Help with Acoustic pickup idea

[peppercorn]

Hello Fellow Groovers!
I have an issue with my acoustic plugged in sound. It is just NOT acoustic or warm enough for me and I have an idea which may help but I need some help from someone with the nous that knows whether it is possible.

The gear!
I have a Martin D1 Acoustic with a Fishman PU system. Like the one here,
i.imgur.com/k0CNnjm.jpg

So, I would like to add a small condenser mic to the system where I could mix between the 2 systems with a blend pot or something.

I have a Audio Technica AT835 mic which comes with a preamp. The preamp is stuffed but a friend said I could build a small preamp by doing this, i.imgur.com/3eXHpPY.png

but he thought that I wouldn't be able to combine the 2 using a blend pot. He reckoned I'd have to run 2 leads from the guitar which would not be practical for me.

Does anyone have any knowledge or insight to any of this and willing to help me???
Thanks in advance

[JohnH]

If you can get your mic through some simple preamp, then this blender module will mix it with your Fishman output:

guitarnuts2.proboards.com/index.cgi?board=schem&action=display&thread=4595

It uses a linear pot to give a full range of blending between two active sources.

You may need to experiment however, to get your mic signal to about the same level, and to do that you may need a bit of gain. In the schematic section is a thread on JFET buffers, including some which amplify a bit. It might also be a good idea to allow an opportunity to reverse phase of the mic, in case it sounds better that way. It would be impossible to guess which phase will sound best combined with the piezo.

I suggest some rough lashed together test first to get the mic and its preamp going and compare it to the piezo

cheers
John

[peppercorn]

Hey thanks heaps John. I remember seeing that post about 2 years back after seeing it again now!

That should work great!! However, I do have one favour IF it is possible?? Well 2....

The picture on that thread shows a PU running on a 3v battery where you used a 10uf Cap and a 10k resistor. What about my Mic which is running of a 1.5volt battery?

The 2nd favour is.....

You obviously designed that and I'm wondering how hard would it be for you to draw a pattern so I could make a small PCB??? I can make it but, don't understand electronics well enough to draw a circuit.
Thanks if you can! But thanks either way.

Apr 2, 2013 2:26:55 GMT -5 JohnH said:

If you can get your mic through some simple preamp, then this blender module will mix it with your Fishman output:

guitarnuts2.proboards.com/index.cgi?board=schem&action=display&thread=4595

It uses a linear pot to give a full range of blending between two active sources.

You may need to experiment however, to get your mic signal to about the same level, and to do that you may need a bit of gain. In the schematic section is a thread on JFET buffers, including some which amplify a bit. It might also be a good idea to allow an opportunity to reverse phase of the mic, in case it sounds better that way. It would be impossible to guess which phase will sound best combined with the piezo.

I suggest some rough lashed together test first to get the mic and its preamp going and compare it to the piezo

cheers
John

[JohnH]

i similar principle could be used to supply your mic. But I thought your mic circuit was broken? therefore, it would be better to get a new mic circuit running on the same voltage as the Fishman. Is that 9v or something else?

The small mic preamp schematic seems to be just a part diagram, no values supplied. also, condenser mics I believe, need some bias voltage and I dont see that there.

So step 1 i suggest is to look for a more complete mic preamp circuit - probably not much more complicated, and test it. I dont have such a design done, and I dont have a mic of that type, but Ill look on the web and see if there is something.

The blender module is designed to be built on strip board, and the strips of copper are on the back - as if the board was see-through in the drawing. If you want to make a pcb, you could just use the same layout just using the strips and holes that you need from the stripboard design. I m not set up to draw different pcb layouts though.

cheers
J

[peppercorn]

Thanks again John.

Firstly, the Mic....

The Mic comes with an external 1.5v pre-amp which IS broken. I have a mate who suggested that diagram, giving me the values of a 1k resistor and a 1uf electrolytic cap. Or was it 10uf?

Anyway I'll have to try and work out what is needed to get it to run from 9 volts.

[JohnH]

Ok..its a good start. I will try working out a likely different resistor value to work at 9v. Is the Fishman also 9v?.

I also think a couple of extra parts are needed to make it work with a condensor mic. Ill suggest something then you can run it past your friend.

[peppercorn]

Yea John the Fishman is also 9v.

Thanks mate for all the help. I really appreciate it!

[JohnH]

Ive had difficulty finding a design that Id be sure would work. I dont know the sensitivity of the mic, and also, there are electret condensor mics that don't need biasing, and condensor mics that do, and I dont knowwhich it is.

If it was mine, I would need to experiment and try to find a suitable design. This would be my starting point for a 9V system:



If it lacks a heap of bass, id make R1 larger. If it was too quiet, Id add a 10uF cap across R4. Id try without R1 to see if it worked.

Any comments from others? the mic is from an Audio Technica AT835 boom mic for a camcorder (is that right?) - any insights into what it might need to make it work?

cheers

John

[peppercorn]

Thanks John!
All I know is what this friend of mine told me who knows a LOT about electronics.
He would help me more but he is tied up at the moment and can't get away.

He said all I needed was the Capacitor and the resistor and the Mic capsule has the transistor and (other stuff) needed in there. Humph?

So, your latest drawing (Please excuse my ignorance) is that whats needed as the blender or is that whats needed after the blender??

Sorry mate!

[JohnH]

Apr 5, 2013 23:14:55 GMT -5 peppercorn said:

Thanks John!
All I know is what this friend of mine told me who knows a LOT about electronics.
He would help me more but he is tied up at the moment and can't get away.

He said all I needed was the Capacitor and the resistor and the Mic capsule has the transistor and (other stuff) needed in there. Humph?

So, your latest drawing (Please excuse my ignorance) is that whats needed as the blender or is that whats needed after the blender??

Sorry mate!

That was my view of what might be needed before the blender - (the pot shown there is part of the blender)

But if you are saying the mic actually has a transistor in it, and if it is not damaged, then why not just try his advice first? - even with a 1.5V battery, and wire it direct to your amp to test it and see if he is right. If you can get something to work, and decide if it is good quality and if it is loud enough, then we will be better informed about how to connect everything up.

[peppercorn]

John the reason is basically because I have conflicting opinions and I need as much info before making a decision on what to do and that decision may save me a lot of time and some money!

Anyway, I was able to get the AT853 preamp apart. It was hard because parts that allowed it to come apart had seized! Anyway, this should answer many question that you are posing John I hope!!
The yellow Cap is 22uf and the red one is 100uf. The jfets or tranny's are K30A's. The switch would switch from "Direct" "Ambience" or "Off". The two blue Caps are different values. The one at the bottom of the photo is 3.3 and the one at the top of the photo is .47

The BIG yellow thing at the front is some type of transformer.

I hope this helps you help me!

[JohnH]

could you clarify - is it an AT853 or an AT835?! both are real mic models!J

[peppercorn]

Sorry mate my addled brain!! AT853!!

I have to go to a gig now so I may be gone for 6 hours or so if you wonder where I hav'nt replied.

Thanks for puttin up with me.

[JohnH]

Its hard to tell much from a picture, except that there are two transistors.

I think if you want to persue this idea, it needs some experimenting time invested and acceptance of a risk of failure, in exchange for an interesting afternoon messing around with wires. A likley outcome is that the output from the mic with any of these circuits is lower than that of your Fishman system. My mixer module would still mix it it but you might wish for more gain to get the blend you want at the level you need.

That being said, digging out the specs for the AT853 it has a sensitivity of 11.2mV/Pa, which is considerably greater than that from a typical dynamic mic (1.8mV/Pa for an SM58). Thats after its built in pre-preamp, but its still a fair bit less than the few hundred mV that you Fishman probably produces.

However, this mic is going to be stuck inside your guitar, a relatively loud place for it to be, so maybe!

Unless you want to troubshoot and fix the current circuit, you might be advised to invest in a few parts. You could get the jfet type that I list, unless your friend has a better suggestion, and start by wiring it up according to his method, then see how it goes. Actually, the circuit I suggested is very closely related to the one you linked to.

Honestly, if he has some experience with these mic circuits then I would try that first, Im just speculating.

If however, messing about is not part of your game plan and you want to move quickly to a working system, then I would abandon ship on this idea and do something different. Maybe a preassembled mic/preamp system. Or how about a magnetic soundhole pickup? The blender module could recieve a signal from that and the Fishman and blend between them with no extra parts.
cheers
John

[peppercorn]

Thanks heaps John.

I am the doodling type so I will probably give this a go at some time over the next few weeks.

I wanted to work out
1 if it was possible and like that it might work well,
2 that I could do it with a reasonable % of it being a success.
3 Basically, what I needed to do to achieve that goal.

So, thanks heaps John. You have stuck with me and given me honest answers to all my queries and I am very thankful to you for that.

cheers.

PS I'll let you know after my attempt and tell you how I went.