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Old 12th March 2006, 04:21 PM   #1
dr dingwhizzer is offline dr dingwhizzer  United States
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I know you all hate equalizers...but I'm gonna build one just for the heck of it. The problem is.....who makes good quality slide potentiometers that are readily available in quantites under...oh i dunno...a bazillion. There seem to be very few out there...ie mouser, digikey..et. al..

I'm looking at Elliots MFB design and he calls for 100K pots. He is a business and of very little help and use to a common do it yourselfer...especially a neophyte such as I...but I can't really blame him either...like I said he is a business. Is there any way that 10K sliders can be used with an MFB type of filter circuit? Do I need to change the op amp to something with a higher gain/bandwidth product?

Can anyone explain how to calculate...or use a R.O.T., to determine the value of the control potentiometer for a circuit such as this? Or....is there even a better circuit topology for something like this?

Like I said I'm very new to this and any help would be greatly appreciated.

Thanks,
Dr. Dingwhizzer
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Old 12th March 2006, 04:26 PM   #2
Cal Weldon is offline Cal Weldon  Canada
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Hi Dr.

We don't all hate EQ's, in fact I couldn't do without one for my outdoor gear. It's just that many persons don't want anything more in the signal path and that if you feel you need one, does that mean you have not done a good job on your speakers?

I'm just wondering if it's financially worth your while. Are you going to save money or is this for the DIY factor?
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Old 12th March 2006, 05:06 PM   #3
Dick West is offline Dick West  United States
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I, also, doubt that building an equalizer is worth the time, effort and cost to DIY. Lower quality equalizers are a dime a dozen and sell for just a few dollars. Better quality ones are often sold used at great discount. I am using two of them in my HT and one in the main music room's stereo system. The one in the stereo room had an original selling price of over $350 but as it has been superceded by more recent models I got it for $79 on an eBay auction. I can't really discern that it is in the signal chain and it helps to make the sound balance so much better that I would not do without it.

My $0.02 . . .
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Old 13th March 2006, 06:32 AM   #4
dr dingwhizzer is offline dr dingwhizzer  United States
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First I'd like to thank you both for your opinions on the matter of equalizers. However, this is not a question of poor speaker design or the allocation of disposable assets. This is about educating myself in a topic that holds a great deal of interest to me at this time....i.e. active filter design and implementation. Instead of opting for the repetative plugging in of components and wires into a prototyping board...okay, I will do that regardless, this is more about a practical application related to a cerebral process. That's why I'm looking for sources of suitable parts and also the design opinion of those much more knowledgable than myself.

Again, I appreciate you checking in with the opinions, however that is not what this is about.
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Old 26th April 2018, 08:55 AM   #5
daljitsinghsaini is offline daljitsinghsaini
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Old 28th April 2018, 08:42 AM   #6
russc is offline russc  England
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You might have to compromise on value - 50K seems to be available.
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Old 28th April 2018, 10:00 PM   #7
MarcelvdG is offline MarcelvdG  Netherlands
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Quote:
Originally Posted by dr dingwhizzer View Post
I'm looking at Elliots MFB design and he calls for 100K pots. He is a business and of very little help and use to a common do it yourselfer...especially a neophyte such as I...but I can't really blame him either...like I said he is a business. Is there any way that 10K sliders can be used with an MFB type of filter circuit? Do I need to change the op amp to something with a higher gain/bandwidth product?
Theoretically, as long as the op-amps can supply the required output signal current, you could scale all impedances by the same factor without affecting the transfer. That is, with 10 kohm instead of 100 kohm sliders, reduce the values of all resistors in the signal path by a factor of ten and increase the values of all capacitors in the signal path by a factor of ten. The trick is to figure out whether the op-amps can indeed handle the higher signal currents.
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Old 29th April 2018, 10:49 AM   #8
russc is offline russc  England
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Assuming you refer to Rod Elliot's project 63 or 64, I would be surprised if Rod would deliberately ignore your question.
However, his website does state he is ill and unable to answer questions at the moment.
Here's wishing him a speedy recovery.
As the design was released in year 2000, it seems unlikely the proposed PCBs will materialise.
As a non-expert, I would have thought reducing the 15K resistor by half to match using a 50K slider and perhaps increasing the 1uf coupling cap (though, the effect of this might be negligible on higher frequencies) would suffice. I suspect the 15K resistor is to create a log effect from a linear pot, borne out by project 84 using "B" type linear pots.
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Old 29th April 2018, 11:07 AM   #9
epicyclic is offline epicyclic  United Kingdom
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Guys have you seen the start date of this thread .
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Old 29th April 2018, 12:09 PM   #10
russc is offline russc  England
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wonder if he finished it?
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