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Tag: lola
CAPI VP312 Preamp Build (and HP Filter Switch Mod)
CAPI is another source for Professional DIY audio kits. They make a bunch of 500 series and rack device kits. It is not by accident that [c]API look very similar to vintage products by API but CAPI has no affiliation with API.
I’ve built most of the components in my 500 rack as kits. As I started down that road, I also got myself pretty deep into microphone mods.
While you’re here, check out our custom microphone modifications and rebuilds. If you have a neglected MXL 990, MXL 910 or similar mic in your locker, we can very affordably turn it into a “go-to”.For this kit, I decided to go simple and build the basic VP312 Preamp. This version has no DI input which greatly simplifies the build. I also chose to buy the Discrete Op Amp pre-assembled. When I built the Lola, I made the mistake of building the DOAs myself. This accounted for more than half of the build time and about 90% of the difficulty so I didn’t want to repeat that mistake.
I had the 312 done and working in less than three hours. It was by far the easiest kit I’ve done.
First few components installed The array of resistors in the top left are for the 12-position stepped input gain switch. This is an upgrade option but you can get the kit with a variable input gain instead. I opted for the stepped version. That said, CAPI has been having a terrible time keeping the Grayhill switches in stock. I even had to pass on a couple of sales in my reverb.com shop because I wouldn’t have been able to replace the kits if I sold them.
Transformers
At the time I ordered the kit, they were out of stock of their own CA2622 Input Transformer. But they did have plenty of the Ed Anderson (EA)2622s in stock. So I ordered the “No Iron” option of the kit and then added the EA input transformer and upgraded to the Litz (red) output transformer.
I also ordered the “stepped” gain version which is a 12-position grayhill switch with an array of resistors.
Finished Kit on the bench Not too many steps along the way and before you know it, the kit is done.
Although the kit was easy to build, this is the first kit where there was an error with the parts inventory. Fortuntely, it was just two missing 4-40 flat head screws. Unfortunately, my local hardware store did not have them so I’ve had to order some. Until they arrive, I can not do final assembly. It’s put together enough to install in the rack and use though.
In the rack with her siblings Room for Mods
Besides being easy to build, an advantage of the low parts count of the CAPI is that there is a lot of room for modifications.
One thing that is missing from the Lola and the MP573 is a Lo Cut (hp filter) switch. These come in handy quite often and it is one reason why I bought the RND 511 preamp (which I don’t love). Adding this function to the CAPI looks to be very easy to do. There is plenty of room to mount an additional toggle switch and I manged to find some very cool mini toggles that have an illuminated handle!
Here’s the general idea: R3 is an optional Load resistor for secondary of the input transformer. I’m installing it and using it as the “R” in the R-C circuit. A trace is cut between transformer and R3 and I’m putting some capacitance across that gap with a switch to short it out. I found some cool illuminated toggle switches which will give me a cool indicator light when the filter is in.
The Switch will short out the cap disabling the filter. With the switch open, the other contact will close and light up the switch LED.
For fun, I also considered a two-position version of the filter whcih would use an on-off-on switch and two capacitors. This ended up being what I finally went with.
A couple variations on the HP Filter mod. The bottom one (two position) is what I went with 
This is the Trace to Cut 
The CAPI vp312 schematic showing where the trace is cut 
Drilling the pilot hole for the new switch Can’t wait for the cool switches to arrive!
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The pilot hole in the front panel Adding the Mod
Well, my fancy illuminated switches were delivered today. That’s the good news. The bad news is I had them sent to the house I lived in six years ago. Oh well I hope the new owners enjoy them once they get over their initial confusion. Being impatient to get this done, I decided to skip the illuminated switch. The switches I had in stock were some SPDT On-Off-On switches. So I was able to do the two-position version of the filter. In hindsight, I’m really glad I didn’t get the illuminated switch. Having two steps for the Lo-Cut frequency is very nice.
Step 1 was to (ugh) drill a hole through the board to provide access for the wires. Next time I build one of these kits, I will think ahead and do the whole mod on the top side of the board which will eliminate the need for this hole. Not a big deal as there is plenty of open acreage on the board.
Step 2. The Two 0.01uF caps are wired in series across the cut circuit board trace.
Step 3 is to get some wires to the caps. I ended up doing two of the connection below the board and the other above. The pin on the input transformer made a nice big fat solder pad to hook one to. The other wire goes to the connection of the two series caps.
Two capacitors wired in Step 4 is to wire the switch. I drew an arrow facing down so I could keep track of which way to install the switch. I want OFF to be with the switch handle down. The two blue wires go across the cut trace (shorting both caps). The red wire goes to where the caps are wired together (shorting one cap).
Switch Installed And there it is with all the gadgets mounted to the panel again. Since this is the last time I hope to disassemble this, I put blue locktite on all the fasteners.
Final mod on the bench The switch works as follows:
- Down: Off
- Middle: 220Hz
- Up: 110Hz
I was a bit concerned that the extra wiring would pick up some hum or noise. They are between the input transformer and the high impedence input of the DOA. But upon testing, the amp is still just as silent as ever. Did I connect it to some expensive signal analyzer? Nope. But I did put on my sennheiser headphones and floor the amp and to my ears, it’s as quiet as it ever was (very). Operating the switch does not produce any clicks or glitches either. I didn’t expect it would as there is no DC anywhere near this part of the circuit.
In the down position, the switch is shorting both caps as if they were not there. In the middle position, both caps are in series producing a total capacitance of 0.005uF. This gives us a 225Hz corner frequency. In the Up position, one cap is shorted so we have 0.01uF which yields a 112Hz corner. I’m assuming the input impedence of the Discrete Op-Amp is much higher than R3’s value of 150K so the R in the RC circuit would be around ~140K.
The illuminated switch would have been cool, but having two settings of the filter is much more valuable. Now, I want to build another one!
And here it is installed in the rack and working.
Final version installed in rack and working Hairball Audio Lola Mic Preamp Build: Adding Another Color
Editor’s Note: Since publishing this post, I have been doing mic mods and builds using my own components rather than kits from mic-parts. As awesome as mic parts is, I’m much more excited about my own products these days. Please see my mic mod shop for more information or contact me with any questions.
My eight space 500 series rack has had only one module in it until now. It was the Sound Skulptor MP573 Mic Preamp kit I built several months ago. My ultimate plan is to get a second one of those and a pair of something else. After a lot of consideration, I decided that the something else would be the Lola from Hairball Audio in Seattle.
While you’re here, check out our custom microphone modifications and rebuilds. If you have a neglected MXL 990, MXL 910 or similar mic in your locker, we can very affordably turn it into a “go-to”.Thanks for visiting. Since writing this article, my DIY activities are mostly centered around microphone mods and custom builds.
Now, enjoy the article about the Lola Build!
The kit arrived a few days ago, and I managed to build it in three sittings. And.. it actually works! Other than the discrete op amps (see below), the build is pretty simple and straightforward.
Early in the build The main board in the vice ready to populate (sorry for the blurry pic. I had my high-mag reading glasses on at the time)
The main board build is actually pretty easy. It’s a very good quality circuit board with decently sized and spaced pads. Resistors, caps, diodes transisitors and relays are all packaged in a series of bags referenced by the build guid. It’s very buildable by anyone with decent soldering skills. The input and output transformers are very easy to mount. I added a little bit of blue locktite on all fasteners for the transformers and other mechanical connections..
Discrete OP Amps
The Lola takes two discrete op amps because it maintains a fully differential signal path through the whole amp. Hairball offers several options for amps – including a DIY version of their own JE990 amp – but you can put any standard footprint DOA in here you want. I went with the Hairball DIY option and that was my one regret. It’s a very challenging build which probably doubled the overall build time. There are 30-ish parts on a 1 sq inch circuit board with very tiny solder pads. I have pretty good soldering skills, but while I was working on the DOAs, I was thinking that the chances of both of these actually working is pretty slim!. If/when I get another Lola, I will certainly not build the OP Amps myself.
Installing the two JE990 Discrete Op Amps Hairball Kit Quality
So far, I’ve built kits by Sound Skulptor, Mic-parts and Hairball. I’m battting a thousand (so far) at having stuff work right off the bench, but that says as much about the quality of the kits as my ability. In terms of parts inventory, the hairball kit was perfect – nothing missing and nothing extra. The build-guide is pretty good, but slightly not as good as the other companys’ kits I’ve built. The guide is written with a little light-hearted dead-pan humor which I appreciate. I don’t own a printer so I was reading the guides on my phone while building. There were a couple times when I should have scrolled down just one more half inch for a warning or tip before I soldered something. The one part of the build guide that stood out as being sub par was for the LED Meter board. The image in the guide for that build is very low res and quite unreadable. The silkscreening on the board is so tiny, it is also unreadable so the image for that board is especially important. I found myself installing the resistors I could read first and then doing the rest when there were fewer choices to guess between.
Finishing the LED board. The idea is to get the LEDs all pointing straight up. 
LED board mounted to Driver Board. The guide for this board was particularly not so good. Hairball Kit Mechanicals
500-series stuff presents a challenge for a designer. There is very limited space (in three dimensions), limited power supply rail voltage and limited heat dissapation. Sometimes to get everything to fit, the parts are very difficult to physically put together. Not so with the Lola. The main board fastens to the back plate with four stand-offs. The back plate wraps around so that the front panel sits against it making alignment of the controls very simple. The LEDs sit behind the panel and a series of clear plastic light pipes are used to get the light outside of the box. It’s a very well-done design overall!
Final assembly complete Fully baked and ready to test 
In the rack and working! 
Mic setup for the a shootout using the matched Mic-parts kit mics First Impression
Well, mainly the fact that it worked at all was a big (and somewhat unexpected) thrill. I was encouraged after the main board and DOAs were done that an initial smoke test in my rack yielded none (smoke, that is).
The Lola has the familiar Grayhill rotary switch for input gain and an output +/- variable trim control. Unlike most of these style preamps, it has a 10 segment LED meter so you can really tell how hard you are hitting it.
The input gain switch on the Lola is awesome – it’s rotates over 270 degrees and covers steps from 17 to 65 db of gain. That 65 instead of the usual 60 is due to the differential signal path. My MP573 by comparison has a switch that is only about 180 degrees with bigger steps. The Lola will definitley be more tweakable in terms of pushing it into saturation with more fine control.
As I was finally installing it in my rack, I heard some birds chirping outside. I put one of my modified 990s out the window (with a tee shirt over it as a wind screen), floored the gain on the Lola and recorded a bit of ambient neighborhood sound. It doesn’t really matter how cool a preamp sounds if it’s noisy, but this thing is really quiet. That was supposed to be one of the Lola’s strong points (wth the fully differential signal path) and it certainly is.
