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this JSX dual pot presence / resonance circuit sounds good on my Ultra+
adds a good low rumble and high end screech, which I like.
adds a good low rumble and high end screech, which I like.
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As mentioned before- I don't think this type of control will work in a TW style design where the output section is distorted. It'll only work when the output section is mostly clean.
jamieComment
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you may well be right for the TW design, I don't know. I can report I run my ULTRA+ PA FULL ON (very crunchy) and the control sounds great!Comment
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Like with the master way up? I guess it's just acting like an active filter. Wouldn't be the first time I was wrong!Originally posted by tedmich View Post
For the record, it would take about ten minutes to try one on a given amp- so why not try it?
jamieComment
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Indeed someone does:Originally posted by leadfootdriver View Post
Guitar Pedals: R-C Filter Calculator
The corner frequency of an RC filter is not affected by a resistor in parallel with the cap, but by the driven impedance (resistor to ground) if the cap is in series (high pass), or by the driving impedance (series resistor) if the cap is to ground (low pass). My understanding is that a resonance circuit is just a high shelving network in the NFB loop, whereas a presence circuit is a variable low shelf.Comment
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Very cool!Originally posted by Chuck H View Post
I didn't know u could rework the Duncan program. I'd like to see what's doin' with the Express TS.
Thanks for the calculator link. I definitely saved that link!Comment
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Originally posted by tedmich View Postthis JSX dual pot presence / resonance circuit sounds good on my Ultra+
adds a good low rumble and high end screech, which I like.
I did find a JSX schematic, and looked it over. I tried to find any schematic with a Res control. But thanks for posting the pics!Comment
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You are correct sir! I bought a few different value caps, and wired them in. I found one I liked best while listening at a human level. Then I put the cab in my closet with a mic on it to do some test clips. Unfortunately, the result was that with the Res on, the tone was unfocused and bloated.Originally posted by imaradiostar View Post
All' that power clip doesn't make good for holding a lot of bass together.
Oh well, the amp still rips, but not with a big bass. That just isn't what this amp was made to do.Comment
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I had a Peavey Classic 120/120 and a 50/50 with the Res, and it worked great.Originally posted by tedmich View PostComment
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I thought it was a done deal, and wired the pot in the amp real nice, only having to pull it back out... Boo.Originally posted by imaradiostar View PostComment
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I searched for these links but didn't find anything! Thanks.Originally posted by jamesmafyew View PostComment
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The URL is:
http://www.muzique.com/schem/filter.htmComment
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the PCB was easy to etch and install, BUT the dual concentric pot is a compromise as its a SWR-Fender 50k/1M and the 50k might work better for the Vox high cut like circuit across the PI that Gaz mentions hereOriginally posted by leadfootdriver View Post
http://music-electronics-forum.com/t14020/Comment
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For those who want a quick and reasonable approximation with mental math, no calculators within 100 feet ; what *I* also use when looking at a schematic and wishing to know in a second "what the h*ck are these guys doing" is to remember the simple "basic trio", which can be any 3 calculated values, but I found these most useful: 100K/.1uF/16Hz
Examples:
1) what does the classic 100pF ceramic in parallel ith, say, 100K, so much used in Op Amp circuits do?
Mentally (in fact it becomes intuitive and gets even faster, but let's go step by step):
"100K is the same ... .1uF=100000pF so 100pF is 1000 times smaller; so frequency must be 1000 times higher= 16000Hz."
Meaning (since it's a feedback loop) they kill frequencies above 16000 Hz. Good for us.
Quick and easy, huh?
Always round to a close "standard"or "easy" value, we want to to "roughly" know what's happening; if we want precision we grab the calculator.
2) 1K5 / 10uF cathode network . 10uF=100 times .1uF (frequency should be 100 times lower) *but* 1K5 (close to 1K) is roughly 100 times lower than 100K , (so frequency should be 100 times higher).
We see that one component would rise frequency by 100 times; the other would lower it by the same amount, they will compensate: the net result will be that the "basic" frequency (16 Hz) will be *about* the same.
If we want more "mental"precision, consider that 1K5 is 1.5 times higher than 1K, so cutoff frequency will be 1.5times lower.
So the correct value will be around 10Hz.
Be it 16 or 10 Hz, now we know for sure that this classic cathode bypass pair will not cut guitar frequencies (which start at 80 HZ) which is the concept we really needed to analyze this circuit.
Knowing that, we can also quickly deduct that the classic Marshall values 2K7 (roughly twice 1K5) and .68 (roughly 15 times smaller than 10uF) will combine to shift bypass frequency upwards by about 15/2 ; roughly 8 times higher, around 80Hz so now we know that Marshall (most certainly by ear, not math
) lowered cathode caps until he started to cut lows (by 6dB), getting tight bass without the amp becoming tinny.
And so on.
When I look at a schematic, rather than "parts values" I see gain stages, headroom or clipping, and cutoff frequencies, either boosting or cutting.
And in the end, that's what we hear.
Without simulation, after a few minutes looking at a schematic, I can have a reasonable idea of what it does or how it sounds.
And no magic or strange powers involved, just the simple things posted above.Juan Manuel FaheyComment
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