Monday, September 3, 2018

Stopping the Squeaks on a Burghardt Scissor-Jack Piano Bench

With a good piano, decent microphones, a [Really] nice preamp, and a not-bad A/D converter, you'd hope that playing ability would be the only thing to prevent a good piano recording in a home studio…  Then you play back to find that the squeaking piano bench is louder than the all but the loudest passages. Judging from the numerous discussion threads on piano-related online forums, I presume it's a common problem.  I discovered a relatively simple solution that might be helpful to others.

My bench is an adjustable Burghardt with a "scissor jack" style lifting mechanism, but my squeak solution should be applicable to some other types of benches.



I searched online for some solutions:

  • "Frequently tightening bolted joints." – Considering the bench came with its own wrench, the manufacturer must have been expecting this approach, but eventually it stops working.  It also only works for squeaks between the legs and apron board.
  • "Ensuring the bench is upright, on a level surface before tightening leg bolts." – I loosened the leg bolts and tried, but there was no difference.
  • "Putting Vaseline (or other lubricants) in wood-to-wood joints between apron and legs." – It seemed like this would be bad for the wood finish.
  • "WD40 at various locations." – Also bad for the wood finish, and not a good long term solution.

As I was reading these aloud, my wife suggested inserting a piece of fabric into the joints, and offered a scrap of nylon. That's when I remembered I had a partial roll of Rockler "Nylo-Tape" from a furniture project.  Nylo-tape is adhesive-backed nylon tape. I had 3/4" wide × 10 mil thick on hand, which worked just right.

First, I removed the legs (keeping track of which goes where!) and applied short pieces of Nylo-tape to the ends of each apron board, where they bear against the legs.

Then I applied long strips of Nylo-tape between the the lifting mechanism and the two wooden frames.  I just cut them a little longer than needed, marked the backing with the position of each hole, and then used a standard handheld office paper punch to make holes for the screws in each strip of tape.  (I actually removed each frame from the mechanism in turn, rather than all at once, to make it easier to put back in the right orientation.)



I did not apply any Nylo-tape between the corner brackets and the apron, partly because the squeaking seemed to stop after the first round of fixes, and partly because I ran out of Nylo-tape.  If new squeaks develop there, I may have to apply some later:

Tuesday, January 26, 2016

The Tube Technology behind Ghost in the Museum

A brief update because Ghost in the Museum by Diane Marie Kloba was released today, and I used some of my homebrew gear in recording my parts for the album:

My BoxHead amplifier was used for the baritone guitar part that's featured throughout the track "Rescued".  It was close-mic'd with an Electro-Voice N/D-468 dynamic, one of my favorite all purpose dynamics. The guitar itself is the Danelectro 63 that I upgraded a while ago:



My re-worked LK5H DI Box was used for the baritone guitar (including EBow passage) on "Only Summer Brings":



The LK5H was also used for the parallel EBow guitar parts on "A Thousand Pretty Strings". I really liked using it on the EBow because it simplified recording, and because the guitars have such a "hot" signal level when driven by the EBow that the pentode input on the LK5H gets some nice clipping character:



Bonus track: This was released on Soundcloud last year and is not part of any album. I played the lead guitar part on "Aching" through my Buffalo Box B175 and my Lama Kazu 8SE Amplifier.  I recorded with a Cascade Vin-Jet ribbon mic.

Sunday, August 2, 2015

Re-imagining the 10LS/1LB Preamp, Part 3: The Lama Kazu LK5H

I built the 10LS/1LB preamp in 2008, and modified it a few times over the years. It has mostly been serving as a direct injection (DI) box for guitars. I recently undertook a major rework. See Part 1  and  Part 2 for more background.

The Final Circuit

The final circuit
For the source follower stage, I selected The STQ2HNK60ZR-AP MOSFET. It is rated at 500V, is zener protected, and comes in a TO-92 package. I essentially kept with my previous plan for the rest of the circuit, except for a couple very minor changes: I added a 1 MΩ grid leak resistor on the pentode and 10 kΩ stopper resistors at the grid of the pentode and gate of the MOSFET; I reduced the source resistor value to 47 kΩ on the source follower section.

Although not depicted in the schematic, I added a textbook regulated DC heater supply, with a couple capacitors and a 7806 linear voltage regulator.  I decided to build this on a miniature terminal strip (0.25" spacing between lugs) that I had on hand.

The Chassis

Since the circuit is so much simpler than its original version, and so much more compact due to the change to a solid-state follower section, it became possible (with a little fussing) to take all the components inside the chassis box:

First steps in chassis modifications
First, I removed the tube socket turretboard and filter capacitor from the "top side" and plugged the holes with electrical box knockout plugs.

Then, I moved the input jack and neon power light off the "front" of the chassis and put them at the "back", i.e. the side that already had the power input, fuse, output connector and phase/lift switches. (I actually put in a different neon— I had bought a few smaller ones from the closing sale at my local Radio Shack.)

The pentode socket turretboard
Once those spaces were clear, I had room to move the filter choke into the area that had mostly been taken up with the old neon and wiring.

I modified the power supply board by removing the old "virtual center tap" heater resistors, adding a turret, and soldering on a monolithic bridge rectifier.  (The rectifier is over-rated for modest needs of the 150 mA, 6V heater, but I also had it on hand from Radio Shack).

The finished "gutshot"
I placed some adhesive bases for later mounting of the filter capacitor, moved the handle to the side, and plugged all the larger holes.  Not visible at the "front" side, I put some copper foil tape (with conductive adhesive) on the inside where all the jacks & potentiometers had been.

Outside back
To get the pentode inside the box, I made a little baby turretboard (about 1.8" × 3.4") mounted on a small section of aluminum angle.

The filter capacitor (with a few resistors directly attached) was attached to the adhesive bases with nylon cable ties.

Front view
The entire source follower circuit, including the 1μF coupling capacitor was assembled onto a miniature terminal strip similar to the one I used for the heater regulated supply.

It all fit, though the last stages of assembly were a bit cramped.  To finish it off, I designed a label and printed it on cardstock.  I put some adhesive aluminum tape on the back, and laminated it to the now blank "front" side of the chassis.  I decided to resurrect the "Lama Kazu" brand that I used for my first guitar amp project. I call this the LK5H, with the "5" referring to the pentode and the "H" for hybrid.

Results

The tone is essentially the same as it was in its earlier incarnations, but it's much cleaner.  Obviously hum has been reduced, down to about -60 dBu with input grounded, which is well below the level of hum picked up by any of my guitar pickups.  Most likely this hum is coupled in from the power transformers to the output transformer.  There's no way to get any mu-metal shielding inside this box, so this is how it will stay.

The noise floor looks to be on the order of -75 dBu, not exactly "audiophile", but good enough for an electric guitar.