rainton's True To The Original PULTEC EQP1-A chassis kit discussion thread

[Quayhog]

send message to noted link for Facebook group.  It's mostly for people who have purchases a chassis from Rainton.    https://www.facebook.com/groups/1615927638648181/?ref=browser

 

[rainton]

I plan to make my pair with Allen Bradley carbon comp all the way...good or bad idea ?..
I plan to build the filter units with tropical fish capacitors, would it be stupid ?
Ty
Hugo

Well, the original units used carbon comps in all positions except for the 470R 2W I think.
I did the same with my unit.
I haven't tried to build it with metal film to compare it.

I did an experiment like that many years ago with 1176s though - I built one with metal film in the signal path and one with carbon comps, ran the same signal through both units, recorded it and had several people listen to both files in a blind test.
And even though the majority preferred the carbon comp one for a little bit warmer sound I think they sounded very close.
But it might very well be the "out of tolerance" factor

In regards to using tropical fish caps - I don't know if there's different kinds of those caps. The ones I found are Polyester film caps which I wouldn't use in a passive EQ circuit. I prefer polystyrene or polypropylene.
There's a very interesting article by Chris Preston @ vintagewindings.com about filter caps for the Pultec. I posted a link to it in my White Market Thread.

But if you have the time I would always suggest to not close and pot the filter units before you tried various different kinds of caps for each Frequency position.
I did so with both - my EQP-1A and my MEQ-5 - always measured the peak frequency and listened to how it sounds and chose the one I liked best.
I spent a lot of time doing that and it was very interesting!
Different kind of caps sometimes sounded VERY different - even though they measured  almost the same when measuring  them for capacitance with a DMM.
From "oh that's rather harsh" to goosebumps  ;D
And I tried all kinds of caps: PIO, polyester film, polypropylene, polystyrene, metallized paper, etc...
Most of them vintage ones or NOS - I guess I thought if i want it to sound like a vintage unit it makes more sense to use components from that era (as I did throughout my units)

Anyway it's really worth trying it for yourself, because only then you will know for sure
I ended up using mostly vintage Good-All polystyrene caps pulled from a Hammond organ (most of them were still very close to spec) for the filter unit, because I really liked their sound, but you might find others to sound much better to your ears. That's the beauty about DIYing one of these gems - you can create YOUR Pultec and select caps for YOUR sound

Martin

 

[hugo]

Thank you very much for the reply. Just a question...Do you think there will be a BOM for the meq5 soon ? Maybe some components are similars and it would help me to save lot of time and shipping cost...

 

[rainton]

Thank you very much for the reply. Just a question...Do you think there will be a BOM for the meq5 soon ? Maybe some components are similars and it would help me to save lot of time and shipping cost...

I don't know how soon Hugo,
but you can check the MEQ5 manual/schematic here:

http://www.vintagewindings.com/gen%20pop/8299543VW8335/ProAudio1/Pultec%20MEQ5%20Manual.pdf

it's a very simple circuit with not many components - especially in the amp circuit

hope that helps
Martin

 

[hugo]

Thank you very much for this helpful link. I will go with CC resistors except for the Power section. If somebody has got a source for those Polystyrene all goods caps..

 

[hugo]

Hi all,
how can i mount the can capacitors on the back ?. I have the metal plates, but should i solder the metal plate to the capacitor ? I can not see on pictures how it works...
Regards,
Hugo

 

[rainton]

Hi all,
how can i mount the can capacitors on the back ?. I have the metal plates, but should i solder the metal plate to the capacitor ? I can not see on pictures how it works...
Regards,
Hugo

That's why they're called "twist lock"
Feed the "-" terminals through the mounting plate and then twist them slightly with pliers

 

[AusTex64]

<In regards to using tropical fish caps - I don't know if there's different kinds of those caps. The ones I found are Polyester film caps which I wouldn't use in a passive EQ circuit. I prefer polystyrene or polypropylene.
There's a very interesting article by Chris Preston @ vintagewindings.com about filter caps for the Pultec. I posted a link to it in my White Market Thread.>

Here's the link you mention: http://vintagewindings.com/tech%20swag/Pultec-Facts-&-Fiction.pdf

A couple of observations from this article:

The Aerovox V161 caps used in the original are Mylar (polyester). The Duranite caps are paper in oil encapsulated in plastic.

Note how much all the caps (except for the mica) were melted and deformed by the hot beeswax applied to the metal can housing the caps and inductor. I would be very concerned about melting polystyrene caps, given they have a known low melting point and can even be damaged by holding a soldering iron on the leads for too long. Not sure how well polypropylene would hold up. Would be a good idea to take one, pour the hot beeswax over it, then take it apart to see how much it deformed or not. I can see why mica caps would be desirable in this application.

As for polyester caps, I used CDE polyester caps in my Drip builds and they sound pretty damn good to me. Both the Lucas CS-1 and CS-4 mics have CDE polyester coupling caps and people rave about the sound of those mics. I understand the custom built mastering EQ's for The Mastering Lab had the dreaded polyester caps. I will be using CDE polyester caps in my MEQ-5 builds. YMMV.

 

[hugo]

Hi, Should i drill new holes for xlr's ?..the actual holes are reversed regarding neutrik d-series.. And one more question : where should i remove some paint of the chassis ?..All parts have to be connected together ?..
Thank you

 

[bancho]

how did you guys make the filter boxes? what comes in which box? molded in wax?

 

[rainton]

Hi, Should i drill new holes for xlr's ?..the actual holes are reversed regarding neutrik d-series.. And one more question : where should i remove some paint of the chassis ?..All parts have to be connected together ?..
Thank you

Yes sorry about the mounting holes for the XLRs - they were reversed in the first run.
It shouldn't be too difficult to drill new ones though.

File/sand off the powder coating around the mounting holes/cutouts  where components should be connected to chassis ground.

You can refer to the graphic layout I made

Hope that helps
Martin

 

[rainton]

how did you guys make the filter boxes? what comes in which box? molded in wax?

Also please refer to my graphic layout  regarding which components go into the filter boxes and how they are routed and connected.

They can be soldered together directly.
In the original units they were potted with bees wax inside the boxes, but you could also wrap them in some insulating material - foam or so.

 

[wmarden]

BTW: one member ran into some incidentals and would like to sell his two Pultec chassis kits including knobs & transformers - so if you thought about jumping the train, but missed it so far, this is your your chance! If interested please let me know

Do you have one still available?  I'm wanting a single unit...

 

[hugo]

...370jx does not fit the chassis....too big.. I am a little bit disappointed because i ordered 4 of them regarding the forum, and it is too heavy to be ship back...500€ just in the garbage. Be careful when you order for this project...

 

[core13]

there is also some mistake about the terminal strip
and the right power tx is the 370bx

 

[rainton]

...370jx does not fit the chassis....too big.. I am a little bit disappointed because i ordered 4 of them regarding the forum, and it is too heavy to be ship back...500€ just in the garbage. Be careful when you order for this project...

Sorry about that

If you're not certain please ask before ordering!
In the BOM I wrote 370BX

There was a mistake regarding the power transformer in the very first revision of the BOM but we found it about 3 or 4 months ago and the BOM was updated immediately.

It was all discussed here in this thread at that time.

Also I wrote that I'm doing all of that stuff to my best knowledge but still mistakes do happen so I already mentioned if you find any mistakes please let me know so I can update the BOM.

And please check my WM thread for the latest BOM revisions before sourcing the parts

Martin

 

[hugo]

Completely right, i am discussing with Mouser to make an exchange. .

 

[core13]

Someone have a link to the last bom please?

 

[rainton]

Someone have a link to the last bom please?

You can find it all in my White Market thread:
https://groupdiy.com/index.php?topic=63423.0

 

[core13]

thank you