My Pultec EQP-1a Filter Section

[adamboon]

Can people tell me if there are any reasons this circuit shouldn't make a kick-ass Pultec style EQ?  I'm planning on 2 toroid inductors (one molypermalloy for the smaller one, one ferrite for the larger one).  Notice there's some funky inductor series/parallel switching going on (and switched parallel capacitors).  I believe the actual Pultec's did a bit of this also.  Most of the design inspiration is from a filter schematic labeled "EQP-1R Equalizer" in the Pultec EQP-1a manual PDF found on danalexanderaudio.com

I am also desperate to find out what capacitors the original Pultec's had where, if anyone can help me.  I was thinking of putting some caps with significant "Character" in the key positions (ie. those that are in circuit all the time)

Forgive the schematic, I haven't used "Eagle" before.

UPDATED SCHEMATIC

 

[lassoharp]

As far as using old caps for character - I would recommend setting up the circuit on a breadboard to experiment first before hunting down reported brands found in originals.  I'd try anything I could find for comparisons. Old hi-fis and guitar amps are full of in the range values.

It can be difficult to evaluate subtle differences on the fly - it usually takes a little usage over a period of time to discover those things.

NOS of a same make will likely age differently than one that's seen some miles.

For a given set inductance value the caps often had to be sorted and at times paralleled to get the right capacitance value for consistent curves.

 

[abbey road d enfer]

I think the construction and design of the inductances are gonna make much more difference than the caps.
The caps used in the Pultec were the best commercial grade available at the time. Today's film capacitors are as good as were the originals (unless you want to use $0.01 ceramics).
There's much more variation in the composition and construction of magnetic cores; different grades of ferrite result in different losses and just the way the laminations are assembled can make a huge difference.

 

[adamboon]

As far as using old caps for character

I was more interested in the character of current caps (eg Ceramic vs Mica vs Poly vs Styrene vs Electro, etc).

I think the construction and design of the inductances are gonna make much more difference than the caps.

Me too, that's why I'm going to great lengths to not miss anything here.

Can anyone see any design flaws? (I was expecting to be shot down by now).  I will post the rest of the Cap values soon too.

 

[adamboon]

EDITED INDUCTOR VALUES

Well I've ordered the bits, and will let you all know how it goes.  I am going try Mica in C1-3 and Solid Tantalum in C20.  Also Nichicon MUSE in most of the LF and the rest will be a mixture of Polyester and Polystyrene Orange Drops. Oh and a couple of TVA Atoms

I havn't fully sorted the inductors yet, so It might start it's life out shelving

This is what I was hoping for inductor-wise, with Inductor 1 being as close to the original as I can and Inductor 2 adding the lower Freq's without adding too much DCR.

Inductor 1:
Core:
Material: Molypermalloy
Size: 23 x 14 x 8 mm (or nearest)
AL: 87.5 - 95
Wire: AWG 34
2 Taps - 0mH - 50mH - 150mH

Inductor 2:
Core:
Material: Most Suitable (Ferrite?)
Size: 23 x 14 x 8 mm (or nearest)
AL: 120 - 160
Wire: AWG 34
2 Taps - 0mH - 150mH - 300mH

I was going to build a PCB, but (depending on how it all fits) I'm thinking of p2p-ing it.

Please let me know what you think. (I especially would appreciate any advise/guidance on the Inductor front.  I have searched and read the other posts by Pat and CJ etc.)

Adam

 

[Wagtbtoobz]

I think the construction and design of the inductances are gonna make much more difference than the caps. There's much more variation in the composition and construction of magnetic cores; different grades of ferrite result in different losses and just the way the laminations are assembled can make a huge difference.

Yep, most of the vintage ferrites used 30 years ago came from telephone circuitry . At this moment, usable grades were on the market... Nowadays, most of the available ferrites are for HF / VHF use    :-[

 

[adamboon]

So I'm looking at winding my own.

Looking at Amidon's bits and using T106-26 (26 Material Iron Powder Toroid) core for inductor 1, FT-100-43 (43 Material Ferrite Toroid) core for Inductor 2 and Their "Enamel-Coated Magnet Wire (AWG# 34)"

Unless anyone can recommend a good, small qty toroid winder (company)?

Otherwise it'll be me, and the paddle-pop stick, and 5000 odd turns to makeup my inductors.

 

[lassoharp]

So I'm looking at winding my own.

Looking at Amidon's bits and using T106-26 (26 Material Iron Powder Toroid) core for inductor 1, FT-100-43 (43 Material Ferrite Toroid) core for Inductor 2 and Their "Enamel-Coated Magnet Wire (AWG# 34)"

Unless anyone can recommend a good, small qty toroid winder (company)?

Otherwise it'll be me, and the paddle-pop stick, and 5000 odd turns to makeup my inductors.

I've checked on that possibility a couple of places and it simply wasn't practical - either a high minimum order or very high price per coil.

I'd say go for it with the paddle sticks.  If you have the extra coils and the mounting space you can do individuals instead of single-tapped. It may be easier to keep track of things.

 

[JTraverse]

Hi there,

Are you trying to change the inductances? According to your schematic they look different from other inductor values I've seen on the EQP1A.