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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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PostPosted: 06 Dec 2011, 17:47 
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Hi, That is the transformer to use. Regarding your thoughts on using a SS in line mode....my question is why? :? The Forewatt is a line stage preamp and can drive power amplifiers directly. If your Pioneer has separate line out from its preamp and line in to the power amp section then you can drive the power amp section directly from the Forewatt. Just remove the jumpers between the sections. I did that for a while with a Marantz integrated amp while I was reworking my reference pair of Oddblocks.

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PostPosted: 07 Dec 2011, 00:14 
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The line input in my SS amp allows it to act as a power amp, amplifying the input with an input sensitivity of 1 V. I think it is the same way you describe above.

Thanks!


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PostPosted: 07 Dec 2011, 11:32 
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Hi, It should work. The Forewatt should add a slight bit of warmth to your system. More like a subtle change in "flavor" than an extreme. It all goes back to an argument I choose not to engage in.... what sounds better and why SS or tubes. I have never heard a convincing argument for either side. More it seems a mater of taste. I personally prefer the tube sound. I have no issue with other folks who prefer SS sound...just don't ask me to design an amp for them. :)

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PostPosted: 07 Dec 2011, 11:48 
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Hi Everyone, Since this thread is all about Forewatts..... You should know that I am working on a second version that has modifications similar to the ones made in the power amps. Two separate possibilities are good depending on what your source of B+ is. If you can raise the anode B+ to 225 and change all the cathode 470R resistors to 680R or if you can "get" 300B+ then the resistors should go to 910R. You will need to adjust the "heater bias" resistors to 220K and 62K-75K in the latter case to insure the tubes heater to cathode voltage is not exceeded. You want to see about 65-80 volts DC from the heaters to the ground. In my prototypes there is a slight increase in the level of "inner detail" and "air". I hate to use terms like those, but I think you will understand what I mean by them. As soon as I can verify the results I'll let you know, but so far it seems like a positive evolution. That BTW is what I do with all my projects. They are not fixed in stone when first posted. I want everyone to have the finest audio reproduction gear possible and thus change is inevitable. :)

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PostPosted: 07 Dec 2011, 12:12 
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I've had to put the forewatt build on hold but will continue to obtain parts. The forewatt will be for my son but he's requested I include a phono stage in the same chassis. (Groovewatt)

A couple of questions:

Would doing this allow a fewer parts count compared to building two separate units?
Would the Edcor XPWR08 handle the power needed for the combined load?

I was contemplating incorporating a Jfet phono stage into the build but after reading several reviews it appears the sonic qualities just aren't up to the Groovewatt.

Allen


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PostPosted: 08 Dec 2011, 17:35 
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Hi Both could share a chassis. I would compartmentalize them so that there is less chance of interactions. I would add an additional filter section to the power supply and feed first the Forewatt and then the phono section. Yes the transformer should be fine. I would be sure to build in the "passive" preamp mode in the Forewatt part. Many sources do not need gain and you will benefit from bypassing the active circuit when it is not needed. Regardless of how good etc a active stage is, it will add its own signature to the sound. The Groovewatt has more gain than most phono preamps and I can easily drive my power amps with the Forewatt in passive mode.

Parts count will be a little less, but not greatly so. Only one power trannie and fewer jacks and such, but most parts will still be needed.

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PostPosted: 09 Dec 2011, 21:08 
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Good to hear the Forewatt tranny will handle both.

Can you point to any examples (drawings) that would help me understand adding the extra filter section and feeding the forewatt first. I was envisioning by your comments to assemble a twin filter section identical to the one for the forewatt but not sure on the meaning of feeding the forewatt first.

Allen


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PostPosted: 15 Dec 2011, 11:13 
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Hi, I just saw this..... I'll do a schematic for you...give me a day or so.

Good Listening
Bruce

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PostPosted: 21 Dec 2011, 20:26 
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I'm going to give the Forewatt a try. All the parts are on their way.


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PostPosted: 21 Dec 2011, 21:24 
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Good Show, If you run into any build problems let me know. I don't expect you will have any, but Murphy's law will catch up with me one day. :)

Good listening
Bruce

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