Input transofmer for Pultec Passive filter section

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craigmorris74

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Sep 9, 2005
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I'm currently assembling the parts to construct the passive EQ section of a Pultec. I assume that I would need a 600:600 for line input.
Have several other questions before I lay this thing out:
1. Could I have a switch that could also select to a 150:600 for mic input?
2. Is the Pultec typically used after a mic pre?
3. Would the output transformer need to be 600:150
Thanks,

Craig
 
Kubi,

Good point about the SNR with such high makup gains. I'll forget that idea.
I think I'll use 2K4:150 for the output, so I can use a mic pre for make up gain.

I haven't ordered an input transformer yet. Could I use it without one until it arrives?

Thanks again,
Craig
 
a dynamic mic would have a hard time driving the passive eq network of a pultec. the network would have a hard time driving the output transformer...
and everything together would hum like hell, i guess.
 
Ok, so my plan is to go mic pre-passive pultec section-mic pre.

I'll have a 600:600 on the input and 10K:150 output.

I've got the Cinnemag EQP-1 inductor ordered, and am thinking about adding a mid cut based on the Sowter MEQ inductor.

Now I've got to read the post about having the EQP-1 and the MEQ in the same box again. Any other thoughts on this would be great.

Craig
 
I am a bit thick on these matters
But I plan to use a 31268 on the input and a Carnhill Neve Output
(no mic pre - just a line input)
 
Regarding Jakob's version (http://www.gyraf.dk/gy_pd/pultec/pultech.gif), any thoughts on replacing the SRPP gain stage after the interstage transformer with something like an API 325 type amplifier?
 
Regarding Jakob's version any thoughts on replacing the SRPP gain stage after the interstage transformer with something like an API 325 type amplifier?
I'm currently toying with the idea of adding a 990 output stage. I always hear them described as big, clear, and open, which sounds like the description of Pultec eq's. I figure building one of these would be cheaper and easier, and different.
An API or Neve would kick put I'm sure.
Does anybody have a layout for a 990 output stage?
Craig
 
[quote author="craigmorris74"]
Regarding Jakob's version any thoughts on replacing the SRPP gain stage after the interstage transformer with something like an API 325 type amplifier?
I'm currently toying with the idea of adding a 990 output stage. I always hear them described as big, clear, and open, which sounds like the description of Pultec eq's. I figure building one of these would be cheaper and easier, and different.
An API or Neve would kick put I'm sure.
Does anybody have a layout for a 990 output stage?
Craig[/quote]


The 325 uses a 2520 opamp... a 990c is a direct replacement
 
Hi all!

I´m building the g-pultec with the srpp stage - using gustavs boards.
i have a question regarding the input transformer.
is it possible to use the OEP A262A2E transformer.
any experiences with that tranny in this design?
I´m also open to other recommendations!! ;D

thank you all!



 
I read this thread quickly and not really, really closely. You should be careful on the input transformer. The input impedance of the passive filter section varies quite a bit depending on the settings. Pultec used a 600:600 on the input. Then, after the filter section, any of the ideas I read will work fine. I built a dual pultec copy with a tube make-up stage. I never could get a hum out of it. So I use the filter without that tube section. I use a mixer input or any good line amp for make-up gain. It works great. 990-based, 2520-based, anything. DW.
 
hey rotation!

which edcor did you use? and do you like it in this design?

thanks,
martin
 
Hi,

i'm using Edcor WSM 600:600 for input and WSM 600:150 for output. I'm not sure if output really is 600:150, so check this others. Also, be carefull what you buy, input transformer need to be real input and not output transformer because there is some difference between them.
Btw, edcor is also making another model which is a copy of Lundahl "Pultec transformer", ou can use it for in and out. But you will need veroboard or something to mount and connect them to main board.

To me WSM sounds quite ok for Pultec; they are colored, make bass sound bigger, highs are smoother and sweeter. I can even hear that they do something with transients, can't explain exactly. Well, if i had money i would buy better transformer because i don't like so much color, specially if preamp is also tube type.
But this is my personal opinion and you might like Edcor better than other less colored transformers. If you are making stereo version maybe buy two different sets and try them.

Miha
 
Going to quote something from the NYD EQ thread:
I suggested a 10K:600 stepdown transformer for my EQ for three reasons. First, it provides a higher input impedance to the source, which is preferable for most modern equipment. Secondly, it reflects a much lower source impedance to the EQ circuit, which maximizes the amount of "boost" available. My EQ works properly with source impedances of 60 ohms or less; with the stepdown transformer, you can use equipment having source impedances of up to 1K. Thirdly, it drops the input level by 12dB, reducing the risk of saturating the inductors in the EQ circuit. The total makeup gain required is 12dB (stepdown of the input transformer) plus the loss of the EQ circuit at its "flat" setting (10dB in the case of my EQ), plus the stepdown of the output transformer, if one is used.

The same concept should work well with other passive EQs such as the Pultec. The Pultec in particular, in its stock form, has an input impedance which can dip to a very low value at certain settings, and most newer gear will not be happy driving it.
Something to think about.
Sleeper
 
alright! thanks alot for the info!
uups! one more ... where did you buy edcors in europe???

cheers,

amrtin
 
Sleeper said:
"The Pultec in particular, in its stock form, has an input impedance which can dip to a very low value at certain settings, and most newer gear will not be happy driving it."
Something to think about.
Sleeper

My last Pultecy-ish effort had the input strapped 600:150.  The filter circuit was scaled up in impedance a bit as I was driving a gate directly, noise being better with a higher source Z. 
 

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