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Old 26th October 2011, 12:14 AM   #11
bcmbob is offline bcmbob  United States
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Michael, Have you built a prototype yet?
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Old 26th October 2011, 01:29 AM   #12
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Yes, I've been using a slightly different version for a few years now.

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Old 26th October 2011, 09:51 AM   #13
bcmbob is offline bcmbob  United States
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Are any pictures, construction details or build threads available? You've got us swimming very close to the hook
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Last edited by bcmbob; 26th October 2011 at 09:54 AM.
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Old 26th October 2011, 11:49 AM   #14
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No pics available, but I'll post more construction details later, right now it's time to go do the work thing.

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Old 27th October 2011, 12:01 AM   #15
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OK, here we go... I built this several years ago, and I'm writing about it from memory, but it's all good, nothing at all difficult about building one. I put the dual OpAmps and surrounding circuitry consisting of the power supply decoupling components, the main signal path resistors and the first order high-pass and low-pass filters on two small PCBs, one for each channel. The two switches are single pole, eleven position, make before break (to prevent switching noises), dual deck rotary type with the cut/boost resistors mounted directly on the terminals. When I built the first prototype I just used a bunch of cheap slide switches I had on hand in place of the rotary switches for testing purposes. Not much else to tell really, like I said before, it's a pretty simple circuit and a relativly easy build. Just use good circuit layout and construction techniques, and decent quality components and you'll end up with a good sounding, usable tone control.

Mike
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Old 27th October 2011, 04:27 AM   #16
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In case anyone wants to check it out, here's the zipped TI-Tina spice simulation file.

Tone Control.zip

TI-Tina is a free SPICE-based analog circuit design and simulation program that can be downloaded here:
TINA-TI License Agreement

Mike
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Old 29th March 2013, 01:56 PM   #17
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Dear Michael, is possible modified it for 10 to 12 dB boost ?
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Old 30th March 2013, 02:43 AM   #18
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I've done some tweeking to the circuit since my last post. It now has a cut / boost range of 11dB in 1dB steps. But what's even better in the new and improved version is that it now has accelerated slope filters based on the work of Dennis Bohn at Rane Corp (Here: http://rane.com/pdf/acceler.pdf.) That type of filter will allow bass and treble adjustment while leaving the mid-band untouched, and it also produces very little phase shift while doing it's thing. Attached below are the schematic, frequency response curves, and a working model in a zipped TI Tina file.

Have fun!

Mike
Attached Images
File Type: jpg _TEST TONE CIRCUIT_.JPG (150.9 KB, 549 views)
File Type: jpg Tone curves.jpg (327.6 KB, 524 views)
Attached Files
File Type: zip _Test Tone circuit_.zip (10.0 KB, 63 views)
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Old 30th March 2013, 04:17 AM   #19
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Hi Michael, you making a great wonderful job, ultra thanks for help me !
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Old 30th March 2013, 02:03 PM   #20
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Michael, that looks a very useful circuit!

Your timing is perfect too; I've just come here looking for a way to add an automatic loudness control to the preamp I am designing. I listen at low volume most of the time due to marriage.

Long story short: My 25yo Technics amp is beyond recovery, I'm a digital guy mostly and I'm trying to build a replacement amplifier using parts in my spares boxes if possible (I've no money, due to marriage!). Despite the amp's humble beginnings, I'm now thinking of using a microcontroller to control it all digitally.

Looking at your circuit, I think that I could replace the boost side of the base and treble sections with two 20KΩ digital potentiometers, with the wipers paralleled to ground with 5KΩ resistors. Since I only need to boost for a loudness control, the other side of the resistor chains could be replaced with a 4KΩ resistors.

That way, I would have about the same range of adjustment on the boost side as your circuit, with the 10-bit digipot scaled appropriately in software. The idea then is for the MCU to automatically control the amount of boost based on the volume level.

Do you think this is a reasonable idea?
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