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Old 7th June 2009, 10:34 PM   #21
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The new transformer has 5 independent secondary windings, so it made a bit of spaghetti hooking it up.
I also added larger 14AWG supply wiring.
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Old 7th June 2009, 10:43 PM   #22
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The new parts (heatsink, PS caps clamps, PS rails, transistor clamps, feet, etc.) were designed in SolidWorks, and I used CNC mills at De Anza College to make everything.
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Old 7th June 2009, 10:49 PM   #23
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Sounds nice, looks nice, so for now I'm done and moving on to upgrading my preamp. Maybe one day I'll put in new soft recovery diodes...
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Old 7th June 2009, 10:58 PM   #24
FSHZ:42 is offline FSHZ:42  United States
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Hi Tosh,

Really nice work! How would you describe the sound with all the mods done to what it sounded like stock? I was wondering if I should measure the bias on my DIA-100? I am not sure what voltage I could bump it up to! Maybe you could let me know.

Emile
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Old 7th June 2009, 11:24 PM   #25
jaycee is offline jaycee  United Kingdom
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I have one gripe with all of these mods - you have increased the power supply's current capacity, but you have NOT considered that the output stage is now undersized... i would want more than 2 pairs of 2SA3281/2SC1302 (if ive read it right) for 60V rails into 4 ohm loads.

Ensuring supply collapse will happen before the output transistor's SOA is a common dodge practiced in commercial gear. This is undoubtedly one of the reasons why the 350VA transformer was picked. Your amp now has the current capacity in the supply to drive 4 ohm loads well, but you are now risking blowing the output transistors.

You would get a performance gain by replacing the 2 large caps with the equivalent capacitance in individual capacitors. Also add some decoupling with 470nF or so polyesters. Larger caps have higher ESR than a few smaller ones in parallel.
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Old 7th June 2009, 11:43 PM   #26
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Hi Emile,
This amp has a lot of authority now (as the reviewers say), and with every change I could notice a slight improvement. As I said, I feel the single biggest improvement at normal volumes came from turning up the bias. So Yes, you should do this as well.

Start by disconnecting all outputs and inputs. Disconnect one rail fuse (either plus or minus side, whichever is easiest to reach) and hook a DC ammeter across the empty fuse clips. Turn on the amp and note the current drawn through meter. Mine measured only about 0.02-0.03A initially, and I kept turning the 1k pot (every 10-15 minutes in about 0.02A increments while the temperature stabilized) until it was out of travel, at which point the current was about 0.17A (and 0.18A on the other channel, which I dialed down to 0.17A so they would be the same). With your original heatsinks, you may not be able to turn it up this much without it getting too hot. On mine, I had to put in larger range pots to go above 0.17A, but I don't think you will need to do that.

Tosh
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Old 8th June 2009, 12:06 AM   #27
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Jaycee, the output stage is what it is, and there was never any chance that I would try to redesign the amp. And it has fuses to prevent it from trying too hard. (Even with smaller 3A fuses on each rail - stock was 4A - it hasn't blown any yet, despite my attempts.)

Per rail, I added 4x15000uF to the existing 23000uF, splitting it up into (15+15) + 0R25 + (15+15+23) CRC per rail and added a 10uF and 0.01uF film. Could I do better?
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Old 17th April 2010, 08:31 AM   #28
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About six months ago I had turned the bias up to 0.24A, and the amp was idling nice and warm. So a few days ago I decided to shoot for 4W of class A (into 8 Ohms), and turned the bias up to 0.36A! (So that's more than 12 times the factory setting!) Warmer, but still within reason, so I reckon these new heat sinks are working pretty good.

Today I finally got around to installing the new rectifiers. They get quite hot when playing very loudly, but I think they'll be fine without a heat sink. It's hard to say if they sound any different (perhaps the top end is a tiny bit better), but I'm pleased that they're in -- and that everything still works!
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Old 17th April 2010, 08:50 AM   #29
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using this metal parts to make the construction might assure perfect conductivity and perfect curent flow but keep in mind that you have actually created huge capacitor (s) with capacity of a few pf ....
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Old 17th April 2010, 09:28 AM   #30
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That's bad right?
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