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treble control centre frequency

polyal

Sep 8, 2011
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1671801334224.png
how can i change the centre frequency from 12k (stated in the spec )
to 6k
thanks ♪reg♪
 

danadak

Feb 19, 2021
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Again a sim changing the pot from 0 to 100% :

Here caps change to get center closer to 6 Khz :

1671813293379.png


Regards, Dana.
 

danadak

Feb 19, 2021
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Several approaches :

1) Cascade second order sections

2) Use Chebyschev LPF with G (Q) peaking

1671840898222.png

3) Resonator bank summing filter approach, sum a LPF and a BPF filter response


You will have to do some experimentation.


Regards, Dana.
 

danadak

Feb 19, 2021
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Range of 5% to 100% on the pot (two pots ganged) :

1671877623900.png


Regards, Dana.
 
Last edited:

hevans1944

Hop - AC8NS
Jun 21, 2012
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@danadak: Thank you for all of your most informative posts on this and other topics. I was wondering where all the "young pros" like you were hanging out. This thread is especially helpful in that it shows a very helpful benefit to using a circuit simulator to perform "what if" substitution of component values. Sometimes a "trial and error-correction" approach is better, or at least quicker, than calculating specific values, especially if the circuit in question already operates nearly where one expects.

In another life and another century, I would "pull" the frequency of crystal-controlled ham radio transmitter oscillators by opening the cover on the crystal holder to gain access to the quartz crystal, and then adding a little bit of pencil graphite to the crystal, increasing its mass slightly and thereby lowering the oscillator frequency. Not a particularly effective means, but as a Novice ham (KN8UTJ) it was the only way available to me to alter my transmitting frequency. Now that I have an Amateur Extra license (AC8NS), a variable frequency oscillator is the way I roll now.
 

hevans1944

Hop - AC8NS
Jun 21, 2012
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The sharp corners at 5k are not physically realizable for reasons I won't go into here. Not even with digital filtering, FIR nor IIR, is this possible. You will discover something called Gibb's Phenomenon if you actually attempt to create such a filter. Try using a circuit simulator as @danadak shows, with multiple stages if necessary, to come close to what you are trying to achieve. Since these are audio frequencies, you ears may be your best "test equipment".
 

danadak

Feb 19, 2021
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The sharp corners at 5k are not physically realizable for reasons I won't go into here. Not even with digital filtering, FIR nor IIR, is this possible. You will discover something called Gibb's Phenomenon if you actually attempt to create such a filter. Try using a circuit simulator as @danadak shows, with multiple stages if necessary, to come close to what you are trying to achieve. Since these are audio frequencies, you ears may be your best "test equipment".

I thought one could theoretically produce a desired response (within non linearity considerations) by doing this
with N (as necessary) stages :

1671909443540.png

Eg sum the various frequency regions with targeted response for that region
and add them all together.

So if I wanted a camel hump filter at w/two freq peaks......



Regards, Dana.
 

hevans1944

Hop - AC8NS
Jun 21, 2012
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I was commenting on the inability of real filters to create a "brick wall" type of transition in frequency response. The problem occurs whenever the desired frequency response has a non-differentiable segment, which also includes any discontinuous jump in frequency response as well as "sharp" corners in frequency response. Such filters cannot be realized, even theoretically. Your twin camel-hump filter with smooth low and high frequency response transitions is of course possible, although possibly not desirable, depending on the state of your hearing. At my age, I need to boost the bass and the treble to make music "sound right" but the biggest problem seems to be audio volume. If I can't feel the bass notes, it isn't loud enough. Bag pipes and theater pipe organs seem to benifit the most from a large bass boost, although some classic rock music also sounds better (to me) when fully boosted, i.e., loud enough to rip the speaker cones right out of their baskets if not careful with the volume control.:cool:

Years ago, when I was a teenager, I was learning how to align the intermediate frequency amplifier stages of vacuum-tube based television sets, working part-time after school for a local TV repair shop in Dayton, Ohio. The stages (typically just two or perhaps three) had ferrite tuning slugs to vary the inductance of the tuned transformer windings. Using an RF sweep frequency generator, synchronized to the horizontal deflection of an oscilloscope, I could display the frequency response of the IF amplifiers. The goal was to adjust for a "flat" response, but invariably a peak at one end with a slow slope to the other end would appear on the 'scope. Sometimes a double "camel hump" response would occur. Sometimes a "helpful" DIYer would "tighten down" all the "loose screws" that tuned the IF transformers, hence the need to reset to original factory specifications. This was fairly easy for monochrome receivers but a real nightmare for color. Then along came "comb" filters and servicing of color TV became somewhat less onerous.

I got out of the radio and TV service business shortly afterwards because it became impossible to earn a living that way: newer, solid-state, radios and televisions didn't fail often enough, and customers were unwilling to pay for repairs when they could replace their failed set with a new one for "just a few pennies more." The throw-away consumer society kept the economy booming back then, so almost everyone was happy.

I did download the Duncan Tonestack Calculator, which is available as a zip file for Windows from Duncan's Amp Pages. Ignore that Windows 10 puts up a warning that the software does not have Microsoft's blessing. Go ahead and run the installation zip file anyway.

The tone-stack calculator was designed for use with various brands of electric guitars, whose output feeds into a tube-type integrated stage-amplifier/speaker box system. The tonestack was located within the guitar body, so the musician could adjust it while playing to achieve whatever effect was desired. All of these tone-stack circuits that consist entirely of passive components (resistors, capacitors, and inductors) introduce considerable attenuation of the input signal before "boosting" the bass or treble output. Hence the need for front-end amplification before the "frequency conditioned" signal can be applied to a power audio amplifier and loudspeakers.

After all has been said so far, it appears to me that the "best" solution is to introduce an active tonestack between the portable radio earphone jack output and the amplified speaker box. I actually did something like this when I connected the earphone-jack output of a portable AM/FM/FM Stereo radio to the "line level" input of a cheap Radio Shack pre-amplifier and low-wattage power amplifier that had built-in bass and treble controls.

Normally I would have the PC's sound card outputs (stereo) feeding this combination, which is ideal for listening to Amazon Music Unlimited (subscription service), either as sent from my Apple iPhone 8 Bluetooth connection to the PC, or directly from the Amazon Music website on the PC. We also have a couple of largish "boom box" type JBL portable Bluetooth speakers that also connect to the iPhones and to various other sound-producing devices, including a Yamaha RX-V377 "surround sound" receiver system that is normally used with a Sony oled flat-screen television. It can get pretty loud inside the house when everything is cranked up to full volume and Wagner's Ride of the Valkyries is blasting away. The twelve-inch sub-woofer has its own power supply and dedicated input, but we hardly ever have it cranked up to maximum loudness. I suspect our so-called "power woofer" is a little on the light side when it comes to pushing out low frequency, window-glass rattling sound.
 
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