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Old 16th November 2013, 05:43 AM   #191
richiem is offline richiem  United States
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@skidave -- nice work -- pretty good results for a first pass. The noise is mostly line-frequency harmonics, usually from the power supplies and the unshielded board, but possibly from the generator too, maybe even mostly from the generator.

Now, about the loss of 1.4dB -- what is the source and what is it's output Z? Is the loss of 1.4dB at 100Hz, say, or at 4kHz, compared to the un-notched signal?

Also note that using the swept frequency response function in ARTA will not show the true notch depth, since is piece-wise and it may not actually be at the exact frequency of the notch, and also it doesn't stay there very long even if it is. The best way to know the notch depth is to use the spectrum analyzer and look at the peak of the fundamental compared to the un-notched signal.

You've definitely got the idea -- now just clean it up.
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Old 17th November 2013, 06:42 PM   #192
skidave is offline skidave  United States
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Thanks for the response Dick. I actually checked the response using my Tek SG-502 w/ a 600 ohm load. I set the Tek for 1KHz and tuned the notch for -30dB using a meter and watching on a scope. I then swept back and forth and saw the notch was tight, like it should be. The images I posted were using ARTA looped back with the notch in place.

When using the real instruments, I measured a 1.4 dB loss (pre notch frequency and post notch frequency) when the notch filter was in the signal path. (ARTA measured a 1.2 dB loss.) Do you have a loss w/ the notch filter in signal path?

Thanks!

Dave
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Old 17th November 2013, 07:46 PM   #193
richiem is offline richiem  United States
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@skidave: At 1kHz, my insertion loss is 0.4dB -- easy to live with. What values of C and R are you using at 1kHz?
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Old 18th November 2013, 01:14 AM   #194
skidave is offline skidave  United States
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Hi Dick,

I'm using 15.9K / 7.95K for the resistors and .010 uF / .020 uF combo. I don't have a high end cap checker, but the caps measure properly on my meter. I have to adjust the multi-turn pots to a bit lower than 15K to get the notch centered on 1KHz, so I'm thinking the cap values are a bit off. Also, the I did not have the exact resistor values for the divider for the feedback op amp. The 2K is 2.2K and the 215 is 268.

I found some Vishay Polypropylene .01uF caps in the cap drawer, so I might substitute them in the circuit.

Obviously, this circuit needs to be finalized w/ better parts. But doing well so far!

Dave
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Old 18th November 2013, 06:00 AM   #195
richiem is offline richiem  United States
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OK, Dave -- good job all around. The PP caps will be a very good choice. Your resistor values are not a problem, but in the final, be sure to use metal films.

I don't know why you have the insertion loss, but you need a FET input opamp at the output of the Twin-T -- the 1458 is completely unacceptable.... An OPA134/2134 is perfectly fine, and I think that will help, and try not to load the output of the opamp too much either.
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Old 18th November 2013, 04:59 PM   #196
skidave is offline skidave  United States
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Hi Dick,

I need to order some parts and put together a final build. I'll post my results and we can go from there. Thanks for your responses.

Dave
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Old 20th January 2014, 03:31 PM   #197
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Skidave... it´s 2014 :-) Everythi´n OK?
Kind of curious.... :-)
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Old 20th January 2014, 05:08 PM   #198
skidave is offline skidave  United States
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Hi esl 63. I fine tuned mine on my bread board. I have a Mouser order that I need to finalize a few things for various projects. An enclosure and some better capacitors (tighter tolerance) will be for the notch filter. As it is on the bread board, I can achieve a -60dB notch like Dick Moore does. For what I DIY, -60 is just fine. I will post pictures once it is all done.

I like your user name. I have several Quad pieces, just not the ESLs. A family member had a nice pair of 57s a while ago.

Dave
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Old 21st January 2014, 12:22 PM   #199
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Love this thread - THANKS everyone

Charles
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Old 13th February 2014, 06:34 PM   #200
Paulwv is offline Paulwv  Netherlands
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Hi all, love sitting on your knee taking it all in (for as far I can follow it). I just picked-up my old hobby again, and building a set of tools for audio analysis of mainly headphone amps and the likes.

After contemplating building the Cordell analyzer, I now switched horses to make it all a bit more simple - and more importantly, to the task. I have a 1KHz "Viktor" sinewave gen on order, and just ordered the parts for a version of the "Moore" Twin-T but tuned for 1KHz only. If that all works, I will add the 10KHz kit as well. As soon as I have all the parts and build the stuff I will report back.

I take it that there will be more folks that will have an interest in building the kit for actual use, rather than participating in the actual design.

I don't have the means to verify and test it all, but I hope that I can get some comments from this forum.

Thank you for my continued education!
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