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Old 4th August 2013, 01:42 AM   #21
RNMarsh is offline RNMarsh  United States
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Location: 2457 Cascade Trail; Cool, CA. 95614
Default Mod pictures to activate the B&K 1607 Notch filter -

Here is my modification work for the active/passive 1607 notch filter. A 2pdt toggle (double contacts for reliable, good contact) switch to select active mode or passive, a 10 turn Spectrol pot with locking mechical turns indicator, circuit board for the opamp hung off the output socket.... plenty of room for batteries inside/below.

Thank you - ghg for the quick feedback/help which makes everything move along much faster for us all.

-Richard Marsh

Active B&K Notch-1.jpg

Active B&K notch-2.jpg

Active B&K Notch-3.jpg

Last edited by RNMarsh; 4th August 2013 at 02:08 AM.
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Old 4th August 2013, 05:10 AM   #22
RNMarsh is offline RNMarsh  United States
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Default active circuit -

Here is ghg's proof of concept circuit that I then used. I am tempted to use it more often now and the low opamp output Z is helpful in many applications.
The improvement in H2 loss is much better now (only 0.3dB) and helps reduce chance of errors; One less correction to think about or remember.

THX-RNMarsh

Active 1607 Notch.jpg

Last edited by RNMarsh; 4th August 2013 at 05:17 AM.
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Old 6th August 2013, 12:54 AM   #23
RNMarsh is offline RNMarsh  United States
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Default Details on Active 1607 modifications -

Last details on active mod ----> The batteries will be mounted on a removable rear panel for quick access for replacement.
The front shows the location of the passive-active switch, and added BNC active output, and new locking dial for the new ten-turn balance control.
Now it is fully self contained without taking up more work bench space.


Thx-RNMarsh


B&K1607 front mod.JPG

B&K 1607 opamp.jpg

Done. Check !!

Last edited by RNMarsh; 6th August 2013 at 01:05 AM.
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Old 13th August 2013, 03:34 AM   #24
RNMarsh is offline RNMarsh  United States
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And, with batteries in place and power on-off switch access via rear opening.

Check !

-Richard

B&K1607 Mod3.jpg

B&K1607 Mod2.jpg
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Old 9th October 2013, 02:37 PM   #25
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Hi all,

Inspired by GHG's 1607 modification here I'm considering changing a twin-t that I make for an HP339A oscillator variant (courtesy richiem's webpages) into a passive/active one.

I've calculated some values that should make it possible to switch between 20 Hz, 1200 Hz & 12 kHz (for 48 kHz multiplas) frequencies. I've drawn up a crude schematic for this (there's just a bit in Danish ). The opamps are not LT1007 but OPA2134s.

Might I have your input on whether or not this is correct - and if I should omit/change something:

- e.g. related to the input buffer?
- or remove the 500 ohm potmeter now that there are potmeters across the resistors?

Cheers,

Jesper
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File Type: jpg twin_t.jpg (304.6 KB, 144 views)
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Old 9th October 2013, 04:27 PM   #26
ghg is offline ghg  Austria
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Well, you already use three pots for finetuning, no need for the 500 Ohm one.

Regarding the buffer, you have to try out.
Buy the 1kHz osc. from Victor and you should get about -150dBc for h2, see post #11

Have fun

Gary
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Old 9th October 2013, 05:04 PM   #27
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Hey Gary,

Thanks for your feedback ;-) I'll omit the 500 ohms then & try to see how it fares with the buffer.

Quote:
Have fun
Likewise

Jesper
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Old 9th October 2013, 11:52 PM   #28
richiem is offline richiem  United States
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I'm not crazy about using the LT1007 as the buffer. I'd choose an LME49710, OPA1641 or LT1468 (using suitable load isolation R) for lowest noise and distortion.
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Old 10th October 2013, 07:29 AM   #29
RNMarsh is offline RNMarsh  United States
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and, I found the best choice when not sure what to use -- is to start with an LT1468.


-RNM
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Old 10th October 2013, 01:43 PM   #30
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Hi Dick & Richard,

Thanks for your suggestions but the LT1468 is one of the (few?) of the opamps you often mention that is not available from Mouser. And Mouser IMHO is very convenient to buy from as they take care of all the tax & customs issues which means that a component may cost the Mouser price + 25% tax whereas Digikey typically is (component cost + USD 25)*1.25. It doesn't matter if I were to buy for much money but in this case ... My intention was to start out with the OPA2134 (as I wrote in the post a bit back) as indicated on Dick's webpages for the other active Twin-T version.

Hope that works ...

Greetings,

Jesper
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