harponica
66 posts
Dec 20, 2012
3:11 PM
|
Need some info on capacitor between crystal cartridge terminals(non-volume control mic).
|
Greg Heumann
1901 posts
Dec 20, 2012
5:01 PM
|
Leave it off. The capacitor acts as a low pass filter and therefore cuts some highs - how much depends on the value of the cap. And to clear up any myths about the so called "Rod Mod" which is nothing more than a circuit borrowed from electric guitar volume controls, THAT is for mics with volume controls. It cuts highs at full volume but the effect is reduced as you reduce the volume, resulting in more linear frequency response across the volume range. Personally, I'd rather have all the highs available at full volume, and am perfectly happy for them to get rolled off a little when I reduce the volume, which is what I do when I'm comping and I don't want to stick out/cut through so much. I tend to solo with the mic at full volume or close to it. YMMV
Note - some CR's and CM's had a RESISTOR between the terminals. The purpose was to alter the frequency response for intelligibility of voice in loud environments. You can decide which you like better, but for a mic with a volume control it should be clipped out of the circuit.
----------
/Greg
Last Edited by on Dec 20, 2012 5:03 PM
|
JD Hoskins
279 posts
Dec 20, 2012
7:32 PM
|
The circuit used in Telecaster guitars beginning in 1967 does not cut highs, it passes highs. Actually what that circuit does in a Tele is that it passes highs straight to output, the higher frequencies bypass the volume pot. The volume pot then attenuates the frequencies below the cutoff point. One of the most misunderstood circuits in guitardom. Probably because many call it a treble bleed circuit, when in reality it is a Hi~Pass filter.
Last Edited by on Dec 23, 2012 10:25 AM
|
harponica
71 posts
Dec 21, 2012
6:09 AM
|
The Rod Mod cap I have is the recomended cap,so lets assume I have the right one(its so small you need to put it under a microscope to read).When jumpered in it lowers the feedback threshhold,telling me its reducing the higher frequencies.Its doing the same thing the resistor does in a green bullet cartridge,and lowering the threshold of feedback without destroying tone ain't a bad thing.
|
HawkeyeKane
1311 posts
Dec 21, 2012
12:42 PM
|
I was gonna say...I do believe Shaker equips most of their crystal cartridges with a little disk cap in between terminals. Course those ARE all volume knob mics.
----------
Hawkeye Kane
|
Greg Heumann
1905 posts
Dec 21, 2012
9:06 PM
|
@JD - I think you're right and I misnamed it - it is a high-pass filter
----------
/Greg
|
barbequebob
2147 posts
Dec 22, 2012
7:27 AM
|
JD, that's exactly what that does in the mikes using the Rod Piazza mod, which I do have. It never kicks in when the pot is all the way and is not supposed to at all, but when the pot is turned down, that's when it kicks in so that the overall tone is as close as possible to be the same when the pot is rolled down as it is when all the way up.
----------
Sincerely,
Barbeque Bob Maglinte
Boston, MA
http://www.barbequebob.com
CD available at http://www.cdbaby.com/cd/bbmaglinte
|
1847
422 posts
Dec 22, 2012
8:21 AM
|
kevin's mic should already have the mod
|
1847
423 posts
Dec 22, 2012
9:02 AM
|
last time i checked it was 150 pf
|
1847
424 posts
Dec 22, 2012
10:06 AM
|
you wrote
but 100pf is a good start. .. according to skip
this is a rod mod... rod's says 150 pf
i have a schematic around here....... somewhere
and i am changing elements next week
so i will check
i would right now cept i have a gig at noon
if skip says 100 is a good place to start then 150
is logical..... it doesn't make that big of a difference
the control is usually all the way on or all the way off
most of the time... very rare to have it half way
|
1847
425 posts
Dec 22, 2012
10:29 AM
|
the guitar had a 250 k
the astatic has 5 meg
does that make a difference?
a on and off switch is a good idea i use the volume control to kill feedback mostly
if i play a fill it gets heard
i do sometimes comp at half volume
but more and more if i do not have something to say i lay out
i bought several mic's off rod
had my tech draw the schematic
got to run peace coop!
|
5F6H
1463 posts
Dec 22, 2012
10:38 AM
|
47-150pf is not unusual for bright cap values on amp volume pots. So it doesn't strike me as impossible, it's in the useable range.
.001uf is 1000pf...seems large?
The amount of gain affects useful cap size. Tele has a lower source impedance/DCR and output voltage.
Some disc caps do indeed carry their exact pf value, rather than multiplier codes.
A tweed presence circuit operates around 12kHz...you can still hear its effect, even though your speakers undoubtedly roll off around 7kHz.
In short, I don't know, I have seen Crystal Balls mics with no cap.
Looks like someone is going to have to measure a cap, which may be tricky as a lot of multimeters that read capacitance don't work that low.
----------
www.myspace.com/markburness
http://www.facebook.com/markburness
|
htownfess
273 posts
Dec 22, 2012
1:31 PM
|
I believe 1847 is correct: Circa 2000, I measured a Rod Piazza mic's cap with a dedicated capacitance meter, and that one must have been 150 pf because that's what's in my mic I put a 5 Meg pot in at that time.
The function of the cap is to reduce the steepness of the roll-off in perceived volume as you turn the mic down, making it more usable at partial settings onstage, if one likes to comp that way or whatever. It puts an edge on the tone that's more insistent right down to where the mic shuts off, rather than dropping out as smoothly as it does w/o the cap, but the cap makes the usable range of the pot noticeably longer. More so with a large value pot like 5M, IIRC. Best to A/B it onstage for yourself, as it's one of those "edgy" mods that may sound better against a band than in your house.
I think I've used 100 and 180 pf caps with good effect, and even tried 500 pf after Don Destefano advocated it; precise value is not critical, and I think Don went as high as 1000 pf. Once the cap value gets big enough, I think the element may inherently have too much output in a feedback-prone range to allow the bypass cap.
You can try a silver mica cap instead of a ceramic disc and decide for yourself whether they sound any different.
|
harponica
75 posts
Dec 22, 2012
1:26 PM
|
I slapped a 150pf cap between the terminals of the Astatic 151 cartridge and it raised the feedback threshhold one bump,similar to my green bullets that I have 39k ohm resistors in.No volume pot,you think it would lower the threshold if it was passing high frequencies.
|
Greg Heumann
1906 posts
Dec 22, 2012
3:18 PM
|
"I slapped a 150pf cap between the terminals of the Astatic 151 cartridge " - all this is doing is reducing the output of the cartridge, particularly in the high frequencies.
If your GOAL is taming feedback, look to the amp, not the mic!!!If your goal is changing tone, so be it.
----------
/Greg
|
1847
429 posts
Dec 24, 2012
8:22 AM
|
here you go jd
this is from the last thread we had on this topic
100 posts
Jul 30, 2012
7:52 PM CM05FD 151JO3 Capacitor silver mica 150pf, 500v,
i just checked one of my mic's it is hard to see
with out completely taking it apart which i will be getting to next week
151 j03
cm4fu?
this appears to be a silver mica cap
pretty sure the one in my other mic is ceramic
|
