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Guitarfreak 20 January 2011

I'm currently using a PreSonus FireBox for an interface and I'd like to try my hand in building some basic outboard preamps for my dynamic mics. Opamps work fine, no need for tubes. I would like (but not necessary) one design that is relatively transparent and one that is more of a 'vintage' or coloring preamp. I'll probably tweak the circuits, add things, change things anyway, so I'm looking for a nice base for that.

I'm undecided as to whether or not I want phantom power, but I would only use it when taking DI recordings of guitar because I use phantom power to power my DI box. Thoughts? I've found a few simple designs, but like I said I'd like a recommendation because I don't know what designs are worth the time and money put in or not.

Really just considering if it's worth it at this point.

Comments

dvdhawk Thu, 01/20/2011 - 20:42

When I'm done throwing money in the hole next to the house, I'm going to have a shot at a few of these guys from Seventh Circle:

DIY Mic Preamp Kits - Seventh Circle Audio

They seem to have a nice variety of faithful vintage recreations. Everything I've read and heard by users has been positive.
Op-amps, transformers, everything you need in a kit, circuit boards - solder 'em up. It seems like a good place to start to me.

Link555 Wed, 01/26/2011 - 10:34

Sure email me at info'at'steller-studios.com

just so we are clear this is not a kit, there is no parts and no PCB, just a schematic.

However I do I have a few unpopulated PCB's left if you want to buy one.
I have no assembly instructions for this pre.

and I have plans on making this into a kit.

This is not for a weekend soldering binge....:)

That said with a decent amount of time spent studying the schematic, this is very do-able. Hell I did it 3 times now ;)

I know have 9 Lucid pres in my racks, and I am very happy with them. Great on Drums, acoustic Guitar, cello, bass, and vocals.

RemyRAD Sun, 02/06/2011 - 12:31

One of the easiest ways to create a DIY preamp, is to just take a lesson from some of those vintage consoles that cut lots of hits. For instance, inside the original Auditronics 501, you'd find a microphone transformer. That was followed by a LM 709, later a Signetics 5534 IC chip op amp. Their original input transformer was their own house brand later replaced by the Dean Jensen 110 series microphone transformer with a 10:1 windings ratio. Then there was a couple of output transistors that was used to buffer the output of the IC chip so as to be able to provide greater current drive. The SSL 4000 was virtually identical. The later Neve consoles utilized the same 5534 chip with output buffer transistors, utilizing their St. Ives windings input transformers and their famous Marinair output transformers. The API 312 also utilized the same microphone input transformer by Dean Jensen which was previously something else just like the Auditronics had, something else. So there is that vintage sound and it's largely dependent upon Transformers as opposed to transistors or chips employed.

If you don't want the classic vintage sound, don't go for a DIY microphone preamp with any kind of transformer. And you'll get some other kind of generic sound. If you like generic sound, purchase a Behringer or Mackie and don't waste your time building your own microphone preamp.

My preamps are as classic as I am, old-school.
Mx. Remy Ann David

So what have we realized here about

4mc2 Sun, 02/06/2011 - 16:20

Transparency

Here , it's for the most fidelity that he can !

My ear is only judge !

For me, for the more transparency sound , the circuit design must have the less transistor or tube ....

With Monteith & Flowers design , if you like to have vintage sound ( most the time tubelike sound ) you can put a transformer for coupling ( not capacitor ) .... it's that I make

Build this circuit and listen to ! ...... and you will never love the opamp !

I am a french canadian .... sorry for my not perfect english.

RemyRAD Mon, 02/07/2011 - 23:37

I utilized the Dean Jensen 990 as the output amplifier, in my custom API on-air console I built for NBC radio. Originally I had put in the 325 cards I had a couple of those 990s lying around the shop. It's definitely a sweet sounding preamp, especially when you use the 6:1 ratio winding microphone transformer, can't remember that part either? One thing you should know John Hardy made a Jensen 990 module in the same form factor as an API 2520. Only problem is, it is not plug-and-play compatible on any API card without adding a few external extra components you must add to the circuit board. So there is really no effective way to be able to just switch your op amp's back-and-forth. For instance, if you were to find an API 312 card or 2, you couldn't just swap out the 2520 with John Hardy's pin compatible 990/2520. Or, whatever his model number is, I can't remember?

So maybe just for fun and giggles, you might consider the number of microphone input transformers available, obtain a few & put them into the same operational amplifier. You'll hear a distinct character difference from each. With some, a clarity & depth, will be realized, that you'll never get with anything transformer less, transformer lite, transformer free, 0 calorie transformer. You may get sterility, neutrality, metallized, homogenized & perfectly lifeless like sound, if that's what you're looking for? Remember, what's old is new again. A perfect example would be ribbon microphone technology. They all but disappeared a few years ago. I've always been a big proponent because I was taught by a master. Now they are the hottest thing. So you are here asking and we are advising in response to what you are requesting. You obviously already know what you don't want and we have provided you with an alignment, free of charge I might add. So? Whadaya' think?

Thinking is overrated. Listening is precious.
Mx. Remy Ann David

JWHardy Tue, 02/08/2011 - 00:11

One thing you should know John [="http://www.johnhardyco.com/"]Hardy[/]="http://www.johnhard…"]Hardy[/] made a Jensen 990 module in the same form factor as an API 2520. Only problem is, it is not plug-and-play compatible on any API card without adding a few external extra components you must add to the circuit board. So there is really no effective way to be able to just switch your op amp's back-and-forth. For instance, if you were to find an API 312 card or 2, you couldn't just swap out the 2520 with John Hardy's pin compatible 990/2520.

Yes and no. API circuits are well designed in terms of basic stability, so installing a 990C in place of a 2520 will at least be stable.

People have installed 990 op-amps in summing circuits of API consoles and have achieved significantly lower noise and better sound quality. No other changes required. Just a swap of op-amps.

The 990 can be used in an API mic preamp, and it should do very well, but it might not be as quiet because the API preamps use input transformers with a 1:8 or 1:10 turns ratio, compared to the 1:2 ratio of the Jensen JT-16-B that is the optimum transformer to use with the 990. The 990 is optimized for low source impedances.

There are always things that can be done to tweak a circuit when using the 990 in place of a 2520 (or other op-amp). There are things that can be done to tweak the original API circuits even with no change of op-amp. It is always a good idea to study circuits to see how stable they are in terms of fundamental design.

There was a custom variation of the API 550 EQ that Sunset Sound used in a custom console that they built in the mid 1980s or so. This EQ had a few "input bias current compensation" components added to compensate for the higher input bias current of the 990 compared to the 2520. This apparently reduced noises when one or more of the switches were adjusted. There were at least a couple hundred 990 op-amps in that console.

Thank you.

John Hardy
The John Hardy Co.
[[url=http://="http://www.johnhard…"]The John Hardy Co. Home[/]="http://www.johnhard…"]The John Hardy Co. Home[/]

RemyRAD Tue, 02/08/2011 - 01:15

Hi John! Wow! I forgot you were here!

But as I remember that's not what you told me at one of the AES shows years ago? Maybe as you have indicated above, you indicated that it was usable that way, without modifications but not optimal? I don't recall. But I wasn't too far off. There are obviously numerous more informed and intelligent tweaks that we may have been talking about? It was back around the time when my friend Paul Wolff had first taken over API from Datatronix and I was working for NBC. You there for my rubber ice cream joke??

Okay, does everybody want to hear the Remy story about the rubber ice cream at the AES??

OK OK, simmer down...
So, I came back from the beach with some of those really cool rubber souvenirs. You know, fake barf, fake dog Doo Doo, fake spilled beer, sushi & chocolate covered vanilla ice cream on a stick. Well that ice cream looked mighty realistic. So I thought it would be fun to take to an AES show? I asked my friend Paul Wolff at that time, the owner of API, if I could put my fake ice cream on his console? I put it there and walked away.

When I returned, the ice cream was gone. Paul had put it away. He told me that a lot of people got very upset over the ice cream melting into his faders. So... I take my ice cream over to the SSL pavilion and place the ice cream on the faders of their most costly show centerpiece. One of the SSL guys is sitting at the desk talking to somebody else that doesn't see me. To which as the SSL guy begins to turn my way, I asked him..." So these faders are easily cleaned?" His response was that of a jack rabbit being surprised by a hungry wolf. I was quickly escorted and ejected from the show! It was only rubber! Thankfully, it was the end of the show and that was my encore number. Yeah, number zero.

I always wanted to get a pair of fake hearing aids
Mx. Remy Ann David

JWHardy Tue, 02/08/2011 - 01:37

But as I remember that's not what you told me at one of the AES shows years ago?

To quote from Casablanca: "That's so long ago I don't remember."

You would have to give me the context and specifics of the conversation from back then, which was something like 20 years ago?

Maybe as you have indicated above, you indicated that it was usable that way, without modifications but not optimal?

It depends on how "optimal" you want to go. The summing amp application that I mentioned is a good example. Reportedly, a direct swap of a 990 for a 2520 provided a big improvement in the sound of the stereo mix-bus. The console was so much quieter that they thought at first that it was broken because there was no residual noise when they turned it back on after the modification. But perhaps some additional filter capacitance near the 990 would have been even better. I've never seen the schematic for that console, so I can't say what other tweaks could be done. A Jensen output transformer with the 80% nickel core would clean things up, if that is what someone wants to do. If they like the 97% iron core of the API output transformer, fine.

There are some circuits where a 990 would not be appropriate. There are some circuits that are so poorly designed that a 990 would oscillate if used in place of the stock op-amp. So it all depends on what you are trying to do and what the original circuit was trying to do.

John Hardy

Guitarfreak Tue, 02/08/2011 - 08:53

RemyRAD, post: 363755 wrote: I utilized the Dean Jensen 990 as the output amplifier, in my custom API on-air console I built for NBC radio. Originally I had put in the 325 cards I had a couple of those 990s lying around the shop. It's definitely a sweet sounding preamp, especially when you use the 6:1 ratio winding microphone transformer, can't remember that part either? One thing you should know John Hardy made a Jensen 990 module in the same form factor as an API 2520. Only problem is, it is not plug-and-play compatible on any API card without adding a few external extra components you must add to the circuit board. So there is really no effective way to be able to just switch your op amp's back-and-forth. For instance, if you were to find an API 312 card or 2, you couldn't just swap out the 2520 with John Hardy's pin compatible 990/2520. Or, whatever his model number is, I can't remember?

So maybe just for fun and giggles, you might consider the number of microphone input transformers available, obtain a few & put them into the same operational amplifier. You'll hear a distinct character difference from each. With some, a clarity & depth, will be realized, that you'll never get with anything transformer less, transformer lite, transformer free, 0 calorie transformer. You may get sterility, neutrality, metallized, homogenized & perfectly lifeless like sound, if that's what you're looking for? Remember, what's old is new again. A perfect example would be ribbon microphone technology. They all but disappeared a few years ago. I've always been a big proponent because I was taught by a master. Now they are the hottest thing. So you are here asking and we are advising in response to what you are requesting. You obviously already know what you don't want and we have provided you with an alignment, free of charge I might add. So? Whadaya' think?

Thinking is overrated. Listening is precious.
Mx. Remy Ann David

I'm listening. I don't necessarily know what I want, so much as knowing what I don't want. I find that the PreSonus pres make everything sound mushy. I just want something that's not terribly difficult to build, not terribly expensive, but better than what I'm using now. From what you are saying, I may not get into the 'better' territory until a transformer is involved. I'll be stuck in the 'different' category instead. After seeing so many recommendations though, I am starting to doubt my own abilities. I have built and modified effects pedals with relative ease, but I really don't know the first thing about studio level audio, or how to transfer my current knowledge to it. But I hope to learn.

fiddler59 Tue, 02/08/2011 - 13:02

Not to keep harping, but here is a transformer in and out pre that you can build on the cheap that sounds great.....I can vouch for it because I have built the 2 channel version of this pre. Scott will help you through if you need it to make sure you have a working unit. The trannies are high nickel. It can go from pristine clean to pushed "fet tranny mojo" depending on how you use it. The build documentation is great as is the online tech support. You can case this pre in a breaker box from home depot for $7.

[[url=http://[/URL]="http://www.hamptone…"]Hamptone HJFP1 Single Channel Preamp[/]="http://www.hamptone…"]Hamptone HJFP1 Single Channel Preamp[/]

Once you hear the difference you will be spoiled !! While your at it check out the other pres on his site.

DB

RemyRAD Tue, 02/08/2011 - 18:25

Let me ask you a simple question. Would you swap soul for specifications? If you can answer yes to that, you want a transformer less microphone preamp. If you answer no to that question, you want a transformer version. Perhaps the question should have been, can you get mother's milk from your father? (okay, so the answer to that one is yes under certain remarkable extreme conditions which don't normally happen in real life but do happen occasionally)

Some of us love Transformers because we love our mothers.
Mx. Remy Ann David

Link555 Wed, 02/09/2011 - 06:18

wow thats the craziest "REMY'd" comment I have read yet. Yes RemyRAD you are now an adjective. I really enjoyed that one.

I think it comes down to the design, a solid state input can be transparent and the pre amp section can be coloured. A 80% nickel Jensen XFMR is pretty darn transparent compared to the iron cores of days gone by. IT really just depends on the how well the design was executed.

RemyRAD Wed, 02/09/2011 - 22:00

I think the point I'm really trying to make is that, we are all artists. None of us paint with a single color and neither should you (you meaning everybody). This requires a wide variety of equipment selections to obtain the proper color for pleasing productions.

Neutrality, transparency, extended high-frequency response does not necessarily denote a recording of the proper color but rather, a recording of a specific color. Of course, if you are looking for a specific color, that is what you should purchase if that is the only color you desire.

I like rainbows don't you?
Mx. Remy Ann David

maxk Mon, 02/28/2011 - 23:26

As [[url=http://[/URL]="http://recording.or…"]dvdhawk[/]="http://recording.or…"]dvdhawk[/] said, seventh circle audio preamps are great... I built their Neve 1073 clone a month or so ago and just finished an API 312 clone this weekend. I'm also using a presonus as an a/d converter and the difference between the pre's on my presonus and the SCA rack is obscene. I am angry at myself for not having built these years ago. My only problem with the seventh circle stuff is once you get one, you will want more.

Guitarfreak Tue, 03/01/2011 - 11:36

maxk, post: 365357 wrote: As [[url=http://[/URL]="http://recording.or…"]dvdhawk[/]="http://recording.or…"]dvdhawk[/] said, seventh circle audio preamps are great... I built their Neve 1073 clone a month or so ago and just finished an API 312 clone this weekend. I'm also using a presonus as an a/d converter and the difference between the pre's on my presonus and the SCA rack is obscene. I am angry at myself for not having built these years ago. My only problem with the seventh circle stuff is once you get one, you will want more.

Excellent input! Which PreSonus interface? Did you buy the chassis, or build/buy one yourself?

maxk Tue, 03/01/2011 - 15:32

I have a Digimax FS that i'm using with a 003 rack running pro tools. I have also used those preamps with a fast track pro.

I did buy their chassis. It is a bit expensive but high quality. You also get a discount on your first pre if you buy the chassis/powersupply and preamp kit in the same order. They also sell a wiring harness to go between preamps in the rack for like $40 or something... I got one and kind of wish I built my own, but i'm not sure if you need the harness to get a discount on the kit. Either way, all of his stuff is high quality and I have yet to hear a bad word about any of his stuff. If you have soldering chops, its a good build.

Link555 Sun, 03/06/2011 - 20:37

Thanks guys.... sorry I have been super busy these last few weeks, my second daughter was born a month ago, so time and sleep is well.....a luxury.
My LA5 optical comp is on my desk at the moment gathering dust. I did fire it up and have one thing left to clean up in the sidechain circuit, then I will get her boxed up and give it a test run.

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