the inductor and be set.

Just to put this in context, the original poor man's Pultec design had no inductor - that was one of the expensive items I wanted to eliminate. However, lot' s of people asked it I could squeeze just one inductor on the board and I did find room for it. However, it only operates at one position of the switch i.e. at one frequency,  Because the other positions are RC based there is always a common resistor in series at every switch position. This is what limits the Q for the inductor position.

I am currently working on the Mark 2 version of the PMEQP1A. This still uses cheap Lorlin switches but does allow you to fit an optional inductor for the HI boost.

Cheers

Ian

 

[snaper]

Have somebody an FPD format, "classic-looking" front panel design for this?

 

[Paradigm X]

Hi there

I got my pcbs a few days ago, and im staring at them, trying to figure out if i can make a stereo pair with only 3 frequencies. Obviously have to manually wire everything, which is a shame, but with 4pole 3 way switches, i should be able to do this, i think (!)

If so, i think 30Hz, 60hz and 120Hz would be good frequencies, and

Ive got a pair of the MK2's to make a 'proper' racked EQ, but i was hoping/thinking about making a master EQ for my soundcraft desk.

I would greatly appreciate any comments.

Many thanks, cheers, Ben

 

[ruffrecords]

With 4 pole 3 way switches there is no reason in principle why you cannot make a stereo EQ. Just populate fewer positions. You could even use s 2 pole 6 way switch for a stereo mid. For the hi boost don't forget that the new MK2 PCB uses an inductor for this function so you need to connect to the appropriate LC combinations for the frequencies you choose.

Cheers

Ian

 

[ilfungo]

Hi
I'm  start to build a Stereo version of EQP1/MEQ5 (IAN pcb)
I want to use lorlin for frequency selections,
Can someone tell me if there is a connector to use for Grayhill substitution on PCB?
Thanks!!!

 

[ruffrecords]

Hi
I'm  start to build a Stereo version of EQP1/MEQ5 (IAN pcb)
I want to use lorlin for frequency selections,
Can someone tell me if there is a connector to use for Grayhill substitution on PCB?
Thanks!!!

There is a separate PCB that implements the same EQ using Grayhill switches. It is called the 3band Pultec PCB.

Check out the Ruff Records PCB Emporium tab at my new web site:

https://sites.google.com/site/customtubeconsoles/

Cheers

Ian

 

[ilfungo]

Hi Ian
yes I'm talking about that PCB, but I want to use Lorlin Switch instead Grayhill
but I'm searching a pin's connector that can insert  into Grayhill housing.
Thanks

 

[ruffrecords]

Hi Ian
yes I'm talking about that PCB, but I want to use Lorlin Switch instead Grayhill
but I'm searching a pin's connector that can insert  into Grayhill housing.
Thanks

Ah, you want to use Lorlin switches on the Grayhill version of the PCB. I did do a Lorlin header board as a group buy a couple of years ago built I am afraid they all sold out (OK I have one left). That design managed to squeeze a pair of switches and headers into a PCB no bigger than 50mm by 39mm to keep the price really low. It meant the two switches were very close together and rather awkward to separate with a hack saw. I would be happy to create an updated PCB layout that was easier to use provided there was enough demand but it would be a larger and more expensive PCB.

Cheers

Ian

 

[Paradigm X]

With 4 pole 3 way switches there is no reason in principle why you cannot make a stereo EQ. Just populate fewer positions. You could even use s 2 pole 6 way switch for a stereo mid. For the hi boost don't forget that the new MK2 PCB uses an inductor for this function so you need to connect to the appropriate LC combinations for the frequencies you choose.

Cheers

Ian

Many thanks. Sadly i think im going to be stuck for space, but nice to know it will work in principle.

Cheer,s Ben

 

[troubleous]

Hello everybody!

It seems the Antek AN-05T240 is currently out of stock - can't find it second hand either.

Can anyone recommend a equivalent trafo to be used with Ian's tube gain make up?

Cheers,
Jarkko

 

[ruffrecords]

Hello everybody!

It seems the Antek AN-05T240 is currently out of stock - can't find it second hand either.

Can anyone recommend a equivalent trafo to be used with Ian's tube gain make up?

Cheers,
Jarkko

I might be worth asking Don-Audio about a custom transformer since the Antek seems to have been out of stock for a long time. The Antek is a bit of an overkill anyway even for a couple of poor man's tube gain make up amps.

To run two PMTGMU amps the transformer secondaries only need at the most:

240VAC @ 35mA
6.3VAC @ 1.2A

Which is little more than 20VA in total. Should be quite small and cheap.

Writing this it occurs to me that I never really documented the PMTGMU PCB. There's a schematic showing it used in the PMEQP1A using 6CG7 tubes but you can also use a 6922 instead and wire it as a mu follower or an SRPP depending on your drive requirements. I will put together a short descriptive document for this.

Cheers

Ian

 

[ruffrecords]

As promised, I have put together a document describing the possible variants of the PMTGMU board you can build and the differences between them. You can find it in the PMEQP1A folder of the DIY section of my whizzy new web site:

https://sites.google.com/site/customtubeconsoles/diy

Cheers

Ian

 

[Rocinante]

Good morning,
I have Pier's App IO boards and would like to use them for the PMEQP1A.  I am debating making a ic/DOA path switchable with the poor mans tube gain make up but for right now I need to get the IO board correct in my head. 
I do understand the PMTGMU but on the IO boards I have a few spots of confusion.
I will be using DOA/IC in but Carnhill transformer out.
I have modified Dave's diagram and am wondering where I would place where "Pin" would go since I am using the IO board.  Also is everything else correct?

Thanks
Dylan

 

[ruffrecords]

All the DPDT switch does is connect a trimmable pad in in place of the EQ  in the EQ OUT position. You adjust it so its loss is the same as the EQ. This trimmable pad exists between Pin, Pout and PG on the PMTGMU board. If you are not using the PMTGMU solution then you need to build this trimmable pad somewhere. The eqsystem.jpeg drawing shows how to do this.

Cheers

Ian

 

[Rocinante]

Ahh.. Thanks I see it now. I'll keep it just PMTGMU I guess. Thanks for the quick response.

 

[Humner]

Do you think you could get away with using a SPDT switch instead? in other words, can you tie and output of the passive EQ and the output of the Pad together going to the makeup gain, and then just switch the input? Or the other way around?