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Author Topic: mic pre's on the cheap.  (Read 6827 times)
manning
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« on: March 11, 2010, 12:43:46 PM »

background...ive used mic pre's in the past
from expensive thru cheap stuff.
if ya got no money for mic pre's whaddya do ??
heres some ideas to consider.
1. some old cassette deks if you choose the right
one have pretty decent mic pre's.
such deks are throwaway these days.
get your aunts or uncles old dek n run tests hooking up a decent dynamic mic .
ie do actual recodings.
heres an example ...of a cass dek mic pre..
http://stashbox.org/653596/mumrap.mp3
2. theres lots of hype in mic pre's.
do you know you can actually build a decent low noise mic pre
out of low noise transistors that you can get 10 for a buk or two ??
lots of schematics on the net.
another good source for mic pre schematics are manufacturers
of op amps. go check out the sites of analog.com,
linear technology and maxim semiconductor.
you can build a nice pre out of low noise op amps.
(commercial mic pre's typically use transistors and/or tubes
and/or op amps.)

hope this helps someone.
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folderol
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« Reply #1 on: March 11, 2010, 04:47:23 PM »

Got to agree here with your last point. I've made loads of small amps over the years, and some of the modern OpAmps are so quiet, clean and stable it's hard to not make a decent preamp!

Personally I don't go for all this hype over different types of amp. Basically they all add some form of distortion - It just means some forms are quite nice. However if you start with the cleanest signal you can possibly get, you can always dirty it up later - can't go the other way though!
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If you have a poem, I have a tune, and we exchange these, we can both have a poem, a tune, and a song.
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manning
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« Reply #2 on: March 12, 2010, 12:09:35 AM »

examples of low noise op amps mate are.
op27/37
lt1028
lt1115
maxim equivalents or analog devices also.
maxim have a 627/637 op amp if i remember.
very rugged.
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Oren
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« Reply #3 on: March 13, 2010, 04:25:41 AM »

...heres some ideas to consider.
1. some old cassette deks if you choose the right
one have pretty decent mic pre's.
2. theres lots of hype in mic pre's.
do you know you can actually build a decent low noise mic pre
out of low noise transistors that you can get 10 for a buk or two ??
lots of schematics on the net.
another good source for mic pre schematics are manufacturers
of op amps. go check out the sites of analog.com,
linear technology and maxim semiconductor.
you can build a nice pre out of low noise op amps.
hope this helps someone.

You know it will! wOO
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manning
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Posts: 142


« Reply #4 on: March 13, 2010, 01:18:21 PM »

oren..
cheers mate.
i'll also share a likkle secret..(on the qt...ssssh..lol..)
some op amps that go into mic pre;s can be very expensive..above 10 buks each for example..for some top grade ones.
BUT..op amp manufacturers will send you free samples if your nice to them.
so on their web sites look for free samples offers.
another tip is dont get fooled by ultra low noise devices with
one nano volt root hertz noise figs..the theoretical limit.
i learnt this the hard way. i had a fancy schmancy op amp i was useing..
but the recorded sound was "clinical" versus a grungy transistor circuit i came up with useing higher noise transistors. for some reason it was a fluke.
i used some transistors that werent supposed to be used in audio circuits..
but they had a "sound mojo" i cant explain.
so if doin a mic pre yourself , in summary experiment with
stuff that isnt necessarily the lowest noise cos you might find some
new mojo. ie..dont be sold on low noise figures alone cos it might sound clinical.
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folderol
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« Reply #5 on: March 13, 2010, 02:35:12 PM »

Many moons ago (when I was still young and pretty) I used a BCY71 as the front-end transistor in a mag cartridge equaliser. It gave remarkable results - especially considering it was listed as a general purpose switching transistor Shocked

The secret was to run it at only 25 microamps.
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If you have a poem, I have a tune, and we exchange these, we can both have a poem, a tune, and a song.
- Will
manning
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Posts: 142


« Reply #6 on: March 14, 2010, 12:08:30 AM »

i'm not surprised.
one of my fav op amps for mic pre's is op37/37..
but the prob is the current draw is rather high.
(no good for battery power).
so ive been watching developments in micro power op amps.

the 27/37 like most op amps need a bipolar power supply.
which are a piglet to build.
so ive been experimenting with circuits n seeing if i can get something
working off a simple 9v dc geetar battery.
but would like to sub a micropower op amp instead of useing transistors.
n see where that leads me.
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