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Old 28th January 2013, 04:53 PM   #81
tomchr is offline tomchr  United States
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The three OPTs I've tried have been E-I cores so I can't speak for advantages/disadvantages of other core types. I can't imagine there'd be a big difference between an E-I core and a C core. Between E-I/C cores and a toroid, I would imagine more potential for differences. But that's a guess.

In the end, I would think that the technique used in winding the transformer has far more impact on the sound that the choice of core shape. By technique, I mean the layering of the different windings, interleaving, multiple strands in parallel, etc. But again, that's a guess.

I leave the winding of OPTs to the pros.

~Tom
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Old 26th March 2013, 02:24 AM   #82
grufti is offline grufti  United States
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Tom, did you ever build a chassis for your Pretty Damn Good 300B Amp?
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Old 26th March 2013, 08:05 AM   #83
tomchr is offline tomchr  United States
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Funny you should ask. I just started on the metalwork for the chassis today. I completed the plans over Christmas so this is not exactly a fast process... But I decided to take this week off from work so I could get some headway on this project. The circuit description of the 300B amp is also slowly taking shape on my website.

The amp is still sitting in "DeathTrap" mode in my living room. Playing Dire Straits right now... /me like.

~Tom
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Old 27th March 2013, 11:44 PM   #84
tomchr is offline tomchr  United States
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The chassis is coming together. As attached image shows, it's work in progress. But you get the general idea. The chassis measures approx. 11x15 inches. The sides are 3" tall, 1/8" thick architectural aluminum channel, the top plate is 1/8" aluminum sheet, and the front 3/8" extruded aluminum rectangle bar stock. I could probably have used thinner materials, but I like having enough material thickness to be able to cut threads so I went with 1/8" thick aluminum.

The type and position of the feet is not finalized. I would prefer them to be less visible.

~Tom
Attached Images
File Type: jpg Chassis.jpg (313.1 KB, 565 views)
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Old 6th April 2013, 07:43 PM   #85
tomchr is offline tomchr  United States
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Ready for sanding and paint...
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File Type: jpg Chassis-2.jpg (494.3 KB, 511 views)
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Old 6th April 2013, 08:25 PM   #86
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I hope you didn't drill those vent hole by hand.

Looks really good. Very Compact and clean.
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Old 6th April 2013, 09:19 PM   #87
grufti is offline grufti  United States
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That looks more like a CNC job than hand drilling.

It is amazingly compact thanks to the unusually small regulators. Having the heat sink out back will also help things stay cooler than they otherwise would.

This amp will have such a crazy size/weight mismatch. Anybody who lifts it up will surely think that they are lifting a block of steel or lead.
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Old 7th April 2013, 12:33 AM   #88
tomchr is offline tomchr  United States
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Thanks! No CNC here. The bottom plate is perforated sheet. The 546 vent holes (per chassis) on the top plate were drilled by hand (using a drill press, obviously). As were all the other holes. I used a stepped drill for the big holes.

For the vent holes, I made a jig from a piece of perf plate and a scrap piece of plywood. The perforated plate was used as a drill template. I held the perf plate, top plate, and plywood together with three brass pins. It worked like a charm and turned out really good.

~Tom
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Last edited by tomchr; 7th April 2013 at 12:38 AM.
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Old 13th May 2013, 06:33 AM   #89
tomchr is offline tomchr  United States
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Default Twins...

This project is finally drawing to a close. I've enjoyed the ride, but am glad to finally see the fruits of my hard work and allow this project to enter "maintenance mode".

I'm really pleased with the results. The sound quality of this amp is quite remarkable. I'm finding new detail in recordings I thought I knew inside and out. But the biggest surprise has been the sound stage. The imaging, width, and depth of the sound stage is unlike anything I've experienced before. I really like it.

I started this project over three years ago and it has spun off two side projects; the 21st Century Maida Regulator and Universal Filament Regulator.

The final amplifier uses three of my circuits:
- 21st Century Maida Regulator for B+ regulation
- 3x Universal Filament Regulator (stacked, 15 mm between boards in the center of the chassis)
- 300B Driver Board

I ended up using JJ 300B tubes and 6N6P drivers. I'm getting about 0.2 % THD (1 kHz, 1 W) and 10 W (3 % THD, 1 kHz). I'll follow up with more measurements at a later date.

Dimensions & weight: Approx. 30 x 40 x 25 cm (W x D x H). 17.3 kg.

For future reference, here are the relevant DIY Audio threads leading up to this design:
RFC: 300B driven by anode follower (6J5/6SN7)
300B (or other DHT) biasing options

~Tom
Attached Images
File Type: jpg 300B_Amps_Front_1000x1500.jpg (358.2 KB, 379 views)
File Type: jpg 300B_Amps_Rear_1000x1500.jpg (338.1 KB, 363 views)
File Type: jpg 300B_Amp_Bottom_1000x1500.jpg (386.6 KB, 306 views)
File Type: jpg 300B_Amp_Open_1000x1500.jpg (831.1 KB, 201 views)
File Type: jpg 300B_Amp_Front_CD_1000x1500.jpg (343.2 KB, 197 views)
File Type: jpg 300B_Amp_Glow_1000x1500.jpg (222.5 KB, 131 views)
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Last edited by tomchr; 13th May 2013 at 06:36 AM.
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Old 13th May 2013, 11:57 PM   #90
grufti is offline grufti  United States
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Very nice!

I noticed the three switches next to your input sockets. What are you switching between? Give me about six months and I should have mine finished.
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