Poor Man's EQP1A (+MID) Mark 2

[ruffrecords]

The poor man's EQP1A is several years old now and its replacement one board 3 band Pultec uses expensive Grayhill switches. I have been asked if I would do a version that uses low cost Lorlin switches. The person who asked might also be able to supply inductors at about half the usual price. I thought I would check here to see if there is any interest.

Cheers

Ian

 

[rock soderstrom]

Hi Ian,  I am interested in the Lorlin version.  Best regards thorsten

 

[ruffrecords]

Hi Ian,  I am interested in the Lorlin version.  Best regards thorsten

THanks Thorsten. I have been looking as the original poor man's PCBs which have provision for two capacitors  per switch position. Looking at the documentation I see that for the bass you can easily get away with a single cap per position. I also think with a little tweaking of frequencies we can get away with one cap per position for the treble as well. This saves 24 caps.

Cheers

Ian

 

[XAXAU]

Why not just use grayhills? They feel better and are not that expensive, compared to elmas anyway! 

 

[Rocinante]

Why not just use grayhills? They feel better and are not that expensive, compared to elmas anyway! 

It adds up quick and it's called the "poor mans" eqp1a.

@ Ian
Im not sure if the caps were ever a concern (they never were for me anyway) but that is great news concerning the inductors.

 

[ruffrecords]

Why not just use grayhills? They feel better and are not that expensive, compared to elmas anyway! 

Yes, but compared to Lorlins they are very expensive!

Cheers

Ian

 

[ForthMonkey]

I love your EQP1A.Used Lang eq solid gain stage with it.Now waiting for PCB from manufacture.Anyway...

Now i want to build DW Fearn VT5 style eq with your EQP1A.Two switches for one pcb.Selectable cut and boost freqs.And i will add mid dip.

 

[ruffrecords]

I am making good progress with the PCB. it is 150mm by 50mm and the pots are on 1.75 inch centres. See attached pic.

Cheers

Ian

 

[tmuikku]

not to discourage but i've made a mental note during the years that poor can't afford to buy cheap because you end up buying the proper part/tool/whatever anyway after the cheap one is tested in action...

also, lorlins are hard to desolder. if one of them gets broken, you more likely need to replace the whole pcb eventually... lorlins break on install if you arent careful. i dont know how long they last in use, not as long as grayhills thats for sure anyway, this is my opinion only

to contribute: would it be hard to get the board 40mm wide to fit 1u? it looks like could be possible with ~20cm length. 15cm length requires 4u front panel if vertically mounted which should accommodate 20cm board as well. seems like it would take less real estate if you can squeeze to 4cm x 20cm board. sorry, i don't remember your other lineage frontpanel dimensions.
cheers!

 

[gyraf]

If treated well (i.e. not exposed to DC, salty air or violence), the Lorlins lasts nearly forever. And in the pultec circuit, there's pretty small chances of catching DC.

Jakob E.

 

[ruffrecords]

also, lorlins are hard to de-solder.

In point of fact they are easier to de solder than Grayhills. They have larger, widely separated  pins, with proportionally larger PCB holes than the Grayhills. This means your solder sucker has a good chance of completely freeing the the pin of solder. Not so with Grayhills with their close packed small pins. Last time I removed a Grayhill it destroyed several PCB tracks. Last time I removed a Lorlin it was quite successful.

Cheers

Ian

 

[tmuikku]

Cool, ignore my ignorant post   my experience is limited to few projects using lorlins and I'm not daily operating studio.

 

[alexc]

Looking good Ian.

wrt Grayhills and Lorlins, the great thing is to have both options - which Ruffrecords eq pcbs cover nicely.

More can only be a great thing   

I sure do like the luxury of the Grayhill design but am also happy for the Lorlin types in many applications.

Thanks RuffRecords!


ps - I'm working a pair of your Poor Mans EQ  mkI into an interesting mash-up of neve-ey and api-e blocks. Tres fun to be had!

 

[Chris_V]

With a slightly over sized pin hole, I have found that solder wick (with sometime additional flux) is the best way to go  even with multilayers pcb.
Solder suckers sucks 

 

[ruffrecords]

I received the prototype PCB a couple of days ago and I just now finished populating the board. Here's a front view:

https://www.dropbox.com/s/j5tsvmirw6op1b5/protobuildfront.png?dl=0

You can see the 6 holes for stand offs. The idea is to mount the board away from the front panel so as to leave room for the pots.

The inductors are mounted on the back of the board to save space. As usual, the Hi boost inductor is optional:

https://www.dropbox.com/s/25tvkgtgjgb7331/protbuildside.png?dl=0

You have to be careful to make sure the metal straps that hold the inductor to its little PCB do not short out on the pins of the Lorlin switches. To reduce this I first trim all the pins of the Lorlin switches after soldering them to the PCB (they must be fitted before the inductors. To prevent shorts I attached a thin piece of card as an insulator to the back of each inductor. It needs to be thin so the inductor pins still protrude through the PCB but thick enough to prevent shorts on the switches:

https://www.dropbox.com/s/kf522yatdfhwf2y/insulator.png?dl=0

And here is the schematic:

https://www.dropbox.com/s/taricbromzz4ejv/Lorlin3BandPultecEQ.png?dl=0

Next step is to wire up some pots and test it out.

Cheers

Ian

 

[Humner]

Looking at the Q control, does more resistance mean narrower bandwidth?

 

[ruffrecords]

Looking at the Q control, does more resistance mean narrower bandwidth?

It's the other way round. Less resistance means narrower bandwidth. The resistor Qmax limits the minimum resistance, and maximum Q. The original Pultec EQP1A high boost Q control varies the Q from about  1 to 3.

Cheers

Ian

 

[ruffrecords]

Initial, tests are very encouraging. everything seems to work as advertised except the hi boost frequencies are all wrong. Just discovered I fitted the RC boost cap values instead of the LC boost cap values. I'll correct and re-test that but it looks like the board is OK. I shall get an initial batch made and offer them on my white market page for £7 each. That's the same price as a pair of the old PMEQP1A boards with a mid section thrown in for free. And you don't have to do all the complicated and confusing wiring between pots. Each pot wires up to three dedicated pads on the board and then you connect to the EQ In and EQ Out pads and you are good to go. I will be putting together an assembly guide document for it and adding it to the documentation available through dropbox.

I have recently been corresponding with the guy who is making low cost inductors for it and prototypes are ready. They measure very close to the required inductance values and the dc resistance is very similar to the Carnhill ones. They should perform just as well but at about half the price. I expect he will make an announcement here before too long.

Let me know it you are interested in this new PCB so I can gauge how many to order in the initial batch - don't want to run out too quickly.

Cheers

Ian

 

[shot]

I think I'll take two!
And keeping my fingers crossed for poorman's inductors!

 

[anjing]

Hi Ian,
  i'll probably take two. It just looks so easy to build! Does the guy making the inductors plan to make some for the helios eq as well?

Regards,

Pierre