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 NEW  Bruce Heran outlines the details and construction of his simple DIY 6DJ8 (ECC88) Tube Hi-Fi Headphone Amplifier Project.

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It is currently 31 Oct 2014, 08:26

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PostPosted: 13 Oct 2014, 19:56 
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Joined: 26 Feb 2012, 13:13
Posts: 23
Location: Virginia
Having had a couple of Tungsol 6550s saved for the last couple of years, and a passion for a SE project being next on my list after my very nice OTL headphone amp, I decided I couldn't wait and dropped a pile of Benjamin's on an Inspire Fire Bottle from Dennis Had :smoking:

A thing of desire!
Image

Comes with NOS 5U4GTB, a Tungsol reissue 6SL7, and I'll be dropping in my NOS Tungsol 6550 matched pair ;)

Now I have a dilemma - preamps! Buy some imported eye candy and change the tubes and other parts to clean it up, buy some vintage Dynaco or similar and do the same, or build something using a PCB copy of Marantz of similar?

The Inspire needs 1.5v input for it's full 10w output, not that I will drive it full throttle. Most of the preamps on evilBay output at 500mv to 700mv. Input sources are MM phono and CD (Quad 67 outputs 300mv - 2v peak).

Am I missing something, or do I need to preamp the preamp :P

Any thoughts to guide my aged mind. Buying would be easier as my project time is limited, but rather build/restore than waste $$ on China junk.

N


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PostPosted: 14 Oct 2014, 20:59 
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Joined: 04 Jun 2008, 20:59
Posts: 2417
Location: Arizona, USA
Hi, If that is your only source, it is probably able to drive the amps to full output. I think I would try to assemble a passive preamp.....basically either a variable resistor or stepped resistor control. Most likely since the power amp is a tube one, I would go for a 100K ohm dual pot. I personally find Alps ones quite suitable. Very simple to do......a case (preferably metal) input and output jacks, the pot, and I would likely insert series resistors in the output to compensate for cable capacitance if the total length of the input and output cables is over about 1.5m. I would probably use 2.2K resistors.

The alternatives are many. I personally like to use a line stage preamp and am preferential (naturally) to ones of my own designs. Fairly simple tube designs and a very high level of performance (project called Forewatt). There are plenty of others that are excellent as well....I would build one if I were you. You get quality audio and the satisfaction of building it.

Good listening
Bruce

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