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If you want to experiment with various capacitor value effects of the frequency cut off point, here’s a nice calculator:
Low Pass Filter Calculator - ElectronicBase
set the resistor value to 1, I don’t think we really need a full RC low pass filter in our application, it drives the cap value down way low.
Given an R=1, C=.047mf as tried above, we are looking at a cut off f=3.39khz.
Given the guitars highest natural f=1200, it’ll be interesting to experiment with different values.
jk
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12-03-2022 02:23 PM
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Is that what this hack is doing? Just weakening frequencies beyond a certain threshold? Or is it cutting them right out?
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Great question Croft!
in theory IIRC, either high or low pass filters theoretically are ‘brick wall’ filters blocking any frequencies above/below the cut off point.
In real life there is a slope of constantly reducing filtration from the cut off point to theoretically zero.
But a couple of functions (iirc) come into play. There’s some really interesting (ok to me) effects of timing in the charge/discharge of the cap vs frequency that affect the wall. The resistance in the RC filter is there to mitigate that timing thing and is so important in radio frequency that an inductor is used rather than a resistance to help the timing.
You can google, the math gets deep quickly as your looking at Fourier transforms but I see some cool interactive graphs out there showing the concept.
Again I’m going with what I recall from my FCC tests, sorta kinda remember this stuff.
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More I think about this, we could calculate out the range of most effective cap values for guitar frequencies by using the post cut off slope to drop the frequencies we want cut as quickly or extremely as possible.
I have a brandy new scope I need a project for… found one)))
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Took a quick google….Here’s for my math buddies:
Rectangular function - Wikipedia
Whittaker–Shannon interpolation formula - Wikipedia
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I have tried the capacitor trick, and found it very useful. I have a US Superblock with a V boutique cab with a Cannabis Rex, and also a 101r with the Blockdock 10. It really helps both setups as far as getting a darker jazz tone. I have been using preamps in my Line 6 Helix into the effects return of both amps. Really like that setup using the Quilters as power amps, but the capacitor trick will be great for a simple direct into amp setup. Thanks for sharing it!
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What value capacitor did you use?
Originally Posted by Ronstuff
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re: capacitor trick, i wish they'd modify the circuit a little and put the bright on a switch! Sorry Woody/Jads...
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I used the same value as mentioned above: 0.047uf Originally Posted by Tal_175
I already had one...Last edited by Ronstuff; 12-05-2022 at 12:28 PM.
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A bright switch would be great indeed! Originally Posted by jzucker
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Unfortunately, you really can't control the slope of the cutoff with a single cap. The attenuation curve is determined by a series of factors, starting with the nature of the overall filter circuit. A cap by itself is a first order high pass filter, so if inserted into the path as a bridge to ground, it would attenaute at 6 dB/octave below the set frequency above which 100% signal flow occurs if there were no other resistances or capacitances in the circuit. But the caps in a guitar's control circuit are part of a more complex filter, along with the pots and wiring. If I remember my electronics theory correctly, the capacitance of the output cable in combination with the resistances of the volume & tone pots and the tone cap(s) form a second order filter. A 2nd order has a 12 dB/octave slope, and a 3rd order filter has an 18 dB/octave slope. Originally Posted by jazzkritter
The combination of capacitance and resistance inline and bridged to ground is a filter whose "cutoff" frequency is determined by both. There's a formula, but it's complex and irrelevant here. And there are several different ways to wire volume and tone pots, along with options for placement of the tone cap(s). All we need to understand is that for most, changing the resistance by rotating the pot shaft changes the frequency at which rolloff starts, along with the signal level. But none of this changes the slope of that rolloff.
Depending on how the guitar is wired, rolling back the volume by more than about 20% will also roll off some highs in most guitars with 250k or 500k pots. If there's a tone cap directly between the wiper of the volume pot and the output lead, it will allow frequencies above its "cutoff" point to pass directly to the output lead regardless of the volume pot's setting. You can add this and use a switch or a switched pot (push-push or push-pull) to insert it when you want more highs. You can use a cap like this on the volume pot along with a traditional "tone cap" on the tone pot that bleeds to ground. This is just a first order filter with a slope of 6 dB/octave away from the plateau.
No matter how you slice it, you can't change the slope of a filter of given order just by changing a cap value. What you can do is use switches to change the architecture of the filter by inserting or removing filtration stages. But it's not really necessary, given how well we've done with the simple use of pots, caps, and cable capacitance for 90+ years.
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Hmm… I secretly hoped that it would have been the same as Fender bright cap, but they are 47-120 pF and this suggested Quilter ”anti bright cap” is something like 47 000 pF. Originally Posted by Ronstuff
I have not considered my TB202s too bright but maybe I just have to test this. Thanks for every investigator!
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The Fender bright cap is a high pass filter. Originally Posted by Herbie
Electrical signal takes the path of least resistance.
A capacitor acts as a low resistance for higher frequency (and high resistance for lower frequencies).
The fender bright cap is connected across the "input" and "output" of the volume pot. The volume pot is a voltage divider which reduces the signal voltage between gain stages. The bright cap adds an additional "low resistance" path for the higher frequencies, between the full signal power and the lower (divided) signal power output. (the bright cap has no effect when the volume pot is on the max setting).
The Quilter FX return is a point in the circuit (late in the preamp) where the FX return jack has a relatively large input resistor to ground. If you connect a capacitor across this resistor it, you are adding a lower resistance path for high frequencies to ground, meaning that part of the higher frequencies will be shorted to ground and the lower frequencies will be pass to the rest of the circuit.
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All caps are high pass filters. It's where you put it in the circuit that determines its effect on the signal. Originally Posted by orri
When using a cap to bridge the volume pot, it's passing the highs directly to the output regardless of the setting of the pot. So the tone gets brighter and brighter the lower the volume pot is set. When the pot is fully open, the cap does nothing because the pot shorts the cap. And because the pot and cap form an R/C filter, the frequency below which rolloff begins changes slightly as you rotate the pot - the changing resistance changes the filter's effective pass band. If I remember correctly, the formula for the frequency at which the signal is 3 dB down from flat in a first order R/C high pass filter is 1/(2 [pi] RC). The symbol ƒc is conventionally used for the effective frequency of a filter and is that frequency at which the signal is atenuated by 3 dB (which is almost at the top of the slope leading to the high pass band).
But when used as we're discussing in this thread to reduce brightness, a cap is passing frequencies above its ƒc to ground - they're being removed from the signal. Because of the inevitable slope below the ƒc, a cap used this way will also affect audible frequencies below the ƒc to some degree. So the best choice for a given guitar and player may be a bit higher than you'd think, since the cap's filtering effect extends beyond the passband.
The other factor here is phase shift. All passive filters cause a frequency dependent phase shift that undoubtedly colors tone at least a tiny bit.
[I couldn't figure out how to get a pi symbol from the kjeyboard.]
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My Tone Block 202 doesn't sound over bright to me so I measured its frequency response from the input to the effects out. With the tone controls flat there is no treble lift at any setting of the input gain control. The frequency response is essentially flat, 1dB down at 75Hz and 20kHz. Originally Posted by jzucker
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Compared to almost every other ss amp out there - clarus, evans, henriksen, raezer's edge, aguilar, it's a brighter sound with an upper mid peak. It doesn't really matter what the measurements are or what it shows on a scope. The only meaningful thing is whether it sounds bright to someone. It's like trying to quantify if a tube amp sounds better than a SS amp. It's enough of an issue that many people have contacted quilter and asked for a solution which is why Pat Quilter has recommended the capacitor-trick. Originally Posted by aquin43
The effect of the quilter to many folks is that they end up turning their guitar tone control way down compared to their other amps, similar to when you plug into a fender amp with the bright switch on. Many people don't consider that "bright" either. If it works for you - as it does for many - that's fantastic (for you). For me it's too bright without turning the guitar's tone control down. I'd rather have it on a switch than have to plug a connector in with the capacitor bypass but knowing that there is a solution at all encourages me to pick up another TB202...It is a great amp.
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Don't most of the Quilter amplifiers have very low damping factor? In other words, high output impedance -- it probably doesn't look flat at the speaker. Originally Posted by aquin43
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Really late to this party and I don’t have a horse in the race. But what I can say is that both times I was at Guitars ‘N Jazz, they set me up with a Quilter to test guitars. I was quite pleased with the sound.
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The original claim was, I think, that the 202 has a treble lift capacitor on the volume control similar to the one on some Fender amps. This would give a treble step up at low settings, gradually reducing to flat response at high settings. I can confirm that No. 0920A420125 at least doesn't have such a capacitor. Originally Posted by jzucker
The 202 has three output settings; low impedance, high impedance and high with Fender scoop added. The latter two will add both bass and treble with typical speakers. High impedance would be inappropriate with a reflex loaded cabinet.
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Just as a side note, the Helix software is one of the fews (that I know) that actually has a high cut (low pass) and a low cut (high pass). If, for some reason, you find the cap in the fx loop bothersome or want to have the ability to change the frequency cut off, it's well worth a try. It should yeld similar results. Originally Posted by Ronstuff
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I'm not sure if that was really a claim. It was just speculation. Originally Posted by aquin43
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I haven't tried the cap clip but the low pass filter in the helix doesn't work like a guitar tone control to my ears. I still find it useful though. But additionally, and IMO, the rolloff should be in the amp although technically if the helix is in the loop I guess it's in the amp. I always use the helix in front of the amp because overdrive effects sound "wrong" to me in a loop Originally Posted by jorgemg1984
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That makes sense. I agree it should be in the amp, I was more pointing out that if you have both an Helix and a Quilter and don't want to bother with the cap in the fx loop, you might as well try it. In theory, I don't see any reason for it not to work, but theory and practice don't always agree. Originally Posted by jzucker
Eq can be very tricky, and I think the filter in the Helix is supposed to sound different than a tone control on the guitar, but the actual why goes beyond my comprehension tbh. But the Helix filter It should work well in front, I guess - a guitar tone control is "in front" after all, and it allows one to keep overdrives in the input, as it should be. Even if works different than the guitar tone control, it should help to tame brightness.
I've never messed much with high-cut filters, I don't even use the tone control on my guitar, but found low-cut filters to be life savers with humbckers, archtops and bass heavy rooms.
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I just went the Henriksen route exactly for the reasons you mention. Was happy to pay for quality tone and portability. Also amazed that they actually had one where I am. I had, contacted the mambo amp guy in the UK, but he told me he wouldn’t sell to anywhere in Asia. Guess he was worried about the evil chinese reverse engineering his design, LOL. Kinda lame, considering I could have just had it mailed to a friend in the UK and then mailed to me. In the end too much hassle. Originally Posted by Jonathan0996
cheers!
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I owned a mambo for a while. To me the henriksen is in a league of its own. I would try the quilter again now that I know about the cap trick but for me, the henriksen bud 6 is a full amp in a package the size and weight of a head. Hard to beat that package. Considering adding a Toob 6.5 as an extension speaker... Originally Posted by Jazzism
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