Tuesday, April 1, 2014

Push-Pull Salvage Amplifier Competion

Push-Pull Salvage Amplifier Competition

Objective: to build a stereo push-pull amplifier based on parts that you already own. Participants may use any design utilizing push-pull output topology. 

The Place: Stirling, VA (near Dulles airport)

The Date: Sunday, October 18 2014. Kickoff probably at 10am.

Building your own amplifier is very dangerous, particularly with the high voltages involved. We will not be held responsible for any injuries caused by you building your amplifier. This competition is not for novice builders. We highly recommend that novices build one or more Bottlehead kits before considering a scratch build like this.

1.  We will not accept entries that are shipped to the competition. You need to carry the amp in through the door at the competition. If you live in another part of the country, you might consider holding a similar competition in your own region. We will not be responsible for items that are shipped to us.

2.   There is no minimum or maximum total cost of the amplifier. We encourage you to use or reuse items that are currently in your stash. We are not religious about this and to be honest, we have no way of knowing what is in your stash anyhow. 

3.   You may use any output tube(s) you like provided there are at least two tubes per channel. Use of output tubes with two sections such as an 829B is permitted. You may use any tubes you like for input, rectifier, regulation, etc. You may also use sand in the driver circuit. Try to be innovative and use some techniques you haven't tried before.

4.    The amp can be any class you like - class A, class AB, class B, class C, triode, ultralinear, screen driven etc

5.  For safety reasons, the amplifier will include an IEC connector, an on-off switch, a fuse, at least one power transformer and a bleeder resistor. Please include an extra fuse taped next to the IEC connector. No wiring carrying more than 1 volt (AC or DC) should be able to be touched from the top or sides. Please observe the voltage and power dissipation limits for all components. All components should be mounted into place. No clip leads are allowed.

6.  A schematic and a list of all materials with part numbers and pricing needs to accompany the amplifier. As much as possible components, both passive and active, should come from your stash. You may use components that are made of unobtanium in addition to components purchased from Ebay vendors. If you do not know the price of a component, make an informed guess.

7.  Just for the fun of it, the case should come from or include some salvaged piece of audio or electrical gear such as an old receiver.  Be imaginative. 

8.    All amps shall be evaluated using the same speakers and source. We currently expect to listen to the amps at Steve’s place in Stirling, VA using speakers with an efficiency of 96 db, possibly higher. 

9. The speaker cables will use banana jacks to allow easy changing of amplifiers. You should include full function binding posts. RCA jacks will be used for input. 

10.    All amps shall be evaluated using an identical compilation of music of approximately 15 - 20 minutes depending on the number of entries. The selection will be eclectic and include classical, blues and other genres. Typically, the music will be from CDs that have been enjoyed at our regular meets.

11.   We will provide simple prizes for best sound, lowest cost and funkiest appearance. If we can come up with a formula we will attempt to give an overall 'First Prize'.

Set up:
  • Prior to the start of the competition, all amplifiers will be turned on to ensure that they are working
  • As much as possible, the same setup and positioning will be used for all equipment
  • A test tone at roughly 440 hz will be used to set the volume with some kind of sound meter in a fixed position.
  • All amplifiers will be invisible to the audience, even while not playing.
  • All amps will be numbered. The order of playing the amps will be drawn from a hat.
  • One designated person will be responsible for hooking up each amp. This person will not take part in the scoring.

The judges:
  • Depending on the number of entries, we may need to limit the number of judges at the discretion of the organizers.
  • If the number of judges is limited, priority will be given to those who regularly attend our Bottleneck meetings.
  • Each judge will be presumed to have either cloth or tin ears.

The judging process:
  • Each judge will be given a score card (and pencil) and will sit in an assigned chair throughout the contest.
  • No discussion while music is playing or for 30 seconds thereafter when the score must be written down.
  • The scoring system is not yet finalized
  •  There will be a preliminary round where all amplifiers are auditioned. The top three amps will go on to a final round with a different music selection.

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