Poor Man's Pultec EQP1-A Build Support Thread

[ruffrecords]

I reversed connection in pins 1 and 12 on one channel and it seems to be working fine as far as I can tell listening in my bench monitor...  ;D

Sounds like you fixed it.

Cheers

Ian

 

[ilfungo]

give me some advice?

2 XSM 10k/10K
2 XSM 600/10k
2 Jensen 11p-1 10k/10k

What do you recommend to use as an input and an output?
thanks

 

[ruffrecords]

give me some advice?

2 XSM 10k/10K
2 XSM 600/10k
2 Jensen 11p-1 10k/10k

What do you recommend to use as an input and an output?
thanks

To be honest I am not very impressed by Edcor transformers so I would not really be able to recommend either of the ones you listed.

The Jensen will be fine for the input.

For the output the Jensen JT-112-LCF would be a good choice.

Cheers

ian

 

[dirtyhanfri]

Well I've tested one channel in a more or less accurate way (Channel EQ Analyzer in Logic Studio ???)

It works fine, but it looks like cutting a lot more than boosting, both in low & high freqs, actually it boost, but is way more evident the cut. I think boosting is the problem, gonna check that tomorrow.

Also, in eq-out mode, the level is much lower, and tweaking the trim doesn't make it as loud as with the eq enabled, I will check for wrong resistor values or something...

 

[ilfungo]

thanks Ian for the suggestions
i 've also 2 x lundahl 1539
can they work well in this situation?
Thanks

 

[dirtyhanfri]

Well, Everything Looks better now, nice boost and cut, I was reversing the high boost and cut switches, also, the bypass issues are gone, but some hum in  the unit, gonna work on the wiring for tidy up a bit everything...

 

[ruffrecords]

Well, Everything Looks better now, nice boost and cut, I was reversing the high boost and cut switches, also, the bypass issues are gone, but some hum in  the unit, gonna work on the wiring for tidy up a bit everything...

What tubes are you using? Sometime NOS tubes have poor heater cathode isolation which shows up as hum. Do you have a steel enclosure? If you do you need to be careful that the power supply transformer does not get magnetically coupled to the input transformers.

Cheers

Ian

 

[dirtyhanfri]

I'm not using input transformers by the moment, actually just taking + from the balanced input (I'd like to make a 2 channel ballancing/unballancing amp based on 5532's posted in this forum by audiox). The tubes are old RCA's, and I think the hum was related to the messy wiring inside the box.

Also I noticed when putting my hand near the wires going to the trimmers it makes some kind of noise, hoping it's nothing relevant qhen it's closed and racked, but, maybe is because the wire, I got for free a coil with hundreds of pure copper wire, like 1.2mm diameter and semi-rigid, ,maybe it's not the best wire to use in audio circuits?

Gonna work on the front panel today, photos coming soon

 

[ruffrecords]

I'm not using input transformers by the moment, actually just taking + from the balanced input (I'd like to make a 2 channel ballancing/unballancing amp based on 5532's posted in this forum by audiox). The tubes are old RCA's, and I think the hum was related to the messy wiring inside the box.

Also I noticed when putting my hand near the wires going to the trimmers it makes some kind of noise, hoping it's nothing relevant qhen it's closed and racked, but, maybe is because the wire, I got for free a coil with hundreds of pure copper wire, like 1.2mm diameter and semi-rigid, ,maybe it's not the best wire to use in audio circuits?

Gonna work on the front panel today, photos coming soon

The audio signals going from the EQ output to and from the trimmers should be carried in screened wire as shown on the latest hook up diagram (attached). The dotted wires represent the screens of the cables.

Cheers

Ian

 

[surfkat]

I built a single channel of this EQ on a perfboard. It's unbalanced so I can patch it into the inserts on my mix board. The make up gain is a TL071 and this thing sounds great! I am making a second channel now to have a stereo pair. Thanks again to Ian for this project.

I came up with a simple mod which I tried on my prototype. I was thinking it would be cool if you could offset the frequency of the boost/cut. By adding a cap in parallel to the other caps the value of each individual cap on the 6 position switch is increased by the value of the parallel cap. Using a SPST switch on the parallel cap, I could compare the new offset freq with the original. I put a 3n3 cap on the hi boost which lowers the freq of the boost. When this is switched in, with the 6 position switch on 16k I can boost 8k and cut 16k. This sounds very musical to me. I also put a switchable 3n3 cap on the lo cut. This lowers the freq of the cut so when I boost 100hz I can cut around 50hz. This sounds like it tightens up the bass a bit.

I only tested this in mono so I am anxious to try it with a stereo pair of EQs. It's not a huge difference but for the cost of a cap and a switch it gives a bit more flexibility to this already great sounding EQ. Try it and let me know what you think.

 

[ilfungo]

surfkat , I think it's a great idea!
you can explain it better, maybe with a drawing?
thanks

 

[surfkat]

This should explain it better.

 

[ilfungo]

Many thanks surfkat
I'll try ....
Thanks Ian!!!
I just finished my Poor Man's Pultec
is beautiful
incredible sound
Thanks
Grazie

 

[ruffrecords]

Hey Surfkat, nice idea!!

Ilfungo - glad  that you finally got it working and you like the sound of the EQ!!

Cheers

Ian

 

[rmaier]

Well, after coming to a bit of an impasse with this EQ and letting it sit for a month or so, I finally got it working, thanks to dirtyhanfri's question about R3 a page back. Thanks, guys, and thanks, Ian for a very satisfying project. Still need to tweak my make-up gain levels and do some more extensive testing, but my initial impression is very positive. Here are a few pictures for your amusement (forgive my messy wiring, but after the hell I went through getting it wired up, there's no way I'm going back to try to make it any prettier).

Cheers,

Ralph

 

[rmaier]

Front panel closeup. I decided to call it an EQP-1A/5.

 

[rmaier]

Another angle. Using a final couple of coats of satin finish helped to cover up most (albeit not all) of the imperfections of my spray-bomb finish.

 

[rmaier]

The rear panel. Gotta love those knock-off greenlee punches (think they were q-max)!

 

[rmaier]

The guts, with a neat little row of Sowter transformers on the right.

 

[rmaier]

A good look at a single channel with Chrion's inductors. All of the rotaries with Dale resistors were my second shot at switches, because the first set were done up as volume pots. Live and learn...