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Topic: Low Pass Filter vs cap mod? |
Dennis Detweiler
From:
Solon, Iowa, US
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Posted 1 Dec 2023 10:12 pm |
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If the treble control on an amp is in the 10K hz range, can a low pass filter pedal gain the same results as changing the treble caps? I ask because the TC Electronic BG250 bass amp treble control frequency is controlling at 10K and is in the presence control range and way too harsh for steel. The other controls: bass 65hz, low mid 400hz and high mid 800 hz is great for steel. It just needs the treble brought down to no more than 6k to round out the tone stack.
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1976 Birdseye U-12 MSA with Telonics 427 pickup, 1975 Birdseye U-12 MSA with Telonics X-12 pickup, Revelation preamp, Carbon Copy Delay and Hall Of Fame Reverb, Crown XLS 1002, 2- 15" Eminence Wheelhouse speakers, ShoBud Pedal, Effects Pedals. 1949 Epiphone D-8. |
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Dave Grafe
From:
Hudson River Valley NY
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Posted 1 Dec 2023 11:37 pm
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One would have to look at the circuit to see what might be done about changing the filter center. As for a "low-pass filter" that's all the tone knob on the steel is, if you have one, and you can use that to tame the unruly highs. Another way to address it is to use a speaker that rolls off at a lower frequency, i.e. if you are driving a JBL K130 switching to a TT15 will take the max highs down an octave or more to around 3kHz.
My Fessy has no tone control so I made a simple plug-in passive low-pass control for it, an easy and inexpensive fix. |
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Larry Dering
From:
Missouri, USA
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Posted 2 Dec 2023 3:42 am
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| Dave, do you have a schematic for that plug or was it just another pot in circuit? What cap was used? |
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Dave Grafe
From:
Hudson River Valley NY
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Posted 2 Dec 2023 4:37 am
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It's the same as any instrument tone contol, cap to ground through a 250k-500k pot. Different cap values change the filter point, depending on the pot value. I have used several different combinations to find what works for my various guitars. Hopefully you can sort it from this image and link. I also include a toggle switch in the circuit to bypass the effect. Remember when choosing components that the pickup impedance of steel pickups is much higher than those found in standard guitars, thus 250k is the minimum for a tone control pot and 470k-500k is going to generally give a better range of control.
I shopped around and found a quality 500k audio taper pot with a pull switch built in to keep the physical design simple.
https://www.fralinpickups.com/2020/09/01/6-powerful-ways-to-wire-up-a-tone-pot/ |
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Larry Dering
From:
Missouri, USA
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Posted 2 Dec 2023 3:37 pm
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| Thanks Dave. |
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Dennis Detweiler
From:
Solon, Iowa, US
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Posted 2 Dec 2023 4:31 pm
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Does an active low pass filter react differently than passive?
_________________
1976 Birdseye U-12 MSA with Telonics 427 pickup, 1975 Birdseye U-12 MSA with Telonics X-12 pickup, Revelation preamp, Carbon Copy Delay and Hall Of Fame Reverb, Crown XLS 1002, 2- 15" Eminence Wheelhouse speakers, ShoBud Pedal, Effects Pedals. 1949 Epiphone D-8. |
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Dave Grafe
From:
Hudson River Valley NY
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Posted 2 Dec 2023 5:10 pm
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| Active filters can be designed to boost or cut chosen frequencies, passive filters can only cut signal as there is no amplification involved, thus the term passive. Also by definition active circuits need a power supply to feed the amplification, as even cutting a filter's output requires negative amplification rather than a simple path to ground. |
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Donny Hinson
From:
Glen Burnie, Md. U.S.A.
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Posted 4 Dec 2023 6:27 am Re: Low Pass Filter vs cap mod?
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| Dennis Detweiler wrote: |
| If the treble control on an amp is in the 10K hz range, can a low pass filter pedal gain the same results as changing the treble caps? I ask because the TC Electronic BG250 bass amp treble control frequency is controlling at 10K and is in the presence control range and way too harsh for steel. The other controls: bass 65hz, low mid 400hz and high mid 800 hz is great for steel. It just needs the treble brought down to no more than 6k to round out the tone stack. |
Bear in mind that the treble control in most amps starts to have effect in the 1-2k HZ range, and even lower in amps like a Fender, depending on the mid settings. The tone circuit in many amps are different, and I have zero experience with TC amps. But if you just want to reduce the high roll-off frequency, the best and easiest place to do that might be at the instrument pickup. And if all you want to reduce are the highest frequencies, I'd consider a standard guitar tone control using a pot value of at least 500k, and a cap value of around 250-500 pf. This circuit could be added to the guitar, the volume pedal, or even built in an outboard box. |
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Mike Auman
From:
North Texas, USA
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Posted 4 Dec 2023 6:58 am Re: Low Pass Filter vs cap mod?
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| Donny Hinson wrote: |
| ... And if all you want to reduce are the highest frequencies, I'd consider a standard guitar tone control using a pot value of at least 500k, and a cap value of around 250-500 pf... |
I think you'd need about 10 times that cap value, or 2500-5000 pF (2.5 to 5 nF) to begin rolling off any highs. The traditional tone cap value is yet another 10 times larger and has a larger effect (22 to 47 nF = 0.022 to 0.047 uF.)
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Long-time guitar player, now wrestling with lap steel. |
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Donny Hinson
From:
Glen Burnie, Md. U.S.A.
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Posted 4 Dec 2023 5:18 pm Re: Low Pass Filter vs cap mod?
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| Mike Auman wrote: |
| Donny Hinson wrote: |
| ... And if all you want to reduce are the highest frequencies, I'd consider a standard guitar tone control using a pot value of at least 500k, and a cap value of around 250-500 pf... |
I think you'd need about 10 times that cap value, or 2500-5000 pF (2.5 to 5 nF) to begin rolling off any highs. The traditional tone cap value is yet another 10 times larger and has a larger effect (22 to 47 nF = 0.022 to 0.047 uF.) |
Not really, Mike. For instance, many players use George-L cables to get maximum highs, and an 8' length of that would measure around 120-130 pf. An average 8' cable of decent quality would probably measure around 250-300 pf, producing slightly less highs. And an 8' length of really cheap cable, one that audibly reduces highs considerably, might measure 475-750 pf. In fact, I sometimes use longer or cheaper cables to tame my highs. Of course, the pickup and amp impedance would also figure into the equation, but it doesn't take much shunt capacitance to affect frequencies in the high ranges. (Note that the "bright" caps used in Fender amps are typically 47 pf or 120 pf, while other brands may use values from 250-500pf.)
After many decades of loud music, shooting, and pyrotechnics, my old ears are only good to around 6k HZ. But even with that limitation, I'm still sentitive to the "ice pick" tendencies of certain amp/guitar combinations. |
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Dennis Detweiler
From:
Solon, Iowa, US
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Posted 4 Dec 2023 9:37 pm
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Correction, I said the TC Electronic BG amp. I meant to say BQ 250. I have a BQ250 which has Bass (65hz), Low Mid (400hz), High Mid (800hz) and Treble (10K hz) controls.
_________________
1976 Birdseye U-12 MSA with Telonics 427 pickup, 1975 Birdseye U-12 MSA with Telonics X-12 pickup, Revelation preamp, Carbon Copy Delay and Hall Of Fame Reverb, Crown XLS 1002, 2- 15" Eminence Wheelhouse speakers, ShoBud Pedal, Effects Pedals. 1949 Epiphone D-8. |
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