Sidney
New Head-Fier
- Joined
- Feb 21, 2002
- Posts
- 13
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Just finished building a Rod Elliott DoZ Headphone Amp (http://sound.westhost.com/project70.htm) . No real engineering brainwork here thanks to Rod and his generous sharing of design work.
Details: I used Rods PCB's, they're tiny and well made. All transistors were matched for gain, with the output driver Q3 selected for higher gain than the source Q5, so that, per the JLH Class A amp site, the output transistor acts as if it has an active load rather than as an emitter follower. The input transistors are high gain Motorola BC559 equivalents I had lying around. I used NTE373's instead of the BD139's and the output TO3's are 2N3055's. The power supply was built from a surplus 2 x 8.5V, 2.1A toroid ($6 from Austin Electronics here outside Atlanta). A 12000uF cap smooths the rail before it goes through the capacitance multiplier on the left rear side of the chassis. This gives 24V when the quiescent current is set to 330mA per channel. Everything is grounded at the –ve lug of the capacitor and the amp is dead silent, with or without an input connected. All resistors are Dale RN55D 1%'ers. The volume control is a cheapo 100K dual linear RS pot with 15K 1% resistors, works fine, sounds fine and is seriously cheaper than an Alps/Noble. The case is surplus, steel with an aluminum face, 2”Hx6”Wx7”D, looks marvellous and was only $5 from Austin! It's a good looking case, the photo doesn't really do it justice and it even has all the right holes in the right places, all I drilled were some extra ventilation in the bottom and screw mounts for the cap multiplier and rectifier in the back. I haven't removed the original manufacturers stick-on label on the front yet but will get around to it. The scrounged heatsinks are thermally isolated by some rubber/cork material that was being sold as non-slip pads. Without the isolation, the heatsinks heat the chassis and you get a bit much thermal creeping for my liking. At 70F room temperature the chassis is now just warm and the heatsinks toasty (100F).
Impression: This amp seems a perfect match for my Senn HD580's. (I didn't use the 120R o/p resistors by the way). Of course I have builders bias, but this thing sounds incredible. I prefer it over my Headroom Supreme with the 580's. I'm rediscovering my CD collection.
I have some other pics but they exceed the posting limit.
Details: I used Rods PCB's, they're tiny and well made. All transistors were matched for gain, with the output driver Q3 selected for higher gain than the source Q5, so that, per the JLH Class A amp site, the output transistor acts as if it has an active load rather than as an emitter follower. The input transistors are high gain Motorola BC559 equivalents I had lying around. I used NTE373's instead of the BD139's and the output TO3's are 2N3055's. The power supply was built from a surplus 2 x 8.5V, 2.1A toroid ($6 from Austin Electronics here outside Atlanta). A 12000uF cap smooths the rail before it goes through the capacitance multiplier on the left rear side of the chassis. This gives 24V when the quiescent current is set to 330mA per channel. Everything is grounded at the –ve lug of the capacitor and the amp is dead silent, with or without an input connected. All resistors are Dale RN55D 1%'ers. The volume control is a cheapo 100K dual linear RS pot with 15K 1% resistors, works fine, sounds fine and is seriously cheaper than an Alps/Noble. The case is surplus, steel with an aluminum face, 2”Hx6”Wx7”D, looks marvellous and was only $5 from Austin! It's a good looking case, the photo doesn't really do it justice and it even has all the right holes in the right places, all I drilled were some extra ventilation in the bottom and screw mounts for the cap multiplier and rectifier in the back. I haven't removed the original manufacturers stick-on label on the front yet but will get around to it. The scrounged heatsinks are thermally isolated by some rubber/cork material that was being sold as non-slip pads. Without the isolation, the heatsinks heat the chassis and you get a bit much thermal creeping for my liking. At 70F room temperature the chassis is now just warm and the heatsinks toasty (100F).
Impression: This amp seems a perfect match for my Senn HD580's. (I didn't use the 120R o/p resistors by the way). Of course I have builders bias, but this thing sounds incredible. I prefer it over my Headroom Supreme with the 580's. I'm rediscovering my CD collection.
I have some other pics but they exceed the posting limit.
