Tiny stereo preamp???

G

guitarlover

New member
Hi, I usually hang out at the mic forum but I have an unusual mic preamp question.

I purchased a Sony mini-disc player/recorder today. My intent was to recorder mp3's to listen as I run/jog...well...amble along anyway. I discovered when I read the instructions that there is a jack to record analog audio. The intent is to record from audio sources with the usual "line" output (1/2 volt?).

Anyway, it dawned on me that the only thing I need is an ultraminiature stereo preamp and I can do some halfassed recordings. I do have a Sony ECM717 stereo mic that I used to record school lectures (really).

The bottom line - is there a tiny stereo preamp out there? I would even settle for a PC board as I can package it. I'm just trying to bring a condenser mic output up to line level.

Thanks in advance, Steve
 
I can't think of anything - the smallest preamp I know is the Audio Buddy.

The problem will be power - if you can find anything that runs off a battery you should buy it.

It need not be stereo/2-channel either. One channel will be ok and only one side of the mic will record - you don't need the stereo effect by the sounds of it.
 
regebro said:
Sure, but it costs a small fortune....


Here is something:
http://www.soundprofessionals.com/cgi-bin/gold/category.cgi?category=540&item=SP-PREAMP-3&type=store
Click to expand...

I found that last night very late after I posted my question. Ohmigod!! I only paid $149 for the recorder!

In my search, however, I came across a couple of other things that may be of interest to others who wish to do some live "micro" recordings.

http://www.electronics123.com/amazon/catalogue/c3-3-1.htm

This place has two different mono preamp modules that are sooo cheap I can buy 2 and put them in a box as a stereo unit. One even has a gain adjustment.

The stereo preamp is both too large and has too much in the way of power requirements. The first 2 I can power with a single 9V battery.

I think I'm going to order 2 of each of the monos and see which I like better. Heck, a trip to Radio Shack for packaging and sundries and I'm in business.

btw, I thought about going the mono route and I have done that in the past with cassette tape. I decided that since I will be doing this in digital, I would go the extra mile and go full stereo. If the preamp is halfway decent, I can try my scheme with discrete mics. It just might make for an ultra portable recording setup!

Wish me luck, Steve :cool:
 
I went to the site I listed above and they were out of stock on both kits! I did, however find something else that I think will work even better. I've ordered 2 of the modules.

http://www.qkits.com/serv/qkits/velleman/pages/K1803.asp

I'll let you know (if you're interested) in how this progresses. So far, this beats the heck out of what that one site wanted.

Thanks all for your input. I guess my problem is just a little unique.

Regards, Steve
 
That little SONY mic is designed to put out -10dbv line level! Just plug it straight into the line in and see what happens. There's already a preamp in the mic.-Richie
 
Richard, I tried that and got barely any signal. I basically had to scream into it to be heard. Maybe the Net md walkman has adjustable gain. I'll have to go looks.

Thanks for the heads up, Steve
 
Interesting- sorry if I'm confused. I use ECM-MS957, and it plugs straight into the line in on my Korg PXR-4, my brothers D6 walkman, or a minidisc. I'm afraid I assumed the lower model would do the same. My bad.-Richie
 
Richard,

It plugs right in, alright. It's just that nothing comes out, well...at least very little.

I'm well underway in building the pre-amp. I have the two mono pre-amps done and tested. I'm building the packaging right now. If you're interested, I can post a picture of the completed unit. This basically takes something not intended for mic input and gives it that capability.

Regards, Steve
 
I assure you, the mic I'm talking about, something comes out all right. I'm pretty sure your mic is looking for a mic input, and mine is looking for a -10 dBV stereo line in.-Richie
 
Richard,

Thanks for the help. I do know that some mini disc recorders have a mic input as well as a line input. Mine just has the line input. This means I need either an amplified mic or a preamp. Since I don't plan on doing a tremendous amount of recording with it, I thought the homebrew preamp route might work OK. It actually works quite well. I just completed the project. My big concern was labeling but I figured that one out.

I wish it had about 10db more gain but I'm running it at 9 volts when the circuit was designed for 12. I suppose I could put in a DC to DC converter but that would just require even more power. So, I'll just be happy with it as it is.

Regards, Steve :D

PS Richard, I just noticed the list of things you tried the mic on. The walkman generally has a mic input, mine does. As for the Korg, I cannot say but I would guess that it has a mic input as well. For some reason, if you want a mic input on the Sony MD players, it about doubles the cost. I'm not sure why except that making it cheaper might make good quality recordings affordable? Who knows...
 
Actually, Guitarlover, the Korg does have a 1/4" mic input for a dynamic, no phantom power, and it's mono. The only way you can record 2 tracks at a time is to go in through a 1/8" stereo mini plug, which is theoretically a -10 dBV line in, not a mic input. The ECM-MS957 works excellently when inserted into that stereo line input. Is the line in on your minidisc mono or stereo, and is it looking for a -10dBV or a +4 dBu input? It sounds like the minidisc is looking for +4, and the mic is delivering -10, so you get some signal, but not enough. If thats right, inserting a line level shifter between them would help lots. - Richie
 
Hi,

I have a couple of pics to put up but I've never done it on this forum so I'm not sure of the procedure. Does the file actually upload or do I have to put it on a hosting site with the address?

Richard,

I understand what you are saying but I'm used to speaking in terms of voltages. If a mic's output is say 1/10 volt and the device(minidisc etc) is looking for 1 volt peak to peak then you need to, as you say raise the level. Isn't that what the preamp does? Or am I missing something?

When I was researching minidiscs, it was made clear that some were for mic input and others for "line level" input. It was my understanding that line level is somewhere near 1/2 volt P to P. I'm not sure how that relates to db but that is what I've always understood. BTW, my tape recorders as well as my Fostex MR-8 all have different settings for line vs mic input. I thought it was just cranking up the gain on the preamp.

If I'm missing something, please let me know. I not trying to be a smartass. I learned what little electronics I know from my ham radio days and I know the language is a little different.

Regards, Steve :confused:
 
I regret to say that my technical kmowledge of electronics is pathetic, and it will take a technogeek with deeper theoretical knowledge than me to answer your question. What I know is that "line level" comes in 2 versions. -10 dBV (consumer level) and +4 dBu (professional level). The consumer level conforms to the "tape in" or "tape out" RCA jacks on a mixer or receiver. +4 is what is put out by most preamps, and is generally, although not always, assosiated with 1/4" TS or TSR connections, or XLR.
Many remote recorders, including my Korg, a Walkman, and I'm assuming some minidisc recorders, have 1/8" line ins, usually stereo, which are looking for a -10 line input, so you can feed them from a CD player, receiver, or the "tape out" of a mixer. Therefore, many stereo mics designed for DAT recording or other remote location recording, particularly those with stereo 1/8" connectors, and which typically run on batteries, are not really made to put out "mic level". They often put out a consumer line level, so as to be compatible with the stereo line ins on remote recorders, not the "mic" input, which is for a dynamic.
If a connector is looking for a +4 line level (the output of most preamps), a -10 input will do exactly what you are saying- the signal will often be too weak to be usable, but will be present. Conversely, a +4 signal inputted to a -10 input jack will clip the receiving unit even at very low gain settings. A simple transformer can be used to change the one to the other. EBTECH LLS-2 (line level shifter) is a good cheap commercial example. It is, however, susceptible to RFI, although its self noise is not real bad. What this works out to in volts, I have no clue. If you know enough to build a preamp, you know more than I do. It's all voodoo to me, but I can usually match the components so they work.-Richie
 
Richard,

Thanks for the longer explanation. I think you and I are talking about the same thing from 2 different angles. I guess that a simple transformer could work but I'm unfamiliar with the model you site. Do you, by chance, have a link so I could check it out?

I a sense, a preamp and a transformer perform the same function. One is an active device, the preamp and the other, passive. If I remember correctly, they each have their good and bad points. One of the bad points is that with a transformer, you have losses. A bad point with peramps, obviously, is noise. I'll check it out further.

Thanks again, Steve

PS do you know how to post pictures on the forum? I'm going to find the faq page and see if I can figure it out.
 
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