The Red Light District - another PP EL84 amp - diyAudio
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Old 14th June 2006, 04:38 PM   #1
SY is offline SY  United States
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Default The Red Light District- another pp EL84 amp

I've got a more complete write-up appearing in Bas Horneman's diy magazine, but wanted to put up some schematics for those who want to get a head start. It's easy to build, sounds great, and is a good answer for the common question, "Does anyone know a good 15W amp I can build...?"

First, the basic signal circuitry. Input stage is ECC81 (preferably JJ). Output stage is EL84 (again, JJ is a good choice).
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Old 14th June 2006, 04:38 PM   #2
SY is offline SY  United States
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The power supply. B+1 is for the output stage and runs 300-350V. The regulator is for the screens (idle current adjustment) and runs from 250-300V. Adjust idle current to 85mA per EL84 pair. B+2 is for the driver stage and is 350-400V.
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Old 14th June 2006, 04:40 PM   #3
SY is offline SY  United States
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The LED array.
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Old 14th June 2006, 04:45 PM   #4
SY is offline SY  United States
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I've run this amp on LS3/5A, modified Acoustat 1+1, and NHT Super Zero. The Acoustat needs more power, but the amp didn't do too badly! On the NHT and Rogers, it was close to optimum.
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Old 14th June 2006, 05:21 PM   #5
navin is offline navin  India
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beautiful SY. I was thinking of mating a small amp like this to a small 4-5" fullrange (tangband, fostex, etc...).
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Old 14th June 2006, 05:45 PM   #6
Giaime is offline Giaime  Italy
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Hello Stuart!

Great design, as usual.

But I NEED to see where you mounted all those leds, how, and would like to see a photo of the amp in the dark
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Old 14th June 2006, 05:49 PM   #7
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Trust me, you really don't want to see any pics of SY's constructions...
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Old 14th June 2006, 05:49 PM   #8
poobah is offline poobah  United States
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Giaime,

The photos are restricted by the US NAVY... they are trying SY's amp for night time carrier landing lights.

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Old 14th June 2006, 06:09 PM   #9
SY is offline SY  United States
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Quote:
Originally posted by Giaime

But I NEED to see where you mounted all those leds, how, and would like to see a photo of the amp in the dark
http://www.diyaudio.com/forums/showt...474#post840474

And a darker shot:
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Old 14th June 2006, 08:52 PM   #10
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and for the more "creative & artistic" you could change a couple of the red led's for another colour and spell something out... EL 84 POWER
or whatever floats your boat. Why worry about a few milliamps one way or the other for the biasing, whats the worst that could happen?
It may stop working, distort, a runaway tube...
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Old 14th June 2006, 09:13 PM   #11
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I say add a bank of flashing blue LEDs and call it the "SYren"
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Old 14th June 2006, 09:49 PM   #12
SY is offline SY  United States
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Well, the alternate name for this amp is the Yoshiwara. If I can get someone fluent in Japanese to draw out the characters, I might arrange the lights that way.
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Old 14th June 2006, 09:57 PM   #13
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You want Kanji or Katakana?
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Old 14th June 2006, 10:10 PM   #14
poobah is offline poobah  United States
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Katakana:

(g)
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Old 14th June 2006, 10:29 PM   #15
Variac is offline Variac  United States
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Poobah,
I think you will need to post a scan or something!!
It would be nice to see it in in both scripts to see which lends itself to the LED's best.

SY's construction skills are only eclipsed by his photographic skills!
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Old 14th June 2006, 10:32 PM   #16
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I have the symbols... the REAL McCoy... kanji!

Can't post em....

I have little books from my time there... MS PAINT maybe...




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Old 14th June 2006, 10:49 PM   #17
poobah is offline poobah  United States
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HERE!
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Old 14th June 2006, 10:55 PM   #18
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Ta.
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Old 15th June 2006, 12:20 AM   #19
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Even with 84 LEDs between the channels, you need five more LEDs to do the job. No great problem; use the extra five in the vertical line on the left character and power them from somewhere else...

Edit: Just realised I'd made an error - it actually needs eight extra LEDs. Perhaps the four either side of the left hand character?
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Old 15th June 2006, 12:23 AM   #20
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Maybe the extra 5 could be flashing?

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Old 15th June 2006, 12:45 AM   #21
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This amp will be a circus! tsc tsc tsc...

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Old 15th June 2006, 02:50 AM   #22
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Building on EC's efforts, 86 LED's. One LED on each symbol could be used as a standby indicator

You have to scroll to see it with my pdf reader
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Old 15th June 2006, 03:20 AM   #23
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Maybe easier to see:
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Old 15th June 2006, 04:51 AM   #24
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Good detail work Variac,

The cat missed one swish on the feet of the second symbol.

My infinitely limited knowledge of Kanji tells me that could be huge.

The first symbol means "city" or "city of". I'll leave it to everyone's imagination as to what the second symbol means.

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Old 15th June 2006, 05:15 AM   #25
SY is offline SY  United States
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Well, it IS the name of Tokyo's Red Light District.
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