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Old 9th November 2013, 03:43 PM   #51
Lid55 is offline Lid55  Canada
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Nigel, how easy is would it be to create a dedicated high pass filter to add to this circuit? I'm wondering if that's the way to go, rather than filtering out the low frequencies via lowering the input impedance.
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Old 9th November 2013, 03:46 PM   #52
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Originally Posted by Lid55 View Post
Well it's currently on a breadboard, but I'll be soldering to one one of those open matrix PCBs
Well there's no use messing about with small capacitors then, the capacitance of the breadboard will be greater than the capacitors you're fitting.

Personally I never use breadboards, far too restrictive on what you can do (although audio preamps 'should' be OK - although anything affected by small capacitance values may well perform differently).
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Old 11th November 2013, 03:21 PM   #53
Lid55 is offline Lid55  Canada
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The breadboard is definitely not ideal. I try and compensate for some of its flaws with a makeshift Faraday Cage (cardboard box lined with aluminum foil)... but it only sortof works. But I don't know of a different way that makes it so easy to test components, for practical listening A/B tests.
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Old 11th November 2013, 08:21 PM   #54
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The breadboard is definitely not ideal. I try and compensate for some of its flaws with a makeshift Faraday Cage (cardboard box lined with aluminum foil)... but it only sortof works.
That seems a pretty pointless exercise

Quote:

But I don't know of a different way that makes it so easy to test components, for practical listening A/B tests.
There's little need or reason to do so, simple design skills let you know what effect most components will have - and as I've said all along, if you're looking for tonal changes, add the circuits for doing it - don't try and bodge the basic circuit (which just stops it working properly).
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Old 11th November 2013, 08:26 PM   #55
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Originally Posted by Lid55 View Post
Nigel, how easy is would it be to create a dedicated high pass filter to add to this circuit? I'm wondering if that's the way to go, rather than filtering out the low frequencies via lowering the input impedance.
You might enjoy a read of this:

http://www.ti.com/lit/ml/sloa088/sloa088.pdf
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Old 13th November 2013, 05:46 PM   #56
mjf is offline mjf  Austria
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hello.
ref. schematic post 46:
you can use the caps around the opamp (c4,c6: and later on perhaps c7) as filter caps to cut off deep frequencies.......
example: magenta curve with origin parts
light blue (c4=22nF, c6=470nF)
blue (c4=10nF, c6= 220nF)
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Old 15th November 2013, 07:58 PM   #57
Lid55 is offline Lid55  Canada
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Thanks mjf and Nigel for the info and guidance.

I'm still getting some "coloration" of tone that I'm trying to track down... and so I've been searching for simpler solutions, and came across the beavisAudio.com website, good info for beginners there

Could you tell me if I replace the opAmp in the following circuit with the OPA2134, will it work, need additional revision, etc ?

If it won't add ANY gain, I'll stick with what I have... but... if this could combine the two circuits well it would simplify everything.
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Old 15th November 2013, 08:46 PM   #58
mjf is offline mjf  Austria
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....this is a unity gain amp, voltage amplifikation=1, a "buffer" amp.......
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Old 15th November 2013, 10:52 PM   #59
Lid55 is offline Lid55  Canada
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....this is a unity gain amp, voltage amplifikation=1, a "buffer" amp.......
I guess it's not as simple as adding a resistor to the feedback loop to increase gain? That would probably be too easy. Just in case this is not possible... I'll continue testing my current combo circuit... trying to learn more about why the processed sound is not as transparent as I would like it.
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Old 16th November 2013, 05:24 AM   #60
Lid55 is offline Lid55  Canada
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Back to "ComboCircuitRevision1" (post 45/46) and the opAmp circuit, do the high frequencies start to cut with even small resistor values at R8?
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