Here is TonyB's description of his Stack-In-A-Box with increased gain, beefed-up power supply and built in Anderton Compressor. The front panel and PCB are from PAIA, so you get to see roughly what the kit looks like, with good clues about the physical aspects of mounting added-on bits.

   This is the first installment of the continuing story of my experiences with the PAIA Stack In A Box, hertofor lovingly referred to as "SIAB".  For many years, I've been interested in building my own tube preamp.  I thought about buying a complete kit from Paia, but decided against it and bought the manual instead.

   Recently, the tube bug bit me again.  I was talking to a fellow worker and learned he played guitar in a band.  He mentioned wanting to buy a tube preamp and mentioned several brand names.  I asked if he had heard of SIAB.  He said "yes he had" and that started it all.

   I told him I was thinking about building a clone of the SIAB, but I could put a SIAB kit together for him first.  This would allow me to try out the mods that I had seen on several web sites including this one.

   We decided on adding a compressor and a headphone amp.  We also decided the FX send and receive would have to go.  The gain and sustain controls for the compressor would fit in their holes nicely.  No sense in drilling extra holes in a nice front panel.

   The first mod would have to be the "gain" mod.  Let me tell you, changing the 680K resistor to 100K really DOES give it punch!  In the photo, it's labeled "S".  It's a small single pole that switched either the stock resistor(680K) or the Mod resistor in.  We almost DID drill a hole in the front panel for the switch.  We thought about naming it "11" after Spinal Taps "go past 10" amps. But, after using it at few practices, he decided he wanted it left on "11" permanently!  No problem.

   The headphone amp is Paia's 9605K.  With the added load of the compressor AND the HPamp, I lessened the values of the pwr limiting resistors in the SIAB.  Otherwise the pwr rails were sucked down to less than 12V and the inverter would not put out 42VDC.

   The 9605K is not the greatest in terms of volume.  I have found many "current booster" designs on the web and plan on implementing several to see(hear) which is best.  I tend to favor the ones that DON'T have matched transistors.  Also, I like the ones with just one more power stage.

   The compressor was a C.  Anderton one I had built over 10yr ago for my first venture into the world of guitar stomp boxes.  I used only 2 opamps.  It works fine.  Again, watch the power rails. With the availability of cheap pos and neg regulators, I would recommend separate ones for HPamp and SIAB.

   Notice how the Compressor and HPamp are mounted.  Instead of drilling new holes in a nice anodized panel, I made aluminum brackets with holes to mount the circuit board and holes for the jack and pots.  Also, makes it easy to remove and bench test as the design was progressing.  The "neg out" jack of the SIAB was removed and a stereo jack put in it's place.  The "neg out" from the pcboard goes to both channels of the HPamp.  Wiring is short, sweet, but, again, the HPamp just isn't quite right.

   The nomenclature on the front of the SIAB had to be changed.  I couldn't use "DRIVE" or "CRUNCH" since they were already on the front panel....so..I came up with "BOOST" and "SQUEEZE" being gain and compression respectively.  The little area was masked off, then lightly sanded w/220 wet to remove the original text.  After wiping with a tack cloth, the 3 areas were painted w/Krylon quick-drying(lacquer) white.  Then, after letting it set for 24hrs, just to be sure, it was labeled w/dry transfer lettering.

   Now look at the back view of the SIAB_clone.  The panel is a full 19in rack that's 5 1/4in tall. Same size as Paia's Frak Rack(FR).  I thought about getting blank FR panels and making each module mountable separately, but decided ONE panel was easier.  Besides, I had this panel already in my aluminum pile, so the price was right.  So it had a few holes in it already.  I plan on countersinking them and filling them with automotive plastic body filler.  Will take some pictures when I start to do this.

   The 2 unconnected pots are for the compressor.  I've decided to use C.  Anderton's newer version compressor(project 8 from EPFM).  It has 3 opamps in it.  The input and output signal are in phase.

   In the SIABclone picture, notice the pwr regulators.  By using a little higher voltage transformer(wall wart), I was able to get full +12 and -12VDC to the pcboard.  This made the inverter output a full 42VDC.  Didn't want to starve the plates any more than necessary.  Notice the third regulator: 12VDC for the fillament.  The adjustable reg was tweeked for 12.6VDC exactly.  So the tube runs at 42VDC with a 12.6V/30ma fillament.  Works great!!

   Next up is to build and mount the compressor.  Have done some preliminary drawings for the SIABclone, but the knob and module arrangement has changed several times.  Originally, I wanted 1compressor, 1SIAB, 2VCFs, 1EnvFol, and possibly a VCA w/EnvGen.  One of the VCFs(the input) changed to a quad parametric.  The 3knob compressor changed to a 2knob.

   Next installment will show the prelim clone drawings along with the small changes I made to the Frak Rack.  BTW, the regulators(2LM317, 1LM337) are all adj ones right from National's data book.  I love these things!  For getting the pwr rails right on, they can't be beat for quickness and simplicity.

   Til next time....TonyB

   Mod Original Front  

   Mod Original Back  

   Home Brew Back