The Black Box

Let’s just say hypothetically that you had to write+ record a tremendous amount of guitar-based music very quickly.  And even though you work at a recording studio filled with numerous custom and vintage-modified tube amps and great microphones, this music needed to be recorded in a modest home-studio using the not-awful but not-awesome Line 6 POD Pro XT.  Could there be some device that might bridge this gap in audio aesthetics, if even a bit?

I’ve used the Line 6 ‘POD’ series of devices for a decade; they are not very good for recording prominently-featured electric guitar parts, but they definitely have their uses in the studio; the Bass Pod Pro has actually worked out well a few times, and the Pod Pro is often good to add grit to synths.   When music must be recorded in a domestic environment, though, a POD can be very helpful, at least logistically.  I recently bought the newer POD ‘PRO XT’ version for around $200 on eBay.  Aside from an annoying but sonically inconsequential mechanical-hum given off by the power transformer it seems to work fine.  It even has the ability to user-adjust the blend between close mics and far mics on the ‘Amps.’   Does it sound just like a good tube amp, well-mic’d, in a great sounding room?  No.  At best, it sounds rather like playback from a 16-bit ADAT, if any of y’all can remember that sound.  Not bad, but not very detailed and overall sterile.   I knew that some tubes, transformers, and real mechanical reverb could help transform the POD sound to something that I would be a little more comfortable with.  So when I found a Fisher Space Expander for $10 at the flea market last fall, this little project went up near the top of the list.

The Fisher is an old home HiFi reverb system with unbalanced -10 input and outputs; I need +4 balanced.  But I did not want to modify the Fisher unit in anyway (other than adding a grounded AC lead), since they are highly sought-after and i might want to sell it someday.  So i rigged it up inside this old salvaged DIY ham-receiver case with one of those MCM electronics balancing amps, and two inexpensive Jensen MOD series 9″ reverb chambers with medium-impedance inputs (around 300 ohms, I believe).  One tank is short decay, the other is long decay.  I realize that the 17″ larger tanks do sound better, but since this box was destined for my tiny home-studio, size is a real issue; I needed everything to fit inside the 14×8″ steel box.   I’ve already enjoyed the benefits of being able to select two different tanks; on tracks that feature two electric guitar parts I am easily able to situate each in its own ‘space.’

Here’s a rear-view of the whole fandango.  Balancing amp is on the right; note that it is stereo, and the unit is fully wired for stereo; that being said, the fisher only generates a mono reverb signal which is then blended into the stereo direct output path; since I am using the unit for mono guitar tracks, I just use one pair of the XLRs at the moment.

At left: the ‘blend’ knob, and below that a DPDT on/on switch that selects one tank versus the other.

Someone very helpfully scanned and uploaded the manual and schematic for this device; click here to download the PDF directly from them.    There are not too many surprises in the schematic, other than that  the first reverb recovery stage has a 330k plate-load resistor; this is the highest value that I have ever seen, and it failed almost immediately.  Twice.  I eventually put a 2-watt CC in place of the original 1/2 watt, and changed the adjacent coupling cap as well.   I had to replace pretty much all the B+ resistors in the unit (and several coupling and bypass caps) in order to get rid of some nasty intermittent noises; now the unit is working fine and it sounds really good!  A word of advice if you get one of these things: run the input hot, and back off on the return level.  It takes A LOT of signal before it distorts or smacks the tank, and you will be rewarded with a much-improved signal-to-noise ratio.   The MCM balancing amp has handy gain-trims that make it easy to achieve overall unity gain on the direct signal while accomplishing this goal.

Click here for some previous tube-reverb system action on PS dot com