Measures and Frequencies on my Pultec EQ.

[b2]

Hi, :grin:

I've just finish a tube preamp with a EQ stage (the Gyraf Pultec EQ).
I used a 12AT7 instead of the 6922,the caps are Wima and the inductors Toko (22,47,100,100mH).

I've done measures,last night with A Neutrik A1 system.
Gain max 58dBu wihout EQ
Gain Max 57dBu with EQ

Frequency response 60Hz at -3dBu to 28Khz at -3dBu.
Level of the signal inside the preamp=0dBu

LOW FREQBoost
1-----28Hz at +4dBu
2-----35Hz at +8dBu
3-----45Hz at +10dBu
4-----55Hz at +12dBu
5-----65Hz at +12dBu
6-----ALL frequencies from 60Hz to 28Khz Boost to +16dBu??????

LOW FREQ Cut
I take a point at -16dBu
1-----50Hz
2-----75Hz
3-----100Hz
4-----140Hz
5-----160Hz
6-----I don't know......

HIGH FREQ-Q=Max-Boost
1-----2.2K----Q=0.48------+5.5dBu
2-----2.9K----Q=0.43------+5.5dBu
3-----3.9K----Q=0.6-------+5.6dBu
4-----7.5K----Q=0.6-------+5.8dBu
5-----12K-----Q=0.6-------+5.8dBu
6-----16K-----Q=0.65------+5.8dBu

HIGH FREQ-Q=Min-Boost
1-----2.2K----Q=0.28-------+4dBu
2-----2.9K----Q=0.28-------+4dBu
3-----3.9K----Q=0.38-------+4dBu
4-----7.5K----Q=0.41-------+4dBu
5-----12K-----Q=0.43-------+4dBu
6-----16K-----Q=0.45-------+4dBu


HIGH FREQ Cut
I take a point at -16dbu.
1------5.6K
2------7K
3------9.3K
4------11.4K
5------12.5K
6------21K

Well, I don't know if this measures are well right....I tried with a 6922 inside this Eq sections,the Frequency response was very very nice from
30Hz at -3dBu to 28Khz at -3dBu.

The Boost was increased max +15dbu in the LOW FREQ section but still around +6dBu in the HIGH FREQ section.The FREQUENCIES were the same.When,I listen my preamp....NO HUM,NO 50Hz HUM very quiet,nice sound with the 12AT7,still neutral and the Eq section do is job very cleaned with this tube.With a 6922 inside very good sound,more impression in the Bass,with Eq on than the 12AT7.

Well,I hope my comments,and those little work,is perhaps interesting for the community. :grin:

A+,B2.
:thumb:

 

[matthias]

did you calculate these values, or have you made some measurements??

 

[b2]

[quote author="matthias"]did you calculate these values, or have you made some measurements??[/quote]
Hi Matthias, :grin:

This measures have been measured by a Neutrik measurement system A1.EXCEPT,the "Q" that I calculate with the Formula,Q=Fr/Bw,Bw=F1-F2,F1 is the Frequency under Fr at -3dBu point ,and F2 is the Frequency after Fr at -3dBu point.Fr is the frequency point at the Max amplifification .

With a signal of 0dBu inside and 600 Ohms Load.
For the HIGH BOOSTwith the pots of Q at the Max,It was:

step 1-----Fr=2.2Khz at +5.5dBu max of amplification,the F1 =1Khz and F2=5.56Khz so I calculate Q,Q=0.48 it's the max value of Q .

For the LOW CUT and HIGH CUT,I done measurement(Graph+Plot) and I've take a point at -16dBu,and I read the values corresponding at this point for all the frequencies.

Well,I've done this measurements because I want to see How the combination of the Wima caps and Toko inductors works in my project(preamp+Eq section).And at all,by listening for me it's work good.

B2.

 

[SSLtech]

Looks to me like there's something wrong with position six LF boost...

-Like an open or shorted cap to be that wideband (I don;t have the schematic in front of me..)

Keith

 

[b2]

[quote author="SSLtech"]Looks to me like there's something wrong with position six LF boost...

-Like an open or shorted cap to be that wideband (I don;t have the schematic in front of me..)

Keith[/quote] :grin: :grin:
Hi,
Well,You were right with the "6 position",there was a big "shit" :green: :green: with the 220nf caps.

So,I' going to change it and after,I'm doing the measurement of the"6 position freq" at Boost and Cut.So,Thanks a lot.
:thumb:
Merci beaucoup.
A+.
B2.