Anyone Designed and Built their own Pre ?????

[MixingStick]

I am just curious to see if anyone here has designed and built their own pre-amp (or EQ, Compressor/ Amp/ or hell even a DI for that matter)? I have been thinking about it for a while now and have some pretty good ideas. I have a B.S, In Electrical Engineering and a nice home lab (Tektronix TDS1002 60MHZ digital scope, nice psu, sig gen and most of the other neccessary tools)

I was hoping to get any insight on approaches/failures/successes/components including chassis material, grounding techniques, tube or solid state (I will be going SS), transformers, and any inspiration (a nice way of saying copying someone else design ;) )

Thanks

Don

BTW: My goal would of course be to build the most high end (read best sounding) pre possible....price no object

[Sonicvalley]

i think tapeop did a whole thing about building your own preamp. check out their website or backissues http://www.tapeop.com/

[DeeDrive]

I have been thinking about tackling an API 312 style pre for a while now. The schematics are all over the web, it's a pretty simple op-amp circuit with an input and output tranny. Seems like a good place to start, since op amp circuits are pretty simple. You can't get the 2520 amps anymore, but there are various other amps out there, John Hardy 990, Forrsell makes one, so I'll probably end up using one of those. The John Hardy amps are around $45 bucks I think.

I'm not sure about trying a discrete transistor or tube design yet. Correct me if I'm wrong, but you would most likely need a curve tracer to know how to bias the tubes, am I right? And I definitely don't have a curve tracer lying around.

Let us know what you end up building, I'm very interested in this topic right now.

[Shandy]

I haven't tackled anything beyond a few distortion pedals, but I think an 1176 might be in the cards soon enough. You should definitely check out the Prodigy forums, and there's tons of great info at Paia too.

With your background and some decent tools, it looks like you're off to a pretty solid start. Let us know how you do...

[TonyBelmont]

I built an API style pre a couple of years ago which has morphed into a summing mixer project that is yet unfinished.

[MixingStick]

ttt. Obviously more "Engineers" than actual ENGINEERS (BSEE'S) around here...Anyone who designs stuff??

[manning1]

Mstick....
theres an example on slutz (search my back posts for TEST.mp3)...of a little mic pre ive built many times for myself n' friends..out of 10 buks of parts. its very low noise/clean.
if you want the schem...shout. its dam simple.
the KEY is the high quality transistor i use....not the normal 10 for a buck transistor junk.
...a couple of my motagator songs have used it as well
frankly i'm not sure its worth building pre's these days....except i do it for fun.
(lol.....me....Bsc Hons....not the other one.....lol.)
also check out prodigy-pro/forum
loads of exceptional diy mic pre types there.
try the g9 mic pre diy on prodigy...sometime.

[DeeDrive]

Originally Posted by MixingStick

ttt. Obviously more "Engineers" than actual ENGINEERS (BSEE'S) around here...Anyone who designs stuff??

You're right, we're all far too stupid to be of any help. You should probably consult the stack of electronics books sitting in your attic for help. Good luck.

[stellar]

I am just getting into this but my first inclination would be that if sound quality is the goal and money is no object the maybe you should just go buy something.

Although I would love to see that very simple transistor schematic.

[MixingStick]

Originally Posted by DeeDrive

You're right, we're all far too stupid to be of any help. You should probably consult the stack of electronics books sitting in your attic for help. Good luck.

Thats not exactly what I was trying to say......not trying to rip on anyone. I do think the term engineer gets thrown around pretty carelessly nowdays. I spent 6 years at a university studying calculus, physics, chemistry, electronics and engineering and still can not LEGALLY consult as a professional engineer. That takes another 4 years of practice under a P.E. and then passing a 16 hour exam.

It is funny when a 16 year old kid with a mackie board, mixing sound for his friends band calls himself an engineer.

[Geoff_T]

Originally Posted by MixingStick

ttt. Obviously more "Engineers" than actual ENGINEERS (BSEE'S) around here...Anyone who designs stuff??

Hi

You can make a really nice sounding pre out of a 5534, a piece of strip board, a couple of 9 volt batteries, a 10K pot you can get from Radio Shack and a few resistors and blocking caps.

And teach yourself how an op amp works at the same time!

[manning1]

stellar...
heres a thread with the schematic of the transistor mic pre attached.(gif)
read the notes in the thread.
hope this helps...
http://www.cockos.com/forum/showthre...ght=transistor
ps..theres a trick also...if you want more gain....pass the output of the schematic to a outboard comp/lim....i use an old ashley that sounds pretty decent or a line mixer ....then onto sound card line input.
its about a one hour build.
note....ive built a hundred different schems diy from simple to exotic....and this one holds its own very well considering minimum parts count.

[MixingStick]

Thanks guys.....good info

[manning1]

geoff....
from my own crazy experiments with 5534's and other op amps,
(non battery applications) actually i preferred the op27 and 37 op amps over the
5534........but ive never been able to explain why.

the tracks i recorded with OP's just seemed much nicer.
its very subjective of course. the only word i can think of is the OP's had more character. i also found differences tween different grades of 5534 as to the result i obtained.
but the negative is current draw with OP. thus its a pity they cant be used
in battery applications .

mixing stick....if you ever want to get a tad adventurous ..raytheon used to have a op amps book showing a design incorporating a jensen transformer front end into a op37 for a mic pre thats rather nice.

[Geoff_T]

Originally Posted by manning1

geoff....
from my own crazy experiments with 5534's and other op amps,
(non battery applications) actually i preferred the op27 and 37 op amps over the
5534........but ive never been able to explain why.

the tracks i recorded with OP's just seemed much nicer.
its very subjective of course. the only word i can think of is the OP's had more character. i also found differences tween different grades of 5534 as to the result i obtained.
but the negative is current draw with OP. thus its a pity they cant be used
in battery applications .

mixing stick....if you ever want to get a tad adventurous ..raytheon used to have a op amps book showing a design incorporating a jensen transformer front end into a op37 for a mic pre thats rather nice.

Hi

Could be... the 5534 is an update on a 30 year old design... there's plenty of newer IC's but it should always be remembered that IC's aren't strictly interchangeable as they all use specific compensation tricks. When Neve introduced the Mullard TDA1034 into their consoles, they had a huge A0 size pert chart with questions and yes/no directors that listed all the tricks you had to do for a specific application.

Of course, if you don't have a 'scope or spectrum analyser that can view oscillations in the 100MHz region your only clue would be that it feels a bit warm and the nearby radio is whistling!

[gregl]

I've designed and built many mic pres for fun (and years ago some of them went into some studios).
I don't have any magical words of wisdom to impart. The DIY forum mentioned above would be a great starting point. Don't use cheap parts. Use you ears and don't let other peoples biases sway you until you've heard the results for yourself.
I've been an EE for a long time and while I think that would help immensly, nothing does it like getting out there and just starting to try out some ideas.
I've done a lot of tube stuff but you can do some pretty OK stuff with IC's too.
There are some great articles on mic preamps and mixers in back issues of the Audio Amatuer (now called Audio Xpress I believe) and Glass Audio. Also Electronics and Wireless World.
Walt Jung at Analog devices has published a lot of info on the IC stuff. As for discrete stuff like Neve, there is info all over the web. Have fun!

[manning1]

geoff T...
as always i bow to your intensive experience compared to myself with op amps etc...and am always up for learning new tricks.
the last two years i had been on a quest to find an op amp with a low current draw in the microamps region....ie..suitable for battery applications driven by a single 9 volt, but gave up (yeah...i know geoff...us englishmen should never give up.....lol...). i always encountered some or other problem.
or they didnt sound good. ie....single supply. thus i stuck with my simple mic pre transistor circuit....which has served me well and gives me v clean tracks.
without needing fancy bipolar power supplies.

ive even talked on occasion to op amp engineers and suggested (heresy !!!!!)...
that they generate the bipolar needs of the op amp within the op amp circuit itself...but have been told not doable.

the problem with the 5534 op amp dual 9v approach is one goes through batteries rather fast.
in contrast a TLO61 has low current draw, and some other op amps , but they just dont sound good.
you could make a small fortune geoff if you made/fabbed an op amp with the following specs...
low noise
sounds great
no bipolar supply needed
microamp current draw for battery apps etc etc.
cos i havent found one.

i'm retired now.....(wifey retires in 4 wks...lol).....and given even a yamaha mg mixer at 90 buks sounds pretty decent i question how much longer i should pursue the diy mic pre madness except for fun.....lol.
ps...geoff...off topic was in uk in june....in folkestone visiting my 87 yr old mum.
if you ever fancy a pint or two....i would cherish learning more from you. peace.

[squeegybug]

Originally Posted by manning1

the last two years i had been on a quest to find an op amp with a low current draw in the microamps region....ie..suitable for battery applications driven by a single 9 volt, but gave up

the problem with the 5534 op amp dual 9v approach is one goes through batteries rather fast.

Why couldn't you use a simple 9v transformer PS?

Steve

[Jim Williams]

Originally Posted by manning1

geoff T...
as always i bow to your intensive experience compared to myself with op amps etc...and am always up for learning new tricks.
the last two years i had been on a quest to find an op amp with a low current draw in the microamps region....ie..suitable for battery applications driven by a single 9 volt, but gave up (yeah...i know geoff...us englishmen should never give up.....lol...). i always encountered some or other problem.
or they didnt sound good. ie....single supply. thus i stuck with my simple mic pre transistor circuit....which has served me well and gives me v clean tracks.
without needing fancy bipolar power supplies.

ive even talked on occasion to op amp engineers and suggested (heresy !!!!!)...
that they generate the bipolar needs of the op amp within the op amp circuit itself...but have been told not doable.

the problem with the 5534 op amp dual 9v approach is one goes through batteries rather fast.
in contrast a TLO61 has low current draw, and some other op amps , but they just dont sound good.
you could make a small fortune geoff if you made/fabbed an op amp with the following specs...
low noise
sounds great
no bipolar supply needed
microamp current draw for battery apps etc etc.
cos i havent found one.

i'm retired now.....(wifey retires in 4 wks...lol).....and given even a yamaha mg mixer at 90 buks sounds pretty decent i question how much longer i should pursue the diy mic pre madness except for fun.....lol.
ps...geoff...off topic was in uk in june....in folkestone visiting my 57 yr old mum.
if you ever fancy a pint or two....i would cherish learning more from you. peace.

Any opamp will require either a bipolar psu or need to be biased at 1/2 the power supply. Plenty of tricks on how to do this in Cookbooks. Most use a couple of resistors to divide the voltage by 1/2 and present that to the non inverting input of the opamp. Blocking caps are then needed for all I/O's as 4.5 volts will be seen.

Now to your request: Linear Technology LT1351/2/3 for single, duals and a quad. S08 or DIP available. 260 ua supply current, about 10 nv/hz/sq noise, 200 v/us slew rate, able to drive capacitive loads, good output current, very low input bias current, almost like fet inputs. 3 mhz gain-bandwidth, easy to use, no instabilities. It will run very well on reduced power voltages, + - 4.5 volts is fine. Or, use a pair of 9 v batteries in a biplolar config and get more headroom and battery life, which should be in months.

Combine with traditional transformers like the Jensen JT-115KE, or get clever and use a pair of low noise bipolar transistors in front. That way, opamp noise will be dominated by the transistor pair at higher gains and -129db EIN can be achieved.


Jim Williams
Audio Upgrades

[mus1k_freak]

i had an old balwin tube organ that i ripped apart and took the pre amp out of it and make it a mic pre, its got like 13 tubes and all the buttons on the front of the organ change the sound of the mic plugged into it, its pretty cool, only thing that sucks is its like 3 feet long, cant quite fit that in my rack haha

[Power Supply]

Originally Posted by manning1

Mstick....
theres an example on slutz (search my back posts for TEST.mp3)...of a little mic pre ive built many times for myself n' friends..out of 10 buks of parts. its very low noise/clean.
if you want the schem...shout. its dam simple.
the KEY is the high quality transistor i use....not the normal 10 for a buck transistor junk.
...a couple of my motagator songs have used it as well
frankly i'm not sure its worth building pre's these days....except i do it for fun.
(lol.....me....Bsc Hons....not the other one.....lol.)
also check out prodigy-pro/forum
loads of exceptional diy mic pre types there.
try the g9 mic pre diy on prodigy...sometime.

I remember when you first posted about that cheap pre
a while back. I've always wanted to try it out.
I like the simplicity.

[manning1]

jim W....
as always its a great pleasure reading your insights/posts.
just like geoff.

you know what i think jim...??
i think there is a huge hole in the market at the bottom end for project studios.

and two great folks like yourself and geoff T should get together over a few beers
and design and sell a 19 inch rack unit for 200 buks with 6 mic pre's in (8 ??.........lol/1 wish...)that
slay the market and folks lust after and wipe all us stupid diy'ers out ........lol lol.

i reckon youd make a slew of pounds/dollars.

[Minion]

Well I have only been doing audio electronics for a few months and have a fairly limited Knowledge but still more than most poeple with 3 months electronics experience and with only the Internet for a resource...

I have built a few project Like some Simple Phantom Powered and Batterey Powered Condenser mics and a 2 Channel Green Pre and a few Power supplies but I have only been doing this for a few months so there is only so much One can learn or do in such a small period of Time.....

about a Month ago after I finnished my 2 channel Green pre I though I would use my limited knowlege to try to design a Mic preamp useing Parts I had laying arround and Info from Data sheets...I spent about a week fidleing with a Simple Clean Mic preamp design and was able to test my First prototype yesterday and I was very Surprised that it actually made some Sound and was even more Surprised that it actually sounded pretty damn Good.....

My design is an all Solid State design with no input/output Transformers and it uses an INA103 Instrument amp IC and a OPA134 for controlling DC Offset and a NE5532 for createing a Ballanced output, It has a 20db Pad with Phantom power CMR adjustment and about 60db of Gain...Even at the Highest gain there is very Little Distortion and when properly grounded it makes little to no Hum at all even with the Gain Cranked up......

What is great about the design For me anyways is that it is very Small and very Simple so It is Cheap to make, It isn"t what I would Call a "High End" pre but that isn"t what I was aiming for, I was aiming for something that was simple, Cheap to Build (Under $30 per Channel) and Small enough so i could Fit 10 or 12 Channels in a 2U Rack Case and had a Clean ,Transparent & Un-Colored sound (Simular to the DMP3).....

There are of cource some Improvements I am going to implement before i am finnished with the design Like I am going to add some Ferrites for EMI and RF Supression and adjust some of the Resistor and Cap Values and Maybe add a Optional Post Gain stage to add some Color Maybe useing Fet Transistors or even maybe some Sub Mini Tubes......

Once I have Implememnted the Changes and have thouroughly tested the Curcuit I might start offering them for sale as Kits and I"ll definately Post the Schematic and some Sound Samples once I have implemented and tested the Changes.....


Cheers

[Geoff_T]

Originally Posted by Minion

Well I have only been doing audio electronics for a few months and have a fairly limited Knowledge but still more than most poeple with 3 months electronics experience and with only the Internet for a resource...

I have built a few project Like some Simple Phantom Powered and Batterey Powered Condenser mics and a 2 Channel Green Pre and a few Power supplies but I have only been doing this for a few months so there is only so much One can learn or do in such a small period of Time.....

about a Month ago after I finnished my 2 channel Green pre I though I would use my limited knowlege to try to design a Mic preamp useing Parts I had laying arround and Info from Data sheets...I spent about a week fidleing with a Simple Clean Mic preamp design and was able to test my First prototype yesterday and I was very Surprised that it actually made some Sound and was even more Surprised that it actually sounded pretty damn Good.....

My design is an all Solid State design with no input/output Transformers and it uses an INA103 Instrument amp IC and a OPA134 for controlling DC Offset and a NE5532 for createing a Ballanced output, It has a 20db Pad with Phantom power CMR adjustment and about 60db of Gain...Even at the Highest gain there is very Little Distortion and when properly grounded it makes little to no Hum at all even with the Gain Cranked up......

What is great about the design For me anyways is that it is very Small and very Simple so It is Cheap to make, It isn"t what I would Call a "High End" pre but that isn"t what I was aiming for, I was aiming for something that was simple, Cheap to Build (Under $30 per Channel) and Small enough so i could Fit 10 or 12 Channels in a 2U Rack Case and had a Clean ,Transparent & Un-Colored sound (Simular to the DMP3).....

There are of cource some Improvements I am going to implement before i am finnished with the design Like I am going to add some Ferrites for EMI and RF Supression and adjust some of the Resistor and Cap Values and Maybe add a Optional Post Gain stage to add some Color Maybe useing Fet Transistors or even maybe some Sub Mini Tubes......

Once I have Implememnted the Changes and have thouroughly tested the Curcuit I might start offering them for sale as Kits and I"ll definately Post the Schematic and some Sound Samples once I have implemented and tested the Changes.....


Cheers

Hi

Sounds good but what do you use for test gear? Do you have a scope? Decent oscillator, etc.?

[stellar]

Geoff,

this is an honest question. I have been reading online and this is some of the stuff that is hard to come by so I really value these kinds of discussions! ok, my question is, what is the big deal if the opamp is oscillating in the 100 MHz region? who cares? No recording device will be able to record that high and even if it could you could simply take the safe route and ground it with a cap....so I don't get it?

[Minion]

Originally Posted by Geoff_T

Hi

Sounds good but what do you use for test gear? Do you have a scope? Decent oscillator, etc.?

My Test Gear as Of Now are my ears and a DMM but I will be investing in a Scope at some point..(Maybe I can Build one??? But I might need a scope for that...LOL)

I mostly right now use the Data sheets for referance which I know aren"t allways the most accurate but what else can a Newbie like me do, I also Borrow Part of other Proven designs and Implement them in mine as I don"t have the Knowlege right now to come up with something Unique and creative on my own??



Cheers

[MixingStick]

Thanks for all the replies guys I am learning alot here.

Keep em coming