Gyraf Pultec EQ

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Corey Y
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Gyraf Pultec EQ

Post by Corey Y » Fri May 22, 2009 1:29 pm

Anyone built/tried out/heard these? I was thinking of building one off their updated A1 schematic. I know there's some room for variation depending on the parts used, especially transformers and inductors. I'm just wondering if building one of these is worth the expense. According to their page it's about an $800 cost typically and I don't know of any decent Pultec type EQ units available for that little or less.
Last edited by Corey Y on Sun May 24, 2009 8:06 pm, edited 1 time in total.

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Z MINOR SOUND
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Post by Z MINOR SOUND » Fri May 22, 2009 2:07 pm

I believe Honky Jonk built a couple of them recently. Send him a pm. He loves them.
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underthebigtree
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Post by underthebigtree » Tue May 26, 2009 7:14 pm

I've built 5 of them. They are awesome. Worth the expense and effort.

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bantam
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Post by bantam » Tue May 26, 2009 7:26 pm

i built one. its unbelievable on the kick and turns one snare into about 6

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Corey Y
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Post by Corey Y » Tue May 26, 2009 10:03 pm

What did you use for the transformers and inductor? Those seem to be the biggest variable in sound character and quality in these. At least according to build reports I've found lately.

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bantam
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Post by bantam » Wed May 27, 2009 3:40 am

edcor makes a lundahl copy they sound great

inductors came from mouser

Kevin S
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Post by Kevin S » Wed May 27, 2009 4:13 pm

http://www.kandkaudio.com/
Stocks the I/O transformers.

Make sure to measure the PCB for lead spacing for the caps, and order proper and it's so much easier. (Taw electronics or mouser can sell you the ones you need)

Sowter makes a custom inductor for the clone version but it's rather spendy, but worth it. There is a user on Prodigy that winds customs also(IOaudio).

Whitemarket/Gustav over at PP can provide the pcb's that fit only the lundahls, (Gyraf version). Just got another G9 PCB in the mail today.

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Post by ckeene » Fri May 29, 2009 7:49 am

The PEQ is a passive EQ with a tube section at the end for make-up gain, am I correct?

If so, has anyone had success in building these with a transistor amp rather than tube? It seems like if you went with that architecture you could get more channels at a better build cost, plus fit it all into a smaller chassis.

Obviously it wouldn't be a clone, but I bet it would still beat the crap out of most cheap analog EQ.

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Post by honkyjonk » Fri May 29, 2009 12:11 pm

Yeah,

Have you searched over at groupdiy.com? (prodigy-pro)

That's really the place to find all the info you need. There are folks that have built them with API 2520 amps, as well as Neve style amps. They're all good. I went with the tube amp because it's more well documented and it's super easy.
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mixedupsteve
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Post by mixedupsteve » Fri May 29, 2009 12:19 pm

bantam wrote:edcor makes a lundahl copy they sound great

inductors came from mouser
Which one is that or is it a custom?
Thanks

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Post by ckeene » Fri May 29, 2009 2:35 pm

honkyjonk wrote:Yeah,

Have you searched over at groupdiy.com? (prodigy-pro)

That's really the place to find all the info you need. There are folks that have built them with API 2520 amps, as well as Neve style amps. They're all good. I went with the tube amp because it's more well documented and it's super easy.
It's a little intimidating over there, the sheer number of pultec threads! But yes, it looks like the 2520 op amp is a valid option.

Are the 2520s meant to run at fixed gain with attenuation applied separately, or can you adjust gain within the op-amp?

Also, is there any reason you couldn't put a 150:600 transformer in front of a PEQ-1 and turn it into a channel strip?

Kevin S
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Post by Kevin S » Sat May 30, 2009 10:21 pm

ckeene wrote:The PEQ is a passive EQ with a tube section at the end for make-up gain, am I correct?

If so, has anyone had success in building these with a transistor amp rather than tube? It seems like if you went with that architecture you could get more channels at a better build cost, plus fit it all into a smaller chassis.

Obviously it wouldn't be a clone, but I bet it would still beat the crap out of most cheap analog EQ.

Done many times over on Prodigy.
http://www.prodigy-pro.com/diy/index.php?topic=29742.0 this should have all you need..


Image from that thread...

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Post by single_fin » Tue Jun 02, 2009 10:05 pm

i finished my gyraf valve eq about six months ago. i used lundahl transformers. probably cost me around $500, but i wasn't being very careful with ordering.
the bottom end sounds absolutely amazing. completely transforms kicks and basses. it's like voodoo.
the high end is good, but doesn't have the same magic -- i used cheap toko inductors, but will be replacing them with sowters.

pretty easy build -- the parts are nice and large and there aren't that many of them.

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