rogonzab
75 posts
Jul 10, 2012
7:32 AM
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Hi to everyone,
Yesterday the ceramic element that I ordered from harpmicshop.com has arrived (http://www.harpmicshop.com/servlet/Detail?no=73), and today I wan to build mi mic.
The thing is, I am not sure of what volume pot do I need.
100k?
250k?
500k?
1M?
I remember reading about the difference values of the pots has something to do whit each type of element (Crystals, Dynamics, Ceramics). But I haven't found that page where I read that.
Thx a lot!!
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barbequebob
1976 posts
Jul 10, 2012
7:51 AM
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For a ceramic or crystal element, 1meg (or ideally a 5meg pot is the correct pot. With dynamics, controlled reluctance/controlled magnetics, this would be far too high and would work as an over glorified on/off switch.
Again, what you need for this is a a minimum of 1meg, but ideally a 5meg pot for a ceramic or a crystal (a ceramic is actually a man made crystal).
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Sincerely,
Barbeque Bob Maglinte
Boston, MA
http://www.barbequebob.com
CD available at http://www.cdbaby.com/cd/bbmaglinte
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barbequebob
1977 posts
Jul 10, 2012
7:53 AM
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For a ceramic or crystal element, 1meg (or ideally a 5meg pot is the correct pot. With dynamics, controlled reluctance/controlled magnetics, this would be far too high and would work as an over glorified on/off switch.
Again, what you need for this is a a minimum of 1meg, but ideally a 5meg pot for a ceramic or a crystal (a ceramic is actually a man made crystal).
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Sincerely,
Barbeque Bob Maglinte
Boston, MA
http://www.barbequebob.com
CD available at http://www.cdbaby.com/cd/bbmaglinte
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rogonzab
76 posts
Jul 10, 2012
7:53 AM
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Thx barbequebob!!
Now I am one trip to the store away from my new mic!!
Thxs!
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HawkeyeKane
1055 posts
Jul 10, 2012
9:40 AM
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Side note...bob, would you happen to know off the top of your head if the stock Bluesblaster/Roadhouse pot is 1M or 5M?
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Hawkeye Kane
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1847
59 posts
Jul 10, 2012
9:58 AM
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HawkeyeKane
1055 posts
if i remember the old
blues blaster was less tha one meg
500k
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HawkeyeKane
1056 posts
Jul 10, 2012
11:53 AM
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With a crystal? Ouchies.
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Hawkeye Kane
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1847
62 posts
Jul 10, 2012
1:14 PM
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i dont think it matters too much
not an expert
but if the volume is all the way up
it should sound fine
if the volume is all the way off
well then for sure that will not matter
it is when you are comping
trying to not play too loud behind someone
you will lose some of the highs.
i remember hearing lester butler
he was playing a stock blues blaster
thru a stock bassman reissue
sounded better than just about anyone!
william clarke did not have a volume control at all
try that some time!
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Greg Heumann
1690 posts
Jul 10, 2012
5:02 PM
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Bob is right on the mark.
@1847 - you're assuming at full volume then there is a 0 ohm path across the pot and therefore it makes no difference. But you would be wrong. A pot has 3 legs - the outer of which are a resistor (the value of the pot) and the middle one a "wiper" which picks some point between the mic end and the ground end. So that resistor places a load on the mic's element - and too low a value will suck the tone right out of a crystal element. As Bob points out, too high a value will cause the volume knob to be extremely sensitive - all of the useful range will be in the 1st 1/8 of a turn of the pot - e.g., a "glorified on-off switch."
In other words - yes, choose the right value pot for your element. Dynamic mics including CR/CM elements like 100K or 250K. Crystals like 1M or 5M.
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/Greg
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1847
63 posts
Jul 10, 2012
5:34 PM
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thanks for the clarification greg!
i know my mic has a 5 meg pot
at one time it had a 1 meg in there
when it wore out someone suggested
the 5 meg pot. i played out both sat and sun.
i was too lazy to haul in my gear
so i just used my buddys rig
he also has a jt 30, but with the one meg pot
i did not hear any difference.
i do not have too much experience with a blues blaster
not sure if the value i commented on is correct
i believe it is. i did know someone who got one for christmas, it had a 151 element, it "seemed" to sound just fine
but i agree you should always use the correct values
whether its in electronics or in life! peace!
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barbequebob
1982 posts
Jul 11, 2012
7:55 AM
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As far as the pot on the BB/Roadhouse goes, the very newer ones have what's now known as the Rod Piazza mod, which is a 5meg volume pot with a low value capacitor in the back of it. The vast majority of the ones made prior to the last 3-4 years have either a 500K pot or a 250K pot (including all the JT30's with the XLR connectors in them.).
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Sincerely,
Barbeque Bob Maglinte
Boston, MA
http://www.barbequebob.com
CD available at http://www.cdbaby.com/cd/bbmaglinte
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HawkeyeKane
1066 posts
Jul 11, 2012
8:02 AM
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I'm betting I've got the 5 meg then. I got my RH back in the fall of '09 if I recall correctly.
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Hawkeye Kane
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Ed80
1 post
Jul 29, 2015
4:47 AM
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Hi All,
I'm new to this forum (just approved yesterday). So, firstly thank you for having me :)
A bit about me: I have been playing for around 15 years. I use a Hohner Blues Blaster. Used to have a Shure Green bullet but prefer the Blues Blaster.
Can anyone help with a self-build project I have on the go? I have got a 200ohm dynamic element and a couple of different pots (a 10k pot and a 100k pot). Will either of these pots work with the element? Or do I need a transformer? (if so which one?). I am planned to hook up to a 1/4" jack.
Any help / advice would be much appreciated before I get my soldering iron out.
Cheers,
Ed
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Bilzharp
98 posts
Jul 29, 2015
7:09 AM
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Do you know what microphone the element came from? It will probably need a transformer, hard to say which one. Is the 200 ohm marked as the impedance of the mic or the resistance you read on a meter? The 10K pot is too low but the 100K pot should work with the Hi-z output side of the transformer. I have a transformer from a Shure mic mixer that would probably work, $10 would include shipping in the U.S. Others might have better advice.
Edit: Oh, and welcome, Ed. You might get more views (and welcomes) by starting your own thread instead of tagging on to this old one. Either way, I'll be interested in how your mic build turns out.
Last Edited by Bilzharp on Jul 29, 2015 7:13 AM
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Greg Heumann
3063 posts
Jul 29, 2015
8:57 AM
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@Ed80 - you have a low impedance element. You need a high impedance signal into the amp. There are many ways to do this - but unless the shell you're putting it in has an XLR connector and you can wire it in balanced mode, I would simply install an impedance matching transformer in the shell if there is room. The output of that can go through a 100K or 250K pot before going to the cable.
If the shell DOES have an XLR connector then you could use a 10K pot at the mic, a balanced XLR to XLR cable, and an in-line impedance matching transformer at the amp end of the cable.
No matter what, I have all these parts available if you need them.
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***************************************************
/Greg
BlowsMeAway Productions
See my Customer Mics album on Facebook
Bluestate on iTunes
Last Edited by Greg Heumann on Jul 29, 2015 8:59 AM
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1847
2603 posts
Jul 29, 2015
10:08 AM
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here is a cool article re: linear taper pots
it was mentioned to me from a very reliable source
that 5 meg honeywell pots, work well with crystal mics
they have been discontinued and are pricey
6 to 8 dollars plus shipping
they are in short supply i have not tried one
however i may just buy one as they have been discontinued
tweeking linear taper pots
Last Edited by 1847 on Jul 29, 2015 10:08 AM
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Greg Heumann
3065 posts
Jul 29, 2015
9:37 PM
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@1847: With all due respect, whoever wrote that article is all theory and no practice. In the real world, he's (saying this politely) way off base. There is a huge difference between a 100K pot and a 5Mohm pot. A 100K pot will suck a HUGE amount of tone and output from a crystal or ceramic element. A 5 Mohm pot will act like an on-off switch with a dynamic element like a Shure CM or CR. And linear pots work just fine, thank you. Audio taper pots may be necessary for the volume control on a stereo - but they're simply not required for microphones into amplifiers. Know how I know this stuff? BECAUSE I ACTUALLY TRIED IT.
I had to say something.
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***************************************************
/Greg
BlowsMeAway Productions
See my Customer Mics album on Facebook
Bluestate on iTunes
Last Edited by Greg Heumann on Jul 29, 2015 9:37 PM
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Ed80
2 posts
Jul 30, 2015
4:53 AM
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@ Greg Heumann,Bilzharp and 1847.
Many thanks for your welcome and advice.
I don't have an XLR input. It will be a 1/4" jack. So, I think I will go wih Greg's idea of simply installing a 100k pot and impedance matching transformer. Which impedance matching transformer do I need? Can anyone provide a link to a suitable product (Greg maybe I can buy from you)?
I'll post a link to a video of how the finished mic turns out.
Cheers guys,
Ed
P.S. This is the element I have:
http://cpc.farnell.com/1/1/31163--sa-18-dynamic-mic-cartridge.html
Reckon it will work?
Last Edited by Ed80 on Jul 30, 2015 5:38 AM
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1847
2613 posts
Jul 30, 2015
9:22 AM
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the article as i read it is about using a 1 meg or larger pot so the element see's a higher impendence
then using a resistor so the amp see a slightly lower impedance, this would be with a crystal mic
it clearly states " A lower impedance element like a Shure CM should be using a lower value for the pot and resistor.'
are you saying you have tried this?
this person claims he has been doing this
” For a while, I’ve been soldering a small resistor between the potentiometer’s sweep and the ground."
so it is not just theoretical. this appears to be an attempt to give a little more sweep to the pot
i have cheap 5 meg pots from mouser they were maybe a buck fifty each
they work ok, it is possible that they could benefit from this mod.
the honeywell pots i mentioned are expensive and are hard to find not sure if they work any better
but i believe they are made to last. which in my opinion would be good to use in a wood shell mic
where it is quite difficult to change the pot if it goes bad.
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Harpaholic
708 posts
Jul 30, 2015
12:07 PM
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If you look at all the old Shure and Astatic spec sheets, Greg is dead on.
Astatic recommends 1 meg minimum for crystals as did Shure crystals.
Shure 100K for CR's.
Notice how Keith Robb added a 5 meg input on the SJ amps for crystals for the same purpose to keep from loading the crystal.
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Harpaholic
709 posts
Jul 30, 2015
6:30 PM
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From what I know, you want the input impedance of a tube amp to be the same or higher than the impedance of the mic otherwise you can loose certain frequencies.
Don't know why you would want to lower the input impedance? Not understanding that?
A lot of vintage amp inputs are not set up ideally for CR's/CM's, never mind crystals.
They can be 33K, 47K, 68K, etc.
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1847
2618 posts
Jul 30, 2015
7:53 PM
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The typical input impedance on a bassman is less than one meg, if I am not mistaken, so the mic gets the proper load, 1 meg and the resister lowers the value to match the inpedance to the amp the difference gives the pot a more audio taper.
That is how I understand it, I am sure it can be explained more accurately
But it does seem to be a brilliant idea
That has not been expressed before, to my knowledge
But the idea is to get a little more sweep to the pot much like using a lower gain tube will give the amp volume control
More usable sweep “theoretically”
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Harpaholic
710 posts
Jul 30, 2015
8:51 PM
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If it works and doesn't effect tone, why not?
Now I need to figure out how and why it works?
What resistor value does he use?
Last Edited by Harpaholic on Jul 30, 2015 8:52 PM
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1847
2619 posts
Jul 30, 2015
9:41 PM
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The best size resistor is about 10 to 20 percent of the pot value.
are your pots 1 meg or 5 meg?
you'll have to ask the experts, i havent read a resistor band since the 7 th grade
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Greg Heumann
3066 posts
Jul 30, 2015
10:40 PM
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I was taking issue with the opening statement "Volume control pots for high impedance mics feeding tube amps should be larger than 100K ohms and a 1-meg pot is a common value. The actual tonal difference, to my ears, between a 100k and a 5-meg is small."
I didn't read the entire article, so if that statement 19 paragraphs down about Shure CM's redeems him - mea culpa.
@ED - YES - I have transformers AND lots of pots, 5K, 10K, 50K, 100K, 250K, 500K, 1Mohm, 5Mohm.
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***************************************************
/Greg
BlowsMeAway Productions
See my Customer Mics album on Facebook
Bluestate on iTunes
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Harpaholic
711 posts
Jul 31, 2015
3:48 PM
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I asked my amp tech (Keith Robb) what would happen if you installed a resistor between the wiper and ground on a pot.
Here is his reply.
"It will “slow down” the volume rise as you turn it louder. If the pot’s too “jumpy”, gets too loud to quickly, it's a paste-on remedy rather than replacing the pot with more suitable characteristics. It works well if you get the right resistor on there".
So it seems to me it would be iideal if your using a 1 meg or 5 meg pot on say a CR because by adding a resistor, your lowering the value of the pot. There is an equation to determine the resistor value and the value of the pot with the resistor, I will try to locate it.
Last Edited by Harpaholic on Jul 31, 2015 5:21 PM
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1847
2624 posts
Jul 31, 2015
4:51 PM
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here is a link for the 5 meg pot i mentioned
this may have a smooth enough travel with no mods
but i have never spent this much for a pot
they have been discontinued and are hard to find.
i am typing as much as i can so the spam monster does not attack
5 meg pot
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Harpaholic
712 posts
Jul 31, 2015
4:57 PM
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I prefer a 1 meg audio taper pot with crystals.
I've AB'd 1 meg and 5 meg, and my ears can't tell the difference as far as tone. A 1 meg pot has a more usable sweep over a 5 meg IMO.
Last Edited by Harpaholic on Jul 31, 2015 4:58 PM
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1847
2625 posts
Jul 31, 2015
5:18 PM
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now that is interesting... well at least to me ha ha
at one time everyone used 1 meg, at some point someone suggested " iron man mike curtis" a 5 meg pot
all my mic's except one have 5 meg
the 1 meg pot does have a more usable sweep now that you mention it. however mine are not audio taper
where the heck do you get those?
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Harpaholic
713 posts
Jul 31, 2015
5:38 PM
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Mouser!
Here's an interesting article I found.
To make a better pseudo-log pot, one places a fixed resistor across the wiper and ground of the pot. The value to use for the fixed is 0.83 x Vr. Now placing a resistor there will drop the value of the pot, so we need to double it. To make a 230k pot we need a 500k linear pot and a 420k resistor. Problem is that as it is wound down towards 1 the load increases, however this does provide a form of treble boost.
Last Edited by Harpaholic on Jul 31, 2015 5:39 PM
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