wheezer
92 posts
Sep 29, 2009
3:12 AM
|
Hi Issac, and anyone else who may be able to help.
I have a Shure Unidyne 515SB-G18 to use as a harp mic.
I have removed the push to talk button and replaced it with a
47k volume pot and now I'm stuck on the wiring set up.
I have figured out the earth lead and put this to ground on the body of the mic. but the rest of it baffles me. The connection at the end of the mic. is XLR.
Is it possible to convert this mic to high impedance (it is manufactured as low). If this is possible I would have to wire an XLR to jack cable for the mic. If it has to remain as low Z I think the cable would have to be XLR to XLR to allow the use of an external impedance converter.
Any help on this would be very much appreciated. Pete
|
Oisin
348 posts
Sep 29, 2009
5:39 AM
|
Hey Wheezer...there is some info here that might help.
http://harpmicgaskets.com/tricks.htm
By the way I was speaking to John O'Leary at our jam on wednesday night and he showed me some Marine Bands you modded for him and he let me play one and it sounded sweet...nice job. I really like the way you painted the covers black also, they looked really cool. You should be advertising man!!!
Oisin
|
wheezer
96 posts
Sep 30, 2009
10:04 AM
|
Thanks for that Oisin, I wiil have a look.
John bought those black harps round to me this week as he had blown some reeds plus a Deluxe I had modded for him. He reckons that the reeds last much longer in the modded harps.
He also had with him his Crate amp which I'm afraid to say I do not like at all. The top end frequencies seem to be at war. Having a closer look (bear in mind that John has had this amp for 2/3 yrs) we dicovered that the switch for changing channela did not work. This is because the effects loop input is now the B channel input. John's reaction to this "oh yes, I forgot that this amp has been modified". You have to love him don't you! In the end we got a good sound by using a Kustom 12w with a tube preamp, turning the treble all the way down, the bass full up and lining that out to the B channel on the Crate.
He is doing a gig this Friday with Alan Glen,somewhere in Lewisham and that is the amp set up he is going to use. Should be fun.
|
isaacullah
372 posts
Sep 30, 2009
10:33 AM
|
Hi Wheezer,
Yes, the link that Oisin posted is a good one. Also, just to clarify, you can't simply rewire a mic to make it High-Z. If the element is Low-Z, then it's Low-Z. You can wire in an impedance matching transformer which will change the output to High-Z, but it's easier to use an in-line version of one of these transformers.
Here's a link to a good quality impedance matching transformer: http://www.audixusa.com/docs/products/T50k.shtml
And here's a link to an article about impedance matching: http://en.wikipedia.org/wiki/Impedance_matching
As for how you were going to wire the mic up, here's some advice. I would not use the mic shell to do the ground connection. I would wire the negative lead from the mic element to pin 3 of the volume pot, and then continue from pin 3 to the negative lug of the output jack. I always convert XLR to 1/4" TRS (guitar) style jacks because I don't have any XLR cables,and I either use PA amps that don't need a High-Z element to drive them, or I up the signal with a booster pedal before going into a regular amp. I use metal bodied jacks so that the shell is automatically grounded, which helps to shield the wiring from interference. You wire the hot lead from the mic element to pin 1 of the volume pot, and then connect pin 2 of the pot to the hot lug of the 1/4" jack.
XLR is a little different. There are three pins. One is the hot pin, and gets connected to pin 2 of the pot. The other two are the shield and the ground. You definitely connect the ground to pin 3 of the pot (and consequently to the negative out from the element). The shield can either be also connect to the ground (just solder these two pins together with a short jumper wire), or you can connect it to the metal chassis. Then use the impedance matching transformer to up the output and change to a 1/4" style plug to get into your amp.
Hope that helps,
Isaac
----------
------------------
The magnificent YouTube channel of the internet user known as "isaacullah"
Last Edited by on Sep 30, 2009 10:36 AM
|
wheezer
97 posts
Oct 01, 2009
2:00 AM
|
Issac, you're a star!
As you can tell from my questions regarding impedance I am a complete novice when it comes to elctrikery.
I was suspicious that I would have to use an external impedence transformer and you have confirmed it.
With regard to the earth wire to the shell of the mic, there are three wires from the element of this mic. (Shure A805LG element), a red on one side that I assume is the hot, a green on the other side which I take to be negative and a blue wire in the centre. It is the blue wire that I have earthed to the shell.
I have to use an XLR cable because the only impedence
converter I can get has an XLR input but with the info. you have given me I can now see how to wire it.
Thanks again, Pete
|
Oisin
351 posts
Oct 01, 2009
2:02 AM
|
Hey Pete...that explains alot. When John was playing on wednesday he was using the effects board and some sort of in-line volume control on the mic lead. When myself and the other harp players went up we used our own mics plugged straight into the amp and it sounded much better.
The last time John played, a couple of months ago,
his set-up sounded way better. He still played great though on the night. He don't half give that harp a good old suck man when he gets going.By the way Pete..how much would you charge to set a harp up?
Oisin
Oisin
|
tookatooka
573 posts
Oct 01, 2009
3:55 AM
|
Wheezer said "With regard to the earth wire to the shell of the mic, there are three wires from the element of this mic. (Shure A805LG element), a red on one side that I assume is the hot, a green on the other side which I take to be negative and a blue wire in the centre. It is the blue wire that I have earthed to the shell".
I may be talking out of turn here wheezer but green used to be the colour for earth or ground connections before the EU bought in the brown, blue, green and yellow system for mains wiring. You may just want to double/treble check your wiring it up correctly before you plug in. It may be different for mics but I'd be just a little bit suspicious.
----------
|
wheezer
99 posts
Oct 01, 2009
9:26 AM
|
Thanks Tookatooka. Problem is that I think Shure are an American company so I have no idea what a colour denotes under their system.
For Oisin.
If you contact John I will ask him to give you my email address or phone number with regards to me setting up a harp for you.
Thank you all for your help. Pete
|
isaacullah
374 posts
Oct 01, 2009
11:49 AM
|
Ahh, you had one of those three wire elements. Yeah, you are probably fine wiring it the way you did. The red is the hot, for sure, and you are probably right about the green being ground and the blue being the shield. In any case, the ground and shield are electrically connect together in the mic. When I wire 1/4" jacks, these are unbalanced, so I would solder both the ground and the shield to pin 3 of the pot and then to the ground lug of the 1/4" jack. For XLR, they are balanced cables, if you have both a ground and a shield lead from the element, you go ground to pin three of pot to ground pin of the XLR jack, and Shield to metal chassis to shield pin of the XLR jack.
A balanced cable has a positive and negative (ground) wire in the center and the shield is a braid of wire that surrounds them. The shield is connected to ground at at least one end of the cable In an unbalanced cable, you just have the hot wire in the center, and the shield braid is also the ground connection.
----------
------------------
The magnificent YouTube channel of the internet user known as "isaacullah"
|
wheezer
101 posts
Oct 02, 2009
8:20 AM
|
Thanks Isaacullah.
If I have this correctly: The red (hot) from the element goes to the 1 pin on the pot.
The green from the element (neutral or ground) goes to the 3 pin of the pot.
The blue from the element (earth or shield) goes to the shell of the mic.
The centre pin of the pot now becomes the hot lead to the 1 pin of the XLR .
The neutral(green)from pin3 of the pot continues down to fix to pin 3 of the XLR.
The blue lead (earth or shield) can be connected to the 2 pin of the XLR.
In this configuration do I still need to bridge between XLR pins 2 & 3?
I hope I've got this right, more likely that I 've made myself look a complete pratt, still, if you don't ask you don't learn.
Thanks again, Pete
|
isaacullah
377 posts
Oct 02, 2009
10:35 AM
|
Pete, that's correct. And you don't have to bridge XLR pin 2 & 3. You only need to do that if your mic element does not have a dedicated shield lead.
Cheers,
Isaac
----------
------------------
The magnificent YouTube channel of the internet user known as "isaacullah"
|
wheezer
102 posts
Oct 03, 2009
1:39 AM
|
O.K. I'll try to get that all soldered today. Or should that be sodered as I am working under your direction lol.
(You see I have watched your videos on mic. building)
I'll let you know how it goes. Pete
|
djm3801
228 posts
Oct 03, 2009
7:01 AM
|
Issac, you do some really interesting things with electronics. I used to have that patience and inquisitive nature when I was young and had hair. Budget constraints were also a driver and now that they are not I remember the satisfaction of building something for myself. Recall wanting a good stereo - built a Dynaco pre-amp, power amp,tuner. A great system and a great lesson. Enjoy it. Now I do woodworking as a hobby - no, not combs.
You are generous with your expertise and ideas. Thanks.
Last Edited by on Oct 03, 2009 7:02 AM
|
isaacullah
379 posts
Oct 03, 2009
12:01 PM
|
djm3801: Thanks for that, I appreciate it! I like sharing my knowledge of stuff. I'm in higher education (hope to be a university prof one day!), so it just feels right to share stuff I know with those who are interested in it!
BTW, I also do a bit of wood working myself. Check out this jewelry armoir I made for my wife.
----------
------------------
The magnificent YouTube channel of the internet user known as "isaacullah"
|
wheezer
112 posts
Oct 05, 2009
4:10 AM
|
It works, volume pot as well!
It works into the amp using the Hohner Bluesblaster
XLR to 1/4 jack and into the p.a. desk using XLR to XLR.
I have two impedence converters here but neither seem to work so now all I need is a new converter.
Thanks for all your help and patience Isaac.
Pete.
|
isaacullah
384 posts
Oct 05, 2009
1:39 PM
|
Great! I'm glad you got it sorted! Good job!
----------
------------------
The magnificent YouTube channel of the internet user known as "isaacullah"
|
jimbo-G
23 posts
Aug 15, 2011
3:02 AM
|
Thought id bring up an old thread here. Does anyone know how to wire a tone pot up in an amp, I looked It up and I think it should just be earthed and hooked into the volume through a 1uf capacitor. But Im not sure.
----------
"Everyone has to start somewhere."
|
wheezer
199 posts
Aug 15, 2011
11:18 AM
|
@jimbo-G.
You could get in touch with Nigel at alnicomagnetic.
I had a a tone control from him for my GA5. It came with all components, wiring diags.and instructions for £11.99.
You can Google him or find him on Ebay.
|
jimbo-G
24 posts
Aug 15, 2011
3:19 PM
|
Cheers man il look him up, thanks.
----------
"Everyone has to start somewhere."
|
jimbo-G
25 posts
Aug 16, 2011
11:21 AM
|
I couldn't find alnicomagnetic anywhere, I have some capacitors and a couple of 50k pots lying around I think I do a bit of trial and error. It's only a solid state so I hope there wont be any potentially fatal currents.
----------
"Everyone has to start somewhere."
And end somewhere.
|
isaacullah
1541 posts
Aug 16, 2011
7:44 PM
|
I've tried quite a few tone control circuits. IMO, if you are going passive (no gain recovery), it's best to do a "one knob" tone control with a simple treble cut filter. I like the one used in the Lone Wolf mods to the Epiphone Valve Junior http://www.lwharpamps.com/projepimod.html. I've used that one in a couple of projects (including a modded Epi VJ), and can vouch for it. It really works well.
~Isaac
----------
== I S A A C ==
View my videos on YouTube!
Last Edited by on Aug 16, 2011 7:46 PM
|
