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VP312DI-VPR-Litz Entire Bundle (Stepped)
Number of Product Bundles in stock: 31

Click to enlarge

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To avoid massive build errors, make sure the BOM Revision you follow matches the Revision of the PCB you are building!!

The VP312DI-VPR-Litz Entire Bundle (Stepped) is a kit comprised of every single part and component needed (sans opamp & HiZ Plug-In) to complete a VP312DI microphone preamplifier. The VP312DI-VPR is a single stage mic preamp for the 500 series format and is fully VPR compatible. The preamp is essentially an exact recreation of the legendary API 312 preamp circuit that has become the benchmark for the API sound. The DI version of the VP312 has very flexible and complete Direct Inject options built in. The aluminum faceplate is wet painted and the aluminum L-bracket is yellow chromated.

***Please note: This kit now ships with a CA2622 in place of the EA2622. To eliminate possible shipping mistakes, I will not be able to substitute or swap these parts. Thanks for understanding.

Following is a list of additional components that are required to complete this build:
(1) 2520 style discrete operational amplifier
A HiZ Plug-In Kit or two
PS: DOA's can be added to this kit at the bottom of this page.

How to add one or many HiZ Plug-In kits to your VP312DI Kit: There are many HiZ Plug-In options that can be used with a VP312DI preamp...passive as well as active. Too many choices to have dedicated kit bundles for each one of them. Instead, it is easier to view them as ala-carte kits that can be purchased separately, along with the DI preamp. You can select one, two or all of them if you so desire. The HiZ Plug-In subcategory can be viewed here.

This kit ships with a Litz wire 2503 output transformer. Kits with EA2503's are also available.

***Please note: The Litz 2503-L wire colors are different than the EA2503. To use the Litz 2503-L on this build, please follow the table on the bottom left of this datasheet.

This kit includes a Grayhill switch for stepped gain control. Kits using a Bourns potentiometer are also available for fully variable gain control.

Rather than be totally redundant and have a product description that is a mile long, I will try and simplify by saying that the VP312DI has the very same classic functions as the VP312 with a few very important exceptions. You can read up on the VP312 by visiting any of the product pages here.

The microphone preamplifier circuit is exactly the same except for the addition of a high-quality Elna blocking cap after the DOA. This 470μF cap is also bypassed with a parallel Wima MKP .01μF cap (for those audiophile types!). I have found significant DC offset from the DOA depending upon which brand of DOA is being used, especially in Bo Mode. The Mute switch is not very quiet this way and we don't want to harm the 2503. For the die-hard vintage enthusiast, I have utilized a 3 position .1" 3M header and shunt so that these coupling caps can be fully bypassing. This will couple the DOA's output to the 2503's primaries for authentic, vintage 312 operation. A close up of this can be seen below.

Next, we get into the DI information. This is quite extensive so take your time!

First off, the Neutrik slim line jack is auto-switching. When a 1/4" plug is inserted, a relay on a Plug-In Relay PCB switches the source to the 1/4" jack's signal.

Default DI mode or Pre 2622, utilizes a brand new concept developed by myself and Volker Mayer, aka [silent:arts]. We call it the HiZ Plug-In. When in this mode, the Direct Inject signal takes the same path as a microphone. From the HiZ Plug-In thru the mic pad and then directly into the 2622 input transformer. This means the normal mic input pad will be available for use while in HiZ Plug-In mode, if required. This path thru the 2622 is very unique to a 312 style preamp. There is not another in the industry to my knowledge, not to mention the near endless possibilities with the HiZ Plug-In board. So far we have a few passive versions, an IC version and a FET version. The operating voltage for the HiZ Plug-In is switchable between 16V and 24V. A 51x rack will be required for 24V operation.

I refer to the secondary or optional DI mode as Bo mode or Post 2622. For this I am utilizing the published circuit created by Bo Hansen. This Bo mode is not the same but is similar to the DI circuit found on the other popular 312 and 512 preamps. The selection for Bo mode and the related options are done via 3 NKK G-Series Ultra Miniature toggle switches. Flipping the top toggle switch to the right, activates a second Plug-In Relay circuit that couples the 1/4" jack signal to Bo's circuit and then directly into the discrete opamp, bypassing the 2622 input transformer. Without a 1/4" jack inserted, this relay cannot be activated.

The second ultra mini toggle switch is for a -10dB pad of the DI signal. This pad switch is only active when a 1/4" jack is inserted and the above Post 2622 switch has been flipped to the right. So, no -10dB pad when in Pre 2622 mode but remember, in that situation the standard -20dB mic pad will still work.

The bottom or third ultra mini toggle is only active if the above two switches have been flipped to the right. This switch creates a Low Pass Filter that mimics the "perfect Jaco Pastorius tone". It's another feature that helps make this preamp unique.

***Please note: For 15-pin VPR use, the PCB must be slightly and permanently modified by cutting off the extra gold finger connectors, as seen in the pic below.

Additional information and photos:

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VPR 500 Mod

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Output Cap Bypass

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Lower Switches

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HiZ Plug-In Options

This product bundle contains the following items:
VP312DI Partial Parts Kit» 1 x VP312DI Partial Parts Kit
   177 pieces in stock
Neutrik Stereo 1/4" PC Mount Jack Set» 1 x Neutrik Stereo 1/4" PC Mount Jack Set
   231 pieces in stock
CA2622 Input Transformer» 1 x CA2622 Input Transformer
   71 pieces in stock
2503-Litz Output Transformer» 1 x 2503-Litz Output Transformer
   31 pieces in stock
Grayhill 1x12 Fixed Stop, Shorting Rotary Switch, Round Shaft» 1 x Grayhill 1x12 Fixed Stop, Shorting Rotary Switch, Round Shaft
   800 pieces in stock
VP-Gainswitch Resistor Set» 1 x VP-Gainswitch Resistor Set
   4202 pieces in stock
Bourns 600 ohm T-Pad Attenuator» 1 x Bourns 600 ohm T-Pad Attenuator
   224 pieces in stock
NKK SPDT Ultra-Miniature Toggle Switch» 3 x NKK SPDT Ultra-Miniature Toggle Switch
   331 pieces in stock
C&K SPDT Flat Lever Toggle Switch» 1 x C&K SPDT Flat Lever Toggle Switch
   168 pieces in stock
Toneluck 2PDT Pushbutton Switch» 3 x Toneluck 2PDT Pushbutton Switch
   1841 pieces in stock
C&K Black Bullet Switch Cap» 2 x C&K Black Bullet Switch Cap
   635 pieces in stock
C&K White Bullet Switch Cap» 1 x C&K White Bullet Switch Cap
   291 pieces in stock
DOA PCB Socket Set» 2 x DOA PCB Socket Set
   4354 pieces in stock
Plug-In Relay.1 PCB» 2 x Plug-In Relay.1 PCB
   198 pieces in stock
Plug-In Relay.1 Parts Kit» 2 x Plug-In Relay.1 Parts Kit
   311 pieces in stock
Panasonic TQ2-12V DPDT Relay» 2 x Panasonic TQ2-12V DPDT Relay
   1156 pieces in stock
.100" 4 Position 90˚ Header» 1 x .100" 4 Position 90˚ Header
   9937 pieces in stock
.100" 3 Position Straight Header» 1 x .100" 3 Position Straight Header
   616 pieces in stock
.100" Gold Plated Shunt» 1 x .100" Gold Plated Shunt
   397 pieces in stock
CAPI 5-50-1A Control Knob» 1 x CAPI 5-50-1A Control Knob
   202 pieces in stock
CAPI 5-62-1B Control Knob» 1 x CAPI 5-62-1B Control Knob
   329 pieces in stock

Cost of separate items: $282.01

Available Add-On Options for the VP312DI-VPR-Litz Entire Bundle (Stepped)
Selected Discrete Op Amp:
 No DOA» No DOAAdd-on to cost » - - -  
 SL-2520 Red Dot» SL-2520 Red DotAdd-on to cost » $65.00  
 gar2520 Full Kit Bundle» gar2520 Full Kit BundleAdd-on to cost » $17.50  
 gar2520 - Assembled» gar2520 - AssembledAdd-on to cost » $60.00  
 gar1731 Full Kit Bundle» gar1731 Full Kit BundleAdd-on to cost » $17.31  
 BB2521 LME49710 Full Kit Bundle» BB2521 LME49710 Full Kit BundleAdd-on to cost » $9.58  
This product was added to our catalog on Saturday June 13, 2015.
Classic Audio Products, Inc.
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Classic Audio Products, Inc. is not affiliated with API. Customers and fans should not refer to Classic Audio Products, Inc. as "Classic API." API is a registered trademark of Automated Processes Incorporated. Classic Audio Products, Inc. has no affiliation with Automated Processes Incorporated.
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