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Old 11th October 2012, 12:30 PM   #11
AndrewT is offline AndrewT  Scotland
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1nF of added capacitance from the interconnect cable would give 100ns filter in addition to any RF filter at the input of the receiver.
That 100ns has a F-3dB~1.6MHz
How many degrees of extra phase shift would that be at 160kHz and at 20kHz?
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Old 11th October 2012, 03:01 PM   #12
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Quote:
Originally Posted by sofaspud View Post
twest820, the only post in this thread mentioning guitars is yours.
Well, and now yours too. Electric guitar rigs tend to wind up with three or four high+low tone controls plus a few mids and some highs---the majority of guitars, amps, and effects pedals have them. I also know harpists, keyboard, and violin players who use tone stacks in pedal form. Whereas my experience is most preamps don't have tone controls. You are correct I shouldn't have been so quick to assume an instrument application but hey, if pinkmouse is happy I'm happy.
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Old 11th October 2012, 05:44 PM   #13
maouna is offline maouna  Greece
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Ι read some articles about Tilt Equalizers and i am thinking of giving it a try.Is this better than a tone control for hi fi use?
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Old 12th October 2012, 11:19 PM   #14
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The input impedance as viewed by the source is only 6.8k. 10 K is a convention minimum, and I usually design for 50K, so the source is less likely to be distorted by driving too heavy a load. Besides potentially causing distortion, you're likely to lose bass if the output cap on the source isn't big enough.

100-200 ohm resistors at the output of an opamp circuit is wise for stability. Linkwitz and all the engineers at Dolby Labs use them. The rolloff they cause is way out in frequency. I've designed and built many of these tone control circuits and used 50KB pots, which generate more noise than 10k, but it's not a problem, and it makes life easier on the opamps (less distortion).

I'd definitely get rid of all the electrolytics and use polyprop or polystyrene caps instead. On the power supply, I'd use electrolytics bypassed with 0.1uF polyprops. Put the bypass caps within an inch of every opamp.

Opamps can be stellar when they are stable (no spurious oscillations), and when they are not asked to do something they can't do well. I always put a passive Rf filter at the input of any opamp circuit, cutting off above about 50kHZ, to accomodate this. Digital sources usually put out energy well above the audio spectrum, which most opamps can have trouble with. If the application is a guitar amp, I'd set the frequency no higher than 15kHZ, since any guitar acts as an antenna and will bring significant Rf into the system, causing slewing related distortions and beat frequency noise in the audio spectrum.

In the case of feeding into the inverting input of an opamp (as you are doing - so the circuit as a whole in non-inverting), I would split the input resistor into two parts that add up to the value you want, and hang a mica, polyprop or polystyrene cap to gnd right there to create the passive input Rf filter. When calculating the value of the cap, it's a matter of what resistance the cap sees looking out into the circuit.

Tone controls are always a good thing when done well. If bypassing them sounds better, the design is bad. Hope this helps.

Last edited by Bob Richards; 12th October 2012 at 11:26 PM.
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Old 13th October 2012, 06:21 AM   #15
maouna is offline maouna  Greece
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Thanks for the info Bob.
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Old 13th October 2012, 10:12 AM   #16
AndrewT is offline AndrewT  Scotland
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Bob R, has given lots of good advice. Adopt when appropriate.
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Old 13th October 2012, 10:20 AM   #17
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Tone controls are always a good thing when done well. If bypassing them sounds better, the design is bad.

A very well said thing ...Also choice and quality of caps will play some role in the tonal response and ""Picture"" aim for less db but nice coloration..

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sakis
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Old 25th October 2012, 08:01 AM   #18
yd1cvj is offline yd1cvj  Indonesia
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Hi Maouna,
Have you build this tone control ? I'm looking for it to combine with LM3886. Appreciate if you can share the result and pcb pic.

Last edited by yd1cvj; 25th October 2012 at 08:02 AM. Reason: pcb
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Old 28th November 2013, 10:18 AM   #19
maouna is offline maouna  Greece
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i updated my tone control. any comments are welcomed
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Old 28th November 2013, 10:27 AM   #20
Mooly is online now Mooly  United Kingdom
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R1 and R2 are high with respect to noise and noise pickup but if you need 100k input impedance...

R8 should be on the other side of the cap. The opamp DC conditions are already defined by the feedback and + input ground reference.

If it is withinn the opamps driving capacity then reducing the impedance of tone network might help with noise. How audible the noise would be is another matter though, it won't be high anyway.

(didn't study your other power amp as its quite an involved and time consuming exercise )
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