Dynamic Mic to Guitar pedal converter - This needs settled!

[fishfude]

Hi Folks,

So I've been asked by a friend to create them a Dynamic Mic to guitar pedal converter. I've been reading up online and there seems to be a consensus that this isn't worth your while bothering with!? Also, there doesn't seem to be an agreed decent schematic for doing it.

I believe the two issues are converting from low impedance to high(er) impedance and then boosting the signal. Surely this is very straight forward. My thought was simply to have an opamp with a pot as the feedback resistor to boost the signal? I assume I'm missing something (as always, that's how I learn!).

Here's the schematic I found:



This should be easy to convert to single supply right, and I just swap out the 100k feedback for an A500k pot for amplification?

Thanks,

ff

[Eddododo]

Well firstly I think you will have two different gains from the two sides..? I am not sure you could simply go at the op-amp in that fashion, but it seems simple enough to simply take both signals in through buffers, one inverting and one non-inverting, and mix with a third op-amp. I haven't played much with truly balanced signals so wait for a more experienced response!

[tubegeek]

Here's the schematic I found:



This should be easy to convert to single supply right,

There's nothing on that schematic about the power supply.

The caps on the input and output ensure that whatever supply setup you use you will be isolated from DC outside the circuit.

and I just swap out the 100k feedback for an A500k pot for amplification?

Maybe 500K linear might be better but I'm not sure - either way it'll increase the inverted signal from the mic coming into the inverting input and also decrease the negative feedback fraction coming from the output back to the inverting input. Outlook Uncertain but most likely either a) louder and more distorted or b) unstable. You'll certainly also disturb the balance on the input and therefore leave you with less protection from common mode noise along the cable than you would have otherwise. That's probably the least of your worries though....

[PRR]

> Here's the schematic I found:

Where do I start?

As said, the power connections are not shown.

Chip not specified, and that hardly matters because....

The hiss is 30 times worse than it needs to be. So bad, that I wonder if he ever compared it to a proper mike preamp. This is just hiss from poor choice of resistor values.

It has NO gain (and you will need some).

The different-value input caps are quite strange, but the whole affair is not truly balanced so that's a small detail.

There are better ways to do a LOW-hiss balanced mike input but they need more parts.

Actually, what you probably want is a simple transformer like--

http://www.radioshack.com/product/index.jsp?productId=2062443

Yes, it is $20, but it already has the right jacks, is true balanced/floating input, has gain (7X), uses NO power and is hard to blow-up. In years of small PA work I always carried several, and used them many times.

If your desert island lacks a Radio Shack (in Europe there is a similar part, maybe badged "Beyer", but probably from the same Japan/China factory).... here is that opamp plan with values that won't hiss horridly, and powered from your single 9V battery/wart:



A TL072 will hiss 10X worse than the mike, and that's audible on stage. An NE/SE5532 will hiss only 3X worse than the mike, which is often acceptable on stage.

For a much better plan, not a lot more complicated, find "$10 mike preamp". This can be a true studio-grade mike preamp, but it does cost more than $10 with power supply and box and jacks.

[fishfude]

OK,

thanks for all the responses. I guess I'm not really any clearer on which way to go with this.

If this is the best alternative:

... does anyone know what's in it so I can replicate it?

Thanks,
ff

[slacker]

Have you tried just plugging the mic into the pedals? You might not need anything extra.

[Seljer]

600ohm:10kiloohm audio transformer

But whatever you do wont be as streamlined, rugged and cheap as the radioshack one PRR linked to

[fishfude]

Thanks Seljer! I'm just looking to make it despite the lack of economic sense.

[wavley]

Thanks Seljer! I'm just looking to make it despite the lack of economic sense.

I agree with PRR, those Rat Shack adapters and the one that goes in the opposite direction are something I always keep around, cheap, rugged, and gets the job done.  I've used it many times to plug a vocal mic or acoustic guitar mic into a pedal.

But, if I were to build anything at all, it would basically be the equivalent circuit that's in the adapter using one of these https://www.edcorusa.com/pc600-10k but really only if I were already making an Edcor order and/or wanted some other bells and whistles.  Otherwise, the Rat Shack adapter is readily available two miles from my house and passive DI boxes which can be used in reverse are plentiful, also there is a pretty good sounding Behringer active DI that will do the job for $29.  So really, I would only build such a thing if I wanted some very specific situation based needs.

Your other option is to buy an ART Tube MP, you can totally get one on sale at a guitar store for $30 and used on ebay for $20 and it's a proper mic pre with gain and has both balanced and 1/4" out, of course it's line level so you would have to keep the gain down.

[Tubebass]

A few years back I did sound for a group of young Japanese musicians. The singer plugged a SM58 into a Boss digital delay pedal via a simple XLR to 1/4 adaptor cable, and took the output the same way. I was dubious, but it worked fine.

[Seljer]

A few years back I did sound for a group of young Japanese musicians. The singer plugged a SM58 into a Boss digital delay pedal via a simple XLR to 1/4 adaptor cable, and took the output the same way. I was dubious, but it worked fine.

Or a band I was in where we plugged a SM58 directly into a bass amp via the same XLR-1/4" adapter for vocals until we got a PA.

[zombiwoof]

Using a common low-to-high impedance mic transformer was my first thought also, I still have two or three old Shure transformers, including one that has switchable ends on it (male, female 1/4").  Does Shure still make these?.  I know they would be more expensive, though, back in the day they were only around $12 but probably three times that now if they still make them.  The Shure mic transformers were the go-to transformers back in the old days.

Al

> Here's the schematic I found:

Where do I start?

As said, the power connections are not shown.

Chip not specified, and that hardly matters because....

The hiss is 30 times worse than it needs to be. So bad, that I wonder if he ever compared it to a proper mike preamp. This is just hiss from poor choice of resistor values.

It has NO gain (and you will need some).

The different-value input caps are quite strange, but the whole affair is not truly balanced so that's a small detail.

There are better ways to do a LOW-hiss balanced mike input but they need more parts.

Actually, what you probably want is a simple transformer like--

http://www.radioshack.com/product/index.jsp?productId=2062443

Yes, it is $20, but it already has the right jacks, is true balanced/floating input, has gain (7X), uses NO power and is hard to blow-up. In years of small PA work I always carried several, and used them many times.

If your desert island lacks a Radio Shack (in Europe there is a similar part, maybe badged "Beyer", but probably from the same Japan/China factory).... here is that opamp plan with values that won't hiss horridly, and powered from your single 9V battery/wart:



A TL072 will hiss 10X worse than the mike, and that's audible on stage. An NE/SE5532 will hiss only 3X worse than the mike, which is often acceptable on stage.

For a much better plan, not a lot more complicated, find "$10 mike preamp". This can be a true studio-grade mike preamp, but it does cost more than $10 with power supply and box and jacks.

[fishfude]

OK folks, starting to make sense now.

One more question though, if I use a transformer will that be enough or will i need to boost the signal as well?

thanks,

ff

[PRR]

> what's in it so I can replicate it?

A 1:7 mike transformer with a little shielding.

You can NOT buy a decent naked transformer and shielding for $20, not to mention the nice-enough jacks and case.

So just buy one. Take out the small screw, it comes apart without TOO much puzzlement.

For "built-in" use I would tend to strap the hole thing in a case with the XLR hanging out, solder to the 1/4", and keep the shielding and case intact. Or carefully unscrew the 1/4" (you may have to undo the XLR end first so the wires don't twist to death), unsolder it, saw-off most of the 1/4" shank, and run coax out the 1/4" hole.

[PRR]

> will i need to boost

This transformer is 1:7. Between a low-Z dynamic mike and a hi-Z input like guitar stuff, it gives a voltage gain near 7. This was typically enough to use mikes with guitar amps or the old mixers that only had hi-Z mic inputs.

If you need to go into a "line" input, you need more gain, more than a simple transformer can do, so an amplifier, and with more than single 9V supply voltage. Go find a mike preamp. Banjo World sells stereo mike-amps with knobs and Phantom for under $99. Or there are the Berhinger mini-mixers at $69 (be sure it has mike preamps, they don't put a pre on every input).

[moosapotamus]

I'm just looking to make it despite the lack of economic sense.

In my mind, one big reason to do this would be to create a building block that could be used in a stand-alone vocal/effects loop blend box. Input/output would be low-Z balanced XLR, and the switchable effects loop would be hi-Z unbalanced 1/4" send/return for use with stompboxes. Not so easy to find something like that commercially, that I know of, anyway.

~ Charlie

[deadastronaut]

^ i built one of those for vocals with the aid of my more knowledgable bass player when i was in my band, it was essential, 

i was sick of mixer guys setting up the 'sound' on soundcheck , then when it came to going  on not giving me any delay/verb on vocals at all 

so i just took control on stage my self with stompbox delay/verb..

mic to short XLR then out to desk XLR but with a send return for FX...it was great and pissed off the inadequate 'sound' guy too...everyone's happy. 

[wavley]

^ i built one of those for vocals with the aid of my more knowledgable bass player when i was in my band, it was essential, 

i was sick of mixer guys setting up the 'sound' on soundcheck , then when it came to going  on not giving me any delay/verb on vocals at all 

so i just took control on stage my self with stompbox delay/verb..

mic to short XLR then out to desk XLR but with a send return for FX...it was great and pissed off the inadequate 'sound' guy too...everyone's happy. 

My vocal chain is: Mic, Roland SVC-350 Vocoder, comp/gate/de-esser, RE-501 Space Echo, EHX Memory Man w/ Hazarai, ADL tube DI.

I hand them an XLR and ask for a channel with flat EQ and no processing, it's been working out a lot better.

You can't build a proper mic pre for the $20 you spend on a use Tube MP, while it might not be my go to pre for accurate recordings, it's certainly close enough for rock and roll and quite good sounding in certain applications.  The Rat Shack deal is the bare minimum I would do in this situation and just like Paul said, you aren't buying all the connectors, shielding, and transformer for $20.  I also really agree that you can totally just take it apart and hack it into what you want for your specific situation.

[deadastronaut]

''I hand them an XLR and ask for a channel with flat EQ and no processing, it's been working out a lot better.''


yep much better than relying on someone elses idea of things...

sounds like a nice setup man..