Custom 500 Series Preamps - Eisen Audio, LLC

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EISEN AUDIO CUSTOM (discontinued)

Some of our customers want a preamp with a particular tone, performance, look, and/or feature set not found in any of the 500 Series preamps available commercially, and they don't want to build it themselves. For these customers, we offer the Eisen Audio Custom preamp service. Using our DIY500 mkII universal template and design expertise, we construct individually tailored preamps, one or two at a time. [This system can also work well for transfering the contents of a vintage plug-in mic pre card, making it into a fully-functioning device which performs like new.] Every unit is given a unique serial number in the format EACxxx, and users often elect to assign a description since there is no model name.

Prices have ranged from $425 to $735 USD per unit, depending on cost/availability of components, and difficulty of build.

Typical lead time to ship is between 3 and 5 weeks.

A 5-year implied service warranty (covering labor) is included.

An e-mail dialogue determines all of the customer's specific requirements and desired results (e.g. tone, mic applications, special features, cosmetics, etc.). We will then formulate a design configuration to meet these requirements and provide a quoted price and lead time. Upon approval of the quote, a $300 USD per module deposit is required to start the build, the balance of which must be paid prior to shipping the completed module(s) 3-5 weeks later.

Standard Features = continuously variable gain control, front panel XLR mic inputs (functions in addition to the rear panel input of your rack/enclosure), front panel hi-Z (DI) input via 1/4" jack, switches for 48V phantom power when supplied by your enclosure (with "ON" indicator LED), PAD (a fixed amount of input attenuation before input transformer: normally -20dBu), and polarity reverse (∅). Standard switch features can be modified, at additional cost, to perform functions such as input impedance select, low-cut filter (HPF), or attenuation elsewhere. Don't be afraid to get creative!

Front Panel = anodized aluminum in black, blue, dark green, red, gold, silver, or brown.

Front Panel Markings = CNC engraved (won't wear off), and can be filled with colored paint in various shades of black, white, gray, orange, red, yellow, brown, or left unfilled for a metallic sheen. Standard markings can be modified upon request.

Buttons = (called "switch caps") Can be round, in any combination of black, gray, and white; or rectangular, in any combination of black, gray, white, and red.

Knobs = We usually use knobs from Kilo International or EHC, though our choices are limited by stocking distributors. While certain plastic knobs, such as the "chicken head" style, come in many colors, most other knobs are available only in black or chrome. Special knobs are available upon request, subject to limited availability.

Connectors = Black plastic 1/4" and XLR front panel connectors are standard. The combination black plastic with chrome 1/4" connector used in the original DIY500 is no longer available, but we can use all chrome instead of all plastic upon request. Also upon request, we can leave out one of these connectors, for example "no XLR, but keep the 1/4"".

Completed Examples:

Please Note: Many of the units pictured below utilized our now discontinued original DIY500 template (serial no. EAC0xx). Identical performance is obtained using the new DIY500 mkII template (serial no. EAC1xx), albeit with a different physical appearance due to updated selection and placement of front panel controls.

Customers: See your photo here? Want it here? Want it removed? Please contact us. Testimonials are encouraged.

EAC135

We were asked to build a mic preamp specifically for mic'ing kick drum (aka bass drum) - something which would deliver big low end presence, and thick punchy midrange, but without sacrificing transient response – having lots of speed and detail in the region of upper midrange/treble frequencies which contain the attack of the drum impact. Our approach was to think of these contrasting requirements as a crossover. We built a rich and punchy sounding module using one of our usual configurations (in this case a Purple Audio KDJ 4 discrete op amp with Crimson steel output transformer and JLM Audio input transformer). This delivered the big low end and lower midrange presence as requested, but what about the transients? Choosing careful loading resistor values (higher than normal, or no loading at all) lead to increased HF presence, and bypassing all of the electrolytic coupling capacitors with incredibly transparent film capacitors at the "crossover point" let this HF information pass through unimpeded for incredible speed.

EAC122, EAC123

This pair of modules was tailored for a natural, yet rich and colorful response when close-mic'ing steel or nylon string acoustic guitar with condensers and high-output dynamics. Note the custom impedance switch (instead of polarity reversal), which changes the ratio of the input transformer, increasing the gain by 6dBu and offering a more forward, immediate response when depressed. This setting is well suited for (passive) ribbon mics, whereas the normal setting is not.

EAC121

This module was constructed to meet a unique and new challenge: Provide a round, inflated representation of low and mid frequency content, as in some very colored british preamps from the 60s/70s, but while leaving the high end response rather fast/open/transparent. The overall picture should then be smooth, 3D, more hifi than its vintage lineage. We started with the biggest, smoothest, most hi-fi yet sweet input transformer we know of – the Lundahl LL1538XL. It has the speed, detail, and headroom necessary for the overall response – just add low/mid inflation further down the chain, but not so heavy-handedly. To do this required the punchy JLM 99V discrete op amp, but configured in such a way as make the lower midrange (1 or 2kHz and below) seem rather "poofy", or blossoming. A Crimson Audio steel output transformer with its parallel windings in parallel was then used to make the low end extra big, but its secondary windings were left unloaded to keep the HF response from rolling off. To top it all off, we wired a front panel toggle switch to rearrange the input transformer primary windings for two different turns ratios and resulting impedances. This was an expensive modification, which isn't always possible, and shouldn't be considered lightly. Note that the engraving of our EA logo was left unfilled for a metallic appearance, whereas the other engravings contain white paint. A Kilo HD series knob was used.

EAC120

A customer wrote to us complaining that his other preamp sounded too cold when using his Gefell large diaphragm condenser mic on vocals. He liked the natural response of his mic (slightly bright, with good depth and width) and wanted a 500 Series preamp which would preserve these characteristics while adding warmth and richness. Our solution, resulting in EAC120, involved a Lundahl LL1587 input transformer (smooth and neutral, but with a bit of compression and sweetening that can add harmonics [warmth]) coupled with a Purple Audio KDJ 4 discrete op amp (the smoothest one we know of, frequency neutral with big bottom and a general richness) and steel output transformer (even more warmth when loaded correctly). These are all colorful parts which can add warmth, weight, richness. The challenge then was choosing capacitor types and loading resistor values which would allow for the correct balance of characteristics, such as not too heavy/thick, open not dark, smooth without midrange bump, big lows without cloudiness, etc. In other words, fine tuning. It worked out well. A Kilo JD series knob was used.

EAC118, EAC119

A pair of "Neve-ish", standard base configuration, in green with gray controls. At the customer's request, we omitted the front panel XLR connectors and used all chrome 1/4" connectors (not recommended) for DI. We had to source vintage Marconi Neve knobs in gray because we've lost our source for new red Marconi knobs. This special knob, if available, is a $30 USD addition to the base price, per module.

EAC117

This is what our "Neve-ish" custom preamp (i.e. EAC057, EAC058) looks like, in the standard base configuration, using the mkII template with default connectors, and a red Marconi knob (no longer available).

EAC114

Pictured is one of a short edition of identical preamps (40 thus far) which we're calling EAC312V. More info here. The op amps come from Scott Liebers, and the knobs and transformers come from Classic Audio Products, should you want to build this configuration yourself using a DIY500 minimal kit.

EAC105, EAC106

The latest variation of our popular "Neve-ish" configuration. Instead of a PAD switch enabling a fixed amount of attenuation before the input transformer (typically -18 dBu), there is a knob which varies attenuation (in this case from 0 to -32 dBu) after the input transformer. This allows for very high level signals to be applied (even line level!), obtaining sought after thickening and compression from the input transformer, without overloading the rest of the circuitry, and while still offering a reasonable level at the output. Kilo JD series knobs were used.

EAC103, EAC104

This pair of preamps was designed to provide uiquely natural midrange reproduction in film scoring (e.g. on orchestral sources with condenser mics). To achieve this level of high-fidelity we used the biggest, baddest Lundahl input transformer available (relatively transparent, lots of headroom, but with subtle smoothing/sweetening) and a JFET-992 op amp directly coupled to the outside world. The resulting response was big a three-dimensional without artifacts. Like wire with gain... and good taste! The downsides to this approach are an unbalanced output having 6dB less headroom and max gain, and the JFET op amps inability to drive a low impedance load such as the 600 ohm input of an 1176 compressor. However, when short lengths of shielded cable connect directly the relatively high impedance input of a transformerless device (such as A/D converter) then no problems will occur. Kilo DDS series knobs were used.

EAC101, EAC102 We built this pair of preamps as part of a tutorial, and they were later sold on eBay. The front panels didn't come out very nicely, as we'd asked a new fabricator to try silk screening (rather than CNC engraved) and they didn't do a very good job. However, the all-black look was nice in dim lighting, and these things sounded incredibly smooth! Not to mention balanced well on a variety of sources. The small, low-ratio lundahl input transformers were the perfect match for the too clean 990C op amps, smoothing out the HF/transients without pushing in too much level, and our steel output transformers inflated the low end response superbly.

EAC057, EAC058 The venerable "Neve-ish"! We built several of these using the original DIY500 template, this pair being the last. It started when a customer described to us quite specifically how he needed a preamp to polish and flatter his recorded singing voice when using a large diaphragm condenser mic - that it needed to impart a big, finished, commercial tonal quality, like a vintage Neve 1073. Using our vast knowlege of both vintage Neve preamps and 500 series components, we approximated said effect using the same classic Neve input transformer (and knob!) with a Purple Audio KDJ 4 discrete op amp (it does that spreading of the lower mids thing) and thick, steel output transformer. The resulting module became quite popular thanks to the Gearslutz discussion forums. Note the input impedance switch. For an additional cost per module, when engaged this changes the input transformer ratio from 1:2 (which offers a wider, more mids scooped response) to 1:4 (which offers a more mids forward response, and about 5dB greater gain). The effect is subtle and source dependent, but can be quite useful - especially with low-output dynamic and ribbon microphones.

EAC047, EAC048 You can find this pair of custom preamps at Crafted Recording in California. Designed visually to match the decor, and sonically to offer a "Neve-ish" complement to the studios selection of API preamps.

EAC025, EAC026 The JLM 99V op amp provides an incredibly clear, 3D, and punchy response, which we find to be rather lean, focused, and frequncy neutral, (though alternatively, it can inflate lower midrange when employed as such). Combine with this the classic beyerdynamic "peanut" input transformers - which create a grainy, aggressive, and compressed upper midrange/treble response while slighty rolling off the bass - and some Jensen nickel output transformers which just let everything pass unchanged, and you have a pair of preamps which are perfect on a drum kit (overhead mics). The mirror finish front panels didn't come out well (rough, flawed finish), so we don't recommend this option.

EAC010 This is an interesting case. We were asked to create a preamp with a sort of "wooden" texture that would excell at capturing steel-stringed acoustic gutiar using high output condenser mics. The huge, zingy Cinemag CMMI-3.5CPC input transformer when combined with a Millennia Media MM99 JFET op amp delivered this effect. Unfortunately, the MM99 can't drive an output transformer, or any low impedance load, so headroom was left severely lacking (not to mention the output unbalanced). To remedy this, we added a pair of external follower transistors (underneath the op amp socket) to drive the excellent Cinemag CMOQ-2L output transformer. No, we're not willing to try that again.
The front panel was a special white anodize (no longer available) with all black engravings and hardware.

EAC042, EAC043 We were asked to deliver a pair of medium/high gain preamps, with a rich and robust sound to them; utilitarian, but far from transparent. The primary application was to be vocal accompanied only by acoustic guitar, and captured using both condenser and ribbon mics. The POL switch was traded for a 12dB/octave high pass filter (aka low cut), which is often useful both on vocals and guitar.

EAC004 Default DIY500 (original) cosmetics, using a rare bti discrete op amp and some NOS transformers. Meant to be driven hard by loud sources for a rich, punchy sound. Note that the front panel engravings are not filled, leaving the exposed polished aluminum. Also, the chrome switch caps shown are no longer available.

EAC028 Please excuse the poor lighting in our first photo. This preamp was designed solely to capture distorted electric guitars, using dynamic mics such as the venerable SM57 dynamic mic, point blank at a speaker cabinet grill. To do this we combined: 1) the unique JLM Audio 1:4 input transformer, which has a naturally rich and aggressive sound to it, compressing the low end and pushing the upper mids slightly forward; 2) a Purple Audio KDJ 4 discrete op amp, which makes everything sound bigger, wider, smoother, with laid back highs; and 3) an all steel Cinemag output transformer (not as heavy/colored as Crimson) to impart extra harmonics without loosing the presence, immediacy of the initial response texture.