Poor Man's Pultec EQP1-A Build Support Thread

TimS · Sep 17, 2012

ruffrecords said:
I just had an order from someone who wanted to do separate frequency switches for bass boost and cut so he could also get 12 frequencies on each instead of the six in the regular poor man's. I had a look at the PCBs and the Lorlin switches and it looks like it can be done quite easily. The 12 way Lorlin has a single wiper connected to the A pas on the PMEQP1A PCB and it will connect to caps C1 thru C12 as is goes through its 12 positions. The capacitor common for the first 6 is T1 and for the second six is T3 so you just strap these togher for 12 positions.

I have no idea if anyone else wants to do this but I thought it was worth passing on.

Cheers

Ian

I take it this can't be done with the 3-band pultec due to the wiring on the PCB?

ruffrecords · Sep 17, 2012

TimS said:
ruffrecords said:

I just had an order from someone who wanted to do separate frequency switches for bass boost and cut so he could also get 12 frequencies on each instead of the six in the regular poor man's. I had a look at the PCBs and the Lorlin switches and it looks like it can be done quite easily. The 12 way Lorlin has a single wiper connected to the A pas on the PMEQP1A PCB and it will connect to caps C1 thru C12 as is goes through its 12 positions. The capacitor common for the first 6 is T1 and for the second six is T3 so you just strap these togher for 12 positions.

I have no idea if anyone else wants to do this but I thought it was worth passing on.

Cheers

Ian

Click to expand...

I take it this can't be done with the 3-band pultec due to the wiring on the PCB?

I am not sure. I don't think you could do it for the lo frequency because the lo boost caps have one end hard wired to the ground plane (0V). You might be able to do it with the hi boost/cut since the capacitor commons all go to the inductor pins or to the hi cut pot and the wiper you need goes to a 470R resistor which you could just omit. So with a bit of judicious track cutting you might do it.

Then again, the original individual poor man's PCBs give you a lot more flexibility to do this sort of thing. The 3Band was intended as much as anything to simplify construction by removing as much of the confusing inter-wiring as possible.

Cheers

Ian

johnnyscotch · Sep 18, 2012

has anyone found a good source for the switches on these boards in the US?

I'm just researching parts and not sure where to go for these......

cheers

ruffrecords · Sep 18, 2012

johnnyscotch said:
has anyone found a good source for the switches on these boards in the US?

I'm just researching parts and not sure where to go for these......

cheers

The 2 pole 6 way used in the original poor man's EQP1A can be got from Farnell:

http://uk.farnell.com/lorlin/ck1050/switch-2pole-6-pos-0-15a-250v/dp/1123696

and also the 1 pole 12 way used for the mid add-on:

http://uk.farnell.com/lorlin/ck1049/switch-1pole-12-pos-0-15a-250v/dp/1123694

I expect Digiekey and Mouser will do them too.

Cheers

Ian

wave · Sep 18, 2012

Mouser page for the Lorlin 2P6W switch

http://www.mouser.com/ProductDetail/Lorlin/CK1055/?qs=sGAEpiMZZMvNbjZ2WlReYu3hsbqI1iNk7sf%252bAWMyL2Y%3d

1P12W

http://www.mouser.com/ProductDetail/Lorlin/CK1034/?qs=sGAEpiMZZMvNbjZ2WlReYu3hsbqI1iNkKp9%2fpytA750%3d

Dave

johnnyscotch · Sep 19, 2012

Great, thanks!

Has anyone done any experimenting with trafos for this?

Less expensive options than the Sowters? I know Ian has said he is not a fan of the Edcors.......

wave · Sep 20, 2012

I was looking at the Cinemag CMOB-1L and the Cinemag CMLI-15/15B.
I believe the pricing is:
CMLI-15/15B - $49.04
CMOB-1L - $36.52

Dave

johnnyscotch · Sep 20, 2012

That's a bit better.

What is the problem with the Edcors? People seem to use them for a lot of projects. Is the nature of this build such that they just don't cut it? Or is it a preference thing?

ruffrecords · Sep 20, 2012

johnnyscotch said:
That's a bit better.

What is the problem with the Edcors? People seem to use them for a lot of projects. Is the nature of this build such that they just don't cut it? Or is it a preference thing?

It is basically an inductance thing - the Edcors generally don't have enough - more inductance means more wire and a bigger core and hence more expense.

At the input side, provided you drive it with pretty low source impedances, 100 ohms or less, you will probably be OK using an Edcor. If your source impedance tends to be higher then the lower inductance Edcors will lose bass response.

On the output side, the source impedance of my tube gain make up amp is about 1500 ohms so you really do need a good quality, high inductance = expensive output transformer. Of course, if you use an op amp gain make up this is not an issue.

Cheers

Ian

funkymonksf · Sep 20, 2012

That's a bummer. Im finishing my dual poor man eq w/ tube gainstage. And I'm using edcors. I decided it was worth the gamble since it only cost $45 for the entire set. I'll post my opinions on them when I fire it up.

ruffrecords · Sep 20, 2012

funkymonksf said:
That's a bummer. Im finishing my dual poor man eq w/ tube gainstage. And I'm using edcors. I decided it was worth the gamble since it only cost $45 for the entire set. I'll post my opinions on them when I fire it up.

That would be useful information. You should have no problems from 100Hz upwards with normal sources and bridging loads. If you were able to measure the frequency response with the EQ out or set flat that would be very useful.

Cheers

Ian

MatthisD · Sep 20, 2012

wave said:
I believe the pricing is:

CMOB-1L - $36.52

Dave

Is that an up to date price by any chance? it seems very cheap for a core like that!

If choosing an Edcor, the WSM15K/15K seems like the best match for the output although its listed as an input, the core size is more suitable as an output. Inductance is given as 15 henries, the low frequency response should be reasonable but the upper end may be a bit wonky even though the Edcor plot for the WSM15k/15K is near flat. Also I would wire it backwards so that the lower DCR winding is used as the primary and the higher DCR side as the secondary which should mean that the secondary winding surrounds the primary winding on the core.

TimS · Sep 22, 2012

What sort of transformers would you recommend for someone wishing to make a completely passive unit from this circuit (with the idea of using a separate preamp for makeup gain)?

ruffrecords · Sep 22, 2012

TimS said:
What sort of transformers would you recommend for someone wishing to make a completely passive unit from this circuit (with the idea of using a separate preamp for makeup gain)?

This as discussed in some detail in the original thread in Drawing Board. Search to that thread and start reading at page 18.

Edit: Here's a link to it: http://www.groupdiy.com/index.php?topic=43859.msg563485#msg563485

Cheers

Ian

wave · Sep 25, 2012

MatthisD said:
wave said:

I believe the pricing is:

CMOB-1L - $36.52

Dave

Click to expand...

Is that an up to date price by any chance? it seems very cheap for a core like that!

If choosing an Edcor, the WSM15K/15K seems like the best match for the output although its listed as an input, the core size is more suitable as an output. Inductance is given as 15 henries, the low frequency response should be reasonable but the upper end may be a bit wonky even though the Edcor plot for the WSM15k/15K is near flat. Also I would wire it backwards so that the lower DCR winding is used as the primary and the higher DCR side as the secondary which should mean that the secondary winding surrounds the primary winding on the core.

That is the price for the 50/50 core not the high nickel. I'm not going to use the high nickel as I feel they are a little to clinical for my tastes
I was quoted that price in Feb I think.

Dave

MatthisD · Sep 26, 2012

wave said:
That is the price for the 50/50 core not the high nickel. I'm not going to use the high nickel as I feel they are a little to clinical for my tastes
I was quoted that price in Feb I think.

Dave

Thanks Dave, I was going to ask if that was for both type. The shipping to EU makes it less viable but nice to know the price. I got a quote for the pushpull output but the price inc. shipping was quite a bit higher than Sowter's equivalent.

wave · Sep 26, 2012

Hey Matthis,
If it was me, I would get the Sowters if the price (with the shipping) was close. Ian did design the circuit with the Sowters in mind...
What is the shipping for the Cinemags?

Dave

MatthisD · Sep 26, 2012

About $50 for shipping for the original Pultec replacement so I presume it would be similar for CMOB-1L, I'm not actually in need of a pair but that price you posted caught my eye considering the core size! Thanks.

johnnyscotch · Sep 29, 2012

Hey everyone, I'm building a 2 ch version with Ian's power supply board.

Will this work for the torroid: http://www.antekinc.com/details.php?p=637

It will be a US build (115v, etc...)

ruffrecords · Sep 29, 2012

johnnyscotch said:
Hey everyone, I'm building a 2 ch version with Ian's power supply board.

Will this work for the torroid: http://www.antekinc.com/details.php?p=637

It will be a US build (115v, etc...)

You really need one with a 240V secondary so this one would probably be better:

http://www.antekinc.com/details.php?p=638

Edit: or even this one which is in stock at present. The HT will be lower because of the 200V secondary but it should be sufficient for a pair of channels.

http://www.antekinc.com/details.php?p=603

Cheers

Ian

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