Non-pedal build: Classic API VP28 mic preamp

[lincolnic]

So, I thought a couple of you from the Ferrite DI thread might be interested in what I've been up to this week. I mentioned that I had a couple of the Classic API VP28 mic pres in the works, and now they're fully armed and operational. I took a bunch of work-in-progress pictures while building the first one, and earlier tonight I finished the second. Here's a slightly more in-depth look at the build:

First: sort the components. Note that this is actually two sets of components - each mic pre will use half of these. At least half of the caps are MLCCs, and man can it be tricky to read the values on those guys.



Here's the PCB with all passive components and op-amp sockets installed.



Next step: install the switches and transformers. I didn't take any pictures of the underside of the PCB, but you can see just how many pins needed soldering here by comparing to the previous picture. There's also a long two-pin header that'll attach to the signal indicator LED in the final step. This completes the main PCB.



Now, we populate the HPF daughterboard. That L-shaped header is how it ultimately connects to the main board. The big holes in the top left and bottom right are for mounting brackets that'll secure it in place. C4 and C6 are intentionally left blank. I really like how the rest of the caps look like candy.



Next, the filter circuit gets mounted to the main PCB, all the switches get colored caps, and the entire PCB assembly gets mounted to its L-bracket.



Here's the naked face of the L-bracket. That empty chunk next to the buttons is where the indicator LEDs go.



At this point, the build is nearly finished. All that's left to do is install the faceplate and solder each switch's indicator LED (these mount on the back of the main PCB), as well as the signal indicator LED (which mounts to those long header pins above the pushbutton switches). Unfortunately, I forgot to get pictures of this part during both builds. After all the soldering is done, the op-amps are installed...



...and you're done!



My second build went a little more smoothly than the first - notably, the wiring on the output transformers is neater - but I didn't take any pictures of that one, as they're almost identical. Right now I've got these mounted in my new Lindell Audio 506 Lunchbox, which is exciting by itself. These kits aren't particularly difficult to build, but they are time consuming. I think each one took about eight hours in all. I made sure to be careful during each build, though - if I didn't like the look of a solder joint as I was working, I'd redo it then and there. I wanted to make sure that these would fire up on the first try, and they did.

So now the obvious question: how do they sound? Well, I haven't had the chance to fully test them yet. I confirmed that all buttons and gain/fader switches work as they should, but I haven't really been able to hear any program material through them. I've got a big tracking session this weekend, though, and you'd better believe I'll be using them. I'll report back after that with my impressions.

I hope this stuff is interesting to you guys! I had a lot of fun putting them together, at least.

[selfdestroyer]

wow.. just wow.. a whole new level of DIY. I bet its a solid pre. congrats on the build as it looks great.

[Vallhagen]

Very cool.

I really got inspired by your Reamp- and Di-boxes. I need them:). I even tried to order, but the Di thing is sold out at the moment. Well i can wait a few Days.

So whats up next? A complete channelstrip?

Where do you buy those kits/pcb-s?

Cheers

[alanp]

... I hope you realise this is kicking up my analog synth lust?

I never actually got to build one, since at the time I made $100 per month, back when the internet was used by university students and hobbyists, and DIY companies charged $400 for a single oscillator kit.

Bloody nice looking preamp. Polystyrene caps?

[raulduke]

Wow that is some quality stuff there (Transformer balanced in and out etc).

Kind of puts the audio fidelity of our standard fuzz boxes to shame ha!

Bet they sound AMAZING on Guitar Amps if they are API clones.

I think 500 series is the way to go for DIY studio kit.

I'm this close to taking the plunge 

[gingataff]

Mmmm... discrete op-amps

[lincolnic]

Thanks for all the compliments, guys! I'm so excited to use these on my session tomorrow, I can't even tell you.

Very cool.

I really got inspired by your Reamp- and Di-boxes. I need them:). I even tried to order, but the Di thing is sold out at the moment. Well i can wait a few Days.

So whats up next? A complete channelstrip?

Where do you buy those kits/pcb-s?

Cheers

I'm going to save up some cash for a little while, but I think my next move is going to be two channels of Hairball Audio's Lola mic pre. At some point, I might build their 1176 clone as well, but that's a ways off. I want to focus on filling out the remaining four channels in my Lunchbox first (the Lola is another 500-series unit). I really like the 550 EQs, so I may try and get ahold of two of those. Someone's got a DIY kit to clone them, but I haven't seen any reviews of it yet, and I don't want to jump into anything without at least a little background.

These kits come from Classic API: http://www.classicapi.com/catalog/

... I hope you realise this is kicking up my analog synth lust?

I never actually got to build one, since at the time I made $100 per month, back when the internet was used by university students and hobbyists, and DIY companies charged $400 for a single oscillator kit.

Bloody nice looking preamp. Polystyrene caps?

Build the synth. Build the synth! I'm sure PAiA can get you started. And yeah, the HPF daughterboard has polystyrene caps.

Bet they sound AMAZING on Guitar Amps if they are API clones.

Yep, that's the plan for the weekend. When I have more time, I want to A/B them against the real API pres we have in our console (212s, if you're wondering).

Mmmm... discrete op-amps

Yes sir. Those are Scott Lieber's Red Dot op-amps, but you can swap in any 2520-style op-amp that you like. The Red Dots are supposed to be the most colored, so that's what I went for.

[lincolnic]

Oh, and I forgot to mention - for everyone who appreciates a good solid click when you turn a rotary switch, the Grayhill switches that run these gain knobs are some of the most satisfying I've ever had the pleasure of turning.

[stecykmi]

cool project! what kind of transformers does it use? I count 3 of them, what function do they each serve?

[sgmezei]

OH man I in love. Totally been drooling over mic pre's. These look awesome man you did a great job.

[lincolnic]

You guys, I used these on my session today (and will continue to do so over the weekend), and I am so pleased. They sound awesome on electric guitar. In time I'll get more familiar with the gain-staging and different flavors it provides, but for the time being I'm running the gain pretty hot with the fader output turned down - that gives me some rich transformer saturation without having to worry about overloading my Pro Tools inputs. I'm using the second channel for an inside kick drum mic, which is doing a good job of accentuating the pointy sound I want there.

It'll be a little while before I fully explore all the tonal options available with these things, but for right now, it's love at first hear.

cool project! what kind of transformers does it use? I count 3 of them, what function do they each serve?

The transformers are custom recreations of the ones that were in the original mid-/late 70s API consoles. The input transformer is is Ed Anderson's EA 2622, which (along with the 2520 op-amps) is really the heart of this mic pre. The two identical output transformers are EA2623-1s. The first one belongs to the mic pre circuit. This pre is a little more complicated than most - it also has some of the same circuitry that an actual console channel strip would have. The mic pre itself is the same as the VP26 (from the same company), but after that it goes through the output fader circuitry and then the HPF. The second output transformer comes last, and gives you a balanced output. (I think. It may already be balanced coming out of the first output transformer, I'm not sure.)

There's some more in-depth talk about all the circuits involved here:
http://classicapi.com/catalog/product_info.php?cPath=22_117_55_169&products_id=318
http://classicapi.com/catalog/product_info.php?cPath=22_47_55_56_59&products_id=85
http://classicapi.com/catalog/product_info.php?cPath=22_117_120&products_id=224

OH man I in love. Totally been drooling over mic pre's. These look awesome man you did a great job.

Thanks! I've been admiring your work for a long time, so your compliments mean a lot to me.

[GrindCustoms]

Nice, really nice!

I feel like i'll get into this faster than what i thought....

[nzCdog]

love it!

[sgmezei]

I'm glad to hear they sound as good as they look man. I am still drooling!