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Old 28th July 2013, 10:11 AM   #1
ghg is offline ghg  Austria
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Default B&K 1607 notch filter activated & Victors oscillators

I decided to activate my B&K 1607 notch filter. Fortunately, I did not have to draw the whole schematics ( no service manual available ). A quick view inside showed the balance pot being in series with the 0.5xR arm ( see Pic_1 ). So, there was no problem to attach an opamp outside the B&K box ( see Pic_2, Pic_4). The choosen R2 R1 values give a h2 insertion loss of ca. 0.3dB, good enough for me. I had to replace the single turn Balance pot of the B&K, a 10 turn Bourns did it, much better control of notch depth.

The measurement chain:
Victors 1k oscillator driven by a 26mA current source, R32/R33 replaced by 10 Ohm resistors, a trick presented by 1audio. Vout: 2,67V rms -> E-MU 1616m(ASIO) -> Arta gives -10dB.

After notch filter insertion ARTA gives:

h2 = ca. -151 +10 -5( notch gain ) = -146dB
h3 = ca. -157 +10 -5( notch gain ) = -152dB

Well done, Victor
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File Type: jpg PIC_3.jpg (264.0 KB, 347 views)
File Type: jpg PIC_4.jpg (135.1 KB, 342 views)
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Last edited by ghg; 28th July 2013 at 06:04 PM.
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Old 28th July 2013, 03:04 PM   #2
RNMarsh is offline RNMarsh  United States
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Very nice modification. Its easier than I though it would be. What changes, if any, have you made to your E-Mu 1616?
Also, please show where 10 Ohm R's are located (schematic/picture?).

Thx-RNMrash

Last edited by RNMarsh; 28th July 2013 at 03:07 PM.
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Old 28th July 2013, 05:08 PM   #3
ghg is offline ghg  Austria
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Thanks, E-MU 1616m stock, just used the line in at the back.

Schematic: Low-distortion Audio-range Oscillator see Post #204

You may checkout R32/R33 easy, just the two resistors after the + - PS terminals.
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Old 28th July 2013, 07:56 PM   #4
1audio is online now 1audio  United States
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What is the value of the balance pot? It seems like this would be an easy retrofit inside and run the opamp from a pair of 9V batteries. The only remaining issue would be the common ground and dealing with those B&K connectors, neither of which is insurmountable.
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Old 29th July 2013, 06:08 AM   #5
ghg is offline ghg  Austria
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Pot 500 Ohm; you just have to break the pot connection to ground and put a switch there ( passive/active mode ), no grounding problems, as I run the opamp from two 12V SLA batteries.

When I got the unit, I immediately drilled out those B&K connectors and put BNC's there, see pics.

Gary
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Old 29th July 2013, 04:02 PM   #6
RNMarsh is offline RNMarsh  United States
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The 500 Ohm rheostat is large in diameter and feels like fine wound wire. I want to find something without greater inductance and doesnt add any distortion. What make, model, brand of pot did you use?

Thx-RNM
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Old 29th July 2013, 06:12 PM   #7
ghg is offline ghg  Austria
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Nothing Special:

http://www.ebay.com/itm/3590S-2-501L-500-Ohm-Rotary-Wirewound-Precision-Potentiometer-Pot-10-Turn-/120985135227
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Old 29th July 2013, 06:57 PM   #8
richiem is offline richiem  United States
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@ghg -- you show one end of 2C at ground, and one end of 0.5R connected to the output of the amp -- usually, these ends are connected together... I haven't seen this configuration for the T-T before -- are you sure that 2C is at ground?

Man, that 1616 sure is quiet.
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Old 29th July 2013, 07:03 PM   #9
ghg is offline ghg  Austria
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Yep, see the reference:

Circuit Design: Know It All: Know It All - Darren Ashby, Bonnie Baker, Ian Hickman, Walt Kester, Robert Pease, Tim Williams, Bob Zeidman - Google Books
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Old 29th July 2013, 07:36 PM   #10
RNMarsh is offline RNMarsh  United States
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Now you got me fired up to do it..... I removed the original 500 Ohm and replaced it with a 10 turn from Beckman Inst/Spectral that i had in my parts bin and am using the turns counter for a knob which can lock the setting.

I also use a banana to BNC adapter that plugs right into the Euro sockets without any problem and is secure.

-RNM
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