Classic Audio Products, Inc.Classic Audio Products, Inc.Classic Audio Products, Inc.
500 Series Rack Kits (40)

Aluminum Control Knobs (23)

Assembled Modules (3)

Attenuators (3)

Capacitors (3)

CAPI Attire (6)

CAPI Nip-N-Tuck Bundles (16)

Connectors (30)

Diodes/Rectifiers (1)

Faders (2)

Floor Box PSU (17)

HiZ Plug-Ins (5)

LED Indication

Meters (1)

Misc Hardware & Bits

Modular Console & Rack Parts (18)

Op Amps (34)

PCB's & Kits (67)

   500 Series Modules (64)

      Mic Preamplifiers (41)

         CAPI VP25 (5)

         CAPI VP26 (5)

         CAPI VP28 (2 Stage) (3)

         CAPI VP312 (10)

         CAPI VP312DI (10)

         No Iron (8)

      Compressor/Limiters (3)

      Equalizers & Filters (15)

      The Missing Link 2 (3)

      Extension Test Jigs (2)

   ACA Summing (2)

   Console Modules

   Misc Utility PCB's (1)

Potentiometers (8)

PSU Items (5)

Relays (6)

Resistors (1)

Ribbon Mic Preamps (2)

Switches (20)

Tools (5)

Transformers (15)

Transistors (4)

Newest Products
What's New? more
CAPI 511-VPR DB25 Filtered Rack Bundle
CAPI 511-VPR DB25 Filtered Rack Bundle
Shipping & Returns
Privacy Notice
Reviews & Testimonials
Audio & Video Clips
Authorized Builders
DOA Install
Support Documents
About Us
Contact Us
VP25-Litz Entire Bundle (Stepped)
Number of Product Bundles in stock: 36

Click to enlarge

Click to enlarge

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

The VP25-Litz Entire Bundle (Stepped) is a kit comprised of every single part and component needed (sans opamp) to complete a VP25 microphone preamplifier. The VP25 is a single stage mic preamp for the 500 series format and is fully VPR compatible. 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
PS: DOA's can be added to this kit at the bottom of this page.

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.

The VP25 preamp is essentially an exact recreation of the legendary preamp circuit found in the vintage API consoles of the mid to late '70's. The 528/536 input modules have precisely this same exact circuit. The only exception being the change to the larger 2503 output transformer. The rest of the circuit is slightly different than the ever popular 312 schematic or what is found on the 312 cards themselves. You will find a few more components in the audio path like coupling capacitors on both sides of the discrete opamp. The use of series and loading resistors, along with a few decoupling capacitors is also faithfully implemented.

The love-hate relationship with the input pad is loyally carried out on this board. The simple voltage divider or U-pad resistor network follows the exact method used on the original module. This method is historically and mathematically correct, unlike many pads implemented into the 312 type circuits. Notes on the schematic give the builder a choice of attenuation levels, with the standard and original version being -20db. You can choose from a few options calculated to represent similar source and load impedances to the ones that exist in the circuit before the pad is engaged. While some of these will provide as little as half of the attenuation, the source and load impedances may be a slight compromise, changing the interaction between microphone and preamplifier. Maybe for the better, maybe for the worse. Experimentation required. Let your ears be the judge!

The mic input transformer is Ed Anderson's EA2622. This transformer mimics the inherent flaws of the vintage AP2622 that we so enjoy and works perfectly in the VP25 circuit. A Zobel network and loading resistor are required and are implemented exactly as the original.

Of course, the discrete operational amplifier is the heart of this preamp. The industry standard 2520 footprint is utilized here.

For the balancing output transformer, the VP25 is using the popular quadfilar 2503. The circuit utilizes two of the secondary windings in series in standard API fashion. Although the 2503 is the most recognized output transformer for an API mic preamp, it should be noted that the console input modules made use of the smaller AP2623-1 for this duty, not the 2503.

The last and possibly most unique feature of the VP25, is the use of a custom, Bourns 600 ohm T-pad output attenuator. The 3-module attenuator gives the user the ability to drive the preamp harder, and simply turn down the output level. The insertion loss of the t-pad is very minimal with a near perfect transfer of power, from input to output. This is the exact same attenuator as used for the input of the popular 1176 compressor builds. The t-pad can be skipped if so desired. The PCB is clearly marked and requires only moving two of the flying leads from the output transformer.

This product bundle contains the following items:
VP25 Partial Parts Kit» 1 x VP25 Partial Parts Kit
   175 pieces in stock
CA2622 Input Transformer» 1 x CA2622 Input Transformer
   36 pieces in stock
2503-Litz Output Transformer» 1 x 2503-Litz Output Transformer
   93 pieces in stock
Grayhill 1x12 Fixed Stop, Shorting Rotary Switch, Round Shaft» 1 x Grayhill 1x12 Fixed Stop, Shorting Rotary Switch, Round Shaft
   597 pieces in stock
VP-Gainswitch Resistor Set» 1 x VP-Gainswitch Resistor Set
   4076 pieces in stock
Bourns 600 ohm T-Pad Attenuator» 1 x Bourns 600 ohm T-Pad Attenuator
   139 pieces in stock
C&K SPDT Toggle Switch» 1 x C&K SPDT Toggle Switch
   331 pieces in stock
Toneluck 2PDT Pushbutton Switch» 3 x Toneluck 2PDT Pushbutton Switch
   1595 pieces in stock
C&K Black Bullet Switch Cap» 2 x C&K Black Bullet Switch Cap
   455 pieces in stock
C&K White Bullet Switch Cap» 1 x C&K White Bullet Switch Cap
   208 pieces in stock
DOA PCB Socket Set» 1 x DOA PCB Socket Set
   4069 pieces in stock
CAPI 5-50-1A Control Knob» 1 x CAPI 5-50-1A Control Knob
   38 pieces in stock
CAPI 5-62-1B Control Knob» 1 x CAPI 5-62-1B Control Knob
   254 pieces in stock

Cost of separate items: $237.85

Available Add-On Options for the VP25-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 Tuesday June 09, 2015.
Classic Audio Products, Inc.
Customers who bought this product also purchased:
CAPI 511-VPR DB25 Filtered Rack Bundle
CAPI 511-VPR DB25 Filtered Rack Bundle
CAPI 511-VPR XLR Filtered Rack Bundle
CAPI 511-VPR XLR Filtered Rack Bundle
VPR Switch Mode PSU
VPR Switch Mode PSU
51x 25 Pack of Module Screws
51x 25 Pack of Module Screws
LC40 Entire Bundle
LC40 Entire Bundle
VP26-Litz Entire Bundle (Variable)
VP26-Litz Entire Bundle (Variable)
Shopping Cart more
0 items
Curative Notice
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.
Notifications more
NotificationsNotify me of updates to VP25-Litz Entire Bundle (Stepped)
Quick Find
Use keywords to find the product you are looking for.
Advanced Search
Tell A Friend
Tell someone you know about this product.
Reviews more
Write ReviewWrite a review on this product!

Copyright © 2018 Classic Audio Products, Inc.
Powered by osCommerce