Neve drive - Pultec passive EQ questions - you are wellcome

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Purusha

Well-known member
Joined
Jan 14, 2006
Messages
1,868
Location
Somewhere on the Planet
I have:

M.Nats PSU,
Fabio's Neve output driver KIT,
Pultec boards stuffed with Panasonic metal poly caps (thanks to Matt)
and a Sowter 8751 output transformer.

1st. Question - Would adding a Lundahl input transformer makes any sense in this combination. Is it needed to get a killer EQ? What would I gain by adding it and which Lundahl tranny would be OK for this?

2nd. Question - Has anyone of you made such version of the P. EQ before? How does it sound compared to G-Pultec with tubes or any other solid state version?
 
[quote author="Purusha"]I have another question, is it hard to change the G-Pultec boards to get the separate LOW CUT and LOW BOOST frequencies?[/quote]

No, not at all. It's a matter of cutting some traces and adding another Lorlin rotary switch. Just look at the schematic (for a while :grin: ), then you'll know what to do. Or look at this schematic Steffen made for his solid state pultec..
 
have a look at my Passive eq schematic. I've splittet Low Boost and Low Cut. Works perfect!

In my opinion adding transformers rocks!! I do it anywhere I can. I'm actually not very skilled at this so I'm not sure how the kit you've shuffled together there. I can't tell. But if there's no transformer in the input right now and the input is similar to the GPultec, which by the way leads straight to the filter section itself, then I would add a Lundahl 5402 in a New York minute! :green:

Listen to the files in the thread where I uploaded the test files with Lundahl and OEP transformers again and have a listen to the file with OEPs in the output and then the file with OEPs in the output and the Lundahl 5402s in the input. The difference there is exactly what you'll get. See?

EDIT:
Oh, I didn't see your post, radiance. Maybe your link is better because it concerns a board. Mine is just an edit of the schematic for the GPultec.
 
[quote author="radiance"]

No, not at all. It's a matter of cutting some traces and adding another Lorlin rotary switch. Just look at the schematic (for a while :grin: ), then you'll know what to do. Or look at this schematic Steffen made for his solid state pultec..[/quote]

Hmm, I was :shock: for some time but so far the :idea: didn't light up in my head yet. Does anyone have a Gyraf's modified schematics or even better, a modified PCB layout. Would anyone of you be so kind to do it for me? The PCB layout would be better.
 
It's a simple matter of splitting the function of the frequency selector up into two switches. All depending on your frontplate layout you could simply physically remove the pins on the 2x6 switch in the current frequency selector and leave it in the pcb and connect another 2x6 switch to the now vacant positions on the back of the pcb with mounting cable.

Or not mount any switch on the pcb but connect them both with mounting cable. One half on one switch and the othe half....well, you got the picture.

It's that easy! :wink:
 
I guess I'll have to :shock: at the schematics a little more :green:

Otherwise I will do all with wires cause I want my knobs differently positioned than the pots on the boards. The cases will also be available for everybody here if somebody likes it. I just started a new discussion about it in the black market.

Pultec_design.jpg
 
Well, it depends on whether you match the filtersections and if you wish to use it as a stereo eq you could notice that when you split the Low Cut and Boost only one half of each switch is occupied! :wink: That means that since you are mounting the switches off-board then you could use one half of the switch for left and the other half for right, and then use dual ganged pots. Then you would have just one set of controls for both sides! That's what I did on mine at it works perfectly fine. Just remember to match the capacitors. :grin:
 
I will order the same capacitors for each ch. Will this be OK, or must I have some specially matched caps for this?

Luny Tune, would you be so kind and help me out with the separated low cut and boost change on the Gyraf's PCB layout? I need some help from more experienced DIYer.
 
I used WIMA caps for mine and ordered 10 of each. Actually, I ordered a wide selection of values as I also wanted to change the frequencies now that Low cut and boost was separated. This way I could experiment. I then measured them to pair up the closest ones. I don't know how tolerant you can be when matching caps but it was a small effort for having good accuracy in frequency selection. Again I just followed Jakob Erland's advise.

However, I'm not familiar with the type of caps you mentioned in your opening post. Maybe tolerance is better with them?

I'm pretty busy the rest of the day, but I will be happy to come up with a suggestion on how to wire those switches. Just give me a day or two.
 
Luny Tune,

I will be so happy if you can help me out here. :grin:

One more question regarding the separation, I just need to get another rotary and a few more caps for the new separated CUT frequencies and that is it?

Do you by any chance have a list of caps you used and which frequencies you went for with your passive P version?
 
You only need an extra 2x6 switch. Then you have all the switches you need for a stereo eq. Just those four 2x6 switches in total. :wink:

This is an insanely simple modification! You'll see shortly. :razz:

Furthermore, if you want to make the high frequency control "shelf" instead of the "bell" curve it's configured for now, simply remove the coils and mount capacitors on the six steps of the switch instead.
I did that on mine, but it's really a matter of style or what you want to use the eq for. What I needed was simply a great sounding eq to open up my mixes before I comp them with the GSSL. The GSSL has a very..."definite" effect to it. The way I use it, anyway. :twisted: So I need to have a more "balanced" mix before I squash it. So I chose to shelf the High Boost.

To give you even more things to consider you could even let some frequencies be "bell" and other "shelf" to your liking. :cool:

Does diy ROCK, or WHAT??? :green:

Here's the schematic for my version of the eq. It's a mono schematic, but as you'll soon see it's easily translated into stereo. (Click it or a larger version. Or right-click and Save As...)
 
I am using Gustav's boards for this and I noticed that the HI FREQ BOOST 12, 18kHz has caps so they are shelf I guess and the other 2, 2.5, 3, 7KHz are bell. Actually I could make the other four switchable with a 4 pole toggle switch isn't it?

I had a look at you schematics yesterday but still can't get it. I admit I have a lot of things on my mind right now with all those cases I have to manage and my newborn son at home to concentrate on so many details :wink:
 
I didn't get it for a long time either. Don't worry! It'll come to you when you work on it. :grin:

You need the caps AND the coils to make the bell curve. The coils are there too on Gustav's boards. (I built the Pultec eq as well using his boards.)

As for the Toggle switch for making it bell/shelf switchable you must remember that for stereo control you would need an 8-pole switch and I'm not even sure that would be enough. I canø't wrap my head around it right now. I'll have a look at it later, 'cause that could be a cool feature. On the mono version as well.

Anyways, using the eq's Wide Q setting gives you a very wide bandwidth when boosting and that can actually be better than shelf sometimes.

If you are very unsure about what happens in the cirquit I suggest that you start out by building it like the Pultec was intended and where the only changes we make are splitting Low cut and boost and possibly changing the values for the Low frequency selectors. It's a simple cirquit (however difficult to grasp for us newbies) and when you're more comfortable with it you can change it to your likings at a later date. How does that sound?
 
As for the Toggle switch for making it bell/shelf switchable you must remember that for stereo control you would need an 8-pole switch and I'm not even sure that would be enough. I canø't wrap my head around it right now. I'll have a look at it later, 'cause that could be a cool feature. On the mono version as well.

I will have everything dual mono so all the pots and switches will be doubled.

If you are very unsure about what happens in the cirquit I suggest that you start out by building it like the Pultec was intended and where the only changes we make are splitting Low cut and boost and possibly changing the values for the Low frequency selectors. It's a simple cirquit (however difficult to grasp for us newbies) and when you're more comfortable with it you can change it to your likings at a later date. How does that sound?

Maybe you are right. But if I want a switch included in my cases design I have to deside this one now before starting the batch production. most probably you are right, it doesn't need a shelf with a wide bell. I also heared somewhere iit can be done even wider.

BTW, Luny I would still like to see some Gustav's PCB layout modification if possible. Any day this week is fine. no hurry. Your list of caps used would be great also.
 
Back
Top