[BUILD] Hairball Audio - Elements

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Echo North

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Elements is built on the classic single op amp, transformer coupled microphone preamplifier circuit found in many classic console designs.  A discrete op-amp in the standard 2520 provides variable gain, while the input and output transformers perform a wide range functions including circuit isolation, impedance matching, additional step up gain, and in some cases much of the tonal color.

This is a tried and true design that forms a simple but classic base for the Elements concept.  Sonically, the possibilities are endless.  The type of transformers, op amp, and capacitor selections have a drastic effect on the final sound. In addition to providing a base template for you to design your own mic pre, we’ve designed three unique mic pres that all have their own distinctive signature.

Offered in 500 series format, these pres will work in any standard 500 series rack and are a great first build for recordists familiar with basic soldering technique.

Features

Metalwork made in the USA:
A different color anodized aluminum faceplate according to which element kit you select.  Clam shell side panel enclosure made from two pieces of 20 gauge steel, zinc electroplated, and coated in trivalent chromate, for maximum noise rejection at low and high frequencies.

Elements PCB:
The Elements PCB has been custom designed by Eisen Audio (Brooklyn, NYC) and draws from their popular DIY500 products (now discontinued), which were the first do-it-yourself kits in 500 series format.

Each kit includes:
Gold contact pushbutton switches and a gold plated DI jack that won’t tarnish over time.  Standard potentiometers for gain and output from BI Tech’s P260 series.  We auditioned several conductive plastic potentiometers, and found that these perform exceptionally well in terms of construction longevity and end-of-track noise.  If you prefer stepped controls, we’ve worked with Eisen Audio and DIYRecordingEquipment.com to offer a simple and easy to install Grayhill switch and circuit that can be used in the gain and/or output position.

Transformers:
Our Gold, Copper, and Bronze Elements kits utilize high quality input and output transformers from Jensen, Cinemag, and Ed Anderson.

Op Amps:
We’ve commissioned two custom-designed discrete op amps in 2520 format: BA512 and Raindog, in addition to our Hairball JE-990 op amp.

DI:
The IC buffered DI is activated by relay when a instrument cable is inserted into the gold plated DI jack.  The on-board DI buffer is prior to the input transformer, meaning the DI utilizes the entire mic pre signal chain.  It’s a built-in complete DI box circuit.

Passives:
Elements complete kits feature only the best board-level passive components.  Hairball Audio worked with Jens Jungkurth of Eisen Audio, leaning on his years of rebuild and design work, to select parts for dependability and performance.  Jens’ years of working on classic recording boxes and consoles were invaluable for the capacitor selection and resistor trimming.

Welcome to the Elements series of Mic Pres!


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Schematic:
http://www.hairballaudio.com/elements/schematic.pdf

Build Guide:
http://www.hairballaudio.com/blog/d_assembly/elements-mic-pre-series/
 

emrr

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How are the output controls implemented?  Sounds like they are not the typical 600 ohm T's. 
 

Echo North

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emrr said:
How are the output controls implemented?  Sounds like they are not the typical 600 ohm T's.

Correct.  There is an class A/B output fader that uses a 10K lin pot (or optional Grayhill).

I'll post the schematic in the first post now.

Mike
 

Indecline

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Any update on the build guide for the Silver?

I think I have parts for at least a couple of pres!  8)
 

Echo North

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Indecline said:
Any update on the build guide for the Silver?

I think I have parts for at least a couple of pres!  8)

It'll be posted by the end of this week.

We'll have the schematic and recommended values for the other parts.

Thanks!

Mike
 

Unit7

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Hi Mike!
I ordered the Gold Element a while ago. As I could eventually go for 10+ of these I'm considering testing different capacitors to see how they'd affect the sound. Would you discourage this, or could you give some directions on which caps that would have the most impact?
Thanks!
Paul
 

LeeYoo

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Nice design.
Bit confused..
Why did you drop the DI's input impedance from the standard 1meg to 200k (R301).
Would't that kill the "tone" of a guitar.
Leo..
 

Echo North

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LeeYoo said:
Nice design.
Bit confused..
Why did you drop the DI's input impedance from the standard 1meg to 200k (R301).
Would't that kill the "tone" of a guitar.
Leo..

Typical DI input Z can range from 100K-several Meg.  The Jensen DI product is 100K IIRC.  We actually found this impedance to work best across a wide variety instruments.  Basically, we thought is sounded best there.

YMMV and of course and you can always put what sounds best for your ears and instrument.

Mike
 

Echo North

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Unit7 said:
Hi Mike!
I ordered the Gold Element a while ago. As I could eventually go for 10+ of these I'm considering testing different capacitors to see how they'd affect the sound. Would you discourage this, or could you give some directions on which caps that would have the most impact?
Thanks!
Paul

The gold actually has the least capacitors.  Many of the caps are omitted or shorted for the sake of keeping it as uncolored as possible. The caps that we needed we selected to be as transparent as possible.

Where there are multi-layer capacitors, they can be switched for polystyrene film or something like that but they add a ton of color.  I would leave the MLCC alone.

You could look at trying different caps for: C505/C601

They would have the most effect.  If you don't see any significant DC voltage at these caps, you could try a polarized cap like a United Chemi-con KZH series cap which may open it up a little.

Mike
 

Greenote

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Just got my copper kit and put it together last eve.

The output is very low unless the gain knob is pinned. Is the 20K rev. log the best choice pot here?
I haven't had much time to test yet perhaps I'll look at the solder joints on both pots.

Pretty smooth assembly thanks to an excellent build guide.  Kit was missing 2 transformer screws and a 20K resistor, but I had spares.

Note: C501 10uF/25V Kemet Tantalum is polarized. Hairball indicated + side is closest to edge connector.

 

Echo North

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Greenote said:
Just got my copper kit and put it together last eve.

The output is very low unless the gain knob is pinned. Is the 20K rev. log the best choice pot here?
I haven't had much time to test yet perhaps I'll look at the solder joints on both pots.

Pretty smooth assembly thanks to an excellent build guide.  Kit was missing 2 transformer screws and a 20K resistor, but I had spares.

Note: C501 10uF/25V Kemet Tantalum is polarized. Hairball indicated + side is closest to edge connector.

Hi,

Most likely it's working correctly.  Especially if you're using a dynamic and quiet source.  It's not the pot value (which needs to be that high), it's really the the limitations of a pot and single op-amp pre.  The gain math is very sensitive at max gain so you see a lot of change at the end of the pot.  It's one of the advantages to using the Grayhill option for the gain knob.  It is more classically stepped like a Lola. (4dBish per step).

Sorry about the transformer screws.  We messed that up.  We're sending those out tomorrow!

Thanks,

Mike
 

Greenote

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Okay, good to know, Might have to order the stepped jobs.
No worries on the screws, although you can pack em with the Bronze.
 

Indecline

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Mike, do you know if the CM-2511 and EA11148 need a zobel network? I checked the data sheets and didn't see any mention of them. EDIT: looking again, I think it's RLoad:150k for the CM-2511?

Also, what is the recommended part for U300?

Thanks!!
 

furn1979

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Apr 18, 2010
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Hi guys...

Just finished my first of two Golds.

After a first power-on, I believe I have a problem:
I am too getting extremely weak signal out of a SM58 with both pots cranked up... And the DI signal is so weak, I am barely getting a signal from my bass with passive pickups. With both pots cranked up I can get a "decent" level, but it is highly distorted and thin.

I am also measuring a slight DC offset.

Where should I start looking?

Thanks!
 

Echo North

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furn1979 said:
Hi guys...

Just finished my first of two Golds.

After a first power-on, I believe I have a problem:
I am too getting extremely weak signal out of a SM58 with both pots cranked up... And the DI signal is so weak, I am barely getting a signal from my bass with passive pickups. With both pots cranked up I can get a "decent" level, but it is highly distorted and thin.

I am also measuring a slight DC offset.

Where should I start looking?

Thanks!

If you have two, I'd start by switching out the op-amp to confirm that is working correct.  Most likely that is fine.

After that, I'd look for bi-polar caps inserted incorrectly then resistor values.  It you can get at them, check your supply rails and make sure one of them isn't tripping a fuse.

You could build the second and see if you have the same issue.

Report back when you go over the build,  we'll get it sorted.  Posting a PCB image here may help.

Mike
 

Echo North

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Indecline said:
Mike, do you know if the CM-2511 and EA11148 need a zobel network? I checked the data sheets and didn't see any mention of them. EDIT: looking again, I think it's RLoad:150k for the CM-2511?

Also, what is the recommended part for U300?

Thanks!!

If you're building your a Bronze, it's in the BOM you can see by downloading the build guide.

If you're building a silver and not using a Raindog op-amp, then you can use those as a starting point and dial it in from there.  That is covered in the Silver guide.
 

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