Guest bassman7755 Posted December 16, 2012 Share Posted December 16, 2012 I would like to make a simple 2 channel mic to line box so that I can add individual outboard effects to two separate mics before they go into a PA mixer (which lacks channel inserts and the effects processors are line level hence my problem). Maplin have a nice op amp based stereo preamp circuit for about a fiver which I presume does high impedance mic level to line level. However dynamic mics AFAIK generally have an output impedance of 600 ohm so my question is basically: what is the simplest possible input circuit I can use ? if I'm happy to operate the circuit in "unbalanced" mode (since I don't need studio quality noise rejection ...) is it just a case of slapping a 600 ohm resistor in parallel with (very high impedence) op amp input ?. Quote Link to comment Share on other sites More sharing options...
Guest bassman7755 Posted December 16, 2012 Share Posted December 16, 2012 Hmmm I think I may have answered my own question, it seems the circuit I was looking at has a 1k ohm input impedance so that would presumably make it compatible with dynamic mics out-of-the-box so to speak. Quote Link to comment Share on other sites More sharing options...
rmorris Posted December 17, 2012 Share Posted December 17, 2012 [quote name='bassman7755' timestamp='1355676622' post='1901243'] Hmmm I think I may have answered my own question, it seems the circuit I was looking at has a 1k ohm input impedance so that would presumably make it compatible with dynamic mics out-of-the-box so to speak. [/quote] I haven't seen the Maplin mic to line box but from those impedance specs it should work fine. Going into a high impedance isn't really a problem in any case whereas too low an input impedance will seriously degrade the sound. It can be more tricky to engineer Hi-Z inputs with low noise / interference though. In fact 1K0 input impedance sounds a bit low. Typical source impedance for a dynamic mic is in the region of 200 ohm and inputs are generally set to have an input impedance of 10x the source impedance so that gives 2K0. But it could be that it's 1K0 per balanced leg giving total 2K0. Anyway it should work fine. Let us know on here how it works out. Quote Link to comment Share on other sites More sharing options...
51m0n Posted December 17, 2012 Share Posted December 17, 2012 You defintely definitely need to stay balanced here. live is a world of hurt regarding noise, especially considering the long cable runs with dollops of all sorts of unknown leaky wiring and crud flying around. A studio is a hugely cleaner environment to work in as often as not IME... Quote Link to comment Share on other sites More sharing options...
Subthumper Posted December 19, 2012 Share Posted December 19, 2012 I like building my own gear too but why not just get a small 4 channel mixer? It will probably work out cheaper and more effective than your own. I think some of the B**********r ones start at about thirty quid. There's quite a good selection in the CPC catalogue too. Cheers Just Quote Link to comment Share on other sites More sharing options...
Seb_C Posted December 19, 2012 Share Posted December 19, 2012 Agree with Subthumper - at this end of the market you cannot and will not beat the likes of Behringer and far eastern mass production for cost or performance. If you DIY, do it becuase you really enjoy DIY. You won't save money and make anything good enough or reliable enough for gigging at the same time. Quote Link to comment Share on other sites More sharing options...
51m0n Posted December 19, 2012 Share Posted December 19, 2012 Errr, no you can definintely DIY mic pres that far outsrips the quality and reliability iof anything with a Behringer sticker on it. It just wont be cheaper I'm afraid:- http://www.seventhcircleaudio.com http://www.soundskulptor.com/ http://www.fivefishstudios.com http://www.hamptone.com/index_old.html All of which will completely blow away said behringer unit. And hurt your wallet a lot more I'm afraid Quote Link to comment Share on other sites More sharing options...
paul_5 Posted December 19, 2012 Share Posted December 19, 2012 [quote name='Seb_C' timestamp='1355911538' post='1904215'] If you DIY, do it becuase you really enjoy DIY. You won't save money and make anything good enough or reliable enough for gigging at the same time. [/quote] Erm, I beg to differ - Both of my basses are DIY and half of my pedalboard is DIY; certainly reliable and sounds great. Much cheaper than buying equivalent specced kit. Quote Link to comment Share on other sites More sharing options...
Phil Starr Posted December 19, 2012 Share Posted December 19, 2012 By the time you have bought two of these kits + a virtual earth mixing module + case+ knobs, sockets etc you aren't going to get away with much less than £30 for your 2 channel mono mixer. Built this way the Behringer would work and probably sound better though if you DIY'd you'd be a lot more knowledgeable. Other brands are also available, if you just want something cheap then http://www.bluearan.co.uk/index.php?id=EVNG105AA&browsemode=category is cheap as chips. Those other kits would cost a lot more and you'd get better quality and if you spend enough you eventually might get top quality a bit cheaper than buying ready made, depending upon how much you've learned in the mean time. Sadly the days when DIY was a cheaper option are just about gone. Quote Link to comment Share on other sites More sharing options...
Monckyman Posted December 19, 2012 Share Posted December 19, 2012 Sub mixer is the better idea. More versatile. The best idea though, is to sell your inadequate P.A mixer amp, and get something that`s properly up to the job of mixing all sorts of inputs with inserts and aux sends. Quote Link to comment Share on other sites More sharing options...
51m0n Posted December 19, 2012 Share Posted December 19, 2012 [quote name='Phil Starr' timestamp='1355918759' post='1904391'] Those other kits would cost a lot more and you'd get better quality and if you spend enough you eventually might get top quality a bit cheaper than buying ready made, depending upon how much you've learned in the mean time. Sadly the days when DIY was a cheaper option are just about gone. [/quote] I know this is getting off topic here, but the seventh circle kits are considered about as good as it gets by very very very many people in the studio world, and better than the vast majority of mic pres available at any price. They are expensive, especuially by bassist terms, but very significantly cheaper than the original items they are based upon (about half price). Quote Link to comment Share on other sites More sharing options...
Guest bassman7755 Posted December 19, 2012 Share Posted December 19, 2012 (edited) [quote name='Monckyman' timestamp='1355919399' post='1904411'] Sub mixer is the better idea. More versatile. The best idea though, is to sell your inadequate P.A mixer amp, and get something that`s properly up to the job of mixing all sorts of inputs with inserts and aux sends. [/quote] Yeah I'm comming round to this, although it will be anoying to have to sell I mixer I bought only 2 weeks ago just so that I can buy an otherwise identical one with two extra sockets in it ... but hay ho. Edited December 19, 2012 by bassman7755 Quote Link to comment Share on other sites More sharing options...
Monckyman Posted December 19, 2012 Share Posted December 19, 2012 I know it`s a ballache,but if that`s what you end up doing, go for 4 or 6 extra inputs, so when you need that ipod/fx ret/drumpad/midi goldfish channel you can handle it without getting Si all het up about building pre-amps from scratch. Quote Link to comment Share on other sites More sharing options...
51m0n Posted December 19, 2012 Share Posted December 19, 2012 Yeah, definitely, I dont need to be getting het up about this, stop it at once And dont knock midi goldfish - its the future... Quote Link to comment Share on other sites More sharing options...
Seb_C Posted December 21, 2012 Share Posted December 21, 2012 [quote name='51m0n' timestamp='1355915847' post='1904309'] Errr, no you can definintely DIY mic pres that far outsrips the quality and reliability iof anything with a Behringer sticker on it. It just wont be cheaper I'm afraid:- [url="http://www.seventhcircleaudio.com"]http://www.seventhcircleaudio.com[/url] [url="http://www.soundskulptor.com/"]http://www.soundskulptor.com/[/url] [url="http://www.fivefishstudios.com"]http://www.fivefishstudios.com[/url] [url="http://www.hamptone.com/index_old.html"]http://www.hamptone.com/index_old.html[/url] All of which will completely blow away said behringer unit. And hurt your wallet a lot more I'm afraid [/quote] Read what I said carefully. "At this end of the market". OP is talking about a Maplin kit that costs "about a fiver". DIY mic pre for a fiver that is going to be good enough to be worthwhile and reliable enough to gig, with the prices you pay when you're buying ones and two of parts? No chance. It will be a waste of a fiver. I'm well aware of what can be built for sensible money. I'm well aware of the exceedingly high quality DIY out there. I built my main valve amp. I've designed and build effects pedals from scratch (no kits). Hell, I've built an analogue synthesiser. But for ultra cheap you cannot compete on price with the bottom end Chinese stuff. Quote Link to comment Share on other sites More sharing options...
pete.young Posted December 21, 2012 Share Posted December 21, 2012 (edited) You might want to crosspost this into the DIY sticky in the 'Effects' forum, the folks who post in there have a lot of useful advice. Edited December 21, 2012 by pete.young Quote Link to comment Share on other sites More sharing options...
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