The VC528 ML2 Entire Bundle is a complete kit bundle that contains most all of the parts and components required (sans opamps) to complete a VC528 ML2 module. The ML2 is physically and electronically fully VPR 500 series compatible.
This kit ships with EA2623-1 output transformers. Kits with Litz wire 2623-1's are also available.
The overall goal of the VC528 is to achieve the complete and lovely sound of a vintage API console channel without the cost of the rest of the console. It is definitely a little something different for the 500/51x format. Basically, it is a two stage console channel with the vintage circuitry of my API board.
The first stage is a 2520 style balanced, transformerless receiver. Everything is true to the original console circuit.
Next in the block diagram comes the fader. Due to space constraints and a request from a friend, I have chosen to use a 24 position Elma with a 1K overall value. Original faders in my board were 600ohm. The fader has 12dB of gain in hand to keep with the vintage API norm. Since the majority of the upper range gain steps are in 2dB increments, I have used a stepped Grayhill for a fader trim that is in 0.5dB increments.
I follow this filter stage with a 3 transistor discrete voltage follower using 5087/5088's. This buffer circuit is very reminiscence of the buffer amp used 4 times in the 550a. Very handy indeed.
Next in line is a 6 position stepped LP filter. This filter was not in my board. I have however implemented the same passive philosophy that they used for the HP filter that was in my board. Since it was easy to implement, I have added a switch to select 6dB or 12dB per octave for the filters. Very smooth and natural sounding, by the way.
A second 3 transistor follower is used to buffer the high and low pass filters from each other.
Next is a 6 position stepped HP filter. This filter can also be switched between a 6dB or 12dB slope per octave. Again, the overall philosophy is the very same that was used in my old board.
The last stage is the post fader booster amp. Again, the same circuit as found in the vintage console. I have modified the feeback R and C to provide unity gain when using the entire VC528 circuit.
The VC528 modules have been given a few nicknames by some happy users. They have been referred to as "Audio Bacon" as well as "The Missing Link".
So, what is new from the first version to the ML2 you ask?
The faceplate has been updated to a wet painted black with the same blue and light gray found on our other black faceplates.
An individual on/off pushbutton has been added to each filter section. This will allow for a quick and easy bypass of either one or both filters. Adding these switches freed up a position on each rotary switch so an extra filter point was added to each filter. 27kHz was added to the LP and 240Hz was added to the HP.
The previous 3-position mute toggle has been changed to a 2-position toggle that operates a hard-wire relay bypass instead of the mute function. This relay bypass has a shunt jumper connected to the Pin-6 DC bus so any adjacent ML2's can be bypassed by activating the toggle on only one unit.
A discrete follower has been added between the stepped trim switch and the LPF to prevent any interaction.
The post fader booster amp has a gain trimmer to precisely set the ML2 to unity gain.
Following is a list of additional components that are required to complete this build:
(2) 2520 style discrete operational amplifier
PS: DOA's can be added to this kit at the bottom of this page.
Here are required items that we do not carry at the store:
Solder, soldering iron and basic small hand tools
Very good assembly skills
A decent understanding of schematics and electronic components
This kit also requires the very same CMR calibration that the LC53A modules require. The extension test jig makes this a snap.
***This is one of the more complicated builds we have at the store. I do not recommend this for a beginner or inexperienced builder. While there are no plans of a dedicated "Assembly Guide", our friend and ex-newbie 'Chunger will be documenting a photo-build-doc like no other can! This may take a while so keep that in mind before purchasing. As always, I will have a build/support thread running at the GDIY forum.
