Microphone Preamplifier

[Steven.kedari]

Hello! i am new to this forum. I had bought an electret condenser professional studio microphone whichI had intended to use with my laptop's mic in. The cable I got with the mic had one XLR end for connecting the mic and one 1/8" TRS male for output. I made connection to my laptop by wiring the TRS jack to a standard 3.5 mm TRS jack and was successful. The problem is the mic output level is too less than the LINE LEVEL. So I need a mic preamplifier for increasing the signal. Please help with cheap solutions.

 

[reubensm]

Hello! i am new to this forum. I had bought an electret condenser professional studio microphone whichI had intended to use with my laptop's mic in. The cable I got with the mic had one XLR end for connecting the mic and one 1/8" TRS male for output. I made connection to my laptop by wiring the TRS jack to a standard 3.5 mm TRS jack and was successful. The problem is the mic output level is too less than the LINE LEVEL. So I need a mic preamplifier for increasing the signal. Please help with cheap solutions.

are you looking for brands or are you looking for DIY?

 

[Thad E Ginathom]

What is the make and model of your mic? Some condenser mics require "phantom power, " some require the power supplied by "plug-in-power" sockets on domestic equipment.

Given that yours came with XLR-to-TRS connections, it is unlikely to be the latter, which would probably plug happily into your laptop.

Maybe you now need something like this: M-audio Fast-Track which will connect to a USB port

 

[Steven.kedari]

My mic is from Ahuja. And the model is CSM 990. It's a shotgun type, but not the typical one. I have read about M Audio Fast Track. But I didn't find it in my budget. Neither I found any preamplifier at hifimart.com. And ebay does not have any options with sellers from india fallign into my budget. Does M Audio have cheaper mono channel preamplifiers? And is there any way I can find these in our own country to save the shipping charges?

 

[Steven.kedari]

Yes I have read about M Audio Fast Track. But I didn't find it in my budget. Neither I found any preamplifier at hifimart.com. And ebay does not have any options with sellers from india falling into my budget. Does M Audio have cheaper mono channel preamplifiers? And is there any way I can find these in our own country to save the shipping charges?

 

[Thad E Ginathom]

Sorry, I don't recognise what kind of thing that is, and don't know enough to work it out from the very sparse description.

Silly question ... but you checked out stuff like levels in Windows mixer? That is something that has caught out many people.

 

[Steven.kedari]

OK First of all. I may explain my problem more elaborately. I have a microphone (check out it's specifications: Ahuja Sound Solutions)

Now the Two Core shielded cable which I got with the mic has one Female XLR end which plugs into the Male XLR socket on the mic. The cable is 10 metres long and ends with a Mono TRS jack (6.3 mm or 1/8"). Since computer sound cards don't have 6.3 mm MIC IN sockets and have 3.5 mm sockets, I made a simple 3.5 mm adapter by joining the tip-tip and sleeve-sleeve.

When I connected the whole thing to my laptop MIC IN, I could see the signal bars rise when I spoke into the mic, but the level was so low that I had to speak loudly and very intimately into the mic to hear a little bit of my voice. And I did this after increasing (boosting) the level to 40 dB from the windows levels. But it didn't help.:sad:

The only solution is a preamplifier. Now while searching for it online, I landed on the Ahuja website itself where I saw an item named 'Microphone Compressor'. Are Microphone compressor and preamplifier the same?

 

[omishra]

I repaired similar mic in Ganesh festival time. It needed one AA battery to work inside. Just rotate the lower part to open that half. There it was placed and condenser mic was in series of connecting wire through 10K resistor.

If you already put the battery then for cheap 200Rs solution you have to do following thing.

- Get mic preamp kit from vega kit or tape head stereo preamp (chip based), cost you approx Rs 50.
- build LM317 based PS for 12V DC, approx 100Rs (this is DC adapter type not in cabinet of preamp)
- chassis Rs 50, in and out connectors, DC chassis mount socket and 10K linear potentiometer.

And get assembled using input, ouput connectors and volume pot of 10K. Less than 250Rs this works. I have given it to one of my friend with buy back option. That guy is not selling back to me.

 

[Thad E Ginathom]

XLR to TRS would usually indicate a balanced cable. Here's an eg of how to connect balanced to unbalanced

My pc audio interface uses balanced cables: the two conducters and the shield makes three ... the three pins of the XLR. But, so far, I am able to give it input from a balanced source, and my monitor speakers have balance input. I have not had to convert, so no practical experience.

But I just noticed this

Balanced wiring is sometimes called XLR wiring because it often uses that kind of three-pin connector. But it's dangerous to assume that an XLR plug or jack is balanced. Although most manufacturers reserve these connectors for balanced circuits, there are exceptions. Check the equipment specs.

... from this link.

ps... I think omishra knows a lot more about this than I do. any comment on the cable?

 

[Steven.kedari]

I repaired similar mic in Ganesh festival time. It needed one AA battery to work inside. Just rotate the lower part to open that half. There it was placed and condenser mic was in series of connecting wire through 10K resistor.

If you already put the battery then for cheap 200Rs solution you have to do following thing.

- Get mic preamp kit from vega kit or tape head stereo preamp (chip based), cost you approx Rs 50.
- build LM317 based PS for 12V DC, approx 100Rs (this is DC adapter type not in cabinet of preamp)
- chassis Rs 50, in and out connectors, DC chassis mount socket and 10K linear potentiometer.

And get assembled using input, ouput connectors and volume pot of 10K. Less than 250Rs this works. I have given it to one of my friend with buy back option. That guy is not selling back to me.

This sounds like a solution...Can you tell me the process more elaborately? Please... And by how my dB does the preamp amplify the signal? I need atleast -15 dB output.

 

[Steven.kedari]

XLR to TRS would usually indicate a balanced cable. Here's an eg of how to connect balanced to unbalanced

My pc audio interface uses balanced cables: the two conducters and the shield makes three ... the three pins of the XLR. But, so far, I am able to give it input from a balanced source, and my monitor speakers have balance input. I have not had to convert, so no practical experience.

But I just noticed this


... from this link.

ps... I think omishra knows a lot more about this than I do. any comment on the cable?

Maybe your are right, But when I used long cable, there was a lot of noise (as it is in case of unbalanced cables) so my sound card is definitely unbalanced.

 

[omishra]

This sounds like a solution...Can you tell me the process more elaborately? Please... And by how my dB does the preamp amplify the signal? I need atleast -15 dB output.

These mics do not have balanced output with the said price. It's unbalanced only. That's just a connection with two wires from balanced pin are used.

First, did your mic has requirement of AA battery? if yes then put it.

Second, I don't know about dB gain but the application was condenser mic (similar) -> preamp -> PC for recording singing + acoustic guitar from single mic. (He created own mobile ringtones with my DIY preamp)

I will draw connection diagram if you wish.

 

[Thad E Ginathom]

Thanks. Sorry for introducing something irrelevant.

 

[Steven.kedari]

These mics do not have balanced output with the said price. It's unbalanced only. That's just a connection with two wires from balanced pin are used.

First, did your mic has requirement of AA battery? if yes then put it.

Second, I don't know about dB gain but the application was condenser mic (similar) -> preamp -> PC for recording singing + acoustic guitar from single mic. (He created own mobile ringtones with my DIY preamp)

I will draw connection diagram if you wish.

Yes, you are right. The mic is unbalanced, but not completely. It's like, Quasi-balanced. Anyways... Yes my mic, which is not the typical condenser, but an electret condenser does need a 1.5 V AA battery. And I have placed it in the cartridge. Also you can check which microphone I have: http://ahujaradios.com/Productdetail.asp?prd_id=126&id=6&sc_id=56

OK, when it comes to application, let me make it clear for you. Actually, I am soon going to shoot my own feature movie. So I want to use the mic for field recording, basically the dialogues of the actors. I know it's ridiculous. But then, my application flowchart would be exactly similar to the one you have mentioned.

Yes I definitely want a circuit diagram. Thanks.

And do you have any knowledge about dBV/Pa and mV/Pa sort of stuff? No, because I don't understand those things. All I know is those values are for the Sensitivity of the mic as I have seen on the mic datasheet.

 

[Steven.kedari]

Thanks. Sorry for introducing something irrelevant.

No problem, never mind.

 

[Thad E Ginathom]

Cheers. Looks like it was quasi-relevant!

The mic is unbalanced, but not completely. It's like, Quasi-balanced.

Your idea does not sound ridiculous at all, and this is what I'd probably look for to do the job --- but will you not be connecting it to the camera?

I have one of these. It used to give excellent results with a mini-disc recorder, and would work on the (red) plug-in-power socket of domestic handi-cam equipment too. It probably wouldn't be good at picking up dialogue from a distance but I had good results for live music practice. At some time, I want to go the other way, and convert its stereo plug-in-power jack to two mono xlr. It needs something like this to provide the power, and you might find that site has something for your application too

 

[omishra]

Yes I definitely want a circuit diagram. Thanks.

Look at this preamp circuit which I used. I used one channel of it. And from Volume control output was taken. Actually you can get it ready/kit for Rs 40/- at students project kit shop. Its up to C5, C10 in diagram from above link. Remaining stuff in not the kit and not required. Use pot of 10K at the output and connect to output jack. Input is provided at the tape head input point through input jack. Power supply is outside 12V regulated low noise adapter. (Best results using LM317 based regulator.) Look for LM 3161 based preamp kit. First 3 are of your interest.

As Thad suggested this mic can not pick dialog from long distance.

 

[Steven.kedari]

Cheers. Looks like it was quasi-relevant!


Your idea does not sound ridiculous at all, and this is what I'd probably look for to do the job --- but will you not be connecting it to the camera?

I have one of these. It used to give excellent results with a mini-disc recorder, and would work on the (red) plug-in-power socket of domestic handi-cam equipment too. It probably wouldn't be good at picking up dialogue from a distance but I had good results for live music practice. At some time, I want to go the other way, and convert its stereo plug-in-power jack to two mono xlr. It needs something like this to provide the power, and you might find that site has something for your application too

Thanks for your suggestion Thad. But I can't spend that high since I am only 16 and hence can spend only from what my dad earns But surely I can look upon your suggestions in the near future. Also I cannot the microphone directly to the camera. As, I said I can't spend much, so I will be using my point and shoot still photo camera which has real good HD video recording. It's not the pro dSLR nor a camcorder as you must have thought.

 

[Steven.kedari]

Look at this preamp circuit which I used. I used one channel of it. And from Volume control output was taken. Actually you can get it ready/kit for Rs 40/- at students project kit shop. Its up to C5, C10 in diagram from above link. Remaining stuff in not the kit and not required. Use pot of 10K at the output and connect to output jack. Input is provided at the tape head input point through input jack. Power supply is outside 12V regulated low noise adapter. (Best results using LM317 based regulator.) Look for LM 3161 based preamp kit. First 3 are of your interest.

As Thad suggested this mic can not pick dialog from long distance.

That was helpful. Thanks for the link too...:clapping: And which mic are you talking about. The Ahuja one which I have or the Sony one which Thad has suggested. No, because if about mine one, then it's a little, jerky shock for me because I has to cry before my dad to buy it from eBay for 2200 bucks

 

[Steven.kedari]

Omishra, the link was very good I had lost all tension. But their page is not wrking correctly i think. I cannot open the page for the preamp model you suggested.